undocker/main.go

76 lines
1.4 KiB
Go

// Package main is a simple command-line application on top of rootfs.Flatten.
package main
import (
"fmt"
"io"
"os"
"path/filepath"
"runtime"
"git.sr.ht/~motiejus/undocker/rootfs"
)
const _usage = `Usage:
%s <infile> <outfile>
Flatten a Docker container image to a root file system.
Arguments:
<infile>: Input Docker container. Tarball.
<outfile>: Output tarball, the root file system. '-' is stdout.
`
func main() {
runtime.GOMAXPROCS(1) // no need to create that many threads
if len(os.Args) != 3 {
fmt.Fprintf(os.Stderr, _usage, filepath.Base(os.Args[0]))
os.Exit(1)
}
c := &command{flattener: rootfs.Flatten, Stdout: os.Stdout}
if err := c.execute(os.Args[1], os.Args[2]); err != nil {
fmt.Errorf("Error: %v", err)
os.Exit(1)
}
os.Exit(0)
}
type command struct {
flattener func(io.ReadSeeker, io.Writer) error
Stdout io.Writer
}
func (c *command) execute(infile string, outfile string) (err error) {
rd, err := os.Open(infile)
if err != nil {
return err
}
defer func() {
err1 := rd.Close()
if err == nil {
err = err1
}
}()
var out io.Writer
if outfile == "-" {
out = c.Stdout
} else {
outf, err := os.Create(outfile)
if err != nil {
return fmt.Errorf("create: %w", err)
}
defer func() {
err1 := outf.Close()
if err == nil {
err = err1
}
}()
out = outf
}
return c.flattener(rd, out)
}