etix
Add Metalink (v4) support
Metalink support would enable traffic distribution, integrity check (file checksum) and nice download resume (most meta4 aware download clients track download progress and can resume download in any point). Optional fragment checksum feature would enable re-downloading only broken parts. New ?meta4 endpoint would contain data from ?mirrorlist and ?sha1/md5, could also contain file size (that currently can be obtained only from Content-Length header) so it would help allocate disk space before downloading.
This is really simple php script that tries to combine data from mirrorbits endpoint and headers and create meta4 file but sadly not all instances provides Link header (https://download.lineageos.org/ is but https://get.videolan.org/ and http://mirrors.kodi.tv/ is not). Working example.
Part of RFC 6249 is already in place, notably the Link rel=duplicate. I can definitely add the remaining parts (digests and describedby). And since the RFC 6249 is supposed to offer the same level of functionality as RFC 5854 is it worth investing time supporting it too?
If Digest, Link (rel=duplicate) (+ Location?), Link (rel=describedby), Content-Length headers are present then it is just one step to return it as XML file instead of headers. I'm not sure which client is rfc6249 compilant but for example aria2 seems is ignoring headers but uses .meta4 file.
TBH from a standard point of view I much prefer the RFC 6249 since it doesn't involve creating "virtual" .meta4 files and requires only one HTTP query instead of two.
IMHO the real question is, how many application do supports RFC 5854 but not RFC 6249. Aria2 for example supports both.