internal/resolver: introduce a new delegating resolver to handle both target URI and proxy address resolution

internal/envconfig/envconfig.go

@@ -55,6 +55,8 @@ var (
 	// setting the environment variable "GRPC_EXPERIMENTAL_ENABLE_NEW_PICK_FIRST"
 	// to "true".
 	NewPickFirstEnabled = boolFromEnv("GRPC_EXPERIMENTAL_ENABLE_NEW_PICK_FIRST", false)
+	//HTTPProxy is set to empty string if HTTPS_PROXY env it is not set.
+	HTTPProxy = stringFromEnv("HTTPS_PROXY", "")
 )
 
 func boolFromEnv(envVar string, def bool) bool {
@@ -79,3 +81,11 @@ func uint64FromEnv(envVar string, def, min, max uint64) uint64 {
 	}
 	return v
 }
+
+func stringFromEnv(envVar string, def string) string {
+	val := os.Getenv(envVar)
+	if val == "" {
+		return def
+	}
+	return val
+}

internal/resolver/delegatingresolver/delegatingresolver.go

@@ -0,0 +1,241 @@
+/*
+ *
+ * Copyright 2024 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package delegatingresolver implements the default resolver for gRPC.
+// It handles both target URI and proxy address resolution, unless:
+//   - A custom dialer is set using WithContextDialer dialoption.
+//   - Proxy usage is explicitly disabled using WithNoProxy dialoption.
+//   - Client-side resolution is explicitly enforced using WithTargetResolutionEnabled.
+package delegatingresolver
+
+import (
+	"fmt"
+	"net/http"
+	"net/url"
+	"sync"
+
+	"google.golang.org/grpc/grpclog"
+	"google.golang.org/grpc/resolver"
+	"google.golang.org/grpc/serviceconfig"
+)
+
+var (
+	// The following variable will be overwritten in the tests.
+	httpProxyFromEnvironment = http.ProxyFromEnvironment
+
+	logger = grpclog.Component("delegatingresolver")
+)
+
+// delegatingResolver manages the resolution of both a target URI and an
+// optional proxy URI. It acts as an intermediary between the underlying
+// resolvers and the gRPC ClientConn. This type implements the
+// resolver.ClientConn interface to intercept state updates from both the target
+// and proxy resolvers, combining the results before forwarding them to the
+// client connection.
+type delegatingResolver struct {
+	target         resolver.Target     // parsed target URI to be resolved
+	cc             resolver.ClientConn // gRPC ClientConn
+	targetResolver resolver.Resolver   // resolver for the target URI, based on its scheme
+	proxyResolver  resolver.Resolver   // resolver for the proxy URI; nil if no proxy is configured
+	targetAddrs    []resolver.Address  // resolved or unresolved target addresses, depending on proxy configuration
+	proxyAddrs     []resolver.Address  // resolved proxy addresses; empty if no proxy is configured
+	proxyURL       *url.URL            // proxy URL, derived from proxy environment and target
+	mu             sync.Mutex          // protects access to the resolver state during updates
+}
+
+func mapAddress(address string) (*url.URL, error) {
+	req := &http.Request{
+		URL: &url.URL{
+			Scheme: "https",
+			Host:   address,
+		},
+	}
+	url, err := httpProxyFromEnvironment(req)
+	if err != nil {
+		return nil, err
+	}
+	return url, nil
+}
+
+// New creates a new delegating resolver that will call the target and proxy
+// child resolvers based on the proxy enviorinment configurations.
+func New(target resolver.Target, cc resolver.ClientConn, opts resolver.BuildOptions, targetResolverBuilder resolver.Builder, targetResolutionEnabled bool) (resolver.Resolver, error) {
+	r := &delegatingResolver{
+		target: target,
+		cc:     cc,
+	}
+
+	var err error
+	r.proxyURL, err = mapAddress(target.Endpoint())
+	if err != nil {
+		return nil, fmt.Errorf("failed to determine proxy URL for target : %v", err)
+	}
+
+	if r.proxyURL == nil {
+		logger.Info("No proxy URL detected")
+		return targetResolverBuilder.Build(target, cc, opts)
+	}
+
+	// When the scheme is 'dns', resolution should be handled by the proxy, not
+	// the client. Therefore, we bypass the target resolver and store the
+	// unresolved target address.
+	if target.URL.Scheme == "dns" && !targetResolutionEnabled {
+		r.targetAddrs = []resolver.Address{{Addr: target.Endpoint()}}
+	} else {
+		// targetResolverBuilder must not be nil. If it is nil, the channel should
+		// error out and not call this function.
+		r.targetResolver, err = targetResolverBuilder.Build(target, &wrappingClientConn{r, "target"}, opts)
+		if err != nil {
+			return nil, fmt.Errorf("delegating_resolver: unable to build the target resolver : %v", err)
+		}
+	}
+	r.proxyResolver, err = proxyURIResolver(r.proxyURL, opts, r)
+	if err != nil {
+		return nil, err
+	}
+	return r, nil
+}
+
+func proxyURIResolver(proxyURL *url.URL, opts resolver.BuildOptions, presolver *delegatingResolver) (resolver.Resolver, error) {
+	scheme := "dns"
+	proxyBuilder := resolver.Get(scheme)
+	if proxyBuilder == nil {
+		return nil, fmt.Errorf("delegating_resolver: resolver for proxy not found")
+	}
+	host := "dns:///" + proxyURL.Host
+	u, err := url.Parse(host)
+	if err != nil {
+		return nil, err
+	}
+
+	proxyTarget := resolver.Target{URL: *u}
+	return proxyBuilder.Build(proxyTarget, &wrappingClientConn{presolver, "proxy"}, opts)
+}
+
+func (r *delegatingResolver) ResolveNow(o resolver.ResolveNowOptions) {
+	if r.targetResolver != nil {
+		r.targetResolver.ResolveNow(o)
+	}
+	if r.proxyResolver != nil {
+		r.proxyResolver.ResolveNow(o)
+	}
+}
+
+func (r *delegatingResolver) Close() {
+	if r.targetResolver != nil {
+		r.targetResolver.Close()
+	}
+	if r.proxyResolver != nil {
+		r.proxyResolver.Close()
+	}
+}
+
+type keyType string
+
+const proxyConnectAddrKey = keyType("grpc.resolver.delegatingresolver.proxyConnectAddr")
+const userKey = keyType("grpc.resolver.delegatingresolver.user")
+
+// SetConnectAddr returns a copy of the provided resolver.Address with attributes
+// containing address to be sent in connect request to proxy.  It's data should
+// not be mutated after calling SetConnectAddr.
+func SetConnectAddr(resAddr resolver.Address, addr string) resolver.Address {
+	resAddr.Attributes = resAddr.Attributes.WithValue(proxyConnectAddrKey, addr)
+	return resAddr
+}
+
+// GetConnectAddr returns the proxy connect address in resolver.Address, or nil
+// if not present. The returned data should not be mutated.
+func GetConnectAddr(addr resolver.Address) string {
+	s, _ := addr.Attributes.Value(proxyConnectAddrKey).(string)
+	return s
+}
+
+// SetUser returns a copy of the provided address with attributes containing
+// user info. It's data should not be mutated after calling SetUser.
+func SetUser(addr resolver.Address, user *url.Userinfo) resolver.Address {
+	addr.Attributes = addr.Attributes.WithValue(userKey, user)
+	return addr
+}
+
+// GetUser returns the user info in the resolver.Address, or nil if not present.
+// The returned data should not be mutated.
+func GetUser(addr resolver.Address) *url.Userinfo {
+	user, _ := addr.Attributes.Value(userKey).(*url.Userinfo)
+	return user
+}
+
+func (r *delegatingResolver) updateState(state resolver.State) resolver.State {
+	var addresses []resolver.Address
+	for _, proxyAddr := range r.proxyAddrs {
+		for _, targetAddr := range r.targetAddrs {
+			newAddr := resolver.Address{
+				Addr: proxyAddr.Addr,
+			}
+			newAddr = SetConnectAddr(newAddr, targetAddr.Addr)
+			if r.proxyURL.User != nil {
+				newAddr = SetUser(newAddr, r.proxyURL.User)
+			}
+			addresses = append(addresses, newAddr)
+		}
+	}
+	// Set the addresses in the current state.
+	state.Addresses = addresses
+	return state
+}
+
+type wrappingClientConn struct {
+	parent       *delegatingResolver
+	resolverType string
+}
+
+// UpdateState intercepts state updates from the target and proxy resolvers.
+func (wcc *wrappingClientConn) UpdateState(state resolver.State) error {
+	wcc.parent.mu.Lock()
+	defer wcc.parent.mu.Unlock()
+	var curState resolver.State
+	if wcc.resolverType == "target" {
+		wcc.parent.targetAddrs = state.Addresses
+		curState = state
+	}
+	if wcc.resolverType == "proxy" {
+		wcc.parent.proxyAddrs = state.Addresses
+	}
+
+	if len(wcc.parent.targetAddrs) == 0 || len(wcc.parent.proxyAddrs) == 0 {
+		return nil
+	}
+	curState = wcc.parent.updateState(curState)
+	return wcc.parent.cc.UpdateState(curState)
+}
+
+// ReportError intercepts errors from the child resolvers and pass to ClientConn.
+func (wcc *wrappingClientConn) ReportError(err error) {
+	wcc.parent.cc.ReportError(err)
+}
+
+// NewAddress intercepts the new resolved address from the chid resolvers and
+// pass to CLientConn
+func (wcc *wrappingClientConn) NewAddress(addrs []resolver.Address) {
+	wcc.UpdateState(resolver.State{Addresses: addrs})
+}
+
+// ParseServiceConfig parses the provided service config and returns an
+// object that provides the parsed config.
+func (wcc *wrappingClientConn) ParseServiceConfig(serviceConfigJSON string) *serviceconfig.ParseResult {
+	return wcc.parent.cc.ParseServiceConfig(serviceConfigJSON)
+}