Several libpqxx users have been reporting odd problems with certain error
messages generated by libpq. One of them was the inclusion of garbage
data.
As it turns out, src/interfaces/libpq/fe-misc.c contains several instances
of this construct:
printfPQExpBuffer(&conn->ErrorMessage,
libpq_gettext("error: %s"),
SOCK_STRERROR(SOCK_ERRNO, buffer, sizeof(buffer)));
This may occur in other source files as well. On Unix-like systems,
SOCK_ERRNO defines to plain errno--which is likely to be overwritten by
the libpq_gettext(). I'm attaching a patch that fixes these instances by
introducing a named pointer to the SOCK_STRERROR message, initialized
before either of the other function calls.
Another approach would have been to make libpq_gettext() preserve errno.
It's tempting, but I'm not sure it would be valid from a language-lawyer
point of view. There is no sequence point between the evaluations of
libpq_gettext() and SOCK_STRERROR(). From what I vaguely remember hearing
somewhere in the distant past, that means that theoretically they may be
evaluated not just in any order but even in parallel. I guess it may
actually happen if both inlining and scheduling are sufficiently
aggressive. Even if libpq_gettext() is made to restore errno, it will
still have to pollute errno at some points during its execution.
Jeroen
--- fe-misc.c.org 2005-07-05 17:48:25.000000000 +0700
+++ fe-misc.c 2005-07-05 18:13:03.000000000 +0700
@@ -23,7 +23,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/interfaces/libpq/fe-misc.c,v 1.113 2005/02/22 04:42:20 momjian Exp $
+ * $PostgreSQL: pgsql/src/interfaces/libpq/fe-misc.c,v 1.114 2005/06/12 00:00:21 neilc Exp $
*
*-------------------------------------------------------------------------
*/
@@ -175,7 +175,8 @@
conn->inCursor += len;
if (conn->Pfdebug)
- fprintf(conn->Pfdebug, libpq_gettext("From backend (%lu)> %.*s\n"), (unsigned long) len, (int) len, s);
+ fprintf(conn->Pfdebug, libpq_gettext("From backend (%lu)> %.*s\n"),
+ (unsigned long) len, (int) len, s);
return 0;
}
@@ -590,6 +591,7 @@
conn->inBufSize - conn->inEnd);
if (nread < 0)
{
+ const char *errstr;
if (SOCK_ERRNO == EINTR)
goto retry3;
/* Some systems return EAGAIN/EWOULDBLOCK for no data */
@@ -606,9 +608,10 @@
if (SOCK_ERRNO == ECONNRESET)
goto definitelyFailed;
#endif
+ errstr = SOCK_STRERROR(SOCK_ERRNO, sebuf, sizeof(sebuf));
printfPQExpBuffer(&conn->errorMessage,
libpq_gettext("could not receive data from server: %s\n"),
- SOCK_STRERROR(SOCK_ERRNO, sebuf, sizeof(sebuf)));
+ errstr);
return -1;
}
if (nread > 0)
@@ -681,6 +684,7 @@
conn->inBufSize - conn->inEnd);
if (nread < 0)
{
+ const char *errstr;
if (SOCK_ERRNO == EINTR)
goto retry4;
/* Some systems return EAGAIN/EWOULDBLOCK for no data */
@@ -697,9 +701,10 @@
if (SOCK_ERRNO == ECONNRESET)
goto definitelyFailed;
#endif
+ errstr = SOCK_STRERROR(SOCK_ERRNO, sebuf, sizeof(sebuf));
printfPQExpBuffer(&conn->errorMessage,
libpq_gettext("could not receive data from server: %s\n"),
- SOCK_STRERROR(SOCK_ERRNO, sebuf, sizeof(sebuf)));
+ errstr);
return -1;
}
if (nread > 0)
@@ -759,6 +764,7 @@
if (sent < 0)
{
+ const char *errstr;
/*
* Anything except EAGAIN/EWOULDBLOCK/EINTR is trouble. If
* it's EPIPE or ECONNRESET, assume we've lost the backend
@@ -799,9 +805,10 @@
return -1;
default:
+ errstr = SOCK_STRERROR(SOCK_ERRNO, sebuf, sizeof(sebuf));
printfPQExpBuffer(&conn->errorMessage,
libpq_gettext("could not send data to server: %s\n"),
- SOCK_STRERROR(SOCK_ERRNO, sebuf, sizeof(sebuf)));
+ errstr);
/* We don't assume it's a fatal error... */
conn->outCount = 0;
return -1;
@@ -986,10 +993,12 @@
if (result < 0)
{
char sebuf[256];
+ const char *errstr;
+ errstr = SOCK_STRERROR(SOCK_ERRNO, sebuf, sizeof(sebuf));
printfPQExpBuffer(&conn->errorMessage,
libpq_gettext("select() failed: %s\n"),
- SOCK_STRERROR(SOCK_ERRNO, sebuf, sizeof(sebuf)));
+ errstr);
}
return result;
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