[Qemu-devel] [RFC PATCH] qmp.py: Fix exception parsing partial JSON

[Philippe Mathieu-Daudé]

The readline() call returns partial data.
Keep appending until the JSON buffer is complete.

This fixes:

    $ scripts/qmp/qmp-shell -v -p /tmp/qmp.sock
    Traceback (most recent call last):
      File "scripts/qmp/qmp-shell", line 456, in <module>
        main()
      File "scripts/qmp/qmp-shell", line 441, in main
        qemu.connect(negotiate)
      File "scripts/qmp/qmp-shell", line 284, in connect
        self._greeting = super(QMPShell, self).connect(negotiate)
      File "scripts/qmp/qmp.py", line 143, in connect
        return self.__negotiate_capabilities()
      File "scripts/qmp/qmp.py", line 71, in __negotiate_capabilities
        greeting = self.__json_read()
      File "scripts/qmp/qmp.py", line 85, in __json_read
        resp = json.loads(data)
      File "/usr/lib/python2.7/json/__init__.py", line 339, in loads
        return _default_decoder.decode(s)
      File "/usr/lib/python2.7/json/decoder.py", line 364, in decode
        obj, end = self.raw_decode(s, idx=_w(s, 0).end())
      File "/usr/lib/python2.7/json/decoder.py", line 380, in raw_decode
        obj, end = self.scan_once(s, idx)
    ValueError: Expecting object: line 1 column 3 (char 2)

Signed-off-by: Philippe Mathieu-Daudé <address@hidden>
---
Daniel suggested this is due to blocking i/o.

I'm sure there is a nicer/more pythonic way to do this, but this works for me,
sorry :)

 scripts/qmp/qmp.py | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/scripts/qmp/qmp.py b/scripts/qmp/qmp.py
index 5c8cf6a056..e8b55dfcc4 100644
--- a/scripts/qmp/qmp.py
+++ b/scripts/qmp/qmp.py
@@ -78,11 +78,16 @@ class QEMUMonitorProtocol(object):
         raise QMPCapabilitiesError
 
     def __json_read(self, only_event=False):
+        data = ""
         while True:
-            data = self.__sockfile.readline()
-            if not data:
+            tmp = self.__sockfile.readline()
+            if not tmp:
                 return
-            resp = json.loads(data)
+            data += tmp
+            try:
+                resp = json.loads(data)
+            except ValueError:
+                continue
             if 'event' in resp:
                 self.logger.debug("<<< %s", resp)
                 self.__events.append(resp)
-- 
2.17.1