Add functions for loading and parsing binary-encoded file decriptor sets

Fixes #1627

packages/proto-loader/src/index.ts

@@ -30,6 +30,17 @@ declare module 'protobufjs' {
       descriptor.IDescriptorProto;
   }
 
+  interface RootConstructor {
+    new (options?: Options): Root;
+    fromDescriptor(
+      descriptorSet:
+        | descriptor.IFileDescriptorSet
+        | Protobuf.Reader
+        | Uint8Array
+    ): Root;
+    fromJSON(json: Protobuf.INamespace, root?: Root): Root;
+  }
+
   interface Root {
     toDescriptor(
       protoVersion: string
@@ -368,6 +379,38 @@ export function loadSync(
   return createPackageDefinition(root, options!);
 }
 
+export async function loadFileDescriptorSet(
+  descriptorSet: Protobuf.Message<descriptor.IFileDescriptorSet> &
+    descriptor.IFileDescriptorSet,
+  options?: Options
+): Promise<PackageDefinition> {
+  options = options || {};
+  const root = (Protobuf.Root as Protobuf.RootConstructor).fromDescriptor(
+    descriptorSet
+  );
+  root.resolveAll();
+  return createPackageDefinition(root, options);
+}
+
+export function loadFileDescriptorSetFile(
+  filename: string,
+  options?: Options
+): Promise<PackageDefinition> {
+  return new Promise((resolve, reject) => {
+    fs.readFile(filename, (err, data) => {
+      if (err) {
+        return reject(err);
+      }
+
+      const descriptorSet = descriptor.FileDescriptorSet.decode(
+        data
+      ) as Protobuf.Message<descriptor.IFileDescriptorSet> &
+        descriptor.IFileDescriptorSet;
+      return resolve(loadFileDescriptorSet(descriptorSet, options));
+    });
+  });
+}
+
 // Load Google's well-known proto files that aren't exposed by Protobuf.js.
 
 // Protobuf.js exposes: any, duration, empty, field_mask, struct, timestamp,

packages/proto-loader/test/descriptor_type_test.ts

@@ -99,4 +99,9 @@ describe('Descriptor types', () => {
     // This will throw if the well known protos are not available.
     proto_loader.loadSync(`${TEST_PROTO_DIR}/well_known.proto`);
   });
+
+  it('Can load binary-encoded proto file descriptor sets', () => {
+    // This will throw if the well known protos are not available.
+    proto_loader.loadFileDescriptorSetFile(`${TEST_PROTO_DIR}/rpc.desc`);
+  });
 });

packages/proto-loader/test_protos/rpc.desc

@@ -0,0 +1,11 @@
+
+˜

+test_protos/rpc.proto"
+	MyRequest
+path
 
(	Rpath"$
+
+MyResponse
+status 
(Rstatus20
+	MyService#
+MyMethod
+.MyRequest.MyResponsebproto3

packages/proto-loader/test_protos/rpc.proto

@@ -0,0 +1,13 @@
+syntax = "proto3";
+
+service MyService {
+    rpc MyMethod (MyRequest) returns (MyResponse);
+}
+
+message MyRequest {
+    string path = 1;
+}
+
+message MyResponse {
+    int32 status = 2;
+}