Custom header for curl request per song

[skidoo23]

I tried to update the SoundCloud plugin and modified src/playlist/plugins/SoundCloudPlaylistPlugin.cxx

static void
soundcloud_parse_json((const char *url, Yajl::Handle &handle, Mutex &mutex)
{
Curl::Headers headers;
headers.insert({"accept", "application/json; charset=utf-8"});
headers.insert({"Authorization", "OAuth " + token});
auto input_stream = OpenCurlInputStream(url, headers, mutex);
Yajl::ParseInputStream(handle, *input_stream);
}

Token is read at soundcloud_init() from mpd.conf code adds tracks to queue but added tracks are skipped. SoundCloud expects OAuth token in request header for song. I am not sure to implement such a feature in a resonable way. Add some kind of "Auth: SoundCloud" property to song and let libcurl plugin take care of the rest?

[MaxKellermann]

Adding the OAuth token to the song would not work properly; there are no such "song properties", and if you need a new token, it would invalidate all songs, because they all have a copy of the old token. And you wouldn't be able to share links with friends who have a different token.

I guess for this to work, we'd need a way for the SoundCloud playlist plugin to intercept all CURL requests matching a hostname and allow it to add HTTP request headers. Something like "plugins for the curl plugin". Maybe like this:

using CurlRequestInterceptFunction = void (*)(CurlEasy &easy);
static constexpr std::array curl_request_intercept_functions = {
#ifdef ENABLE_SOUNDCLOUD
  SoundCloudRequestIntercept,
#endif
};

[skidoo23]

Thanks for your advice Max. I'm going to implement custom http headers depending on url. Code may lack some elegance compared to your draft.