appquic: silence quic-go warnings (#202)

* appquic: silence quic-go warnings

quic-go wants to set the read buffer size for the Conn, but snet and the
dispatcher setup does not support this.
Faking the operations to set the read buffer size does not work, as
quic-go also checks directly with a system call whether the operation
was successful.
As a hacky workaround, we simply silence the logger during the quic.Dial
and quic.Listen calls.

* ci: bump image version to get go-1.16

And btw remove workaround for go-1.15 in circleci config.

Author: matzf

.circleci/config.yml

@@ -32,7 +32,7 @@ jobs:
 
   integration:
     machine:
-      image: ubuntu-2004:202101-01
+      image: ubuntu-2004:202107-02
 
     steps:
       - checkout
@@ -92,9 +92,6 @@ jobs:
       - run:
           name: Integration tests
           command: |
-            # XXX: hack, don't build skip here, needs go-1.16, currently this runs on go-1.15.
-            # As there are currently no integration tests for scion-skip, we don't need it here.
-            sed -i '/^\s*scion-skip\s*\\$/d' Makefile
             make integration
       - store_artifacts:
           path: /tmp/scion-apps-integration/

pkg/appnet/appquic/appquic.go

@@ -20,8 +20,11 @@ package appquic
 import (
 	"crypto/tls"
 	"fmt"
+	"io"
+	"log"
 	"net"
 	"sync"
+	"sync/atomic"
 
 	"github.com/lucas-clemente/quic-go"
 
@@ -86,6 +89,10 @@ func DialAddr(raddr *snet.UDPAddr, host string, tlsConf *tls.Config, quicConf *q
 		return nil, err
 	}
 	host = appnet.MangleSCIONAddr(host)
+	// HACK: we silence the log here to shut up quic-go's warning about trying to
+	// set receive buffer size (it's not a UDPConn, we know).
+	silenceLog()
+	defer unsilenceLog()
 	session, err := quic.Dial(sconn, raddr, host, tlsConf, quicConf)
 	if err != nil {
 		return nil, err
@@ -113,6 +120,10 @@ func DialAddrEarly(raddr *snet.UDPAddr, host string, tlsConf *tls.Config, quicCo
 		return nil, err
 	}
 	host = appnet.MangleSCIONAddr(host)
+	// HACK: we silence the log here to shut up quic-go's warning about trying to
+	// set receive buffer size (it's not a UDPConn, we know).
+	silenceLog()
+	defer unsilenceLog()
 	session, err := quic.DialEarly(sconn, raddr, host, tlsConf, quicConf)
 	if err != nil {
 		return nil, err
@@ -132,18 +143,18 @@ func ensurePathDefined(raddr *snet.UDPAddr) error {
 //
 // See note on wildcard addresses in the appnet package documentation.
 func ListenPort(port uint16, tlsConf *tls.Config, quicConfig *quic.Config) (quic.Listener, error) {
-	sconn, err := appnet.ListenPort(port)
-	if err != nil {
-		return nil, err
-	}
-	return quic.Listen(sconn, tlsConf, quicConfig)
+	return Listen(&net.UDPAddr{Port: int(port)}, tlsConf, quicConfig)
 }
 
 func Listen(listen *net.UDPAddr, tlsConf *tls.Config, quicConfig *quic.Config) (quic.Listener, error) {
 	sconn, err := appnet.Listen(listen)
 	if err != nil {
 		return nil, err
 	}
+	// HACK: we silence the log here to shut up quic-go's warning about trying to
+	// set receive buffer size (it's not a UDPConn, we know).
+	silenceLog()
+	defer unsilenceLog()
 	return quic.Listen(sconn, tlsConf, quicConfig)
 }
 
@@ -163,3 +174,33 @@ func GetDummyTLSCerts() []tls.Certificate {
 	}
 	return srvTLSDummyCerts
 }
+
+var logSilencerCount int32
+var logSilencerOriginal io.Writer
+
+// silenceLog redirects the log.Default writer to a black hole.
+// It can be reenabled by calling unsilenceLog.
+// These functions can safely be called from multiple goroutines concurrently;
+// the log will remain silenced until unsilenceLog was called for each
+// silenceLog call.
+func silenceLog() {
+	count := atomic.AddInt32(&logSilencerCount, 1)
+	if count == 1 {
+		logSilencerOriginal = log.Default().Writer()
+		log.Default().SetOutput(blackhole{})
+	}
+}
+
+func unsilenceLog() {
+	count := atomic.AddInt32(&logSilencerCount, -1)
+	if count == 0 {
+		log.Default().SetOutput(logSilencerOriginal)
+		logSilencerOriginal = nil
+	}
+}
+
+type blackhole struct{}
+
+func (w blackhole) Write(p []byte) (n int, err error) {
+	return len(p), nil
+}