From Music Player Daemon Community Wiki

Note: this page only exists for historical reasons. This (mis)-feature will never be accepted into mpd because it directly conflicts with What_MPD_Is_and_Is_Not.

This protocol is implemented in this patch. It adds the command

download <string filename>:

Send the file _filename_ to the client. This allows clients to fetch songs and playlists from MPD's databse. _filename_ should be either a file name relative to the music directory or an absolute file name starting with "/playlist/" in which case the rest of the file name is interpreted as being relative to the playlist directory.

The file's content is sent with the following encoding: every line is preceded by a ">" and the last byte is followed by a "\n". This ensures that the final OK\n stands on its own line and that none of the file's data can be confused for a command termination.

Why not just tell the client what the length is? Something like:

filesize: 41987109
filedata: [file data here, with length of exactly <filesize>]
OK

This seems less annoying than parsing of >'s and \n's.

It also avoids the situation where the data actually happens to contain "\nOK\n" (0a4f4b0a). This may not be very likely but it is certainly not impossible.