When attempting to parse a single string stored in a cookie with JSON.parse, it results in a "SyntaxError: Unexpected Number" error being thrown

Question

When attempting to parse a single string stored in a cookie with JSON.parse, it results in a "SyntaxError: Unexpected Number" error being thrown

I am facing an issue with parsing a string stored in a cookie.

"d967fac49ef2466239168bbbde0a8d755a27ba81$[[\"__json_message\"\05425\054\"This is a message.\"]]"

Also known as

"\"d967fac49ef2466239168bbbde0a8d755a27ba81$[[\\\"__json_message\\\"\\05425\\054\\\"This is a message.\\\"]]\""

(to be used in console)

Although I cannot parse it using JSON.parse and resort to eval, which poses security risks. The error message states SyntaxError: Unexpected number.

The presence of escaped commas is noteworthy, indicating that this was generated utilizing the Django messaging API.

Can anyone suggest a suitable regex or alternative method to resolve this?

The initial step involves unescaping the string (as it is a valid JavaScript string) followed by obtaining the array after the dollar sign (s.substring(s.indexOf("$")+1)).

javascript django

Answer 1

Answer №1

Apologies for any confusion earlier, but I have managed to resolve it thanks to the helpful link provided by jfriend00 to json.org. Below is a modified string that now works correctly and displays the intended output. It involves unescaping a JSON array within an already encoded string.

var s = JSON.parse("\"d967fac49ef2466239168bbbde0a8d755a27ba81$[[\\\"__json_message\\\"\\u002C25\\u002C\\\"This is a message.\\\"]]\"")
// s = "d967fac49ef2466239168bbbde0a8d755a27ba81$[["__json_message",25,"This is a message."]]"
// Correct output achieved
var a = JSON.parse(s.substring(s.indexOf("$")+1))

The issue stemmed from converting commas to octal escape codes in the string preparation for the cookie, which is not allowed in JSON formatting. The related error message should have been JSON forbids octal prefixes. Once this is rectified by replacing octal with hex escape codes, it will function properly. Therefore, I will implement a check for octal escapes and substitute them with hex equivalents.

TL;DR: "SyntaxError: Unexpected Number" equates to "SyntaxError: JSON forbids octal prefixes"

Below is the function I employed

var s = "\"d967fac49ef2466239168bbbde0a8d755a27ba81$[[\\\"__json_message\\\"\\05425\\054\\\"This is a message.\\\"]]\"""
var re = /\\0([0-7]{2})/g
JSON.parse(s.replace(re, function(m, n){return "\\x"+("0000"+parseInt(n,8).toString(16)).slice(-4)}))

Answer 2

Apologies for any confusion earlier, but I have managed to resolve it thanks to the helpful link provided by jfriend00 to json.org. Below is a modified string that now works correctly and displays the intended output. It involves unescaping a JSON array within an already encoded string.

var s = JSON.parse("\"d967fac49ef2466239168bbbde0a8d755a27ba81$[[\\\"__json_message\\\"\\u002C25\\u002C\\\"This is a message.\\\"]]\"")
// s = "d967fac49ef2466239168bbbde0a8d755a27ba81$[["__json_message",25,"This is a message."]]"
// Correct output achieved
var a = JSON.parse(s.substring(s.indexOf("$")+1))

The issue stemmed from converting commas to octal escape codes in the string preparation for the cookie, which is not allowed in JSON formatting. The related error message should have been JSON forbids octal prefixes. Once this is rectified by replacing octal with hex escape codes, it will function properly. Therefore, I will implement a check for octal escapes and substitute them with hex equivalents.

TL;DR: "SyntaxError: Unexpected Number" equates to "SyntaxError: JSON forbids octal prefixes"

Below is the function I employed

var s = "\"d967fac49ef2466239168bbbde0a8d755a27ba81$[[\\\"__json_message\\\"\\05425\\054\\\"This is a message.\\\"]]\"""
var re = /\\0([0-7]{2})/g
JSON.parse(s.replace(re, function(m, n){return "\\x"+("0000"+parseInt(n,8).toString(16)).slice(-4)}))

When attempting to parse a single string stored in a cookie with JSON.parse, it results in a "SyntaxError: Unexpected Number" error being thrown

Answer №1

TL;DR: "SyntaxError: Unexpected Number" equates to "SyntaxError: JSON forbids octal prefixes"

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