Breaking change: deserializing JSON string into a char requires single-character string

[buyaa-n]

Deserializing JSON string into a char is now more strict to match user expectations

JsonSerializer.Deserialize<char>(payload) the payload must contain a single-character string for deserialization to succeed.
Related to dotnet/runtime#528 (comment)

Version introduced

5.0

Old behavior

When deserializing a char with JsonSerializer if payload consists multicharacter string first character was deserialized.

public static void TestDeserializeToChar()
{
    // Before (3.1): Returns the first character - 'a'
    JsonSerializer.Deserialize<char>("\"abc\"");
}

New behavior

When deserializing a char with JsonSerializer payload must contain a single-character string for deserialization to succeed, throws JsonException otherwise.

public static void TestDeserializeToChar()
{
    // After (5.0): throw JsonException because payload has more than one character
    JsonSerializer.Deserialize<char>("\"abc\"");
}

Reason for change

JsonSerializer.Deserialize<TValue>("payload") parses the text representing a single JSON value into an instance of the type specified by a generic type parameter. Parsing should only succeed when the provided payload is valid for the specified generic type parameter. For char value type a valid payload is expected to be a single character string.

Recommended action

When parsing a string to a char type using JsonSerializer.Deserialize<char>(payload) make sure the payload is non-null, non-empty, and contain a single-character string for a successful deserialization.

Category

• ASP.NET Core
• C#
• Code analysis
• Core .NET libraries
• Cryptography
• Data
• Debugger
• Deployment
• Globalization
• Interop
• JIT
• LINQ
• Managed Extensibility Framework (MEF)
• MSBuild
• Networking
• Printing
• Security
• Serialization
• Visual Basic
• Windows Forms
• Windows Presentation Foundation (WPF)
• XML, XSLT

Affected APIs

System.Text.Json.JsonSerializer.Deserialize(String, JsonSerializerOptions)

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Issue metadata

• Issue type: breaking-change