move protocol-related code into internal/protocols (#2572)

internal/protocols/rtmp/chunk/chunk3.go

@@ -0,0 +1,39 @@
+package chunk
+
+import (
+	"io"
+)
+
+// Chunk3 is a type 3 chunk.
+// Type 3 chunks have no message header. The stream ID, message length
+// and timestamp delta fields are not present; chunks of this type take
+// values from the preceding chunk for the same Chunk Stream ID. When a
+// single message is split into chunks, all chunks of a message except
+// the first one SHOULD use this type.
+type Chunk3 struct {
+	ChunkStreamID byte
+	Body          []byte
+}
+
+// Read reads the chunk.
+func (c *Chunk3) Read(r io.Reader, chunkBodyLen uint32) error {
+	header := make([]byte, 1)
+	_, err := io.ReadFull(r, header)
+	if err != nil {
+		return err
+	}
+
+	c.ChunkStreamID = header[0] & 0x3F
+
+	c.Body = make([]byte, chunkBodyLen)
+	_, err = io.ReadFull(r, c.Body)
+	return err
+}
+
+// Marshal writes the chunk.
+func (c Chunk3) Marshal() ([]byte, error) {
+	buf := make([]byte, 1+len(c.Body))
+	buf[0] = 3<<6 | c.ChunkStreamID
+	copy(buf[1:], c.Body)
+	return buf, nil
+}