avformat/id3v2: Don't reverse the order of id3v2 APICs

When parsing ID3v2 tags, special (non-text) metadata is not applied
directly and unconditionally; instead it is stored in a linked list
in which elements are prepended. When traversing the list to add APICs
(or private tags) at the end, the order is reversed. The same also
happens for chapters and therefore the chapter parsing code already
reverses the chapters.

This commit changes this: By keeping pointers to both head and tail
of the linked list one can preserve the order of the entries and
remove the reordering code for chapters. Only the pointer to head
will be exported: No current caller uses a nonempty list, so exporting
both head and tail is unnecessary. This removes the functionality
to combine the lists of special metadata read from different ID3v2 tags,
but that doesn't make really much sense anyway (and would be trivial
to implement if desired) and allows to remove the now unnecessary
initializations performed by the callers.

The FATE-reference for the id3v2-priv test had to be updated
because the order of the tags read into the dict is reversed;
for id3v2-priv-remux only the md5 and not the ffprobe output
of the remuxed file changes because the order of the private tags
has up until now been reversed twice.

The references for the aiff/mp3 cover-art tests needed to be updated,
because the order of the attached pics is reversed upon reading.
It is still not correct, because the muxers write the pics in the order
in which they arrive at the muxer instead of the order given by
pkt->stream_index.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

1 files changed, 42 insertions, 53 deletions

diff --git a/libavformat/id3v2.c b/libavformat/id3v2.c
index 863709abbf..e0fef08789 100644
--- a/libavformat/id3v2.c
+++ b/libavformat/id3v2.c
@@ -443,12 +443,24 @@ static void read_comment(AVFormatContext *s, AVIOContext *pb, int taglen,
         av_dict_set(metadata, key, (const char *) dst, dict_flags);
 }
 
+typedef struct ExtraMetaList {
+    ID3v2ExtraMeta *head, *tail;
+} ExtraMetaList;
+
+static void list_append(ID3v2ExtraMeta *new_elem, ExtraMetaList *list)
+{
+    if (list->tail)
+        list->tail->next = new_elem;
+    else
+        list->head = new_elem;
+    list->tail = new_elem;
+}
+
 /**
  * Parse GEOB tag into a ID3v2ExtraMetaGEOB struct.
  */
 static void read_geobtag(AVFormatContext *s, AVIOContext *pb, int taglen,
-                         const char *tag, ID3v2ExtraMeta **extra_meta,
-                         int isv34)
+                         const char *tag, ExtraMetaList *extra_meta, int isv34)
 {
     ID3v2ExtraMetaGEOB *geob_data = NULL;
     ID3v2ExtraMeta *new_extra     = NULL;
@@ -505,8 +517,7 @@ static void read_geobtag(AVFormatContext *s, AVIOContext *pb, int taglen,
 
     /* add data to the list */
     new_extra->tag  = "GEOB";
-    new_extra->next = *extra_meta;
-    *extra_meta     = new_extra;
+    list_append(new_extra, extra_meta);
 
     return;
 
@@ -580,8 +591,7 @@ static void rstrip_spaces(char *buf)
 }
 
 static void read_apic(AVFormatContext *s, AVIOContext *pb, int taglen,
-                      const char *tag, ID3v2ExtraMeta **extra_meta,
-                      int isv34)
+                      const char *tag, ExtraMetaList *extra_meta, int isv34)
 {
     int enc, pic_type;
     char mimetype[64] = {0};
@@ -654,12 +664,11 @@ static void read_apic(AVFormatContext *s, AVIOContext *pb, int taglen,
     memset(apic->buf->data + taglen, 0, AV_INPUT_BUFFER_PADDING_SIZE);
 
     new_extra->tag  = "APIC";
-    new_extra->next = *extra_meta;
-    *extra_meta     = new_extra;
 
     // The description must be unique, and some ID3v2 tag writers add spaces
     // to write several APIC entries with the same description.
     rstrip_spaces(apic->description);
+    list_append(new_extra, extra_meta);
 
     return;
 
@@ -677,7 +686,8 @@ static void free_chapter(void *obj)
     av_dict_free(&chap->meta);
 }
 
-static void read_chapter(AVFormatContext *s, AVIOContext *pb, int len, const char *ttag, ID3v2ExtraMeta **extra_meta, int isv34)
+static void read_chapter(AVFormatContext *s, AVIOContext *pb, int len,
+                         const char *ttag, ExtraMetaList *extra_meta, int isv34)
 {
     int taglen;
     char tag[5];
@@ -721,8 +731,7 @@ static void read_chapter(AVFormatContext *s, AVIOContext *pb, int len, const cha
     ff_metadata_conv(&chap->meta, NULL, ff_id3v2_4_metadata_conv);
 
     new_extra->tag  = "CHAP";
-    new_extra->next = *extra_meta;
-    *extra_meta     = new_extra;
+    list_append(new_extra, extra_meta);
 
     return;
 
@@ -739,7 +748,7 @@ static void free_priv(void *obj)
 }
 
 static void read_priv(AVFormatContext *s, AVIOContext *pb, int taglen,
-                      const char *tag, ID3v2ExtraMeta **extra_meta, int isv34)
+                      const char *tag, ExtraMetaList *extra_meta, int isv34)
 {
     ID3v2ExtraMeta *meta;
     ID3v2ExtraMetaPRIV *priv;
@@ -763,8 +772,7 @@ static void read_priv(AVFormatContext *s, AVIOContext *pb, int taglen,
         goto fail;
 
     meta->tag   = "PRIV";
-    meta->next  = *extra_meta;
-    *extra_meta = meta;
+    list_append(meta, extra_meta);
 
     return;
 
@@ -777,7 +785,7 @@ typedef struct ID3v2EMFunc {
     const char *tag3;
     const char *tag4;
     void (*read)(AVFormatContext *s, AVIOContext *pb, int taglen,
-                 const char *tag, ID3v2ExtraMeta **extra_meta,
+                 const char *tag, ExtraMetaList *extra_meta,
                  int isv34);
     void (*free)(void *obj);
 } ID3v2EMFunc;
@@ -811,7 +819,7 @@ static const ID3v2EMFunc *get_extra_meta_func(const char *tag, int isv34)
 
 static void id3v2_parse(AVIOContext *pb, AVDictionary **metadata,
                         AVFormatContext *s, int len, uint8_t version,
-                        uint8_t flags, ID3v2ExtraMeta **extra_meta)
+                        uint8_t flags, ExtraMetaList *extra_meta)
 {
     int isv34, unsync;
     unsigned tlen;
@@ -1063,13 +1071,17 @@ error:
 
 static void id3v2_read_internal(AVIOContext *pb, AVDictionary **metadata,
                                 AVFormatContext *s, const char *magic,
-                                ID3v2ExtraMeta **extra_meta, int64_t max_search_size)
+                                ID3v2ExtraMeta **extra_metap, int64_t max_search_size)
 {
     int len, ret;
     uint8_t buf[ID3v2_HEADER_SIZE];
+    ExtraMetaList extra_meta = { NULL };
     int found_header;
     int64_t start, off;
 
+    if (extra_metap)
+        *extra_metap = NULL;
+
     if (max_search_size && max_search_size < ID3v2_HEADER_SIZE)
         return;
 
@@ -1096,7 +1108,8 @@ static void id3v2_read_internal(AVIOContext *pb, AVDictionary **metadata,
                   ((buf[7] & 0x7f) << 14) |
                   ((buf[8] & 0x7f) << 7) |
                    (buf[9] & 0x7f);
-            id3v2_parse(pb, metadata, s, len, buf[3], buf[5], extra_meta);
+            id3v2_parse(pb, metadata, s, len, buf[3], buf[5],
+                        extra_metap ? &extra_meta : NULL);
         } else {
             avio_seek(pb, off, SEEK_SET);
         }
@@ -1105,6 +1118,8 @@ static void id3v2_read_internal(AVIOContext *pb, AVDictionary **metadata,
     ff_metadata_conv(metadata, NULL, id3v2_2_metadata_conv);
     ff_metadata_conv(metadata, NULL, ff_id3v2_4_metadata_conv);
     merge_date(metadata);
+    if (extra_metap)
+        *extra_metap = extra_meta.head;
 }
 
 void ff_id3v2_read_dict(AVIOContext *pb, AVDictionary **metadata,
@@ -1166,55 +1181,29 @@ int ff_id3v2_parse_apic(AVFormatContext *s, ID3v2ExtraMeta *extra_meta)
     return 0;
 }
 
-int ff_id3v2_parse_chapters(AVFormatContext *s, ID3v2ExtraMeta *extra_meta)
+int ff_id3v2_parse_chapters(AVFormatContext *s, ID3v2ExtraMeta *cur)
 {
-    int ret = 0;
-    ID3v2ExtraMeta *cur;
     AVRational time_base = {1, 1000};
-    ID3v2ExtraMetaCHAP **chapters = NULL;
-    int num_chapters = 0;
-    int i;
+    int ret;
 
-    // since extra_meta is a linked list where elements are prepended,
-    // we need to reverse the order of chapters
-    for (cur = extra_meta; cur; cur = cur->next) {
+    for (unsigned i = 0; cur; cur = cur->next) {
         ID3v2ExtraMetaCHAP *chap;
+        AVChapter *chapter;
 
         if (strcmp(cur->tag, "CHAP"))
             continue;
-        chap = &cur->data.chap;
-
-        if ((ret = av_dynarray_add_nofree(&chapters, &num_chapters, chap)) < 0)
-            goto end;
-    }
-
-    for (i = 0; i < (num_chapters / 2); i++) {
-        ID3v2ExtraMetaCHAP *right;
-        int right_index;
-
-        right_index = (num_chapters - 1) - i;
-        right = chapters[right_index];
 
-        chapters[right_index] = chapters[i];
-        chapters[i] = right;
-    }
-
-    for (i = 0; i < num_chapters; i++) {
-        ID3v2ExtraMetaCHAP *chap;
-        AVChapter *chapter;
-
-        chap = chapters[i];
-        chapter = avpriv_new_chapter(s, i, time_base, chap->start, chap->end, chap->element_id);
+        chap = &cur->data.chap;
+        chapter = avpriv_new_chapter(s, i++, time_base, chap->start,
+                                     chap->end, chap->element_id);
         if (!chapter)
             continue;
 
         if ((ret = av_dict_copy(&chapter->metadata, chap->meta, 0)) < 0)
-            goto end;
+            return ret;
     }
 
-end:
-    av_freep(&chapters);
-    return ret;
+    return 0;
 }
 
 int ff_id3v2_parse_priv_dict(AVDictionary **metadata, ID3v2ExtraMeta *extra_meta)