Further thoughts about lo_export/lo_import error handling: if one of

the lower-level large object functions fails, it will have already set
a suitable error message --- probably something from the backend ---
and it is not useful to overwrite that with a generic 'error while
reading large object' message.  So remove redundant messages.

diff --git a/src/interfaces/libpq/fe-lobj.c b/src/interfaces/libpq/fe-lobj.c
index 5e11b0e3059bd857efd409d5f1adba1547d85f10..f8859ca32dfb0abb5ac8e7f5f01c5fac433eafcd 100644 (file)
--- a/src/interfaces/libpq/fe-lobj.c
+++ b/src/interfaces/libpq/fe-lobj.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *       $PostgreSQL: pgsql/src/interfaces/libpq/fe-lobj.c,v 1.57 2006/06/14 01:28:55 tgl Exp $
+ *       $PostgreSQL: pgsql/src/interfaces/libpq/fe-lobj.c,v 1.58 2006/06/14 17:49:25 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -32,7 +32,6 @@
 
 #include <fcntl.h>
 #include <sys/stat.h>
-#include <errno.h>
 
 #include "libpq-fe.h"
 #include "libpq-int.h"
@@ -458,9 +457,7 @@ lo_import(PGconn *conn, const char *filename)
        lobjOid = lo_creat(conn, INV_READ | INV_WRITE);
        if (lobjOid == InvalidOid)
        {
-               printfPQExpBuffer(&conn->errorMessage,
-                       libpq_gettext("could not create large object for file \"%s\"\n"),
-                                                 filename);
+               /* we assume lo_creat() already set a suitable error message */
                (void) close(fd);
                return InvalidOid;
        }
@@ -468,9 +465,7 @@ lo_import(PGconn *conn, const char *filename)
        lobj = lo_open(conn, lobjOid, INV_WRITE);
        if (lobj == -1)
        {
-               printfPQExpBuffer(&conn->errorMessage,
-                                                 libpq_gettext("could not open large object %u\n"),
-                                                 lobjOid);
+               /* we assume lo_open() already set a suitable error message */
                (void) close(fd);
                return InvalidOid;
        }
@@ -484,16 +479,11 @@ lo_import(PGconn *conn, const char *filename)
                if (tmp != nbytes)
                {
                        /*
-                        * If the lo_write failed, we are probably in an aborted
-                        * transaction and so lo_close will fail.  Try it anyway for
-                        * cleanliness, but don't let it determine the returned error
-                        * message.
+                        * If lo_write() failed, we are now in an aborted transaction
+                        * so there's no need for lo_close(); furthermore, if we tried
+                        * it we'd overwrite the useful error result with a useless one.
+                        * So just nail the doors shut and get out of town.
                         */
-                       (void) lo_close(conn, lobj);
-
-                       printfPQExpBuffer(&conn->errorMessage,
-                                               libpq_gettext("error while writing large object %u\n"),
-                                                         lobjOid);
                        (void) close(fd);
                        return InvalidOid;
                }
@@ -511,9 +501,7 @@ lo_import(PGconn *conn, const char *filename)
 
        if (lo_close(conn, lobj) != 0)
        {
-               printfPQExpBuffer(&conn->errorMessage,
-                                               libpq_gettext("error while writing large object %u\n"),
-                                                 lobjOid);
+               /* we assume lo_close() already set a suitable error message */
                return InvalidOid;
        }
 
@@ -542,8 +530,7 @@ lo_export(PGconn *conn, Oid lobjId, const char *filename)
        lobj = lo_open(conn, lobjId, INV_READ);
        if (lobj == -1)
        {
-               printfPQExpBuffer(&conn->errorMessage,
-                                 libpq_gettext("could not open large object %u\n"), lobjId);
+               /* we assume lo_open() already set a suitable error message */
                return -1;
        }
 
@@ -569,7 +556,7 @@ lo_export(PGconn *conn, Oid lobjId, const char *filename)
                if (tmp != nbytes)
                {
                        printfPQExpBuffer(&conn->errorMessage,
-                                          libpq_gettext("error while writing to file \"%s\": %s\n"),
+                                          libpq_gettext("could not write to file \"%s\": %s\n"),
                                                  filename, pqStrerror(errno, sebuf, sizeof(sebuf)));
                        (void) lo_close(conn, lobj);
                        (void) close(fd);
@@ -577,18 +564,23 @@ lo_export(PGconn *conn, Oid lobjId, const char *filename)
                }
        }
 
-       if (lo_close(conn, lobj) != 0 || nbytes < 0)
+       /*
+        * If lo_read() failed, we are now in an aborted transaction
+        * so there's no need for lo_close(); furthermore, if we tried
+        * it we'd overwrite the useful error result with a useless one.
+        * So skip lo_close() if we got a failure result.
+        */
+       if (nbytes < 0 ||
+               lo_close(conn, lobj) != 0)
        {
-               printfPQExpBuffer(&conn->errorMessage,
-                                               libpq_gettext("error while reading large object %u\n"),
-                                                 lobjId);
+               /* assume lo_read() or lo_close() left a suitable error message */
                result = -1;
        }
 
        if (close(fd))
        {
                printfPQExpBuffer(&conn->errorMessage,
-                                          libpq_gettext("error while writing to file \"%s\": %s\n"),
+                                          libpq_gettext("could not write to file \"%s\": %s\n"),
                                                  filename, pqStrerror(errno, sebuf, sizeof(sebuf)));
                result = -1;
        }