rotate_writer

Generic GoLang Rotate Writer (io.Writer and io.WriterCloser)

rotate_writer is a Go package that provides a RotateWriter struct, which implements an io.Writer that automatically rotates its underlying io.WriteCloser based on custom-defined conditions. This is useful for scenarios such as log file rotation where a new writer needs to be created periodically or based on certain size or time conditions.

Installation

To use rotate_writer, install it using:

go get -u github.com/mohammadT77/rotate_writer

Usage

Creating a RotateWriter First, you need to define a rotation condition function of type RotatorFn, which takes a RotateStatus and returns a new io.WriteCloser when a rotation is needed. Here’s an example condition that rotates based on a maximum size:

The name, type, and rotation triggerer can be fully customized within this function.

func rotateOnSize(status rotate_writer.RotateStatus) io.WriteCloser {
    if status.CurrentSize+status.AddedSize > maxSize {
        // Return a new writer if the size exceeds maxSize
        return openNewLogFile() // Can be buffer, stdio, logger or any other kind of Writers 
    }
    return nil
}

Then, create a RotateWriter with an initial writer and the condition function:

initialWriter := openNewLogFile() // Initial writer (e.g., an open file)
rw := rotate_writer.NewRotateWriter(initialWriter, rotateOnSize)

Writing to RotateWriter To write data, simply call the Write method:

_, err := rw.Write([]byte("Some log message")) // implemented io.Writer
if err != nil {
    log.Fatalf("Failed to write: %v", err)
}

The RotateWriter will automatically rotate the writer if the rotateCondition returns a new writer.

Manually Rotating the Writer

If needed, you can manually rotate the writer by calling Rotate with a new io.WriteCloser

Closing the RotateWriter Always close the RotateWriter to ensure all resources are properly released:

err := rw.Close()  // implemented io.WriteCloser
if err != nil {
    log.Fatalf("Failed to close: %v", err)
}