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Commit5c76714

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Fix an ancient oversight in libpq's handling of V3-protocol COPY OUT mode:
we need to be able to swallow NOTICE messages, and potentially alsoParameterStatus messages (although the latter would be a bit weird),without exiting COPY OUT state. Fix it, and adjust the protocol documentationto emphasize the need for this. Per off-list report from Alexander Galler.
1 parent7aa4164 commit5c76714

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2 files changed

+104
-48
lines changed

2 files changed

+104
-48
lines changed

‎doc/src/sgml/protocol.sgml‎

Lines changed: 11 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -1,4 +1,4 @@
1-
<!-- $PostgreSQL: pgsql/doc/src/sgml/protocol.sgml,v 1.70 2008/01/09 05:27:22 alvherre Exp $ -->
1+
<!-- $PostgreSQL: pgsql/doc/src/sgml/protocol.sgml,v 1.71 2008/01/14 18:46:17 tgl Exp $ -->
22

33
<chapter id="protocol">
44
<title>Frontend/Backend Protocol</title>
@@ -1039,9 +1039,16 @@
10391039
<para>
10401040
In the event of a backend-detected error during copy-out mode,
10411041
the backend will issue an ErrorResponse message and revert to normal
1042-
processing. The frontend should treat receipt of ErrorResponse (or
1043-
indeed any message type other than CopyData or CopyDone) as terminating
1044-
the copy-out mode.
1042+
processing. The frontend should treat receipt of ErrorResponse as
1043+
terminating the copy-out mode.
1044+
</para>
1045+
1046+
<para>
1047+
It is possible for NoticeResponse messages to be interspersed between
1048+
CopyData messages; frontends must handle this case, and should be
1049+
prepared for other asynchronous message types as well (see <xref
1050+
linkend="protocol-async">). Otherwise, any message type other than
1051+
CopyData or CopyDone may be treated as terminating copy-out mode.
10451052
</para>
10461053

10471054
<para>

‎src/interfaces/libpq/fe-protocol3.c‎

Lines changed: 93 additions & 44 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/interfaces/libpq/fe-protocol3.c,v 1.31 2008/01/01 19:46:00 momjian Exp $
11+
* $PostgreSQL: pgsql/src/interfaces/libpq/fe-protocol3.c,v 1.32 2008/01/14 18:46:17 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -1274,16 +1274,13 @@ getReadyForQuery(PGconn *conn)
12741274
}
12751275

12761276
/*
1277-
*PQgetCopyData -read a row of data from the backend during COPY OUT
1277+
*getCopyDataMessage -fetch next CopyData message, process async messages
12781278
*
1279-
* If successful, sets *buffer to point to a malloc'd row of data, and
1280-
* returns row length (always > 0) as result.
1281-
* Returns 0 if no row available yet (only possible if async is true),
1282-
* -1 if end of copy (consult PQgetResult), or -2 if error (consult
1283-
* PQerrorMessage).
1279+
* Returns length word of CopyData message (> 0), or 0 if no complete
1280+
* message available, -1 if end of copy, -2 if error.
12841281
*/
1285-
int
1286-
pqGetCopyData3(PGconn*conn,char**buffer,intasync)
1282+
staticint
1283+
getCopyDataMessage(PGconn*conn)
12871284
{
12881285
charid;
12891286
intmsgLength;
@@ -1298,22 +1295,94 @@ pqGetCopyData3(PGconn *conn, char **buffer, int async)
12981295
*/
12991296
conn->inCursor=conn->inStart;
13001297
if (pqGetc(&id,conn))
1301-
gotonodata;
1298+
return0;
13021299
if (pqGetInt(&msgLength,4,conn))
1303-
gotonodata;
1300+
return0;
1301+
if (msgLength<4)
1302+
{
1303+
handleSyncLoss(conn,id,msgLength);
1304+
return-2;
1305+
}
13041306
avail=conn->inEnd-conn->inCursor;
13051307
if (avail<msgLength-4)
1306-
gotonodata;
1308+
return0;
13071309

13081310
/*
1309-
* If it's anything except Copy Data, exit COPY_OUT mode and let
1310-
* caller read status with PQgetResult(). The normal case is that
1311-
* it's Copy Done, but we let parseInput read that.
1311+
* If it's a legitimate async message type, process it. (NOTIFY
1312+
* messages are not currently possible here, but we handle them for
1313+
* completeness. NOTICE is definitely possible, and ParameterStatus
1314+
* could probably be made to happen.) Otherwise, if it's anything
1315+
* except Copy Data, report end-of-copy.
13121316
*/
1313-
if (id!='d')
1317+
switch (id)
13141318
{
1315-
conn->asyncStatus=PGASYNC_BUSY;
1316-
return-1;
1319+
case'A':/* NOTIFY */
1320+
if (getNotify(conn))
1321+
return0;
1322+
break;
1323+
case'N':/* NOTICE */
1324+
if (pqGetErrorNotice3(conn, false))
1325+
return0;
1326+
break;
1327+
case'S':/* ParameterStatus */
1328+
if (getParameterStatus(conn))
1329+
return0;
1330+
break;
1331+
case'd':/* Copy Data, pass it back to caller */
1332+
returnmsgLength;
1333+
default:/* treat as end of copy */
1334+
return-1;
1335+
}
1336+
1337+
/* Drop the processed message and loop around for another */
1338+
conn->inStart=conn->inCursor;
1339+
}
1340+
}
1341+
1342+
/*
1343+
* PQgetCopyData - read a row of data from the backend during COPY OUT
1344+
*
1345+
* If successful, sets *buffer to point to a malloc'd row of data, and
1346+
* returns row length (always > 0) as result.
1347+
* Returns 0 if no row available yet (only possible if async is true),
1348+
* -1 if end of copy (consult PQgetResult), or -2 if error (consult
1349+
* PQerrorMessage).
1350+
*/
1351+
int
1352+
pqGetCopyData3(PGconn*conn,char**buffer,intasync)
1353+
{
1354+
intmsgLength;
1355+
1356+
for (;;)
1357+
{
1358+
/*
1359+
* Collect the next input message. To make life simpler for async
1360+
* callers, we keep returning 0 until the next message is fully
1361+
* available, even if it is not Copy Data.
1362+
*/
1363+
msgLength=getCopyDataMessage(conn);
1364+
if (msgLength<0)
1365+
{
1366+
/*
1367+
* On end-of-copy, exit COPY_OUT mode and let caller read status
1368+
* with PQgetResult(). The normal case is that it's Copy Done,
1369+
* but we let parseInput read that. If error, we expect the
1370+
* state was already changed.
1371+
*/
1372+
if (msgLength==-1)
1373+
conn->asyncStatus=PGASYNC_BUSY;
1374+
returnmsgLength;/* end-of-copy or error */
1375+
}
1376+
if (msgLength==0)
1377+
{
1378+
/* Don't block if async read requested */
1379+
if (async)
1380+
return0;
1381+
/* Need to load more data */
1382+
if (pqWait(TRUE, FALSE,conn)||
1383+
pqReadData(conn)<0)
1384+
return-2;
1385+
continue;
13171386
}
13181387

13191388
/*
@@ -1341,16 +1410,6 @@ pqGetCopyData3(PGconn *conn, char **buffer, int async)
13411410

13421411
/* Empty, so drop it and loop around for another */
13431412
conn->inStart=conn->inCursor;
1344-
continue;
1345-
1346-
nodata:
1347-
/* Don't block if async read requested */
1348-
if (async)
1349-
return0;
1350-
/* Need to load more data */
1351-
if (pqWait(TRUE, FALSE,conn)||
1352-
pqReadData(conn)<0)
1353-
return-2;
13541413
}
13551414
}
13561415

@@ -1413,7 +1472,6 @@ pqGetline3(PGconn *conn, char *s, int maxlen)
14131472
int
14141473
pqGetlineAsync3(PGconn*conn,char*buffer,intbufsize)
14151474
{
1416-
charid;
14171475
intmsgLength;
14181476
intavail;
14191477

@@ -1424,22 +1482,13 @@ pqGetlineAsync3(PGconn *conn, char *buffer, int bufsize)
14241482
* Recognize the next input message. To make life simpler for async
14251483
* callers, we keep returning 0 until the next message is fully available
14261484
* even if it is not Copy Data. This should keep PQendcopy from blocking.
1485+
* (Note: unlike pqGetCopyData3, we do not change asyncStatus here.)
14271486
*/
1428-
conn->inCursor=conn->inStart;
1429-
if (pqGetc(&id,conn))
1430-
return0;
1431-
if (pqGetInt(&msgLength,4,conn))
1432-
return0;
1433-
avail=conn->inEnd-conn->inCursor;
1434-
if (avail<msgLength-4)
1435-
return0;
1436-
1437-
/*
1438-
* Cannot proceed unless it's a Copy Data message. Anything else means
1439-
* end of copy mode.
1440-
*/
1441-
if (id!='d')
1442-
return-1;
1487+
msgLength=getCopyDataMessage(conn);
1488+
if (msgLength<0)
1489+
return-1;/* end-of-copy or error */
1490+
if (msgLength==0)
1491+
return0;/* no data yet */
14431492

14441493
/*
14451494
* Move data from libpq's buffer to the caller's. In the case where a

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