rtmp: add message reader / writer

internal/rtmp/chunk/chunk0.go

@@ -0,0 +1,66 @@
+package chunk
+
+import (
+	"io"
+)
+
+// Chunk0 is a type 0 chunk.
+// This type MUST be used at
+// the start of a chunk stream, and whenever the stream timestamp goes
+// backward (e.g., because of a backward seek).
+type Chunk0 struct {
+	ChunkStreamID   byte
+	Timestamp       uint32
+	Type            MessageType
+	MessageStreamID uint32
+	BodyLen         uint32
+	Body            []byte
+}
+
+// Read reads the chunk.
+func (c *Chunk0) Read(r io.Reader, chunkMaxBodyLen int) error {
+	header := make([]byte, 12)
+	_, err := r.Read(header)
+	if err != nil {
+		return err
+	}
+
+	c.ChunkStreamID = header[0] & 0x3F
+	c.Timestamp = uint32(header[1])<<16 | uint32(header[2])<<8 | uint32(header[3])
+	c.BodyLen = uint32(header[4])<<16 | uint32(header[5])<<8 | uint32(header[6])
+	c.Type = MessageType(header[7])
+	c.MessageStreamID = uint32(header[8])<<24 | uint32(header[9])<<16 | uint32(header[10])<<8 | uint32(header[11])
+
+	chunkBodyLen := int(c.BodyLen)
+	if chunkBodyLen > chunkMaxBodyLen {
+		chunkBodyLen = chunkMaxBodyLen
+	}
+
+	c.Body = make([]byte, chunkBodyLen)
+	_, err = r.Read(c.Body)
+	return err
+}
+
+// Write writes the chunk.
+func (c Chunk0) Write(w io.Writer) error {
+	header := make([]byte, 12)
+	header[0] = c.ChunkStreamID
+	header[1] = byte(c.Timestamp >> 16)
+	header[2] = byte(c.Timestamp >> 8)
+	header[3] = byte(c.Timestamp)
+	header[4] = byte(c.BodyLen >> 16)
+	header[5] = byte(c.BodyLen >> 8)
+	header[6] = byte(c.BodyLen)
+	header[7] = byte(c.Type)
+	header[8] = byte(c.MessageStreamID >> 24)
+	header[9] = byte(c.MessageStreamID >> 16)
+	header[10] = byte(c.MessageStreamID >> 8)
+	header[11] = byte(c.MessageStreamID)
+	_, err := w.Write(header)
+	if err != nil {
+		return err
+	}
+
+	_, err = w.Write(c.Body)
+	return err
+}