posix-read
v0.2.0
Published
Do POSIX read on files and sockets with Node.js
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posix-read
Do POSIX read on files and sockets with Node.js.
Motivation
In Node.js, reading from sockets is performed using uv_read_start()
from
libuv
. This consumes data from the file descriptor whenever it is available,
but consumes it all. There is not built-in way to read a fixed amount, let's say
n
bytes.
This is a problem when you want to read only n
bytes and leave the rest in
the socket (so that, for instance, another process reads remaining data).
posix-read is a module to perform a POSIX read on a socket. That way, only n
bytes are brought up to user-space and the rest remains in kernel-space, ready
to be read(2)
by any other process.
Usage
Warning
For posix-read to work, your code must prevent libuv
to start reading from the
socket. That means the socket must have the pauseOnCreate
property.
In practice: if you get the socket from a net.Server
, this server has to be
created with the pauseOnConnect
set to true
.
Example
const net = require('net');
const posixRead = require('posix-read');
const server = net.createServer({ pauseOnConnect: true }, function (socket) {
// Just got an incoming connection. Let's read 10 bytes from it (but DO NOT
// consume more than 10 bytes from the socket).
posixRead.read(socket, 10, function (err, buffer) {
if (err && err.endOfFile)
return process.stderr.write('peer sent less than 10 bytes\n');
if (err)
return process.stderr.write(`error: ${err}\n`);
return process.stdout.write(`10 first bytes: ${buffer}\n`);
});
}).listen(1234);
Error types
If a problem happens, the Error
object passed to the callback has helpful
properties:
error.badStream === true
if the socket is malformed or its file descriptor is not availableerror.endOfFile === true
if the end-of-file was reached before having read all the bytes requestederror.systemError === true
in case of a system call error (in such a case,error.message
should contain more useful information.
License
MIT license