grpcutil: add ValidateTargetURI function

balancer/rls/config.go

@@ -22,12 +22,12 @@ import (
 	"bytes"
 	"encoding/json"
 	"fmt"
-	"net/url"
 	"time"
 
 	"google.golang.org/grpc/balancer"
 	"google.golang.org/grpc/balancer/rls/internal/keys"
 	"google.golang.org/grpc/internal"
+	"google.golang.org/grpc/internal/grpcutil"
 	"google.golang.org/grpc/internal/pretty"
 	rlspb "google.golang.org/grpc/internal/proto/grpc_lookup_v1"
 	"google.golang.org/grpc/resolver"
@@ -195,16 +195,9 @@ func parseRLSProto(rlsProto *rlspb.RouteLookupConfig) (*lbConfig, error) {
 	if lookupService == "" {
 		return nil, fmt.Errorf("rls: empty lookup_service in route lookup config %+v", rlsProto)
 	}
-	parsedTarget, err := url.Parse(lookupService)
+	parsedTarget, err := grpcutil.ParseTarget(lookupService, resolver.GetDefaultScheme())
 	if err != nil {
-		// url.Parse() fails if scheme is missing. Retry with default scheme.
-		parsedTarget, err = url.Parse(resolver.GetDefaultScheme() + ":///" + lookupService)
-		if err != nil {
-			return nil, fmt.Errorf("rls: invalid target URI in lookup_service %s", lookupService)
-		}
-	}
-	if parsedTarget.Scheme == "" {
-		parsedTarget.Scheme = resolver.GetDefaultScheme()
+		return nil, fmt.Errorf("rls: invalid target URI in lookup_service %s: %v", lookupService, err)
 	}
 	if resolver.Get(parsedTarget.Scheme) == nil {
 		return nil, fmt.Errorf("rls: unregistered scheme in lookup_service %s", lookupService)

clientconn.go

@@ -23,7 +23,6 @@ import (
 	"errors"
 	"fmt"
 	"math"
-	"net/url"
 	"slices"
 	"strings"
 	"sync"
@@ -40,6 +39,7 @@ import (
 	"google.golang.org/grpc/internal"
 	"google.golang.org/grpc/internal/channelz"
 	"google.golang.org/grpc/internal/grpcsync"
+	"google.golang.org/grpc/internal/grpcutil"
 	"google.golang.org/grpc/internal/idle"
 	iresolver "google.golang.org/grpc/internal/resolver"
 	istats "google.golang.org/grpc/internal/stats"
@@ -1799,11 +1799,11 @@ func (cc *ClientConn) initParsedTargetAndResolverBuilder() error {
 	logger.Infof("original dial target is: %q", cc.target)
 
 	var rb resolver.Builder
-	parsedTarget, err := parseTarget(cc.target)
+	u, err := grpcutil.ParseTarget(cc.target, "")
 	if err == nil {
-		rb = cc.getResolver(parsedTarget.URL.Scheme)
+		rb = cc.getResolver(u.Scheme)
 		if rb != nil {
-			cc.parsedTarget = parsedTarget
+			cc.parsedTarget = resolver.Target{URL: *u}
 			cc.resolverBuilder = rb
 			return nil
 		}
@@ -1820,32 +1820,19 @@ func (cc *ClientConn) initParsedTargetAndResolverBuilder() error {
 	}
 
 	canonicalTarget := defScheme + ":///" + cc.target
-
-	parsedTarget, err = parseTarget(canonicalTarget)
+	u, err = grpcutil.ParseTarget(canonicalTarget, "")
 	if err != nil {
 		return err
 	}
-	rb = cc.getResolver(parsedTarget.URL.Scheme)
+	rb = cc.getResolver(u.Scheme)
 	if rb == nil {
-		return fmt.Errorf("could not get resolver for default scheme: %q", parsedTarget.URL.Scheme)
+		return fmt.Errorf("could not get resolver for default scheme: %q", u.Scheme)
 	}
-	cc.parsedTarget = parsedTarget
+	cc.parsedTarget = resolver.Target{URL: *u}
 	cc.resolverBuilder = rb
 	return nil
 }
 
-// parseTarget uses RFC 3986 semantics to parse the given target into a
-// resolver.Target struct containing url. Query params are stripped from the
-// endpoint.
-func parseTarget(target string) (resolver.Target, error) {
-	u, err := url.Parse(target)
-	if err != nil {
-		return resolver.Target{}, err
-	}
-
-	return resolver.Target{URL: *u}, nil
-}
-
 // encodeAuthority escapes the authority string based on valid chars defined in
 // https://datatracker.ietf.org/doc/html/rfc3986#section-3.2.
 func encodeAuthority(authority string) string {

internal/grpcutil/target.go

@@ -0,0 +1,63 @@
+/*
+ *
+ * Copyright 2025 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 grpcutil
+
+import (
+	"fmt"
+	"net/url"
+
+	"google.golang.org/grpc/resolver"
+)
+
+// ParseTarget parses a gRPC target string into a URL. If parsing fails,
+// it prepends defaultScheme and retries. If the scheme is empty after
+// parsing, it is set to defaultScheme. If defaultScheme is empty, no
+// fallback is attempted.
+func ParseTarget(target, defaultScheme string) (*url.URL, error) {
+	u, err := url.Parse(target)
+	if err != nil {
+		if defaultScheme == "" {
+			return nil, fmt.Errorf("invalid target URI %q: %w", target, err)
+		}
+		u, err = url.Parse(defaultScheme + ":///" + target)
+		if err != nil {
+			return nil, fmt.Errorf("invalid target URI %q: %w", target, err)
+		}
+	}
+	if u.Scheme == "" {
+		if defaultScheme == "" {
+			return nil, fmt.Errorf("target URI %q has no scheme", target)
+		}
+		u.Scheme = defaultScheme
+	}
+	return u, nil
+}
+
+// ValidateTargetURI validates that target is a valid RFC 3986 URI
+// and that a resolver is registered for its scheme.
+func ValidateTargetURI(target string) error {
+	u, err := ParseTarget(target, "")
+	if err != nil {
+		return err
+	}
+	if resolver.Get(u.Scheme) == nil {
+		return fmt.Errorf("no resolver registered for scheme %q", u.Scheme)
+	}
+	return nil
+}

internal/grpcutil/target_test.go

@@ -0,0 +1,166 @@
+/*
+ *
+ * Copyright 2025 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 grpcutil
+
+import (
+	"strings"
+	"testing"
+
+	_ "google.golang.org/grpc/resolver/dns"         // Register dns resolver
+	_ "google.golang.org/grpc/resolver/passthrough" // Register passthrough resolver
+)
+
+func TestParseTarget(t *testing.T) {
+	tests := []struct {
+		name          string
+		target        string
+		defaultScheme string
+		wantScheme    string
+		wantErr       bool
+		errContain    string
+	}{
+		{
+			name:          "valid dns scheme",
+			target:        "dns:///example.com:443",
+			defaultScheme: "",
+			wantScheme:    "dns",
+			wantErr:       false,
+		},
+		{
+			name:          "valid passthrough scheme",
+			target:        "passthrough:///localhost:8080",
+			defaultScheme: "",
+			wantScheme:    "passthrough",
+			wantErr:       false,
+		},
+		{
+			name:          "missing scheme with default",
+			target:        "/path/to/socket",
+			defaultScheme: "unix",
+			wantScheme:    "unix",
+			wantErr:       false,
+		},
+		{
+			name:          "missing scheme without default",
+			target:        "/path/to/socket",
+			defaultScheme: "",
+			wantErr:       true,
+			errContain:    "has no scheme",
+		},
+		{
+			name:          "host:port parsed as scheme",
+			target:        "localhost:8080",
+			defaultScheme: "dns",
+			wantScheme:    "localhost",
+			wantErr:       false,
+		},
+		{
+			name:          "invalid URI without default",
+			target:        "dns:///example\x00.com",
+			defaultScheme: "",
+			wantErr:       true,
+			errContain:    "invalid target URI",
+		},
+		{
+			name:          "invalid URI with default still fails",
+			target:        "dns:///example\x00.com",
+			defaultScheme: "dns",
+			wantErr:       true,
+			errContain:    "invalid target URI",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			u, err := ParseTarget(tt.target, tt.defaultScheme)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("ParseTarget(%q, %q) error = %v, wantErr %v", tt.target, tt.defaultScheme, err, tt.wantErr)
+				return
+			}
+			if tt.wantErr {
+				if tt.errContain != "" && !strings.Contains(err.Error(), tt.errContain) {
+					t.Errorf("ParseTarget(%q, %q) error = %v, want error containing %q", tt.target, tt.defaultScheme, err, tt.errContain)
+				}
+				return
+			}
+			if u.Scheme != tt.wantScheme {
+				t.Errorf("ParseTarget(%q, %q).Scheme = %q, want %q", tt.target, tt.defaultScheme, u.Scheme, tt.wantScheme)
+			}
+		})
+	}
+}
+
+func TestValidateTargetURI(t *testing.T) {
+	tests := []struct {
+		name       string
+		target     string
+		wantErr    bool
+		errContain string
+	}{
+		{
+			name:    "valid dns scheme",
+			target:  "dns:///example.com:443",
+			wantErr: false,
+		},
+		{
+			name:    "valid passthrough scheme",
+			target:  "passthrough:///localhost:8080",
+			wantErr: false,
+		},
+		{
+			name:       "missing scheme",
+			target:     "/path/to/socket",
+			wantErr:    true,
+			errContain: "has no scheme",
+		},
+		{
+			name:       "host:port parsed as scheme",
+			target:     "example.com:443",
+			wantErr:    true,
+			errContain: "no resolver registered for scheme",
+		},
+		{
+			name:       "unregistered scheme",
+			target:     "unknown:///example.com:443",
+			wantErr:    true,
+			errContain: "no resolver registered for scheme",
+		},
+		{
+			name:       "invalid URI with control character",
+			target:     "dns:///example\x00.com",
+			wantErr:    true,
+			errContain: "invalid target URI",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := ValidateTargetURI(tt.target)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("ValidateTargetURI(%q) error = %v, wantErr %v", tt.target, err, tt.wantErr)
+				return
+			}
+			if tt.wantErr && tt.errContain != "" {
+				if !strings.Contains(err.Error(), tt.errContain) {
+					t.Errorf("ValidateTargetURI(%q) error = %v, want error containing %q", tt.target, err, tt.errContain)
+				}
+			}
+		})
+	}
+}