MusicPlayer/server/music_server_client.gd

extends Node
## Client for the MusicServer REST API ([code]/api/v1[/code]).
##
## Registered as the [code]MusicServerClient[/code] autoload, so every script can call it
## directly, e.g. [code]MusicServerClient.fetch_song_list(on_done)[/code]. All HTTP traffic
## goes through [member transport]; tests replace it with a fake to answer requests
## without a running server.
##
## The server keeps a play queue for each client, identified by the [code]X-Queue-Id[/code]
## header. The client sends the ID it has for the server with every request and keeps the
## one in each response, which is new when the server started a new queue (after a reset
## or a sync). The IDs are kept in [code]Settings.queue_ids[/code], which saves them.
##
## Requests need a token, which the client gets with [code]Settings.api_password[/code]
## the first time it is needed and then reuses. When the server answers 401 (the token
## expired, or the server restarted), it gets a new token and sends the request once
## more. Callers never see the token.
##
## JSON objects are handed to [code]on_done[/code] as the classes generated from the
## server's OpenAPI spec (see [code]server/generated/[/code]), lists of them as typed
## Arrays. [code]on_failed[/code] is called with no arguments when a request fails,
## including when no token could be had; [member last_error] then has the server's reason.

## Path of the API on the server, added between [code]Settings.default_path[/code] and
## each endpoint.
const API_PATH: String = "/api/v1"
## Sent when asking for a token, so the server can tell its clients apart.
const CLIENT_TYPE: String = "godot"
## Header with the ID of the client's play queue, in requests and responses.
const QUEUE_HEADER: String = "X-Queue-Id"
## The type of the JSON bodies sent.
const JSON_TYPE: String = "application/json"
## The files of a MusicPlayer release that can be downloaded: the Windows game, the Linux
## game, and the Linux package with an installer.
const DOWNLOAD_ASSETS: Array[String] = ["windows", "linux", "linux-package"]
## Where the cover of a soundtrack can be picked from, by the game's or anime's ID there.
const COVER_SOURCES: Array[String] = ["steamgriddb", "anilist"]

## Sends the actual HTTP requests. Swap it out in tests.
var transport: HttpTransport
## The server's message for the request that failed last, e.g. [code]"covers are
## disabled"[/code], or empty when it gave none. Read it in an [code]on_failed[/code]
## callback, before another request can fail.
var last_error: String = ""

var _token: String = ""
# The server the token is for; switching server in the settings needs a new token
var _token_server: String = ""
# [on_token, on_failed] pairs waiting for the token request that is under way
var _token_waiters: Array[Array] = []


func _ready() -> void:
	if transport == null:
		transport = HttpTransport.new(self)


# Queue

## Fetches the songs already in the server playlist as an [code]Array[SongInfo][/code].
func fetch_song_list(on_done: Callable, on_failed: Callable = Callable()) -> void:
	get_json_list("/music/list", SongInfo, on_done, on_failed)


## Downloads a random song as MP3 bytes, picked the way [param mode] (a
## [code]Settings.RandomMode[/code]) says: a random soundtrack and then one of its songs,
## the same but preferring soundtracks played less than average, or every song with the
## same chance.
func fetch_random_song(mode: int, on_done: Callable, on_failed: Callable = Callable()) -> void:
	get_bytes(random_song_path(mode), on_done, on_failed)


## The endpoint for random songs picked the way [param mode] says.
static func random_song_path(mode: int) -> String:
	match mode:
		Settings.RandomMode.LOW_PLAYED:
			return "/music/rand/low"
		Settings.RandomMode.CLASSIC:
			return "/music/rand/classic"
	return "/music/rand"


## Adds the most recently fetched random song to the server playlist.
func add_to_queue(on_done: Callable, on_failed: Callable = Callable()) -> void:
	send("/music/addQue", on_done, on_failed)


## Fetches the [SongInfo] of the most recently queued song.
func fetch_song_info(on_done: Callable, on_failed: Callable = Callable()) -> void:
	get_json_object("/music/info", SongInfo, on_done, on_failed)


## Downloads a song from the server playlist as MP3 bytes.
func fetch_song(song_no: int, on_done: Callable, on_failed: Callable = Callable()) -> void:
	get_bytes("/music?song=" + str(song_no), on_done, on_failed)


## Downloads the song after the current one in the server playlist as MP3 bytes.
func fetch_next_song(on_done: Callable, on_failed: Callable = Callable()) -> void:
	get_bytes("/music/next", on_done, on_failed)


## Downloads the song before the current one in the server playlist as MP3 bytes.
func fetch_previous_song(on_done: Callable, on_failed: Callable = Callable()) -> void:
	get_bytes("/music/previous", on_done, on_failed)


## Downloads the sound test song as MP3 bytes.
func fetch_sound_test_song(on_done: Callable, on_failed: Callable = Callable()) -> void:
	get_bytes("/music/soundTest", on_done, on_failed)


## Clears the server playlist.
func reset_playlist(on_done: Callable, on_failed: Callable = Callable()) -> void:
	send("/music/reset", on_done, on_failed)


## Records in the server statistics that a song has been played.
func mark_song_played(song_no: int) -> void:
	send("/music/played?song=" + str(song_no), Callable(), Callable(), HTTPClient.METHOD_PUT)


## Records in the server statistics that the current song has been played.
func mark_current_song_played(on_done: Callable, on_failed: Callable = Callable()) -> void:
	send("/music/addPlayed", on_done, on_failed)


# Soundtracks and songs

## Fetches every soundtrack name, shuffled, as an Array of Strings.
func fetch_all_soundtracks(on_done: Callable, on_failed: Callable = Callable()) -> void:
	get_json("/music/all", on_done, on_failed)


## Fetches every soundtrack name, sorted, as an Array of Strings.
func fetch_all_soundtracks_ordered(on_done: Callable, on_failed: Callable = Callable()) -> void:
	get_json("/music/all/order", on_done, on_failed)


## Fetches every soundtrack as an [code]Array[Soundtrack][/code].
func fetch_soundtracks(on_done: Callable, on_failed: Callable = Callable()) -> void:
	get_json_list("/soundtracks", Soundtrack, on_done, on_failed)


## Downloads the cover picture of the soundtrack with [param uuid] as bytes (JPEG or
## PNG). The server answers 404 while it has no cover for it.
func fetch_soundtrack_cover(
		uuid: String, on_done: Callable, on_failed: Callable = Callable()) -> void:
	get_bytes(_cover_path(uuid), on_done, on_failed)


## Stores [param image], a JPEG, PNG or WebP picture of [param content_type] such as
## [code]"image/png"[/code], as the cover of the soundtrack with [param uuid]. The
## server's automatic search never replaces it.
func upload_soundtrack_cover(uuid: String, image: PackedByteArray, content_type: String,
		on_done: Callable, on_failed: Callable = Callable()) -> void:
	_request(_cover_path(uuid), HTTPClient.METHOD_PUT, _call_ignoring_body.bind(on_done),
			on_failed, true, image, content_type)


## Makes the cover of the game or anime with [param id] on [param source], one of
## [constant COVER_SOURCES], the cover of the soundtrack with [param uuid]. The server
## downloads it before answering.
func set_soundtrack_cover_source(uuid: String, source: String, id: String,
		on_done: Callable, on_failed: Callable = Callable()) -> void:
	var request: CoverSource = CoverSource.new()
	request.source = source
	request.id = id
	_request(_cover_path(uuid) + "/source", HTTPClient.METHOD_PUT,
			_call_ignoring_body.bind(on_done), on_failed, true,
			JSON.stringify(request.to_dict()).to_utf8_buffer())


## Deletes the cover of the soundtrack with [param uuid], also one set by hand, so the
## server's automatic search looks for a new one.
func delete_soundtrack_cover(
		uuid: String, on_done: Callable, on_failed: Callable = Callable()) -> void:
	_request(_cover_path(uuid), HTTPClient.METHOD_DELETE, _call_ignoring_body.bind(on_done),
			on_failed)


## Replaces the alternative names of the soundtrack with [param uuid] with
## [param names]. The server trims them, drops duplicates and the soundtrack's own name,
## and calls [param on_done] with the updated [Soundtrack].
func set_alternative_names(uuid: String, names: Array[String], on_done: Callable,
		on_failed: Callable = Callable()) -> void:
	var request: AlternativeNames = AlternativeNames.new()
	request.names = names
	var path: String = "/soundtracks/%s/alternative-names" % uuid.uri_encode()
	var saved: Callable = func saved(data: Variant) -> void:
		if !(data is Dictionary):
			push_warning("Expected a JSON object from " + path)
			_call_if_valid(on_failed)
			return
		on_done.call(Soundtrack.from_dict(data))
	_request(path, HTTPClient.METHOD_PUT, _parse_json.bind(path, saved, on_failed), on_failed,
			true, JSON.stringify(request.to_dict()).to_utf8_buffer())


## Fetches a soundtrack and its songs as a [SoundtrackWithSongList].
func fetch_soundtrack(
		uuid: String, on_done: Callable, on_failed: Callable = Callable()) -> void:
	get_json_object("/soundtracks/" + uuid.uri_encode(), SoundtrackWithSongList, on_done,
			on_failed)


## Fetches a song as a [Song].
func fetch_song_by_uuid(
		uuid: String, on_done: Callable, on_failed: Callable = Callable()) -> void:
	get_json_object("/songs/" + uuid.uri_encode(), Song, on_done, on_failed)


## Downloads a song by its UUID as MP3 bytes.
func fetch_song_file(uuid: String, on_done: Callable, on_failed: Callable = Callable()) -> void:
	get_bytes("/songs/%s/file" % uuid.uri_encode(), on_done, on_failed)


# Statistics

## Fetches the play statistics of the whole library as a [StatisticsSummary].
func fetch_statistics_summary(on_done: Callable, on_failed: Callable = Callable()) -> void:
	get_json_object("/statistics/summary", StatisticsSummary, on_done, on_failed)


## Fetches every soundtrack with its songs and play counts, sorted by name, as an
## [code]Array[SoundtrackWithSongs][/code].
func fetch_soundtrack_statistics(on_done: Callable, on_failed: Callable = Callable()) -> void:
	get_json_list("/statistics/soundtracks", SoundtrackWithSongs, on_done, on_failed)


## Fetches the [param limit] most played soundtracks as an
## [code]Array[SoundtrackWithSongs][/code]. The server allows a limit of 1 to 100.
func fetch_most_played_soundtracks(
		limit: int, on_done: Callable, on_failed: Callable = Callable()) -> void:
	_fetch_soundtrack_statistics("most-played", limit, on_done, on_failed)


## Fetches the [param limit] least played soundtracks as an
## [code]Array[SoundtrackWithSongs][/code].
func fetch_least_played_soundtracks(
		limit: int, on_done: Callable, on_failed: Callable = Callable()) -> void:
	_fetch_soundtrack_statistics("least-played", limit, on_done, on_failed)


## Fetches the [param limit] most recently played soundtracks as an
## [code]Array[SoundtrackWithSongs][/code].
func fetch_last_played_soundtracks(
		limit: int, on_done: Callable, on_failed: Callable = Callable()) -> void:
	_fetch_soundtrack_statistics("last-played", limit, on_done, on_failed)


## Fetches the [param limit] soundtracks that were played longest ago, leaving out those
## never played, as an [code]Array[SoundtrackWithSongs][/code].
func fetch_oldest_played_soundtracks(
		limit: int, on_done: Callable, on_failed: Callable = Callable()) -> void:
	_fetch_soundtrack_statistics("oldest-played", limit, on_done, on_failed)


## Fetches every soundtrack that has never been played as an
## [code]Array[SoundtrackWithSongs][/code].
func fetch_never_played_soundtracks(
		on_done: Callable, on_failed: Callable = Callable()) -> void:
	get_json_list("/statistics/soundtracks/never-played", SoundtrackWithSongs, on_done,
			on_failed)


## Fetches the [param limit] most played songs as an
## [code]Array[SongInfoForStats][/code].
func fetch_most_played_songs(
		limit: int, on_done: Callable, on_failed: Callable = Callable()) -> void:
	get_json_list("/statistics/songs/most-played?limit=%d" % limit, SongInfoForStats,
			on_done, on_failed)


## Fetches the [param limit] least played songs as an
## [code]Array[SongInfoForStats][/code].
func fetch_least_played_songs(
		limit: int, on_done: Callable, on_failed: Callable = Callable()) -> void:
	get_json_list("/statistics/songs/least-played?limit=%d" % limit, SongInfoForStats,
			on_done, on_failed)


# Characters

## Fetches the names of all character images.
func fetch_character_list(on_done: Callable, on_failed: Callable = Callable()) -> void:
	get_json("/character/list", on_done, on_failed)


## Fetches every character image with when it was last changed, as an
## [code]Array[CharacterDetails][/code]. Servers older than this endpoint answer 404.
func fetch_character_details(on_done: Callable, on_failed: Callable = Callable()) -> void:
	get_json_list("/character/details", CharacterDetails, on_done, on_failed)


## Downloads a character image as PNG bytes.
func fetch_character_image(
		character_name: String, on_done: Callable, on_failed: Callable = Callable()) -> void:
	get_bytes("/character?name=" + character_name.uri_encode(), on_done, on_failed)


# Sync

## Starts syncing the server's soundtrack library with its music folder, looking only
## at what changed. The server answers 423 if a sync is already running.
func start_sync(on_done: Callable, on_failed: Callable = Callable()) -> void:
	send("/sync", on_done, on_failed, HTTPClient.METHOD_POST)


## Starts syncing every soundtrack again, changed or not.
func start_full_sync(on_done: Callable, on_failed: Callable = Callable()) -> void:
	send("/sync/full", on_done, on_failed, HTTPClient.METHOD_POST)


## Fetches the sync state: [code]{progress, time_spent}[/code] while running, or the
## sync result once finished.
func fetch_sync_progress(on_done: Callable, on_failed: Callable = Callable()) -> void:
	get_json("/sync/progress", on_done, on_failed)


# Server

## Checks that the server is up, without a token. Calls [param on_done] with its status
## Dictionary.
func fetch_health(on_done: Callable, on_failed: Callable = Callable()) -> void:
	_send_once("/health", HTTPClient.METHOD_GET, "",
			_parse_json.bind("/health", on_done, on_failed), on_failed)


## Fetches the server version and its changes as a [VersionData].
func fetch_version(on_done: Callable, on_failed: Callable = Callable()) -> void:
	get_json_object("/version", VersionData, on_done, on_failed)


## Fetches every server version as an [code]Array[VersionData][/code].
func fetch_version_history(on_done: Callable, on_failed: Callable = Callable()) -> void:
	get_json_list("/version/history", VersionData, on_done, on_failed)


# Game downloads

## Fetches the name of the newest MusicPlayer release.
func fetch_latest_client_version(on_done: Callable, on_failed: Callable = Callable()) -> void:
	get_json("/download", on_done, on_failed)


## Fetches the file names in the newest MusicPlayer release.
func fetch_client_assets(on_done: Callable, on_failed: Callable = Callable()) -> void:
	get_json("/download/list", on_done, on_failed)


## Calls [param on_done] with the link to download the newest MusicPlayer file
## [param asset] from, one of [constant DOWNLOAD_ASSETS]. The server answers with a
## redirect to the release on Gitea, which is not followed: the link needs no token, so
## the browser can open it.
func fetch_client_download_url(
		asset: String, on_done: Callable, on_failed: Callable = Callable()) -> void:
	_request("/download/" + asset, HTTPClient.METHOD_GET, on_done, on_failed, true,
			PackedByteArray(), JSON_TYPE, false)


# Tokens

## Tells the server to forget the token, e.g. when quitting. The next request gets a
## new one.
func delete_token(on_done: Callable = Callable(), on_failed: Callable = Callable()) -> void:
	if _token.is_empty():
		_call_if_valid(on_done)
		return
	var token: String = _token
	clear_token()
	_send_once("/token", HTTPClient.METHOD_DELETE, token, func(_body: PackedByteArray) -> void:
		_call_if_valid(on_done)
	, on_failed)


## Asks the server to remove expired tokens of all clients.
func cleanup_tokens(on_done: Callable, on_failed: Callable = Callable()) -> void:
	send("/token/cleanup", on_done, on_failed, HTTPClient.METHOD_POST)


## Forgets the token without telling the server, so the next request gets a new one.
func clear_token() -> void:
	_token = ""
	_token_server = ""


# Queue IDs

## The ID of the play queue on the selected server, or "" before the server has sent one.
func queue_id() -> String:
	return Settings.queue_ids.get(Settings.default_path, "")


# Keeps the queue ID in [param headers] from [param server] when it is new
func _remember_queue_id(server: String, headers: PackedStringArray) -> void:
	var id: String = header_value(headers, QUEUE_HEADER)
	if !id.is_empty() && Settings.queue_ids.get(server, "") != id:
		Settings.set_queue_id(server, id)


# Generic requests

## Requests [param path] and calls [param on_done] with the parsed JSON.
## [param on_failed] is called with no arguments if the request fails or the body is
## not valid JSON.
func get_json(path: String, on_done: Callable, on_failed: Callable = Callable()) -> void:
	_request(path, HTTPClient.METHOD_GET, _parse_json.bind(path, on_done, on_failed),
			on_failed)


## Requests [param path], which answers with a JSON object, and calls [param on_done]
## with it read into [param type], one of the generated API classes.
func get_json_object(
		path: String, type: GDScript, on_done: Callable, on_failed: Callable = Callable(),
) -> void:
	get_json(path, func(data: Variant) -> void:
		if !(data is Dictionary):
			push_warning("Expected a JSON object from " + path)
			_call_if_valid(on_failed)
			return
		on_done.call(type.from_dict(data))
	, on_failed)


## Requests [param path], which answers with a JSON array of objects, and calls
## [param on_done] with a typed Array of [param type], one of the generated API classes.
## The server sends [code]null[/code] for an empty list, which gives an empty Array.
func get_json_list(
		path: String, type: GDScript, on_done: Callable, on_failed: Callable = Callable(),
) -> void:
	get_json(path, func(data: Variant) -> void:
		if data == null:
			data = []
		if !(data is Array):
			push_warning("Expected a JSON array from " + path)
			_call_if_valid(on_failed)
			return
		var items: Array = Array([], TYPE_OBJECT, "RefCounted", type)
		for item: Variant in data:
			if item is Dictionary:
				items.append(type.from_dict(item))
		on_done.call(items)
	, on_failed)


## Requests [param path] and calls [param on_done] with the raw response body, or
## [param on_failed] with no arguments if the request fails.
func get_bytes(path: String, on_done: Callable, on_failed: Callable = Callable()) -> void:
	_request(path, HTTPClient.METHOD_GET, on_done, on_failed)


## Requests [param path] and calls [param on_done] with no arguments when it succeeds,
## or [param on_failed] when it fails. Either may be an empty Callable.
func send(
		path: String,
		on_done: Callable,
		on_failed: Callable = Callable(),
		method: int = HTTPClient.METHOD_GET,
) -> void:
	_request(path, method, func(_body: PackedByteArray) -> void:
		_call_if_valid(on_done)
	, on_failed)


func _fetch_soundtrack_statistics(
		list_name: String, limit: int, on_done: Callable, on_failed: Callable) -> void:
	get_json_list("/statistics/soundtracks/%s?limit=%d" % [list_name, limit],
			SoundtrackWithSongs, on_done, on_failed)


func _parse_json(
		body: PackedByteArray, path: String, on_done: Callable, on_failed: Callable) -> void:
	var json: JSON = JSON.new()
	if json.parse(body.get_string_from_utf8()) != OK:
		push_warning("Invalid JSON from %s: %s" % [path, json.get_error_message()])
		_call_if_valid(on_failed)
		return
	on_done.call(json.data)


# Sends the request with the token, and once more with a new token if the server
# answers 401. A [param body] of the type [param content_type] is sent with it. Without
# [param follow_redirects], a redirect is a success and [param on_success] gets where it
# points to.
func _request(
		path: String,
		method: int,
		on_success: Callable,
		on_failed: Callable,
		may_retry: bool = true,
		body: PackedByteArray = PackedByteArray(),
		content_type: String = JSON_TYPE,
		follow_redirects: bool = true,
) -> void:
	_with_token(func(token: String) -> void:
		_send(path, method, token, func(response_code: int, response: PackedByteArray,
				headers: PackedStringArray) -> void:
			if response_code == 401 && may_retry:
				GameLog.debug("Token refused by the server, getting a new one")
				if _token == token:
					clear_token()
				_request(path, method, on_success, on_failed, false, body, content_type,
						follow_redirects)
				return
			var location: String = header_value(headers, "Location")
			if !follow_redirects && response_code >= 300 && response_code < 400 \
					&& !location.is_empty():
				on_success.call(location)
				return
			_handle_response(path, response_code, response, on_success, on_failed)
		, body, content_type, follow_redirects)
	, on_failed)


# Sends the request once, with [param token] if it is not empty
func _send_once(
		path: String, method: int, token: String, on_success: Callable, on_failed: Callable,
) -> void:
	_send(path, method, token, func(response_code: int, body: PackedByteArray,
			_headers: PackedStringArray) -> void:
		_handle_response(path, response_code, body, on_success, on_failed)
	)


func _send(
		path: String,
		method: int,
		token: String,
		on_complete: Callable,
		body: PackedByteArray = PackedByteArray(),
		content_type: String = JSON_TYPE,
		follow_redirects: bool = true,
) -> void:
	var server: String = Settings.default_path
	var headers: PackedStringArray = []
	if !token.is_empty():
		headers.append("Authorization: Bearer " + token)
	if !body.is_empty() || method == HTTPClient.METHOD_PUT:
		headers.append("Content-Type: " + content_type)
	var queue: String = Settings.queue_ids.get(server, "")
	if !queue.is_empty():
		headers.append("%s: %s" % [QUEUE_HEADER, queue])
	transport.request(server + API_PATH + path, method,
			func(response_code: int, response_body: PackedByteArray,
					response_headers: PackedStringArray) -> void:
				_remember_queue_id(server, response_headers)
				on_complete.call(response_code, response_body, response_headers)
	, headers, body, follow_redirects)


func _handle_response(
		path: String,
		response_code: int,
		body: PackedByteArray,
		on_success: Callable,
		on_failed: Callable,
) -> void:
	# Requests that change something may answer 204 No Content
	if response_code < 200 || response_code >= 300:
		last_error = _error_message(body).trim_prefix(": ")
		push_warning("Request to %s failed with response code %d%s"
				% [path, response_code, _error_message(body)])
		_call_if_valid(on_failed)
		return
	on_success.call(body)


# Calls [param on_token] with the token, asking the server for one first if needed.
# Requests made while asking wait for the same token instead of asking again.
func _with_token(on_token: Callable, on_failed: Callable) -> void:
	if _token_server != Settings.default_path:
		clear_token()
	if !_token.is_empty():
		on_token.call(_token)
		return
	_token_waiters.append([on_token, on_failed])
	if _token_waiters.size() == 1:
		_request_token()


func _request_token() -> void:
	var token_request: TokenRequest = TokenRequest.new()
	token_request.password = Settings.api_password
	token_request.client_type = CLIENT_TYPE
	var server: String = Settings.default_path
	_send("/token", HTTPClient.METHOD_POST, "",
			func(response_code: int, body: PackedByteArray, _headers: PackedStringArray) -> void:
				var waiters: Array[Array] = _token_waiters.duplicate()
				_token_waiters.clear()
				var token: String = _read_token(response_code, body)
				if token.is_empty():
					for waiter: Array in waiters:
						_call_if_valid(waiter[1])
					return
				_token = token
				_token_server = server
				for waiter: Array in waiters:
					waiter[0].call(token)
	, JSON.stringify(token_request.to_dict()).to_utf8_buffer())


func _read_token(response_code: int, body: PackedByteArray) -> String:
	if response_code != 200:
		push_warning("Could not get an API token, response code %d%s"
				% [response_code, _error_message(body)])
		return ""
	var data: Variant = _parse_or_null(body)
	var token: String = TokenResponse.from_dict(data).token if data is Dictionary else ""
	if token.is_empty():
		push_warning("The server answered without an API token")
	return token


# The server's {"error": "..."} message, for logging
static func _error_message(body: PackedByteArray) -> String:
	var data: Variant = _parse_or_null(body)
	if data is Dictionary && data.has("error"):
		return ": " + ApiError.from_dict(data).error
	return ""


# Error pages are not always JSON, so failing to parse is not worth a warning here
static func _parse_or_null(body: PackedByteArray) -> Variant:
	var json: JSON = JSON.new()
	return json.data if json.parse(body.get_string_from_utf8()) == OK else null


## The value of the header [param header_name] in [param headers], given as
## [code]"Name: value"[/code] lines, or empty when it isn't there. Names are matched
## without regard to case.
static func header_value(headers: PackedStringArray, header_name: String) -> String:
	for header: String in headers:
		var colon: int = header.find(":")
		if colon > 0 && header.left(colon).strip_edges().to_lower() == header_name.to_lower():
			return header.substr(colon + 1).strip_edges()
	return ""


static func _cover_path(uuid: String) -> String:
	return "/soundtracks/%s/cover" % uuid.uri_encode()


static func _call_ignoring_body(_body: PackedByteArray, callback: Callable) -> void:
	_call_if_valid(callback)


static func _call_if_valid(callback: Callable) -> void:
	if callback.is_valid():
		callback.call()