python: backport 'feat: allow setting read buffer limit'

Expose the limit parameter of the underlying StreamReader and StreamWriter
instances.

This is helpful for the use case of transferring files in and out of a VM
via the QEMU guest agent's guest-file-open, guest-file-read, guest-file-write,
and guest-file-close methods, as it allows pushing the buffer size up to the
guest agent's limit of 48MB per transfer.

Signed-off-by: Adam Dorsey <adam@dorseys.email>
cherry picked from commit python-qemu-qmp@9ba6a698344eb3b570fa4864e906c54042824cd6
cherry picked from commit python-qemu-qmp@e4d0d3f835d82283ee0e48438d1b154e18303491
[Squashed in linter fixups. --js]
Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

1 files changed, 14 insertions, 4 deletions

diff --git a/python/qemu/qmp/qmp_client.py b/python/qemu/qmp/qmp_client.py
index a87fb565ab..d826331b6d 100644
--- a/python/qemu/qmp/qmp_client.py
+++ b/python/qemu/qmp/qmp_client.py
@@ -170,6 +170,12 @@ class QMPClient(AsyncProtocol[Message], Events):
 
     :param name: Optional nickname for the connection, used for logging.
 
+    :param readbuflen:
+        The maximum buffer length for reads and writes to and from the QMP
+        server, in bytes. Default is 10MB. If `QMPClient` is used to
+        connect to a guest agent to transfer files via ``guest-file-read``/
+        ``guest-file-write``, increasing this value may be required.
+
     Basic script-style usage looks like this::
 
       qmp = QMPClient('my_virtual_machine_name')
@@ -203,14 +209,18 @@ class QMPClient(AsyncProtocol[Message], Events):
     #: Logger object used for debugging messages.
     logger = logging.getLogger(__name__)
 
-    # Read buffer limit; 10MB like libvirt default
-    _limit = 10 * 1024 * 1024
+    # Read buffer default limit; 10MB like libvirt default
+    _readbuflen = 10 * 1024 * 1024
 
     # Type alias for pending execute() result items
     _PendingT = Union[Message, ExecInterruptedError]
 
-    def __init__(self, name: Optional[str] = None) -> None:
-        super().__init__(name)
+    def __init__(
+        self,
+        name: Optional[str] = None,
+        readbuflen: int = _readbuflen
+    ) -> None:
+        super().__init__(name, readbuflen)
         Events.__init__(self)
 
         #: Whether or not to await a greeting after establishing a connection.