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Contributing to mongo-c-driver

Thanks for considering contributing to the mongo-c-driver!

This document intends to be a short guide to helping you contribute to the codebase. It expects a familiarity with the C programming language and writing portable software. Whenever in doubt, feel free to ask others that have contributed or look at the existing body of code.

Guidelines

The mongo-c-driver has a few guidelines that help direct the process.

Portability

mongo-c-driver is portable software. It needs to run on a multitude of Supported Platforms.

Licensing

Some of the mongo-c-driver users embed the library statically in their products. Therefore, the driver and all contributions must be liberally licensed. As a policy, we have chosen Apache 2.0 as the license for the project.

Coding Style

We try not to be pedantic with taking contributions that are not properly formatted, but we will likely perform a followup commit that cleans things up. The basics are, in vim:

 : set ts=3 sw=3 et

3 space tabs, insert spaces instead of tabs.

For all the gory details, see .clang-format

Commit Style

Commit messages follow this pattern:

CDRIVER-#### lowercase commit message

There's no colon after the ticket number, and no period at the end of the subject line. If there's no related Jira ticket, then the message is simply all lowercase:

typos in NEWS

We follow the widely adopted "50/72" rule: the subject line is ideally only 50 characters, but definitely only 72 characters. This requires some thoughtful writing but it's worthwhile when you're scrolling through commits. The message body can be as large as you want, wrapped at 72 columns.

Adding a new error code or domain

When adding a new error code or domain, you must do the following. This is most applicable if you are adding a new symbol with a bson_error_t as a parameter, and the existing codes or domains are inappropriate.

  • Add the domain to mongoc_error_domain_t in src/mongoc/mongoc-error.h
  • Add the code to mongoc_error_code_t in src/mongoc/mongoc-error.h
  • Add documentation for the domain or code to the table in doc/mongoc_errors.rst

Adding a new symbol

This should be done rarely but there are several things that you need to do when adding a new symbol.

  • Add documentation for the new symbol in doc/mongoc_your_new_symbol_name.rst

Documentation

We strive to document all symbols. See doc/ for documentation examples. If you add a new public function, add a new .rst file describing the function so that we can generate man pages and HTML for it.

For complex internal functions, comment above the function definition with a block comment like the following:

/*--------------------------------------------------------------------------
 *
 * mongoc_cmd_parts_append_read_write --
 *
 *       Append user-supplied options to @parts->command_extra, taking the
 *       selected server's max wire version into account.
 *
 * Return:
 *       True if the options were successfully applied. If any options are
 *       invalid, returns false and fills out @error. In that case @parts is
 *       invalid and must not be used.
 *
 * Side effects:
 *       May partly apply options before returning an error.
 *
 *--------------------------------------------------------------------------
 */

Public functions do not need these comment blocks, since they are documented in the .rst files.

To build the documentation, it is recommended to use the Poetry-managed Python project to ensure that the exact tooling versions match. If you do not have Poetry installed, you can use the poetry.sh or poetry.ps1 scripts in the tools/ directory. First, install dependencies:

./tools/poetry.sh install --with=docs

Then, execute sphinx-build in the Python environment, using the paths to the documentation to be generated:

./tools/poetry.sh run sphinx-build -WEn -bhtml src/libmongoc/doc/ src/libmongoc/doc/html

sphinx-autobuild can be used to serve docs locally. This can be convenient when editing. Files are rebuilt when changes are detected:

./tools/poetry.sh run sphinx-autobuild -b html src/libmongoc/doc/ src/libmongoc/doc/html --re-ignore ".*.pickle" --re-ignore ".*.doctree" -j auto

Testing

To run the entire test suite, including authentication and support for the configureFailPoint command, start mongod with security and test commands enabled:

$ mkdir db
$ mongod --auth --setParameter enableTestCommands=1 --dbpath db/

In another terminal, use the mongosh shell to create a user:

$ mongosh --eval "db.createUser({user: 'admin', pwd: 'pass', roles: ['root']})" admin

Authentication in MongoDB 3.0 and later uses SCRAM-SHA-1, which in turn requires a driver built with SSL.

Set the user and password environment variables, then build and run the tests:

$ export MONGOC_TEST_USER=admin
$ export MONGOC_TEST_PASSWORD=pass
$ ./test-libmongoc

Additional environment variables:

  • MONGOC_TEST_HOST: default localhost, the host running MongoDB.
  • MONGOC_TEST_PORT: default 27017, MongoDB's listening port.
  • MONGOC_TEST_URI: override both host and port with a full connection string, like "mongodb://server1,server2".
  • MONGOC_TEST_SERVER_LOG: set to stdout or stderr for wire protocol logging from tests that use mock_server_t. Set to json to include these logs in the test framework's JSON output, in a format compatible with Evergreen.
  • MONGOC_TEST_MONITORING_VERBOSE: set to on for verbose output from Application Performance Monitoring tests.
  • MONGOC_TEST_COMPRESSORS=snappy,zlib: wire protocol compressors to use
  • MONGOC_TEST_IS_SERVERLESS (bool): defaults to false. Used to indicate that tests are run against a serverless cluster.

If you start mongod with SSL, set these variables to configure how test-libmongoc connects to it:

  • MONGOC_TEST_SSL: set to on to connect to the server with SSL.
  • MONGOC_TEST_SSL_PEM_FILE: path to a client PEM file.
  • MONGOC_TEST_SSL_PEM_PWD: the PEM file's password.
  • MONGOC_TEST_SSL_CA_FILE: path to a certificate authority file.
  • MONGOC_TEST_SSL_CA_DIR: path to a certificate authority directory.
  • MONGOC_TEST_SSL_CRL_FILE: path to a certificate revocation list.
  • MONGOC_TEST_SSL_WEAK_CERT_VALIDATION: set to on to relax the client's validation of the server's certificate.

The SASL / GSSAPI / Kerberos tests are skipped by default. To run them, set up a separate mongod with Kerberos and set its host and Kerberos principal name as environment variables:

  • MONGOC_TEST_GSSAPI_HOST
  • MONGOC_TEST_GSSAPI_USER

URI-escape the username, for example write "user@realm" as "user%40realm". The user must be authorized to query kerberos.test.

MongoDB 3.2 adds support for readConcern, but does not enable support for read concern majority by default. mongod must be launched using --enableMajorityReadConcern. The test framework does not (and can't) automatically discover if this option was provided to MongoDB, so an additional variable must be set to enable these tests:

  • MONGOC_ENABLE_MAJORITY_READ_CONCERN

Set this environment variable to on if MongoDB has enabled majority read concern.

Some tests require Internet access, e.g. to check the error message when failing to open a MongoDB connection to example.com. Skip them with:

  • MONGOC_TEST_OFFLINE=on

Some tests require a running MongoDB server. Skip them with:

  • MONGOC_TEST_SKIP_LIVE=on

For quick checks during development, disable long-running tests:

  • MONGOC_TEST_SKIP_SLOW=on

Some tests run against a local mock server, these can be skipped with:

  • MONGOC_TEST_SKIP_MOCK=on

The tests for mongodb+srv:// connection strings require some setup, see the Initial DNS Seedlist Discovery Spec. By default these connection strings are NOT tested, enable them with:

  • MONGOC_TEST_DNS=on assumes a replica set is running with TLS enabled on ports 27017, 27018, and 27019.

  • MONGOC_TEST_DNS_LOADBALANCED=on assumes a load balanced sharded cluster is running with mongoses on ports 27017 and 27018 and TLS enabled. The load balancer can be listening on any port.

  • MONGOC_TEST_DNS_SRV_POLLING=on assumes a sharded cluster is running with mongoses on ports 27017, 27018, 27019, and 27020 and TLS enabled.

The mock server timeout threshold for future functions can be set with:

  • MONGOC_TEST_FUTURE_TIMEOUT_MS=<int>

This is useful for debugging, so future calls don't timeout when stepping through code.

Tests of In-Use Encryption require credentials to external KMS providers.

For AWS:

  • MONGOC_TEST_AWS_SECRET_ACCESS_KEY=<string>
  • MONGOC_TEST_AWS_ACCESS_KEY_ID=<string>
  • MONGOC_TEST_AWSNAME2_SECRET_ACCESS_KEY=<string>
  • MONGOC_TEST_AWSNAME2_ACCESS_KEY_ID=<string>

An Azure:

  • MONGOC_TEST_AZURE_TENANT_ID=<string>
  • MONGOC_TEST_AZURE_CLIENT_ID=<string>
  • MONGOC_TEST_AZURE_CLIENT_SECRET=<string>

For GCP:

  • MONGOC_TEST_GCP_EMAIL=<string>
  • MONGOC_TEST_GCP_PRIVATEKEY=<string>

Tests of In-Use Encryption also require temporary credentials to external KMS providers.

For AWS:

  • MONGOC_TEST_AWS_TEMP_SECRET_ACCESS_KEY=<string>
  • MONGOC_TEST_AWS_TEMP_ACCESS_KEY_ID=<string>
  • MONGOC_TEST_AWS_TEMP_SESSION_TOKEN=<string>

Tests of In-Use Encryption spawn an extra process, "mongocryptd", by default. To bypass this spawning, start mongocryptd on port 27020 and set the following:

  • MONGOC_TEST_MONGOCRYPTD_BYPASS_SPAWN=on

KMS TLS tests for In-Use Encryption require mock KMS servers to be running in the background.

The Setup instructions given in the Client Side Encryption Tests specification provide additional information.

The mock server scripts are located in the mongodb-labs/drivers-evergreen-tools in the csfle directory. The mock servers use certificates located in the x509gen directory.

The set of mock KMS servers running in the background and their corresponding invocation command must be as follows:

Port CA File Cert File Command
8999 ca.pem server.pem python -u kms_http_server.py --ca_file ../x509gen/ca.pem --cert_file ../x509gen/server.pem --port 8999
9000 ca.pem expired.pem python -u kms_http_server.py --ca_file ../x509gen/ca.pem --cert_file ../x509gen/expired.pem --port 9000
9001 ca.pem wrong-host.pem python -u kms_http_server.py --ca_file ../x509gen/ca.pem --cert_file ../x509gen/wrong-host.pem --port 9001
9002 ca.pem server.pem python -u kms_http_server.py --ca_file ../x509gen/ca.pem --cert_file ../x509gen/server.pem --port --require_client_cert 9002
5698 ca.pem server.pem python -u kms_kmip_server.py

The path to ca.pem and client.pem must be passed through the following environment variables:

  • MONGOC_TEST_CSFLE_TLS_CA_FILE=<string>
  • MONGOC_TEST_CSFLE_TLS_CERTIFICATE_KEY_FILE=<string>

Specification tests may be filtered by their description:

  • MONGOC_JSON_SUBTEST=<string>

This can be useful in debugging a specific test case in a spec test file with multiple tests. Example:

MONGOC_JSON_SUBTEST="Insert with randomized encryption, then find it" \
  ./cmake-build/src/libmongoc/test-libmongoc -l "/client_side_encryption/legacy/basic"

To test with a declared API version, you can pass the API version using an environment variable:

  • MONGODB_API_VERSION=<string>

This will ensure that all tests declare the indicated API version when connecting to a server.

To test a load balanced deployment, set the following environment variables:

  • MONGOC_TEST_LOADBALANCED=on
  • SINGLE_MONGOS_LB_URI=<string> to a MongoDB URI with a host of a load balancer fronting one mongos.
  • MULTI_MONGOS_LB_URI=<string> to a MongoDB URI with a host of a load balancer fronting multiple mongos processes.

To run test cases with large allocations, set:

  • MONGOC_TEST_LARGE_ALLOCATIONS=on This may result in sudden test suite termination due to allocation failure. Use with caution.

All tests should pass before submitting a patch.

Configuring the test runner

The test runner can be configured with command-line options. Run test-libmongoc --help for details.

To run just a specific portion of the test suite use the -l option like so:

$ ./test-libmongoc -l "/server_selection/*"

The full list of tests is shown in the help.