add simple zip example

zip/README.md

@@ -0,0 +1,34 @@
+# Go Zip Example
+
+An example of how to zip a directory in Go.
+
+-   Utilizes `filepath.Walk` to traverse a directory (or single file)
+-   Handles each of
+    -   Files (deflated, compressed)
+    -   Directories (empty, not compressed)
+    -   Symlinks (not compressed)
+    -   Skips irregular files (pipes, sockets, devices, chars)
+-   Names zip file after the name of the directory
+-   Trims path prefix
+
+```bash
+git clone https://git.coolaj86.com/coolaj86/go-examples.git
+pushd go-examples/zip
+```
+
+```bash
+go run . path/to/whatever
+```
+
+```txt
+wrote whatever.zip
+```
+
+Separates concerns into functions for readability:
+
+-   func main()
+-   func Zip(w io.Writer, src string, trim string) error
+    -   zipOne
+        -   zipDirectory
+        -   zipFile
+        -   zipSymlink

zip/main.go

@@ -0,0 +1,45 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+func usage() {
+	fmt.Println("Usage: go run go-zip.go <path/to/things>")
+}
+
+func main() {
+	if len(os.Args) < 2 || len(os.Args) > 3 {
+		usage()
+		os.Exit(1)
+	}
+
+	dir := strings.TrimSuffix(os.Args[1], string(filepath.Separator))
+	base := filepath.Base(dir)
+	// ../foo/whatever => ../foo/
+	trim := strings.TrimSuffix(dir, base)
+
+	// ./ => error
+	// ../../ => error
+	if "" == base || "." == base || ".." == base {
+		// TODO also don't allow ../self
+		fmt.Println("Error: Cannot zip the directory containing the output file")
+		os.Exit(1)
+	}
+
+	f, err := os.OpenFile(base+".zip", os.O_CREATE|os.O_TRUNC|os.O_WRONLY, 0644)
+	if nil != err {
+		panic(err)
+	}
+	defer f.Close()
+
+	// ./whatever => whatever.zip
+	// ./path/to/whatever => whatever.zip
+	if err := Zip(f, dir, trim); nil != err {
+		panic(err)
+	}
+	fmt.Println("wrote", base+".zip")
+}

zip/zip.go

@@ -0,0 +1,113 @@
+package main
+
+import (
+	"archive/zip"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+// Zip walks `src`, omitting `trim`, writing to `w`
+func Zip(w io.Writer, src string, trim string) error {
+	zw := zip.NewWriter(w)
+	defer zw.Close()
+
+	return filepath.Walk(src, func(path string, fi os.FileInfo, err error) error {
+		// path includes fi.Name() already
+		if nil != err {
+			fmt.Println("warning: skipped", path+": ", err)
+			return nil
+		}
+
+		zipOne(zw, path, fi, trim)
+		return nil
+	})
+}
+
+func zipOne(zw *zip.Writer, path string, fi os.FileInfo, trim string) error {
+	h, err := zip.FileInfoHeader(fi)
+	if nil != err {
+		return err
+	}
+	h.Name = strings.TrimPrefix(strings.TrimPrefix(path, trim), string(filepath.Separator))
+
+	if fi.IsDir() {
+		fmt.Printf("directory: %s\n\t%q\n", path, h.Name)
+		return zipDirectory(zw, h)
+	}
+
+	// Allow zipping a single file
+	if "" == h.Name {
+		h.Name = path
+	}
+	if fi.Mode().IsRegular() {
+		fmt.Printf("file: %s\n\t%q\n", path, h.Name)
+		return zipFile(zw, h, path)
+	}
+
+	if os.ModeSymlink == (fi.Mode() & os.ModeType) {
+		fmt.Printf("symlink: %s\n\t%q\n", path, h.Name)
+		return zipSymlink(zw, h, path)
+	}
+
+	fmt.Printf("skipping: %s\n\t(irregular file type)\n", path)
+	return nil
+}
+
+func zipDirectory(zw *zip.Writer, h *zip.FileHeader) error {
+	// directories must end in / for go
+	h.Name = strings.TrimPrefix(h.Name+"/", "/")
+
+	// skip top-level, trimmed directory
+	if "" == h.Name {
+		return nil
+	}
+
+	if _, err := zw.CreateHeader(h); nil != err {
+		return err
+	}
+
+	return nil
+}
+
+func zipFile(zw *zip.Writer, h *zip.FileHeader, path string) error {
+	r, err := os.Open(path)
+	if nil != err {
+		return err
+	}
+	defer r.Close()
+
+	// Files should be zipped (not dirs, and symlinks... meh)
+	// TODO investigate if files below a certain size shouldn't be deflated
+	h.Method = zip.Deflate
+	w, err := zw.CreateHeader(h)
+	if nil != err {
+		return err
+	}
+
+	if _, err := io.Copy(w, r); nil != err {
+		return err
+	}
+
+	return nil
+}
+
+func zipSymlink(zw *zip.Writer, h *zip.FileHeader, path string) error {
+	w, err := zw.CreateHeader(h)
+	if nil != err {
+		return err
+	}
+
+	// TODO make sure that this is within the root directory
+	targetpath, err := os.Readlink(path)
+	if nil != err {
+		return err
+	}
+	if _, err := w.Write([]byte(targetpath)); nil != err {
+		return err
+	}
+
+	return nil
+}