build: handle lowercase Dockerfile name as a fallback

[tonistiigi]

fixes #415

This was supported by the legacy builder: moby/moby#10858

Signed-off-by: Tonis Tiigi tonistiigi@gmail.com

[thaJeztah]

Was wondering why you were using f.Readdirnames here, but then realisedos.Stat() returns the name you pass to it, not the actual filename on disk (preserving case) 😞

Wondering, if Readdirnames() would be an issue if there's lots of files in the directory.

Would something like this work?

dockerfiles, err := filepath.Glob(dir + "/[Dd]ockerfile")

I did a quick test on my machine;

package main

import (
	"fmt"
	"path/filepath"
)

func main() {
	dockerfileDir, _ := filepath.Abs(".")
	dockerfileName := "Dockerfile"
	f := handleLowercaseDockerfile(dockerfileDir, dockerfileName)
	fmt.Println("Using:", f)
}

// handle https://github.com/moby/moby/pull/10858
func handleLowercaseDockerfile(dir, p string) string {
	if filepath.Base(p) != "Dockerfile" {
		return p
	}
	dockerfiles, err := filepath.Glob(filepath.Join(dir, "[Dd]ockerfile"))
	if err != nil || len(dockerfiles) != 1 {
		return p
	}
	// either Dockerfile or dockerfile was found; use what's found
	return filepath.Base(dockerfiles[0])
}

rm -f Dockerfile && touch dOckErFILE && go run main.go
rm -f Dockerfile && touch Dockerfile && go run main.go
rm -f Dockerfile && touch dockerfile && go run main.go

Using: Dockerfile
Using: Dockerfile
Using: dockerfile

[tonistiigi]

Glob is implemented with Readdirnames(-1)

[thaJeztah]

sigh 😔

it really surprised me that os.Stat doesn't return the actual filename

[thaJeztah]

LGTM