feat: incomplete C bindings for client configuration (#45)

* add c_bindings/config/client.h

* add error conversion helper

* rename LDError to LDStatus

* add config unit test

Author: cwaldren-ld

libs/common/include/c_binding_helpers.hpp

@@ -0,0 +1,65 @@
+#include <functional>
+#include <tl/expected.hpp>
+#include "c_bindings/status.h"
+#include "error.hpp"
+
+template <typename T, typename = void>
+struct has_result_type : std::false_type {};
+
+template <typename T>
+struct has_result_type<T, std::void_t<typename T::Result>> : std::true_type {};
+
+template <typename T, typename ReturnType, typename = void>
+struct has_build_method : std::false_type {};
+
+template <typename T, typename ReturnType>
+struct has_build_method<T,
+                        ReturnType,
+                        std::void_t<decltype(std::declval<T>().Build())>>
+    : std::integral_constant<
+          bool,
+          std::is_same_v<decltype(std::declval<T>().Build()), ReturnType>> {};
+
+// NOLINTBEGIN cppcoreguidelines-pro-type-reinterpret-cast
+
+/*
+ * Given a Builder, calls the Build() method and converts it into an
+ * OpaqueResult if successful, or an LDError if unsuccessful.
+ *
+ * In the case of an error, out_result is set to nullptr.
+ *
+ * In all cases, the given builder is freed.
+ */
+template <typename Builder, typename OpaqueBuilder, typename OpaqueResult>
+LDStatus ConsumeBuilder(OpaqueBuilder opaque_builder,
+                        OpaqueResult* out_result) {
+    using ReturnType =
+        tl::expected<typename Builder::Result, launchdarkly::Error>;
+
+    static_assert(has_result_type<Builder>::value,
+                  "Builder must have an associated type named Result");
+
+    static_assert(
+        has_build_method<Builder, ReturnType>::value,
+        "Builder must have a Build method that returns "
+        "tl::expected<typename Builder::Result, launchdarkly::Error>");
+
+    auto builder = reinterpret_cast<Builder*>(opaque_builder);
+
+    tl::expected<typename Builder::Result, launchdarkly::Error> res =
+        builder->Build();
+
+    delete builder;
+
+    if (!res) {
+        *out_result = nullptr;
+        return reinterpret_cast<LDStatus>(new launchdarkly::Error(res.error()));
+    }
+
+    *out_result = reinterpret_cast<OpaqueResult>(
+        new typename Builder::Result(std::move(res.value())));
+
+    return LDStatus_Success();
+}
+
+// NOLINTEND cppcoreguidelines-pro-type-reinterpret-cast

libs/common/include/c_bindings/config/builder.h

@@ -0,0 +1,43 @@
+// NOLINTBEGIN modernize-use-using
+
+#pragma once
+
+#include "../export.h"
+#include "../status.h"
+#include "./config.h"
+
+#ifdef __cplusplus
+extern "C" {  // only need to export C interface if
+// used by C++ source code
+#endif
+
+typedef struct _LDClientConfigBuilder* LDClientConfigBuilder;
+
+LD_EXPORT(LDClientConfigBuilder) LDClientConfigBuilder_New(char const* sdk_key);
+
+/**
+ * Creates an LDClientConfig. The LDClientConfigBuilder is consumed.
+ * On success, the config will be stored in out_config; otherwise,
+ * out_config will be set to NULL and the returned LDStatus will indicate the
+ * error.
+ * @param builder Builder to consume.
+ * @param out_config Pointer to where the built config will be
+ * stored.
+ * @return Error status on failure.
+ */
+LD_EXPORT(LDStatus)
+LDClientConfigBuilder_Build(LDClientConfigBuilder builder,
+                            LDClientConfig* out_config);
+
+/**
+ * Frees the builder; only necessary if not calling Build.
+ * @param builder Builder to free.
+ */
+LD_EXPORT(void)
+LDClientConfigBuilder_Free(LDClientConfigBuilder builder);
+
+#ifdef __cplusplus
+}
+#endif
+
+// NOLINTEND modernize-use-using

libs/common/include/c_bindings/config/config.h

@@ -0,0 +1,26 @@
+// NOLINTBEGIN modernize-use-using
+
+#pragma once
+
+#include "../export.h"
+#include "../status.h"
+
+#ifdef __cplusplus
+extern "C" {  // only need to export C interface if
+// used by C++ source code
+#endif
+
+typedef struct _LDClientConfig* LDClientConfig;
+
+/**
+ * Free the configuration. Configurations passed into an LDClient do not need to
+ * be freed.
+ * @param config Config to free.
+ */
+LD_EXPORT(void) LDClientConfig_Free(LDClientConfig config);
+
+#ifdef __cplusplus
+}
+#endif
+
+// NOLINTEND modernize-use-using

libs/common/include/c_bindings/status.h

@@ -0,0 +1,47 @@
+// NOLINTBEGIN modernize-use-using
+
+#pragma once
+
+#include "./export.h"
+
+#ifdef __cplusplus
+extern "C" {  // only need to export C interface if
+// used by C++ source code
+#endif
+
+typedef struct _LDStatus* LDStatus;
+
+/**
+ * Returns a string representing the error stored in an LDStatus, or
+ * NULL if the result indicates success.
+ * @param error Result to inspect.
+ * @return String or NULL. The returned string is valid only while the LDStatus
+ * is alive.
+ */
+LD_EXPORT(char const*) LDStatus_Error(LDStatus res);
+
+/**
+ * Checks if a result indicates success.
+ * @param result Result to inspect.
+ * @return True if the result indicates success.
+ */
+LD_EXPORT(bool) LDStatus_Ok(LDStatus res);
+
+/**
+ * Frees an LDStatus. It is only necessary to call LDStatus_Free if LDStatus_Ok
+ * returns false.
+ * @param res Result to free.
+ */
+LD_EXPORT(void) LDStatus_Free(LDStatus res);
+
+/**
+ * Returns a status representing success.
+ * @return Successful status.
+ */
+LD_EXPORT(LDStatus) LDStatus_Success(void);
+
+#ifdef __cplusplus
+}
+#endif
+
+// NOLINTEND modernize-use-using

libs/common/include/config/detail/builders/config_builder.hpp

@@ -22,9 +22,9 @@ namespace launchdarkly::config::detail::builders {
 template <typename SDK>
 class ConfigBuilder {
    public:
+    using Result = detail::Config<SDK>;
     using EndpointsBuilder = detail::builders::EndpointsBuilder<SDK>;
     using EventsBuilder = detail::builders::EventsBuilder<SDK>;
-    using ConfigResult = tl::expected<detail::Config<SDK>, Error>;
     using DataSourceBuilder = detail::builders::DataSourceBuilder<SDK>;
     using HttpPropertiesBuilder = detail::builders::HttpPropertiesBuilder<SDK>;
     /**
@@ -85,7 +85,7 @@ class ConfigBuilder {
      * Builds a Configuration, suitable for passing into an instance of Client.
      * @return
      */
-    ConfigResult Build() const;
+    tl::expected<Result, Error> Build() const;
 
    private:
     std::string sdk_key_;

libs/common/src/CMakeLists.txt

@@ -53,7 +53,11 @@ add_library(${LIBNAME}
         c_bindings/array_builder.cpp
         c_bindings/object_builder.cpp
         c_bindings/context_builder.cpp
-        c_bindings/context.cpp)
+        c_bindings/status.cpp
+        c_bindings/context.cpp
+        c_bindings/config/builder.cpp
+        c_bindings/config/config.cpp
+        )
 
 
 add_library(launchdarkly::common ALIAS ${LIBNAME})

libs/common/src/c_bindings/config/builder.cpp

@@ -0,0 +1,33 @@
+// NOLINTBEGIN cppcoreguidelines-pro-type-reinterpret-cast
+// NOLINTBEGIN OCInconsistentNamingInspection
+
+#include "c_bindings/config/builder.h"
+
+#include "c_binding_helpers.hpp"
+#include "config/client.hpp"
+
+using namespace launchdarkly::client_side;
+
+#define TO_BUILDER(ptr) (reinterpret_cast<ConfigBuilder*>(ptr))
+#define FROM_BUILDER(ptr) (reinterpret_cast<LDClientConfigBuilder>(ptr))
+
+LD_EXPORT(LDClientConfigBuilder)
+LDClientConfigBuilder_New(char const* sdk_key) {
+    return FROM_BUILDER(new ConfigBuilder(sdk_key ? sdk_key : ""));
+}
+
+LD_EXPORT(void)
+LDClientConfigBuilder_Free(LDClientConfigBuilder builder) {
+    if (ConfigBuilder* b = TO_BUILDER(builder)) {
+        delete b;
+    }
+}
+
+LD_EXPORT(LDStatus)
+LDClientConfigBuilder_Build(LDClientConfigBuilder builder,
+                            LDClientConfig* out_config) {
+    return ConsumeBuilder<ConfigBuilder>(builder, out_config);
+}
+
+// NOLINTEND cppcoreguidelines-pro-type-reinterpret-cast
+// NOLINTEND OCInconsistentNamingInspection

libs/common/src/c_bindings/config/config.cpp

@@ -0,0 +1,19 @@
+// NOLINTBEGIN cppcoreguidelines-pro-type-reinterpret-cast
+// NOLINTBEGIN OCInconsistentNamingInspection
+
+#include "c_bindings/config/config.h"
+#include "config/client.hpp"
+
+#define TO_CONFIG(ptr) (reinterpret_cast<Config*>(ptr))
+#define FROM_CONFIG(ptr) (reinterpret_cast<LDClientConfig>(ptr))
+
+using namespace launchdarkly::client_side;
+
+LD_EXPORT(void) LDClientConfig_Free(LDClientConfig config) {
+    if (Config* c = TO_CONFIG(config)) {
+        delete c;
+    }
+}
+
+// NOLINTEND cppcoreguidelines-pro-type-reinterpret-cast
+// NOLINTEND OCInconsistentNamingInspection

libs/common/src/c_bindings/status.cpp

@@ -0,0 +1,37 @@
+// NOLINTBEGIN cppcoreguidelines-pro-type-reinterpret-cast
+// NOLINTBEGIN OCInconsistentNamingInspection
+
+#include "c_bindings/status.h"
+
+#include "error.hpp"
+
+using namespace launchdarkly;
+
+#define TO_ERROR(ptr) (reinterpret_cast<Error*>(ptr))
+
+LD_EXPORT(char const*) LDStatus_Error(LDStatus res) {
+    if (Error* e = TO_ERROR(res)) {
+        return ErrorToString(*e);
+    }
+    return nullptr;
+}
+
+LD_EXPORT(bool) LDStatus_Ok(LDStatus res) {
+    if (TO_ERROR(res) == nullptr) {
+        return true;
+    }
+    return false;
+}
+
+LD_EXPORT(void) LDStatus_Free(LDStatus error) {
+    if (Error* e = TO_ERROR(error)) {
+        delete e;
+    }
+}
+
+LD_EXPORT(LDStatus) LDStatus_Success(void) {
+    return nullptr;
+}
+
+// NOLINTEND cppcoreguidelines-pro-type-reinterpret-cast
+// NOLINTEND OCInconsistentNamingInspection

libs/common/src/config/config_builder.cpp

@@ -47,7 +47,7 @@ ConfigBuilder<SDK>& ConfigBuilder<SDK>::HttpProperties(
 }
 
 template <typename SDK>
-[[nodiscard]] typename ConfigBuilder<SDK>::ConfigResult
+[[nodiscard]] tl::expected<typename ConfigBuilder<SDK>::Result, Error>
 ConfigBuilder<SDK>::Build() const {
     auto sdk_key = sdk_key_;
     if (sdk_key.empty()) {

libs/common/tests/client_config_c_binding_test.cpp

@@ -0,0 +1,34 @@
+#include <gtest/gtest.h>
+#include "c_bindings/config/builder.h"
+
+TEST(ClientConfigBindings, ConfigBuilderNewFree) {
+    LDClientConfigBuilder builder = LDClientConfigBuilder_New("sdk-123");
+    ASSERT_TRUE(builder);
+    LDClientConfigBuilder_Free(builder);
+}
+
+TEST(ClientConfigBindings, ConfigBuilderEmptyResultsInError) {
+    LDClientConfigBuilder builder = LDClientConfigBuilder_New(nullptr);
+
+    LDClientConfig config = nullptr;
+    LDStatus status = LDClientConfigBuilder_Build(builder, &config);
+
+    ASSERT_FALSE(config);
+    ASSERT_FALSE(LDStatus_Ok(status));
+    ASSERT_TRUE(LDStatus_Error(status));
+
+    LDStatus_Free(status);
+    // LDClientConfigBuilder is consumed by Build; no need to free it.
+}
+
+TEST(ClientConfigBindings, MinimalValidConfig) {
+    LDClientConfigBuilder builder = LDClientConfigBuilder_New("sdk-123");
+
+    LDClientConfig config = nullptr;
+    LDStatus status = LDClientConfigBuilder_Build(builder, &config);
+    ASSERT_TRUE(LDStatus_Ok(status));
+    ASSERT_TRUE(config);
+
+    LDClientConfig_Free(config);
+    // LDClientConfigBuilder is consumed by Build; no need to free it.
+}

libs/common/tests/status_c_binding_test.cpp

@@ -0,0 +1,28 @@
+#include <gtest/gtest.h>
+
+#include "error.hpp"
+
+#include "c_bindings/status.h"
+
+// NOLINTBEGIN cppcoreguidelines-pro-type-reinterpret-cast
+
+TEST(StatusBindingTests, StatusOk) {
+    LDStatus status = LDStatus_Success();
+    ASSERT_TRUE(LDStatus_Ok(status));
+    ASSERT_FALSE(LDStatus_Error(status));
+    LDStatus_Free(status);
+}
+
+TEST(StatusBindingTests, StatusError) {
+    using namespace launchdarkly;
+
+    Error err = Error::kConfig_SDKKey_Empty;
+
+    auto status = reinterpret_cast<LDStatus>(new Error(err));
+    ASSERT_FALSE(LDStatus_Ok(status));
+    ASSERT_TRUE(LDStatus_Error(status));
+    ASSERT_STREQ(LDStatus_Error(status), ErrorToString(err));
+    LDStatus_Free(status);
+}
+
+// NOLINTEND cppcoreguidelines-pro-type-reinterpret-cast