ffprobe: rework/fix ini writer

Do not build from scratch the section header for each section, but build
it using the previous level buffer, thus improving efficiency.

Also fix some few corner cases related to numbering which are exposed by
the pending disposition patch.

ffprobe.c

@@ -956,6 +956,7 @@ static const Writer flat_writer = {
 typedef struct {
     const AVClass *class;
     int hierarchical;
+    AVBPrint section_header[SECTION_MAX_NB_LEVELS];
 } INIContext;
 
 #undef OFFSET
@@ -969,6 +970,25 @@ static const AVOption ini_options[] = {
 
 DEFINE_WRITER_CLASS(ini);
 
+static int ini_init(WriterContext *wctx)
+{
+    INIContext *ini = wctx->priv;
+    int i;
+
+    for (i = 0; i < SECTION_MAX_NB_LEVELS; i++)
+        av_bprint_init(&ini->section_header[i], 1, AV_BPRINT_SIZE_UNLIMITED);
+    return 0;
+}
+
+static void ini_uninit(WriterContext *wctx)
+{
+    INIContext *ini = wctx->priv;
+    int i;
+
+    for (i = 0; i < SECTION_MAX_NB_LEVELS; i++)
+        av_bprint_finalize(&ini->section_header[i], NULL);
+}
+
 static char *ini_escape_str(AVBPrint *dst, const char *src)
 {
     int i = 0;
@@ -999,14 +1019,13 @@ static char *ini_escape_str(AVBPrint *dst, const char *src)
 static void ini_print_section_header(WriterContext *wctx)
 {
     INIContext *ini = wctx->priv;
-    AVBPrint buf;
-    int i;
+    AVBPrint *buf = &ini->section_header[wctx->level];
     const struct section *section = wctx->section[wctx->level];
     const struct section *parent_section = wctx->level ?
         wctx->section[wctx->level-1] : NULL;
 
-    av_bprint_init(&buf, 1, AV_BPRINT_SIZE_UNLIMITED);
-    if (wctx->level == 0) {
+    av_bprint_clear(buf);
+    if (!parent_section) {
         printf("# ffprobe output\n\n");
         return;
     }
@@ -1014,21 +1033,20 @@ static void ini_print_section_header(WriterContext *wctx)
     if (wctx->nb_item[wctx->level-1])
         printf("\n");
 
-    for (i = 1; i <= wctx->level; i++) {
-        if (ini->hierarchical ||
-            !(section->flags & (SECTION_FLAG_IS_ARRAY|SECTION_FLAG_IS_WRAPPER)))
-            av_bprintf(&buf, "%s%s", i>1 ? "." : "", wctx->section[i]->name);
-    }
+    av_bprintf(buf, "%s", ini->section_header[wctx->level-1].str);
+    if (ini->hierarchical ||
+        !(section->flags & (SECTION_FLAG_IS_ARRAY|SECTION_FLAG_IS_WRAPPER))) {
+        av_bprintf(buf, "%s%s", buf->str[0] ? "." : "", wctx->section[wctx->level]->name);
 
-    if (parent_section->flags & SECTION_FLAG_IS_ARRAY) {
-        int n = parent_section->id == SECTION_ID_PACKETS_AND_FRAMES ?
-            wctx->nb_section_packet_frame : wctx->nb_item[wctx->level-1];
-        av_bprintf(&buf, ".%d", n);
+        if (parent_section->flags & SECTION_FLAG_IS_ARRAY) {
+            int n = parent_section->id == SECTION_ID_PACKETS_AND_FRAMES ?
+                wctx->nb_section_packet_frame : wctx->nb_item[wctx->level-1];
+            av_bprintf(buf, ".%d", n);
+        }
     }
 
     if (!(section->flags & (SECTION_FLAG_IS_ARRAY|SECTION_FLAG_IS_WRAPPER)))
-        printf("[%s]\n", buf.str);
-    av_bprint_finalize(&buf, NULL);
+        printf("[%s]\n", buf->str);
 }
 
 static void ini_print_str(WriterContext *wctx, const char *key, const char *value)
@@ -1050,6 +1068,8 @@ static void ini_print_int(WriterContext *wctx, const char *key, long long int va
 static const Writer ini_writer = {
     .name                  = "ini",
     .priv_size             = sizeof(INIContext),
+    .init                  = ini_init,
+    .uninit                = ini_uninit,
     .print_section_header  = ini_print_section_header,
     .print_integer         = ini_print_int,
     .print_string          = ini_print_str,