add more methods to the protocol.ConnectionID

This will make it easier to change the underlying type of the connection
ID (potentially an array is faster than a byte slice).

internal/protocol/connection_id.go

@@ -3,6 +3,8 @@ package protocol
 import (
 	"bytes"
 	"crypto/rand"
+	"fmt"
+	"io"
 )
 
 // A ConnectionID in QUIC
@@ -17,7 +19,38 @@ func GenerateConnectionID() (ConnectionID, error) {
 	return ConnectionID(b), nil
 }
 
+// ReadConnectionID reads a connection ID of length len from the given io.Reader.
+// It returns io.EOF if there are not enough bytes to read.
+func ReadConnectionID(r io.Reader, len int) (ConnectionID, error) {
+	if len == 0 {
+		return nil, nil
+	}
+	c := make(ConnectionID, len)
+	_, err := io.ReadFull(r, c)
+	if err == io.ErrUnexpectedEOF {
+		return nil, io.EOF
+	}
+	return c, err
+}
+
 // Equal says if two connection IDs are equal
 func (c ConnectionID) Equal(other ConnectionID) bool {
 	return bytes.Equal(c, other)
 }
+
+// Len returns the length of the connection ID in bytes
+func (c ConnectionID) Len() int {
+	return len(c)
+}
+
+// Bytes returns the byte representation
+func (c ConnectionID) Bytes() []byte {
+	return []byte(c)
+}
+
+func (c ConnectionID) String() string {
+	if c.Len() == 0 {
+		return "(empty)"
+	}
+	return fmt.Sprintf("%#x", c.Bytes())
+}