Add pipeto --as_file option. Resolve #703.

There just doesn't seem to be any way to invoke a usable editor with a
subprocess that's passed stdin. Therefore this option doesn't literally
pipe mail into the command but writes mail to a temporary file and
passes the filename at the end of the external command.

alot/commands/thread.py

@@ -12,6 +12,7 @@
 from email.utils import getaddresses, parseaddr
 from email.message import Message
 
+import urwid
 from io import BytesIO
 
 from . import Command, registerCommand
@@ -634,6 +635,8 @@ def matches(msgt):
                     'choices': [
                         'raw', 'decoded', 'id', 'filepath', 'mimepart',
                         'plain', 'html']}),
+    (['--as_file'], {'action': 'store_true',
+                     'help': 'pass mail as a file to the given application'}),
     (['--separately'], {'action': 'store_true',
                         'help': 'call command once for each message'}),
     (['--background'], {'action': 'store_true',
@@ -651,7 +654,7 @@ class PipeCommand(Command):
     repeatable = True
 
     def __init__(self, cmd, all=False, separately=False, background=False,
-                 shell=False, notify_stdout=False, format='raw',
+                 shell=False, notify_stdout=False, format='raw', as_file=False,
                  add_tags=False, noop_msg='no command specified',
                  confirm_msg='', done_msg=None, **kwargs):
         """
@@ -674,6 +677,8 @@ def __init__(self, cmd, all=False, separately=False, background=False,
             'filepath': paths to message files on disk
             'mimepart': only pipe the currently selected mime part
         :type format: str
+        :param as_file: pass mail as a file to the given application
+        :type as_file: bool
         :param add_tags: add 'Tags' header to the message
         :type add_tags: bool
         :param noop_msg: error notification to show if `cmd` is empty
@@ -694,6 +699,7 @@ def __init__(self, cmd, all=False, separately=False, background=False,
         self.shell = shell
         self.notify_stdout = notify_stdout
         self.output_format = format
+        self.as_file = as_file
         self.add_tags = add_tags
         self.noop_msg = noop_msg
         self.confirm_msg = confirm_msg
@@ -758,14 +764,29 @@ async def apply(self, ui):
             self.cmd = [' '.join(self.cmd)]
 
         # do the monkey
-        def callback(out):
-            if self.notify_stdout:
-                ui.notify(out)
-            if self.done_msg:
-                ui.notify(self.done_msg)
-
         for mail in pipestrings:
-            await ui.apply_command(ExternalCommand(self.cmd,
+            cmd = self.cmd
+
+            # Pass mail as temporary file rather than piping through stdin.
+            if self.as_file:
+                with tempfile.NamedTemporaryFile(delete=False) as tmpfile:
+                    tmpfile.write(mail.encode(urwid.util.detected_encoding))
+                    tempfile_name = tmpfile.name
+                mail = None
+                if self.shell:
+                    cmd = [' '.join([cmd[0], tempfile_name])]
+                else:
+                    cmd.append(tempfile_name)
+
+            def callback(out):
+                if self.as_file:
+                    os.unlink(tempfile_name)
+                if self.notify_stdout:
+                    ui.notify(out)
+                if self.done_msg:
+                    ui.notify(self.done_msg)
+
+            await ui.apply_command(ExternalCommand(cmd,
                                                    stdin=mail,
                                                    shell=True,
                                                    thread=self.background,

docs/source/usage/modes/thread.rst

@@ -73,6 +73,7 @@ The following commands are available in thread mode:
     optional arguments
         :---all: pass all messages
         :---format: output format; valid choices are: 'raw','decoded','id','filepath','mimepart','plain','html' (defaults to: 'raw')
+        :---as_file: pass mail as a file to the given application
         :---separately: call command once for each message
         :---background: don't stop the interface
         :---add_tags: add 'Tags' header to the message