mirrors/postgres
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Don't let libpq "event" procs break the state of PGresult objects.

Browse Source 
As currently implemented, failure of a PGEVT_RESULTCREATE callback
causes the PGresult to be converted to an error result.  This is
intellectually inconsistent (shouldn't a failing callback likewise
prevent creation of the error result? what about side-effects on the
behavior seen by other event procs? why does PQfireResultCreateEvents
act differently from PQgetResult?), but more importantly it destroys
any promises we might wish to make about the behavior of libpq in
nontrivial operating modes, such as pipeline mode.  For example,
it's not possible to promise that PGRES_PIPELINE_SYNC results will
be returned if an event callback fails on those.  With this
definition, expecting applications to behave sanely in the face of
possibly-failing callbacks seems like a very big lift.

Hence, redefine the result of a callback failure as being simply
that that event procedure won't be called any more for this PGresult
(which was true already).  Event procedures can still signal failure
back to the application through out-of-band mechanisms, for example
via their passthrough arguments.

Similarly, don't let failure of a PGEVT_RESULTCOPY callback prevent
PQcopyResult from succeeding.  That definition allowed a misbehaving
event proc to break single-row mode (our sole internal use of
PQcopyResult), and it probably had equally deleterious effects for
outside uses.

Discussion: https://postgr.es/m/3185105.1644960083@sss.pgh.pa.us
This commit is contained in:
Tom Lane 2022-02-18 11:37:27 -05:00
parent de447bb8e6
commit ce1e7a2f71
3 changed files with 31 additions and 51 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

31
doc/src/sgml/libpq.sgml
View File

@ -6831,6 +6831,7 @@ PGresult *PQcopyResult(const PGresult *src, int flags);
<literal>PG_COPYRES_EVENTS</literal> specifies copying the source
result's events. (But any instance data associated with the source
is not copied.)
The event procedures receive <literal>PGEVT_RESULTCOPY</literal> events.
</para>
</listitem>
</varlistentry>
@ -7126,7 +7127,7 @@ defaultNoticeProcessor(void *arg, const char *message)
<xref linkend="libpq-PQinstanceData"/>,
<xref linkend="libpq-PQsetInstanceData"/>,
<xref linkend="libpq-PQresultInstanceData"/> and
<function>PQsetResultInstanceData</function> functions. Note that
<xref linkend="libpq-PQresultSetInstanceData"/> functions. Note that
unlike the pass-through pointer, instance data of a <structname>PGconn</structname>
is not automatically inherited by <structname>PGresult</structname>s created from
it. <application>libpq</application> does not know what pass-through
@ -7154,7 +7155,7 @@ defaultNoticeProcessor(void *arg, const char *message)
is called. It is the ideal time to initialize any
<literal>instanceData</literal> an event procedure may need. Only one
register event will be fired per event handler per connection. If the
event procedure fails, the registration is aborted.
event procedure fails (returns zero), the registration is cancelled.
<synopsis>
typedef struct
@ -7261,11 +7262,11 @@ typedef struct
<parameter>conn</parameter> is the connection used to generate the
result. This is the ideal place to initialize any
<literal>instanceData</literal> that needs to be associated with the
result. If the event procedure fails, the result will be cleared and
the failure will be propagated. The event procedure must not try to
<xref linkend="libpq-PQclear"/> the result object for itself. When returning a
failure code, all cleanup must be performed as no
<literal>PGEVT_RESULTDESTROY</literal> event will be sent.
result. If an event procedure fails (returns zero), that event
procedure will be ignored for the remaining lifetime of the result;
that is, it will not receive <literal>PGEVT_RESULTCOPY</literal>
or <literal>PGEVT_RESULTDESTROY</literal> events for this result or
results copied from it.
</para>
</listitem>
</varlistentry>
@ -7295,12 +7296,12 @@ typedef struct
<parameter>src</parameter> result is what was copied while the
<parameter>dest</parameter> result is the copy destination. This event
can be used to provide a deep copy of <literal>instanceData</literal>,
since <literal>PQcopyResult</literal> cannot do that. If the event
procedure fails, the entire copy operation will fail and the
<parameter>dest</parameter> result will be cleared. When returning a
failure code, all cleanup must be performed as no
<literal>PGEVT_RESULTDESTROY</literal> event will be sent for the
destination result.
since <literal>PQcopyResult</literal> cannot do that. If an event
procedure fails (returns zero), that event procedure will be
ignored for the remaining lifetime of the new result; that is, it
will not receive <literal>PGEVT_RESULTCOPY</literal>
or <literal>PGEVT_RESULTDESTROY</literal> events for that result or
results copied from it.
</para>
</listitem>
</varlistentry>
@ -7618,7 +7619,7 @@ myEventProc(PGEventId evtId, void *evtInfo, void *passThrough)
mydata *res_data = dup_mydata(conn_data);
/* associate app specific data with result (copy it from conn) */
PQsetResultInstanceData(e->result, myEventProc, res_data);
PQresultSetInstanceData(e->result, myEventProc, res_data);
break;
}
@ -7629,7 +7630,7 @@ myEventProc(PGEventId evtId, void *evtInfo, void *passThrough)
mydata *dest_data = dup_mydata(src_data);
/* associate app specific data with result (copy it from a result) */
PQsetResultInstanceData(e->dest, myEventProc, dest_data);
PQresultSetInstanceData(e->dest, myEventProc, dest_data);
break;
}

37
src/interfaces/libpq/fe-exec.c
View File

@ -363,19 +363,16 @@ PQcopyResult(const PGresult *src, int flags)
/* Okay, trigger PGEVT_RESULTCOPY event */
for (i = 0; i < dest->nEvents; i++)
{
/* We don't fire events that had some previous failure */
if (src->events[i].resultInitialized)
{
PGEventResultCopy evt;
evt.src = src;
evt.dest = dest;
if (!dest->events[i].proc(PGEVT_RESULTCOPY, &evt,
dest->events[i].passThrough))
{
PQclear(dest);
return NULL;
}
dest->events[i].resultInitialized = true;
if (dest->events[i].proc(PGEVT_RESULTCOPY, &evt,
dest->events[i].passThrough))
dest->events[i].resultInitialized = true;
}
}
@ -2124,29 +2121,9 @@ PQgetResult(PGconn *conn)
break;
}
if (res)
{
int i;
for (i = 0; i < res->nEvents; i++)
{
PGEventResultCreate evt;
evt.conn = conn;
evt.result = res;
if (!res->events[i].proc(PGEVT_RESULTCREATE, &evt,
res->events[i].passThrough))
{
appendPQExpBuffer(&conn->errorMessage,
libpq_gettext("PGEventProc \"%s\" failed during PGEVT_RESULTCREATE event\n"),
res->events[i].name);
pqSetResultError(res, &conn->errorMessage);
res->resultStatus = PGRES_FATAL_ERROR;
break;
}
res->events[i].resultInitialized = true;
}
}
/* Time to fire PGEVT_RESULTCREATE events, if there are any */
if (res && res->nEvents > 0)
(void) PQfireResultCreateEvents(conn, res);
return res;
}

14
src/interfaces/libpq/libpq-events.c
View File

@ -184,6 +184,7 @@ PQresultInstanceData(const PGresult *result, PGEventProc proc)
int
PQfireResultCreateEvents(PGconn *conn, PGresult *res)
{
int result = true;
int i;
if (!res)
@ -191,19 +192,20 @@ PQfireResultCreateEvents(PGconn *conn, PGresult *res)
for (i = 0; i < res->nEvents; i++)
{
/* It's possible event was already fired, if so don't repeat it */
if (!res->events[i].resultInitialized)
{
PGEventResultCreate evt;
evt.conn = conn;
evt.result = res;
if (!res->events[i].proc(PGEVT_RESULTCREATE, &evt,
res->events[i].passThrough))
return false;
res->events[i].resultInitialized = true;
if (res->events[i].proc(PGEVT_RESULTCREATE, &evt,
res->events[i].passThrough))
res->events[i].resultInitialized = true;
else
result = false;
}
}
return true;
return result;
}