async-read-lines v0.1.0

async-read-lines

Library for asynchronous line-by-line reading from big text files. Ideal for iterating over the log file entries.

Installation

npm install async-read-lines

Example

How to count entries in the server access log file:

var asyncReadLines = require('async-read-lines');

var count = 0;

asyncReadLines('access.log', function (line, callback) {
    count += 1;

    callback();
}, function (err) {
    console.log(count);
});

Method

Complete signature of the method:

asyncReadLines(file, [options], lineCallback, doneCallback)

options := { }
    encoding - 'utf8' (default) or 'ascii',
    lineTerminator - any character represented by single byte in specified
                     encoding, default is '\n'
lineCallback := function (line, callback) { ... }
doneCallback := function (err) { ... }

Details

The library reads file chunks one by one and saves them into the buffer. When the line terminator is detected in the buffer, the content of the buffer is decoded and the line callback is called. Reading is continued when the callback resumes reading by calling supplied callback.

This approach allows to control reading process, which is necessary while reading very big files and execute asynchronous tasks for every line.

The method is safe for the Unicode sequences as the buffer is binary and line is decoded before calling the callback.

For empty file the method calls lineCallback once with empty string.