Consuming empty messages caused fatal error (issue #29)

kafkacat.c

@@ -387,7 +387,8 @@ static void consume_cb (rd_kafka_message_t *rkmessage, void *opaque) {
                         (int)rkmessage->key_len, (const char *)rkmessage->key,
                         conf.key_delim);
 
-        if (fwrite(rkmessage->payload, rkmessage->len, 1, fp) != 1 ||
+        if ((rkmessage->len > 0 &&
+             fwrite(rkmessage->payload, rkmessage->len, 1, fp) != 1) ||
             fwrite(&conf.delim, 1, 1, fp) != 1)
                 FATAL("Write error for message "
                       "of %zd bytes at offset %"PRId64"): %s",
@@ -670,7 +671,7 @@ static void __attribute__((noreturn)) usage (const char *argv0, int exitcode,
                "  -z snappy|gzip     Message compression. Default: none\n"
                "  -p -1              Use random partitioner\n"
                "  -D <delim>         Delimiter to split input into messages\n"
-               "  -K <delim>         Parse key prefix for producing.\n"
+               "  -K <delim>         Delimiter to split input key and message\n"
                "  -T                 Output sent messages to stdout, acting like tee.\n"
                "  -c <cnt>           Exit after producing this number "
                "of messages\n"