avfilter/avfilter: Allow to free non-static pads generically

This can be enabled/disabled on a per-pad basis by setting
the AVFILTERPAD_FLAG_FREE_NAME flag; variants of ff_append_(in|out)pads
that do this for you have been added and will be put to use in the
following commits.

Reviewed-by: Nicolas George <george@nsup.org>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavfilter/avfilter.c

@@ -123,8 +123,11 @@ static int append_pad(unsigned *count, AVFilterPad **pads,
         *pads  = newpads;
     if (newlinks)
         *links = newlinks;
-    if (!newpads || !newlinks)
+    if (!newpads || !newlinks) {
+        if (newpad->flags & AVFILTERPAD_FLAG_FREE_NAME)
+            av_freep(&newpad->name);
         return AVERROR(ENOMEM);
+    }
 
     memcpy(*pads + idx, newpad, sizeof(AVFilterPad));
     (*links)[idx] = NULL;
@@ -139,11 +142,23 @@ int ff_append_inpad(AVFilterContext *f, AVFilterPad *p)
     return append_pad(&f->nb_inputs, &f->input_pads, &f->inputs, p);
 }
 
+int ff_append_inpad_free_name(AVFilterContext *f, AVFilterPad *p)
+{
+    p->flags |= AVFILTERPAD_FLAG_FREE_NAME;
+    return ff_append_inpad(f, p);
+}
+
 int ff_append_outpad(AVFilterContext *f, AVFilterPad *p)
 {
     return append_pad(&f->nb_outputs, &f->output_pads, &f->outputs, p);
 }
 
+int ff_append_outpad_free_name(AVFilterContext *f, AVFilterPad *p)
+{
+    p->flags |= AVFILTERPAD_FLAG_FREE_NAME;
+    return ff_append_outpad(f, p);
+}
+
 int avfilter_link(AVFilterContext *src, unsigned srcpad,
                   AVFilterContext *dst, unsigned dstpad)
 {
@@ -754,9 +769,13 @@ void avfilter_free(AVFilterContext *filter)
 
     for (i = 0; i < filter->nb_inputs; i++) {
         free_link(filter->inputs[i]);
+        if (filter->input_pads[i].flags  & AVFILTERPAD_FLAG_FREE_NAME)
+            av_freep(&filter->input_pads[i].name);
     }
     for (i = 0; i < filter->nb_outputs; i++) {
         free_link(filter->outputs[i]);
+        if (filter->output_pads[i].flags & AVFILTERPAD_FLAG_FREE_NAME)
+            av_freep(&filter->output_pads[i].name);
     }
 
     if (filter->filter->priv_class)

libavfilter/internal.h

@@ -68,6 +68,11 @@ struct AVFilterPad {
      */
 #define AVFILTERPAD_FLAG_NEEDS_WRITABLE                  (1 << 0)
 
+    /**
+     * The pad's name is allocated and should be freed generically.
+     */
+#define AVFILTERPAD_FLAG_FREE_NAME                       (1 << 1)
+
     /**
      * A combination of AVFILTERPAD_FLAG_* flags.
      */
@@ -231,9 +236,14 @@ void ff_tlog_link(void *ctx, AVFilterLink *link, int end);
 
 /**
  * Append a new input/output pad to the filter's list of such pads.
+ *
+ * The *_free_name versions will set the AVFILTERPAD_FLAG_FREE_NAME flag
+ * ensuring that the name will be freed generically (even on insertion error).
  */
 int ff_append_inpad (AVFilterContext *f, AVFilterPad *p);
 int ff_append_outpad(AVFilterContext *f, AVFilterPad *p);
+int ff_append_inpad_free_name (AVFilterContext *f, AVFilterPad *p);
+int ff_append_outpad_free_name(AVFilterContext *f, AVFilterPad *p);
 
 /**
  * Request an input frame from the filter at the other end of the link.