// Module: FileLineReader
// Constructor: FileLineReader(filename, bufferSize = 8192)
// Methods: hasNextLine() -> boolean
// nextLine() -> String
//
//
var fs = require("fs");
var sys = require("sys");
exports.FileLineReader = function(filename, bufferSize) {
if(!bufferSize) {
bufferSize = 8192;
}
//private:
var currentPositionInFile = 0;
var buffer = "";
var fd = fs.openSync(filename, "r");
// return -1
// when EOF reached
// fills buffer with next 8192 or less bytes
var fillBuffer = function(position) {
var res = fs.readSync(fd, bufferSize, position, "ascii");
buffer += res[0];
if (res[1] == 0) {
return -1;
}
return position + res[1];
};
currentPositionInFile = fillBuffer(0);
//public:
this.hasNextLine = function() {
while (buffer.indexOf("\n") == -1) {
currentPositionInFile = fillBuffer(currentPositionInFile);
if (currentPositionInFile == -1) {
return false;
}
}
if (buffer.indexOf("\n") > -1) {
return true;
}
return false;
};
//public:
this.nextLine = function() {
var lineEnd = buffer.indexOf("\n");
var result = buffer.substring(0, lineEnd);
buffer = buffer.substring(result.length + 1, buffer.length);
return result;
};
return this;
};
And some TestCode:
var assert = require("assert"),
sys = require("sys"),
flr = require("./FileLineReader");
try {
var reader = new flr.FileLineReader("top-5.txt", 10);
sys.debug(__filename + " First line...");
assert.equal(reader.hasNextLine(), true);
assert.equal(reader.nextLine(), "yahoo.com");
sys.debug(__filename + " Next line...");
assert.equal(reader.hasNextLine(), true);
assert.equal(reader.nextLine(), "youtube.com");
sys.debug(__filename + " Next line...");
assert.equal(reader.hasNextLine(), true);
assert.equal(reader.nextLine(), "facebook.com");
sys.debug(__filename + " Next line...");
assert.equal(reader.hasNextLine(), true);
assert.equal(reader.nextLine(), "live.com");
assert.equal(reader.hasNextLine(), true);
assert.equal(reader.nextLine(), "msn.com");
assert.equal(reader.hasNextLine(), false);
} catch (err) {
sys.debug(__filename + ": ERROR: " + err);
}
The testdata file top-5.txt looked like this:
yahoo.com youtube.com facebook.com live.com msn.com
This code works perfectly for what I needed. I am using it within some tools that I would like to release to GitHub eventually. Would you mind releasing the code under MIT license, or another?
ReplyDelete- Josh Du Lac
joshdulac.com
I like to close my files early to keep the number of open file descriptors to a minimum so I added the following 'public' method:
ReplyDeletethis.close = function(cb) {
fs.close(fd, cb);
}
what about CRLF? i mean support files with windows EOL
ReplyDeleteThanks for this code. It is very helpful for me and my research.
ReplyDeleteWorks well for loading in enormous files - added an encoding parameter to handle other file types (obviously, no big deal).
ReplyDeleteHey Dirk,
ReplyDeleteCouldn't find your email but I made this into an NPM package (https://github.com/davidbenhaim/FileLineReader). You're listed as one of the authors.
- David
your readSync usage appears to be currently deprecated. i changed things to use buffers & made it a class 'cuz i'm a .js noob and don't really know how to deal with exports:
ReplyDeleteconst fs = require('fs')
class LineReader {
constructor (filename, bufSize) {
this.bufferSize = bufSize ? bufSize : 8192;
this.fd = fs.openSync(filename, "r");
this.buffer = Buffer.alloc(this.bufferSize);
this.filePos = 0;
this.bufferPos = 0;
this.bufferBytes = 0;
this.fillBuffer()
}
// fills buffer with next this.bufferSize bytes
fillBuffer () {
// use buffered readSync instead:
let bytesRead = fs.readSync(this.fd, this.buffer, 0, this.bufferSize, this.filePos)
this.bufferBytes = bytesRead
this.filePos += bytesRead
this.bufferPos = 0
return bytesRead
};
//public:
nextLine() {
if (this.bufferBytes <= 0) {
// last fillBuffer() was @ or past end of file
return null
}
let line = ""
let lineEnd = -1;
while ((lineEnd = this.buffer.indexOf("\n", this.bufferPos)) < 0) {
line += this.buffer.toString("utf8", this.bufferPos, this.bufferBytes)
if (this.fillBuffer() <= 0) {
return line;
}
}
line += this.buffer.toString("utf8", this.bufferPos, lineEnd)
this.bufferPos = lineEnd + 1
return line;
};
close(cb) {
fs.close(this.fd, cb);
}
};
// make a 3 line test file with no trailing newline:
var path = "bozo.txt"
var data = "one line\nanother line\nand another"
fs.writeFileSync(path, data)
// test using small buffer size to make sure we cross boundaries properly:
var line = ""
reader = new LineReader(path, 4)
while ((line = reader.nextLine()) != null) {
console.log(line)
}
reader.close()
console.log("Done !")
I got an error that the close(cb) method required a callback, so I changed it to the following code and everything worked:
ReplyDeleteclose() {
fs.close(this.fd, function(err) {
if (err) throw err;
console.log("file closed.");
});
}