Repository navigation
node:zlib: dictionary option is silently ignored by deflate/inflate #37035
Description
Version: Deno 2.9.4 (aarch64-apple-darwin)
The dictionary option of node:zlib is silently ignored. Compressing with a dictionary produces byte-for-byte the same output as compressing without one, and inflating ignores the dictionary too, so streams compressed with a preset dictionary by Node (or any zlib) can't be decompressed in Deno. Applies to both raw (deflateRawSync/inflateRawSync) and zlib-wrapped (deflateSync) formats.
import zlib from "node:zlib";
const dictionary = Buffer.from("hello world hello world");
const input = Buffer.from("hello world");
const withDict = zlib.deflateRawSync(input, { dictionary });
const noDict = zlib.deflateRawSync(input);
console.log("with dictionary:", withDict.toString("hex"));
console.log("no dictionary: ", noDict.toString("hex"));
console.log("identical:", withDict.equals(noDict));
// Output produced by Node for the same input + dictionary:
const fromNode = Buffer.from("43620200", "hex");
try {
console.log("inflate Node output:", zlib.inflateRawSync(fromNode, { dictionary }).toString());
} catch (e) {
console.log("inflate Node output threw:", e.message);
}Node v24.18.1:
with dictionary: 43620200
no dictionary: cb48cdc9c95728cf2fca490100
identical: false
inflate Node output: hello world
Deno 2.9.4:
with dictionary: cb48cdc9c95728cf2fca490100
no dictionary: cb48cdc9c95728cf2fca490100
identical: true
inflate Node output threw: invalid distance too far back
Related: #29638 (closed node:zlib tracking issue).
Activity