Preserve specific error types for ingress errors (#591)

Summary:

Previously, `RequestHandlerAdaptor::onError` would convert ALL ingress
errors to `kErrorRead`, losing the specific error type from the HTTP codec.
For example, a chunked encoding parse error (`kErrorParseBody`) would be
reported as generic `kErrorRead`, making debugging difficult.

This change preserves the specific `ProxygenError` from the `HTTPException`
when available, falling back to `kErrorRead` only when no specific error
is set. This matches the behavior already used for egress errors.

Before: Malformed chunked encoding → `kErrorRead`
After:  Malformed chunked encoding → `kErrorParseBody`

For upload service we log the specific proxygen error but all I saw was "READ" making it difficult to figure out what the actual issue was, seeing "ParseBody" would've made the error clear

Reviewed By: dddmello

Differential Revision: D92352456

Author: Raj Shah

proxygen/httpserver/RequestHandlerAdaptor.cpp

@@ -116,7 +116,7 @@ void RequestHandlerAdaptor::onError(const HTTPException& error) noexcept {
           .sendWithEOM();
     }
   } else if (error.getDirection() == HTTPException::Direction::INGRESS) {
-    setError(kErrorRead);
+    setError(error.hasProxygenError() ? error.getProxygenError() : kErrorRead);
 
     if (!txn_->canSendHeaders()) {
       sendAbort(folly::none);

proxygen/httpserver/tests/RequestHandlerAdaptorTest.cpp

@@ -97,6 +97,22 @@ TEST(RequestHandlerAdaptorTest, onStreamAbortError) {
   txn.onError(ex);
 }
 
+TEST(RequestHandlerAdaptorTest, onIngressErrorPreservesSpecificError) {
+  NiceMock<MockRequestHandler> requestHandler_;
+  auto adaptor = new RequestHandlerAdaptor(&requestHandler_);
+  NiceMock<MockHTTPTransactionTransport> transport;
+  HTTP2PriorityQueue egressQueue;
+  HTTPTransaction txn(
+      TransportDirection::DOWNSTREAM, 1, 1, transport, egressQueue);
+  txn.setHandler(adaptor);
+  // ingress error with specific error type (e.g., chunk parse error)
+  HTTPException ex(HTTPException::Direction::INGRESS, "chunk parse error");
+  ex.setProxygenError(kErrorParseBody);
+  // expect the specific error type is preserved, not converted to kErrorRead
+  EXPECT_CALL(requestHandler_, onError(kErrorParseBody));
+  txn.onError(ex);
+}
+
 TEST(RequestHandlerAdaptorTest, onGoaway) {
   NiceMock<MockRequestHandler> requestHandler_;
   auto adaptor = std::make_shared<RequestHandlerAdaptor>(&requestHandler_);