Add functionality to export proto files

Added a new function, `WriteProtoFiles` in `desc_source.go` which is used to generate .proto files. The process involves resolving symbols from the descriptor source and writing their definitions to a designated output directory. The corresponding flag `--proto-out` has been included in `grpcurl.go` to allow users to specify the directory path.

README.md

@@ -159,6 +159,11 @@ grpcurl -protoset my-protos.bin list
 
 # Using proto sources
 grpcurl -import-path ../protos -proto my-stuff.proto list
+
+# Export proto files
+grpcurl -plaintext -proto-out "out_protos" "192.168.100.1:9200" describe Api.Service
+
+
 ```
 
 The "list" verb also lets you see all methods in a particular service:

cmd/grpcurl/grpcurl.go

@@ -151,6 +151,14 @@ var (
 		file if this option is given. When invoking an RPC and this option is
 		given, the method being invoked and its transitive dependencies will be
 		included in the output file.`))
+	protoOut = flags.String("proto-out", "", prettify(`
+		The name of a directory where the generated .proto files will be written.
+		With the list and describe verbs, the listed or described elements and
+		their transitive dependencies will be written as .proto files in the
+		specified directory if this option is given. When invoking an RPC and
+		this option is given, the method being invoked and its transitive
+		dependencies will be included in the generated .proto files in the
+		output directory.`))
 	msgTemplate = flags.Bool("msg-template", false, prettify(`
 		When describing messages, show a template of input data.`))
 	verbose = flags.Bool("v", false, prettify(`
@@ -645,6 +653,9 @@ func main() {
 			if err := writeProtoset(descSource, svcs...); err != nil {
 				fail(err, "Failed to write protoset to %s", *protosetOut)
 			}
+			if err := writeProtos(descSource, svcs...); err != nil {
+				fail(err, "Failed to write protos to %s", *protoOut)
+			}
 		} else {
 			methods, err := grpcurl.ListMethods(descSource, symbol)
 			if err != nil {
@@ -660,6 +671,9 @@ func main() {
 			if err := writeProtoset(descSource, symbol); err != nil {
 				fail(err, "Failed to write protoset to %s", *protosetOut)
 			}
+			if err := writeProtos(descSource, symbol); err != nil {
+				fail(err, "Failed to write protos to %s", *protoOut)
+			}
 		}
 
 	} else if describe {
@@ -764,6 +778,9 @@ func main() {
 		if err := writeProtoset(descSource, symbols...); err != nil {
 			fail(err, "Failed to write protoset to %s", *protosetOut)
 		}
+		if err := writeProtos(descSource, symbol); err != nil {
+			fail(err, "Failed to write protos to %s", *protoOut)
+		}
 
 	} else {
 		// Invoke an RPC
@@ -923,6 +940,13 @@ func writeProtoset(descSource grpcurl.DescriptorSource, symbols ...string) error
 	return grpcurl.WriteProtoset(f, descSource, symbols...)
 }
 
+func writeProtos(descSource grpcurl.DescriptorSource, symbols ...string) error {
+	if *protoOut == "" {
+		return nil
+	}
+	return grpcurl.WriteProtoFiles(*protoOut, descSource, symbols...)
+}
+
 type optionalBoolFlag struct {
 	set, val bool
 }

desc_source.go

@@ -4,8 +4,10 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"github.com/jhump/protoreflect/desc/protoprint"
 	"io"
 	"os"
+	"path/filepath"
 	"sync"
 
 	"github.com/golang/protobuf/proto" //lint:ignore SA1019 we have to import this because it appears in exported API
@@ -258,19 +260,9 @@ func reflectionSupport(err error) error {
 // given output. The output will include descriptors for all files in which the
 // symbols are defined as well as their transitive dependencies.
 func WriteProtoset(out io.Writer, descSource DescriptorSource, symbols ...string) error {
-	// compute set of file descriptors
-	filenames := make([]string, 0, len(symbols))
-	fds := make(map[string]*desc.FileDescriptor, len(symbols))
-	for _, sym := range symbols {
-		d, err := descSource.FindSymbol(sym)
+	filenames, fds, err := getFileDescriptors(symbols, descSource)
 	if err != nil {
-			return fmt.Errorf("failed to find descriptor for %q: %v", sym, err)
-		}
-		fd := d.GetFile()
-		if _, ok := fds[fd.GetName()]; !ok {
-			fds[fd.GetName()] = fd
-			filenames = append(filenames, fd.GetName())
-		}
+		return err
 	}
 	// now expand that to include transitive dependencies in topologically sorted
 	// order (such that file always appears after its dependencies)
@@ -302,3 +294,71 @@ func addFilesToSet(allFiles []*descriptorpb.FileDescriptorProto, expanded map[st
 	}
 	return append(allFiles, fd.AsFileDescriptorProto())
 }
+
+// WriteProtoFiles will use the given descriptor source to resolve all the given
+// symbols and write proto files with their definitions to the given output directory.
+func WriteProtoFiles(outProtoDirPath string, descSource DescriptorSource, symbols ...string) error {
+	filenames, fds, err := getFileDescriptors(symbols, descSource)
+	if err != nil {
+		return err
+	}
+	// now expand that to include transitive dependencies in topologically sorted
+	// order (such that file always appears after its dependencies)
+	expandedFiles := make(map[string]struct{}, len(fds))
+	allFilesSlice := make([]*desc.FileDescriptor, 0, len(fds))
+	for _, filename := range filenames {
+		allFilesSlice = addFilesToFileDescriptorList(allFilesSlice, expandedFiles, fds[filename])
+	}
+	pr := protoprint.Printer{}
+	// now we can serialize to files
+	for _, fd := range allFilesSlice {
+		fdFQName := fd.GetFullyQualifiedName()
+		dirPath := filepath.Dir(fdFQName)
+		outFilepath := filepath.Join(outProtoDirPath, dirPath)
+		if err := os.MkdirAll(outFilepath, 0755); err != nil {
+			return fmt.Errorf("failed to create directory %q: %v", outFilepath, err)
+		}
+		fileName := filepath.Base(fdFQName)
+		filePath := filepath.Join(outFilepath, fileName)
+		f, err := os.Create(filePath)
+		defer f.Close()
+		if err != nil {
+			return fmt.Errorf("failed to create file %q: %v", filePath, err)
+		}
+		if err := pr.PrintProtoFile(fd, f); err != nil {
+			return fmt.Errorf("failed to write file %q: %v", filePath, err)
+		}
+	}
+	return nil
+}
+
+func getFileDescriptors(symbols []string, descSource DescriptorSource) ([]string, map[string]*desc.FileDescriptor, error) {
+	// compute set of file descriptors
+	filenames := make([]string, 0, len(symbols))
+	fds := make(map[string]*desc.FileDescriptor, len(symbols))
+	for _, sym := range symbols {
+		d, err := descSource.FindSymbol(sym)
+		if err != nil {
+			return nil, nil, fmt.Errorf("failed to find descriptor for %q: %v", sym, err)
+		}
+		fd := d.GetFile()
+		if _, ok := fds[fd.GetName()]; !ok {
+			fds[fd.GetName()] = fd
+			filenames = append(filenames, fd.GetName())
+		}
+	}
+	return filenames, fds, nil
+}
+
+func addFilesToFileDescriptorList(allFiles []*desc.FileDescriptor, expanded map[string]struct{}, fd *desc.FileDescriptor) []*desc.FileDescriptor {
+	if _, ok := expanded[fd.GetName()]; ok {
+		// already seen this one
+		return allFiles
+	}
+	expanded[fd.GetName()] = struct{}{}
+	// add all dependencies first
+	for _, dep := range fd.GetDependencies() {
+		allFiles = addFilesToFileDescriptorList(allFiles, expanded, dep)
+	}
+	return append(allFiles, fd)
+}