Sometimes I get JSON from a backend that contains unencoded/invalid characters. For example, they might contain an (unencoded) character with ASCII code 31, which means that when I try to do jsonDecode, it fails. Don't ask why the JSON-encoding on the backend is broken, it just is.
Anyway, I was wondering if there is a way to replace all unencoded characters with their encoded representations so I will be able to decode the JSON?
The solution I came up with is this. It basically checks every character in the JSON and if it is outside the "safe range" of ASCII 32-255, it JSON-encodes the character, strips any surrounding "" and adds the JSON-encoded representation instead of the unencoded character.
It could probably be improved, but it seems to do the job at least.
/// Replaces all characters that can not exist unencoded in a JSON
/// with their JSON-encoded representations.
String replaceInvalidJsonCharacters(String json) {
var charCodes = <int>[];
for (final int codeUnit in json.codeUnits) {
if( codeUnit >= 32 && codeUnit <=255 ){
// ASCII 32...255 are guaranteed to be valid in a JSON
charCodes.add(codeUnit);
}
else {
// Json-encode the character and add the encoded version.
// For characters that are valid in a JSON, the encoded version is the same
// as the original (possibly surrounded by "").
String encoded = jsonEncode(String.fromCharCode(codeUnit));
if( encoded.length > 1 ){
if( encoded.startsWith('"') ) encoded = encoded.substring(1,encoded.length);
if( encoded.endsWith('"') ) encoded = encoded.substring(0,encoded.length-1);
}
charCodes.addAll(encoded.codeUnits);
}
}
return String.fromCharCodes(charCodes);
}