Clean up error cases in psql's COPY TO STDOUT/FROM STDIN code.

Adjust handleCopyOut() to stop trying to write data once it's failed
one time.  For typical cases such as out-of-disk-space or broken-pipe,
additional attempts aren't going to do anything but waste time, and
in any case clean truncation of the output seems like a better behavior
than randomly dropping blocks in the middle.

Also remove dubious (and misleadingly documented) attempt to force our way
out of COPY_OUT state if libpq didn't do that.  If we did have a situation
like that, it'd be a bug in libpq and would be better fixed there, IMO.
We can hope that commit fa4440f51628d692f077d54b8313aea31af087ea took care
of any such problems, anyway.

Also fix longstanding bug in handleCopyIn(): PQputCopyEnd() only supports
a non-null errormsg parameter in protocol version 3, and will actively
fail if one is passed in version 2.  This would've made our attempts
to get out of COPY_IN state after a failure into infinite loops when
talking to pre-7.4 servers.

Back-patch the COPY_OUT state change business back to 9.2 where it was
introduced, and the other two fixes into all supported branches.

diff --git a/src/bin/psql/copy.c b/src/bin/psql/copy.c
index b5732c797097c836fa55824c8097c1efd6d40fb1..3300fd15f7145d22b7751406058837aaf8512fc7 100644 (file)
--- a/src/bin/psql/copy.c
+++ b/src/bin/psql/copy.c
@@ -447,15 +447,15 @@ handleCopyOut(PGconn *conn, FILE *copystream)
        ret = PQgetCopyData(conn, &buf, 0);
 
        if (ret < 0)
-           break;              /* done or error */
+           break;              /* done or server/connection error */
 
        if (buf)
        {
-           if (fwrite(buf, 1, ret, copystream) != ret)
+           if (OK && fwrite(buf, 1, ret, copystream) != ret)
            {
-               if (OK)         /* complain only once, keep reading data */
-                   psql_error("could not write COPY data: %s\n",
-                              strerror(errno));
+               psql_error("could not write COPY data: %s\n",
+                          strerror(errno));
+               /* complain only once, keep reading data from server */
                OK = false;
            }
            PQfreemem(buf);
@@ -476,29 +476,18 @@ handleCopyOut(PGconn *conn, FILE *copystream)
    }
 
    /*
-    * Check command status and return to normal libpq state.  After a
-    * client-side error, the server will remain ready to deliver data.  The
-    * cleanest thing is to fully drain and discard that data.  If the
-    * client-side error happened early in a large file, this takes a long
-    * time.  Instead, take advantage of the fact that PQexec() will silently
-    * end any ongoing PGRES_COPY_OUT state.  This does cause us to lose the
-    * results of any commands following the COPY in a single command string.
-    * It also only works for protocol version 3.  XXX should we clean up
-    * using the slow way when the connection is using protocol version 2?
+    * Check command status and return to normal libpq state.
     *
-    * We must not ever return with the status still PGRES_COPY_OUT.  Our
-    * caller is unable to distinguish that situation from reaching the next
-    * COPY in a command string that happened to contain two consecutive COPY
-    * TO STDOUT commands.  We trust that no condition can make PQexec() fail
-    * indefinitely while retaining status PGRES_COPY_OUT.
+    * If for some reason libpq is still reporting PGRES_COPY_OUT state, we
+    * would like to forcibly exit that state, since our caller would be
+    * unable to distinguish that situation from reaching the next COPY in a
+    * command string that happened to contain two consecutive COPY TO STDOUT
+    * commands.  However, libpq provides no API for doing that, and in
+    * principle it's a libpq bug anyway if PQgetCopyData() returns -1 or -2
+    * but hasn't exited COPY_OUT state internally.  So we ignore the
+    * possibility here.
     */
-   while (res = PQgetResult(conn), PQresultStatus(res) == PGRES_COPY_OUT)
-   {
-       OK = false;
-       PQclear(res);
-
-       PQexec(conn, "-- clear PGRES_COPY_OUT state");
-   }
+   res = PQgetResult(conn);
    if (PQresultStatus(res) != PGRES_COMMAND_OK)
    {
        psql_error("%s", PQerrorMessage(conn));
@@ -541,7 +530,9 @@ handleCopyIn(PGconn *conn, FILE *copystream, bool isbinary)
        /* got here with longjmp */
 
        /* Terminate data transfer */
-       PQputCopyEnd(conn, _("canceled by user"));
+       PQputCopyEnd(conn,
+                    (PQprotocolVersion(conn) < 3) ? NULL :
+                    _("canceled by user"));
 
        OK = false;
        goto copyin_cleanup;
@@ -662,29 +653,37 @@ handleCopyIn(PGconn *conn, FILE *copystream, bool isbinary)
    if (ferror(copystream))
        OK = false;
 
-   /* Terminate data transfer */
+   /*
+    * Terminate data transfer.  We can't send an error message if we're using
+    * protocol version 2.
+    */
    if (PQputCopyEnd(conn,
-                    OK ? NULL : _("aborted because of read failure")) <= 0)
+                    (OK || PQprotocolVersion(conn) < 3) ? NULL :
+                    _("aborted because of read failure")) <= 0)
        OK = false;
 
 copyin_cleanup:
 
    /*
-    * Check command status and return to normal libpq state
+    * Check command status and return to normal libpq state.
     *
-    * We must not ever return with the status still PGRES_COPY_IN.  Our
-    * caller is unable to distinguish that situation from reaching the next
-    * COPY in a command string that happened to contain two consecutive COPY
-    * FROM STDIN commands.  XXX if something makes PQputCopyEnd() fail
-    * indefinitely while retaining status PGRES_COPY_IN, we get an infinite
-    * loop.  This is more realistic than handleCopyOut()'s counterpart risk.
+    * We do not want to return with the status still PGRES_COPY_IN: our
+    * caller would be unable to distinguish that situation from reaching the
+    * next COPY in a command string that happened to contain two consecutive
+    * COPY FROM STDIN commands.  We keep trying PQputCopyEnd() in the hope
+    * it'll work eventually.  (What's actually likely to happen is that in
+    * attempting to flush the data, libpq will eventually realize that the
+    * connection is lost.  But that's fine; it will get us out of COPY_IN
+    * state, which is what we need.)
     */
    while (res = PQgetResult(conn), PQresultStatus(res) == PGRES_COPY_IN)
    {
        OK = false;
        PQclear(res);
-
-       PQputCopyEnd(pset.db, _("trying to exit copy mode"));
+       /* We can't send an error message if we're using protocol version 2 */
+       PQputCopyEnd(conn,
+                    (PQprotocolVersion(conn) < 3) ? NULL :
+                    _("trying to exit copy mode"));
    }
    if (PQresultStatus(res) != PGRES_COMMAND_OK)
    {