Initial commit

A half-working prototype.

1 files changed, 253 insertions, 0 deletions

diff --git a/bbc-on-ice.go b/bbc-on-ice.go
new file mode 100644
index 0000000..cf290d7
--- /dev/null
+++ b/bbc-on-ice.go
@@ -0,0 +1,253 @@
+package main
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"log"
+	"net/http"
+	"os"
+	"path"
+	"regexp"
+	"strings"
+	"time"
+	"unicode/utf8"
+)
+
+type meta struct {
+	title   string // What's playing right now
+	timeout uint   // Timeout for the next poll in ms
+}
+
+// Retrieve and decode metadata information from an independent webservice
+func getMeta(name string) (*meta, error) {
+	const metaBaseURI = "http://polling.bbc.co.uk/radio/nhppolling/"
+	resp, err := http.Get(metaBaseURI + name)
+	if err != nil {
+		return nil, err
+	}
+	b, err := ioutil.ReadAll(resp.Body)
+	resp.Body.Close()
+	if len(b) < 2 {
+		// There needs to be an enclosing () pair
+		return nil, errors.New("invalid metadata response")
+	}
+
+	// TODO: also retrieve richtracks/is_now_playing, see example file
+	type broadcast struct {
+		Title      string `json:"title"`      // Title of the broadcast
+		Percentage int    `json:"percentage"` // How far we're in
+	}
+	var v struct {
+		Packages struct {
+			OnAir struct {
+				Broadcasts        []broadcast `json:"broadcasts"`
+				BroadcastNowIndex uint        `json:"broadcastNowIndex"`
+			} `json:"on-air"`
+		} `json:"packages"`
+		Timeouts struct {
+			PollingTimeout uint `json:"polling_timeout"`
+		} `json:"timeouts"`
+	}
+	err = json.Unmarshal(b[1:len(b)-1], &v)
+	if err != nil {
+		return nil, errors.New("invalid metadata response")
+	}
+	onAir := v.Packages.OnAir
+	if onAir.BroadcastNowIndex >= uint(len(onAir.Broadcasts)) {
+		return nil, errors.New("no active broadcast")
+	}
+	return &meta{
+		timeout: v.Timeouts.PollingTimeout,
+		title:   onAir.Broadcasts[onAir.BroadcastNowIndex].Title,
+	}, nil
+}
+
+// Resolve an M3U8 playlist to the first link that seems to be playable
+func resolveM3U8(target string) (out []string, err error) {
+	resp, err := http.Get(target)
+	if err != nil {
+		return nil, err
+	}
+	b, err := ioutil.ReadAll(resp.Body)
+	resp.Body.Close()
+	if !utf8.Valid(b) {
+		return nil, errors.New("invalid UTF-8")
+	}
+	lines := strings.Split(string(b), "\n")
+	for _, line := range lines {
+		if strings.HasPrefix(line, "#") {
+			continue
+		}
+		if !strings.Contains(line, "/") {
+			// Seems to be a relative link, let's make it absolute
+			dir, _ := path.Split(target)
+			line = dir + line
+		}
+		if strings.HasSuffix(line, "m3u8") {
+			// The playlist seems to recurse, and so do we
+			return resolveM3U8(line)
+		}
+		out = append(out, line)
+	}
+	return out, nil
+}
+
+var pathRE = regexp.MustCompile("^/(.*?)/(.*?)/(.*?)$")
+
+func proxy(w http.ResponseWriter, req *http.Request) {
+	const targetURI = "http://a.files.bbci.co.uk/media/live/manifesto/" +
+		"audio/simulcast/hls/%s/%s/ak/%s.m3u8"
+	const metaint = 1 << 16
+	m := pathRE.FindStringSubmatch(req.URL.Path)
+	if m == nil {
+		http.NotFound(w, req)
+		return
+	}
+	hijacker, ok := w.(http.Hijacker)
+	if !ok {
+		// We're not using TLS where HTTP/2 could have caused this
+		panic("cannot hijack connection")
+	}
+
+	// E.g. `nonuk`, `sbr_low` `bbc_radio_one`, or `uk`, `sbr_high`, `bbc_1xtra`
+	region, quality, name := m[1], m[2], m[3]
+	// This validates the params as a side-effect
+	target, err := resolveM3U8(fmt.Sprintf(targetURI, region, quality, name))
+	if err == nil && len(target) == 0 {
+		err = errors.New("cannot resolve playlist")
+	}
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+
+	wantMeta := false
+	if icyMeta, ok := req.Header["Icy-MetaData"]; ok {
+		wantMeta = len(icyMeta) == 1 && icyMeta[0] == "1"
+	}
+	resp, err := http.Get(target[0])
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+
+	conn, bufrw, err := hijacker.Hijack()
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	defer conn.Close()
+
+	// TODO: retrieve some general information from somewhere?
+	//   There's nothing interesting in the playlist files.
+	fmt.Fprintf(bufrw, "ICY 200 OK\r\n")
+	fmt.Fprintf(bufrw, "icy-name:%s\r\n", name)
+	// BBC marks this as a video type, maybe just force audio/mpeg
+	fmt.Fprintf(bufrw, "content-type:%s\r\n", resp.Header["Content-Type"][0])
+	fmt.Fprintf(bufrw, "icy-pub:%d\r\n", 0)
+	if wantMeta {
+		fmt.Fprintf(bufrw, "icy-metaint: %d\r\n", metaint)
+	}
+	fmt.Fprintf(bufrw, "\r\n")
+
+	// TODO: move to a normal function
+	metaChan := make(chan string)
+	go func() {
+		var current, last string
+		var interval time.Duration
+		for {
+			meta, err := getMeta(name)
+			if err != nil {
+				current = "Error: " + err.Error()
+				interval = 30 * time.Second
+			} else {
+				current = meta.title
+				interval = time.Duration(meta.timeout)
+			}
+			if current != last {
+				metaChan <- current
+				last = current
+			}
+
+			select {
+			case <-time.After(time.Duration(interval) * time.Millisecond):
+			case <-req.Context().Done():
+				return
+			}
+		}
+	}()
+
+	// TODO: move to a normal function
+	// FIXME: this will load a few seconds (one URL) and die
+	//   - we can either try to implement this and hope for the best
+	//     https://tools.ietf.org/html/draft-pantos-http-live-streaming-20
+	//     then like https://github.com/kz26/gohls/blob/master/main.go
+	//   - or we can become more of a proxy, which complicates ICY
+	chunkChan := make(chan []byte)
+	go func() {
+		defer resp.Body.Close()
+		defer close(chunkChan)
+		for {
+			chunk := make([]byte, metaint)
+			n, err := io.ReadFull(resp.Body, chunk)
+			chunkChan <- chunk[:n]
+			if err != nil {
+				return
+			}
+
+			select {
+			default:
+			case <-req.Context().Done():
+				return
+			}
+		}
+	}()
+
+	var queuedMeta []byte
+	makeMetaChunk := func() []byte {
+		meta := queuedMeta
+		queuedMeta = nil
+		for len(meta)%16 != 0 {
+			meta = append(meta, 0)
+		}
+		if len(meta) > 16*255 {
+			meta = meta[:16*255]
+		}
+		chunk := []byte{byte(len(meta) / 16)}
+		return append(chunk, meta...)
+	}
+
+	for {
+		select {
+		case title := <-metaChan:
+			queuedMeta = []byte(fmt.Sprintf("StreamTitle='%s'", title))
+		case chunk, connected := <-chunkChan:
+			if !connected {
+				return
+			}
+			if wantMeta {
+				chunk = append(chunk, makeMetaChunk()...)
+			}
+			if _, err := bufrw.Write(chunk); err != nil {
+				return
+			}
+			if err := bufrw.Flush(); err != nil {
+				return
+			}
+		}
+	}
+}
+
+func main() {
+	// TODO: also try to support systemd socket activation
+	address := ":8000"
+	if len(os.Args) == 2 {
+		address = os.Args[1]
+	}
+
+	http.HandleFunc("/", proxy)
+	log.Fatal(http.ListenAndServe(address, nil))
+}