From 6b255f2a4e6874d9bd9d20bd0dfd0e6be2cbf8d3 Mon Sep 17 00:00:00 2001
From: Leokuma <leonardo.okuma@gmail.com>
Date: Thu, 2 Nov 2023 03:30:50 -0300
Subject: [PATCH] fix: prevent hanging when the first character is invalid
 (#31)

---
 parse_test.ts   | 15 +++++++++++++++
 utils/parser.ts | 12 ++++++++----
 2 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/parse_test.ts b/parse_test.ts
index f165e8db..369fc0f0 100644
--- a/parse_test.ts
+++ b/parse_test.ts
@@ -494,6 +494,21 @@ Deno.test("parse: xml syntax attributes properly quoted", () =>
 `)
   ))
 
+Deno.test("parse: xml syntax first character", () => {
+  assertThrows(() =>
+    parse(`a>1</a>`)
+  )
+  assertThrows(() =>
+    parse(`xml`)
+  )
+  assertThrows(() =>
+    parse(`""`)
+  )
+  assertThrows(() =>
+    parse(`{a: 1}`)
+  )
+})
+
 //Example below were taken from https://www.w3schools.com/xml/default.asp
 
 Deno.test("parse: xml example w3schools.com#1", () =>
diff --git a/utils/parser.ts b/utils/parser.ts
index 2515af95..8c0ee56c 100644
--- a/utils/parser.ts
+++ b/utils/parser.ts
@@ -57,7 +57,7 @@ export class Parser {
         }
 
         //Extract prolog, stylesheets and doctype
-        if ((this.#peek(tokens.prolog.start)) && (!this.#peek(tokens.stylesheet.start))) {
+        else if ((this.#peek(tokens.prolog.start)) && (!this.#peek(tokens.stylesheet.start))) {
           if (document.xml) {
             throw Object.assign(new SyntaxError("Multiple prolog declaration found"), { stack: false })
           }
@@ -65,13 +65,13 @@ export class Parser {
           Object.assign(document, this.#prolog({ path }))
           continue
         }
-        if (this.#peek(tokens.stylesheet.start)) {
+        else if (this.#peek(tokens.stylesheet.start)) {
           clean = false
           const stylesheets = (document[schema.stylesheets] ??= []) as unknown[]
           stylesheets.push(this.#stylesheet({ path }).stylesheet)
           continue
         }
-        if (this.#peek(tokens.doctype.start)) {
+        else if (this.#peek(tokens.doctype.start)) {
           if (document.doctype) {
             throw Object.assign(new SyntaxError("Multiple doctype declaration found"), { stack: false })
           }
@@ -81,7 +81,7 @@ export class Parser {
         }
 
         //Extract root node
-        if (this.#peek(tokens.tag.start)) {
+        else if (this.#peek(tokens.tag.start)) {
           if (root) {
             throw Object.assign(new SyntaxError("Multiple root elements found"), { stack: false })
           }
@@ -91,6 +91,10 @@ export class Parser {
           root = true
           continue
         }
+
+        else {
+          throw Object.assign(new SyntaxError("Invalid XML structure"), { stack: false })
+        }
       }
     } catch (error) {
       if ((error instanceof Deno.errors.UnexpectedEof) && (clean)) {