issue #186: move target._get_file into mitogen.service

For lack of a better place to keep the client function, make it a
classmethod of FileService itself for now.

The old _get_file() is removed in a subsequent commit.

ansible_mitogen/target.py

@@ -53,6 +53,7 @@ import ansible_mitogen.runner
 import mitogen.core
 import mitogen.fork
 import mitogen.parent
+import mitogen.service
 
 
 LOG = logging.getLogger(__name__)
@@ -168,7 +169,11 @@ def transfer_file(context, in_path, out_path, sync=False, set_owner=False):
 
     try:
         try:
-            ok, metadata = _get_file(context, in_path, fp)
+            ok, metadata = mitogen.service.FileService.get(
+                context=context,
+                path=in_path,
+                out_fp=fp,
+            )
             if not ok:
                 raise IOError('transfer of %r was interrupted.' % (in_path,))
 

mitogen/service.py

@@ -669,9 +669,8 @@ class PushFileService(Service):
 
 class FileService(Service):
     """
-    Streaming file server, used to serve small files and huge files alike.
-    Paths must be registered by a trusted context before they will be served to
-    a child.
+    Streaming file server, used to serve small and huge files alike. Paths must
+    be registered by a trusted context before they will be served to a child.
 
     Transfers are divided among the physical streams that connect external
     contexts, ensuring each stream never has excessive data buffered in RAM,
@@ -889,3 +888,49 @@ class FileService(Service):
             self._schedule_pending_unlocked(state)
         finally:
             state.lock.release()
+
+    @classmethod
+    def get(cls, context, path, out_fp):
+        """
+        Streamily download a file from the connection multiplexer process in
+        the controller.
+
+        :param mitogen.core.Context context:
+            Reference to the context hosting the FileService that will be used
+            to fetch the file.
+        :param bytes in_path:
+            FileService registered name of the input file.
+        :param bytes out_path:
+            Name of the output path on the local disk.
+        :returns:
+            :data:`True` on success, or :data:`False` if the transfer was
+            interrupted and the output should be discarded.
+        """
+        LOG.debug('get_file(): fetching %r from %r', path, context)
+        t0 = time.time()
+        recv = mitogen.core.Receiver(router=context.router)
+        metadata = context.call_service(
+            service_name=cls.name(),
+            method_name='fetch',
+            path=path,
+            sender=recv.to_sender(),
+        )
+
+        for chunk in recv:
+            s = chunk.unpickle()
+            LOG.debug('get_file(%r): received %d bytes', path, len(s))
+            context.call_service_async(
+                service_name=cls.name(),
+                method_name='acknowledge',
+                size=len(s),
+            ).close()
+            out_fp.write(s)
+
+        ok = out_fp.tell() == metadata['size']
+        if not ok:
+            LOG.error('get_file(%r): receiver was closed early, controller '
+                      'is likely shutting down.', path)
+
+        LOG.debug('target.get_file(): fetched %d bytes of %r from %r in %dms',
+                  metadata['size'], path, context, 1000 * (time.time() - t0))
+        return ok, metadata