decode: concentrate JSON formatting in a single location

It's incredible how a single arbitrary choice of not supporting trailing
commas complicates generator code which immediately writes its output,
instead of accumulating pieces and separating but not terminating them
before transmitting the result.

Concentrate all text to open and close the file and array items, as well
as to separate the array item fields, in the jsontrace_open_close()
routine. This makes calling code more verbose, but heavily simplifies
the sequence and allows to shuffle items without unnecessary manual
adjustment of formatting details. Added complexity to make some of the
closing calls optional also helps.

When this DIY code is considered unmaintainable, the alternative is to
introduce another dependency on a JSON library.

diff --git a/decode.c b/decode.c
index 06400f36e87516caa56a97d2cd14e5e9bf88d9fb..e0b27fd2938636350a4ab9b70e8b709f6ab3a8e8 100644 (file)
--- a/decode.c
+++ b/decode.c
@@ -487,27 +487,56 @@ int setup_pd_binary(char *opt_pd_binary)
  * the output and late flush (and to keep the state strictly local to the
  * routine). Some additional complexity due to JSON's inability to handle
  * a trailing comma at the last item. Code phrased such that text literals
- * are kept in their order of appearance in the output text.
+ * are kept in their order of appearance in the output (where possible).
  */
-static void jsontrace_open_close(gboolean is_close_req)
+static void jsontrace_open_close(gboolean is_close_req,
+       gboolean open_item, gboolean close_item)
 {
-       static gboolean is_opened;
+       static gboolean is_file_open;
+       static gboolean is_item_open;
 
-       if (!is_close_req) {
-               if (!is_opened) {
+       if (is_close_req && is_item_open)
+               close_item = TRUE;
+
+       /* Automatic file header, and array item separation. */
+       if (open_item) {
+               if (!is_file_open)
                        printf("{\"traceEvents\": [\n");
-                       is_opened = TRUE;
-               } else {
-                       printf(",\n");
+               if (is_item_open) {
+                       printf("}");
+                       is_item_open = FALSE;
                }
-       } else {
-               if (is_opened) {
-                       printf("\n");
-                       printf("]}\n");
-                       fflush(stdout);
+               if (is_file_open) {
+                       printf(",\n");
                }
-               is_opened = FALSE;
+               is_file_open = TRUE;
+       }
+
+       /* Array item open/append/close. */
+       if (open_item) {
+               printf("{");
+               is_item_open = TRUE;
        }
+       if (!open_item && !close_item && !is_close_req) {
+               printf(", ");
+               is_item_open = TRUE;
+       }
+       if (close_item) {
+               printf("}");
+               is_item_open = FALSE;
+       }
+
+       /* Automatic file footer on shutdown. */
+       if (is_close_req && is_file_open) {
+               printf("\n");
+               printf("]}\n");
+       }
+       if (is_close_req)
+               is_file_open = FALSE;
+
+       /* Flush at end of lines, or end of file. */
+       if (close_item || is_close_req)
+               fflush(stdout);
 }
 
 /* Convert uint64 sample number to double timestamp in microseconds. */
@@ -565,29 +594,37 @@ static void jsontrace_annotation(struct srd_decoder *dec,
         * BEWARE of the unfortunate JSON format comma limitation. And
         * some of the output formatting is motivated by the desire to
         * further reduce text size, by eliminating some of the spaces.
+        * TODO Want to introduce a cJSON dependency to delegate the
+        * construction of output text?
         *
         * This implementation is strictly compatible to the initial
         * implementation. Which might change in the future to increase
         * readability of the output to humans, by generating a layout
         * which is closer to other output modes.
         */
-       jsontrace_open_close(FALSE);
-       printf("{");
+       jsontrace_open_close(FALSE, TRUE, FALSE);
        printf("\"%s\": \"%s\"", "name", pda->ann_text[0]);
-       printf(", \"%s\": \"%s\"", "ph", "B");
-       printf(", \"%s\": \"%s\"", "pid", pdata->pdo->proto_id);
-       printf(", \"%s\": \"%s\"", "tid", row_text);
-       printf(", \"%s\": %lf", "ts", jsontrace_ts_usec(pdata->start_sample));
-       printf("}");
-
-       jsontrace_open_close(FALSE);
-       printf("{");
+       jsontrace_open_close(FALSE, FALSE, FALSE);
+       printf("\"%s\": \"%s\"", "ph", "B");
+       jsontrace_open_close(FALSE, FALSE, FALSE);
+       printf("\"%s\": \"%s\"", "pid", pdata->pdo->proto_id);
+       jsontrace_open_close(FALSE, FALSE, FALSE);
+       printf("\"%s\": \"%s\"", "tid", row_text);
+       jsontrace_open_close(FALSE, FALSE, FALSE);
+       printf("\"%s\": %lf", "ts", jsontrace_ts_usec(pdata->start_sample));
+
+       jsontrace_open_close(FALSE, TRUE, FALSE);
        printf("\"%s\": \"%s\"", "name", pda->ann_text[0]);
-       printf(", \"%s\": \"%s\"", "ph", "E");
-       printf(", \"%s\": \"%s\"", "pid", pdata->pdo->proto_id);
-       printf(", \"%s\": \"%s\"", "tid", row_text);
-       printf(", \"%s\": %lf", "ts", jsontrace_ts_usec(pdata->end_sample));
-       printf("}");
+       jsontrace_open_close(FALSE, FALSE, FALSE);
+       printf("\"%s\": \"%s\"", "ph", "E");
+       jsontrace_open_close(FALSE, FALSE, FALSE);
+       printf("\"%s\": \"%s\"", "pid", pdata->pdo->proto_id);
+       jsontrace_open_close(FALSE, FALSE, FALSE);
+       printf("\"%s\": \"%s\"", "tid", row_text);
+       jsontrace_open_close(FALSE, FALSE, FALSE);
+       printf("\"%s\": %lf", "ts", jsontrace_ts_usec(pdata->end_sample));
+
+       jsontrace_open_close(FALSE, FALSE, TRUE);
 }
 
 void show_pd_annotations(struct srd_proto_data *pdata, void *cb_data)
@@ -721,12 +758,12 @@ void show_pd_binary(struct srd_proto_data *pdata, void *cb_data)
 void show_pd_prepare(void)
 {
        if (opt_pd_jsontrace)
-               jsontrace_open_close(TRUE);
+               jsontrace_open_close(TRUE, FALSE, FALSE);
 }
 
 void show_pd_close(void)
 {
        if (opt_pd_jsontrace)
-               jsontrace_open_close(TRUE);
+               jsontrace_open_close(TRUE, FALSE, FALSE);
 }
 #endif