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Global Filters

4/22/26Less than 1 minute

Global Filters

In addition to applying IApiFilterAttribute subclass attributes in interface declarations, you can also register IApiFilter type filters during interface configuration.

These filters apply to the entire interface and execute before IApiFilterAttribute filters applied via attributes.

Configuring Global Filters

services.AddHttpApi<IUserApi>().ConfigureHttpApi(o =>
{
    o.GlobalFilters.Add(new UserFilter());
});

Implementing Custom Filters

public class UserFilter : IApiFilter
{
    public async Task OnRequestAsync(ApiRequestContext context)
    {
        // Pre-request processing
        var userContext = context.HttpContext.ServiceProvider.GetRequiredService<IUserContext>();
        context.HttpContext.RequestMessage.Headers.Add("X-User-Id", userContext.UserId);
    }

    public async Task OnResponseAsync(ApiResponseContext context)
    {
        // Post-response processing
        var response = context.HttpContext.ResponseMessage;
        // Logging, monitoring, etc.
    }
}

Filter Execution Order

  1. Interface-level GlobalFilters (in order of addition)
  2. Interface-declared IApiFilterAttribute attributes
  3. Method-declared IApiFilterAttribute attributes

Common Use Cases

Request Signing

public class SignFilter : IApiFilter
{
    public async Task OnRequestAsync(ApiRequestContext context)
    {
        var signService = context.HttpContext.ServiceProvider.GetRequiredService<SignService>();
        var sign = signService.SignValue(DateTime.Now);
        context.HttpContext.RequestMessage.AddUrlQuery("sign", sign);
    }

    public Task OnResponseAsync(ApiResponseContext context) => Task.CompletedTask;
}

services.AddHttpApi<IExternalApi>().ConfigureHttpApi(o =>
{
    o.GlobalFilters.Add(new SignFilter());
});

Request Logging

public class RequestLoggingFilter : IApiFilter
{
    private readonly ILogger<RequestLoggingFilter> _logger;

    public RequestLoggingFilter(ILogger<RequestLoggingFilter> logger)
    {
        _logger = logger;
    }

    public async Task OnRequestAsync(ApiRequestContext context)
    {
        var request = context.HttpContext.RequestMessage;
        _logger.LogInformation("Request: {Method} {Uri}", request.Method, request.RequestUri);
    }

    public async Task OnResponseAsync(ApiResponseContext context)
    {
        var response = context.HttpContext.ResponseMessage;
        _logger.LogInformation("Response: {StatusCode}", response.StatusCode);
    }
}

Tenant Context Injection

public class TenantFilter : IApiFilter
{
    public async Task OnRequestAsync(ApiRequestContext context)
    {
        var tenantContext = context.HttpContext.ServiceProvider.GetRequiredService<ITenantContext>();
        context.HttpContext.RequestMessage.Headers.Add("X-Tenant-Id", tenantContext.TenantId);
    }

    public Task OnResponseAsync(ApiResponseContext context) => Task.CompletedTask;
}

Dependency Injection

Global filters support constructor dependency injection:

services.AddHttpApi<IUserApi>().ConfigureHttpApi(o =>
{
    o.GlobalFilters.Add(new SignFilter());  // If SignFilter has dependencies, register it in DI first
});

// Or use factory method
services.AddHttpApi<IUserApi>().ConfigureHttpApi((o, sp) =>
{
    o.GlobalFilters.Add(sp.GetRequiredService<SignFilter>());
});