telegabber/xmpp/jingle/sdp.go

package jingle

import (
	"fmt"
	"strings"
)

const sdpLineDivider = "\r\n"

// one SDP "a=" attribute line
type kv struct {
	k, v string
}

// one m= block + its connection line and ordered attrs
type mediaSection struct {
	media      string
	port       string
	protocol   string
	formats    []string
	connection string
	attrs      []kv
}

type sdpDoc struct {
	sessionAttrs []kv
	media        []mediaSection
}

// preserves attribute order (SDP repeats keys; order matters for
// rtpmap/candidate)
func parseSDP(s string) (*sdpDoc, error) {
	doc := &sdpDoc{}
	var cur *mediaSection

	for _, raw := range strings.Split(s, "\n") {
		line := strings.TrimRight(raw, "\r")
		if len(line) < 2 || line[1] != '=' {
			continue
		}
		key := line[0]
		value := line[2:]
		switch key {
		case 'm':
			if cur != nil {
				doc.media = append(doc.media, *cur)
			}
			parts := strings.Split(value, " ")
			if len(parts) < 3 {
				return nil, fmt.Errorf("malformed m= line: %q", value)
			}
			ms := mediaSection{
				media:    parts[0],
				port:     parts[1],
				protocol: parts[2],
			}
			if len(parts) > 3 {
				ms.formats = parts[3:]
			}
			cur = &ms
		case 'c':
			if cur != nil {
				cur.connection = value
			}
		case 'a':
			k, v := splitAttr(value)
			if cur == nil {
				doc.sessionAttrs = append(doc.sessionAttrs, kv{k, v})
			} else {
				cur.attrs = append(cur.attrs, kv{k, v})
			}
		}
	}
	if cur != nil {
		doc.media = append(doc.media, *cur)
	}
	return doc, nil
}

// value is everything after the first colon; later colons are preserved
func splitAttr(body string) (string, string) {
	if i := strings.IndexByte(body, ':'); i >= 0 {
		return body[:i], body[i+1:]
	}
	return body, ""
}

func mmGetAll(mm []kv, key string) []string {
	var out []string
	for _, p := range mm {
		if p.k == key {
			out = append(out, p.v)
		}
	}
	return out
}

func mmFirst(mm []kv, key, def string) string {
	for _, p := range mm {
		if p.k == key {
			return p.v
		}
	}
	return def
}

func mmHas(mm []kv, key string) bool {
	for _, p := range mm {
		if p.k == key {
			return true
		}
	}
	return false
}

type sdpBuilder struct {
	lines []string
}

func (b *sdpBuilder) line(s string) {
	b.lines = append(b.lines, s)
}

// empty value emits "a=key" (no colon)
func (b *sdpBuilder) attr(k, v string) {
	if v == "" {
		b.lines = append(b.lines, "a="+k)
	} else {
		b.lines = append(b.lines, "a="+k+":"+v)
	}
}

func (b *sdpBuilder) appendAttrs(mm []kv) {
	for _, p := range mm {
		b.attr(p.k, p.v)
	}
}

func (b *sdpBuilder) String() string {
	return strings.Join(b.lines, sdpLineDivider) + sdpLineDivider
}