fix: add bounds check for lexer position while parsing array and dictionary (#327)

* fix: add bounds check for lexer position while parsing array and dictionary

* refactor: better position for checks is inside the while loop

* fix(lexer): prevent buffer overread in getString by adding bounds check

* refactor

Author: nupurchh

lib/parser/lexer.js

@@ -20,6 +20,11 @@ class Lexer {
   }
 
   getString(len) {
+    if (this.pos + len > this.buf.length) {
+      throw new Error(
+        `Lexer buffer overread: trying to read ${len} bytes from position ${this.pos}, but buffer length is ${this.buf.length}`
+      );
+    }
     return String.fromCharCode.apply(
       null,
       this.buf.subarray(this.pos, this.pos + len),