line-chomper

Chomps utf-8 based byte stream into lines.

  • Interactive line processing (callback-based, no loading the entire file into RAM)
  • Optionally, return all lines in an array (detailed or raw mode)
  • Interactively interrupt streaming, or perform map/filter like processing
  • Detect any newline convention (PC/Mac/Linux)
  • Correct eof / last line treatment
  • Correct handling of multi-byte UTF-8 characters
  • Retrieve byte offset and byte length information on per-line basis
  • Random access, using line-based or byte-based offsets
  • Automatically map line-offset information, to speed up random access
  • Zero dependencies
  • Tests

Basic usage

var chomp = require("line-chomper").chomp;

chomp("/path/to/file.txt", function (err, lines) {
    lines.forEach(function (line) {
        console.log(line);
    });
});

Interactive processing

chomp(
    "/path/to/large-file.txt",
    function (line, offset, sizeInBytes) {
        console.log("At " + offset + ": " + line + " (size: " + sizeInBytes + " b)");
    },
    function (err, count) {
        console.log("Processed " + count + " lines");
    });
});

Process arbitrary stream

var req = http.request({ host: url }, function (resStream) {
    chomp(resStream, function (err, lines) {
        /* process lines */
    });
});

req.on("error", function (e) {
    console.log("problem with request: " + e.message);
});

req.end();

Map / filter using lineCallback

var counter = 0;
chomp(
    "/path/to/file.txt",
    {
        returnLines: true,
        lineCallback: function (line) {
            if (counter === 10) {
                return false; // stop streaming
            }
            counter++;
            if (!line) {
                return null; // filter out
            }
            return line.toUpperCase(); // map to uppercase
        }
    },
    function (err, lines) {
        console.log(lines); // First 10 non-empty lines, converted to uppercase
    });
});

Random access based on line numbers (also can accept byte offsets)

chomp(
    fs.createReadStream("path/to/file"),
    {
        fromLine: 100,
        toLine: 199
    },
    function (err, lines) {
    }
);

Map line offsets to speed up random access in large files

require("line-chomper").mapLineOffsets(fileName, function (err, lineOffsets) {
    redis.save("offsets." + fileName, lineOffsets);
});

// later...

function getExcerpt(fileName, start, count, callback) {
    redis.get("offsets." + fileName, function (err, lineOffsets) {
        chomp(
            fileName,
            {
                lineOffsets: lineOffsets,
                fromLine: start,
                lineCount: count
            },
            callback
        );
    });
}

For more usage examples, check out the spec folder.

Options

All options with defaults and helpful comments can be seen here.

FAQ

Q: Why another line splitter library?

A: I was frustrated with other libraries being
1. too old / outdated
2. nice but (I hear) buggy
3. lacking advanced options for random access that I need for my project

Q: Why the name '*-chomper'? That word doesn't mean what you think it means

A: All the good, obvious names were taken

Q: What's next?

A: Probably a slow decline into the maintenance mode, unless there is pressing need to expand. Bug fixes are always welcome. Also, I might add an advanced asynchronous chunk-by-chunk processing mode, suitable for handling large files with progress reports, buffered DB access and such.
TL;DR:
1. Bug fixes
2. Maybe a new feature or two
3. Profit

Update log

Date Version Description
2015-05-06 0.5.0 Added lineCallback argument to mapLineOffsets()

Licence

Apache v2. I'm told it's nice and fluffy. Read it here.