added optiobal max length for variable values (fix #349)

Former-commit-id: 362069cf22639863960eb8e20e5ee502689c266c

extension/ui/pages/help.html

@@ -237,7 +237,7 @@
 							without altering the document. It may also increase the CPU consumption and the time needed
 							to save a page.</p>
 						<p class="notice">It is recommended to <u>uncheck</u> this option</p>
-					</li>					
+					</li>
 				</ul>
 				<p>Images</p>
 				<ul>
@@ -448,6 +448,10 @@
 			<li><a id="template-variables">Template variables</a>
 				<p>The template variables are used to customize the infobar content or the file name of a saved page.
 					They help to insert dynamic values like the save date or the page title.</p>
+				<p>
+					You can limit the length of a dynamic value by adding <code>[<em>maxByteSize</em>]</code> just after
+					the variable name. The <code>maxByteSize</code> value is the maximum length of the value in bytes
+					(e.g. `{page-title}[20]` to limit the title to 20 bytes).</p>
 				<ul>
 					<li><code>{page-title}</code>: the title of the page</li>
 					<li><code>{page-language}</code>: the language of the page</li>

lib/single-file/single-file-core.js

@@ -1901,13 +1901,29 @@ this.singlefile.lib.core = this.singlefile.lib.core || (() => {
 		}
 
 		static async evalTemplateVariable(template, variableName, valueGetter, dontReplaceSlash, replacementCharacter) {
-			const replaceRegExp = new RegExp("{\\s*" + variableName.replace(/\W|_/g, "[$&]") + "\\s*}", "g");
-			if (template && template.match(replaceRegExp)) {
-				let value = await valueGetter();
-				if (!dontReplaceSlash) {
-					value = value.replace(/\/+/g, replacementCharacter);
+			let maxLength;
+			if (template) {
+				const regExpVariable = "{\\s*" + variableName.replace(/\W|_/g, "[$&]") + "\\s*}";
+				let replaceRegExp = new RegExp(regExpVariable + "\\[\\d+\\]", "g");
+				if (template.match(replaceRegExp)) {
+					const matchedLength = template.match(replaceRegExp)[0];
+					maxLength = Number(matchedLength.match(/\[(\d+)\]$/)[1]);
+					if (isNaN(maxLength) || maxLength <= 0) {
+						maxLength = null;
+					}
+				} else {
+					replaceRegExp = new RegExp(regExpVariable, "g");
+				}
+				if (template.match(replaceRegExp)) {
+					let value = await valueGetter();
+					if (!dontReplaceSlash) {
+						value = value.replace(/\/+/g, replacementCharacter);
+					}
+					if (maxLength) {
+						value = await util.truncateText(value, maxLength);
+					}
+					return template.replace(replaceRegExp, value);
 				}
-				return template.replace(replaceRegExp, value);
 			}
 			return template;
 		}