frontend: move file (on the same partition) instead of open, write, close the final file

frontend/main.go

@@ -17,6 +17,7 @@ const startedFile = "started"
 
 var TeamsDir string
 var SubmissionDir string
+var TmpSubmissionDir string
 
 var touchTimer *time.Timer = nil
 
@@ -70,10 +71,11 @@ func main() {
 	log.SetPrefix("[frontend] ")
 
 	SubmissionDir = path.Clean(SubmissionDir)
+	TmpSubmissionDir = path.Join(SubmissionDir, ".tmp")
 
 	log.Println("Creating submission directory...")
-	if _, err := os.Stat(SubmissionDir); os.IsNotExist(err) {
-		if err := os.MkdirAll(SubmissionDir, 0777); err != nil {
+	if _, err := os.Stat(TmpSubmissionDir); os.IsNotExist(err) {
+		if err := os.MkdirAll(TmpSubmissionDir, 0777); err != nil {
 			log.Fatal("Unable to create submission directory: ", err)
 		}
 	}

frontend/save.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"bufio"
 	"io/ioutil"
 	"log"
 	"net/http"
@@ -42,40 +43,27 @@ func saveFile(dirname string, filename string, r *http.Request) error {
 		}
 	}
 
-	var f *os.File
+	// Write content to temp file
+	tmpfile, err := ioutil.TempFile(TmpSubmissionDir, "")
+	if err != nil {
+		return err
+	}
+
+	writer := bufio.NewWriter(tmpfile)
+	reader := bufio.NewReader(r.Body)
+	if _, err := reader.WriteTo(writer); err != nil {
+		return err
+	}
+	writer.Flush()
+	tmpfile.Close()
 
 	if filename == "" {
-		if fd, err := ioutil.TempFile(dirname, ""); err != nil {
-			return err
-		} else {
-			defer f.Close()
-			f = fd
-		}
-	} else {
-		if fd, err := os.Create(path.Join(dirname, filename)); err != nil {
-			return err
-		} else {
-			defer f.Close()
-			f = fd
-		}
+		filename = path.Base(tmpfile.Name())
 	}
 
-	// Read request body
-	var body []byte
-	if r.ContentLength > 0 {
-		tmp := make([]byte, 1024)
-		for {
-			n, err := r.Body.Read(tmp)
-			for j := 0; j < n; j++ {
-				body = append(body, tmp[j])
-			}
-			if err != nil || n <= 0 {
-				break
-			}
-		}
+	if err := os.Rename(tmpfile.Name(), path.Join(dirname, filename)); err != nil {
+		log.Println("[ERROR] Unable to move file: ", err)
 	}
 
-	f.Write(body)
-
 	return nil
 }