Erofs

erofs

Pure-Go [EROFS](https://erofs.docs.kernel.org/en/latest/) (Enhanced Read-Only File System) reader and writer. Read EROFS images through Go's `fs.FS` interface, or create new ones with `Builder`. Output is bytewise compatible with the Linux kernel EROFS driver and `mkfs.erofs`.

Reads LZ4, LZMA, DEFLATE, and Zstandard compressed images. Writes LZ4 compressed images with automatic incompressibility detection.

Install

go get github.com/Xe/erofs@latest

Reading an EROFS image

`erofs.Open` accepts any `io.ReaderAt` and returns an `*erofs.FS` implementing `fs.FS`, `fs.StatFS`, and `fs.ReadLinkFS`:

package main

import (
    "fmt"
    "io/fs"
    "log"
    "os"

    "github.com/Xe/erofs"
)

func main() {
    f, err := os.Open("rootfs.erofs")
    if err != nil {
        log.Fatal(err)
    }
    defer f.Close()

    fsys, err := erofs.Open(f)
    if err != nil {
        log.Fatal(err)
    }

    // Read a file.
    data, err := fs.ReadFile(fsys, "etc/hostname")
    if err != nil {
        log.Fatal(err)
    }
    fmt.Println(string(data))

    // List a directory.
    entries, err := fs.ReadDir(fsys, "usr/bin")
    if err != nil {
        log.Fatal(err)
    }
    for _, e := range entries {
        fmt.Println(e.Name())
    }

    // Stat a file.
    info, err := fsys.Stat("etc/passwd")
    if err != nil {
        log.Fatal(err)
    }
    fmt.Printf("%s: %d bytes\n", info.Name(), info.Size())

    // Read a symlink.
    target, err := fsys.ReadLink("usr/bin/vi")
    if err != nil {
        log.Fatal(err)
    }
    fmt.Println("vi ->", target)
}

Creating an EROFS image

`erofs.NewBuilder` writes to any `io.WriterAt`. Add files individually or walk an existing `fs.FS`:

package main

import (
    "log"
    "os"
    "time"

    "github.com/Xe/erofs"
)

func main() {
    out, err := os.Create("output.erofs")
    if err != nil {
        log.Fatal(err)
    }
    defer out.Close()

    b := erofs.NewBuilder(out,
        erofs.WithBlo