Add "decompress" response utility

lib/web/fetch/decompress.js

@@ -0,0 +1,80 @@
+const { pipeline } = require('node:stream')
+const zlib = require('node:zlib')
+const { redirectStatusSet, nullBodyStatus } = require('./constants')
+const { createInflate } = require('./util')
+
+/**
+ * Decompress the given response body.
+ * @param {Request} request
+ * @param {Response} response
+ * @returns {ReadableStream<Uint8Array> | null}
+ */
+function decompress (request, response) {
+  const contentEncoding = response.headers.get('content-encoding')
+
+  if (!contentEncoding) {
+    return response.body
+  }
+
+  // https://www.rfc-editor.org/rfc/rfc7231#section-3.1.2.1
+  // "All content-coding values are case-insensitive..."
+  const codings = contentEncoding
+    .toLowerCase()
+    .split(',')
+    .map((coding) => coding.trim())
+
+  if (codings.length === 0) {
+    return response.body
+  }
+
+  const willFollow =
+    response.headers.get('location') &&
+    request.redirect === 'follow' &&
+    redirectStatusSet.has(response.status)
+
+  if (
+    request.method === 'HEAD' ||
+    request.method === 'CONNECT' ||
+    nullBodyStatus.includes(response.status) ||
+    willFollow
+  ) {
+    return response.body
+  }
+
+  const decoders = []
+
+  for (let i = codings.length - 1; i >= 0; --i) {
+    const coding = codings[i]
+
+    // https://www.rfc-editor.org/rfc/rfc9112.html#section-7.2
+    if (coding === 'x-gzip' || coding === 'gzip') {
+      decoders.push(
+        zlib.createGunzip({
+          // Be less strict when decoding compressed responses, since sometimes
+          // servers send slightly invalid responses that are still accepted
+          // by common browsers.
+          // Always using Z_SYNC_FLUSH is what cURL does.
+          flush: zlib.constants.Z_SYNC_FLUSH,
+          finishFlush: zlib.constants.Z_SYNC_FLUSH
+        })
+      )
+    } else if (coding === 'deflate') {
+      decoders.push(createInflate())
+    } else if (coding === 'br') {
+      decoders.push(zlib.createBrotliDecompress())
+    } else {
+      decoders.length = 0
+      break
+    }
+  }
+
+  if (decoders.length === 0) {
+    return response.body
+  }
+
+  return pipeline(response.body, ...decoders)
+}
+
+module.exports = {
+  decompress
+}