Add code to generate ZIP files (part of #28)

pkg/zipper/testdata/executable.sh

@@ -0,0 +1,2 @@
+#!/bin/bash
+exit 0

pkg/zipper/testdata/notzip.txt

@@ -0,0 +1 @@
+hello

pkg/zipper/testdata/short.txt

@@ -0,0 +1 @@
+he

pkg/zipper/zipper.go

@@ -0,0 +1,118 @@
+package zipper
+
+import (
+	"archive/zip"
+	"fmt"
+	"github.com/pkg/errors"
+	"io"
+	"io/ioutil"
+	"net/http"
+	"os"
+	"path/filepath"
+)
+
+func Zip(path string) (string, error) {
+	path, err := filepath.Abs(path)
+	if err != nil {
+		return "", errors.Wrap(err, "determining absolute path")
+	}
+
+	fi, err := os.Stat(path)
+	if os.IsNotExist(err) {
+		return "", errors.Errorf("no file exists at '%s'", path)
+	}
+
+	if isZip(path) {
+		return path, nil
+	}
+
+	fw, err := ioutil.TempFile("", fmt.Sprintf("%s*.zip", filepath.Base(path)))
+	if err != nil {
+		return "", errors.Wrap(err, "creating temporary file to write to")
+	}
+	defer fw.Close()
+
+	zw := zip.NewWriter(fw)
+
+	if fi.IsDir() {
+		err = filepath.Walk(path, func(subpath string, info os.FileInfo, err error) error {
+			if info.IsDir() {
+				return nil
+			}
+
+			return addFileToZip(zw, path, subpath)
+		})
+	} else {
+		err = addFileToZip(zw, path, path)
+	}
+	if err != nil {
+		return "", err
+	}
+
+	err = zw.Close()
+	if err != nil {
+		return "", errors.Wrap(err, "finialising zip file")
+	}
+
+	return fw.Name(), nil
+}
+
+func addFileToZip(zw *zip.Writer, topPath, path string) error {
+	inputFile, err := os.Open(path)
+	if err != nil {
+		return err
+	}
+	defer inputFile.Close()
+
+	info, err := os.Stat(path)
+	if err != nil {
+		return err
+	}
+
+	fh, err := zip.FileInfoHeader(info)
+	if err != nil {
+		return err
+	}
+
+	relPath, err := filepath.Rel(topPath, path)
+	if err != nil {
+		return err
+	}
+	if relPath == "." {
+		relPath = filepath.Base(path)
+	}
+
+	fh.Name = relPath
+	fh.Method = zip.Deflate
+
+	zf, err := zw.CreateHeader(fh)
+	if err != nil {
+		return err
+	}
+
+	_, err = io.Copy(zf, inputFile)
+	return err
+}
+
+func isZip(path string) bool {
+	if fi, err := os.Stat(path); fi != nil && fi.IsDir() {
+		return false
+	} else if os.IsNotExist(err) {
+		return false
+	} else {
+		f, err := os.Open(path)
+		if err != nil {
+			return false
+		}
+		defer f.Close()
+
+		buf := make([]byte, 4)
+		_, err = io.ReadAtLeast(f, buf, 4)
+		if err != nil {
+			return false
+		}
+
+		contentType := http.DetectContentType(buf)
+		return contentType == "application/zip"
+	}
+}

pkg/zipper/zipper_test.go

@@ -0,0 +1,35 @@
+package zipper
+
+import (
+	"archive/zip"
+	"github.com/stretchr/testify/assert"
+	"os"
+	"testing"
+)
+
+func TestIsZip(t *testing.T) {
+	assert.False(t, isZip("testdata/notzip.txt"))
+	assert.False(t, isZip("testdata/short.txt"))
+	assert.False(t, isZip("testdata/dir"))
+	assert.True(t, isZip("testdata/realzip.zip"))
+	assert.True(t, isZip("./testdata/../testdata/realzip.zip"))
+}
+
+func TestZipMaintainsPermissions(t *testing.T) {
+	path, err := Zip("testdata")
+	assert.NoError(t, err)
+
+	zf, err := zip.OpenReader(path)
+	assert.NoError(t, err)
+
+	foundExecutable := false
+
+	for _, f := range zf.File {
+		if f.Name == "executable.sh" {
+			foundExecutable = true
+			assert.Equal(t, f.Mode().Perm(), os.FileMode(0755))
+		}
+	}
+
+	assert.True(t, foundExecutable)
+}