From 7f1efa17cb91049f78b58e4826f9837e58a5b293 Mon Sep 17 00:00:00 2001
From: rom1504 <rom1504@users.noreply.github.com>
Date: Tue, 31 Mar 2026 05:52:32 +0000
Subject: [PATCH] Use sync zlib in packet compression to avoid uncaught errors
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Node's async zlib (deflate/unzip) creates internal C++ Zlib handles
that run on the libuv thread pool. When a client disconnects while
decompression is in progress, the C++ callback fires after the JS
error listener is removed, causing an uncaught exception:

  Uncaught Error: unexpected end of file
    at Zlib.zlibOnError [as onerror]

This is a known Node.js issue — see:
- nodejs/node#62325 (use-after-free fix for reset during write)
- nodejs/node#61202 (zlib stream corruption with multiple instances)
- nodejs/node#43868 (uncaught zlib exception in fetch)

Switch to deflateSync/unzipSync which complete synchronously with no
lingering C++ handles. Each call processes one MC packet (~few KB),
so event loop impact is negligible.

Also wrap gunzipSync in minecraft.js NBT parsing with try/catch.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
---
 src/datatypes/minecraft.js    |  7 ++++++-
 src/transforms/compression.js | 32 +++++++++++++++++---------------
 2 files changed, 23 insertions(+), 16 deletions(-)

diff --git a/src/datatypes/minecraft.js b/src/datatypes/minecraft.js
index 83ab50e8a..1b6161862 100644
--- a/src/datatypes/minecraft.js
+++ b/src/datatypes/minecraft.js
@@ -56,7 +56,12 @@ function readCompressedNbt (buffer, offset) {
 
   const compressedNbt = buffer.slice(offset + 2, offset + 2 + length)
 
-  const nbtBuffer = zlib.gunzipSync(compressedNbt) // TODO: async
+  let nbtBuffer
+  try {
+    nbtBuffer = zlib.gunzipSync(compressedNbt) // TODO: async
+  } catch (err) {
+    throw new PartialReadError('zlib decompress failed: ' + err.message)
+  }
 
   const results = nbt.proto.read(nbtBuffer, 0, 'nbt')
   return {
diff --git a/src/transforms/compression.js b/src/transforms/compression.js
index 45b063522..718e7fed9 100644
--- a/src/transforms/compression.js
+++ b/src/transforms/compression.js
@@ -20,14 +20,16 @@ class Compressor extends Transform {
 
   _transform (chunk, enc, cb) {
     if (chunk.length >= this.compressionThreshold) {
-      zlib.deflate(chunk, (err, newChunk) => {
-        if (err) { return cb(err) }
+      try {
+        const newChunk = zlib.deflateSync(chunk)
         const buf = Buffer.alloc(sizeOfVarInt(chunk.length) + newChunk.length)
         const offset = writeVarInt(chunk.length, buf, 0)
         newChunk.copy(buf, offset)
         this.push(buf)
         return cb()
-      })
+      } catch (err) {
+        return cb(err)
+      }
     } else {
       const buf = Buffer.alloc(sizeOfVarInt(0) + chunk.length)
       const offset = writeVarInt(0, buf, 0)
@@ -52,23 +54,23 @@ class Decompressor extends Transform {
       this.push(chunk.slice(size))
       return cb()
     } else {
-      zlib.unzip(chunk.slice(size), { finishFlush: 2 /*  Z_SYNC_FLUSH = 2, but when using Browserify/Webpack it doesn't exist */ }, (err, newBuf) => { /** Fix by lefela4. */
-        if (err) {
-          if (!this.hideErrors) {
-            console.error('problem inflating chunk')
-            console.error('uncompressed length ' + value)
-            console.error('compressed length ' + chunk.length)
-            console.error('hex ' + chunk.toString('hex'))
-            console.log(err)
-          }
-          return cb()
-        }
+      try {
+        const newBuf = zlib.unzipSync(chunk.slice(size), { finishFlush: 2 })
         if (newBuf.length !== value && !this.hideErrors) {
           console.error('uncompressed length should be ' + value + ' but is ' + newBuf.length)
         }
         this.push(newBuf)
         return cb()
-      })
+      } catch (err) {
+        if (!this.hideErrors) {
+          console.error('problem inflating chunk')
+          console.error('uncompressed length ' + value)
+          console.error('compressed length ' + chunk.length)
+          console.error('hex ' + chunk.toString('hex'))
+          console.log(err)
+        }
+        return cb()
+      }
     }
   }
 }