Allow extra descriptor sources in reflection mode

Allows descriptors or proto files to be supplied that are used as an
additional descriptor source when server reflection is used. This is
needed to resolve message types, embedded in an Any message, that the
server has no knowledge of.

Resolves: #135

cmd/grpcurl/grpcurl.go

@@ -9,6 +9,7 @@ import (
 	"io"
 	"os"
 	"path/filepath"
+	"strconv"
 	"strings"
 	"time"
 
@@ -126,6 +127,7 @@ var (
 		an error to use both -authority and -servername (though this will be
 		permitted if they are both set to the same value, to increase backwards
 		compatibility with earlier releases that allowed both to be set).`))
+	reflection = optionalBoolFlag{val: true}
 )
 
 func init() {
@@ -168,6 +170,12 @@ func init() {
 		order given. If no import paths are given, all files (including all
 		imports) must be provided as -proto flags, and grpcurl will attempt to
 		resolve all import statements from the set of file names given.`))
+	flags.Var(&reflection, "use-reflection", prettify(`
+		When true, server reflection will be used to determine the RPC schema.
+		Defaults to true unless a -proto or -protoset option is provided. If
+		-use-reflection is used in combination with a -proto or -protoset flag,
+		the provided descriptor sources will be used in addition to server
+		reflection to resolve messages and extensions.`))
 }
 
 type multiString []string
@@ -181,6 +189,49 @@ func (s *multiString) Set(value string) error {
 	return nil
 }
 
+// Uses a file source as a fallback for resolving symbols and extensions, but
+// only uses the reflection source for listing services
+type compositeSource struct {
+	reflection grpcurl.DescriptorSource
+	file       grpcurl.DescriptorSource
+}
+
+func (cs compositeSource) ListServices() ([]string, error) {
+	return cs.reflection.ListServices()
+}
+
+func (cs compositeSource) FindSymbol(fullyQualifiedName string) (desc.Descriptor, error) {
+	d, err := cs.reflection.FindSymbol(fullyQualifiedName)
+	if err == nil {
+		return d, nil
+	}
+	return cs.file.FindSymbol(fullyQualifiedName)
+}
+
+func (cs compositeSource) AllExtensionsForType(typeName string) ([]*desc.FieldDescriptor, error) {
+	exts, err := cs.reflection.AllExtensionsForType(typeName)
+	if err != nil {
+		// On error fall back to file source
+		return cs.file.AllExtensionsForType(typeName)
+	}
+	// Track the tag numbers from the reflection source
+	tags := make(map[int32]bool)
+	for _, ext := range exts {
+		tags[ext.GetNumber()] = true
+	}
+	fileExts, err := cs.file.AllExtensionsForType(typeName)
+	if err != nil {
+		return exts, nil
+	}
+	for _, ext := range fileExts {
+		// Prioritize extensions found via reflection
+		if !tags[ext.GetNumber()] {
+			exts = append(exts, ext)
+		}
+	}
+	return exts, nil
+}
+
 func main() {
 	flags.Usage = usage
 	flags.Parse(os.Args[1:])
@@ -288,6 +339,14 @@ func main() {
 	if len(importPaths) > 0 && len(protoFiles) == 0 {
 		warn("The -import-path argument is not used unless -proto files are used.")
 	}
+	if !reflection.val && len(protoset) == 0 && len(protoFiles) == 0 {
+		fail(nil, "No protoset files or proto files specified and -use-reflection set to false.")
+	}
+
+	// Protoset or protofiles provided and -use-reflection unset
+	if !reflection.set && (len(protoset) > 0 || len(protoFiles) > 0) {
+		reflection.val = false
+	}
 
 	ctx := context.Background()
 	if *maxTime > 0 {
@@ -372,24 +431,33 @@ func main() {
 	var cc *grpc.ClientConn
 	var descSource grpcurl.DescriptorSource
 	var refClient *grpcreflect.Client
+	var fileSource grpcurl.DescriptorSource
 	if len(protoset) > 0 {
 		var err error
-		descSource, err = grpcurl.DescriptorSourceFromProtoSets(protoset...)
+		fileSource, err = grpcurl.DescriptorSourceFromProtoSets(protoset...)
 		if err != nil {
 			fail(err, "Failed to process proto descriptor sets.")
 		}
 	} else if len(protoFiles) > 0 {
 		var err error
-		descSource, err = grpcurl.DescriptorSourceFromProtoFiles(importPaths, protoFiles...)
+		fileSource, err = grpcurl.DescriptorSourceFromProtoFiles(importPaths, protoFiles...)
 		if err != nil {
 			fail(err, "Failed to process proto source files.")
 		}
-	} else {
+	}
+	if reflection.val {
 		md := grpcurl.MetadataFromHeaders(append(addlHeaders, reflHeaders...))
 		refCtx := metadata.NewOutgoingContext(ctx, md)
 		cc = dial()
 		refClient = grpcreflect.NewClient(refCtx, reflectpb.NewServerReflectionClient(cc))
-		descSource = grpcurl.DescriptorSourceFromServer(ctx, refClient)
+		reflSource := grpcurl.DescriptorSourceFromServer(ctx, refClient)
+		if fileSource != nil {
+			descSource = compositeSource{reflSource, fileSource}
+		} else {
+			descSource = reflSource
+		}
+	} else {
+		descSource = fileSource
 	}
 
 	// arrange for the RPCs to be cleanly shutdown
@@ -672,3 +740,28 @@ func writeProtoset(descSource grpcurl.DescriptorSource, symbols ...string) error
 	defer f.Close()
 	return grpcurl.WriteProtoset(f, descSource, symbols...)
 }
+
+type optionalBoolFlag struct {
+	set, val bool
+}
+
+func (f *optionalBoolFlag) String() string {
+	if !f.set {
+		return "unset"
+	}
+	return strconv.FormatBool(f.val)
+}
+
+func (f *optionalBoolFlag) Set(s string) error {
+	v, err := strconv.ParseBool(s)
+	if err != nil {
+		return err
+	}
+	f.set = true
+	f.val = v
+	return nil
+}
+
+func (f *optionalBoolFlag) IsBoolFlag() bool {
+	return true
+}