upload: check remote before uploading

cmd/dkl-store-upload/main.go

@@ -30,6 +30,8 @@ func main() {
 	in, err := os.Open(inPath)
 	fail(err)
 
+	defer in.Close()
+
 	// hash the file
 	log.Print("hashing...")
 	h := sha1.New()
@@ -40,6 +42,18 @@ func main() {
 
 	log.Print("SHA1 of source: ", sha1Hex)
 
+	// check remote
+	head, err := http.Head(outURL)
+	fail(err)
+
+	if head.StatusCode == 200 {
+		remoteSHA1 := head.Header.Get("X-Content-SHA1")
+		if sha1Hex == remoteSHA1 {
+			log.Print("remote is already up-to-date")
+			return
+		}
+	}
+
 	// rewind
 	_, err = in.Seek(0, os.SEEK_SET)
 	fail(err)

modd.conf

@@ -0,0 +1,4 @@
+**/*.go go.* {
+  prep: go test ./...
+  prep: go install ./cmd/...
+}