exebook exebook - 1 month ago 11
Node.js Question

Stdin read fails on some input

#!/usr/bin/env node

function stdinReadSync() {
var b = new Buffer(1024);
var data = '';

while (true) {
var n = require('fs').readSync(process.stdin.fd, b, 0, b.length);
if (!n) break;
data += b.toString(null, 0, n);
}
return data;
}

var s = stdinReadSync();
console.log(s.length);


The above code (taken from Stackoverflow) works just fine if you feed it with
echo
,
cat
,
ls
, but will fail with
curl
output.

$ echo abc | ./test.js
4

$ ls | ./test.js
1056

$ cat 1.txt | ./test.js
78

$ curl -si wikipedia.org | ./test.js
fs.js:725
var r = binding.read(fd, buffer, offset, length, position);
^

Error: EAGAIN: resource temporarily unavailable, read
at Error (native)
at Object.fs.readSync (fs.js:725:19)
at stdinReadSync (/home/ya/2up/api/stdinrd.js:8:29)
at Object.<anonymous> (/home/ya/2up/api/stdinrd.js:15:9)
at Module._compile (module.js:541:32)
at Object.Module._extensions..js (module.js:550:10)
at Module.load (module.js:456:32)
at tryModuleLoad (module.js:415:12)
at Function.Module._load (module.js:407:3)
at Function.Module.runMain (module.js:575:10)
(23) Failed writing body


Why? How to fix?

Answer

It's a bit of a hack, but this seems to work:

var n = require('fs').readSync(0, b, 0, b.length);

I think (pure conjecture) that process.stdin.fd is a getter that, when referenced, will put stdin in non-blocking mode (which is causing the error). When you use the file descriptor directly, you work around that.

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