attestedtls/attestation: send report asynchronously

Signed-off-by: Simon Ott <[email protected]>

attestedtls/attestation.go

@@ -65,6 +65,8 @@ func atlsHandshakeStart(conn *tls.Conn, chbindings []byte, cc CmcConfig, endpoin
 	}
 
 	// Wait for attestation request to be received
+	log.Debugf("Prover %v: waiting for atls handshake request mode %v from %v",
+		ownAddr, cc.Attest.String(), peerAddr)
 	req, err := receiveAtlsRequest(conn)
 	if err != nil {
 		return fmt.Errorf("prover %v: failed to receive attestation request from %v: %w",
@@ -98,16 +100,15 @@ func atlsHandshakeStart(conn *tls.Conn, chbindings []byte, cc CmcConfig, endpoin
 		Error:  reportErr,
 	}
 
-	// Send created atls handshake response to listener
+	// Send created atls handshake response to listener asynchronously to avoid TCP deadlock
 	log.Debugf("Prover %v: sending atls handshake response with report length %v to %v",
 		ownAddr, len(ownReport), peerAddr)
-
-	err = sendAtlsResponse(conn, report)
-	if err != nil {
-		return fmt.Errorf("prover %v: failed to send AR to %v: %w", ownAddr, peerAddr, err)
-	}
-	log.Debugf("Prover %v: finished sending atls handshake response to %v",
-		ownAddr, peerAddr)
+	errChan := make(chan error)
+	go func() {
+		err := sendAtlsResponse(conn, report)
+		errChan <- err
+		close(errChan)
+	}()
 
 	log.Debugf("Verifier %v: waiting for atls handshake response from %v", ownAddr, peerAddr)
 	resp, err := receiveAtlsResponse(conn)
@@ -122,6 +123,15 @@ func atlsHandshakeStart(conn *tls.Conn, chbindings []byte, cc CmcConfig, endpoin
 	log.Debugf("Verifier %v: received atls handshake response mode %v from %v",
 		ownAddr, resp.Attest.String(), peerAddr)
 
+	// Wait until sending of own handshake response is finished
+	log.Debugf("Prover %v: Waiting for atls handshake response sending to be completed", ownAddr)
+	err = <-errChan
+	if err != nil {
+		return fmt.Errorf("prover %v: failed to send atls handshake response: %w", ownAddr, err)
+	}
+	log.Debugf("Prover %v: finished sending atls handshake response to %v",
+		ownAddr, peerAddr)
+
 	// Check that configured attestation mode matches peers attestation mode
 	err = checkAttestationMode(cc.Attest, req.Attest)
 	if err != nil {
@@ -152,12 +162,17 @@ func aTlsHandshakeComplete(conn *tls.Conn, handshakeError error) error {
 	if handshakeError != nil {
 		complete.Error = handshakeError.Error()
 	}
+
+	log.Debugf("Prover %v: sending atls handshake complete to %v",
+		conn.LocalAddr().String(), conn.RemoteAddr().String())
 	err := sendAtlsComplete(conn, complete)
 	if err != nil {
 		return fmt.Errorf("%v: failed to send handshake complete to %v: %w",
 			conn.LocalAddr().String(), conn.RemoteAddr().String(), err)
 	}
 
+	log.Debugf("Verifier %v: waiting for atls handshake complete from %v",
+		conn.LocalAddr().String(), conn.RemoteAddr().String())
 	resp, err := receiveAtlsComplete(conn)
 	if err != nil {
 		return fmt.Errorf("%v: failed to receive handshake complete from %v: %w",