add go example

Author: stuartnelson3

samples/Backend on Go.md

@@ -0,0 +1,126 @@
+# Backend in Go
+
+Each `POST` request is parsed and then saved to disk. After the final chunk is uploaded, the chunks are stitched together in a separate go routine and then deleted.
+
+This implementation assumes that the final chunk is the last piece of the file being uploaded.
+
+Full working code available at https://github.com/stuartnelson3/golang-flowjs-upload
+
+The above repo includes an additional handler that streams the `POST` request chunks to disk, lowering the overall memory footprint.
+
+```go
+package main
+
+import (
+	"bytes"
+	"github.com/codegangsta/martini"
+	"github.com/codegangsta/martini-contrib/render"
+	"io"
+	"io/ioutil"
+	"net/http"
+	"os"
+	"sort"
+	"strconv"
+	"strings"
+)
+
+var completedFiles = make(chan string, 100)
+
+func main() {
+	for i := 0; i < 3; i++ {
+		go assembleFile(completedFiles)
+	}
+
+	m := martini.Classic()
+	m.Use(render.Renderer(render.Options{
+		Layout:     "layout",
+		Delims:     render.Delims{"{[{", "}]}"},
+		Extensions: []string{".html"}}))
+
+	m.Get("/", func(r render.Render) {
+		r.HTML(200, "index", nil)
+	})
+
+	m.Post("/upload", streamHandler(chunkedReader))
+
+	m.Run()
+}
+
+type ByChunk []os.FileInfo
+
+func (a ByChunk) Len() int      { return len(a) }
+func (a ByChunk) Swap(i, j int) { a[i], a[j] = a[j], a[i] }
+func (a ByChunk) Less(i, j int) bool {
+	ai, _ := strconv.Atoi(a[i].Name())
+	aj, _ := strconv.Atoi(a[j].Name())
+	return ai < aj
+}
+
+type streamHandler func(http.ResponseWriter, *http.Request) error
+
+func (fn streamHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	if err := fn(w, r); err != nil {
+		http.Error(w, err.Error(), 500)
+	}
+}
+
+func chunkedReader(w http.ResponseWriter, r *http.Request) error {
+	r.ParseMultipartForm(25)
+
+	chunkDirPath := "./incomplete/" + r.FormValue("flowFilename")
+	_, err := os.Stat(chunkDirPath)
+	if err != nil {
+		err := os.MkdirAll(chunkDirPath, 02750)
+		if err != nil {
+			return err
+		}
+	}
+
+	for _, fileHeader := range r.MultipartForm.File["file"] {
+		src, err := fileHeader.Open()
+		if err != nil {
+			return err
+		}
+		defer src.Close()
+
+		dst, err := os.Create(chunkDirPath + "/" + r.FormValue("flowChunkNumber"))
+		if err != nil {
+			return err
+		}
+		defer dst.Close()
+		io.Copy(dst, src)
+
+		if r.FormValue("flowChunkNumber") == r.FormValue("flowTotalChunks") {
+			completedFiles <- chunkDirPath
+		}
+	}
+	return nil
+}
+
+func assembleFile(jobs <-chan string) {
+	for path := range jobs {
+		fileInfos, err := ioutil.ReadDir(path)
+		if err != nil {
+			return
+		}
+
+		// create final file to write to
+		dst, err := os.Create(strings.Split(path, "/")[2])
+		if err != nil {
+			return
+		}
+		defer dst.Close()
+
+		sort.Sort(ByChunk(fileInfos))
+		for _, fs := range fileInfos {
+			src, err := os.Open(path + "/" + fs.Name())
+			if err != nil {
+				return
+			}
+			defer src.Close()
+			io.Copy(dst, src)
+		}
+		os.RemoveAll(path)
+	}
+}
+```