From 9ea068bf647afea9f1d1dfb7711ec7d21feca1fa Mon Sep 17 00:00:00 2001
From: Trevor Buckner <calculuschild@gmail.com>
Date: Sat, 7 Aug 2021 00:48:59 -0400
Subject: [PATCH] Fix catastrophic backtracking and trim starting pipes

---
 shared/naturalcrit/markdown.js | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/shared/naturalcrit/markdown.js b/shared/naturalcrit/markdown.js
index 2a6f0e3b9..01abc33a7 100644
--- a/shared/naturalcrit/markdown.js
+++ b/shared/naturalcrit/markdown.js
@@ -240,7 +240,7 @@ const spanTable = {
 	start(src) { return src.match(/^\n *([^\n ].*\|.*)\n/)?.index; },  // Hint to Marked.js to stop and check for a match
 	tokenizer(src, tokens) {
 		//const regex = this.tokenizer.rules.block.table;
-		const regex = new RegExp('^ *([^\\n ].*\\|.*\\n(?:.*?[^\\s].*\\n)*?)' // Header
+		const regex = new RegExp('^ *([^\\n ].*\\|.*\\n(?: *[^\\s].*\\n)*?)' // Header
 		    + ' {0,3}(?:\\| *)?(:?-+:? *(?:\\| *:?-+:? *)*)\\|?' // Align
 		    + '(?:\\n *((?:(?!\\n| {0,3}((?:- *){3,}|(?:_ *){3,}|(?:\\* *){3,})' // Cells
 				+ '(?:\\n+|$)| {0,3}#{1,6} | {0,3}>| {4}[^\\n]| {0,3}(?:`{3,}'
@@ -369,9 +369,9 @@ const getTableCell = (text, cell, type, align)=>{
 };
 
 const splitCells = (tableRow, count, prevRow = [])=>{
-	// ensure that every cell-delimiting pipe has a space
-	// before it to distinguish it from an escaped pipe
-	const row = tableRow.replace(/(\|+)/g, (match, p1, offset, str)=>{
+	// trim any excessive pipes at start of row
+	tableRow = tableRow.replace(/^\|+(?=\|)/, '')
+	.replace(/(\|+)/g, (match, p1, offset, str)=>{
 		let escaped = false,
 			curr = offset;
 		while (--curr >= 0 && str[curr] === '\\') escaped = !escaped;
@@ -380,12 +380,12 @@ const splitCells = (tableRow, count, prevRow = [])=>{
 			// so we leave it and the slashes alone
 			return p1;
 		} else {
-			// add space before unescaped |
+			// add space before unescaped | to distinguish it from an escaped pipe
 			return ` ${p1}`;
 		}
 	});
 
-	const cells = row.split(/(?: \||(?<=\|)\|)(?=[^\|]|$)/g);
+	const cells = tableRow.split(/(?: \||(?<=\|)\|)(?=[^\|]|$)/g);
 	let i = 0;
 
 	// First/last cell in a row cannot be empty if it has no leading/trailing pipe
@@ -400,7 +400,7 @@ const splitCells = (tableRow, count, prevRow = [])=>{
 			rowspan : 1,
 			colspan : Math.max(cells[i].length - trimmedCell.length, 1),
 			text    : trimmedCell.trim().replace(/\\\|/g, '|')
-			// leading or trailing whitespace is ignored per the gfm spec
+			// trim whitespace and display escaped pipes as normal character
 		};
 
 		// Handle Rowspan
@@ -411,6 +411,7 @@ const splitCells = (tableRow, count, prevRow = [])=>{
 			for (j = 0; j < prevRow.length; j++) {
 				prevCell = prevRow[j];
 				if((prevCols == numCols) && (prevCell.colspan == cells[i].colspan)) {
+					// merge into matching cell in previous row (the "target")
 					cells[i].rowSpanTarget = prevCell.rowSpanTarget ?? prevCell;
 					cells[i].rowSpanTarget.text += ` ${cells[i].text.slice(0, -1)}`;
 					cells[i].rowSpanTarget.rowspan += 1;