avformat/utils: add ff_bprint_finalize_as_fam to put bprint strings to flexible array members

Signed-off-by: Marton Balint <cus@passwd.hu>

libavformat/internal.h

@@ -700,4 +700,17 @@ int ff_parse_opts_from_query_string(void *obj, const char *str, int allow_unkown
 int ff_make_codec_str(void *logctx, const AVCodecParameters *par,
                       const AVRational *frame_rate, struct AVBPrint *out);
 
+/**
+ * Allocate copy of a structure and copy contents of an AVBPrint buffer to the
+ * flexible array member of the copied struct. AVBPrint buffer is freed.
+ *
+ * @param bp pointer to an AVBprint struct
+ * @param struct_ptr pointer to the struct to be copied
+ * @param struct_size must be sizeof(*struct_ptr)
+ * @param flex_member must be struct_ptr->flexible_array_member
+ * @return pointer to the newly allocated struct, NULL on allocation error or
+ *         if the AVBPrint buffer is not complete
+ */
+void *ff_bprint_finalize_as_fam(struct AVBPrint *bp, const void *struct_ptr, size_t struct_size, void *flex_member);
+
 #endif /* AVFORMAT_INTERNAL_H */

libavformat/utils.c

@@ -684,3 +684,22 @@ int ff_parse_opts_from_query_string(void *obj, const char *str, int allow_unknow
     }
     return 0;
 }
+
+void *ff_bprint_finalize_as_fam(struct AVBPrint *bp, const void *struct_ptr, size_t struct_size, void *flex_member)
+{
+    if (!av_bprint_is_complete(bp)) {
+        av_bprint_finalize(bp, NULL);
+        return NULL;
+    }
+
+    void *p = av_malloc(struct_size + bp->len);
+    if (!p) {
+        av_bprint_finalize(bp, NULL);
+        return NULL;
+    }
+    memcpy(p, struct_ptr, struct_size);
+    memcpy(p + (flex_member - struct_ptr), bp->str, bp->len);
+    av_bprint_finalize(bp, NULL);
+
+    return p;
+}