flutter data_error ai_generated true

FormatException: Unexpected character (at character 2)

ID: flutter/dart-format-exception-json-decode

Also available as: JSON · Markdown · 中文
90%Fix Rate
85%Confidence
1Evidence
2023-11-20First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
Flutter 3.22.0 active — — —
Dart 3.4.0 active — — —
http 1.2.1 active — — —
dio 5.4.0 active — — —

Root Cause

Invalid JSON string received from a network request or local file, possibly truncated or malformed.

generic

中文

从网络请求或本地文件接收到的 JSON 字符串无效，可能被截断或格式错误。

Official Documentation

https://api.dart.dev/stable/3.4.0/dart-convert/FormatException-class.html

Workarounds

  1. 95% success Log the raw response body before decoding to inspect the actual content: `print(response.body);` and check for truncation or extra characters. 
    Log the raw response body before decoding to inspect the actual content: `print(response.body);` and check for truncation or extra characters.
  2. 80% success Use a JSON preprocessor to remove BOM or control characters: `String cleaned = response.body.replaceAll(RegExp(r'[\x00-\x1F\x7F]'), '');` then decode. 
    Use a JSON preprocessor to remove BOM or control characters: `String cleaned = response.body.replaceAll(RegExp(r'[\x00-\x1F\x7F]'), '');` then decode.
  3. 70% success Add a retry mechanism with exponential backoff for network requests to handle transient truncation. 
    Add a retry mechanism with exponential backoff for network requests to handle transient truncation.

中文步骤

  1. Log the raw response body before decoding to inspect the actual content: `print(response.body);` and check for truncation or extra characters.
  2. Use a JSON preprocessor to remove BOM or control characters: `String cleaned = response.body.replaceAll(RegExp(r'[\x00-\x1F\x7F]'), '');` then decode.
  3. Add a retry mechanism with exponential backoff for network requests to handle transient truncation.

Dead Ends

Common approaches that don't work:

  1. 90% fail

    Ignoring the error leaves the app in an inconsistent state with null data, causing downstream crashes.

  2. 95% fail

    The format exception is raised by Dart's standard decoder; other libraries use the same parser.

  3. 85% fail

    The error is about JSON syntax, not character encoding; changing encoding may worsen the issue.