Fix lo_import and lo_export to return useful error messages more often.

I found that these functions tend to return -1 while leaving an empty error
message string in the PGconn, if they suffer some kind of I/O error on the
file.  The reason is that lo_close, which thinks it's executed a perfectly
fine SQL command, clears the errorMessage.  The minimum-change workaround
is to reorder operations here so that we don't fill the errorMessage until
after lo_close.

diff --git a/src/interfaces/libpq/fe-lobj.c b/src/interfaces/libpq/fe-lobj.c
index a98bfec2bf46a097c0aecf27d0a672f5d3158ff5..15a3b5ef4d0851a7f4f4d1ba37d94c50e1eec0a8 100644 (file)
--- a/src/interfaces/libpq/fe-lobj.c
+++ b/src/interfaces/libpq/fe-lobj.c
@@ -571,10 +571,16 @@ lo_import_internal(PGconn *conn, const char *filename, const Oid oid)
 
        if (nbytes < 0)
        {
+               /* We must do lo_close before setting the errorMessage */
+               int                     save_errno = errno;
+
+               (void) lo_close(conn, lobj);
+               (void) close(fd);
                printfPQExpBuffer(&conn->errorMessage,
                                          libpq_gettext("could not read from file \"%s\": %s\n"),
-                                                 filename, pqStrerror(errno, sebuf, sizeof(sebuf)));
-               lobjOid = InvalidOid;
+                                                 filename,
+                                                 pqStrerror(save_errno, sebuf, sizeof(sebuf)));
+               return InvalidOid;
        }
 
        (void) close(fd);
@@ -619,11 +625,15 @@ lo_export(PGconn *conn, Oid lobjId, const char *filename)
         */
        fd = open(filename, O_CREAT | O_WRONLY | O_TRUNC | PG_BINARY, 0666);
        if (fd < 0)
-       {                                                       /* error */
+       {
+               /* We must do lo_close before setting the errorMessage */
+               int                     save_errno = errno;
+
+               (void) lo_close(conn, lobj);
                printfPQExpBuffer(&conn->errorMessage,
                                                  libpq_gettext("could not open file \"%s\": %s\n"),
-                                                 filename, pqStrerror(errno, sebuf, sizeof(sebuf)));
-               (void) lo_close(conn, lobj);
+                                                 filename,
+                                                 pqStrerror(save_errno, sebuf, sizeof(sebuf)));
                return -1;
        }
 
@@ -635,11 +645,15 @@ lo_export(PGconn *conn, Oid lobjId, const char *filename)
                tmp = write(fd, buf, nbytes);
                if (tmp != nbytes)
                {
-                       printfPQExpBuffer(&conn->errorMessage,
-                                          libpq_gettext("could not write to file \"%s\": %s\n"),
-                                                 filename, pqStrerror(errno, sebuf, sizeof(sebuf)));
+                       /* We must do lo_close before setting the errorMessage */
+                       int                     save_errno = errno;
+
                        (void) lo_close(conn, lobj);
                        (void) close(fd);
+                       printfPQExpBuffer(&conn->errorMessage,
+                                          libpq_gettext("could not write to file \"%s\": %s\n"),
+                                                         filename,
+                                                         pqStrerror(save_errno, sebuf, sizeof(sebuf)));
                        return -1;
                }
        }
@@ -657,7 +671,8 @@ lo_export(PGconn *conn, Oid lobjId, const char *filename)
                result = -1;
        }
 
-       if (close(fd))
+       /* if we already failed, don't overwrite that msg with a close error */
+       if (close(fd) && result >= 0)
        {
                printfPQExpBuffer(&conn->errorMessage,
                                           libpq_gettext("could not write to file \"%s\": %s\n"),