Represents a predicate that evaluates to true if a header value matches a specified condition.
Namespace: System.Net.Http.Headers
Assembly: System.Net.Http.dll
Initializes a new instance of the HttpPredicateHeaderValue class with the specified header name and predicate.
Initializes a new instance of the HttpPredicateHeaderValue class with the specified header name and an exact header value to match.
Evaluate(
string headerValue
)
Evaluates the predicate against the given header value.
| Name | Type | Description |
|---|---|---|
headerValue |
string |
The header value to evaluate. |
true if the header value satisfies the predicate; otherwise, false.
The HttpPredicateHeaderValue class is useful for scenarios where you need to conditionally process HTTP requests or responses based on the values of specific headers. For example, you might use it to check for the presence or specific format of headers like Accept, Content-Type, or custom headers.
The predicate function allows for flexible matching logic, going beyond simple equality checks. You can define complex rules based on string manipulation, regular expressions, or any other custom logic.
When initializing with an exact string value, it creates a predicate that checks for strict equality.
using System;
using System.Net.Http.Headers;
public class Example
{
public static void Main(string[] args)
{
// Create a predicate to match 'application/json' Content-Type
var jsonPredicate = new HttpPredicateHeaderValue("Content-Type", "application/json");
// Create a predicate with a custom logic for checking if a header value starts with 'image/'
var imagePredicate = new HttpPredicateHeaderValue("Content-Type", value => value.StartsWith("image/", StringComparison.OrdinalIgnoreCase));
string contentType1 = "application/json; charset=utf-8";
string contentType2 = "image/png";
string contentType3 = "text/plain";
Console.WriteLine($"Is '{contentType1}' a JSON content type? {jsonPredicate.Evaluate(contentType1)}"); // Output: True
Console.WriteLine($"Is '{contentType2}' a JSON content type? {jsonPredicate.Evaluate(contentType2)}"); // Output: False
Console.WriteLine($"Is '{contentType1}' an image content type? {imagePredicate.Evaluate(contentType1)}"); // Output: False
Console.WriteLine($"Is '{contentType2}' an image content type? {imagePredicate.Evaluate(contentType2)}"); // Output: True
Console.WriteLine($"Is '{contentType3}' an image content type? {imagePredicate.Evaluate(contentType3)}"); // Output: False
}
}