sdp: Parse option media description fields

The parsing logic has become pretty tricky! Tests pass, so refactoring
can be done pretty safely as long as we still get the Session struct
out that we expect.

sdp/sdp.go

@@ -17,12 +17,14 @@ type Session struct {
 	Origin Origin
 	Name   string
 
-	Info      string
-	URI       *url.URL
-	Email     *mail.Address
-	Phone     string
-	Bandwidth *Bandwidth
-	Media     []Media
+	Info       string
+	URI        *url.URL
+	Email      *mail.Address
+	Phone      string
+	Connection *ConnInfo
+	Bandwidth  *Bandwidth
+	Media      []Media
+	Attributes []string
 	// TODO(otl): add rest of fields
 }
 
@@ -34,7 +36,9 @@ type Origin struct {
 	Address     string // IPv4, IPv6 literal or a hostname
 }
 
-var fchars = [...]string{"i", "u", "e", "p", "c", "b", "t", "r", "z", "m"}
+var fchars = [...]string{"i", "u", "e", "p", "c", "b", "t", "r", "z", "m", "a"}
+
+var mchars = [...]string{"i", "c", "b", "a", "m"}
 
 func ReadSession(rd io.Reader) (*Session, error) {
 	session, sc, err := readSession(rd)
@@ -44,7 +48,7 @@ func ReadSession(rd io.Reader) (*Session, error) {
 
 	// Time for optional fields. We keep a slice...
 	// TODO(otl): document in plain language what's going on here.
-	onext := fchars[:]
+	next := fchars[:]
 	for sc.Scan() {
 		if sc.Text() == "" {
 			return nil, fmt.Errorf("illegal empty line")
@@ -55,52 +59,121 @@ func ReadSession(rd io.Reader) (*Session, error) {
 		}
 
 		var allowed bool
-		for i := range onext {
-			if onext[i] == k {
+		for i := range next {
+			if next[i] == k {
 				allowed = true
 			}
 		}
 		if !allowed {
-			return nil, fmt.Errorf("unexpected field %q: expected one of %q", k, onext)
+			return nil, fmt.Errorf("unexpected field %q: expected one of %q", k, next)
 		}
 
 		switch k {
 		case "i":
 			session.Info = v
-			onext = fchars[1:]
+			next = fchars[1:]
 		case "u":
 			u, err := url.Parse(v)
 			if err != nil {
 				return nil, fmt.Errorf("parse uri: %w", err)
 			}
 			session.URI = u
-			onext = fchars[2:]
+			next = fchars[2:]
 		case "e":
 			addr, err := parseEmail(v)
 			if err != nil {
 				return nil, fmt.Errorf("parse email: %w", err)
 			}
 			session.Email = addr
-			onext = fchars[3:]
+			next = fchars[3:]
 		case "p":
 			session.Phone = cleanPhone(v)
-			onext = fchars[4:]
+			next = fchars[4:]
+		case "c":
+			conn, err := parseConnInfo(v)
+			if err != nil {
+				return nil, fmt.Errorf("parse connection info: %w", err)
+			}
+			session.Connection = &conn
+			next = fchars[5:]
 		case "b":
 			bw, err := parseBandwidth(v)
 			if err != nil {
 				return nil, fmt.Errorf("parse bandwidth line %q: %w", v, err)
 			}
 			session.Bandwidth = &bw
-			onext = fchars[5:]
+			next = fchars[6:]
+		case "a":
+			session.Attributes = strings.Fields(v)
+			next = fchars[7:]
 		case "m":
 			m, err := parseMedia(v)
 			if err != nil {
 				return nil, fmt.Errorf("parse media info from %q: %w", v, err)
 			}
 			session.Media = append(session.Media, m)
+			next = mchars[:]
+			goto Media
 		}
 	}
 
+Media:
+	var media *Media
+	if len(session.Media) > 0 {
+		media = &session.Media[len(session.Media)-1]
+	}
+	for sc.Scan() {
+		if sc.Text() == "" {
+			return nil, fmt.Errorf("illegal empty line")
+		}
+		k, v, found := strings.Cut(sc.Text(), "=")
+		if !found {
+			return nil, fmt.Errorf("parse field %q: missing %q", k, "=")
+		}
+
+		var allowed bool
+		for i := range next {
+			if next[i] == k {
+				allowed = true
+			}
+		}
+		if !allowed {
+			return nil, fmt.Errorf("unexpected field %q: expected one of %q", k, next)
+		}
+
+		switch k {
+		case "i":
+			media.Title = v
+			next = mchars[1:]
+		case "c":
+			conn, err := parseConnInfo(v)
+			if err != nil {
+				return nil, fmt.Errorf("parse connection info: %w", err)
+			}
+			media.Connection = &conn
+			next = mchars[2:]
+		case "b":
+			bw, err := parseBandwidth(v)
+			if err != nil {
+				return nil, fmt.Errorf("parse bandwidth: %w", err)
+			}
+			media.Bandwidth = &bw
+			next = mchars[3:]
+		case "a":
+			media.Attributes = strings.Fields(v)
+			next = mchars[4:]
+		case "m":
+			m, err := parseMedia(v)
+			if err != nil {
+				return nil, fmt.Errorf("parse media description: %w", err)
+			}
+			session.Media = append(session.Media, m)
+			media = &session.Media[len(session.Media)-1]
+			next = mchars[:]
+		default:
+			return nil, fmt.Errorf("unsupported field char %s", k)
+		}
+	}
 	return session, sc.Err()
 }
 
@@ -227,6 +300,12 @@ type Media struct {
 	PortCount int
 	Protocol  uint8
 	Format    []string
+	// Optional fields
+	Title      string
+	Connection *ConnInfo
+	Bandwidth  *Bandwidth
+	// TODO(otl): store as k, v pairs
+	Attributes []string
 }
 
 const (

sdp/sdp_test.go

@@ -27,10 +27,31 @@ func TestReadSession(t *testing.T) {
 				},
 				Email: &mail.Address{"Jane Doe", "jane@jdoe.example.com"},
 				Phone: "+16175556011",
+				Connection: &ConnInfo{
+					Type:    "IP4",
+					Address: "198.51.100.1",
+				},
 				Media: []Media{
-					{"audio", 49170, 0, ProtoRTP, []string{"0"}},
-					{"audio", 49180, 0, ProtoRTP, []string{"0"}},
-					{"video", 51372, 0, ProtoRTP, []string{"99"}},
+					Media{
+						Type:     "audio",
+						Port:     49170,
+						Protocol: ProtoRTP,
+						Format:   []string{"0"},
+					},
+					Media{
+						Type:     "audio",
+						Port:     49180,
+						Protocol: ProtoRTP,
+						Format:   []string{"0"},
+					},
+					Media{
+						Type:       "video",
+						Port:       51372,
+						Protocol:   ProtoRTP,
+						Format:     []string{"99"},
+						Connection: &ConnInfo{"IP6", "2001:db8::2", 0, 0},
+						Attributes: []string{"rtpmap:99", "h263-1998/90000"},
+					},
 				},
 			},
 		},
@@ -71,7 +92,6 @@ func TestReadSession(t *testing.T) {
 			if !reflect.DeepEqual(*session, tt.want) {
 				t.Errorf("got %+v\nwant %+v\n", *session, tt.want)
 			}
-			t.Errorf("TODO still not parsing all fields")
 		})
 	}
 }