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fix: Gzip comment with header checksum produces corrupt streams

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The Gzip operation manually set the FCOMMENT flag bit after zlibjs
had already calculated the header CRC16, corrupting the checksum.
Fix by setting options.flags.fcomment before calling compress(),
letting zlibjs handle the flag internally.

Closes #2243
This commit is contained in:
Willi Ballenthin 2026-03-24 09:31:47 +01:00
parent b0fa1f8d1b
commit ceeefda024
2 changed files with 61 additions and 3 deletions
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4
src/core/operations/Gzip.mjs
View File

@ -74,13 +74,11 @@ class Gzip extends Operation {
}
if (comment.length) {
options.flags.comment = true;
options.flags.fcomment = true;
options.comment = comment;
}
const gzipObj = new Zlib.Gzip(new Uint8Array(input), options);
const compressed = new Uint8Array(gzipObj.compress());
if (options.flags.comment && !(compressed[3] & 0x10)) {
compressed[3] |= 0x10;
}
return compressed.buffer;
}

60
tests/operations/tests/Gzip.mjs
View File

@ -86,4 +86,64 @@ TestRegister.addTests([
}
]
},
{
name: "Gzip: Comment with checksum round-trips through Gunzip",
input: "hello hello hello",
expectedOutput: "hello hello hello",
recipeConfig: [
{
op: "Gzip",
args: ["Dynamic Huffman Coding", "", "test", true]
},
{
op: "Gunzip",
args: []
}
]
},
{
name: "Gzip: Filename and comment with checksum round-trips through Gunzip",
input: "The quick brown fox jumped over the slow dog",
expectedOutput: "The quick brown fox jumped over the slow dog",
recipeConfig: [
{
op: "Gzip",
args: ["Dynamic Huffman Coding", "file.txt", "a comment", true]
},
{
op: "Gunzip",
args: []
}
]
},
{
name: "Gzip: No comment, with checksum round-trips through Gunzip",
input: "The quick brown fox jumped over the slow dog",
expectedOutput: "The quick brown fox jumped over the slow dog",
recipeConfig: [
{
op: "Gzip",
args: ["Dynamic Huffman Coding", "", "", true]
},
{
op: "Gunzip",
args: []
}
]
},
{
name: "Gzip: No options round-trips through Gunzip",
input: "The quick brown fox jumped over the slow dog",
expectedOutput: "The quick brown fox jumped over the slow dog",
recipeConfig: [
{
op: "Gzip",
args: ["Dynamic Huffman Coding", "", "", false]
},
{
op: "Gunzip",
args: []
}
]
},
]);