feat: allow file uploads on mobile chat

closes https://github.com/NodeBB/NodeBB/issues/11217

public/src/client/chats.js

@@ -74,6 +74,7 @@ define('forum/chats', [
 			dragDropAreaEl: $('.chats-full'),
 			pasteEl: $('[component="chat/input"]'),
 			uploadFormEl: $('[component="chat/upload"]'),
+			uploadBtnEl: $('[component="chat/upload/button"]'),
 			inputEl: $('[component="chat/input"]'),
 		});
 
@@ -87,6 +88,7 @@ define('forum/chats', [
 			dragDropAreaEl: options.dragDropAreaEl,
 			pasteEl: options.pasteEl,
 			uploadFormEl: options.uploadFormEl,
+			uploadBtnEl: options.uploadBtnEl,
 			route: '/api/post/upload', // using same route as post uploads
 			callback: function (uploads) {
 				const inputEl = options.inputEl;

public/src/modules/chat.js

@@ -304,6 +304,7 @@ define('chat', [
 					dragDropAreaEl: chatModal.find('.modal-content'),
 					pasteEl: chatModal,
 					uploadFormEl: chatModal.find('[component="chat/upload"]'),
+					uploadBtnEl: $('[component="chat/upload/button"]'),
 					inputEl: chatModal.find('[component="chat/input"]'),
 				});
 

public/src/modules/uploadHelpers.js

@@ -36,6 +36,27 @@ define('uploadHelpers', ['alerts'], function (alerts) {
 				},
 			});
 		}
+
+		if (options.uploadBtnEl) {
+			const fileInput = formEl.find('input[name="files[]"]');
+			options.uploadBtnEl.on('click', function () {
+				fileInput.trigger('click');
+			});
+			fileInput.on('change', function (e) {
+				const files = (e.target || {}).files ||
+					($(this).val() ? [{ name: $(this).val(), type: utils.fileMimeType($(this).val()) }] : null);
+				if (files) {
+					uploadHelpers.ajaxSubmit({
+						uploadForm: formEl,
+						upload: {
+							files: files,
+							fileNames: Array.from(files).map(f => f.name),
+						},
+						callback: options.callback,
+					});
+				}
+			});
+		}
 	};
 
 	uploadHelpers.handleDragDrop = function (options) {