Refactor authentication message handling

authentication_md5_password.go

@@ -0,0 +1,43 @@
+package pgproto3
+
+import (
+	"encoding/binary"
+	"errors"
+
+	"github.com/jackc/pgio"
+)
+
+// AuthenticationMD5Password is a message sent from the backend indicating that an MD5 hashed password is required.
+type AuthenticationMD5Password struct {
+	Salt [4]byte
+}
+
+// Backend identifies this message as sendable by the PostgreSQL backend.
+func (*AuthenticationMD5Password) Backend() {}
+
+// Decode decodes src into dst. src must contain the complete message with the exception of the initial 1 byte message
+// type identifier and 4 byte message length.
+func (dst *AuthenticationMD5Password) Decode(src []byte) error {
+	if len(src) != 8 {
+		return errors.New("bad authentication message size")
+	}
+
+	authType := binary.BigEndian.Uint32(src)
+
+	if authType != AuthTypeMD5Password {
+		return errors.New("bad auth type")
+	}
+
+	copy(dst.Salt[:], src[4:8])
+
+	return nil
+}
+
+// Encode encodes src into dst. dst will include the 1 byte message type identifier and the 4 byte message length.
+func (src *AuthenticationMD5Password) Encode(dst []byte) []byte {
+	dst = append(dst, 'R')
+	dst = pgio.AppendInt32(dst, 12)
+	dst = pgio.AppendUint32(dst, AuthTypeOk)
+	dst = append(dst, src.Salt[:]...)
+	return dst
+}