Adjust the behavior of the PQExpBuffer code to make it have well-defined

results (ie, an empty "broken" buffer) if memory overrun occurs anywhere
along the way to filling the buffer.  The previous coding would just silently
discard portions of the intended buffer contents, as exhibited in trouble
report from Sam Mason.  Also, tweak psql's main loop to correctly detect
and report such overruns.  There's probably much more that should be done
in this line, but this is a start.

1 files changed, 18 insertions, 2 deletions

diff --git a/src/interfaces/libpq/pqexpbuffer.h b/src/interfaces/libpq/pqexpbuffer.h
index b834ac48082..3acca24b569 100644
--- a/src/interfaces/libpq/pqexpbuffer.h
+++ b/src/interfaces/libpq/pqexpbuffer.h
@@ -18,7 +18,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/interfaces/libpq/pqexpbuffer.h,v 1.19 2008/01/01 19:46:00 momjian Exp $
+ * $PostgreSQL: pgsql/src/interfaces/libpq/pqexpbuffer.h,v 1.20 2008/11/26 00:26:23 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -35,6 +35,10 @@
  *				string size (including the terminating '\0' char) that we can
  *				currently store in 'data' without having to reallocate
  *				more space.  We must always have maxlen > len.
+ *
+ * An exception occurs if we failed to allocate enough memory for the string
+ * buffer.  In that case data points to a statically allocated empty string,
+ * and len = maxlen = 0.
  *-------------------------
  */
 typedef struct PQExpBufferData
@@ -47,6 +51,15 @@ typedef struct PQExpBufferData
 typedef PQExpBufferData *PQExpBuffer;
 
 /*------------------------
+ * Test for a broken (out of memory) PQExpBuffer.
+ * When a buffer is "broken", all operations except resetting or deleting it
+ * are no-ops.
+ *------------------------
+ */
+#define PQExpBufferBroken(str)  \
+	(!(str) || (str)->maxlen == 0)
+
+/*------------------------
  * Initial size of the data buffer in a PQExpBuffer.
  * NB: this must be large enough to hold error messages that might
  * be returned by PQrequestCancel().
@@ -103,6 +116,8 @@ extern void termPQExpBuffer(PQExpBuffer str);
 /*------------------------
  * resetPQExpBuffer
  *		Reset a PQExpBuffer to empty
+ *
+ * Note: if possible, a "broken" PQExpBuffer is returned to normal.
  */
 extern void resetPQExpBuffer(PQExpBuffer str);
 
@@ -111,7 +126,8 @@ extern void resetPQExpBuffer(PQExpBuffer str);
  * Make sure there is enough space for 'needed' more bytes in the buffer
  * ('needed' does not include the terminating null).
  *
- * Returns 1 if OK, 0 if failed to enlarge buffer.
+ * Returns 1 if OK, 0 if failed to enlarge buffer.  (In the latter case
+ * the buffer is left in "broken" state.)
  */
 extern int	enlargePQExpBuffer(PQExpBuffer str, size_t needed);