From b3e9ef244a7542cdc9f6975fdc183b263bd6f305 Mon Sep 17 00:00:00 2001
From: Nathan Friedly <nathan@nfriedly.com>
Date: Wed, 20 Dec 2023 15:17:28 -0500
Subject: [PATCH] WIP Brotli support may be related to
 https://github.com/nfriedly/node-unblocker/issues/243

---
 lib/decompress.js | 41 ++++++++++++++++++++++++++++-------------
 1 file changed, 28 insertions(+), 13 deletions(-)

diff --git a/lib/decompress.js b/lib/decompress.js
index 7f25fc37..3ddbb50f 100644
--- a/lib/decompress.js
+++ b/lib/decompress.js
@@ -5,14 +5,26 @@ var zlib = require("zlib");
 var contentTypes = require("./content-types.js");
 var debug = require("debug")("unblocker:decompress");
 
+const SUPPORTED_ENCODINGS = [
+  'deflate',
+  'gzip',
+  'br' // brotli
+];
+
+const REQUESTED_ENCODINGS = [
+  // deflate is tricky, so we don't request it
+  'gzip',
+  'br'
+]
+
 module.exports = function (config) {
   function acceptableCompression(data) {
-    // deflate is tricky so we're only going to ask for gzip if the client allows it
-    if (
-      data.headers["accept-encoding"] &&
-      data.headers["accept-encoding"].includes("gzip")
-    ) {
-      data.headers["accept-encoding"] = "gzip";
+    var encodings = (data.headers["accept-encoding"] || '')
+      .split(',')
+      .map(s => s.trim())
+      .filter(s => REQUESTED_ENCODINGS.includes(s));
+    if (encodings.length) {
+      data.headers["accept-encoding"] = encodings.join(', ');
     } else {
       delete data.headers["accept-encoding"];
     }
@@ -31,11 +43,8 @@ module.exports = function (config) {
       return false;
     }
 
-    // decompress if it's gzipped or deflate'd
-    return (
-      headers["content-encoding"] == "gzip" ||
-      headers["content-encoding"] == "deflate"
-    );
+    // decompress if it's in a supported encoding
+    return SUPPORTED_ENCODINGS.includes(headers["content-encoding"]);
   }
 
   function decompressResponse(data) {
@@ -54,6 +63,11 @@ module.exports = function (config) {
       var placeHolder = new PassThrough();
       data.stream = placeHolder;
 
+      const encoding = data.headers["content-encoding"];
+
+      // we're decoding it here, so this won't by the time it gets to the client
+      delete data.headers["content-encoding"];
+
       var handleData = function handleData() {
         var firstChunk = sourceStream.read();
 
@@ -65,11 +79,13 @@ module.exports = function (config) {
         }
 
         var decompressStream;
-        if (data.headers["content-encoding"] == "deflate") {
+        if (encoding == "deflate") {
           // https://github.com/nfriedly/node-unblocker/issues/12
           // inflateRaw seems to work here wheras inflate and unzip do not.
           // todo: validate this against other sites - if some require raw and others require non-raw, then maybe just rewrite the accept-encoding header to gzip only
           decompressStream = zlib.createInflateRaw();
+        } else if (encoding == 'br') {
+          decompressStream = zlib.createBrotliDecompress();
         } else {
           decompressStream = zlib.createUnzip();
         }
@@ -83,7 +99,6 @@ module.exports = function (config) {
       // if we do get data, create a decompression stream and pipe through it
       sourceStream.once("readable", handleData);
 
-      delete data.headers["content-encoding"];
     }
   }