vweb: fix parsing of form fields, send with multipart/form-data (by JS fetch)

vlib/vweb/parse.v

@@ -67,22 +67,25 @@ fn parse_query_from_url(url urllib.URL) map[string]string {
 	return query
 }
 
+const boundary_start = 'boundary='
+
 fn parse_form_from_request(request http.Request) !(map[string]string, map[string][]http.FileData) {
-	mut form := map[string]string{}
-	mut files := map[string][]http.FileData{}
-	if request.method in methods_with_form {
-		ct := request.header.get(.content_type) or { '' }.split(';').map(it.trim_left(' \t'))
-		if 'multipart/form-data' in ct {
-			boundary := ct.filter(it.starts_with('boundary='))
-			if boundary.len != 1 {
-				return error('detected more that one form-data boundary')
-			}
-			// omit 'boundary="' and the last '"'
-			boundary_str := boundary[0].substr(10, boundary[0].len - 1)
-			form, files = http.parse_multipart_form(request.data, boundary_str)
-		} else {
-			form = http.parse_form(request.data)
-		}
+	if request.method !in [http.Method.post, .put, .patch] {
+		return map[string]string{}, map[string][]http.FileData{}
 	}
-	return form, files
+	ct := request.header.get(.content_type) or { '' }.split(';').map(it.trim_left(' \t'))
+	if 'multipart/form-data' in ct {
+		boundaries := ct.filter(it.starts_with(vweb.boundary_start))
+		if boundaries.len != 1 {
+			return error('detected more that one form-data boundary')
+		}
+		boundary := boundaries[0].all_after(vweb.boundary_start)
+		if boundary.len > 0 && boundary[0] == `"` {
+			// quotes are send by our http.post_multipart_form/2:
+			return http.parse_multipart_form(request.data, boundary.trim('"'))
+		}
+		// Firefox and other browsers, do not use quotes around the boundary:
+		return http.parse_multipart_form(request.data, boundary)
+	}
+	return http.parse_form(request.data), map[string][]http.FileData{}
 }

vlib/vweb/tests/vweb_test.v

@@ -238,6 +238,19 @@ fn test_http_client_multipart_form_data() {
 	assert x.body == files[0].data
 }
 
+fn test_login_with_multipart_form_data_send_by_fetch() {
+	mut form_config := http.PostMultipartFormConfig{
+		form: {
+			'username': 'myusername'
+			'password': 'mypassword123'
+		}
+	}
+	x := http.post_multipart_form('http://${localserver}/login', form_config)!
+	assert x.status_code == 200
+	assert x.status_msg == 'OK'
+	assert x.body == 'username: xmyusernamex | password: xmypassword123x'
+}
+
 fn test_host() {
 	mut req := http.Request{
 		url: 'http://${localserver}/with_host'

vlib/vweb/tests/vweb_test_server.v

@@ -89,6 +89,11 @@ pub fn (mut app App) json_echo() vweb.Result {
 	return app.ok(app.req.data)
 }
 
+['/login'; post]
+pub fn (mut app App) login_form(username string, password string) vweb.Result {
+	return app.html('username: x${username}x | password: x${password}x')
+}
+
 ['/form_echo'; post]
 pub fn (mut app App) form_echo() vweb.Result {
 	app.set_content_type(app.req.header.get(.content_type) or { '' })