JS: Make fetch response headers a Map again (#1898)

Since we are using browser fetch when available it makes more sense
to use a Map.

js/src/browser/fetch.js

@@ -4,6 +4,7 @@
 // Licensed under the Apache License, version 2.0:
 // http://www.apache.org/licenses/LICENSE-2.0
 
+import {notNull} from '../assert.js';
 
 export type FetchOptions = {
   method?: string,
@@ -12,7 +13,7 @@ export type FetchOptions = {
   withCredentials? : boolean,
 };
 
-type Response<T> = {headers: {[key: string]: string}, buf: T};
+type Response<T> = {headers: Map<string, string>, buf: T};
 type TextResponse = Response<string>;
 type BufResponse = Response<Uint8Array>;
 
@@ -22,12 +23,12 @@ function fetch<T>(url: string, responseType: string, options: FetchOptions = {})
   xhr.responseType = responseType;
   const method = options.method || 'GET';
   xhr.open(method, url, true);
-  const p = new Promise((res, rej) => {
+  const p = new Promise((resolve, reject) => {
     xhr.onloadend = () => {
       if (xhr.status >= 200 && xhr.status < 300) {
-        res({headers: res.headers, buf: xhr.response});
+        resolve({headers: makeHeaders(xhr), buf: xhr.response});
       } else {
-        rej(new Error(`HTTP Error: ${xhr.status}`));
+        reject(new Error(`HTTP Error: ${xhr.status}`));
       }
     };
   });
@@ -46,6 +47,7 @@ function fetch<T>(url: string, responseType: string, options: FetchOptions = {})
 export function fetchText(url: string, options: FetchOptions = {}): Promise<TextResponse> {
   if (self.fetch) {
     return self.fetch(url, options)
+      // resp.headers is a Headers which is a multi map, which is similar enough for now.
       .then(resp => ({headers: resp.headers, buf: resp.text()}));
   }
 
@@ -55,8 +57,19 @@ export function fetchText(url: string, options: FetchOptions = {}): Promise<Text
 export function fetchUint8Array(url: string, options: FetchOptions = {}): Promise<BufResponse> {
   if (self.fetch) {
     return self.fetch(url, options)
+      // resp.headers is a Headers which is a multi map, which is similar enough for now.
       .then(resp => ({headers: resp.headers, buf: new Uint8Array(resp.arrayBuffer())}));
   }
 
   return fetch(url, 'arraybuffer', options);
 }
+
+function makeHeaders(xhr: XMLHttpRequest): Map<string, string> {
+  const m = new Map();
+  const headers = xhr.getAllResponseHeaders().split(/\r\n/);  // spec requires \r\n
+  for (const header of headers) {
+    const [, name, value] = notNull(header.match(/([^:]+): (.*)/));
+    m.set(name, value);
+  }
+  return m;
+}

js/src/fetch.js

@@ -15,10 +15,18 @@ export type FetchOptions = {
   withCredentials? : boolean,
 };
 
-type Response<T> = {headers: {[key: string]: string}, buf: T};
+type Response<T> = {headers: Map<string, string>, buf: T};
 type TextResponse = Response<string>;
 type BufResponse = Response<Uint8Array>;
 
+function objectToMap<T>(object: {[key: string]: T}): Map<string, T> {
+  const m = new Map();
+  for (const k in object) {
+    m.set(k, object[k]);
+  }
+  return m;
+}
+
 function fetch(url: string, options: FetchOptions = {}): Promise<BufResponse> {
   const opts: any = parse(url);
   opts.method = options.method || 'GET';
@@ -54,7 +62,7 @@ function fetch(url: string, options: FetchOptions = {}): Promise<BufResponse> {
         offset += size;
       });
       res.on('end', () => {
-        resolve({headers: res.headers, buf: Bytes.subarray(buf, 0, offset)});
+        resolve({headers: objectToMap(res.headers), buf: Bytes.subarray(buf, 0, offset)});
       });
     });
     req.on('error', err => {

js/src/http-batch-store.js

@@ -159,8 +159,8 @@ export class Delegate {
   }
 }
 
-function checkVersion(headers: {[key: string]: string}): ?Error {
-  const version = headers[versionHeader];
+function checkVersion(headers: Map<string, string>): ?Error {
+  const version = headers.get(versionHeader);
   if (version !== nomsVersion) {
     return new Error(
       `SDK version ${nomsVersion} is not compatible with data of version ${version}.`);