Add C++ builder pattern #1018

JasonZhang517 · 2025-11-04T09:33:05Z

Corresponding to #978
Based on existing create method:
static std::optional<std::shared_ptr> Create(
const std::string& local_hostname,
const std::string& metadata_connstring, const std::string& protocol,
const std::optionalstd::string& device_names = std::nullopt,
const std::string& master_server_entry = kDefaultMasterAddress,
const std::shared_ptr& transfer_engine = nullptr);

Added builder functions with std::move to reduce copy.

gemini-code-assist · 2025-11-04T09:33:21Z

Summary of Changes

Hello @JasonZhang517, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a C++ builder pattern for the mooncake::Client class, enhancing the client creation process by offering a more structured, readable, and flexible API. The new MooncakeStoreBuilder allows for step-by-step configuration of client parameters, including validation for required fields, and optimizes string handling by leveraging std::move. This change aims to improve the maintainability and usability of client instantiation, moving away from a single, potentially complex Create method.

Highlights

New Builder Pattern: Introduced a MooncakeStoreBuilder class to provide a fluent, type-safe, and more readable way to configure and create mooncake::Client instances.
Parameter Handling: The builder methods (WithLocalHostname, WithMetadataConnectionString, etc.) utilize std::move for string parameters to reduce unnecessary copies during client configuration.
Required Field Validation: The Build() method within MooncakeStoreBuilder now includes validation to ensure essential parameters like local_hostname and metadata_connstring are provided before attempting to create a Client.
Deprecation Notice: The existing PyClient::setup method has been marked as deprecated, encouraging future use of the new MooncakeStoreBuilder for client initialization.
Internal Refactoring: The internal PyClient::setup_internal method has been updated to use the new MooncakeStoreBuilder for constructing Client objects, demonstrating its intended usage.

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Code Review

This pull request introduces a MooncakeStoreBuilder to provide a fluent and readable API for constructing mooncake::Client instances. This is a great improvement over the static Create method with many parameters. The implementation is solid, and it's correctly used to refactor PyClient::setup_internal.

My review includes a few suggestions to further enhance the new builder:

Making the Build() method const to improve API correctness.
Simplifying the usage of the builder in pybind_client.cpp to a single fluent chain.
A minor refinement in the Build() method's error message construction for better performance and C++ idiomaticity.

Overall, this is a well-executed enhancement.

gemini-code-assist · 2025-11-04T09:35:10Z

mooncake-store/include/client.h

+    MooncakeStoreBuilder& WithExistingTransferEngine(
+        std::shared_ptr<TransferEngine> transfer_engine);
+
+    [[nodiscard]] std::optional<std::shared_ptr<Client>> Build();


The Build() method does not modify the state of the MooncakeStoreBuilder. It's good practice to mark such methods as const. This improves API correctness by clearly stating the method's intent and allows it to be called on const builder instances. You'll also need to update the implementation in client.cpp.

Suggested change

[[nodiscard]] std::optional<std::shared_ptr<Client>> Build();

[[nodiscard]] std::optional<std::shared_ptr<Client>> Build() const;

gemini-code-assist · 2025-11-04T09:35:10Z

mooncake-store/src/client.cpp

+    return *this;
+}
+
+std::optional<std::shared_ptr<Client>> MooncakeStoreBuilder::Build() {


To match the const qualifier added to the declaration in the header file, the implementation of Build() should also be marked as const.

Suggested change

std::optional<std::shared_ptr<Client>> MooncakeStoreBuilder::Build() {

std::optional<std::shared_ptr<Client>> MooncakeStoreBuilder::Build() const {

gemini-code-assist · 2025-11-04T09:35:10Z

mooncake-store/src/client.cpp

+        for (size_t i = 0; i < missing.size(); ++i) {
+            if (i != 0) {
+                joined.append(", ");
+            }
+            joined.append(missing[i]);
+        }


This loop for joining strings with a separator can be made slightly more efficient and idiomatic by handling the first element outside the loop. This avoids the conditional check if (i != 0) in every iteration.

joined.append(missing[0]); for (size_t i = 1; i < missing.size(); ++i) { joined.append(", "); joined.append(missing[i]); }

gemini-code-assist · 2025-11-04T09:35:10Z

mooncake-store/src/pybind_client.cpp

+    MooncakeStoreBuilder builder;
+    builder.WithLocalHostname(this->local_hostname)
+        .WithMetadataConnectionString(metadata_server)
+        .UsingProtocol(protocol)
+        .WithMasterServerEntry(master_server_addr);
+
+    if (device_name) {
+        builder.WithRdmaDeviceNames(*device_name);
+    }
+    if (transfer_engine) {
+        builder.WithExistingTransferEngine(transfer_engine);
+    }
+
+    auto client_opt = builder.Build();


The builder pattern is most powerful when its methods are chained fluently. The current implementation can be simplified into a single, more readable statement. The if conditions for optional parameters can be avoided by using std::optional::value_or for device_name and by passing the (potentially null) transfer_engine shared_ptr directly, as the builder handles these cases gracefully.

auto client_opt = MooncakeStoreBuilder() .WithLocalHostname(this->local_hostname) .WithMetadataConnectionString(metadata_server) .UsingProtocol(protocol) .WithMasterServerEntry(master_server_addr) .WithRdmaDeviceNames(device_name.value_or("")) .WithExistingTransferEngine(transfer_engine) .Build();

stmatengss · 2025-11-04T09:54:45Z

Use clang-format to fix code format issue.

xiaguan

Add a simple unit test for the builder.

mooncake-store/include/client.h

mooncake-store/src/client.cpp

xiaguan · 2025-11-05T09:34:46Z

mooncake-store/src/pybind_client.cpp

-    auto client_opt = mooncake::Client::Create(
-        this->local_hostname, metadata_server, protocol, device_name,
-        master_server_addr, transfer_engine);
+    MooncakeStoreBuilder builder;


revert this? just use create is good enough i think

mooncake-store/include/pybind_client.h

mooncake-store/tests/builder_test.cpp

nickyc975

Hi, @JasonZhang517. Glad to see the improvement of client initializition! I have several naming suggestions on this PR.

mooncake-store/include/client.h

nickyc975 · 2025-11-14T02:06:46Z

mooncake-store/include/client.h

+ * specify only the options they need while reusing existing Client::Create
+ * logic under the hood.
+ */
+class MooncakeStoreBuilder {


I think ClientBuilder should be a better name in the context, as we are infact building a Client, not a MooncakeStore.

How about MooncakeStoreClientBuilder? Don't be afraid of a long name.

nickyc975

Hi, @JasonZhang517. I have found several problems in the PR. Please take a look.

nickyc975 · 2025-11-14T02:43:19Z

mooncake-store/src/client.cpp


+MooncakeStoreBuilder& MooncakeStoreBuilder::WithLocalHostname(
+    std::string local_hostname) {
+    local_hostname_ = std::move(local_hostname);


Use const std::string& instead of std::string for the parameter, and don't move the parameter. Please also update the other "WithXXX" methods that taking strings as arguments.

nickyc975 · 2025-11-14T02:43:23Z

mooncake-store/src/client.cpp

+    return *this;
+}
+
+tl::expected<std::shared_ptr<Client>, std::string> MooncakeStoreBuilder::Build()


Returning string for errors is not a good practice. String is not structured and hard to be programmatically processed. You can see the bad result in the unit tests that you must search the returned string to check whether it is expected.

I suggest to return an ErrorCode for failure. For example, INVALID_PARAMS for missing required field, INTERNAL_ERROR for client creation failure. And provide a GetMissingFields() method to get the missing fields if needed.

nickyc975 · 2025-11-14T02:43:26Z

mooncake-store/src/client.cpp

+
+    if (!missing.empty()) {
+        std::string joined;
+        joined.reserve(missing.size() * 16);


The reserve is not necessary because this is not a performance critical path and 16 is a magic number. It's fine to let the string allocate space as needed.

nickyc975 · 2025-11-14T02:43:28Z

mooncake-store/src/client.cpp

+        for (size_t i = 0; i < missing.size(); ++i) {
+            if (i != 0) {
+                joined.append(", ");
+            }


This for loop and the if (i != 0) is redundent and confusing, just remove them.

JasonZhang517 added 2 commits November 4, 2025 17:25

add C++ builder for client

47add82

Merge branch 'main' into builder_cpp

9c644f0

gemini-code-assist bot reviewed Nov 4, 2025

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JasonZhang517 added 2 commits November 4, 2025 17:42

changed builder to const

58650f8

reformat the code

4fbe66a

stmatengss requested a review from xiaguan November 4, 2025 09:54

xiaguan requested changes Nov 5, 2025

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JasonZhang517 added 3 commits November 5, 2025 15:56

1. fixed names and return value types 2. added tests for the builder

2fb2b7e

reformat the codes

a9aa54c

style: clang-format-16 for pybind_client.h

58766bc

xiaguan approved these changes Nov 5, 2025

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xiaguan requested changes Nov 5, 2025

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revert create in setup_internal function

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xiaguan approved these changes Nov 6, 2025

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stmatengss requested changes Nov 6, 2025

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mooncake-store/include/pybind_client.h Outdated Show resolved Hide resolved

mooncake-store/tests/builder_test.cpp Outdated Show resolved Hide resolved

1. revert deprecated 2. integrate builder test to client builder tests.

a6a7dc3

nickyc975 reviewed Nov 7, 2025

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mooncake-store/include/client.h Outdated Show resolved Hide resolved

mooncake-store/include/client.h Outdated Show resolved Hide resolved

JasonZhang517 added 5 commits November 7, 2025 11:45

fixed naming bugs

ff674c5

reformat the code

9ebae76

fixed names

1daeb48

fixed names of Protocol and ProtocolArgs

1780a31

Reformat the codes

67d1268

stmatengss requested a review from nickyc975 November 13, 2025 15:58

nickyc975 reviewed Nov 14, 2025

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nickyc975 suggested changes Nov 14, 2025

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nickyc975 reviewed Nov 14, 2025

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	[[nodiscard]] std::optional<std::shared_ptr<Client>> Build();
	[[nodiscard]] std::optional<std::shared_ptr<Client>> Build() const;

	std::optional<std::shared_ptr<Client>> MooncakeStoreBuilder::Build() {
	std::optional<std::shared_ptr<Client>> MooncakeStoreBuilder::Build() const {

Add C++ builder pattern #1018

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