Always compress DNS responses

dns/client_truncate.go

@@ -14,13 +14,15 @@ func TruncateDNSMessage(request *dns.Msg, response *dns.Msg, frontHeadroom int,
 		}
 	}
 	responseLen := response.Len()
-	if responseLen > maxLen {
-		response = response.Copy()
-		response.Truncate(maxLen)
+	compressedResponse := *response
+	compressedResponse.Compress = true
+	if compressedResponse.Len() > maxLen {
+		compressedResponse = *response.Copy()
+		compressedResponse.Truncate(maxLen)
 	}
 	buffer := buf.NewSize(frontHeadroom + responseLen + 1 + rearHeadroom)
 	buffer.Resize(frontHeadroom, 0)
-	rawMessage, err := response.PackBuffer(buffer.FreeBytes())
+	rawMessage, err := compressedResponse.PackBuffer(buffer.FreeBytes())
 	if err != nil {
 		buffer.Release()
 		return nil, err

protocol/dns/handle.go

@@ -55,7 +55,9 @@ func writeStreamResponse(conn net.Conn, response *mDNS.Msg) {
 	responseBuffer := buf.NewSize(3 + responseLength)
 	defer responseBuffer.Release()
 	responseBuffer.Resize(2, 0)
-	n, err := response.PackBuffer(responseBuffer.FreeBytes())
+	compressedResponse := *response
+	compressedResponse.Compress = true
+	n, err := compressedResponse.PackBuffer(responseBuffer.FreeBytes())
 	if err != nil {
 		return
 	}

protocol/tailscale/endpoint.go

@@ -1085,5 +1085,7 @@ func (t *peerDNSQueryHandler) HandlePeerDNSQuery(ctx context.Context, query []by
 		}
 		return nil, err
 	}
-	return response.Pack()
+	compressedResponse := *response
+	compressedResponse.Compress = true
+	return compressedResponse.Pack()
 }