Input formatters are specialized components in ASP.NET Core MVC responsible for deserializing data from the body of HTTP requests. When a request arrives with a payload, the input formatter decodes this data into a format (e.g., C# objects, collections) that your action methods can readily work with.
How Input Formatters Work Content Negotiation: The model binding process begins with content negotiation, where ASP.NET Core examines the Content-Type header of the request to determine the format of the incoming data (e.g., JSON, XML). Input Formatter Selection: Based on the Content-Type, ASP.NET Core selects an appropriate input formatter that knows how to handle that specific data format. Deserialization: The selected input formatter deserializes the raw data from the request body into C# objects, collections, or other supported types. Model Binding: The deserialized data is then passed to the model binder, which populates the parameters of your action method.
Common Input Formatters NewtonsoftJsonInputFormatter: Handles JSON (JavaScript Object Notation) data using the popular Newtonsoft.Json library. SystemTextJsonInputFormatter: Handles JSON data using the built-in System.Text.Json serializer. XmlSerializerInputFormatter: Handles XML (Extensible Markup Language) data using the XmlSerializer.
Configuring Input Formatters Default Formatters: ASP.NET Core MVC includes NewtonsoftJsonInputFormatter as a default formatter. Additional Formatters: You can add support for other formatters (like XmlSerializerInputFormatter) by explicitly registering them in your application’s startup configuration.
Code var builder = WebApplication.CreateBuilder(args); builder.Services.AddControllers().AddXmlSerializerFormatters(); // … other configuration … In this code, the .AddXmlSerializerFormatters() extension method registers the XmlSerializerInputFormatter, enabling your application to handle requests with an application/xml content type.
Using Input Formatters Implicit Binding: If the Content-Type header of the request matches a supported format, the corresponding input formatter is automatically used. You don’t need to explicitly specify which formatter to use in your action method. Explicit Binding ([FromBody]): You can use the [FromBody] attribute on an action method parameter to explicitly tell the model binder to look for the data in the request body. This is often used when you have complex objects that need to be deserialized.
Important Considerations Content Negotiation: The success of model binding depends on the client sending a valid Content-Type header that your application supports. Error Handling: Handle potential deserialization errors gracefully. If the input formatter cannot parse the request body, return an appropriate error response (e.g., 400 Bad Request). Security: Always validate and sanitize data deserialized from the request body to protect against security vulnerabilities. Custom Input Formatters: For highly specialized scenarios or custom data formats, you can create your own input formatters by implementing the IInputFormatter interface.
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FromBody Attribute in Asp.net Core