[Qemu-devel] [PATCH v2] qmp-shell: fix pretty printing of JSON responses

[Daniel P. Berrange]

Pretty printing of JSON responses is important to be able to understand
large responses from query commands in particular. Unfortunately this
was broken during the addition of the verbose flag in

  commit 1ceca07e48ead0dd2e41576c81d40e6a91cafefd
  Author: John Snow <address@hidden>
  Date:   Wed Apr 29 15:14:04 2015 -0400

    scripts: qmp-shell: Add verbose flag

This is because that change turned the python data structure into a
formatted JSON string before the pretty print was given it. So we're
just pretty printing a string, which is a no-op.

The original pretty printer would output python objects.

(QEMU) query-chardev
{   u'return': [   {   u'filename': u'vc',
                       u'frontend-open': False,
                       u'label': u'parallel0'},
                   {   u'filename': u'vc',
                       u'frontend-open': True,
                       u'label': u'serial0'},
                   {   u'filename': u'unix:/tmp/qemp,server',
                       u'frontend-open': True,
                       u'label': u'compat_monitor0'}]}

This fixes the problem by switching to outputting pretty formatted JSON
text instead. This has the added benefit that the pretty printed output
is now valid JSON text. Due to the way the verbose flag was handled, the
pretty printing now applies to the command sent, as well as its response:

(QEMU) query-chardev
{
    "execute": "query-chardev",
    "arguments": {}
}
{
    "return": [
        {
            "frontend-open": false,
            "label": "parallel0",
            "filename": "vc"
        },
        {
            "frontend-open": true,
            "label": "serial0",
            "filename": "vc"
        },
        {
            "frontend-open": true,
            "label": "compat_monitor0",
            "filename": "unix:/tmp/qmp,server"
        }
    ]
}

Signed-off-by: Daniel P. Berrange <address@hidden>
---
 scripts/qmp/qmp-shell | 23 ++++++++++-------------
 1 file changed, 10 insertions(+), 13 deletions(-)

diff --git a/scripts/qmp/qmp-shell b/scripts/qmp/qmp-shell
index 7a402ed..0373b24 100755
--- a/scripts/qmp/qmp-shell
+++ b/scripts/qmp/qmp-shell
@@ -70,7 +70,6 @@ import json
 import ast
 import readline
 import sys
-import pprint
 
 class QMPCompleter(list):
     def complete(self, text, state):
@@ -103,11 +102,11 @@ class FuzzyJSON(ast.NodeTransformer):
 # TODO: QMPShell's interface is a bit ugly (eg. _fill_completion() and
 #       _execute_cmd()). Let's design a better one.
 class QMPShell(qmp.QEMUMonitorProtocol):
-    def __init__(self, address, pp=None):
+    def __init__(self, address, pretty=False):
         qmp.QEMUMonitorProtocol.__init__(self, self.__get_address(address))
         self._greeting = None
         self._completer = None
-        self._pp = pp
+        self._pretty = pretty
         self._transmode = False
         self._actions = list()
 
@@ -231,11 +230,11 @@ class QMPShell(qmp.QEMUMonitorProtocol):
         return qmpcmd
 
     def _print(self, qmp):
-        jsobj = json.dumps(qmp)
-        if self._pp is not None:
-            self._pp.pprint(jsobj)
-        else:
-            print str(jsobj)
+        indent = None
+        if self._pretty:
+            indent = 4
+        jsobj = json.dumps(qmp, indent=indent)
+        print str(jsobj)
 
     def _execute_cmd(self, cmdline):
         try:
@@ -377,7 +376,7 @@ def main():
     addr = ''
     qemu = None
     hmp = False
-    pp = None
+    pretty = False
     verbose = False
 
     try:
@@ -387,9 +386,7 @@ def main():
                     fail_cmdline(arg)
                 hmp = True
             elif arg == "-p":
-                if pp is not None:
-                    fail_cmdline(arg)
-                pp = pprint.PrettyPrinter(indent=4)
+                pretty = True
             elif arg == "-v":
                 verbose = True
             else:
@@ -398,7 +395,7 @@ def main():
                 if hmp:
                     qemu = HMPShell(arg)
                 else:
-                    qemu = QMPShell(arg, pp)
+                    qemu = QMPShell(arg, pretty)
                 addr = arg
 
         if qemu is None:
-- 
2.5.0