Refactor loadFileDescriptorSet

This change refactors the loadFileDescriptorSetFile function to take
a plain Buffer or Javascript object as input.

packages/proto-loader/src/index.ts

@@ -379,14 +379,30 @@ export function loadSync(
   return createPackageDefinition(root, options!);
 }
 
-export async function loadFileDescriptorSet(
-  descriptorSet: Protobuf.Message<descriptor.IFileDescriptorSet> &
-    descriptor.IFileDescriptorSet,
+export function loadFileDescriptorSet(
+  descriptorSet:
+    | Buffer
+    | ReturnType<typeof descriptor.FileDescriptorSet.toObject>,
   options?: Options
-): Promise<PackageDefinition> {
+): PackageDefinition {
+  type DecodedDescriptorSet = Protobuf.Message<descriptor.IFileDescriptorSet> &
+    descriptor.IFileDescriptorSet;
+
   options = options || {};
+
+  let decodedDescriptorSet: DecodedDescriptorSet;
+  if (typeof descriptorSet === 'object') {
+    decodedDescriptorSet = descriptor.FileDescriptorSet.fromObject(
+      descriptorSet
+    ) as DecodedDescriptorSet;
+  } else {
+    decodedDescriptorSet = descriptor.FileDescriptorSet.decode(
+      descriptorSet
+    ) as DecodedDescriptorSet;
+  }
+
   const root = (Protobuf.Root as Protobuf.RootConstructor).fromDescriptor(
-    descriptorSet
+    decodedDescriptorSet
   );
   root.resolveAll();
   return createPackageDefinition(root, options);
@@ -402,11 +418,7 @@ export function loadFileDescriptorSetFile(
         return reject(err);
       }
 
-      const descriptorSet = descriptor.FileDescriptorSet.decode(
-        data
-      ) as Protobuf.Message<descriptor.IFileDescriptorSet> &
-        descriptor.IFileDescriptorSet;
-      return resolve(loadFileDescriptorSet(descriptorSet, options));
+      return resolve(loadFileDescriptorSet(data, options));
     });
   });
 }

packages/proto-loader/test/descriptor_type_test.ts

@@ -16,6 +16,7 @@
  */
 
 import * as assert from 'assert';
+import { rpcFileDescriptorSet } from '../test_protos/rpc.desc';
 
 import * as proto_loader from '../src/index';
 
@@ -101,7 +102,12 @@ describe('Descriptor types', () => {
   });
 
   it('Can load binary-encoded proto file descriptor sets', () => {
-    // This will throw if the well known protos are not available.
+    // This will throw if the rpc descriptor cannot be decoded
     proto_loader.loadFileDescriptorSetFile(`${TEST_PROTO_DIR}/rpc.desc`);
   });
+
+  it('Can parse plain file descriptor set objects', () => {
+    // This will throw if the file descriptor object cannot be parsed
+    proto_loader.loadFileDescriptorSet(rpcFileDescriptorSet);
+  });
 });

packages/proto-loader/test_protos/rpc.desc.ts

@@ -0,0 +1,46 @@
+export const rpcFileDescriptorSet = {
+  "file": [
+    {
+      "name": "test_protos/rpc.proto",
+      "messageType": [
+        {
+          "name": "MyRequest",
+          "field": [
+            {
+              "name": "path",
+              "number": 1,
+              "label": "LABEL_OPTIONAL",
+              "type": "TYPE_STRING",
+              "jsonName": "path"
+            }
+          ]
+        },
+        {
+          "name": "MyResponse",
+          "field": [
+            {
+              "name": "status",
+              "number": 2,
+              "label": "LABEL_OPTIONAL",
+              "type": "TYPE_INT32",
+              "jsonName": "status"
+            }
+          ]
+        }
+      ],
+      "service": [
+        {
+          "name": "MyService",
+          "method": [
+            {
+              "name": "MyMethod",
+              "inputType": ".MyRequest",
+              "outputType": ".MyResponse"
+            }
+          ]
+        }
+      ],
+      "syntax": "proto3"
+    }
+  ]
+}