fix: ensure HMR requests can be streamed (#5200)

* feat: add mode for streamed responses

* chore: update contributors field

* chore: update contributors field

* fix: prettier

* chore: update contributors field

* chore: update contributors field

* Update src/utils/proxy.cjs

Co-authored-by: Kunal Kundu <kunal99kundu@gmail.com>

* chore: update contributors field

* chore: update contributors field

* fix: write test to ensure edge functions can be streamed

* chore: update contributors field

* fix: remove .only

* chore: update contributors field

* chore: update contributors field

* chore: update contributors field

* fix: snapshots (see #5194 (comment))

* chore: update contributors field

* chore: update contributors field

* fix: windows doesn't like overriding sites

* chore: update contributors field

* chore: update contributors field

Co-authored-by: Skn0tt <Skn0tt@users.noreply.github.com>
Co-authored-by: token-generator-app[bot] <token-generator-app[bot]@users.noreply.github.com>
Co-authored-by: Kunal Kundu <kunal99kundu@gmail.com>

Author: 3 people

package.json

@@ -79,6 +79,7 @@
     "Krasimir Nedelchev (https://github.com/kaykayehnn)",
     "Kunal Kundu (https://twitter.com/kunal__kundu)",
     "Kyle Rollins <kyleblankrollins@gmail.com> (kyleblankrollins.com)",
+    "Lana Vorozheykina",
     "Leon Hennings",
     "Liran Tal <liran.tal@gmail.com> (https://twitter.com/liran_tal)",
     "Louis DeScioli (https://twitter.com/descioli)",

src/utils/proxy.cjs

@@ -379,6 +379,26 @@ const initializeProxy = async function ({ configPath, distDir, host, port, proje
     const requestURL = new URL(req.url, `http://${req.headers.host || '127.0.0.1'}`)
     const headersRules = headersForPath(headers, requestURL.pathname)
 
+    // for streamed responses, we can't do etag generation nor error templates.
+    // we'll just stream them through!
+    const isStreamedResponse = proxyRes.headers['content-length'] === undefined
+    if (isStreamedResponse) {
+      Object.entries(headersRules).forEach(([key, val]) => {
+        res.setHeader(key, val)
+      })
+      res.writeHead(req.proxyOptions.status || proxyRes.statusCode, proxyRes.headers)
+
+      proxyRes.on('data', function onData(data) {
+        res.write(data)
+      })
+
+      proxyRes.on('end', function onEnd() {
+        res.end()
+      })
+
+      return
+    }
+
     proxyRes.on('data', function onData(data) {
       responseData.push(data)
     })

tests/integration/100.command.dev.test.cjs

@@ -420,6 +420,70 @@ test('Serves an Edge Function that transforms the response', async (t) => {
   })
 })
 
+test('Serves an Edge Function that streams the response', async (t) => {
+  await withSiteBuilder('site-with-edge-function-that-streams-response', async (builder) => {
+    const publicDir = 'public'
+    builder
+      .withNetlifyToml({
+        config: {
+          build: {
+            publish: publicDir,
+            edge_functions: 'netlify/edge-functions',
+          },
+          edge_functions: [
+            {
+              function: 'stream',
+              path: '/stream',
+            },
+          ],
+        },
+      })
+      .withEdgeFunction({
+        handler: async () => {
+          // eslint-disable-next-line no-undef -- `ReadableStream` is a global in Deno
+          const body = new ReadableStream({
+            async start(controller) {
+              setInterval(() => {
+                const msg = new TextEncoder().encode(`${Date.now()}\r\n`)
+                controller.enqueue(msg)
+              }, 100)
+
+              setTimeout(() => {
+                controller.close()
+              }, 500)
+            },
+          })
+
+          return new Response(body, {
+            headers: {
+              'content-type': 'text/event-stream',
+            },
+            status: 200,
+          })
+        },
+        name: 'stream',
+      })
+
+    await builder.buildAsync()
+
+    await withDevServer({ cwd: builder.directory }, async (server) => {
+      let numberOfChunks = 0
+
+      await new Promise((resolve, reject) => {
+        const stream = got.stream(`${server.url}/stream`)
+        stream.on('data', () => {
+          numberOfChunks += 1
+        })
+        stream.on('end', resolve)
+        stream.on('error', reject)
+      })
+
+      // streamed responses arrive in more than one batch
+      t.not(numberOfChunks, 1)
+    })
+  })
+})
+
 test('redirect with country cookie', async (t) => {
   await withSiteBuilder('site-with-country-cookie', async (builder) => {
     builder

tests/integration/snapshots/320.command.help.test.cjs.md

@@ -21,7 +21,7 @@ Generated by [AVA](https://avajs.dev).
       $ completion   (Beta) Generate shell completion script␊
       $ deploy       Create a new deploy from the contents of a folder␊
       $ dev          Local dev server␊
-      $ env          (Beta) Control environment variables for the current site␊
+      $ env          Control environment variables for the current site␊
       $ functions    Manage netlify functions␊
       $ recipes      (Beta) Create and modify files in a project using pre-defined␊
                      recipes␊