Custom batch handler in asp.net webapi - api

Question

I want to write custom batch handler in my webapi.
Requirement for this : I am not able to identify weather the incoming request is part of batch or independent.
By writing custom batch handler i will be able to add value in header of each request, which i can use later to identify.

Answer 1

First we need to write custom batch hahttps://stackoverflow.blog/2011/07/01/its-ok-to-ask-and-answer-your-own-questions/ndler
For this we need to override HttpMessageHandler. Below is code
public class BatchHandler : HttpMessageHandler
{
HttpMessageInvoker _server;
public BatchHandler(HttpConfiguration config)
{
// BatchServer is a class which overrides
_server = new HttpMessageInvoker(new BatchServer(config));
}
protected override async Task<HttpResponseMessage> SendAsync(
HttpRequestMessage request,
CancellationToken cancellationToken)
{
// Return 400 for the wrong MIME type
// As batch request will always be of MIME type
if ("multipart/mixed" !=
request.Content.Headers.ContentType.MediaType)
{
return request.CreateResponse(HttpStatusCode.BadRequest);
}
// Start a multipart response
var outerContent = new MultipartContent("batch");
var outerResp = request.CreateResponse();
outerResp.Content = outerContent;
// Read the multipart request
var multipart = await request.Content.ReadAsMultipartAsync();
foreach (var httpContent in multipart.Contents)
{
HttpResponseMessage innerResp = null;
try
{
// Decode the request object
var innerReq = await
httpContent.ReadAsHttpRequestMessageAsync();
innerReq.Headers.Add("IsBatch", "true");
// Send the request through the pipeline
innerResp = await _server.SendAsync(
innerReq,
cancellationToken
);
}
catch (Exception ex)
{
// If exceptions are thrown, send back generic 400
innerResp = new HttpResponseMessage(
HttpStatusCode.BadRequest
);
}
// Wrap the response in a message content and put it
// into the multipart response
outerContent.Add(new HttpMessageContent(innerResp));
}
return outerResp;
}
}
in above code their is this line
// BatchServer is a class which overrides HttpServer
_server = new HttpMessageInvoker(new BatchServer(config));
if we don't do this we gets an error
The 'DelegatingHandler' list is invalid because the property
'InnerHandler' of 'xxhandler' is not null.\r\nParameter
name: handlers
Below is the BatchServer class which overrides HttpServer
public class BatchServer : HttpServer
{
private readonly HttpConfiguration _config;
public BatchServer(HttpConfiguration configuration)
: base(configuration)
{
_config = configuration;
}
protected override void Initialize()
{
var firstInPipeline = _config.MessageHandlers.FirstOrDefault();
if (firstInPipeline != null && firstInPipeline.InnerHandler != null)
{
InnerHandler = firstInPipeline;
}
else
{
base.Initialize();
}
}
}
Now we want to hit batch request on BatchHandler
For this we need configure route to BatchHandler
Add below code to your AppStart
var batchHandler = new BatchHandler(config);
config.Routes.MapHttpRoute("batch", "api/batch", null, null, batchHandler);