First draft of toxic-comments

graph/errorHandler.js

@@ -0,0 +1,70 @@
+const {
+  GraphQLObjectType,
+  GraphQLInterfaceType
+} = require('graphql');
+const {maskErrors} = require('graphql-errors');
+const errors = require('../errors');
+const {Error: {ValidationError}} = require('mongoose');
+
+// This function is pretty much copied verbatim from the graphql-tools repo:
+// https://github.com/apollographql/graphql-tools/blob/b12973c86e00be209d04af0184780998056051c4/src/schemaGenerator.ts#L180-L194
+const forEachField = (schema, fn) => {
+  const typeMap = schema.getTypeMap();
+  Object.keys(typeMap).forEach((typeName) => {
+    const type = typeMap[typeName];
+
+    if (type instanceof GraphQLObjectType || type instanceof GraphQLInterfaceType) {
+      const fields = type.getFields();
+      Object.keys(fields).forEach((fieldName) => {
+        const field = fields[fieldName];
+        fn(field, typeName, fieldName);
+      });
+    }
+  });
+};
+
+// If an APIError happens in a mutation, then respond with `{errors: Array}`
+// according to the schema.
+const decorateWithMutationErrorHandler = (field) => {
+  const fieldResolver = field.resolve;
+  field.resolve = async (obj, args, ctx, info) => {
+    try {
+      return await fieldResolver(obj, args, ctx, info);
+    }
+    catch(err) {
+      if (err instanceof errors.APIError) {
+        return {
+          errors: [err]
+        };
+      } else if (err instanceof ValidationError) {
+
+        // TODO: wrap this with one of our internal errors.
+        throw err;
+      }
+
+      throw err;
+    }
+  };
+};
+
+// Masks errors during production and handle mutation errors inside the schema.
+const decorateWithErrorHandler = (schema) => {
+  forEachField(schema, (field, typeName) => {
+
+    // Handle mutation errors.
+    if (typeName === 'RootMutation') {
+      decorateWithMutationErrorHandler(field);
+    }
+
+    // If we are in production mode, don't show server errors to the front end.
+    if (process.env.NODE_ENV === 'production') {
+
+      // Mask errors that are thrown if we are in a production environment.
+      maskErrors(field);
+    }
+  });
+};
+
+module.exports = {
+  decorateWithErrorHandler,
+};