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, 91 insertions, 1 deletions

diff --git a/src/zenserver-test/objectstore-tests.cpp b/src/zenserver-test/objectstore-tests.cpp
index f3db5fdf6..1f6a7675c 100644
--- a/src/zenserver-test/objectstore-tests.cpp
+++ b/src/zenserver-test/objectstore-tests.cpp
@@ -2,10 +2,12 @@
 
 #if ZEN_WITH_TESTS
 #	include "zenserver-test.h"
+#	include <zencore/memoryview.h>
 #	include <zencore/testing.h>
 #	include <zencore/testutils.h>
-#	include <zenutil/zenserverprocess.h>
 #	include <zenhttp/httpclient.h>
+#	include <zenutil/cloud/s3client.h>
+#	include <zenutil/zenserverprocess.h>
 
 ZEN_THIRD_PARTY_INCLUDES_START
 #	include <tsl/robin_set.h>
@@ -68,6 +70,94 @@ TEST_CASE("objectstore.blobs")
 	}
 }
 
+TEST_CASE("objectstore.s3client")
+{
+	ZenServerInstance Instance(TestEnv);
+	const uint16_t	  Port = Instance.SpawnServerAndWaitUntilReady("--objectstore-enabled");
+	CHECK_MESSAGE(Port != 0, Instance.GetLogOutput());
+
+	// S3Client in path-style builds paths as /{bucket}/{key}.
+	// The objectstore routes objects at bucket/{bucket}/{key} relative to its base.
+	// Point the S3Client endpoint at {server}/obj/bucket so the paths line up.
+	S3ClientOptions Opts;
+	Opts.BucketName					 = "s3test";
+	Opts.Region						 = "us-east-1";
+	Opts.Endpoint					 = fmt::format("http://localhost:{}/obj/bucket", Port);
+	Opts.PathStyle					 = true;
+	Opts.Credentials.AccessKeyId	 = "testkey";
+	Opts.Credentials.SecretAccessKey = "testsecret";
+
+	S3Client Client(Opts);
+
+	// -- PUT + GET roundtrip --
+	std::string_view TestData = "hello from s3client via objectstore"sv;
+	IoBuffer		 Content  = IoBufferBuilder::MakeFromMemory(MakeMemoryView(TestData));
+	S3Result		 PutRes	  = Client.PutObject("test/hello.txt", std::move(Content));
+	REQUIRE_MESSAGE(PutRes.IsSuccess(), PutRes.Error);
+
+	S3GetObjectResult GetRes = Client.GetObject("test/hello.txt");
+	REQUIRE_MESSAGE(GetRes.IsSuccess(), GetRes.Error);
+	CHECK(GetRes.AsText() == TestData);
+
+	// -- PUT overwrites --
+	IoBuffer Original  = IoBufferBuilder::MakeFromMemory(MakeMemoryView("original"sv));
+	IoBuffer Overwrite = IoBufferBuilder::MakeFromMemory(MakeMemoryView("overwritten"sv));
+	REQUIRE(Client.PutObject("overwrite/file.txt", std::move(Original)).IsSuccess());
+	REQUIRE(Client.PutObject("overwrite/file.txt", std::move(Overwrite)).IsSuccess());
+
+	S3GetObjectResult OverwriteGet = Client.GetObject("overwrite/file.txt");
+	REQUIRE(OverwriteGet.IsSuccess());
+	CHECK(OverwriteGet.AsText() == "overwritten"sv);
+
+	// -- GET not found --
+	S3GetObjectResult NotFoundGet = Client.GetObject("nonexistent/file.dat");
+	CHECK_FALSE(NotFoundGet.IsSuccess());
+
+	// -- HEAD found --
+	std::string_view HeadData	 = "head test data"sv;
+	IoBuffer		 HeadContent = IoBufferBuilder::MakeFromMemory(MakeMemoryView(HeadData));
+	REQUIRE(Client.PutObject("head/meta.txt", std::move(HeadContent)).IsSuccess());
+
+	S3HeadObjectResult HeadRes = Client.HeadObject("head/meta.txt");
+	REQUIRE_MESSAGE(HeadRes.IsSuccess(), HeadRes.Error);
+	CHECK(HeadRes.Status == HeadObjectResult::Found);
+	CHECK(HeadRes.Info.Size == HeadData.size());
+
+	// -- HEAD not found --
+	S3HeadObjectResult HeadNotFound = Client.HeadObject("nonexistent/file.dat");
+	CHECK(HeadNotFound.IsSuccess());
+	CHECK(HeadNotFound.Status == HeadObjectResult::NotFound);
+
+	// -- LIST objects --
+	for (int i = 0; i < 3; ++i)
+	{
+		std::string Key		= fmt::format("listing/item-{}.txt", i);
+		std::string Payload = fmt::format("content-{}", i);
+		IoBuffer	Buf		= IoBufferBuilder::MakeFromMemory(MakeMemoryView(Payload));
+		REQUIRE(Client.PutObject(Key, std::move(Buf)).IsSuccess());
+	}
+
+	S3ListObjectsResult ListRes = Client.ListObjects("listing/");
+	REQUIRE_MESSAGE(ListRes.IsSuccess(), ListRes.Error);
+	REQUIRE(ListRes.Objects.size() == 3);
+
+	std::vector<std::string> Keys;
+	for (const S3ObjectInfo& Obj : ListRes.Objects)
+	{
+		Keys.push_back(Obj.Key);
+		CHECK(Obj.Size > 0);
+	}
+	std::sort(Keys.begin(), Keys.end());
+	CHECK(Keys[0] == "listing/item-0.txt");
+	CHECK(Keys[1] == "listing/item-1.txt");
+	CHECK(Keys[2] == "listing/item-2.txt");
+
+	// -- LIST empty prefix --
+	S3ListObjectsResult EmptyList = Client.ListObjects("no-such-prefix/");
+	REQUIRE(EmptyList.IsSuccess());
+	CHECK(EmptyList.Objects.empty());
+}
+
 TEST_SUITE_END();
 
 }  // namespace zen::tests