rtmp: add message reader / writer

internal/rtmp/chunk/chunk1.go

@@ -0,0 +1,62 @@
+package chunk
+
+import (
+	"io"
+)
+
+// Chunk1 is a type 1 chunk.
+// The message stream ID is not
+// included; this chunk takes the same stream ID as the preceding chunk.
+// Streams with variable-sized messages (for example, many video
+// formats) SHOULD use this format for the first chunk of each new
+// message after the first.
+type Chunk1 struct {
+	ChunkStreamID  byte
+	TimestampDelta uint32
+	Type           MessageType
+	BodyLen        uint32
+	Body           []byte
+}
+
+// Read reads the chunk.
+func (c *Chunk1) Read(r io.Reader, chunkMaxBodyLen int) error {
+	header := make([]byte, 8)
+	_, err := r.Read(header)
+	if err != nil {
+		return err
+	}
+
+	c.ChunkStreamID = header[0] & 0x3F
+	c.TimestampDelta = 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])
+
+	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 Chunk1) Write(w io.Writer) error {
+	header := make([]byte, 8)
+	header[0] = 1<<6 | c.ChunkStreamID
+	header[1] = byte(c.TimestampDelta >> 16)
+	header[2] = byte(c.TimestampDelta >> 8)
+	header[3] = byte(c.TimestampDelta)
+	header[4] = byte(c.BodyLen >> 16)
+	header[5] = byte(c.BodyLen >> 8)
+	header[6] = byte(c.BodyLen)
+	header[7] = byte(c.Type)
+	_, err := w.Write(header)
+	if err != nil {
+		return err
+	}
+
+	_, err = w.Write(c.Body)
+	return err
+}