wip - support streamable

Author: sebsto

Sources/AWSLambdaRuntime/Lambda+LocalServer.swift

@@ -243,22 +243,36 @@ internal struct LambdaHTTPServer {
                             requestHead = head
 
                         case .body(let body):
-                            requestBody.setOrWriteImmutableBuffer(body)
+                            precondition(requestHead != nil, "Received .body without .head")
+
+                            // if this is a request from a Streaming Lambda Handler,
+                            // stream the response instead of buffering it
+                            if self.isStreamingResponse(requestHead) {
+                                // we are receiving a chunked body,
+                                // we can stream the response and not accumulate the chunks 
+                                print(String(buffer: body))
+                            } else {
+                                requestBody.setOrWriteImmutableBuffer(body)
+                            }
 
                         case .end:
                             precondition(requestHead != nil, "Received .end without .head")
-                            // process the request
-                            let response = try await self.processRequest(
-                                head: requestHead,
-                                body: requestBody,
-                                logger: logger
-                            )
-                            // send the responses
-                            try await self.sendResponse(
-                                response: response,
-                                outbound: outbound,
-                                logger: logger
-                            )
+                            
+                            // process the buffered response for non streaming requests
+                            if !self.isStreamingResponse(requestHead) {
+                                // process the complete request
+                                let response = try await self.processCompleteRequest(
+                                    head: requestHead,
+                                    body: requestBody,
+                                    logger: logger
+                                )
+                                // send the responses
+                                try await self.sendCompleteResponse(
+                                    response: response,
+                                    outbound: outbound,
+                                    logger: logger
+                                )
+                            }
 
                             requestHead = nil
                             requestBody = nil
@@ -273,6 +287,15 @@ internal struct LambdaHTTPServer {
         }
     }
 
+    /// This function checks if the request is a streaming response request
+    /// verb = POST, uri = :requestID/response, HTTP Header contains "Transfer-Encoding: chunked"
+    private func isStreamingResponse(_ requestHead: HTTPRequestHead) -> Bool {
+        requestHead.method == .POST &&
+        requestHead.uri.hasSuffix(Consts.postResponseURLSuffix) &&
+        requestHead.headers.contains(name: "Transfer-Encoding") &&
+        requestHead.headers["Transfer-Encoding"].contains("chunked")
+    }
+
     /// This function process the URI request sent by the client and by the Lambda function
     ///
     /// It enqueues the client invocation and iterate over the invocation queue when the Lambda function sends /next request
@@ -283,7 +306,7 @@ internal struct LambdaHTTPServer {
     ///   - body: the HTTP request body
     /// - Throws:
     /// - Returns: the response to send back to the client or the Lambda function
-    private func processRequest(
+    private func processCompleteRequest(
         head: HTTPRequestHead,
         body: ByteBuffer?,
         logger: Logger
@@ -406,7 +429,7 @@ internal struct LambdaHTTPServer {
         }
     }
 
-    private func sendResponse(
+    private func sendCompleteResponse(
         response: LocalServerResponse,
         outbound: NIOAsyncChannelOutboundWriter<HTTPServerResponsePart>,
         logger: Logger