Custom error formatting function

README.md

@@ -33,6 +33,11 @@ The `graphqlHTTP` function accepts the following options:
 
   * **`pretty`**: If `true`, any JSON response will be pretty-printed.
 
+  * **`formatError`**: An optional function which will be used to format any
+    errors produced by fulfilling a GraphQL operation. If no function is
+    provided, GraphQL's default spec-compliant [`formatError`][] function will
+    be used. *To enable stack traces, provide the function: `error => error`.*
+
   * **`graphiql`**: If `true`, may present [GraphiQL][] when loaded directly
     from a browser (a useful tool for debugging and exploration).
 
@@ -124,6 +129,7 @@ new GraphQLObjectType({
 ```
 
 [`graphql-js`]: https://github.com/graphql/graphql-js
+[`formatError`]: https://github.com/graphql/graphql-js/blob/master/src/error/formatError.js
 [GraphiQL]: https://github.com/graphql/graphiql
 [`multer`]: https://github.com/expressjs/multer
 [`express-session`]: https://github.com/expressjs/session

src/__tests__/http-test.js

@@ -797,8 +797,7 @@ describe('test harness', () => {
         var app = express();
 
         app.use(urlString(), graphqlHTTP({
-          schema: TestSchema,
-          pretty: true
+          schema: TestSchema
         }));
 
         var response = await request(app)
@@ -816,12 +815,65 @@ describe('test harness', () => {
         });
       });
 
+      it('allows for custom error formatting to sanitize', async () => {
+        var app = express();
+
+        app.use(urlString(), graphqlHTTP({
+          schema: TestSchema,
+          formatError(error) {
+            return { message: 'Custom error format: ' + error.message };
+          }
+        }));
+
+        var response = await request(app)
+          .get(urlString({
+            query: '{thrower}',
+          }));
+
+        expect(response.status).to.equal(200);
+        expect(JSON.parse(response.text)).to.deep.equal({
+          data: null,
+          errors: [ {
+            message: 'Custom error format: Throws!',
+          } ]
+        });
+      });
+
+      it('allows for custom error formatting to elaborate', async () => {
+        var app = express();
+
+        app.use(urlString(), graphqlHTTP({
+          schema: TestSchema,
+          formatError(error) {
+            return {
+              message: error.message,
+              locations: error.locations,
+              stack: 'Stack trace'
+            };
+          }
+        }));
+
+        var response = await request(app)
+          .get(urlString({
+            query: '{thrower}',
+          }));
+
+        expect(response.status).to.equal(200);
+        expect(JSON.parse(response.text)).to.deep.equal({
+          data: null,
+          errors: [ {
+            message: 'Throws!',
+            locations: [ { line: 1, column: 2 } ],
+            stack: 'Stack trace',
+          } ]
+        });
+      });
+
       it('handles syntax errors caught by GraphQL', async () => {
         var app = express();
 
         app.use(urlString(), graphqlHTTP({
           schema: TestSchema,
-          pretty: true
         }));
 
         var error = await catchError(
@@ -846,7 +898,6 @@ describe('test harness', () => {
 
         app.use(urlString(), graphqlHTTP({
           schema: TestSchema,
-          pretty: true
         }));
 
         var error = await catchError(
@@ -864,7 +915,6 @@ describe('test harness', () => {
 
         app.use(urlString(), graphqlHTTP({
           schema: TestSchema,
-          pretty: true
         }));
 
         var error = await catchError(
@@ -885,7 +935,6 @@ describe('test harness', () => {
 
         app.use(urlString(), graphqlHTTP({
           schema: TestSchema,
-          pretty: true
         }));
 
         var error = await catchError(

src/index.js

@@ -46,7 +46,14 @@ export type OptionsObj = {
   pretty?: ?boolean,
 
   /**
-   * A boolean to optionally enable GraphiQL mode
+   * An optional function which will be used to format any errors produced by
+   * fulfilling a GraphQL operation. If no function is provided, GraphQL's
+   * default spec-compliant `formatError` function will be used.
+   */
+  formatError?: ?Function,
+
+  /**
+   * A boolean to optionally enable GraphiQL mode.
    */
   graphiql?: ?boolean,
 };
@@ -69,6 +76,7 @@ export default function graphqlHTTP(options: Options): Middleware {
     let rootValue;
     let pretty;
     let graphiql;
+    let formatErrorFn;
     let showGraphiQL;
     let query;
     let variables;
@@ -84,6 +92,7 @@ export default function graphqlHTTP(options: Options): Middleware {
       rootValue = optionsObj.rootValue;
       pretty = optionsObj.pretty;
       graphiql = optionsObj.graphiql;
+      formatErrorFn = optionsObj.formatError;
 
       // GraphQL HTTP only supports GET and POST methods.
       if (request.method !== 'GET' && request.method !== 'POST') {
@@ -177,7 +186,7 @@ export default function graphqlHTTP(options: Options): Middleware {
     }).then(result => {
       // Format any encountered errors.
       if (result && result.errors) {
-        result.errors = result.errors.map(formatError);
+        result.errors = result.errors.map(formatErrorFn || formatError);
       }
 
       // If allowed to show GraphiQL, present it instead of JSON.