libpq: Make error checks in the new buffer draining code more robust

Check explicitly for pqsecure_read() returning an error. It shouldn't
fail, and we would've caught it in the check for a short read, but
better to be explicit so that the error message is more informative.
We also shouldn't update 'inEnd' when the read fails, although that
too is just pro forma as we will bail out and close the connection on
error.

Reported-by: Peter Eisentraut <peter@eisentraut.org>
Discussion: https://www.postgresql.org/message-id/34844e8c-267c-4daf-b1e0-f26059a4a7d3@eisentraut.org
Backpatch-through: 14

diff --git a/src/interfaces/libpq/fe-misc.c b/src/interfaces/libpq/fe-misc.c
index ea4f952550177e3b636e4d3f63db955e4f2b32fa..e7231d834f1c10d548df7e74e4dd10f746e37123 100644 (file)
--- a/src/interfaces/libpq/fe-misc.c
+++ b/src/interfaces/libpq/fe-misc.c
@@ -913,13 +913,18 @@ pqDrainPending(PGconn *conn)
 
        nread = pqsecure_read(conn, conn->inBuffer + conn->inEnd,
                                                  bytes_pending);
-       conn->inEnd += nread;
 
-       /* When there are bytes pending, the read function is not supposed to fail */
+       /*
+        * When there are bytes pending, pqsecure_read() is not supposed to fail
+        * or do a short read, but let's check anyway to be safe.
+        */
+       if (nread < 0)
+               return -1;
+       conn->inEnd += nread;
        if (nread != bytes_pending)
        {
                libpq_append_conn_error(conn,
-                                                               "drained only %zu of %zd pending bytes in transport buffer",
+                                                               "drained only %zd of %zd pending bytes in transport buffer",
                                                                nread, bytes_pending);
                return -1;
        }

diff --git a/src/interfaces/libpq/fe-secure.c b/src/interfaces/libpq/fe-secure.c
index f68c2d4d12c79a8dd7e54765e00a3da62232b118..c86341a4bf5c88807382e62a8dc17e16240fee3d 100644 (file)
--- a/src/interfaces/libpq/fe-secure.c
+++ b/src/interfaces/libpq/fe-secure.c
@@ -262,8 +262,9 @@ pqsecure_raw_read(PGconn *conn, void *ptr, size_t len)
  *     Return the number of bytes available in the transport buffer.
  *
  * If pqsecure_read() is called for this number of bytes, it's guaranteed to
- * return successfully without reading from the underlying socket.  See
- * pqDrainPending() for a more complete discussion of the concepts involved.
+ * return successfully with the same number of bytes, without reading from the
+ * underlying socket.  See pqDrainPending() for a more complete discussion of
+ * the concepts involved.
  */
 ssize_t
 pqsecure_bytes_pending(PGconn *conn)