Simplification based on review comments

packages/driver/cypress/integration/commands/files_spec.js

@@ -40,7 +40,7 @@ describe('src/cy/commands/files', () => {
     // https://github.com/cypress-io/cypress/issues/1558
     it('passes explicit null encoding through to server and decodes response', () => {
       Cypress.backend.resolves({
-        contents: Buffer.from('\n').toString('base64'),
+        contents: Buffer.from('\n'),
         filePath: '/path/to/foo.json',
       })
 
@@ -357,16 +357,16 @@ describe('src/cy/commands/files', () => {
     })
 
     // https://github.com/cypress-io/cypress/issues/1558
-    it('explicit null encoding is sent to server as base64 string', () => {
+    it('explicit null encoding is sent to server as Buffer', () => {
       Cypress.backend.resolves(okResponse)
 
       cy.writeFile('foo.txt', Buffer.from([0, 0, 54, 255]), null).then(() => {
         expect(Cypress.backend).to.be.calledWith(
           'write:file',
           'foo.txt',
-          'AAA2/w==',
+          Buffer.from([0, 0, 54, 255]),
           {
-            encoding: 'base64',
+            encoding: null,
             flag: 'w',
           },
         )

packages/driver/src/cy/commands/files.ts

@@ -58,10 +58,12 @@ export default (Commands, Cypress, cy) => {
             args: { cmd: 'readFile', action: 'read', file, filePath: err.filePath, error: err.message },
           })
         }).then(({ contents, filePath }) => {
-          // Binary files (read with explicit `null` encoding by the user) are transmitted over the
-          // websocket base64 encoded. See packages/server/lib/files.js.
+          // https://github.com/cypress-io/cypress/issues/1558
+          // We invoke Buffer.from() in order to transform this from an ArrayBuffer -
+          // which socket.io uses to transfer the file over the websocket - into a
+          // `Buffer`, which webpack polyfills in the browser.
           if (options.encoding === null) {
-            contents = Buffer.from(contents, 'base64')
+            contents = Buffer.from(contents)
           }
 
           consoleProps['File Path'] = filePath
@@ -136,12 +138,7 @@ export default (Commands, Cypress, cy) => {
         })
       }
 
-      if (Buffer.isBuffer(contents)) {
-        contents = contents.toString('base64')
-        options.encoding = 'base64'
-      }
-
-      if (_.isObject(contents)) {
+      if (_.isObject(contents) && !Buffer.isBuffer(contents)) {
         contents = JSON.stringify(contents, null, 2)
       }
 

packages/driver/src/cy/commands/fixtures.ts

@@ -69,10 +69,11 @@ export default (Commands, Cypress, cy, state, config) => {
         }
 
         // https://github.com/cypress-io/cypress/issues/1558
-        // Binary files (read with explicit `null` encoding by the user) are transmitted over the
-        // websocket base64 encoded. See packages/server/lib/fixture.js.
+        // We invoke Buffer.from() in order to transform this from an ArrayBuffer -
+        // which socket.io uses to transfer the file over the websocket - into a
+        // `Buffer`, which webpack polyfills in the browser.
         if (options.encoding === null) {
-          response = Buffer.from(response, 'base64')
+          response = Buffer.from(response)
         }
 
         // add the fixture to the cache

packages/server/lib/files.js

@@ -4,7 +4,7 @@ const { fs } = require('./util/fs')
 module.exports = {
   readFile (projectRoot, file, options = {}) {
     const filePath = path.resolve(projectRoot, file)
-    const readFn = path.extname(filePath) === '.json' ? fs.readJsonAsync : fs.readFileAsync
+    const readFn = (path.extname(filePath) === '.json' && options.encoding !== null) ? fs.readJsonAsync : fs.readFileAsync
 
     // https://github.com/cypress-io/cypress/issues/1558
     // If no encoding is specified, then Cypress has historically defaulted
@@ -14,9 +14,7 @@ module.exports = {
     return readFn(filePath, options.encoding === undefined ? 'utf8' : options.encoding)
     .then((contents) => {
       return {
-        // For binary files, we base64 encode them for transmission over the websocket
-        // There is a matching Buffer.from() in packages/driver/src/cy/commands/files.ts
-        contents: options.encoding === null ? contents.toString('base64') : contents,
+        contents,
         filePath,
       }
     })

packages/server/lib/socket-base.ts

@@ -375,10 +375,6 @@ export class SocketBase {
               return firefoxUtil.windowFocus()
             case 'get:fixture':
               return getFixture(args[0], args[1])
-              // Buffers are base64 encoded for sending over the websocket. This is done
-              // here rather than in fixture code because net stubbing wants to send the
-              // unencoded buffer, and it also relies on the same fixture loading code.
-              .then((resp) => Buffer.isBuffer(resp) ? resp.toString('base64') : resp)
             case 'read:file':
               return files.readFile(config.projectRoot, args[0], args[1])
             case 'write:file':

packages/server/test/unit/files_spec.js

@@ -42,9 +42,9 @@ describe('lib/files', () => {
     })
 
     // https://github.com/cypress-io/cypress/issues/1558
-    it('explicit null encoding is sent to driver as base64 string', function () {
+    it('explicit null encoding is sent to driver as a Buffer', function () {
       return files.readFile(this.projectRoot, 'tests/_fixtures/ascii.foo', { encoding: null }).then(({ contents }) => {
-        expect(contents).to.eql(Buffer.from('\n').toString('base64'))
+        expect(contents).to.eql(Buffer.from('\n'))
       })
     })
 
@@ -83,10 +83,10 @@ describe('lib/files', () => {
     })
 
     // https://github.com/cypress-io/cypress/issues/1558
-    it('explicit null encoding is read from driver as base64 string', function () {
+    it('explicit null encoding is written exactly as received', function () {
       return files.writeFile(this.projectRoot, '.projects/write_file.txt', Buffer.from(''), { encoding: null }).then(() => {
         return files.readFile(this.projectRoot, '.projects/write_file.txt', { encoding: null }).then(({ contents }) => {
-          expect(contents).to.eql(Buffer.from('').toString('base64'))
+          expect(contents).to.eql(Buffer.from(''))
         })
       })
     })

packages/server/test/unit/socket_spec.js

@@ -457,9 +457,9 @@ describe('lib/socket', () => {
         return this.client.emit('backend:request', 'get:fixture', 'does-not-exist.txt', {}, cb)
       })
 
-      it('converts Buffers to base64 strings', function (done) {
+      it('passes Buffers through intact', function (done) {
         const cb = function (resp) {
-          expect(resp.response).to.eq('W3sianNvbiI6IHRydWV9XQ==')
+          expect(resp.response).to.eql(Buffer.from('[{"json": true}]'))
 
           return done()
         }