Simple S3 client (#836)

This functionality is intended to be used to manage datasets for test cases, but may be useful elsewhere in the future.

- **Add S3 client with AWS Signature V4 (SigV4) signing** — new `S3Client` in `zenutil/cloud/` supporting `GetObject`, `PutObject`, `DeleteObject`, `HeadObject`, and `ListObjects` operations
- **Add EC2 IMDS credential provider** — automatically fetches and refreshes temporary AWS credentials from the EC2 Instance Metadata Service (IMDSv2) for use by the S3 client
- **Add SigV4 signing library** — standalone implementation of AWS Signature Version 4 request signing (headers and query-string presigning)
- **Add path-style addressing support** — enables compatibility with S3-compatible stores like MinIO (in addition to virtual-hosted style)
- **Add S3 integration tests** — includes a `MinioProcess` test helper that spins up a local MinIO server, plus integration tests exercising the S3 client end-to-end
- **Add S3-backed `HttpObjectStoreService` tests** — integration tests verifying the zenserver object store works against an S3 backend
- **Refactor mock IMDS into `zenutil/cloud/`** — moved and generalized the mock IMDS server from `zencompute` so it can be reused by both compute and S3 credential tests

1 files changed, 1 insertions, 204 deletions

diff --git a/src/zencompute/testing/mockimds.cpp b/src/zencompute/testing/mockimds.cpp
index dd09312df..5415f48f3 100644
--- a/src/zencompute/testing/mockimds.cpp
+++ b/src/zencompute/testing/mockimds.cpp
@@ -1,205 +1,2 @@
 // Copyright Epic Games, Inc. All Rights Reserved.
-
-#include <zencompute/mockimds.h>
-
-#include <zencore/fmtutils.h>
-
-#if ZEN_WITH_TESTS
-
-namespace zen::compute {
-
-const char*
-MockImdsService::BaseUri() const
-{
-	return "/";
-}
-
-void
-MockImdsService::HandleRequest(HttpServerRequest& Request)
-{
-	std::string_view Uri = Request.RelativeUri();
-
-	// AWS endpoints live under /latest/
-	if (Uri.starts_with("latest/"))
-	{
-		if (ActiveProvider == CloudProvider::AWS)
-		{
-			HandleAwsRequest(Request);
-			return;
-		}
-		Request.WriteResponse(HttpResponseCode::NotFound);
-		return;
-	}
-
-	// Azure endpoints live under /metadata/
-	if (Uri.starts_with("metadata/"))
-	{
-		if (ActiveProvider == CloudProvider::Azure)
-		{
-			HandleAzureRequest(Request);
-			return;
-		}
-		Request.WriteResponse(HttpResponseCode::NotFound);
-		return;
-	}
-
-	// GCP endpoints live under /computeMetadata/
-	if (Uri.starts_with("computeMetadata/"))
-	{
-		if (ActiveProvider == CloudProvider::GCP)
-		{
-			HandleGcpRequest(Request);
-			return;
-		}
-		Request.WriteResponse(HttpResponseCode::NotFound);
-		return;
-	}
-
-	Request.WriteResponse(HttpResponseCode::NotFound);
-}
-
-// ---------------------------------------------------------------------------
-// AWS
-// ---------------------------------------------------------------------------
-
-void
-MockImdsService::HandleAwsRequest(HttpServerRequest& Request)
-{
-	std::string_view Uri = Request.RelativeUri();
-
-	// IMDSv2 token acquisition (PUT only)
-	if (Uri == "latest/api/token" && Request.RequestVerb() == HttpVerb::kPut)
-	{
-		Request.WriteResponse(HttpResponseCode::OK, HttpContentType::kText, Aws.Token);
-		return;
-	}
-
-	// Instance identity
-	if (Uri == "latest/meta-data/instance-id")
-	{
-		Request.WriteResponse(HttpResponseCode::OK, HttpContentType::kText, Aws.InstanceId);
-		return;
-	}
-
-	if (Uri == "latest/meta-data/placement/availability-zone")
-	{
-		Request.WriteResponse(HttpResponseCode::OK, HttpContentType::kText, Aws.AvailabilityZone);
-		return;
-	}
-
-	if (Uri == "latest/meta-data/instance-life-cycle")
-	{
-		Request.WriteResponse(HttpResponseCode::OK, HttpContentType::kText, Aws.LifeCycle);
-		return;
-	}
-
-	// Autoscaling lifecycle state — 404 when not in an ASG
-	if (Uri == "latest/meta-data/autoscaling/target-lifecycle-state")
-	{
-		if (Aws.AutoscalingState.empty())
-		{
-			Request.WriteResponse(HttpResponseCode::NotFound);
-			return;
-		}
-		Request.WriteResponse(HttpResponseCode::OK, HttpContentType::kText, Aws.AutoscalingState);
-		return;
-	}
-
-	// Spot interruption notice — 404 when no interruption pending
-	if (Uri == "latest/meta-data/spot/instance-action")
-	{
-		if (Aws.SpotAction.empty())
-		{
-			Request.WriteResponse(HttpResponseCode::NotFound);
-			return;
-		}
-		Request.WriteResponse(HttpResponseCode::OK, HttpContentType::kText, Aws.SpotAction);
-		return;
-	}
-
-	Request.WriteResponse(HttpResponseCode::NotFound);
-}
-
-// ---------------------------------------------------------------------------
-// Azure
-// ---------------------------------------------------------------------------
-
-void
-MockImdsService::HandleAzureRequest(HttpServerRequest& Request)
-{
-	std::string_view Uri = Request.RelativeUri();
-
-	// Instance metadata (single JSON document)
-	if (Uri == "metadata/instance")
-	{
-		std::string Json = fmt::format(R"({{"compute":{{"vmId":"{}","location":"{}","priority":"{}","vmScaleSetName":"{}"}}}})",
-									   Azure.VmId,
-									   Azure.Location,
-									   Azure.Priority,
-									   Azure.VmScaleSetName);
-
-		Request.WriteResponse(HttpResponseCode::OK, HttpContentType::kText, Json);
-		return;
-	}
-
-	// Scheduled events for termination monitoring
-	if (Uri == "metadata/scheduledevents")
-	{
-		std::string Json;
-		if (Azure.ScheduledEventType.empty())
-		{
-			Json = R"({"Events":[]})";
-		}
-		else
-		{
-			Json = fmt::format(R"({{"Events":[{{"EventType":"{}","EventStatus":"{}"}}]}})",
-							   Azure.ScheduledEventType,
-							   Azure.ScheduledEventStatus);
-		}
-
-		Request.WriteResponse(HttpResponseCode::OK, HttpContentType::kText, Json);
-		return;
-	}
-
-	Request.WriteResponse(HttpResponseCode::NotFound);
-}
-
-// ---------------------------------------------------------------------------
-// GCP
-// ---------------------------------------------------------------------------
-
-void
-MockImdsService::HandleGcpRequest(HttpServerRequest& Request)
-{
-	std::string_view Uri = Request.RelativeUri();
-
-	if (Uri == "computeMetadata/v1/instance/id")
-	{
-		Request.WriteResponse(HttpResponseCode::OK, HttpContentType::kText, Gcp.InstanceId);
-		return;
-	}
-
-	if (Uri == "computeMetadata/v1/instance/zone")
-	{
-		Request.WriteResponse(HttpResponseCode::OK, HttpContentType::kText, Gcp.Zone);
-		return;
-	}
-
-	if (Uri == "computeMetadata/v1/instance/scheduling/preemptible")
-	{
-		Request.WriteResponse(HttpResponseCode::OK, HttpContentType::kText, Gcp.Preemptible);
-		return;
-	}
-
-	if (Uri == "computeMetadata/v1/instance/maintenance-event")
-	{
-		Request.WriteResponse(HttpResponseCode::OK, HttpContentType::kText, Gcp.MaintenanceEvent);
-		return;
-	}
-
-	Request.WriteResponse(HttpResponseCode::NotFound);
-}
-
-}  // namespace zen::compute
-
-#endif	// ZEN_WITH_TESTS
+// Moved to zenutil/cloud/mockimds.cpp