# CZMQ - High-level C binding for ØMQ

## Contents

Overview  Scope and Goals  Ownership and License  Commercial Support  Contributing

Using CZMQ  Building and Installing  Linking with an Application  API Summary  zauth - authentication for ZeroMQ security mechanisms  zbeacon - LAN service announcement and discovery  zcert - work with CURVE security certificates  zcertstore - work with CURVE security certificate stores  zchunk - work with memory chunks  zclock - millisecond clocks and delays  zconfig - work with config files written in rfc.zeromq.org/spec:4/ZPL.  zctx - working with ØMQ contexts  zdir - work with file-system directories  zfile - work with files  zframe - working with single message frames  zhash - generic hash table container  zlist - generic list container  zloop - event-driven reactor  zmonitor - socket event monitor  zmsg - working with multipart messages  zmutex - wrap lightweight mutexes  zpoller - trivial socket poller class  zproxy - convenient zmq_proxy API  zsocket - working with ØMQ sockets  zsockopt - working with ØMQ socket options  zstr - sending and receiving strings  zsys - system-level methods  zrex - working with regular expressions  zthread - working with system threads  ztree - generic red-black tree container

Under the Hood  Adding a New Class  Documentation  Development  Porting CZMQ  Code Generation  This Document

## Overview ### Scope and Goals

CZMQ has these goals:

• To wrap the ØMQ core API in semantics that are natural and lead to shorter, more readable applications.
• To hide the differences between versions of ØMQ, particularly 2.x and 3.x.
• To provide a space for development of more sophisticated API semantics.
• To wrap the ØMQ security features with high-level tools and APIs.
• To become the basis for other language bindings built on top of CZMQ.

CZMQ grew out of concepts developed in ØMQ - The Guide.

### Ownership and License

CZMQ's contributors are listed in the AUTHORS file. It is held by the ZeroMQ organization at github.com. The authors of CZMQ grant you use of this software under the terms of the GNU Lesser General Public License (LGPL). For details see the files COPYING and COPYING.LESSER in this directory.

### Commercial Support

CZMQ is actively developed and maintained by iMatix Corporation, who provide support to commercial users that need it. Contact Pieter Hintjens vai [email protected] for more information. Note that CZMQ is licensed exclusively under the same LGPLv3 + static link exception as libzmq. This lets you use CZMQ freely in any application, with the requirement that you publish patches to the code.

### Contributing

CZMQ uses the C4.1 (Collective Code Construction Contract) process for contributions.

CZMQ uses the CLASS (C Language Style for Scalabilty) guide for code style.

To report an issue, use the CZMQ issue tracker at github.com.

## Using CZMQ ### Building and Installing

Here's how to build CZMQ from GitHub (building from packages is very similar, you don't clone a repo but unpack a tarball), including the libsodium (for security) and libzmq (ZeroMQ core) libraries:

git clone git://github.com/jedisct1/libsodium.git
cd libsodium
./autogen.sh
./configure && make check
sudo make install
sudo ldconfig
cd ..

git clone git://github.com/zeromq/libzmq.git
cd libzmq
./autogen.sh
./configure && make check
sudo make install
sudo ldconfig
cd ..

git clone git://github.com/zeromq/czmq.git
cd czmq
./autogen.sh
./configure && make check
sudo make install
sudo ldconfig
cd ..

In general CZMQ works best with the latest libzmq master. If you already have an older version of libzmq installed on your system, e.g. in /usr/, then you can install libzmq master to your home directory ($HOME/local):

#   Building libzmq in our home directory
./configure --prefix=$HOME/local

And then to build CZMQ against this installation of libzmq:

export CFLAGS=-I$HOME/local/include
export LDFLAGS=-L$HOME/local/lib64
./configure

You will need the libtool and autotools packages. After building, run the CZMQ selftests:

make check

### Linking with an Application

Include czmq.h in your application and link with libczmq. Here is a typical gcc link command:

gcc -lczmq -lzmq myapp.c -o myapp

### API Summary #### zauth - authentication for ZeroMQ security mechanisms

A zauth object takes over authentication for all incoming connections in its context. Note that libzmq provides four levels of security: default NULL (which zauth does not see), and authenticated NULL, PLAIN, and CURVE, which zauth can see.

This is the class interface:

#define CURVE_ALLOW_ANY "*"

//  Constructor
//  Install authentication for the specified context. Returns a new zauth
//  object that you can use to configure authentication. Note that until you
//  add policies, all incoming NULL connections are allowed (classic ZeroMQ
//  behaviour), and all PLAIN and CURVE connections are denied. If there was
//  an error during initialization, returns NULL.
CZMQ_EXPORT zauth_t *
    zauth_new (zctx_t *ctx);
    
//  Allow (whitelist) a single IP address. For NULL, all clients from this
//  address will be accepted. For PLAIN and CURVE, they will be allowed to
//  continue with authentication. You can call this method multiple times 
//  to whitelist multiple IP addresses. If you whitelist a single address,
//  any non-whitelisted addresses are treated as blacklisted.
CZMQ_EXPORT void
    zauth_allow (zauth_t *self, char *address);

//  Deny (blacklist) a single IP address. For all security mechanisms, this
//  rejects the connection without any further authentication. Use either a
//  whitelist, or a blacklist, not not both. If you define both a whitelist 
//  and a blacklist, only the whitelist takes effect.
CZMQ_EXPORT void
    zauth_deny (zauth_t *self, char *address);

//  Configure PLAIN authentication for a given domain. PLAIN authentication
//  uses a plain-text password file. The filename is treated as a printf 
//  format. To cover all domains, use "*". You can modify the password file
//  at any time; it is reloaded automatically.
CZMQ_EXPORT void
    zauth_configure_plain (zauth_t *self, char *domain, char *filename, ...);
    
//  Configure CURVE authentication for a given domain. CURVE authentication
//  uses a directory that holds all public client certificates, i.e. their
//  public keys. The certificates must be in zcert_save () format. The 
//  location is treated as a printf format. To cover all domains, use "*". 
//  You can add and remove certificates in that directory at any time. 
//  To allow all client keys without checking, specify CURVE_ALLOW_ANY
//  for the location.
CZMQ_EXPORT void
    zauth_configure_curve (zauth_t *self, char *domain, char *location, ...);
    
//  Enable verbose tracing of commands and activity
CZMQ_EXPORT void
    zauth_set_verbose (zauth_t *self, bool verbose);
    
//  Destructor
CZMQ_EXPORT void
    zauth_destroy (zauth_t **self_p);

//  Selftest
CZMQ_EXPORT int
    zauth_test (bool verbose);

#### zbeacon - LAN service announcement and discovery

The zbeacon class implements a peer-to-peer discovery service for local networks. A beacon can broadcast and/or capture service announcements using UDP messages on the local area network. This implementation uses IPv4 UDP broadcasts. You can define the format of your outgoing beacons, and set a filter that validates incoming beacons. Beacons are sent and received asynchronously in the background. The zbeacon API provides a incoming beacons on a ZeroMQ socket (the pipe) that you can configure, poll on, and receive messages on. Incoming beacons are always delivered as two frames: the ipaddress of the sender (a string), and the beacon data itself (binary, as published).

This is the class interface:

//  Create a new beacon on a certain UDP port
CZMQ_EXPORT zbeacon_t *
    zbeacon_new (zctx_t *ctx, int port_nbr);
    
//  Destroy a beacon
CZMQ_EXPORT void
    zbeacon_destroy (zbeacon_t **self_p);

//  Return our own IP address as printable string
CZMQ_EXPORT char *
    zbeacon_hostname (zbeacon_t *self);

//  Set broadcast interval in milliseconds (default is 1000 msec)
CZMQ_EXPORT void
    zbeacon_set_interval (zbeacon_t *self, int interval);

//  Filter out any beacon that looks exactly like ours
CZMQ_EXPORT void
    zbeacon_noecho (zbeacon_t *self);

//  Start broadcasting beacon to peers at the specified interval
CZMQ_EXPORT void
    zbeacon_publish (zbeacon_t *self, byte *transmit, size_t size);
    
//  Stop broadcasting beacons
CZMQ_EXPORT void
    zbeacon_silence (zbeacon_t *self);

//  Start listening to other peers; zero-sized filter means get everything
CZMQ_EXPORT void
    zbeacon_subscribe (zbeacon_t *self, byte *filter, size_t size);

//  Stop listening to other peers
CZMQ_EXPORT void
    zbeacon_unsubscribe (zbeacon_t *self);

//  Get beacon ZeroMQ socket, for polling or receiving messages
CZMQ_EXPORT void *
    zbeacon_socket (zbeacon_t *self);

//  Self test of this class
CZMQ_EXPORT void
    zbeacon_test (bool verbose);

#### zcert - work with CURVE security certificates

The zcert class provides a way to create and work with security certificates for the ZMQ CURVE mechanism. A certificate contains a public + secret key pair, plus metadata. It can be used as a temporary object in memory, or persisted to disk. On disk, a certificate is stored as two files. One is public and contains only the public key. The second is secret and contains both keys. The two have the same filename, with the secret file adding "_secret". To exchange certificates, send the public file via some secure route. Certificates are not signed but are text files that can be verified by eye.

This is the class interface:

//  Create and initialize a new certificate in memory
CZMQ_EXPORT zcert_t *
    zcert_new (void);

//  Constructor, accepts public/secret key pair from caller
CZMQ_EXPORT zcert_t *
    zcert_new_from (byte *public_key, byte *secret_key);

//  Destroy a certificate in memory
CZMQ_EXPORT void
    zcert_destroy (zcert_t **self_p);

//  Return public part of key pair as 32-byte binary string
CZMQ_EXPORT byte *
    zcert_public_key (zcert_t *self);

//  Return secret part of key pair as 32-byte binary string
CZMQ_EXPORT byte *
    zcert_secret_key (zcert_t *self);

//  Return public part of key pair as Z85 armored string
CZMQ_EXPORT char *
    zcert_public_txt (zcert_t *self);

//  Return secret part of key pair as Z85 armored string
CZMQ_EXPORT char *
    zcert_secret_txt (zcert_t *self);

//  Set certificate metadata from formatted string.
CZMQ_EXPORT void
    zcert_set_meta (zcert_t *self, char *name, char *format, ...);

//  Get metadata value from certificate; if the metadata value doesn't 
//  exist, returns NULL.
CZMQ_EXPORT char *
    zcert_meta (zcert_t *self, char *name);

//  Get list of metadata fields from certificate. Caller is responsible for
//  destroying list. Caller should not modify the values of list items.
CZMQ_EXPORT zlist_t *
    zcert_meta_keys (zcert_t *self);

//  Load certificate from file (constructor)
//  The filename is treated as a printf format specifier.
CZMQ_EXPORT zcert_t *
    zcert_load (char *filename, ...);

//  Save full certificate (public + secret) to file for persistent storage
//  This creates one public file and one secret file (filename + "_secret").
//  The filename is treated as a printf format specifier.
CZMQ_EXPORT int
    zcert_save (zcert_t *self, char *filename, ...);

//  Save public certificate only to file for persistent storage
//  The filename is treated as a printf format specifier.
CZMQ_EXPORT int
    zcert_save_public (zcert_t *self, char *filename, ...);

//  Apply certificate to socket, i.e. use for CURVE security on socket.
//  If certificate was loaded from public file, the secret key will be
//  undefined, and this certificate will not work successfully.
CZMQ_EXPORT void
    zcert_apply (zcert_t *self, void *zocket);

//  Return copy of certificate
CZMQ_EXPORT zcert_t *
    zcert_dup (zcert_t *self);

//  Return true if two certificates have the same keys
CZMQ_EXPORT bool
    zcert_eq (zcert_t *self, zcert_t *compare);

//  Print certificate contents to open stream
CZMQ_EXPORT void
    zcert_fprint (zcert_t *self, FILE *file);

//  Print certificate contents to stdout
CZMQ_EXPORT void
    zcert_print (zcert_t *self);

//  Self test of this class
CZMQ_EXPORT int
    zcert_test (bool verbose);

Certificates are stored in the ZPL (ZMQ RFC 4) format. They have two sections, "metadata" and "curve". The first contains a list of 'name = value' pairs, one per line. Values may be enclosed in quotes. The curve section has a 'public-key = keyvalue' and, for secret certificates, a 'secret-key = keyvalue' line. The keyvalue is a Z85-encoded CURVE key.

#### zcertstore - work with CURVE security certificate stores

To authenticate new clients using the ZeroMQ CURVE security mechanism, we have to check that the client's public key matches a key we know and accept. There are numerous ways to store accepted client public keys. The mechanism CZMQ implements is "certificates" (plain text files) held in a "certificate store" (a disk directory). This class works with such certificate stores, and lets you easily load them from disk, and check if a given client public key is known or not. The zcert class does the work of managing a single certificate.

This is the class interface:

//  Create a new certificate store from a disk directory, loading and 
//  indexing all certificates in that location. The directory itself may be
//  absent, and created later, or modified at any time. The certificate store 
//  is automatically refreshed on any zcertstore_lookup() call. If the 
//  location is specified as NULL, creates a pure-memory store, which you 
//  can work with by inserting certificates at runtime. The location is
//  treated as a printf format.
CZMQ_EXPORT zcertstore_t *
    zcertstore_new (char *location, ...);

//  Destroy a certificate store object in memory. Does not affect anything
//  stored on disk.
CZMQ_EXPORT void
    zcertstore_destroy (zcertstore_t **self_p);

//  Look up certificate by public key, returns zcert_t object if found, 
//  else returns NULL. The public key is provided in Z85 text format.
CZMQ_EXPORT zcert_t *
    zcertstore_lookup (zcertstore_t *self, char *public_key);

//  Insert certificate into certificate store in memory. Note that this 
//  does not save the certificate to disk. To do that, use zcert_save()
//  directly on the certificate. Takes ownership of zcert_t object.
CZMQ_EXPORT void
    zcertstore_insert (zcertstore_t *self, zcert_t **cert_p);

//  Print list of certificates in store to open stream
CZMQ_EXPORT void
    zcertstore_fprint (zcertstore_t *self, FILE *file);

//  Print list of certificates in store to stdout
CZMQ_EXPORT void
    zcertstore_print (zcertstore_t *self);

//  Self test of this class
CZMQ_EXPORT int
    zcertstore_test (bool verbose);

The certificate store can be memory-only, in which case you can load it yourself by inserting certificate objects one by one, or it can be loaded from disk, in which case you can add, modify, or remove certificates on disk at any time, and the store will detect such changes and refresh itself automatically. In most applications you won't use this class directly but through the zauth class, which provides a high-level API for authentication (and manages certificate stores for you). To actually create certificates on disk, use the zcert class in code, or the tools/makecert.c command line tool, or any text editor. The format of a certificate file is defined in the zcert man page.

#### zchunk - work with memory chunks

The zchunk class works with variable sized blobs. Not as efficient as ØMQ's messages but they do less weirdness and so are easier to understand. The chunk class has methods to read and write chunks from disk.

This is the class interface:

//  Create new chunk
CZMQ_EXPORT zchunk_t *
    zchunk_new (const void *data, size_t size);

//  Destroy a chunk
CZMQ_EXPORT void
    zchunk_destroy (zchunk_t **self_p);

//  Resizes chunk max_size as requested; chunk_cur size is set to zero
CZMQ_EXPORT void
    zchunk_resize (zchunk_t *self, size_t size);

//  Return chunk cur size
CZMQ_EXPORT size_t
    zchunk_size (zchunk_t *self);

//  Return chunk max size
CZMQ_EXPORT size_t
    zchunk_max_size (zchunk_t *self);

//  Return chunk data
CZMQ_EXPORT byte *
    zchunk_data (zchunk_t *self);

//  Set chunk data from user-supplied data; truncate if too large
CZMQ_EXPORT size_t
    zchunk_set (zchunk_t *self, const void *data, size_t size);

//  Fill chunk data from user-supplied octet
CZMQ_EXPORT size_t
    zchunk_fill (zchunk_t *self, byte filler, size_t size);

//  Read chunk from an open file descriptor
CZMQ_EXPORT zchunk_t *
    zchunk_read (FILE *handle, size_t bytes);
    
//  Write chunk to an open file descriptor
CZMQ_EXPORT int
    zchunk_write (zchunk_t *self, FILE *handle);

//  Self test of this class
CZMQ_EXPORT int
    zchunk_test (bool verbose);

#### zclock - millisecond clocks and delays

The zclock class provides essential sleep and system time functions, used to slow down threads for testing, and calculate timers for polling. Wraps the non-portable system calls in a simple portable API.

This is the class interface:

//  Sleep for a number of milliseconds
CZMQ_EXPORT void
    zclock_sleep (int msecs);

//  Return current system clock as milliseconds
CZMQ_EXPORT int64_t
    zclock_time (void);

//  Print formatted string to stdout, prefixed by date/time and
//  terminated with a newline.
CZMQ_EXPORT void
    zclock_log (const char *format, ...);

//  Return formatted date/time as fresh string. Free using zstr_free().
CZMQ_EXPORT char *
    zclock_timestr (void);

//  Self test of this class
CZMQ_EXPORT int
    zclock_test (bool verbose);

The Win32 Sleep() call defaults to 16ms resolution unless the system timer resolution is increased with a call to timeBeginPeriod() permitting 1ms granularity.

#### zconfig - work with config files written in rfc.zeromq.org/spec:4/ZPL.

Lets applications load, work with, and save configuration files. This implements rfc.zeromq.org/spec:4/ZPL, which is a simple structured text format for configuration files.

This is the class interface:

//  Function that executes config
typedef int (zconfig_fct) (zconfig_t *self, void *arg, int level);

//  Create new config item
CZMQ_EXPORT zconfig_t *
    zconfig_new (char *name, zconfig_t *parent);

//  Destroy a config item and all its children
CZMQ_EXPORT void
    zconfig_destroy (zconfig_t **self_p);

//  Return name of config item
CZMQ_EXPORT char *
    zconfig_name (zconfig_t *self);

//  Return value of config item
CZMQ_EXPORT char *
    zconfig_value (zconfig_t *self);

//  Insert or update configuration key with value
CZMQ_EXPORT void
    zconfig_put (zconfig_t *self, char *path, char *value);

//  Set config item name, name may be NULL
CZMQ_EXPORT void
    zconfig_set_name (zconfig_t *self, char *name);

//  Set new value for config item. The new value may be a string, a printf
//  format, or NULL. Note that if string may possibly contain '%', or if it
//  comes from an insecure source, you must use '%s' as the format, followed
//  by the string.
CZMQ_EXPORT void
    zconfig_set_value (zconfig_t *self, char *format, ...);

//  Find our first child, if any
CZMQ_EXPORT zconfig_t *
    zconfig_child (zconfig_t *self);

//  Find our first sibling, if any
CZMQ_EXPORT zconfig_t *
    zconfig_next (zconfig_t *self);

//  Find a config item along a path; leading slash is optional and ignored.
CZMQ_EXPORT zconfig_t *
    zconfig_locate (zconfig_t *self, char *path);

//  Resolve a config path into a string value; leading slash is optional
//  and ignored.
CZMQ_EXPORT char *
    zconfig_resolve (zconfig_t *self, char *path, char *default_value);

//  Set config item name, name may be NULL
CZMQ_EXPORT void
    zconfig_set_path (zconfig_t *self, char *path, char *value);

//  Locate the last config item at a specified depth
CZMQ_EXPORT zconfig_t *
    zconfig_at_depth (zconfig_t *self, int level);

//  Execute a callback for each config item in the tree
CZMQ_EXPORT int
    zconfig_execute (zconfig_t *self, zconfig_fct handler, void *arg);

//  Add comment to config item before saving to disk. You can add as many
//  comment lines as you like. If you use a null format, all comments are
//  deleted.
CZMQ_EXPORT void
    zconfig_set_comment (zconfig_t *self, char *format, ...);

//  Return comments of config item, as zlist.
CZMQ_EXPORT zlist_t *
    zconfig_comments (zconfig_t *self);

//  Load a config item tree from a specified ZPL text file
CZMQ_EXPORT zconfig_t *
    zconfig_load (char *filename);

//  Save a config item tree to a specified ZPL text file, where a filename
//  "-" means dump to standard output.
CZMQ_EXPORT int
    zconfig_save (zconfig_t *self, char *filename);

//  Print the config file to open stream
CZMQ_EXPORT void
    zconfig_fprint (zconfig_t *self, FILE *file);

//  Print the config file to stdout
CZMQ_EXPORT void
    zconfig_print (zconfig_t *self);

#### zctx - working with ØMQ contexts

The zctx class wraps ØMQ contexts. It manages open sockets in the context and automatically closes these before terminating the context. It provides a simple way to set the linger timeout on sockets, and configure contexts for number of I/O threads. Sets-up signal (interrupt) handling for the process.

The zctx class has these main features:

• Tracks all open sockets and automatically closes them before calling zmq_term(). This avoids an infinite wait on open sockets.

• Automatically configures sockets with a ZMQ_LINGER timeout you can define, and which defaults to zero. The default behavior of zctx is therefore like ØMQ/2.0, immediate termination with loss of any pending messages. You can set any linger timeout you like by calling the zctx_set_linger() method.

• Moves the iothreads configuration to a separate method, so that default usage is 1 I/O thread. Lets you configure this value.

• Sets up signal (SIGINT and SIGTERM) handling so that blocking calls such as zmq_recv() and zmq_poll() will return when the user presses Ctrl-C.

This is the class interface:

//  Create new context, returns context object, replaces zmq_init
CZMQ_EXPORT zctx_t *
    zctx_new (void);

//  Destroy context and all sockets in it, replaces zmq_term
CZMQ_EXPORT void
    zctx_destroy (zctx_t **self_p);

//  Create new shadow context, returns context object
CZMQ_EXPORT zctx_t *
    zctx_shadow (zctx_t *self);
//  Raise default I/O threads from 1, for crazy heavy applications
//  The rule of thumb is one I/O thread per gigabyte of traffic in
//  or out. Call this method before creating any sockets on the context,
//  or calling zctx_shadow, or the setting will have no effect.
CZMQ_EXPORT void
    zctx_set_iothreads (zctx_t *self, int iothreads);

//  Set msecs to flush sockets when closing them, see the ZMQ_LINGER
//  man page section for more details. By default, set to zero, so
//  any in-transit messages are discarded when you destroy a socket or
//  a context.
CZMQ_EXPORT void
    zctx_set_linger (zctx_t *self, int linger);

//  Set initial high-water mark for inter-thread pipe sockets. Note that
//  this setting is separate from the default for normal sockets. You 
//  should change the default for pipe sockets *with care*. Too low values
//  will cause blocked threads, and an infinite setting can cause memory
//  exhaustion. The default, no matter the underlying ZeroMQ version, is
//  1,000.
CZMQ_EXPORT void
    zctx_set_pipehwm (zctx_t *self, int pipehwm);
    
//  Set initial send HWM for all new normal sockets created in context.
//  You can set this per-socket after the socket is created.
//  The default, no matter the underlying ZeroMQ version, is 1,000.
CZMQ_EXPORT void
    zctx_set_sndhwm (zctx_t *self, int sndhwm);
    
//  Set initial receive HWM for all new normal sockets created in context.
//  You can set this per-socket after the socket is created.
//  The default, no matter the underlying ZeroMQ version, is 1,000.
CZMQ_EXPORT void
    zctx_set_rcvhwm (zctx_t *self, int rcvhwm);

//  Return low-level ØMQ context object, will be NULL before first socket
//  is created. Use with care.
CZMQ_EXPORT void *
    zctx_underlying (zctx_t *self);

//  Self test of this class
CZMQ_EXPORT int
    zctx_test (bool verbose);

//  Global signal indicator, TRUE when user presses Ctrl-C or the process
//  gets a SIGTERM signal.
CZMQ_EXPORT extern volatile int zctx_interrupted;

#### zdir - work with file-system directories

The zdir class gives access to the file system index. It will load a directory tree (a directory plus all child directories) into a zdir structure and then let you navigate that structure. It exists mainly to wrap non-portable OS functions to do this.

This is the class interface:

//  Create a new directory item that loads in the full tree of the
//  specified path, optionally located under some parent path.
CZMQ_EXPORT zdir_t *
    zdir_new (const char *path, const char *parent);

//  Destroy a directory tree and all children it contains.
CZMQ_EXPORT void
    zdir_destroy (zdir_t **self_p);

//  Return directory path
CZMQ_EXPORT char *
    zdir_path (zdir_t *self);

//  Return last modification time for directory.
CZMQ_EXPORT time_t
    zdir_modified (zdir_t *self);

//  Return total hierarchy size, in bytes of data contained in all files
//  in the directory tree.
CZMQ_EXPORT off_t
    zdir_cursize (zdir_t *self);

//  Return directory count
CZMQ_EXPORT size_t
    zdir_count (zdir_t *self);
    
//  Returns a sorted array of zfile objects; returns a single block of memory,
//  that you destroy by calling zstr_free(). Each entry in the array is a pointer
//  to a zfile_t item already allocated in the zdir tree. The array ends with
//  a null pointer. Do not destroy the original zdir tree until you are done
//  with this array.
CZMQ_EXPORT zfile_t **
    zdir_flatten (zdir_t *self);

//  Free a provided string, and nullify the parent pointer. Safe to call on
//  a null pointer.
CZMQ_EXPORT void
    zdir_flatten_free (zfile_t ***files_p);

//  Remove directory, optionally including all files that it contains, at
//  all levels. If force is false, will only remove the directory if empty.
//  If force is true, will remove all files and all subdirectories.
CZMQ_EXPORT void
    zdir_remove (zdir_t *self, bool force);

//  Calculate differences between two versions of a directory tree.
//  Returns a list of zdir_patch_t patches. Either older or newer may
//  be null, indicating the directory is empty/absent. If alias is set,
//  generates virtual filename (minus path, plus alias).
CZMQ_EXPORT zlist_t *
    zdir_diff (zdir_t *older, zdir_t *newer, char *alias);

//  Return full contents of directory as a zdir_patch list.
CZMQ_EXPORT zlist_t *
    zdir_resync (zdir_t *self, char *alias);

//  Load directory cache; returns a hash table containing the SHA-1 digests
//  of every file in the tree. The cache is saved between runs in .cache.
//  The caller must destroy the hash table when done with it.
CZMQ_EXPORT zhash_t *
    zdir_cache (zdir_t *self);

//  Print contents of directory to open stream
CZMQ_EXPORT void
    zdir_fprint (zdir_t *self, FILE *file, int indent);

//  Print contents of directory to stdout
CZMQ_EXPORT void
    zdir_print (zdir_t *self, int indent);

//  Self test of this class
CZMQ_EXPORT int
    zdir_test (bool verbose);

#### zfile - work with files

The zfile class provides methods to work with disk files. A file object provides the modified date, current size, and type of the file. You can create a file object for a filename that does not yet exist. To read or write data from the file, use the input and output methods, and then read and write chunks. The output method lets you both read and write chunks, at any offset. Finally, this class provides portable symbolic links. If a filename ends in ".ln", the first line of text in the file is read, and used as the underlying file for read/write operations. This lets you manipulate (e.g.) copy symbolic links without copying the perhaps very large files they point to.

This is the class interface:

//  Create new file item
CZMQ_EXPORT zfile_t *
    zfile_new (const char *path, const char *name);

//  Destroy a file item
CZMQ_EXPORT void
    zfile_destroy (zfile_t **self_p);

//  Duplicate a file item, returns a newly constructed item
CZMQ_EXPORT zfile_t *
    zfile_dup (zfile_t *self);

//  Return file name, remove path if provided
CZMQ_EXPORT char *
    zfile_filename (zfile_t *self, char *path);

//  Refresh file properties from disk; this is not done automatically
//  on access methods, otherwise it is not possible to compare directory
//  snapshots.
CZMQ_EXPORT void
    zfile_restat (zfile_t *self);

//  Return when the file was last modified. If you want this to reflect the
//  current situation, call zfile_restat before checking this property.
CZMQ_EXPORT time_t
    zfile_modified (zfile_t *self);

//  Return the last-known size of the file. If you want this to reflect the
//  current situation, call zfile_restat before checking this property.
CZMQ_EXPORT off_t
    zfile_cursize (zfile_t *self);

//  Return true if the file is a directory. If you want this to reflect
//  any external changes, call zfile_restat before checking this property.
CZMQ_EXPORT bool
    zfile_is_directory (zfile_t *self);

//  Return true if the file is a regular file. If you want this to reflect
//  any external changes, call zfile_restat before checking this property.
CZMQ_EXPORT bool
    zfile_is_regular (zfile_t *self);

//  Return true if the file is readable by this process. If you want this to
//  reflect any external changes, call zfile_restat before checking this
//  property.
CZMQ_EXPORT bool
    zfile_is_readable (zfile_t *self);

//  Return true if the file is writeable by this process. If you want this
//  to reflect any external changes, call zfile_restat before checking this
//  property.
CZMQ_EXPORT bool
    zfile_is_writeable (zfile_t *self);

//  Check if file has stopped changing and can be safely processed.
//  Updates the file statistics from disk at every call.
CZMQ_EXPORT bool
    zfile_is_stable (zfile_t *self);

//  Remove the file from disk
CZMQ_EXPORT void
    zfile_remove (zfile_t *self);

//  Open file for reading
//  Returns 0 if OK, -1 if not found or not accessible
CZMQ_EXPORT int
    zfile_input (zfile_t *self);

//  Open file for writing, creating directory if needed
//  File is created if necessary; chunks can be written to file at any
//  location. Returns 0 if OK, -1 if error.
CZMQ_EXPORT int
    zfile_output (zfile_t *self);

//  Read chunk from file at specified position. If this was the last chunk,
//  sets self->eof. Returns a null chunk in case of error.
CZMQ_EXPORT zchunk_t *
    zfile_read (zfile_t *self, size_t bytes, off_t offset);

//  Write chunk to file at specified position
//  Return 0 if OK, else -1
CZMQ_EXPORT int
    zfile_write (zfile_t *self, zchunk_t *chunk, off_t offset);

//  Close file, if open
CZMQ_EXPORT void
    zfile_close (zfile_t *self);

//  Return file handle, if opened
CZMQ_EXPORT FILE *
    zfile_handle (zfile_t *self);

//  Calculate SHA1 digest for file, using zdigest class. Caller should not
//  modify digest.
CZMQ_EXPORT char *
    zfile_digest (zfile_t *self);

//  Self test of this class
CZMQ_EXPORT int
    zfile_test (bool verbose);
//  These methods are deprecated, and now moved to zsys class.
CZMQ_EXPORT bool
    zfile_exists (const char *filename);
CZMQ_EXPORT ssize_t
    zfile_size   (const char *filename);
CZMQ_EXPORT mode_t
    zfile_mode   (const char *filename);
CZMQ_EXPORT int
    zfile_delete (const char *filename);
CZMQ_EXPORT bool
    zfile_stable (const char *filename);
CZMQ_EXPORT int
    zfile_mkdir  (const char *pathname);
CZMQ_EXPORT int
    zfile_rmdir  (const char *pathname);
CZMQ_EXPORT void
    zfile_mode_private (void);
CZMQ_EXPORT void
    zfile_mode_default (void);

This class is a new API, deprecating the old zfile class (which still exists but is implemented in zsys now).

#### zframe - working with single message frames

The zframe class provides methods to send and receive single message frames across ØMQ sockets. A 'frame' corresponds to one zmq_msg_t. When you read a frame from a socket, the zframe_more() method indicates if the frame is part of an unfinished multipart message. The zframe_send method normally destroys the frame, but with the ZFRAME_REUSE flag, you can send the same frame many times. Frames are binary, and this class has no special support for text data.

This is the class interface:

#define ZFRAME_MORE     1
#define ZFRAME_REUSE    2
#define ZFRAME_DONTWAIT 4

//  Create a new frame with optional size, and optional data
CZMQ_EXPORT zframe_t *
    zframe_new (const void *data, size_t size);

//  Create an empty (zero-sized) frame
CZMQ_EXPORT zframe_t *
    zframe_new_empty (void);

//  Destroy a frame
CZMQ_EXPORT void
    zframe_destroy (zframe_t **self_p);

//  Receive frame from socket, returns zframe_t object or NULL if the recv
//  was interrupted. Does a blocking recv, if you want to not block then use
//  zframe_recv_nowait().
CZMQ_EXPORT zframe_t *
    zframe_recv (void *socket);

//  Receive a new frame off the socket. Returns newly allocated frame, or
//  NULL if there was no input waiting, or if the read was interrupted.
CZMQ_EXPORT zframe_t *
    zframe_recv_nowait (void *socket);

// Send a frame to a socket, destroy frame after sending.
// Return -1 on error, 0 on success.
CZMQ_EXPORT int
    zframe_send (zframe_t **self_p, void *socket, int flags);

//  Return number of bytes in frame data
CZMQ_EXPORT size_t
    zframe_size (zframe_t *self);

//  Return address of frame data
CZMQ_EXPORT byte *
    zframe_data (zframe_t *self);

//  Create a new frame that duplicates an existing frame
CZMQ_EXPORT zframe_t *
    zframe_dup (zframe_t *self);

//  Return frame data encoded as printable hex string
CZMQ_EXPORT char *
    zframe_strhex (zframe_t *self);

//  Return frame data copied into freshly allocated string
CZMQ_EXPORT char *
    zframe_strdup (zframe_t *self);

//  Return TRUE if frame body is equal to string, excluding terminator
CZMQ_EXPORT bool
    zframe_streq (zframe_t *self, const char *string);

//  Return frame MORE indicator (1 or 0), set when reading frame from socket
//  or by the zframe_set_more() method
CZMQ_EXPORT int
    zframe_more (zframe_t *self);

//  Set frame MORE indicator (1 or 0). Note this is NOT used when sending 
//  frame to socket, you have to specify flag explicitly.
CZMQ_EXPORT void
    zframe_set_more (zframe_t *self, int more);
    
//  Return TRUE if two frames have identical size and data
//  If either frame is NULL, equality is always false.
CZMQ_EXPORT bool
    zframe_eq (zframe_t *self, zframe_t *other);

//   Print contents of the frame to FILE stream.
CZMQ_EXPORT void
    zframe_fprint (zframe_t *self, const char *prefix, FILE *file);

//  Print contents of frame to stderr
CZMQ_EXPORT void
    zframe_print (zframe_t *self, const char *prefix);

//  Set new contents for frame
CZMQ_EXPORT void
    zframe_reset (zframe_t *self, const void *data, size_t size);

//  Self test of this class
CZMQ_EXPORT int
    zframe_test (bool verbose);

//  Put a block of data to the frame payload.
CZMQ_EXPORT int
    zframe_put_block (zframe_t *self, byte *data, size_t size);

//  Put a string to frame payload. Returns 0 if successful else -1.
//  The string length limited to 2^16 - 1 for '\0' => 65535 characters.
//  For allocation purpose calculate: (string length + 2) bytes
CZMQ_EXPORT int
    zframe_put_string (zframe_t *self, char *data);

//  Put 1-byte to frame payload. Returns 0 if successful else -1.
CZMQ_EXPORT int
    zframe_put_uint8 (zframe_t *self, uint8_t data);

//  Put 2-byte to frame payload. Returns 0 if successful else -1.
CZMQ_EXPORT int
    zframe_put_uint16 (zframe_t *self, uint16_t data);

//  Put 4-byte to frame payload. Returns 0 if successful else -1.
CZMQ_EXPORT int
    zframe_put_uint32 (zframe_t *self, uint32_t data);

//  Put 8-byte to frame payload. Returns 0 if successful else -1.
CZMQ_EXPORT int
    zframe_put_uint64 (zframe_t *self, uint64_t data);

//  Get a block of data from the frame payload.
CZMQ_EXPORT int
    zframe_get_block (zframe_t *self, byte *data, size_t size);

//  Get a newly allocated string from frame payload. Returns char pointer to
//  a string. The max string size can be 2^16 and is 0 terminated.
CZMQ_EXPORT char *
    zframe_get_string (zframe_t *self);

//  Get a 1-byte integer from the frame payload. If there was insufficient
//  data in the frame, returns zero.
CZMQ_EXPORT uint8_t
    zframe_get_uint8 (zframe_t *self);

//  Get a 2-byte integer from the frame payload. If there was insufficient
//  data in the frame, returns zero.
CZMQ_EXPORT uint16_t
    zframe_get_uint16 (zframe_t *self);

//  Get a 4-byte integer from the frame payload. If there was insufficient
//  data in the frame, returns zero.
CZMQ_EXPORT uint32_t
    zframe_get_uint32 (zframe_t *self);

//  Get a 8-byte integer from the frame payload. If there was insufficient
//  data in the frame, returns zero.
CZMQ_EXPORT uint64_t
    zframe_get_uint64 (zframe_t *self);

#### zhash - generic hash table container

Expandable hash table container

This is the class interface:

//  Callback function for zhash_foreach method
typedef int (zhash_foreach_fn) (const char *key, void *item, void *argument);
//  Callback function for zhash_freefn method
typedef void (zhash_free_fn) (void *data);

//  Create a new, empty hash container
CZMQ_EXPORT zhash_t *
    zhash_new (void);

//  Destroy a hash container and all items in it
CZMQ_EXPORT void
    zhash_destroy (zhash_t **self_p);

//  Insert item into hash table with specified key and item.
//  If key is already present returns -1 and leaves existing item unchanged
//  Returns 0 on success.
CZMQ_EXPORT int
    zhash_insert (zhash_t *self, const char *key, void *item);

//  Update item into hash table with specified key and item.
//  If key is already present, destroys old item and inserts new one.
//  Use free_fn method to ensure deallocator is properly called on item.
CZMQ_EXPORT void
    zhash_update (zhash_t *self, const char *key, void *item);

//  Remove an item specified by key from the hash table. If there was no such
//  item, this function does nothing.
CZMQ_EXPORT void
    zhash_delete (zhash_t *self, const char *key);

//  Return the item at the specified key, or null
CZMQ_EXPORT void *
    zhash_lookup (zhash_t *self, const char *key);

//  Reindexes an item from an old key to a new key. If there was no such
//  item, does nothing. Returns 0 if successful, else -1.
CZMQ_EXPORT int
    zhash_rename (zhash_t *self, const char *old_key, const char *new_key);

//  Set a free function for the specified hash table item. When the item is
//  destroyed, the free function, if any, is called on that item.
//  Use this when hash items are dynamically allocated, to ensure that
//  you don't have memory leaks. You can pass 'free' or NULL as a free_fn.
//  Returns the item, or NULL if there is no such item.
CZMQ_EXPORT void *
    zhash_freefn (zhash_t *self, const char *key, zhash_free_fn *free_fn);

//  Return the number of keys/items in the hash table
CZMQ_EXPORT size_t
    zhash_size (zhash_t *self);

//  Make copy of hash table
CZMQ_EXPORT zhash_t *
    zhash_dup (zhash_t *self);

//  Return keys for items in table
CZMQ_EXPORT zlist_t *
    zhash_keys (zhash_t *self);
    
//  Apply function to each item in the hash table. Items are iterated in no
//  defined order. Stops if callback function returns non-zero and returns
//  final return code from callback function (zero = success).
CZMQ_EXPORT int
    zhash_foreach (zhash_t *self, zhash_foreach_fn *callback, void *argument);

//  Add comment to hash table before saving to disk. You can add as many
//  comment lines as you like. These comment lines are discarded when loading
//  the file. If you use a null format, all comments are deleted.
CZMQ_EXPORT void
    zhash_comment (zhash_t *self, char *format, ...);

//  Save hash table to a text file in name=value format. Hash values must be
//  printable strings; keys may not contain '=' character. Returns 0 if OK,
//  else -1 if a file error occurred.
CZMQ_EXPORT int
    zhash_save (zhash_t *self, char *filename);

//  Load hash table from a text file in name=value format; hash table must
//  already exist. Hash values must printable strings; keys may not contain
//  '=' character. Returns 0 if OK, else -1 if a file was not readable.
CZMQ_EXPORT int
    zhash_load (zhash_t *self, char *filename);

//  When a hash table was loaded from a file by zhash_load, this method will
//  reload the file if it has been modified since, and is "stable", i.e. not
//  still changing. Returns 0 if OK, -1 if there was an error reloading the 
//  file.
CZMQ_EXPORT int
    zhash_refresh (zhash_t *self);

//  Set hash for automatic value destruction
CZMQ_EXPORT void
    zhash_autofree (zhash_t *self);
    
//  Serialize hash table to a binary frame that can be sent in a message.
//  The packed format is compatible with the 'dictionary' type defined in
//  rfc.zeromq.org/spec:19/FILEMQ. Comments are not included in the packed
//  data. Item values MUST be strings.
CZMQ_EXPORT zframe_t *
    zhash_pack (zhash_t *self);
    
//  Unpack binary frame into a new hash table. Packed data must follow format
//  defined by zhash_pack. Hash table is set to autofree. An empty frame
//  unpacks to an empty hash table.
zhash_t *
    zhash_unpack (zframe_t *frame);

//  Self test of this class
CZMQ_EXPORT void
    zhash_test (int verbose);

Note that it's relatively slow (~50K insertions/deletes per second), so don't do inserts/updates on the critical path for message I/O. It can do ~2.5M lookups per second for 16-char keys. Timed on a 1.6GHz CPU.

#### zlist - generic list container

Provides a generic container implementing a fast singly-linked list. You can use this to construct multi-dimensional lists, and other structures together with other generic containers like zhash.

This is the class interface:

//  Comparison function for zlist_sort method
typedef bool (zlist_compare_fn) (void *item1, void *item2);

//  Create a new list container
CZMQ_EXPORT zlist_t *
    zlist_new (void);

//  Destroy a list container
CZMQ_EXPORT void
    zlist_destroy (zlist_t **self_p);

//  Return first item in the list, or null
CZMQ_EXPORT void *
    zlist_first (zlist_t *self);

//  Return last item in the list, or null
CZMQ_EXPORT void *
    zlist_last (zlist_t *self);

//  Return first item in the list, or null, leaves the cursor
CZMQ_EXPORT void *
    zlist_head (zlist_t *self);

//  Return last item in the list, or null, leaves the cursor
CZMQ_EXPORT void *
    zlist_tail (zlist_t *self);

//  Return next item in the list, or null
CZMQ_EXPORT void *
    zlist_next (zlist_t *self);

//  Append an item to the end of the list
CZMQ_EXPORT int
    zlist_append (zlist_t *self, void *item);

//  Push an item to the start of the list
CZMQ_EXPORT int
    zlist_push (zlist_t *self, void *item);

//  Pop the item off the start of the list, if any
CZMQ_EXPORT void *
    zlist_pop (zlist_t *self);

//  Remove the specified item from the list if present
CZMQ_EXPORT void
    zlist_remove (zlist_t *self, void *item);

//  Make a copy of list. If the list has autofree set, the copied list will
//  duplicate all items, which must be strings. Otherwise, the list will hold
//  pointers back to the items in the original list.
CZMQ_EXPORT zlist_t *
    zlist_dup (zlist_t *self);

//  Return number of items in the list
CZMQ_EXPORT size_t
    zlist_size (zlist_t *self);

//  Sort the list by ascending key value using a straight ASCII comparison.
//  The sort is not stable, so may reorder items with the same keys.
CZMQ_EXPORT void
    zlist_sort (zlist_t *self, zlist_compare_fn *compare);

//  Set list for automatic item destruction; item values MUST be strings.
//  By default a list item refers to a value held elsewhere. When you set
//  this, each time you append or push a list item, zlist will take a copy
//  of the string value. Then, when you destroy the list, it will free all
//  item values automatically. If you use any other technique to allocate
//  list values, you must free them explicitly before destroying the list.
//  The usual technique is to pop list items and destroy them, until the
//  list is empty.
CZMQ_EXPORT void
    zlist_autofree (zlist_t *self);

//  Self test of this class
CZMQ_EXPORT void
    zlist_test (int verbose);

To iterate through a list, use zlist_first to get the first item, then loop while not null, and do zlist_next at the end of each iteration.

#### zloop - event-driven reactor

The zloop class provides an event-driven reactor pattern. The reactor handles zmq_pollitem_t items (pollers or writers, sockets or fds), and once-off or repeated timers. Its resolution is 1 msec. It uses a tickless timer to reduce CPU interrupts in inactive processes.

This is the class interface:

//  Callback function for reactor events
typedef int (zloop_fn) (zloop_t *loop, zmq_pollitem_t *item, void *arg);

// Callback for reactor timer events
typedef int (zloop_timer_fn) (zloop_t *loop, int timer_id, void *arg);

//  Create a new zloop reactor
CZMQ_EXPORT zloop_t *
    zloop_new (void);

//  Destroy a reactor
CZMQ_EXPORT void
    zloop_destroy (zloop_t **self_p);

//  Register pollitem with the reactor. When the pollitem is ready, will call
//  the handler, passing the arg. Returns 0 if OK, -1 if there was an error.
//  If you register the pollitem more than once, each instance will invoke its
//  corresponding handler.
CZMQ_EXPORT int
    zloop_poller (zloop_t *self, zmq_pollitem_t *item, zloop_fn handler, void *arg);

//  Cancel a pollitem from the reactor, specified by socket or FD. If both
//  are specified, uses only socket. If multiple poll items exist for same
//  socket/FD, cancels ALL of them.
CZMQ_EXPORT void
    zloop_poller_end (zloop_t *self, zmq_pollitem_t *item);

//  Configure a registered pollitem to ignore errors. If you do not set this, 
//  then pollitems that have errors are removed from the reactor silently.
CZMQ_EXPORT void
    zloop_set_tolerant (zloop_t *self, zmq_pollitem_t *item);

//  Register a timer that expires after some delay and repeats some number of
//  times. At each expiry, will call the handler, passing the arg. To
//  run a timer forever, use 0 times. Returns a timer_id that is used to cancel
//  the timer in the future. Returns -1 if there was an error.
CZMQ_EXPORT int
    zloop_timer (zloop_t *self, size_t delay, size_t times, zloop_timer_fn handler, void *arg);

//  Cancel a specific timer identified by a specific timer_id (as returned by
//  zloop_timer).
CZMQ_EXPORT int
    zloop_timer_end (zloop_t *self, int timer_id);

//  Set verbose tracing of reactor on/off
CZMQ_EXPORT void
    zloop_set_verbose (zloop_t *self, bool verbose);

//  Start the reactor. Takes control of the thread and returns when the ØMQ
//  context is terminated or the process is interrupted, or any event handler
//  returns -1. Event handlers may register new sockets and timers, and
//  cancel sockets. Returns 0 if interrupted, -1 if cancelled by a handler.
CZMQ_EXPORT int
    zloop_start (zloop_t *self);

//  Self test of this class
CZMQ_EXPORT void
    zloop_test (bool verbose);

#### zmonitor - socket event monitor

The zmonitor class provides an API for obtaining socket events such as connected, listen, disconnected, etc. Socket events are only available for sockets connecting or bound to ipc:// and tcp:// endpoints.

This is the class interface:

//  Create a new socket monitor
CZMQ_EXPORT zmonitor_t *
    zmonitor_new (zctx_t *ctx, void *socket, int events);

//  Destroy a socket monitor
CZMQ_EXPORT void
    zmonitor_destroy (zmonitor_t **self_p);

//  Receive a status message from the monitor; if no message arrives within
//  500 msec, or the call was interrupted, returns NULL.
CZMQ_EXPORT zmsg_t *
    zmonitor_recv (zmonitor_t *self);

//  Get the ZeroMQ socket, for polling 
CZMQ_EXPORT void *
    zmonitor_socket (zmonitor_t *self);

//  Enable verbose tracing of commands and activity
CZMQ_EXPORT void
    zmonitor_set_verbose (zmonitor_t *self, bool verbose);

// Self test of this class
CZMQ_EXPORT void
    zmonitor_test (bool verbose);

This class wraps the ZMQ socket monitor API, see zmq_socket_monitor for details. Currently this class requires libzmq v4.0 or later and is empty on older versions of libzmq.

#### zmsg - working with multipart messages

The zmsg class provides methods to send and receive multipart messages across ØMQ sockets. This class provides a list-like container interface, with methods to work with the overall container. zmsg_t messages are composed of zero or more zframe_t frames.

This is the class interface:

//  Create a new empty message object
CZMQ_EXPORT zmsg_t *
    zmsg_new (void);

//  Destroy a message object and all frames it contains
CZMQ_EXPORT void
    zmsg_destroy (zmsg_t **self_p);

//  Receive message from socket, returns zmsg_t object or NULL if the recv
//  was interrupted. Does a blocking recv, if you want to not block then use
//  the zloop class or zmq_poll to check for socket input before receiving.
CZMQ_EXPORT zmsg_t *
    zmsg_recv (void *socket);

//  Send message to socket, destroy after sending. If the message has no
//  frames, sends nothing but destroys the message anyhow. Safe to call
//  if zmsg is null.
CZMQ_EXPORT int
    zmsg_send (zmsg_t **self_p, void *socket);

//  Return size of message, i.e. number of frames (0 or more).
CZMQ_EXPORT size_t
    zmsg_size (zmsg_t *self);

//  Return total size of all frames in message.
CZMQ_EXPORT size_t
    zmsg_content_size (zmsg_t *self);

//  Push frame to the front of the message, i.e. before all other frames.
//  Message takes ownership of frame, will destroy it when message is sent.
//  Returns 0 on success, -1 on error.
CZMQ_EXPORT int
    zmsg_push (zmsg_t *self, zframe_t *frame);

//  Remove first frame from message, if any. Returns frame, or NULL. Caller
//  now owns frame and must destroy it when finished with it.
CZMQ_EXPORT zframe_t *
    zmsg_pop (zmsg_t *self);

//  Add frame to the end of the message, i.e. after all other frames.
//  Message takes ownership of frame, will destroy it when message is sent.
//  Returns 0 on success. Deprecates zmsg_add, which did not nullify the
//  caller's frame reference.
CZMQ_EXPORT int
    zmsg_append (zmsg_t *self, zframe_t **frame_p);

//  Add frame to the end of the message, i.e. after all other frames.
//  Message takes ownership of frame, will destroy it when message is sent.
//  Returns 0 on success.
//  DEPRECATED - will be removed for next stable release
CZMQ_EXPORT int
    zmsg_add (zmsg_t *self, zframe_t *frame);

//  Push block of memory to front of message, as a new frame.
//  Returns 0 on success, -1 on error.
CZMQ_EXPORT int
    zmsg_pushmem (zmsg_t *self, const void *src, size_t size);

//  Add block of memory to the end of the message, as a new frame.
//  Returns 0 on success, -1 on error.
CZMQ_EXPORT int
    zmsg_addmem (zmsg_t *self, const void *src, size_t size);
    
//  Push string as new frame to front of message.
//  Returns 0 on success, -1 on error.
CZMQ_EXPORT int
    zmsg_pushstr (zmsg_t *self, const char *format, ...);

//  Push string as new frame to end of message.
//  Returns 0 on success, -1 on error.
CZMQ_EXPORT int
    zmsg_addstr (zmsg_t *self, const char *format, ...);

//  Pop frame off front of message, return as fresh string. If there were
//  no more frames in the message, returns NULL.
CZMQ_EXPORT char *
    zmsg_popstr (zmsg_t *self);

//  Push frame plus empty frame to front of message, before first frame.
//  Message takes ownership of frame, will destroy it when message is sent.
CZMQ_EXPORT void
    zmsg_wrap (zmsg_t *self, zframe_t *frame);

//  Pop frame off front of message, caller now owns frame
//  If next frame is empty, pops and destroys that empty frame.
CZMQ_EXPORT zframe_t *
    zmsg_unwrap (zmsg_t *self);

//  Remove specified frame from list, if present. Does not destroy frame.
CZMQ_EXPORT void
    zmsg_remove (zmsg_t *self, zframe_t *frame);

//  Set cursor to first frame in message. Returns frame, or NULL, if the 
//  message is empty. Use this to navigate the frames as a list.
CZMQ_EXPORT zframe_t *
    zmsg_first (zmsg_t *self);

//  Return the next frame. If there are no more frames, returns NULL. To move
//  to the first frame call zmsg_first(). Advances the cursor.
CZMQ_EXPORT zframe_t *
    zmsg_next (zmsg_t *self);

//  Return the last frame. If there are no frames, returns NULL.
CZMQ_EXPORT zframe_t *
    zmsg_last (zmsg_t *self);

//  Save message to an open file, return 0 if OK, else -1. The message is 
//  saved as a series of frames, each with length and data. Note that the
//  file is NOT guaranteed to be portable between operating systems, not
//  versions of CZMQ. The file format is at present undocumented and liable
//  to arbitrary change.
CZMQ_EXPORT int
    zmsg_save (zmsg_t *self, FILE *file);

//  Load/append an open file into message, create new message if
//  null message provided. Returns NULL if the message could not 
//  be loaded.
CZMQ_EXPORT zmsg_t *
    zmsg_load (zmsg_t *self, FILE *file);

//  Serialize multipart message to a single buffer. Use this method to send
//  structured messages across transports that do not support multipart data.
//  Allocates and returns a new buffer containing the serialized message.
//  To decode a serialized message buffer, use zmsg_decode ().
CZMQ_EXPORT size_t
    zmsg_encode (zmsg_t *self, byte **buffer);

//  Decodes a serialized message buffer created by zmsg_encode () and returns
//  a new zmsg_t object. Returns NULL if the buffer was badly formatted or 
//  there was insufficient memory to work.
CZMQ_EXPORT zmsg_t *
    zmsg_decode (byte *buffer, size_t buffer_size);

//  Create copy of message, as new message object. Returns a fresh zmsg_t
//  object, or NULL if there was not enough heap memory.
CZMQ_EXPORT zmsg_t *
    zmsg_dup (zmsg_t *self);

//  Print message to open stream
//  Truncates to first 10 frames, for readability.
CZMQ_EXPORT void
    zmsg_fprint (zmsg_t *self, FILE *file);

//  Print message to stdout
CZMQ_EXPORT void
    zmsg_print (zmsg_t *self);

//  Self test of this class
CZMQ_EXPORT int
    zmsg_test (bool verbose);

#### zmutex - wrap lightweight mutexes

The zmutex class provides a portable wrapper for mutexes. Please do not use this class to do multi-threading. It is for the rare case where you absolutely need thread-safe global state. This should happen in system code only. DO NOT USE THIS TO SHARE SOCKETS BETWEEN THREADS, OR DARK THINGS WILL HAPPEN TO YOUR CODE.

This is the class interface:

//  Create a new mutex container
CZMQ_EXPORT zmutex_t *
    zmutex_new (void);

//  Destroy a mutex container
CZMQ_EXPORT void
    zmutex_destroy (zmutex_t **self_p);

//  Lock mutex
CZMQ_EXPORT void
    zmutex_lock (zmutex_t *self);

//  Unlock mutex
CZMQ_EXPORT void
    zmutex_unlock (zmutex_t *self);

//  Try to lock mutex
CZMQ_EXPORT int
    zmutex_try_lock (zmutex_t *self);


//  Self test of this class
CZMQ_EXPORT int
    zmutex_test (bool verbose);

#### zpoller - trivial socket poller class

The zpoller class provides a minimalist interface to ZeroMQ's zmq_poll API, for the very common case of reading from a number of sockets. It does not provide polling for output, nor polling on file handles. If you need either of these, use the zmq_poll API directly.

This is the class interface:

//  Create new poller
CZMQ_EXPORT zpoller_t *
    zpoller_new (void *reader, ...);

//  Destroy a poller
CZMQ_EXPORT void
    zpoller_destroy (zpoller_t **self_p);

// Add a reader to be polled.
CZMQ_EXPORT int
    zpoller_add (zpoller_t *self, void *reader);

//  Poll the registered readers for I/O, return first socket that has input.
//  This means the order that sockets are defined in the poll list affects
//  their priority. If you need a balanced poll, use the low level zmq_poll
//  method directly. If the poll call was interrupted (SIGINT), or the ZMQ
//  context was destroyed, or the timeout expired, returns NULL. You can
//  test the actual exit condition by calling zpoller_expired () and
//  zpoller_terminated (). Timeout is in msec.
CZMQ_EXPORT void *
    zpoller_wait (zpoller_t *self, int timeout);

//  Return true if the last zpoller_wait () call ended because the timeout
//  expired, without any error.
CZMQ_EXPORT bool
    zpoller_expired (zpoller_t *self);

//  Return true if the last zpoller_wait () call ended because the process
//  was interrupted, or the parent context was destroyed.
CZMQ_EXPORT bool
    zpoller_terminated (zpoller_t *self);

//  Self test of this class
CZMQ_EXPORT int
    zpoller_test (bool verbose);

#### zproxy - convenient zmq_proxy API

The zproxy class simplifies working with the zmq_proxy_steerable API.

This is the class interface:

//  Constructor
//  Create a new zproxy object. You must create the frontend and backend
//  sockets, configure them, and connect or bind them, before you pass them
//  to the constructor. Do NOT use the sockets again, after passing them to
//  this method.
CZMQ_EXPORT zproxy_t *
    zproxy_new (zctx_t *ctx, void *frontend, void *backend);

//  Destructor
//  Destroy a zproxy object; note this first stops the proxy.
CZMQ_EXPORT void
    zproxy_destroy (zproxy_t **self_p);

//  Copy all proxied messages to specified endpoint; if this is NULL, any
//  in-progress capturing will be stopped. You must already have bound the
//  endpoint to a PULL socket.
CZMQ_EXPORT void
    zproxy_capture (zproxy_t *self, char *endpoint);

//  Pauses a zproxy object; a paused proxy will cease processing messages,
//  causing them to be queued up and potentially hit the high-water mark on
//  the frontend socket, causing messages to be dropped, or writing
//  applications to block.
CZMQ_EXPORT void
    zproxy_pause (zproxy_t *self);

//  Resume a zproxy object
CZMQ_EXPORT void
    zproxy_resume (zproxy_t *self);

// Self test of this class
CZMQ_EXPORT void
    zproxy_test (bool verbose);

There's no fallback to the older zmq_proxy, since that does not allow dynamic control. If you need zmq_proxy (if you are using an older version of libzmq), use that directly in your code.

#### zsocket - working with ØMQ sockets

The zsocket class provides helper functions for ØMQ sockets. It doesn't wrap the ØMQ socket type, to avoid breaking all libzmq socket-related calls.

This is the class interface:

//  This port range is defined by IANA for dynamic or private ports
//  We use this when choosing a port for dynamic binding.
#define ZSOCKET_DYNFROM     0xc000
#define ZSOCKET_DYNTO       0xffff

//  Callback function for zero-copy methods
typedef void (zsocket_free_fn) (void *data, void *arg);

//  Create a new socket within our CZMQ context, replaces zmq_socket.
//  Use this to get automatic management of the socket at shutdown.
//  Note: SUB sockets do not automatically subscribe to everything; you
//  must set filters explicitly.
CZMQ_EXPORT void *
    zsocket_new (zctx_t *self, int type);

//  Destroy a socket within our CZMQ context, replaces zmq_close.
CZMQ_EXPORT void
    zsocket_destroy (zctx_t *self, void *socket);

//  Bind a socket to a formatted endpoint. If the port is specified as
//  '*', binds to any free port from ZSOCKET_DYNFROM to ZSOCKET_DYNTO
//  and returns the actual port number used. Otherwise asserts that the
//  bind succeeded with the specified port number. Always returns the
//  port number if successful.
CZMQ_EXPORT int
    zsocket_bind (void *socket, const char *format, ...);

//  Unbind a socket from a formatted endpoint.
//  Returns 0 if OK, -1 if the endpoint was invalid or the function
//  isn't supported.
CZMQ_EXPORT int
    zsocket_unbind (void *socket, const char *format, ...);

//  Connect a socket to a formatted endpoint
//  Returns 0 if OK, -1 if the endpoint was invalid.
CZMQ_EXPORT int
    zsocket_connect (void *socket, const char *format, ...);

//  Disonnect a socket from a formatted endpoint
//  Returns 0 if OK, -1 if the endpoint was invalid or the function
//  isn't supported.
CZMQ_EXPORT int
    zsocket_disconnect (void *socket, const char *format, ...);

//  Poll for input events on the socket. Returns TRUE if there is input
//  ready on the socket, else FALSE.
CZMQ_EXPORT bool
    zsocket_poll (void *socket, int msecs);

//  Returns socket type as printable constant string
CZMQ_EXPORT char *
    zsocket_type_str (void *socket);

//  Send data over a socket as a single frame
//  Returns -1 on error, 0 on success
CZMQ_EXPORT int
    zsocket_sendmem (void *socket, const void* data, size_t size, int flags);

//  Self test of this class
CZMQ_EXPORT int
    zsocket_test (bool verbose);

#### zsockopt - working with ØMQ socket options

The zsockopt class provides access to the ØMQ getsockopt/setsockopt API.

This is the class interface:

#if (ZMQ_VERSION_MAJOR == 4)
//  Get socket options
CZMQ_EXPORT int zsocket_tos (void *zocket);
CZMQ_EXPORT int zsocket_plain_server (void *zocket);
CZMQ_EXPORT char * zsocket_plain_username (void *zocket);
CZMQ_EXPORT char * zsocket_plain_password (void *zocket);
CZMQ_EXPORT int zsocket_curve_server (void *zocket);
CZMQ_EXPORT char * zsocket_curve_publickey (void *zocket);
CZMQ_EXPORT char * zsocket_curve_secretkey (void *zocket);
CZMQ_EXPORT char * zsocket_curve_serverkey (void *zocket);
CZMQ_EXPORT char * zsocket_zap_domain (void *zocket);
CZMQ_EXPORT int zsocket_mechanism (void *zocket);
CZMQ_EXPORT int zsocket_ipv6 (void *zocket);
CZMQ_EXPORT int zsocket_immediate (void *zocket);
CZMQ_EXPORT int zsocket_ipv4only (void *zocket);
CZMQ_EXPORT int zsocket_type (void *zocket);
CZMQ_EXPORT int zsocket_sndhwm (void *zocket);
CZMQ_EXPORT int zsocket_rcvhwm (void *zocket);
CZMQ_EXPORT int zsocket_affinity (void *zocket);
CZMQ_EXPORT char * zsocket_identity (void *zocket);
CZMQ_EXPORT int zsocket_rate (void *zocket);
CZMQ_EXPORT int zsocket_recovery_ivl (void *zocket);
CZMQ_EXPORT int zsocket_sndbuf (void *zocket);
CZMQ_EXPORT int zsocket_rcvbuf (void *zocket);
CZMQ_EXPORT int zsocket_linger (void *zocket);
CZMQ_EXPORT int zsocket_reconnect_ivl (void *zocket);
CZMQ_EXPORT int zsocket_reconnect_ivl_max (void *zocket);
CZMQ_EXPORT int zsocket_backlog (void *zocket);
CZMQ_EXPORT int zsocket_maxmsgsize (void *zocket);
CZMQ_EXPORT int zsocket_multicast_hops (void *zocket);
CZMQ_EXPORT int zsocket_rcvtimeo (void *zocket);
CZMQ_EXPORT int zsocket_sndtimeo (void *zocket);
CZMQ_EXPORT int zsocket_tcp_keepalive (void *zocket);
CZMQ_EXPORT int zsocket_tcp_keepalive_idle (void *zocket);
CZMQ_EXPORT int zsocket_tcp_keepalive_cnt (void *zocket);
CZMQ_EXPORT int zsocket_tcp_keepalive_intvl (void *zocket);
CZMQ_EXPORT char * zsocket_tcp_accept_filter (void *zocket);
CZMQ_EXPORT int zsocket_rcvmore (void *zocket);
CZMQ_EXPORT int zsocket_fd (void *zocket);
CZMQ_EXPORT int zsocket_events (void *zocket);
CZMQ_EXPORT char * zsocket_last_endpoint (void *zocket);

//  Set socket options
CZMQ_EXPORT void zsocket_set_tos (void *zocket, int tos);
CZMQ_EXPORT void zsocket_set_router_handover (void *zocket, int router_handover);
CZMQ_EXPORT void zsocket_set_router_mandatory (void *zocket, int router_mandatory);
CZMQ_EXPORT void zsocket_set_probe_router (void *zocket, int probe_router);
CZMQ_EXPORT void zsocket_set_req_relaxed (void *zocket, int req_relaxed);
CZMQ_EXPORT void zsocket_set_req_correlate (void *zocket, int req_correlate);
CZMQ_EXPORT void zsocket_set_conflate (void *zocket, int conflate);
CZMQ_EXPORT void zsocket_set_plain_server (void *zocket, int plain_server);
CZMQ_EXPORT void zsocket_set_plain_username (void *zocket, const char * plain_username);
CZMQ_EXPORT void zsocket_set_plain_password (void *zocket, const char * plain_password);
CZMQ_EXPORT void zsocket_set_curve_server (void *zocket, int curve_server);
CZMQ_EXPORT void zsocket_set_curve_publickey (void *zocket, const char * curve_publickey);
CZMQ_EXPORT void zsocket_set_curve_publickey_bin (void *zocket, const byte *curve_publickey);
CZMQ_EXPORT void zsocket_set_curve_secretkey (void *zocket, const char * curve_secretkey);
CZMQ_EXPORT void zsocket_set_curve_secretkey_bin (void *zocket, const byte *curve_secretkey);
CZMQ_EXPORT void zsocket_set_curve_serverkey (void *zocket, const char * curve_serverkey);
CZMQ_EXPORT void zsocket_set_curve_serverkey_bin (void *zocket, const byte *curve_serverkey);
CZMQ_EXPORT void zsocket_set_zap_domain (void *zocket, const char * zap_domain);
CZMQ_EXPORT void zsocket_set_ipv6 (void *zocket, int ipv6);
CZMQ_EXPORT void zsocket_set_immediate (void *zocket, int immediate);
CZMQ_EXPORT void zsocket_set_router_raw (void *zocket, int router_raw);
CZMQ_EXPORT void zsocket_set_ipv4only (void *zocket, int ipv4only);
CZMQ_EXPORT void zsocket_set_delay_attach_on_connect (void *zocket, int delay_attach_on_connect);
CZMQ_EXPORT void zsocket_set_sndhwm (void *zocket, int sndhwm);
CZMQ_EXPORT void zsocket_set_rcvhwm (void *zocket, int rcvhwm);
CZMQ_EXPORT void zsocket_set_affinity (void *zocket, int affinity);
CZMQ_EXPORT void zsocket_set_subscribe (void *zocket, const char * subscribe);
CZMQ_EXPORT void zsocket_set_unsubscribe (void *zocket, const char * unsubscribe);
CZMQ_EXPORT void zsocket_set_identity (void *zocket, const char * identity);
CZMQ_EXPORT void zsocket_set_rate (void *zocket, int rate);
CZMQ_EXPORT void zsocket_set_recovery_ivl (void *zocket, int recovery_ivl);
CZMQ_EXPORT void zsocket_set_sndbuf (void *zocket, int sndbuf);
CZMQ_EXPORT void zsocket_set_rcvbuf (void *zocket, int rcvbuf);
CZMQ_EXPORT void zsocket_set_linger (void *zocket, int linger);
CZMQ_EXPORT void zsocket_set_reconnect_ivl (void *zocket, int reconnect_ivl);
CZMQ_EXPORT void zsocket_set_reconnect_ivl_max (void *zocket, int reconnect_ivl_max);
CZMQ_EXPORT void zsocket_set_backlog (void *zocket, int backlog);
CZMQ_EXPORT void zsocket_set_maxmsgsize (void *zocket, int maxmsgsize);
CZMQ_EXPORT void zsocket_set_multicast_hops (void *zocket, int multicast_hops);
CZMQ_EXPORT void zsocket_set_rcvtimeo (void *zocket, int rcvtimeo);
CZMQ_EXPORT void zsocket_set_sndtimeo (void *zocket, int sndtimeo);
CZMQ_EXPORT void zsocket_set_xpub_verbose (void *zocket, int xpub_verbose);
CZMQ_EXPORT void zsocket_set_tcp_keepalive (void *zocket, int tcp_keepalive);
CZMQ_EXPORT void zsocket_set_tcp_keepalive_idle (void *zocket, int tcp_keepalive_idle);
CZMQ_EXPORT void zsocket_set_tcp_keepalive_cnt (void *zocket, int tcp_keepalive_cnt);
CZMQ_EXPORT void zsocket_set_tcp_keepalive_intvl (void *zocket, int tcp_keepalive_intvl);
CZMQ_EXPORT void zsocket_set_tcp_accept_filter (void *zocket, const char * tcp_accept_filter);

//  Emulation of widely-used 2.x socket options
CZMQ_EXPORT void zsocket_set_hwm (void *zocket, int hwm);
#endif

#if (ZMQ_VERSION_MAJOR == 3)
//  Get socket options
CZMQ_EXPORT int zsocket_ipv4only (void *zocket);
CZMQ_EXPORT int zsocket_type (void *zocket);
CZMQ_EXPORT int zsocket_sndhwm (void *zocket);
CZMQ_EXPORT int zsocket_rcvhwm (void *zocket);
CZMQ_EXPORT int zsocket_affinity (void *zocket);
CZMQ_EXPORT char * zsocket_identity (void *zocket);
CZMQ_EXPORT int zsocket_rate (void *zocket);
CZMQ_EXPORT int zsocket_recovery_ivl (void *zocket);
CZMQ_EXPORT int zsocket_sndbuf (void *zocket);
CZMQ_EXPORT int zsocket_rcvbuf (void *zocket);
CZMQ_EXPORT int zsocket_linger (void *zocket);
CZMQ_EXPORT int zsocket_reconnect_ivl (void *zocket);
CZMQ_EXPORT int zsocket_reconnect_ivl_max (void *zocket);
CZMQ_EXPORT int zsocket_backlog (void *zocket);
CZMQ_EXPORT int zsocket_maxmsgsize (void *zocket);
CZMQ_EXPORT int zsocket_multicast_hops (void *zocket);
CZMQ_EXPORT int zsocket_rcvtimeo (void *zocket);
CZMQ_EXPORT int zsocket_sndtimeo (void *zocket);
CZMQ_EXPORT int zsocket_tcp_keepalive (void *zocket);
CZMQ_EXPORT int zsocket_tcp_keepalive_idle (void *zocket);
CZMQ_EXPORT int zsocket_tcp_keepalive_cnt (void *zocket);
CZMQ_EXPORT int zsocket_tcp_keepalive_intvl (void *zocket);
CZMQ_EXPORT char * zsocket_tcp_accept_filter (void *zocket);
CZMQ_EXPORT int zsocket_rcvmore (void *zocket);
CZMQ_EXPORT int zsocket_fd (void *zocket);
CZMQ_EXPORT int zsocket_events (void *zocket);
CZMQ_EXPORT char * zsocket_last_endpoint (void *zocket);

//  Set socket options
CZMQ_EXPORT void zsocket_set_router_raw (void *zocket, int router_raw);
CZMQ_EXPORT void zsocket_set_ipv4only (void *zocket, int ipv4only);
CZMQ_EXPORT void zsocket_set_delay_attach_on_connect (void *zocket, int delay_attach_on_connect);
CZMQ_EXPORT void zsocket_set_sndhwm (void *zocket, int sndhwm);
CZMQ_EXPORT void zsocket_set_rcvhwm (void *zocket, int rcvhwm);
CZMQ_EXPORT void zsocket_set_affinity (void *zocket, int affinity);
CZMQ_EXPORT void zsocket_set_subscribe (void *zocket, const char * subscribe);
CZMQ_EXPORT void zsocket_set_unsubscribe (void *zocket, const char * unsubscribe);
CZMQ_EXPORT void zsocket_set_identity (void *zocket, const char * identity);
CZMQ_EXPORT void zsocket_set_rate (void *zocket, int rate);
CZMQ_EXPORT void zsocket_set_recovery_ivl (void *zocket, int recovery_ivl);
CZMQ_EXPORT void zsocket_set_sndbuf (void *zocket, int sndbuf);
CZMQ_EXPORT void zsocket_set_rcvbuf (void *zocket, int rcvbuf);
CZMQ_EXPORT void zsocket_set_linger (void *zocket, int linger);
CZMQ_EXPORT void zsocket_set_reconnect_ivl (void *zocket, int reconnect_ivl);
CZMQ_EXPORT void zsocket_set_reconnect_ivl_max (void *zocket, int reconnect_ivl_max);
CZMQ_EXPORT void zsocket_set_backlog (void *zocket, int backlog);
CZMQ_EXPORT void zsocket_set_maxmsgsize (void *zocket, int maxmsgsize);
CZMQ_EXPORT void zsocket_set_multicast_hops (void *zocket, int multicast_hops);
CZMQ_EXPORT void zsocket_set_rcvtimeo (void *zocket, int rcvtimeo);
CZMQ_EXPORT void zsocket_set_sndtimeo (void *zocket, int sndtimeo);
CZMQ_EXPORT void zsocket_set_xpub_verbose (void *zocket, int xpub_verbose);
CZMQ_EXPORT void zsocket_set_tcp_keepalive (void *zocket, int tcp_keepalive);
CZMQ_EXPORT void zsocket_set_tcp_keepalive_idle (void *zocket, int tcp_keepalive_idle);
CZMQ_EXPORT void zsocket_set_tcp_keepalive_cnt (void *zocket, int tcp_keepalive_cnt);
CZMQ_EXPORT void zsocket_set_tcp_keepalive_intvl (void *zocket, int tcp_keepalive_intvl);
CZMQ_EXPORT void zsocket_set_tcp_accept_filter (void *zocket, const char * tcp_accept_filter);

//  Emulation of widely-used 2.x socket options
CZMQ_EXPORT void zsocket_set_hwm (void *zocket, int hwm);
#endif

#if (ZMQ_VERSION_MAJOR == 2)
//  Get socket options
CZMQ_EXPORT int zsocket_hwm (void *zocket);
CZMQ_EXPORT int zsocket_swap (void *zocket);
CZMQ_EXPORT int zsocket_affinity (void *zocket);
CZMQ_EXPORT char * zsocket_identity (void *zocket);
CZMQ_EXPORT int zsocket_rate (void *zocket);
CZMQ_EXPORT int zsocket_recovery_ivl (void *zocket);
CZMQ_EXPORT int zsocket_recovery_ivl_msec (void *zocket);
CZMQ_EXPORT int zsocket_mcast_loop (void *zocket);
#   if (ZMQ_VERSION_MINOR == 2)
CZMQ_EXPORT int zsocket_rcvtimeo (void *zocket);
#   endif
#   if (ZMQ_VERSION_MINOR == 2)
CZMQ_EXPORT int zsocket_sndtimeo (void *zocket);
#   endif
CZMQ_EXPORT int zsocket_sndbuf (void *zocket);
CZMQ_EXPORT int zsocket_rcvbuf (void *zocket);
CZMQ_EXPORT int zsocket_linger (void *zocket);
CZMQ_EXPORT int zsocket_reconnect_ivl (void *zocket);
CZMQ_EXPORT int zsocket_reconnect_ivl_max (void *zocket);
CZMQ_EXPORT int zsocket_backlog (void *zocket);
CZMQ_EXPORT int zsocket_type (void *zocket);
CZMQ_EXPORT int zsocket_rcvmore (void *zocket);
CZMQ_EXPORT int zsocket_fd (void *zocket);
CZMQ_EXPORT int zsocket_events (void *zocket);

//  Set socket options
CZMQ_EXPORT void zsocket_set_hwm (void *zocket, int hwm);
CZMQ_EXPORT void zsocket_set_swap (void *zocket, int swap);
CZMQ_EXPORT void zsocket_set_affinity (void *zocket, int affinity);
CZMQ_EXPORT void zsocket_set_identity (void *zocket, const char * identity);
CZMQ_EXPORT void zsocket_set_rate (void *zocket, int rate);
CZMQ_EXPORT void zsocket_set_recovery_ivl (void *zocket, int recovery_ivl);
CZMQ_EXPORT void zsocket_set_recovery_ivl_msec (void *zocket, int recovery_ivl_msec);
CZMQ_EXPORT void zsocket_set_mcast_loop (void *zocket, int mcast_loop);
#   if (ZMQ_VERSION_MINOR == 2)
CZMQ_EXPORT void zsocket_set_rcvtimeo (void *zocket, int rcvtimeo);
#   endif
#   if (ZMQ_VERSION_MINOR == 2)
CZMQ_EXPORT void zsocket_set_sndtimeo (void *zocket, int sndtimeo);
#   endif
CZMQ_EXPORT void zsocket_set_sndbuf (void *zocket, int sndbuf);
CZMQ_EXPORT void zsocket_set_rcvbuf (void *zocket, int rcvbuf);
CZMQ_EXPORT void zsocket_set_linger (void *zocket, int linger);
CZMQ_EXPORT void zsocket_set_reconnect_ivl (void *zocket, int reconnect_ivl);
CZMQ_EXPORT void zsocket_set_reconnect_ivl_max (void *zocket, int reconnect_ivl_max);
CZMQ_EXPORT void zsocket_set_backlog (void *zocket, int backlog);
CZMQ_EXPORT void zsocket_set_subscribe (void *zocket, const char * subscribe);
CZMQ_EXPORT void zsocket_set_unsubscribe (void *zocket, const char * unsubscribe);
#endif

//  Self test of this class
int zsockopt_test (bool verbose);

This class is generated, using the GSL code generator. See the sockopts XML file, which provides the metadata, and the sockopts.gsl template, which does the work.

#### zstr - sending and receiving strings

The zstr class provides utility functions for sending and receiving C strings across ØMQ sockets. It sends strings without a terminating null, and appends a null byte on received strings. This class is for simple message sending.

This is the class interface:

//  Receive C string from socket. Caller must free returned string using
//  zstr_free(). Returns NULL if the context is being terminated or the
//  process was interrupted.
CZMQ_EXPORT char *
    zstr_recv (void *socket);

//  Receive C string from socket, if socket had input ready. Caller must
//  free returned string using zstr_free. Returns NULL if there was no input
//  waiting, or if the context was terminated. Use zctx_interrupted to exit
//  any loop that relies on this method.
CZMQ_EXPORT char *
    zstr_recv_nowait (void *socket);

//  Send a formatted string to a socket
CZMQ_EXPORT int
    zstr_send (void *socket, const char *format, ...);

//  Send a formatted string to a socket, with MORE flag
CZMQ_EXPORT int
    zstr_sendm (void *socket, const char *format, ...);

//  Send a series of strings (until NULL) as multipart data
//  Returns 0 if the strings could be sent OK, or -1 on error.
CZMQ_EXPORT int
    zstr_sendx (void *socket, const char *string, ...);

//  Receive a series of strings (until NULL) from multipart data.
//  Each string is allocated and filled with string data; if there
//  are not enough frames, unallocated strings are set to NULL.
//  Returns -1 if the message could not be read, else returns the
//  number of strings filled, zero or more. Free each returned string
//  using zstr_free().
CZMQ_EXPORT int
    zstr_recvx (void *socket, char **string_p, ...);

//  Free a provided string, and nullify the parent pointer. Safe to call on
//  a null pointer.
CZMQ_EXPORT void
    zstr_free (char **string_p);

//  Self test of this class
CZMQ_EXPORT int
    zstr_test (bool verbose);

#### zsys - system-level methods

The zsys class provides a portable wrapper for miscellaneous functions that we want to wrap but which don't fit into any of the existing classes. Eventually all non-portable functionality might be moved here but for now it covers only file systems.

This is the class interface:

#define UDP_FRAME_MAX   255         //  Max size of UDP frame

//  Callback for interrupt signal handler
typedef void (zsys_handler_fn) (int signal_value);

//  Set interrupt handler (NULL means external handler)
CZMQ_EXPORT void
    zsys_handler_set (zsys_handler_fn *handler_fn);

//  Reset interrupt handler, call this at exit if needed
CZMQ_EXPORT void
    zsys_handler_reset (void);

//  Set network interface name to use for broadcasts
//  Use this to force the interface for beacons
//  This is experimental; may be merged into zbeacon class.
CZMQ_EXPORT void
    zsys_set_interface (char *iinterface);

//  Return network interface name to use for broadcasts.
//  Returns "" if no interface was set.
//  This is experimental; may be merged into zbeacon class.
CZMQ_EXPORT char *
    zsys_interface (void);

//  Return 1 if file exists, else zero
CZMQ_EXPORT bool
    zsys_file_exists (const char *filename);

//  Return size of file, or -1 if not found
CZMQ_EXPORT ssize_t
    zsys_file_size (const char *filename);

//  Return file modification time. Returns 0 if the file does not exist.
CZMQ_EXPORT time_t
    zsys_file_modified (const char *filename);

//  Return file mode
CZMQ_EXPORT mode_t
    zsys_file_mode (const char *filename);

//  Delete file. Does not complain if the file is absent
CZMQ_EXPORT int
    zsys_file_delete (const char *filename);

//  Check if file is 'stable'
CZMQ_EXPORT bool
    zsys_file_stable (const char *filename);

//  Create a file path if it doesn't exist. The file path is treated as a 
//  printf format.
CZMQ_EXPORT int
    zsys_dir_create (const char *pathname, ...);

//  Remove a file path if empty; the pathname is treated as printf format.
CZMQ_EXPORT int
    zsys_dir_delete (const char *pathname, ...);

//  Set private file creation mode; all files created from here will be
//  readable/writable by the owner only.
CZMQ_EXPORT void
    zsys_file_mode_private (void);

//  Reset default file creation mode; all files created from here will use
//  process file mode defaults.
CZMQ_EXPORT void
    zsys_file_mode_default (void);

//  Return the czmq version for run-time API detection
CZMQ_EXPORT void
    zsys_version (int *major, int *minor, int *patch);

//  Format a string with variable arguments, returning a freshly allocated
//  buffer. If there was insufficient memory, returns NULL. Free the returned
//  string using zstr_free().
CZMQ_EXPORT char *
    zsys_vprintf (const char *format, va_list argptr);

//  Create UDP beacon socket; if the routable option is true, uses
//  multicast (not yet implemented), else uses broadcast. This method
//  and related ones might _eventually_ be moved to a zudp class.
CZMQ_EXPORT SOCKET
    zsys_udp_new (bool routable);

//  Send zframe to UDP socket
CZMQ_EXPORT void
    zsys_udp_send (SOCKET udpsock, zframe_t *frame, inaddr_t *address);

//  Receive zframe from UDP socket, and set address of peer that sent it
//  The peername must be a char [INET_ADDRSTRLEN] array.
CZMQ_EXPORT zframe_t *
    zsys_udp_recv (SOCKET udpsock, char *peername);

//  Handle an I/O error on some socket operation; will report and die on
//  fatal errors, and continue silently on "try again" errors.
CZMQ_EXPORT void
    zsys_socket_error (char *reason);
    
//  Self test of this class
CZMQ_EXPORT int
    zsys_test (bool verbose);

#### zrex - working with regular expressions

The zrex class provides a simple API for regular expressions, wrapping Alberto Demichelis's T-Rex library from http://tiny-rex.sourceforge.net/.

This is the class interface:

//  Constructor. Optionally, sets an expression against which we can match
//  text and capture hits. If there is an error in the expression, reports
//  zrex_valid() as false and provides the error in zrex_strerror(). If you
//  set a pattern, you can call zrex_hits() to test it against text.
CZMQ_EXPORT zrex_t *
    zrex_new (const char *expression);

//  Destructor
CZMQ_EXPORT void
    zrex_destroy (zrex_t **self_p);

//  Return true if the expression was valid and compiled without errors.
CZMQ_EXPORT bool
    zrex_valid (zrex_t *self);

//  Return the error message generated during compilation of the expression.
CZMQ_EXPORT const char *
    zrex_strerror (zrex_t *self);

//  Matches the text against a previously set expression, and reports the
//  number of hits (aka "capture groups" in e.g. Perl). If the text does
//  not match, returns 0. If it matches, returns 1 or greater, depending on
//  how many "(...)" groups the expression has. An expression with one group
//  will produce 2 hits, one for the whole expression and one for the group.
//  To retrieve the individual hits, call zrex_hit ().
CZMQ_EXPORT int
    zrex_hits (zrex_t *self, const char *text);

//  Matches the text against a new expression, and reports the number of
//  hits. If the text does not match, returns 0. If it matches, returns 1 or
//  greater, depending on how many "(...)" groups the expression has. An
//  expression with one group will produce 2 hits, one for the whole
//  expression and one for the group. To retrieve the individual hits, call
//  zrex_hit ().
CZMQ_EXPORT int
    zrex_eq (zrex_t *self, const char *text, const char *expression);

//  Returns the Nth sequence captured from the last expression match, where
//  N is 0 to the value returned by zrex_hits() or zrex_eq(). Sequence 0
//  is always the whole matching string. Sequence 1 is the first capture
//  group, if any, and so on.
CZMQ_EXPORT const char *
    zrex_hit (zrex_t *self, uint index);

//  Self test of this class
CZMQ_EXPORT int
    zrex_test (bool verbose);

The underlying TRex class implements the following expressions:

\ Quote the next metacharacter ^ Match the beginning of the string . Match any character $ Match the end of the string | Alternation () Grouping (captures a 'hit') [] Character class

==GREEDY CLOSURES==

•  Match 0 or more times
  

•  Match 1 or more times
  

? Match 1 or 0 times {n} Match exactly n times {n,} Match at least n times {n,m} Match at least n but not more than m times

==ESCAPE CHARACTERS== \t tab (HT, TAB) \n newline (LF, NL) \r return (CR) \f form feed (FF)

==PREDEFINED CLASSES== \l lowercase next char \u uppercase next char \a alpha [a-zA-Z] \w alphanumeric [0-9a-zA-Z] \s space characters \d decimal digits \x hexadecimal digits \c control characters \p punctuation \b word boundary \A non letters \W non alphanumeric \S non space \D non decimal digits \X non hexadecimal digits \C non control characters \P non punctuation \B non word boundary

#### zthread - working with system threads

The zthread class wraps OS thread creation. It creates detached threads that look like normal OS threads, or attached threads that share the caller's ØMQ context, and get an inproc pipe to talk back to the parent thread. Detached threads create their own ØMQ contexts as needed.

This is the class interface:

//  Detached threads follow POSIX pthreads API
typedef void *(zthread_detached_fn) (void *args);

//  Attached threads get context and pipe from parent
typedef void (zthread_attached_fn) (void *args, zctx_t *ctx, void *pipe);

//  Create a detached thread. A detached thread operates autonomously
//  and is used to simulate a separate process. It gets no ctx, and no
//  pipe.
CZMQ_EXPORT int
    zthread_new (zthread_detached_fn *thread_fn, void *args);

//  Create an attached thread. An attached thread gets a ctx and a PAIR
//  pipe back to its parent. It must monitor its pipe, and exit if the
//  pipe becomes unreadable. Do not destroy the ctx, the thread does this
//  automatically when it ends.
CZMQ_EXPORT void *
    zthread_fork (zctx_t *ctx, zthread_attached_fn *thread_fn, void *args);

//  Self test of this class
CZMQ_EXPORT int
    zthread_test (bool verbose);

We have several use cases for multiple threads. One is to simulate many processes, so we can test ØMQ designs and flows more easily. Another is to create APIs that can send and receive ØMQ messages in the background.

zthread solves these two use cases separately, using the zthread_new and zthead_fork methods respectively. These methods wrap the native system calls needed to start threads, so your code can remain fully portable.

Detached threads follow the POSIX pthreads API; they accept a void * argument and return a void * result (always NULL in our case).

Attached thread receive a void * argument, a zctx_t context, and a pipe socket. The pipe socket is a PAIR socket that is connected back to the caller. When you call zthread_fork, it returns you a PAIR socket that is the other end of this pipe. Thus attached threads can talk back to their parent threads over the pipe. We use this very heavily when making so-called "asynchronous" APIs, which you can see in the Guide examples like 'clone'.

To recap some rules about threading: do not share sockets between threads or your code will crash. You can migrate a socket from one thread to a child thread, if you stop using it in the parent thread immediately after creating the child thread. If you want to connect sockets over inproc:// they must share the same ØMQ context, i.e. be attached threads. You should always use zthread_fork to create an attached thread; it is not sufficient to pass a zctx_t structure to a detached thread (this will crash).

If you want to communicate over ipc:// or tcp:// you may be sharing the same context, or use separate contexts. Thus, every detached thread usually starts by creating its own zctx_t instance.

#### ztree - generic red-black tree container

Red black tree container Derived from Emin Martianan's Red Black which is licensed for free use. http://web.mit.edu/~emin/www.old/source_code/red_black_tree/index.html

This is the class interface:

//  Callback function for ztee_walk method
typedef int (ztree_walk_fn) (const char *key, void *value, void *argument);

//  Callback function for ztree_freefn method
typedef void (ztree_free_fn) (void *data);

//  Comparison function for ztree ordering
//  returns -1 for key1 < key2, 0 if key1 == key 2, 1 for key1 > key2
//  if key's are strings okay to use strcmp as function
typedef int (ztree_compare_fn) (const char *key1, const char *key2);

//  Create a new tree container
CZMQ_EXPORT ztree_t *
    ztree_new (ztree_compare_fn *compare_func);

//  Destroy a tree container
CZMQ_EXPORT void
    ztree_destroy (ztree_t **self_p);

//  Insert node into tree with specified key and value
//  If key is already present returns -1 and leaves existing node unchanged
//  Returns 0 on success.
CZMQ_EXPORT int
    ztree_insert (ztree_t *self, const char *key, void *value);

//  Update node in tree with specified key and value.
//  If key is already present, destroys old value and inserts new one.
//  Use free_fn method to ensure deallocator is properly called on value.
CZMQ_EXPORT void
    ztree_update (ztree_t *self, const char *key, void *value);

//  Remove a node specified by key from the tree. If there was no such
//  node, this function does nothing.
CZMQ_EXPORT void
    ztree_delete (ztree_t *self, const char *key);

//  Return the value at the specified key, or null
CZMQ_EXPORT void *
    ztree_lookup (ztree_t *self, const char *key);

//  Set a free function for the specified tree node. When the value is
//  destroyed, the free function, if any, is called on that node.
//  Use this when tree values are dynamically allocated, to ensure that
//  you don't have memory leaks. You can pass 'free' or NULL as a free_fn.
//  Returns the item, or NULL if there is no such item.
CZMQ_EXPORT void *
    ztree_freefn (ztree_t *self, const char *key, ztree_free_fn *free_fn);

//  Return the number of keys/values in the tree
CZMQ_EXPORT size_t
    ztree_size (ztree_t *self);

//  Return keys for nodes in tree
CZMQ_EXPORT zlist_t *
    ztree_keys (ztree_t *self);

//  Copy the entire tree, return the copy
CZMQ_EXPORT ztree_t *
    ztree_dup (ztree_t *self);

// Walk the tree depth-first, left-to-right order.
// Stops if callback function returns non-zero and returns
// final return code from callback function (zero = success).
CZMQ_EXPORT int
    ztree_walk (ztree_t *self, ztree_walk_fn *callback, void *argument);

//  Save tree to a text file in name=value format. Values must be
//  printable strings; keys may not contain '=' character. Returns 0 if OK,
//  else -1 if a file error occurred.
CZMQ_EXPORT int
    ztree_save (ztree_t *self, const char *filename);

//  Load tree from a text file in name=value format; tree must
//  already exist. Tree values must printable strings; keys may not contain
//  '=' character. Returns 0 if OK, else -1 if a file was not readable.
CZMQ_EXPORT int
    ztree_load (ztree_t *self, const char *filename);

//  Set tree for automatic value destruction
CZMQ_EXPORT void
    ztree_autofree (ztree_t *self);

//  Self test of this class
CZMQ_EXPORT void
    ztree_test (int verbose);

TODO: code style needs cleanup to match CLASS guideliness - poor variable names like 'x' - indentation and if/else layouts - possibly removal of all tree code to foreign/

## Under the Hood ### Adding a New Class

If you define a new CZMQ class myclass you need to:

• Write the zmyclass.c and zmyclass.h source files, in src and include respectively.
• Add#include <zmyclass.h> to include/czmq.h.
• Add the myclass header and test call to src/czmq_selftest.c.
• Add a reference documentation to 'doc/zmyclass.txt'.
• Add myclass to 'model/projects.xml` and read model/README.txt.
• Add a section to README.txt.

### Documentation

Man pages are generated from the class header and source files via the doc/mkman tool, and similar functionality in the gitdown tool (http://github.com/imatix/gitdown). The header file for a class must wrap its interface as follows (example is from include/zclock.h):

//  @interface
//  Sleep for a number of milliseconds
void
    zclock_sleep (int msecs);

//  Return current system clock as milliseconds
int64_t
    zclock_time (void);

//  Self test of this class
int
    zclock_test (Bool verbose);
//  @end

The source file for a class must provide documentation as follows:

/*
@header
...short explanation of class...
@discuss
...longer discussion of how it works...
@end
*/

The source file for a class then provides the self test example as follows:

//  @selftest
int64_t start = zclock_time ();
zclock_sleep (10);
assert ((zclock_time () - start) >= 10);
//  @end

The template for man pages is in doc/mkman.

### Development

CZMQ is developed through a test-driven process that guarantees no memory violations or leaks in the code:

• Modify a class or method.
• Update the test method for that class.
• Run the 'selftest' script, which uses the Valgrind memcheck tool.
• Repeat until perfect.

### Porting CZMQ

When you try CZMQ on an OS that it's not been used on (ever, or for a while), you will hit code that does not compile. In some cases the patches are trivial, in other cases (usually when porting to Windows), the work needed to build equivalent functionality may be non-trivial. In any case, the benefit is that once ported, the functionality is available to all applications.

Before attempting to patch code for portability, please read the czmq_prelude.h header file. There are several typical types of changes you may need to make to get functionality working on a specific operating system:

• Defining typedefs which are missing on that specific compiler: do this in czmq_prelude.h.
• Defining macros that rename exotic library functions to more conventional names: do this in czmq_prelude.h.
• Reimplementing specific methods to use a non-standard API: this is typically needed on Windows. Do this in the relevant class, using #ifdefs to properly differentiate code for different platforms.

### Code Generation

We generate the zsockopt class using [https://github.com/imatix/gsl GSL], using a code generator script in scripts/sockopts.gsl.

### This Document

This document is originally at README.txt and is built using gitdown.