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id3tag.d
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id3tag.d
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// ID3 Tag retrieval D module.
// written by James Dunne
// (c) Copyright James Dunne 2004, 2005
// 06 Dec. 2004
module id3tag;
import std.stream;
import std.intrinsic;
import std.string;
// A very simple tag structure, only
// concerned with simple song details.
struct ID3Tag {
// 1 for ID3v1, 2 for ID3v2
int id3version;
// The common fields:
char[] title;
char[] artist;
char[] album;
int year;
int track, tracks;
char[] genre;
};
// Exception thrown by readID3Tag():
class ID3Exception : Exception {
this(char[] msg) {
super(msg);
}
}
// Reads an ID3 tag from an MP3 stream.
// Stream must be at least both seekable and readable.
// This function returns an ID3Tag structure representing the
// ID3 information read in. ID3v2 tag is searched for first,
// and if not found, ID3v1 is searched for. If neither is found
// the function returns 'null'.
ID3Tag* readID3Tag(Stream stream) {
ID3Tag* tag;
// Read a string from a stream:
char[] readString(Stream stream, int taglen) {
// Read the string:
char* str = new char[taglen];
stream.readBlock(cast(void*)str, taglen);
return str[0 .. taglen].dup;
}
// Test stream properties:
if (!stream.seekable) throw new ID3Exception("Stream must be seekable");
if (!stream.readable) throw new ID3Exception("Stream must be readable");
char* blk = new char[4];
const char[3] head = "ID3";
// Look for an ID3 v2 tag at the start of the stream:
stream.seek(0x00, SeekPos.Set);
stream.readBlock(cast(void*)blk, 4);
if ((blk[0 .. 3] == head) && (blk[3] == 3)) {
// The code below is based totally on my hacking ability, and I know it
// to be incorrect for certain ID3v2 layouts. I have yet to hack out
// that format.
bool done = false;
uint taglen;
ushort dummy;
tag = new ID3Tag;
tag.id3version = 2;
// Skip 6 bytes:
stream.seek(0x06, SeekPos.Current);
// Keep reading blocks of 4-character identifiers:
while (!done) {
// Read the block identifier:
stream.readBlock(cast(void*)blk, 4);
if (blk[0] == 0) break;
// Read the length:
stream.readBlock(cast(void*)&taglen, 4);
version (LittleEndian) taglen = bswap(taglen);
// Read 2 dumb bytes:
stream.readBlock(cast(void*)&dummy, 2);
// dummy should be byte-swapped also (only as a ushort)
// however, it is never used.
// Now, what to do with the string?
switch (blk[0 .. 4]) {
// Song title:
case "TIT2":
stream.seek(1, SeekPos.Current); --taglen;
tag.title = readString(stream, taglen);
break;
// Song artist:
case "TPE1", "TPE2":
stream.seek(1, SeekPos.Current); --taglen;
tag.artist = readString(stream, taglen);
break;
// Album title:
case "TALB":
stream.seek(1, SeekPos.Current); --taglen;
tag.album = readString(stream, taglen);
break;
// Song genre:
case "TCON":
stream.seek(1, SeekPos.Current); --taglen;
tag.genre = readString(stream, taglen);
break;
// Song track: (can also be "n/N" format where n is track and N is tracks)
case "TRCK":
stream.seek(1, SeekPos.Current); --taglen;
char[][] trkstrs = split(readString(stream, taglen), "/");
tag.track = atoi(trkstrs[0]);
// If no / separator, just set a dumb default for maxtracks:
if (trkstrs.length == 2)
tag.tracks = atoi(trkstrs[1]);
else
tag.tracks = 0;
break;
// Album year release:
case "TYER":
stream.seek(1, SeekPos.Current); --taglen;
tag.year = atoi(readString(stream, taglen));
break;
// Dummy fields ignored:
default:
stream.seek(taglen, SeekPos.Current);
break;
}
}
return tag;
} else {
// Look for an ID3 v1 tag 0x80 bytes from end of stream:
stream.seek(-0x80, SeekPos.End);
stream.readBlock(cast(void*)blk, 3);
if (blk[0 .. 3] == "TAG") {
char* str = new char[30];
ubyte trk = 0;
tag = new ID3Tag;
tag.id3version = 1;
// All fields are 30 characters long:
stream.readBlock(cast(void*)str, 30);
tag.title = strip(std.string.toString(str));
str = new char[30];
stream.readBlock(cast(void*)str, 30);
tag.artist = strip(std.string.toString(str));
str = new char[30];
stream.readBlock(cast(void*)str, 30);
tag.album = strip(std.string.toString(str));
str = new char[4];
stream.readBlock(cast(void*)str, 4);
tag.year = atoi(str[0 .. 4]);
// I'm not 100% sure, but this seems to be the case:
stream.seek(-1, SeekPos.End);
stream.readBlock(cast(void*)&trk, 1);
tag.track = trk;
// No max tracks provided in ID3v1:
tag.tracks = 0;
// Who knows after this?
return tag;
} else {
// No ID3v1 or ID3v2 tag found.
// Please note that I do NOT throw an exception here,
// since it is NOT an error that an ID3 tag is not found.
// Some files simply do not contain them. Also, there is
// the possibility that the stream being scanned is NOT
// an MP3 file.
return null;
}
}
return null;
}
// A dummy test:
debug {
int main(char[][] args) {
// Check command arguments:
if (args.length < 2) {
printf("%.*s <filename.mp3>\n", args[0]);
return 1;
}
// Open the mp3 file:
File mp3 = new File(args[1]);
// Search for ID3 tag (v2 first, then v1):
ID3Tag* tag = readID3Tag(mp3);
if (!(tag is null)) {
printf("ID3v%d tag\n", tag.id3version);
printf("Title: '%.*s'\n", tag.title);
printf("Arist: '%.*s'\n", tag.artist);
printf("Album: '%.*s'\n", tag.album);
printf("Album Year: %d\n", tag.year);
printf("Track: %d/%d\n", tag.track, tag.tracks);
printf("Genre: '%.*s'\n", tag.genre);
} else {
printf("No ID3 tag found\n");
}
// Close that mp3 file:
mp3.close();
// That's it!
return 0;
}
}