response.redirect: extract special-cased back

lib/context.js

@@ -204,6 +204,7 @@ delegate(proto, 'response')
   .method('set')
   .method('append')
   .method('flushHeaders')
+  .method('back')
   .access('status')
   .access('message')
   .access('body')

lib/response.js

@@ -18,6 +18,7 @@ const only = require('./only.js')
 const util = require('util')
 const encodeUrl = require('encodeurl')
 const Stream = require('stream')
+const deprecate = require('depd')('koa');
 
 /**
  * Prototype.
@@ -293,7 +294,11 @@ module.exports = {
 
   redirect (url, alt) {
     // location
-    if (url === 'back') url = this.ctx.get('Referrer') || alt || '/'
+    if (url === 'back') {
+      deprecate('Special-cased string "back" through redirect will be removed in v3, ' +
+        'consider migrating usage to ctx.back() instead.');
+      url = this.ctx.get('Referrer') || alt || '/';
+    }
     if (/^https?:\/\//i.test(url)) {
       // formatting url again avoid security escapes
       url = new URL(url).toString()
@@ -316,6 +321,24 @@ module.exports = {
     this.body = `Redirecting to ${url}.`
   },
 
+  /**
+   * Perform a special-cased "back" to provide Referrer support.
+   * When Referrer is not present, `alt` or "/" is used.
+   *
+   * Examples:
+   *
+   *    ctx.back()
+   *    ctx.back('/index.html')
+   *
+   * @param {String} [alt]
+   * @api public
+   */
+
+  back(alt) {
+    const url = this.ctx.get('Referrer') || alt || '/';
+    this.redirect(url);
+  },
+
   /**
    * Set Content-Disposition header to "attachment" with optional `filename`.
    *

test/response/back.js

@@ -0,0 +1,33 @@
+
+'use strict';
+
+const assert = require('assert');
+const context = require('../helpers/context');
+
+describe('ctx.back([alt])', () => {
+  it('should redirect to Referrer', () => {
+    const ctx = context();
+    ctx.req.headers.referrer = '/login';
+    ctx.back();
+    assert.equal(ctx.response.header.location, '/login');
+  });
+
+  it('should redirect to Referer', () => {
+    const ctx = context();
+    ctx.req.headers.referer = '/login';
+    ctx.back();
+    assert.equal(ctx.response.header.location, '/login');
+  });
+
+  it('should default to alt', () => {
+    const ctx = context();
+    ctx.back('/index.html');
+    assert.equal(ctx.response.header.location, '/index.html');
+  });
+
+  it('should default redirect to /', () => {
+    const ctx = context();
+    ctx.back();
+    assert.equal(ctx.response.header.location, '/');
+  });
+});