[Xen-devel] [RFC v2 4/9] libxl_qmp: Move the buffer realloc to the same scope level as read

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

In qmp_next(), the inner loop should only try to parse messages from
QMP, if there is more than one.

The handling of the receive buffer ('incomplete'), should be done at the
same scope level as read(). It doesn't need to be handle more that once
after a read.

Before this patch, when on message what handled, the inner loop would
restart by adding the 'buffer' into 'incomplete' (after reallocation).
Since 'rd' was not reset, the buffer would be strcat a second time.
After that, the stream from the QMP server would have syntax error, and
the parsor would throw errors.

This is unlikely to happen as the receive buffer is very large. And
receiving two messages in a row is unlikely. In the current case, this
could be an event and a response to a command.

Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
---
 tools/libxl/libxl_qmp.c | 31 ++++++++++++++++---------------
 1 file changed, 16 insertions(+), 15 deletions(-)

diff --git a/tools/libxl/libxl_qmp.c b/tools/libxl/libxl_qmp.c
index 4d207c3842..a25f445fb6 100644
--- a/tools/libxl/libxl_qmp.c
+++ b/tools/libxl/libxl_qmp.c
@@ -524,23 +524,24 @@ static int qmp_next(libxl__gc *gc, libxl__qmp_handler 
*qmp)
 
         DEBUG_REPORT_RECEIVED(qmp->domid, qmp->buffer, (int)rd);
 
+        if (incomplete) {
+            size_t current_pos = s - incomplete;
+            incomplete = libxl__realloc(gc, incomplete,
+                                        incomplete_size + rd + 1);
+            strncat(incomplete + incomplete_size, qmp->buffer, rd);
+            s = incomplete + current_pos;
+            incomplete_size += rd;
+            s_end = incomplete + incomplete_size;
+        } else {
+            incomplete = libxl__strndup(gc, qmp->buffer, rd);
+            incomplete_size = rd;
+            s = incomplete;
+            s_end = s + rd;
+            rd = 0;
+        }
+
         do {
             char *end = NULL;
-            if (incomplete) {
-                size_t current_pos = s - incomplete;
-                incomplete = libxl__realloc(gc, incomplete,
-                                            incomplete_size + rd + 1);
-                strncat(incomplete + incomplete_size, qmp->buffer, rd);
-                s = incomplete + current_pos;
-                incomplete_size += rd;
-                s_end = incomplete + incomplete_size;
-            } else {
-                incomplete = libxl__strndup(gc, qmp->buffer, rd);
-                incomplete_size = rd;
-                s = incomplete;
-                s_end = s + rd;
-                rd = 0;
-            }
 
             end = strstr(s, "\r\n");
             if (end) {
-- 
Anthony PERARD


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