Fetch

FetchExpression performs an HTTP request via IHttpClientFactory within an expression tree. It resolves IHttpClientFactory from the service provider at compile time and produces a Task<HttpResponseMessage>.

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Factory Methods

using static Hyperbee.Expressions.Lab.ExpressionExtensions;

FetchExpression Fetch(
    Expression url,
    Expression? method = null,
    Expression? headers = null,
    Expression? content = null )

FetchExpression Fetch(
    Expression clientName,
    Expression url,
    Expression? method = null,
    Expression? headers = null,
    Expression? content = null )

Parameter	Type	Description
clientName	Expression (string)	Named HTTP client (from IHttpClientFactory)
url	Expression (string)	Request URL
method	Expression? (string)	HTTP method – "GET", "POST", etc. Default: "GET"
headers	Expression? (IDictionary<string,string>)	Additional request headers
content	Expression? (HttpContent)	Request body content

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Usage

Simple GET Request

using static System.Linq.Expressions.Expression;
using static Hyperbee.Expressions.Lab.ExpressionExtensions;

var response = Variable( typeof(HttpResponseMessage), "response" );

var asyncBlock = BlockAsync(
    [response],
    Assign(
        response,
        Await( Fetch( Constant( "https://api.example.com/data" ) ) )
    ),
    response
);

var lambda = Lambda<Func<Task<HttpResponseMessage>>>( asyncBlock );
var fn = lambda.Compile( serviceProvider );
var result = await fn();

Read Response as JSON

using static Hyperbee.Expressions.Lab.FetchExpressionExtensions;

var fetch = Fetch( Constant( "https://api.example.com/user/1" ) );

// ReadJson<T> chains the deserialization onto the fetch
var user = Variable( typeof(User), "user" );

var asyncBlock = BlockAsync(
    [user],
    Assign( user, Await( ReadJson( fetch, typeof(User) ) ) ),
    user
);

POST with Content

var fetch = Fetch(
    url: Constant( "https://api.example.com/data" ),
    method: Constant( "POST" ),
    content: Constant( new StringContent( """{"key":"value"}""", Encoding.UTF8, "application/json" ) )
);

Named HTTP Client

// Uses the named client registered as "api-client" in AddHttpClient(...)
var fetch = Fetch(
    clientName: Constant( "api-client" ),
    url: Constant( "https://internal.api/endpoint" )
);

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FetchExpressionExtensions

FetchExpressionExtensions provides helper methods to chain response reading:

Method	Returns	Description
ReadJson( fetch, type )	Task<T>	Deserialize response body as JSON
ReadText( fetch )	Task<string>	Read response body as string
ReadBytes( fetch )	Task<byte[]>	Read response body as bytes
ReadStream( fetch )	Task<Stream>	Read response body as stream

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Notes

• FetchExpression implements IDependencyInjectionExpression. IHttpClientFactory is resolved from the service provider when Compile(serviceProvider) is called.
• If no named client is specified, the default HttpClient is used.
• FetchExpression.Type is typeof(Task<HttpResponseMessage>) – wrap in Await inside an async block.