fix: adds html injections to dev proxy

src/commands/base-command.ts

@@ -7,7 +7,6 @@ import { format } from 'util'
 
 import { DefaultLogger, Project } from '@netlify/build-info'
 import { NodeFS, NoopLogger } from '@netlify/build-info/node'
-// @ts-expect-error TS(7016) FIXME: Could not find a declaration file for module '@net... Remove this comment to see the full error message
 import { resolveConfig } from '@netlify/config'
 import { Command, Help, Option } from 'commander'
 // @ts-expect-error TS(7016) FIXME: Could not find a declaration file for module 'debu... Remove this comment to see the full error message

src/commands/dev/dev.ts

@@ -1,6 +1,5 @@
 import process from 'process'
 
-// @ts-expect-error TS(7016) FIXME: Could not find a declaration file for module '@net... Remove this comment to see the full error message
 import { applyMutations } from '@netlify/config'
 import { Option, OptionValues } from 'commander'
 

src/commands/types.d.ts

@@ -1,4 +1,5 @@
-import { NetlifyTOML } from '@netlify/build-info'
+import type { NetlifyConfig } from "@netlify/build";
+import type { NetlifyTOML } from '@netlify/build-info'
 import type { NetlifyAPI } from 'netlify'
 
 import StateConfig from '../utils/state-config.js'
@@ -14,16 +15,37 @@ export type NetlifySite = {
   set id(id: string): void
 }
 
-type PatchedConfig = NetlifyTOML & {
+type PatchedConfig = NetlifyTOML & Pick<NetlifyConfig, 'images'> & {
   functionsDirectory?: string
   build: NetlifyTOML['build'] & {
     functionsSource?: string
   }
   dev: NetlifyTOML['dev'] & {
     functions?: string
+    processing?: DevProcessing
   }
 }
 
+type DevProcessing = {
+  html?: HTMLProcessing
+}
+
+type HTMLProcessing = {
+  injections?: HTMLInjection[]
+}
+
+type HTMLInjection = {
+  /**
+   * The location at which the `html` will be injected.
+   * Defaults to `before_closing_head_tag` which will inject the HTML before the </head> tag.
+   */
+  location?: 'before_closing_head_tag' | 'before_closing_body_tag',
+  /**
+   * The injected HTML code.
+   */
+  html: string
+}
+
 type EnvironmentVariableScope = 'builds' | 'functions' | 'runtime' | 'post_processing'
 type EnvironmentVariableSource = 'account' | 'addons' | 'configFile' | 'general' |  'internal' | 'ui'
 

src/utils/proxy.ts

@@ -26,7 +26,7 @@ import pFilter from 'p-filter'
 import toReadableStream from 'to-readable-stream'
 
 import { BaseCommand } from '../commands/index.js'
-import { $TSFixMe } from '../commands/types.js'
+import { $TSFixMe, NetlifyOptions } from '../commands/types.js'
 import {
   handleProxyRequest,
   initializeProxy as initializeEdgeFunctionsProxy,
@@ -47,8 +47,11 @@ import { signRedirect } from './sign-redirect.js'
 import { Request, Rewriter, ServerSettings } from './types.js'
 
 const gunzip = util.promisify(zlib.gunzip)
+const gzip = util.promisify(zlib.gzip)
 const brotliDecompress = util.promisify(zlib.brotliDecompress)
+const brotliCompress = util.promisify(zlib.brotliCompress)
 const deflate = util.promisify(zlib.deflate)
+const inflate = util.promisify(zlib.inflate)
 const shouldGenerateETag = Symbol('Internal: response should generate ETag')
 
 const decompressResponseBody = async function (body: Buffer, contentEncoding = ''): Promise<Buffer> {
@@ -58,12 +61,48 @@ const decompressResponseBody = async function (body: Buffer, contentEncoding = '
     case 'br':
       return await brotliDecompress(body)
     case 'deflate':
-      return await deflate(body)
+      return await inflate(body)
     default:
       return body
   }
 }
 
+const compressResponseBody = async function (body: string, contentEncoding = ''): Promise<Buffer> {
+  switch (contentEncoding) {
+    case 'gzip':
+      return await gzip(body)
+    case 'br':
+      return await brotliCompress(body)
+    case 'deflate':
+      return await deflate(body)
+    default:
+      return Buffer.from(body, 'utf8')
+  }
+}
+
+type HTMLInjections = NonNullable<NonNullable<NetlifyOptions['config']['dev']['processing']>['html']>['injections']
+
+const injectHtml = async function (
+  responseBody: Buffer,
+  proxyRes: http.IncomingMessage,
+  htmlInjections: HTMLInjections,
+): Promise<Buffer> {
+  const decompressedBody: Buffer = await decompressResponseBody(responseBody, proxyRes.headers['content-encoding'])
+  const bodyWithInjections: string = (htmlInjections ?? []).reduce((accum, htmlInjection) => {
+    if (!htmlInjection.html || typeof htmlInjection.html !== 'string') {
+      return accum
+    }
+    const location = htmlInjection.location ?? 'before_closing_head_tag'
+    if (location === 'before_closing_head_tag') {
+      accum = accum.replace('</head>', `${htmlInjection.html}</head>`)
+    } else if (location === 'before_closing_body_tag') {
+      accum = accum.replace('</body>', `${htmlInjection.html}</body>`)
+    }
+    return accum
+  }, decompressedBody.toString())
+  return await compressResponseBody(bodyWithInjections, proxyRes.headers['content-encoding'])
+}
+
 // @ts-expect-error TS(7006) FIXME: Parameter 'errorBuffer' implicitly has an 'any' ty... Remove this comment to see the full error message
 const formatEdgeFunctionError = (errorBuffer, acceptsHtml) => {
   const {
@@ -416,25 +455,16 @@ const reqToURL = function (req, pathname) {
 const MILLISEC_TO_SEC = 1e3
 
 const initializeProxy = async function ({
-  // @ts-expect-error TS(7031) FIXME: Binding element 'configPath' implicitly has an 'any... Remove this comment to see the full error message
   config,
-  // @ts-expect-error TS(7031) FIXME: Binding element 'distDir' implicitly has an 'any... Remove this comment to see the full error message
   configPath,
-  // @ts-expect-error TS(7031) FIXME: Binding element 'env' implicitly has an 'any... Remove this comment to see the full error message
   distDir,
-  // @ts-expect-error TS(7031) FIXME: Binding element 'host' implicitly has an 'any... Remove this comment to see the full error message
   env,
-  // @ts-expect-error TS(7031) FIXME: Binding element 'imageProxy' implicitly has an 'any... Remove this comment to see the full error message
   host,
-  // @ts-expect-error TS(7031) FIXME: Binding element 'port' implicitly has an 'any... Remove this comment to see the full error message
   imageProxy,
-  // @ts-expect-error TS(7031) FIXME: Binding element 'projectDir' implicitly has an 'any... Remove this comment to see the full error message
   port,
-  // @ts-expect-error TS(7031) FIXME: Binding element 'siteInfo' implicitly has an 'any... Remove this comment to see the full error message
   projectDir,
-  // @ts-expect-error TS(7031) FIXME: Binding element 'config' implicitly has an 'any... Remove this comment to see the full error message
   siteInfo,
-}) {
+}: { config: NetlifyOptions['config'] } & Record<string, $TSFixMe>) {
   const proxy = httpProxy.createProxyServer({
     selfHandleResponse: true,
     target: {
@@ -568,10 +598,18 @@ const initializeProxy = async function ({
     const requestURL = new URL(req.url, `http://${req.headers.host || '127.0.0.1'}`)
     const headersRules = headersForPath(headers, requestURL.pathname)
 
+    const htmlInjections =
+      config.dev?.processing?.html?.injections &&
+      config.dev.processing.html.injections.length !== 0 &&
+      proxyRes.headers?.['content-type']?.startsWith('text/html')
+        ? config.dev.processing.html.injections
+        : undefined
+
     // for streamed responses, we can't do etag generation nor error templates.
     // we'll just stream them through!
+    // when html_injections are present in dev config, we can't use streamed response
     const isStreamedResponse = proxyRes.headers['content-length'] === undefined
-    if (isStreamedResponse) {
+    if (isStreamedResponse && !htmlInjections) {
       Object.entries(headersRules).forEach(([key, val]) => {
         // @ts-expect-error TS(2345) FIXME: Argument of type 'unknown' is not assignable to pa... Remove this comment to see the full error message
         res.setHeader(key, val)
@@ -596,7 +634,7 @@ const initializeProxy = async function ({
 
     proxyRes.on('end', async function onEnd() {
       // @ts-expect-error TS(7005) FIXME: Variable 'responseData' implicitly has an 'any[]' ... Remove this comment to see the full error message
-      const responseBody = Buffer.concat(responseData)
+      let responseBody = Buffer.concat(responseData)
 
       // @ts-expect-error TS(2339) FIXME: Property 'proxyOptions' does not exist on type 'In... Remove this comment to see the full error message
       let responseStatus = req.proxyOptions.status || proxyRes.statusCode
@@ -640,7 +678,17 @@ const initializeProxy = async function ({
         return res.end()
       }
 
-      res.writeHead(responseStatus, proxyRes.headers)
+      let proxyResHeaders = proxyRes.headers
+
+      if (htmlInjections) {
+        responseBody = await injectHtml(responseBody, proxyRes, htmlInjections)
+        proxyResHeaders = {
+          ...proxyResHeaders,
+          'content-length': String(responseBody.byteLength),
+        }
+      }
+
+      res.writeHead(responseStatus, proxyResHeaders)
 
       if (responseStatus !== 304) {
         res.write(responseBody)