zlib: the gzip header#os is weird in macos

[yorkie]

• Version: v8.9.0+
• Platform: macos
• Subsystem: zlib

To reproduce, see the following source code:

var fs = require('fs');
var fstream = fs.createReadStream('some-file');
var gzip = new require('zlib').Gzip();
gzip.on('data', function(chunk) {
  console.log(chunk);
});
fstream.pipe(gzip);

It would output the gzip format header in first log as:

<Buffer 1f 8b 08 00 00 00 00 00 00 13>

In the GZIP RFC, the flag#13 is marked to "Acorn RISCOS", this might be not correct?

/cc @indutny

[yorkie]

I used the zlib in the same machine to write a simple program outside of Node.js, the generated header is:

<Buffer 1f 8b 08 00 00 00 00 00 00 03>

The 03 means Unix system, it seems right than 13 :)

[bnoordhuis]

Note that's 0x13, not 13 in decimal. 0x13 or 19 in decimal is zlib's identifier for macos >= 10. The "Macintosh" the RFC mentions is classic macos (macos <= 9).

[yorkie]

Sorry, my mistake :)

[bnoordhuis]

No problem. :-)

[dennisvang]

Note that's 0x13, not 13 in decimal. 0x13 or 19 in decimal is zlib's identifier for macos >= 10. The "Macintosh" the RFC mentions is classic macos (macos <= 9).

@bnoordhuis Sorry to bother you regarding this old post, but would you happen to know of a reference for this? RFC 1952 does not mention 19 (decimal), and I've not been able to track down another source.