Pattern to identify a JSON string with Regular Expressions

Currently, I am working on developing a JSON validator from the ground up and have hit a roadblock when it comes to the string component. My original plan was to create a regex pattern that aligns with the sequence specified on JSON.org:

https://i.sstatic.net/JKW9V.gif

Here is the regex I have come up with so far:

/^\"((?=\\)\\(\"|\/|\\|b|f|n|r|t|u[0-9a-f]{4}))*\"$/

This regex successfully matches instances where there is a backslash followed by a character and an empty string. However, my dilemma lies in incorporating UNICODE characters.

Is there a regex pattern that can identify any UNICODE character excluding " or \ or control characters? Will it also detect a newline or horizontal tab?

I noticed that while the regex matches the string "\t", it does not recognize " " (four spaces meant to signify a tab). While extending the regex is an option, my hunch is that the horizontal tab is a UNICODE character.

Credit goes to Jaeger Kor for updating my regex to the following:

/^\"((?=\\)\\(\"|\/|\\|b|f|n|r|t|u[0-9a-f]{4})|[^\\"]*)*\"$/

This revised regex seems accurate, but should I be checking for control characters separately? Or is this unnecessary considering they fall under non-printable characters as per regular-expressions.info? The input being validated always originates from a textarea.

As an update, here is the finalized regex for reference:

/^("(((?=\\)\\(["\\\/bfnrt]|u[0-9a-fA-F]{4}))|[^"\\\0-\x1F\x7F]+)*")$/
javascriptjsonregexunicode

Answer №1

If you have a specific question, you can create a character class for it:

# Use this to match any character except \ or "
/[^\\"]/

You can then add * at the end for zero or unlimited occurrences, or use + for one or more:

/[^\\"]*/

Another option is provided below, found on https://regex101.com/ under the library tab when searching for json:

/(?(DEFINE)
# This regex defines atomic patterns for JSON without backtracking
(?<json>(?>\s*(?&object)\s*|\s*(?&array)\s*))
(?<object>(?>\{\s*(?>(?&pair)(?>\s*,\s*(?&pair))*)?\s*\}))
(?<pair>(?>(?&STRING)\s*:\s*(?&value)))
(?<array>(?>>\[\s*(?>(?&value)(?>\s*,\s*(?&value))*)?\s*\]))
(?<value>(?>>true|false|null|(?&STRING)|(?&NUMBER)|(?&object)|(?&array)))
(?<STRING>(?>>"(?>\\(?>["\\\/bfnrt]|u[a-fA-F0-9]{4})|[^"\\\0-\x1F\x7F]+)*"))
(?<NUMBER>(?>>-?(?>0|[1-9][0-9]*)(?>.\.[0-9]+)?(?>[eE][+-]?[0-9]+)?))
)
\A(?&json)\z/x

This regex matches any valid JSON format and can be tested on the website mentioned above.

EDIT:

Link to the regex

Answer №2

Try using this regular expression, which can also handle arrays of JSON objects:

((\[[^\}]{3,})?\{s*[^\}\{]{3,}?:.*\}([^\{]+\])?)

Check out the demo here: https://regex101.com/r/aHAnJL/1

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