On Jun 16 08:21, Tom Lane wrote:
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > Volkan YAZICI wrote:
> >> The problem is, AFAICS, it's not possible to distinguish between a tuple
> >> returning query (T, ..., C, Z or T, E) and a description of a portal (T,
> >> Z). Therefore, I've created a global flag (parsing_row_desc) which is
> >> turned on when we receive a 'T' and turned off if we receive a 'C' or
> >> 'E'. It's a kind of ugly method but the only solution I could come up
> >> with.
>
> > The problem with this solution is that it is not thread-safe. Perhaps
> > you can use a per-PGconn boolean?
Ie replaced the static flag with a conn->queryclass value using
PGQueryClass as Tom suggested. Also updated patch to be compatible with
exports.txt stuff.
> The whole thing sounds like brute force to me. Shouldn't you be adding
> states to enum PGQueryClass, if you need to track what sort of Describe
> you're doing?
I totally agree with the followed ugly style. But IMHO the recursive
parsing (that is followed in pqParseInputN()) of received data is the main
problem behind this. I think, it will even get harder everytime somebody
try to to add another type of message parsing capability to that loop.
For instance, isn't pollution of PGQueryClass with state variables (like
PGQUERY_PREPARE or PGQUERY_DESCRIBE) one of the proofs of this.
While playing with pqParseInputN loops, I feel like coding Lisp recursions
using C syntax; it's quite ridiculous.
Regards.
Index: src/backend/tcop/postgres.c
===================================================================
RCS file: /projects/cvsroot/pgsql/src/backend/tcop/postgres.c,v
retrieving revision 1.489
diff -c -r1.489 postgres.c
*** src/backend/tcop/postgres.c 20 Jun 2006 22:52:00 -0000 1.489
--- src/backend/tcop/postgres.c 24 Jun 2006 11:31:10 -0000
***************
*** 1853,1858 ****
--- 1853,1859 ----
static void
exec_describe_statement_message(const char *stmt_name)
{
+ MemoryContext oldContext;
PreparedStatement *pstmt;
TupleDesc tupdesc;
ListCell *l;
***************
*** 1865,1871 ****
start_xact_command();
/* Switch back to message context */
! MemoryContextSwitchTo(MessageContext);
/* Find prepared statement */
if (stmt_name[0] != '\0')
--- 1866,1872 ----
start_xact_command();
/* Switch back to message context */
! oldContext = MemoryContextSwitchTo(MessageContext);
/* Find prepared statement */
if (stmt_name[0] != '\0')
***************
*** 1923,1929 ****
--- 1924,1933 ----
NULL);
else
pq_putemptymessage('n'); /* NoData */
+
+ MemoryContextSwitchTo(oldContext);
+ finish_xact_command();
}
/*
***************
*** 1934,1939 ****
--- 1938,1944 ----
static void
exec_describe_portal_message(const char *portal_name)
{
+ MemoryContext oldContext;
Portal portal;
/*
***************
*** 1943,1949 ****
start_xact_command();
/* Switch back to message context */
! MemoryContextSwitchTo(MessageContext);
portal = GetPortalByName(portal_name);
if (!PortalIsValid(portal))
--- 1948,1954 ----
start_xact_command();
/* Switch back to message context */
! oldContext = MemoryContextSwitchTo(MessageContext);
portal = GetPortalByName(portal_name);
if (!PortalIsValid(portal))
***************
*** 1975,1980 ****
--- 1980,1989 ----
portal->formats);
else
pq_putemptymessage('n'); /* NoData */
+
+ MemoryContextSwitchTo(oldContext);
+
+ finish_xact_command();
}
Index: src/interfaces/libpq/exports.txt
===================================================================
RCS file: /projects/cvsroot/pgsql/src/interfaces/libpq/exports.txt,v
retrieving revision 1.11
diff -c -r1.11 exports.txt
*** src/interfaces/libpq/exports.txt 28 May 2006 22:42:05 -0000 1.11
--- src/interfaces/libpq/exports.txt 24 Jun 2006 11:31:10 -0000
***************
*** 130,132 ****
--- 130,134 ----
PQencryptPassword 128
PQisthreadsafe 129
enlargePQExpBuffer 130
+ PQdescribePrepared 131
+ PQdescribePortal 132
Index: src/interfaces/libpq/fe-exec.c
===================================================================
RCS file: /projects/cvsroot/pgsql/src/interfaces/libpq/fe-exec.c,v
retrieving revision 1.186
diff -c -r1.186 fe-exec.c
*** src/interfaces/libpq/fe-exec.c 28 May 2006 21:13:54 -0000 1.186
--- src/interfaces/libpq/fe-exec.c 24 Jun 2006 11:31:12 -0000
***************
*** 61,66 ****
--- 61,68 ----
static void parseInput(PGconn *conn);
static bool PQexecStart(PGconn *conn);
static PGresult *PQexecFinish(PGconn *conn);
+ static int pqDescribe(PGconn *conn, const char desc_type,
+ const char *desc_target);
/* ----------------
***************
*** 2304,2309 ****
--- 2306,2415 ----
return 0;
}
+
+ /*
+ * pqDescribe - Describe given prepared statement or portal.
+ *
+ * Available options for target_type are
+ * 'S' to describe a prepared statement; or
+ * 'P' to describe a portal.
+ * Returns 0 on success and 1 on failure.
+ *
+ * By issuing a PQgetResult(), response from the server will be placed
+ * in an empty PGresult which will be extractable via PQf*() function family.
+ */
+ static int
+ pqDescribe(PGconn *conn, const char desc_type, const char *desc_target)
+ {
+ int ret;
+
+ /* This isn't gonna work on a 2.0 server. */
+ if (PG_PROTOCOL_MAJOR(conn->pversion) < 3)
+ {
+ printfPQExpBuffer(&conn->errorMessage,
+ libpq_gettext("function
requires at least protocol version 3.0\n"));
+ return 1;
+ }
+
+ if (!conn)
+ return 1;
+
+ /* Clear the connection error message. */
+ resetPQExpBuffer(&conn->errorMessage);
+
+ /* Don't try to send if we know there's no live connection. */
+ if (conn->status != CONNECTION_OK)
+ {
+ printfPQExpBuffer(&conn->errorMessage,
+ libpq_gettext("no connection
to the server\n"));
+ return 1;
+ }
+
+ /* Can't send while already busy, either. */
+ if (conn->asyncStatus != PGASYNC_IDLE)
+ {
+ printfPQExpBuffer(&conn->errorMessage,
+ libpq_gettext("another
command is already in progress\n"));
+ return 1;
+ }
+
+ /* Initialize async result-accumulation state. */
+ conn->result = NULL;
+ conn->curTuple = NULL;
+
+ if (desc_target)
+ ret = (pqPutMsgStart('D', false, conn) < 0 ||
+ pqPutc(desc_type, conn) < 0 ||
+ pqPuts(desc_target, conn) < 0 ||
+ pqPutMsgEnd(conn) < 0);
+
+ /* NULL desc_target values will be treated as an empty string. */
+ else
+ ret = (pqPutMsgStart('D', false, conn) < 0 ||
+ pqPutc(desc_type, conn) < 0 ||
+ pqPutc('\0', conn) < 0 ||
+ pqPutMsgEnd(conn) < 0);
+
+ if (ret)
+ goto SendFailure;
+
+ /* Extended protocol requires a Sync message. */
+ if (pqPutMsgStart('S', false, conn) < 0 ||
+ pqPutMsgEnd(conn) < 0)
+ goto SendFailure;
+
+ /* Remember we'll parse a Describe response. */
+ conn->queryclass = PGQUERY_DESCRIBE;
+
+ /* Free last query string. */
+ if (conn->last_query)
+ {
+ free(conn->last_query);
+ conn->last_query = NULL;
+ }
+
+ /* Describe request is sent. */
+ conn->asyncStatus = PGASYNC_BUSY;
+ return 0;
+
+ SendFailure:
+ pqHandleSendFailure(conn);
+ return 1;
+ }
+
+ int
+ PQdescribePrepared(PGconn *conn, const char *stmt)
+ {
+ return pqDescribe(conn, 'S', stmt);
+ }
+
+ int
+ PQdescribePortal(PGconn *conn, const char *portal)
+ {
+ return pqDescribe(conn, 'P', portal);
+ }
+
+
/* PQsetnonblocking:
* sets the PGconn's database connection non-blocking if the arg is TRUE
* or makes it non-blocking if the arg is FALSE, this will not protect
***************
*** 2381,2386 ****
--- 2487,2493 ----
free(ptr);
}
+
/*
* PQfreeNotify - free's the memory associated with a PGnotify
*
Index: src/interfaces/libpq/fe-protocol3.c
===================================================================
RCS file: /projects/cvsroot/pgsql/src/interfaces/libpq/fe-protocol3.c,v
retrieving revision 1.26
diff -c -r1.26 fe-protocol3.c
*** src/interfaces/libpq/fe-protocol3.c 14 Mar 2006 22:48:23 -0000 1.26
--- src/interfaces/libpq/fe-protocol3.c 24 Jun 2006 11:31:13 -0000
***************
*** 45,50 ****
--- 45,51 ----
static void handleSyncLoss(PGconn *conn, char id, int msgLength);
static int getRowDescriptions(PGconn *conn);
+ static int getParamDescriptions(PGconn *conn);
static int getAnotherTuple(PGconn *conn, int msgLength);
static int getParameterStatus(PGconn *conn);
static int getNotify(PGconn *conn);
***************
*** 81,87 ****
if (pqGetc(&id, conn))
return;
if (pqGetInt(&msgLength, 4, conn))
! return;
/*
* Try to validate message type/length here. A length less
than 4 is
--- 82,88 ----
if (pqGetc(&id, conn))
return;
if (pqGetInt(&msgLength, 4, conn))
! return;
/*
* Try to validate message type/length here. A length less
than 4 is
***************
*** 206,211 ****
--- 207,213 ----
}
strncpy(conn->result->cmdStatus,
conn->workBuffer.data,
CMDSTATUS_LEN);
+
conn->asyncStatus = PGASYNC_READY;
break;
case 'E': /* error return */
***************
*** 216,221 ****
--- 218,236 ----
case 'Z': /* backend is ready for
new query */
if (getReadyForQuery(conn))
return;
+
+ /*
+ * If there's any previosly available
result and this is
+ * received from a Describe query's
response, consume it
+ * first.
+ */
+ if (conn->result && conn->queryclass ==
PGQUERY_DESCRIBE)
+ {
+ conn->asyncStatus =
PGASYNC_READY;
+ return;
+ }
+
+ /* Backend is ready for a new query. */
conn->asyncStatus = PGASYNC_IDLE;
break;
case 'I': /* empty query */
***************
*** 294,299 ****
--- 309,338 ----
conn->result =
PQmakeEmptyPGresult(conn,
PGRES_COMMAND_OK);
break;
+ case 't': /* Parameter
Description */
+ /* Parse after a pqDescribe call only.
*/
+ if (conn->queryclass ==
PGQUERY_DESCRIBE)
+ {
+ if (!conn->result)
+ {
+ /* A new PGresult will
be created to load parsed data into. */
+ if
(getParamDescriptions(conn))
+ return;
+
+ /* Result is ready. */
+ conn->asyncStatus =
PGASYNC_READY;
+ }
+ else
+ {
+ /*
+ * We'll wait until the
application accepts the current
+ * existing result.
+ */
+ conn->asyncStatus =
PGASYNC_READY;
+ return;
+ }
+ }
+ break;
case 'D': /* Data Row */
if (conn->result != NULL &&
conn->result->resultStatus ==
PGRES_TUPLES_OK)
***************
*** 500,505 ****
--- 539,611 ----
}
/*
+ * parseInput subroutine to read a 't' (ParameterDescription) message.
+ * Returns 0 if parsing is completed, 1 if there isn't enough data yet
+ * and EOF if an error occurs.
+ *
+ * Parsed data will get loaded into the existing conn->result.
+ */
+ static int
+ getParamDescriptions(PGconn *conn)
+ {
+ PGresult *res;
+ int nattr;
+ int i;
+ Oid typid;
+
+ res = PQmakeEmptyPGresult(conn, PGRES_COMMAND_OK);
+ if (!res)
+ {
+ printfPQExpBuffer(&conn->errorMessage,
+ libpq_gettext("out of
memory\n"));
+ goto Error;
+ }
+
+ /* First extracting number of attributes from the message. */
+ if (pqGetInt(&nattr, 2, conn) < 0)
+ goto NotEnoughData;
+ res->numAttributes = nattr;
+
+ /* Allocate space for the attribute descriptors. */
+ if (nattr > 0)
+ {
+ int sz = nattr * sizeof(PGresAttDesc);
+
+ res->attDescs = (PGresAttDesc *) pqResultAlloc(res, sz, TRUE);
+ if (!res->attDescs)
+ {
+ printfPQExpBuffer(&conn->errorMessage,
+ libpq_gettext("out of
memory\n"));
+ goto Error;
+ }
+
+ /* Reset attribute values. */
+ MemSet(res->attDescs, 0, sz);
+ }
+
+ /* Loop through attribute's type OIDs. */
+ for (i = 0; i < nattr; i++)
+ {
+ if (pqGetInt(&typid, 4, conn) < 0)
+ goto NotEnoughData;
+ res->attDescs[i].typid = typid;
+ }
+
+ /* Success. */
+ conn->result = res;
+ return 0;
+
+ NotEnoughData:
+ PQclear(res);
+ return 1;
+
+ Error:
+ if (res)
+ PQclear(res);
+ return EOF;
+ }
+
+ /*
* parseInput subroutine to read a 'D' (row data) message.
* We add another tuple to the existing PGresult structure.
* Returns: 0 if completed message, EOF if error or not enough data yet.
Index: src/interfaces/libpq/libpq-fe.h
===================================================================
RCS file: /projects/cvsroot/pgsql/src/interfaces/libpq/libpq-fe.h,v
retrieving revision 1.129
diff -c -r1.129 libpq-fe.h
*** src/interfaces/libpq/libpq-fe.h 23 May 2006 22:13:19 -0000 1.129
--- src/interfaces/libpq/libpq-fe.h 24 Jun 2006 11:31:14 -0000
***************
*** 407,412 ****
--- 407,416 ----
extern int PQgetlength(const PGresult *res, int tup_num, int field_num);
extern int PQgetisnull(const PGresult *res, int tup_num, int field_num);
+ /* Describe prepared statements and portals. */
+ extern int PQdescribePrepared(PGconn *conn, const char *stmt);
+ extern int PQdescribePortal(PGconn *conn, const char *portal);
+
/* Delete a PGresult */
extern void PQclear(PGresult *res);
Index: src/interfaces/libpq/libpq-int.h
===================================================================
RCS file: /projects/cvsroot/pgsql/src/interfaces/libpq/libpq-int.h,v
retrieving revision 1.113
diff -c -r1.113 libpq-int.h
*** src/interfaces/libpq/libpq-int.h 21 May 2006 20:19:23 -0000 1.113
--- src/interfaces/libpq/libpq-int.h 24 Jun 2006 11:31:14 -0000
***************
*** 193,199 ****
{
PGQUERY_SIMPLE, /* simple Query protocol
(PQexec) */
PGQUERY_EXTENDED, /* full Extended protocol
(PQexecParams) */
! PGQUERY_PREPARE /* Parse only (PQprepare) */
} PGQueryClass;
/* PGSetenvStatusType defines the state of the PQSetenv state machine */
--- 193,200 ----
{
PGQUERY_SIMPLE, /* simple Query protocol
(PQexec) */
PGQUERY_EXTENDED, /* full Extended protocol
(PQexecParams) */
! PGQUERY_PREPARE, /* Parse only (PQprepare) */
! PGQUERY_DESCRIBE /* Parse only (pqDescribe) */
} PGQueryClass;
/* PGSetenvStatusType defines the state of the PQSetenv state machine */
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