5 files changed, 214 insertions(+), 0 deletions(-)

A LICENSE
A README.md
A go.mod
A go.sum
A main.go

@@ 1,19 @@
+Copyright (c) 2020 Joram Schrijver
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

@@ 1,104 @@
+# Transcoding music server
+
+This is a simple, quick-and-dirty HTTP server that transcodes music files
+before serving them. You can give it a directory containing music, and when a
+music file is requested it is first converted to Opus, using FFmpeg. Other
+files are served directly.
+
+This is useful when playing remotely hosted music on a phone with a data plan,
+because the transcoded Opus files are significantly smaller than the originals.
+The file is converted before responding to the request, so there will be a
+small delay while FFmpeg is doing its job. Converted files are saved, so the
+next request will be near-instant.
+
+Note that this means a HTTP request for a file called `example.flac` will
+return an Opus file, with `Content-Type: audio/ogg`. The transcoded file will
+be saved as `example.flac.opus`.
+
+File extensions that will be transcoded are `.flac`, `.mp3` and `.m4a` (not
+case sensitive).
+
+## Usage
+
+First build the program:
+
+```sh
+go build
+```
+
+Now consider a directory `music` that looks like this:
+
+```
+music
++ artist
+  + example.flac
+  + example.mp3
+  + example.m4a
+  + cover.jpg
+```
+
+Run the server:
+
+```sh
+transcoding-music-server --origin music --target transcoded-music --bind :8844
+```
+
+Note that it calls out to `ffmpeg` to do the transcoding.
+
+Request some files:
+
+```sh
+curl -I -X GET http://localhost:8844/artist/example.flac
+# HTTP/1.1 200 OK
+# Content-Type: audio/ogg
+# ...
+curl -I -X GET http://localhost:8844/artist/example.mp3
+# HTTP/1.1 200 OK
+# Content-Type: audio/ogg
+# ...
+curl -I -X GET http://localhost:8844/artist/example.m4a
+# HTTP/1.1 200 OK
+# Content-Type: audio/ogg
+# ...
+curl -I -X GET http://localhost:8844/artist/cover.jpg
+# HTTP/1.1 200 OK
+# Content-Type: image/jpeg
+# ...
+```
+
+The directory `transcoded-music` will now look like this:
+
+```
+transcoded-music
++ artist
+  + example.flac.opus
+  + example.mp3.opus
+  + example.m4a.opus
+```
+
+The music files have been converted, but the cover image was served directly
+from the origin directory.
+
+## License
+
+```
+Copyright (c) 2020 Joram Schrijver
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+```

@@ 1,5 @@
+module transcoding-music-server
+
+go 1.13
+
+require github.com/gorilla/handlers v1.4.2

@@ 1,2 @@
+github.com/gorilla/handlers v1.4.2 h1:0QniY0USkHQ1RGCLfKxeNHK9bkDHGRYGNDFBCS+YARg=
+github.com/gorilla/handlers v1.4.2/go.mod h1:Qkdc/uu4tH4g6mTK6auzZ766c4CA0Ng8+o/OAirnOIQ=

@@ 1,84 @@
+package main
+
+import (
+	"errors"
+	"flag"
+	"github.com/gorilla/handlers"
+	"log"
+	"net/http"
+	"os"
+	"os/exec"
+	"path"
+	"path/filepath"
+	"strings"
+)
+
+type TranscodedDirectory struct {
+	Origin string
+	Target string
+}
+
+func (d TranscodedDirectory) Open(name string) (http.File, error) {
+	if filepath.Separator != '/' && strings.ContainsRune(name, filepath.Separator) {
+		return nil, errors.New("invalid character in file path")
+	}
+
+	originName := filepath.Join(d.Origin, filepath.FromSlash(path.Clean("/"+name)))
+	lowerOriginName := strings.ToLower(originName)
+
+	if strings.HasSuffix(lowerOriginName, ".flac") || strings.HasSuffix(lowerOriginName, ".mp3") || strings.HasSuffix(lowerOriginName, ".m4a") {
+		targetName := filepath.Join(d.Target, filepath.FromSlash(path.Clean("/"+name))) + ".opus"
+		targetFile, targetErr := os.Open(targetName)
+		if targetErr == nil {
+			return targetFile, nil
+		}
+
+		if _, originErr := os.Stat(originName); originErr != nil {
+			return nil, originErr
+		}
+
+		baseName := filepath.Dir(targetName)
+		if dirErr := os.MkdirAll(baseName, 0755); dirErr != nil {
+			return nil, dirErr
+		}
+
+		ffmpeg := exec.Command("ffmpeg", "-i", originName, "-b:a", "80K", targetName)
+		ffmpegErr := ffmpeg.Run()
+		if ffmpegErr != nil {
+			return nil, ffmpegErr
+		}
+
+		targetFile, targetErr = os.Open(targetName)
+		if targetErr != nil {
+			return nil, targetErr
+		}
+		return targetFile, nil
+	}
+
+	originFile, originErr := os.Open(originName)
+	return originFile, originErr
+}
+
+func main() {
+	var bind string
+	var origin string
+	var target string
+
+	flag.StringVar(&bind, "bind", ":8844", "port to serve files on")
+	flag.StringVar(&origin, "origin", "origin", "origin directory")
+	flag.StringVar(&target, "target", "target", "target directory to store transcoded files in")
+	flag.Parse()
+
+	fileServer := http.FileServer(TranscodedDirectory{
+		Origin: origin,
+		Target: target,
+	})
+
+	server := http.Server{
+		Addr:    bind,
+		Handler: handlers.LoggingHandler(os.Stdout, fileServer),
+	}
+
+	log.Printf("Starting transcoding server on %s", bind)
+	log.Fatal(server.ListenAndServe())
+}