Fix unwanted flushing of libpq's input buffer when socket EOF is seen.

In commit 210eb9b743c0645d I centralized libpq's logic for closing down
the backend communication socket, and made the new pqDropConnection
routine always reset the I/O buffers to empty.  Many of the call sites
previously had not had such code, and while that amounted to an oversight
in some cases, there was one place where it was intentional and necessary
*not* to flush the input buffer: pqReadData should never cause that to
happen, since we probably still want to process whatever data we read.

This is the true cause of the problem Robert was attempting to fix in
c3e7c24a1d60dc6a, namely that libpq no longer reported the backend's final
ERROR message before reporting "server closed the connection unexpectedly".
But that only accidentally fixed it, by invoking parseInput before the
input buffer got flushed; and very likely there are timing scenarios
where we'd still lose the message before processing it.

To fix, pass a flag to pqDropConnection to tell it whether to flush the
input buffer or not.  On review I think flushing is actually correct for
every other call site.

Back-patch to 9.3 where the problem was introduced.  In HEAD, also improve
the comments added by c3e7c24a1d60dc6a.

diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 1721b3146663dc95089205fd87fa1bca3aa955b7..aabdc0ffb0299d855e7243970238557bc6c1f20b 100644 (file)
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -391,9 +391,13 @@ pgthreadlock_t pg_g_threadlock = default_threadlock;
  * Close any physical connection to the server, and reset associated
  * state inside the connection object.  We don't release state that
  * would be needed to reconnect, though.
+ *
+ * We can always flush the output buffer, since there's no longer any hope
+ * of sending that data.  However, unprocessed input data might still be
+ * valuable, so the caller must tell us whether to flush that or not.
  */
 void
-pqDropConnection(PGconn *conn)
+pqDropConnection(PGconn *conn, bool flushInput)
 {
    /* Drop any SSL state */
    pqsecure_close(conn);
@@ -401,8 +405,10 @@ pqDropConnection(PGconn *conn)
    if (conn->sock >= 0)
        closesocket(conn->sock);
    conn->sock = -1;
-   /* Discard any unread/unsent data */
-   conn->inStart = conn->inCursor = conn->inEnd = 0;
+   /* Optionally discard any unread data */
+   if (flushInput)
+       conn->inStart = conn->inCursor = conn->inEnd = 0;
+   /* Always discard any unsent data */
    conn->outCount = 0;
 }
 
@@ -1493,7 +1499,7 @@ connectDBStart(PGconn *conn)
        return 1;
 
 connect_errReturn:
-   pqDropConnection(conn);
+   pqDropConnection(conn, true);
    conn->status = CONNECTION_BAD;
    return 0;
 }
@@ -1731,7 +1737,7 @@ keep_going:                       /* We will come back to here until there is
                    {
                        if (!connectNoDelay(conn))
                        {
-                           pqDropConnection(conn);
+                           pqDropConnection(conn, true);
                            conn->addr_cur = addr_cur->ai_next;
                            continue;
                        }
@@ -1741,7 +1747,7 @@ keep_going:                       /* We will come back to here until there is
                        appendPQExpBuffer(&conn->errorMessage,
                                          libpq_gettext("could not set socket to nonblocking mode: %s\n"),
                            SOCK_STRERROR(SOCK_ERRNO, sebuf, sizeof(sebuf)));
-                       pqDropConnection(conn);
+                       pqDropConnection(conn, true);
                        conn->addr_cur = addr_cur->ai_next;
                        continue;
                    }
@@ -1752,7 +1758,7 @@ keep_going:                       /* We will come back to here until there is
                        appendPQExpBuffer(&conn->errorMessage,
                                          libpq_gettext("could not set socket to close-on-exec mode: %s\n"),
                            SOCK_STRERROR(SOCK_ERRNO, sebuf, sizeof(sebuf)));
-                       pqDropConnection(conn);
+                       pqDropConnection(conn, true);
                        conn->addr_cur = addr_cur->ai_next;
                        continue;
                    }
@@ -1799,7 +1805,7 @@ keep_going:                       /* We will come back to here until there is
 
                        if (err)
                        {
-                           pqDropConnection(conn);
+                           pqDropConnection(conn, true);
                            conn->addr_cur = addr_cur->ai_next;
                            continue;
                        }
@@ -1886,7 +1892,7 @@ keep_going:                       /* We will come back to here until there is
                     * failure and keep going if there are more addresses.
                     */
                    connectFailureMessage(conn, SOCK_ERRNO);
-                   pqDropConnection(conn);
+                   pqDropConnection(conn, true);
 
                    /*
                     * Try the next address, if any.
@@ -1931,7 +1937,7 @@ keep_going:                       /* We will come back to here until there is
                     * error message.
                     */
                    connectFailureMessage(conn, optval);
-                   pqDropConnection(conn);
+                   pqDropConnection(conn, true);
 
                    /*
                     * If more addresses remain, keep trying, just as in the
@@ -2213,7 +2219,7 @@ keep_going:                       /* We will come back to here until there is
                        /* only retry once */
                        conn->allow_ssl_try = false;
                        /* Must drop the old connection */
-                       pqDropConnection(conn);
+                       pqDropConnection(conn, true);
                        conn->status = CONNECTION_NEEDED;
                        goto keep_going;
                    }
@@ -2324,7 +2330,7 @@ keep_going:                       /* We will come back to here until there is
                    {
                        conn->pversion = PG_PROTOCOL(2, 0);
                        /* Must drop the old connection */
-                       pqDropConnection(conn);
+                       pqDropConnection(conn, true);
                        conn->status = CONNECTION_NEEDED;
                        goto keep_going;
                    }
@@ -2390,7 +2396,7 @@ keep_going:                       /* We will come back to here until there is
                        /* only retry once */
                        conn->wait_ssl_try = false;
                        /* Must drop the old connection */
-                       pqDropConnection(conn);
+                       pqDropConnection(conn, true);
                        conn->status = CONNECTION_NEEDED;
                        goto keep_going;
                    }
@@ -2406,7 +2412,7 @@ keep_going:                       /* We will come back to here until there is
                        /* only retry once */
                        conn->allow_ssl_try = false;
                        /* Must drop the old connection */
-                       pqDropConnection(conn);
+                       pqDropConnection(conn, true);
                        conn->status = CONNECTION_NEEDED;
                        goto keep_going;
                    }
@@ -2567,7 +2573,7 @@ keep_going:                       /* We will come back to here until there is
                            PQclear(res);
                            conn->send_appname = false;
                            /* Must drop the old connection */
-                           pqDropConnection(conn);
+                           pqDropConnection(conn, true);
                            conn->status = CONNECTION_NEEDED;
                            goto keep_going;
                        }
@@ -2962,7 +2968,7 @@ closePGconn(PGconn *conn)
    /*
     * Close the connection, reset all transient state, flush I/O buffers.
     */
-   pqDropConnection(conn);
+   pqDropConnection(conn, true);
    conn->status = CONNECTION_BAD;      /* Well, not really _bad_ - just
                                         * absent */
    conn->asyncStatus = PGASYNC_IDLE;

diff --git a/src/interfaces/libpq/fe-misc.c b/src/interfaces/libpq/fe-misc.c
index 002675d2eed6dce9cb40c48e40d975df32779ff5..84ce6aca5ced353ff12400498990ea60561cbbd9 100644 (file)
--- a/src/interfaces/libpq/fe-misc.c
+++ b/src/interfaces/libpq/fe-misc.c
@@ -814,7 +814,8 @@ definitelyEOF:
 
    /* Come here if lower-level code already set a suitable errorMessage */
 definitelyFailed:
-   pqDropConnection(conn);
+   /* Do *not* drop any already-read data; caller still wants it */
+   pqDropConnection(conn, false);
    conn->status = CONNECTION_BAD;      /* No more connection to backend */
    return -1;
 }

diff --git a/src/interfaces/libpq/fe-protocol3.c b/src/interfaces/libpq/fe-protocol3.c
index 290f93c6ab10038feb59b59437fb9866315cd111..4bfdc0f4710fb8625896b0c9f0fbed3337b75a73 100644 (file)
--- a/src/interfaces/libpq/fe-protocol3.c
+++ b/src/interfaces/libpq/fe-protocol3.c
@@ -446,8 +446,8 @@ handleSyncLoss(PGconn *conn, char id, int msgLength)
    /* build an error result holding the error message */
    pqSaveErrorResult(conn);
    conn->asyncStatus = PGASYNC_READY;  /* drop out of GetResult wait loop */
-
-   pqDropConnection(conn);
+   /* flush input data since we're giving up on processing it */
+   pqDropConnection(conn, true);
    conn->status = CONNECTION_BAD;      /* No more connection to backend */
 }
 

diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 11f66e1b4d73ab4b775701c9c05d0b30449473b8..f14cf2b4a718ac946e542a18b87a2c3daa64b6b2 100644 (file)
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -492,7 +492,7 @@ extern char *const pgresStatus[];
 
 /* === in fe-connect.c === */
 
-extern void pqDropConnection(PGconn *conn);
+extern void pqDropConnection(PGconn *conn, bool flushInput);
 extern int pqPacketSend(PGconn *conn, char pack_type,
             const void *buf, size_t buf_len);
 extern bool pqGetHomeDirectory(char *buf, int bufsize);