DESIGN-NOTES.md

Handle HTTP

• Router - Incoming - Read Request (writes response to Lambda, sending the request)
  • The request is already parsed by Kestrel
  • We just need to write out the headers, a blank line, then the body
  • Incoming/Outgoing: We don't even have to figure out the chunk lengths as Kestrel is doing that for us
• Router - Callback - Read Request (receives response from Lambda, writes response to incoming)
  • The response is written via Kestrel
  • The chunk lengths are already parsed by Kestrel and removed from the body
  • We can write directly to the Incoming response as we read from the Callback Request
  • We can possibly use a CopyToAsync to write the body
  • The only tricky bit is not using StreamReader for the headers
  • This should look most like the ResponseParser in Kestrel
• Lambda - Incoming - Read Request
  • HttpClient supports response before request for HTTP2 and HTTP3
  • System.Net.Http.HttpRequestMessage can be used to represent the parsed request
  • We have to read the chunk sizes, read the headers in the body, then read the body while removing the chunk sizes from the body
  • The actual request could be chunked too in which case there would be chunking within chunking which is fine
  • Could we use Kestrels classes to parse the request?
  • https://github.com/dotnet/runtime/blob/main/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/ChunkedEncodingReadStream.cs
• Lambda - Proxy - Write Response
  • HttpClient supports response before request for HTTP2 and HTTP3
  • We have to write the chunk sizes, write the headers in the body, then write the body
  • https://github.com/dotnet/runtime/blob/main/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/ChunkedEncodingWriteStream.cs
• Lambda - KeepAlive on HTTP
  • KeepAlive can be used if we:
    • Read and discard a blank line after the response from the Router
    • Write a blank line after the request to the Router
    • We can then reuse the same socket for the next request/response
    • Use a loop on GetRequest before destroying the TcpReverseRequester
  • This will significantly reduce the socket churn and CPU overhead from that

Kestrel C# Request/Response Parser

Http1ParsingHandler

https://github.com/dotnet/aspnetcore/blob/52364da7f2d8e8956085a92c2f6b9dae48ac130d/src/Servers/Kestrel/Core/src/Internal/Http/Http1ParsingHandler.cs

HttpParser

https://github.com/dotnet/aspnetcore/blob/52364da7f2d8e8956085a92c2f6b9dae48ac130d/src/Servers/Kestrel/Core/src/Internal/Http/HttpParser.cs

AWS Docs

Lambda Invoke Request

https://docs.aws.amazon.com/lambda/latest/dg/API_Invoke.html

Lambda Runtime Endpoints and Requests

https://docs.aws.amazon.com/lambda/latest/dg/runtimes-api.html