fix grpc parsing error causing an exception from the plugin

packages/datadog-plugin-grpc/src/util.js

@@ -25,6 +25,8 @@ module.exports = {
   },
 
   addMetadataTags (span, metadata, filter, type) {
+    if (!metadata) return
+
     const values = filter(metadata.getMap())
 
     for (const key in values) {

packages/datadog-plugin-grpc/test/client.spec.js

@@ -13,16 +13,18 @@ describe('Plugin', () => {
   let port
   let server
   let tracer
+  let loader
 
-  function buildClient (service) {
+  function buildClient (service, ClientService) {
     service = Object.assign({
       getBidi: () => {},
       getServerStream: () => {},
       getClientStream: () => {},
       getUnary: () => {}
     }, service)
 
-    const loader = require('../../../versions/@grpc/proto-loader').get()
+    loader = require('../../../versions/@grpc/proto-loader').get()
+
     const definition = loader.loadSync(`${__dirname}/test.proto`)
     const TestService = grpc.loadPackageDefinition(definition).test.TestService
 
@@ -32,7 +34,9 @@ describe('Plugin', () => {
     server.addService(TestService.service, service)
     server.start()
 
-    return new TestService(`localhost:${port}`, grpc.credentials.createInsecure())
+    ClientService = ClientService || TestService
+
+    return new ClientService(`localhost:${port}`, grpc.credentials.createInsecure())
   }
 
   describe('grpc/client', () => {
@@ -260,6 +264,36 @@ describe('Plugin', () => {
           client.getUnary({ first: 'foobar' }, () => {})
         })
 
+        it('should handle protocol errors', done => {
+          const definition = loader.loadSync(`${__dirname}/invalid.proto`)
+          const test = grpc.loadPackageDefinition(definition).test
+          const client = buildClient({
+            getUnary: (_, callback) => callback(null)
+          }, test.TestService)
+
+          agent
+            .use(traces => {
+              expect(traces[0][0]).to.have.property('error', 1)
+              expect(traces[0][0].meta).to.include({
+                'error.msg': '13 INTERNAL: Failed to parse server response',
+                'error.type': 'Error',
+                'grpc.method.name': 'getUnary',
+                'grpc.method.service': 'TestService',
+                'grpc.method.package': 'test',
+                'grpc.method.path': '/test.TestService/getUnary',
+                'grpc.method.kind': kinds.unary,
+                'grpc.status.code': '13',
+                'span.kind': 'client',
+                'component': 'grpc'
+              })
+              expect(traces[0][0].meta).to.have.property('error.stack')
+            })
+            .then(done)
+            .catch(done)
+
+          client.getUnary({ first: 'foobar' }, () => {})
+        })
+
         it('should handle a missing callback', done => {
           const client = buildClient({
             getUnary: (_, callback) => callback()

packages/datadog-plugin-grpc/test/invalid.proto

@@ -0,0 +1,19 @@
+syntax = "proto3";
+
+package test;
+
+service TestService {
+  rpc get_Bidi (stream Request) returns (stream Response) {} // test rename support
+  rpc getServerStream (Request) returns (stream Response) {}
+  rpc getClientStream (stream Request) returns (Response) {}
+  rpc getUnary (Request) returns (Response) {}
+}
+
+message Request {
+  string first = 1;
+  int32 second = 2;
+}
+
+message Response {
+  required string first = 1;
+}

packages/datadog-plugin-grpc/test/test.proto

@@ -3,16 +3,15 @@ syntax = "proto3";
 package test;
 
 service TestService {
-  rpc get_Bidi (stream Request) returns (stream Empty) {} // test rename support
-  rpc getServerStream (Request) returns (stream Empty) {}
-  rpc getClientStream (stream Request) returns (Empty) {}
-  rpc getUnary (Request) returns (Empty) {}
+  rpc get_Bidi (stream Request) returns (stream Response) {} // test rename support
+  rpc getServerStream (Request) returns (stream Response) {}
+  rpc getClientStream (stream Request) returns (Response) {}
+  rpc getUnary (Request) returns (Response) {}
 }
 
 message Request {
   string first = 1;
   int32 second = 2;
 }
 
-message Empty {
-}
+message Response {}