Prevent overwriting files

Closes #3

handlers-s3.go

@@ -71,6 +71,12 @@ func handleCreateMultipartUpload(w http.ResponseWriter, req *http.Request) {
 	// Derive the object key
 	key := formatKey(cred.Prefix, r.Filename)
 
+	// Ensure that the file does not exist
+	err = headObject(key, cred)
+	if !errors.Is(err, errNotFound) {
+		errorResponse(w, req, fmt.Errorf("%w: the provided key exists", errConflict))
+	}
+
 	result, err := initiateMultipartUpload(key, cred)
 	if err != nil {
 		errorResponse(w, req, err)
@@ -104,7 +110,7 @@ func handleGetUploadedParts(w http.ResponseWriter, req *http.Request) {
 		return
 	}
 
-	parts := make(getUploadedPartsRes, 0, 0)
+	parts := make(getUploadedPartsRes, 0)
 	var nextPartNumberMarker uint32
 	for {
 		page, err := listParts(key, uploadID, cred, nextPartNumberMarker)

handlers.go

@@ -148,3 +148,9 @@ func handleCreateForm(w http.ResponseWriter, req *http.Request) {
 
 	w.Write([]byte(id))
 }
+
+/* help template */
+
+func handleHelp(w http.ResponseWriter, req *http.Request) {
+	executeTemplate(w, "help.tmpl", nil)
+}

helpers.go

@@ -10,6 +10,7 @@ var errBadRequest = errors.New("bad request")
 var errInternalServerError = errors.New("internal server error")
 var errUnauthorized = errors.New("unauthorized")
 var errForbidden = errors.New("forbidden")
+var errConflict = errors.New("conflict")
 
 func errorResponseStatus(w http.ResponseWriter, req *http.Request, err error) {
 	errorStatus := http.StatusInternalServerError
@@ -24,6 +25,8 @@ func errorResponseStatus(w http.ResponseWriter, req *http.Request, err error) {
 		errorStatus = http.StatusUnauthorized
 	} else if errors.Is(err, errForbidden) {
 		errorStatus = http.StatusForbidden
+	} else if errors.Is(err, errConflict) {
+		errorStatus = http.StatusConflict
 	}
 
 	w.WriteHeader(errorStatus)
@@ -50,6 +53,8 @@ func responseToError(resp *http.Response) error {
 		return errUnauthorized
 	} else if resp.StatusCode == http.StatusForbidden {
 		return errForbidden
+	} else if resp.StatusCode == http.StatusConflict {
+		return errConflict
 	}
 	return nil
 }

main.go

@@ -28,6 +28,7 @@ func main() {
 
 	router.Methods(http.MethodGet).Path("/").HandlerFunc(handleCreate)
 	router.Methods(http.MethodPost).Path("/").HandlerFunc(handleCreateForm)
+	router.Methods(http.MethodGet).Path("/help").HandlerFunc(handleHelp)
 	uploadRouter := router.PathPrefix("/{id}").Subrouter()
 
 	uploadTemplateRouter := uploadRouter.Path("").Subrouter()

s3.go

@@ -307,3 +307,34 @@ func abortMultipartUpload(
 
 	return nil
 }
+
+/* headObject */
+
+func headObject(
+	key string,
+	cred credential,
+) error {
+	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+	defer cancel()
+
+	unsignedReq, err := http.NewRequestWithContext(ctx, http.MethodHead, cred.Endpoint+"/"+key, nil)
+	if err != nil {
+		log.Printf("failure creating request: %v", err)
+		return err
+	}
+
+	signedReq := sign(unsignedReq, cred)
+	resp, err := httpClientS3.Do(signedReq)
+	if err != nil {
+		log.Printf("failure connecting to endpoint: %v", err)
+		return err
+	}
+	defer resp.Body.Close()
+	err = endpointReturnedError(resp)
+	if err != nil {
+		log.Printf("endpoint responded negatively: %v", err)
+		return err
+	}
+
+	return nil
+}

web/src/upload.js

@@ -14,6 +14,7 @@ uploadAreas.forEach(uploadArea => {
 	const logClearBtn = uploadArea.querySelector('.log-clear')
 	const dropArea = uploadArea.querySelector('.drop-area');
 	const statusArea = uploadArea.querySelector('.status-area');
+	const noticeArea = uploadArea.querySelector('.notice-area');
 
 	/* Components */
 
@@ -25,6 +26,20 @@ uploadAreas.forEach(uploadArea => {
 		log.clear();
 	});
 
+	/* Error */
+
+	function showError(error='') {
+		let message = error.message || error.toString();
+		if (message !== '') {
+			noticeArea.classList.remove('hidden');
+			noticeArea.innerText = message;
+		} else {
+			noticeArea.classList.add('hidden');
+			noticeArea.innerText = message;
+		}
+		window.scrollTo({ top: 0 });
+	}
+
 	/* Uppy */
 
 	const uppy = new Uppy({
@@ -42,7 +57,19 @@ uploadAreas.forEach(uploadArea => {
 		companionUrl: window.location.pathname,
 	});
 
+	uppy.on('upload-error', (f, error, res) => {
+		window.e = { f, error, res };
+		if (error.message.contains('status: 409')) {
+			showError('A file with the same name already exists. Rename your file and try again');
+			return;
+		}
+		showError(error);
+	});
+	uppy.on('upload-retry', (id) => {
+		showError();
+	});
 	uppy.on('upload-success', (f, res) => {
+		showError();
 		log.add({
 			name: f.name,
 			size: f.size,