grpc: do not use balancer attributes during address comparison

attributes/attributes.go

@@ -112,19 +112,31 @@ func (a *Attributes) String() string {
 	sb.WriteString("{")
 	first := true
 	for k, v := range a.m {
-		var key, val string
-		if str, ok := k.(interface{ String() string }); ok {
-			key = str.String()
-		}
-		if str, ok := v.(interface{ String() string }); ok {
-			val = str.String()
-		}
 		if !first {
 			sb.WriteString(", ")
 		}
-		sb.WriteString(fmt.Sprintf("%q: %q, ", key, val))
+		sb.WriteString(fmt.Sprintf("%q: %q ", str(k), str(v)))
 		first = false
 	}
 	sb.WriteString("}")
 	return sb.String()
 }
+
+func str(x interface{}) string {
+	if v, ok := x.(fmt.Stringer); ok {
+		return v.String()
+	} else if v, ok := x.(string); ok {
+		return v
+	}
+	return fmt.Sprintf("<%p>", x)
+}
+
+// MarshalJSON helps implement the json.Marshaler interface, thereby rendering
+// the Attributes correctly when printing (via pretty.JSON) structs containing
+// Attributes as fields.
+//
+// Is it impossible to unmarshal attributes from a JSON representation and this
+// method is meant only for debugging purposes.
+func (a *Attributes) MarshalJSON() ([]byte, error) {
+	return []byte(a.String()), nil
+}

clientconn.go

@@ -37,6 +37,7 @@ import (
 	"google.golang.org/grpc/internal/backoff"
 	"google.golang.org/grpc/internal/channelz"
 	"google.golang.org/grpc/internal/grpcsync"
+	"google.golang.org/grpc/internal/pretty"
 	iresolver "google.golang.org/grpc/internal/resolver"
 	"google.golang.org/grpc/internal/transport"
 	"google.golang.org/grpc/keepalive"
@@ -867,14 +868,28 @@ func (cc *ClientConn) handleSubConnStateChange(sc balancer.SubConn, s connectivi
 	cc.balancerWrapper.updateSubConnState(sc, s, err)
 }
 
+// Makes a copy of the input addresses slice and clears out the balancer
+// attributes field. Addresses are passed during subconn creation and address
+// update operations. In both cases, we will clear the balancer attributes by
+// calling this function, and therefore we will be able to use the Equal method
+// provided by the resolver.Address type for comparison.
+func copyAddressesWithoutBalancerAttributes(in []resolver.Address) []resolver.Address {
+	out := make([]resolver.Address, len(in))
+	for i := range in {
+		out[i] = in[i]
+		out[i].BalancerAttributes = nil
+	}
+	return out
+}
+
 // newAddrConn creates an addrConn for addrs and adds it to cc.conns.
 //
 // Caller needs to make sure len(addrs) > 0.
 func (cc *ClientConn) newAddrConn(addrs []resolver.Address, opts balancer.NewSubConnOptions) (*addrConn, error) {
 	ac := &addrConn{
 		state:        connectivity.Idle,
 		cc:           cc,
-		addrs:        addrs,
+		addrs:        copyAddressesWithoutBalancerAttributes(addrs),
 		scopts:       opts,
 		dopts:        cc.dopts,
 		czData:       new(channelzData),
@@ -995,8 +1010,9 @@ func equalAddresses(a, b []resolver.Address) bool {
 // connections or connection attempts.
 func (ac *addrConn) updateAddrs(addrs []resolver.Address) {
 	ac.mu.Lock()
-	channelz.Infof(logger, ac.channelzID, "addrConn: updateAddrs curAddr: %v, addrs: %v", ac.curAddr, addrs)
+	channelz.Infof(logger, ac.channelzID, "addrConn: updateAddrs curAddr: %v, addrs: %v", pretty.ToJSON(ac.curAddr), pretty.ToJSON(addrs))
 
+	addrs = copyAddressesWithoutBalancerAttributes(addrs)
 	if equalAddresses(ac.addrs, addrs) {
 		ac.mu.Unlock()
 		return

internal/stubserver/stubserver.go

@@ -60,6 +60,10 @@ type StubServer struct {
 	Address string
 	Target  string
 
+	// Custom listener to use for serving. If unspecified, a new listener is
+	// created on a local port.
+	Listener net.Listener
+
 	cleanups []func() // Lambdas executed in Stop(); populated by Start().
 
 	// Set automatically if Target == ""
@@ -118,9 +122,13 @@ func (ss *StubServer) StartServer(sopts ...grpc.ServerOption) error {
 		ss.R = manual.NewBuilderWithScheme("whatever")
 	}
 
-	lis, err := net.Listen(ss.Network, ss.Address)
-	if err != nil {
-		return fmt.Errorf("net.Listen(%q, %q) = %v", ss.Network, ss.Address, err)
+	lis := ss.Listener
+	if lis == nil {
+		var err error
+		lis, err = net.Listen(ss.Network, ss.Address)
+		if err != nil {
+			return fmt.Errorf("net.Listen(%q, %q) = %v", ss.Network, ss.Address, err)
+		}
 	}
 	ss.Address = lis.Addr().String()
 	ss.cleanups = append(ss.cleanups, func() { lis.Close() })

resolver/resolver.go

@@ -142,6 +142,10 @@ type Address struct {
 
 // Equal returns whether a and o are identical.  Metadata is compared directly,
 // not with any recursive introspection.
+//
+// This method compares all fields of the address. When used to tell apart
+// addresses during subchannel creation or connection establishment, it might be
+// more appropriate for the caller to implement custom equality logic.
 func (a Address) Equal(o Address) bool {
 	return a.Addr == o.Addr && a.ServerName == o.ServerName &&
 		a.Attributes.Equal(o.Attributes) &&