feat: add C language binding

CMakeLists.txt

@@ -18,6 +18,7 @@ project(
 
 option(BUILD_SHARED_LIBS "Build shared libraries" ON)
 option(BUILD_STATIC_LIBS "Build static libraries" ON)
+option(DD_TRACE_BUILD_C_BINDING "Build C binding" OFF)
 
 if (WIN32)
   option(DD_TRACE_STATIC_CRT "Build dd-trace-cpp with static CRT with MSVC" OFF)
@@ -104,6 +105,10 @@ if (DD_TRACE_BUILD_TOOLS)
   add_subdirectory(tools/config-inversion)
 endif ()
 
+if (DD_TRACE_BUILD_C_BINDING)
+  add_subdirectory(binding/c)
+endif ()
+
 add_library(dd-trace-cpp-objects OBJECT)
 add_library(dd-trace-cpp::obj ALIAS dd-trace-cpp-objects)
 
@@ -294,11 +299,11 @@ if (BUILD_SHARED_LIBS)
   )
 
   install(
-    TARGETS dd-trace-cpp-shared 
+    TARGETS dd-trace-cpp-shared
     EXPORT dd-trace-cpp-targets
     LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
     ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
-    RUNTIME DESTINATION ${CMAKE_INSTALL_LIBDIR}
+    RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
   )
 endif ()
 
@@ -350,7 +355,7 @@ if (BUILD_STATIC_LIBS)
     EXPORT dd-trace-cpp-targets
     LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
     ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
-    RUNTIME DESTINATION ${CMAKE_INSTALL_LIBDIR}
+    RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
   )
 endif ()
 

bin/check-format

@@ -1,4 +1,4 @@
 #!/bin/sh
 
-find include/ src/ examples/ test/ -type f \( -name '*.h' -o -name '*.cpp' \) -print0 | \
+find binding/ examples/ fuzz/ include/ src/ test/ -type f \( -name '*.h' -o -name '*.cpp' \) -print0 | \
     xargs -0 clang-format-14 --style=file --dry-run -Werror

bin/format

@@ -18,7 +18,7 @@ formatter=clang-format-$version
 formatter_options="--style=file -i $*"
 
 find_sources() {
-    find include/ src/ examples/ test/ fuzz/ -type f \( -name '*.h' -o -name '*.cpp' \) "$@"
+    find binding/ examples/ fuzz/ include/ src/ test/ -type f \( -name '*.h' -o -name '*.cpp' \) "$@"
 }
 
 # If the correct version of clang-format is installed, then use it and quit.

binding/c/CMakeLists.txt

@@ -0,0 +1,66 @@
+add_library(dd_trace_c)
+add_library(dd-trace-cpp::c_binding ALIAS dd_trace_c)
+
+target_compile_definitions(dd_trace_c PRIVATE DD_TRACE_C_BUILDING)
+
+target_sources(dd_trace_c
+  PRIVATE
+    $<TARGET_OBJECTS:dd-trace-cpp::obj>
+    src/tracer.cpp
+)
+
+if (DD_TRACE_TRANSPORT STREQUAL "curl")
+  target_sources(dd_trace_c
+    PRIVATE
+      ${CMAKE_SOURCE_DIR}/src/datadog/curl.cpp
+      ${CMAKE_SOURCE_DIR}/src/datadog/default_http_client_curl.cpp
+  )
+
+  target_link_libraries(dd_trace_c
+    PRIVATE
+      CURL::libcurl_shared
+  )
+else ()
+  target_sources(dd_trace_c
+    PRIVATE
+      ${CMAKE_SOURCE_DIR}/src/datadog/default_http_client_null.cpp
+  )
+endif ()
+
+target_include_directories(dd_trace_c
+  PUBLIC
+    $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>
+    $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
+  PRIVATE
+    ${CMAKE_SOURCE_DIR}/src
+)
+
+target_link_libraries(dd_trace_c
+  PRIVATE
+    dd-trace-cpp::obj
+    dd-trace-cpp::specs
+)
+
+install(TARGETS dd_trace_c
+  EXPORT dd-trace-cpp-targets
+  LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
+  ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
+  RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
+)
+
+install(
+  DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/include/datadog
+  DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}
+)
+
+if (DD_TRACE_BUILD_TESTING)
+  target_sources(tests PRIVATE
+    ${CMAKE_CURRENT_SOURCE_DIR}/test/test_c_binding.cpp
+  )
+
+  target_include_directories(tests PRIVATE
+    ${CMAKE_CURRENT_SOURCE_DIR}/include
+  )
+
+  target_link_libraries(tests PRIVATE dd_trace_c)
+endif ()

binding/c/README.md

@@ -0,0 +1,17 @@
+# C Binding for dd-trace-cpp
+
+A C binding interface on the C++ tracing library for
+integration from C-based projects.
+
+## Building
+
+```sh
+cmake -B build -DDD_TRACE_BUILD_C_BINDING=ON -DDD_TRACE_BUILD_TESTING=ON
+cmake --build build -j
+```
+
+## Running Tests
+
+```sh
+./build/binding/c/test_c_binding
+```

binding/c/include/datadog/c/tracer.h

@@ -0,0 +1,204 @@
+#pragma once
+
+#include <stddef.h>
+
+#if defined(_WIN32)
+#if defined(DD_TRACE_C_BUILDING)
+#define DD_TRACE_C_API __declspec(dllexport)
+#else
+#define DD_TRACE_C_API __declspec(dllimport)
+#endif
+#elif defined(__GNUC__) || defined(__clang__)
+#define DD_TRACE_C_API __attribute__((visibility("default")))
+#else
+#define DD_TRACE_C_API
+#endif
+
+#if defined(__cplusplus)
+extern "C" {
+#endif
+
+// Callback used during trace context extraction. The tracer calls this
+// function for each propagation header it needs to read (e.g. "x-datadog-*").
+//
+// @param key  Header name to look up
+// @return     Header value, or NULL if the header is not present.
+//             The returned pointer must remain valid until
+//             dd_tracer_extract_or_create_span returns.
+typedef const char* (*dd_context_read_callback)(const char* key);
+
+// Callback used during trace context injection. The tracer calls this
+// function for each propagation header it needs to write.
+//
+// @param key    Header name to set
+// @param value  Header value to set
+typedef void (*dd_context_write_callback)(const char* key, const char* value);
+
+typedef enum {
+  DD_OPT_SERVICE_NAME = 0,
+  DD_OPT_ENV = 1,
+  DD_OPT_VERSION = 2,
+  DD_OPT_AGENT_URL = 3,
+  DD_OPT_INTEGRATION_NAME = 4,
+  DD_OPT_INTEGRATION_VERSION = 5
+} dd_tracer_option;
+
+// Options for creating a span. Unset fields default to NULL.
+typedef struct {
+  const char* name;
+  const char* resource;
+  const char* service;
+} dd_span_options_t;
+
+// Error details populated on failure. Caller provides the struct,
+// callee fills it in. Pass NULL to ignore errors.
+typedef struct {
+  int code;
+  char message[256];
+} dd_error_t;
+
+typedef struct dd_conf_s dd_conf_t;
+typedef struct dd_tracer_s dd_tracer_t;
+typedef struct dd_span_s dd_span_t;
+
+// Creates a tracer configuration instance.
+//
+// @return Configuration handle, or NULL on allocation failure
+DD_TRACE_C_API dd_conf_t* dd_tracer_conf_new(void);
+
+// Release a tracer configuration. Safe to call with NULL.
+//
+// @param handle Configuration handle to release
+DD_TRACE_C_API void dd_tracer_conf_free(dd_conf_t* handle);
+
+// Set or update a configuration field. No-op if handle is NULL.
+//
+// @param handle  Configuration handle
+// @param option  Configuration option
+// @param value   Configuration value (interpretation depends on option)
+DD_TRACE_C_API void dd_tracer_conf_set(dd_conf_t* handle,
+                                       dd_tracer_option option, void* value);
+
+// Creates a tracer instance. The configuration handle may be freed with
+// dd_tracer_conf_free after this call returns.
+//
+// @param conf_handle Configuration handle (not modified)
+// @param error       Optional error output (may be NULL)
+//
+// @return Tracer handle, or NULL on error
+DD_TRACE_C_API dd_tracer_t* dd_tracer_new(const dd_conf_t* conf_handle,
+                                          dd_error_t* error);
+
+// Release a tracer instance. Safe to call with NULL.
+//
+// @param tracer_handle Tracer handle to release
+DD_TRACE_C_API void dd_tracer_free(dd_tracer_t* tracer_handle);
+
+// Create a span using a Tracer.
+//
+// @param tracer_handle Tracer handle
+// @param options       Span options (name must not be NULL)
+//
+// @return Span handle, or NULL on error
+DD_TRACE_C_API dd_span_t* dd_tracer_create_span(
+    dd_tracer_t* tracer_handle, const dd_span_options_t* options);
+
+// Extract trace context from incoming headers, or create a new root span
+// if extraction fails. Never returns an error span; on extraction failure
+// a fresh root span is created.
+//
+// @param tracer_handle    Tracer handle
+// @param on_context_read  Callback invoked to read propagation headers
+// @param options          Span options (name must not be NULL)
+//
+// @return Span handle, or NULL if arguments are invalid
+DD_TRACE_C_API dd_span_t* dd_tracer_extract_or_create_span(
+    dd_tracer_t* tracer_handle, dd_context_read_callback on_context_read,
+    const dd_span_options_t* options);
+
+// Release a span instance. Safe to call with NULL.
+// If the span has not been finished with dd_span_finish, it is
+// automatically finished (its end time is recorded) before being freed.
+//
+// @param span_handle Span handle
+DD_TRACE_C_API void dd_span_free(dd_span_t* span_handle);
+
+// Set a tag (key-value pair) on a span. No-op if any argument is NULL.
+//
+// @param span_handle Span handle
+// @param key         Tag key
+// @param value       Tag value
+DD_TRACE_C_API void dd_span_set_tag(dd_span_t* span_handle, const char* key,
+                                    const char* value);
+
+// Mark a span as erroneous. No-op if span_handle is NULL.
+//
+// @param span_handle Span handle
+// @param error_value Non-zero to mark as error, zero to clear
+DD_TRACE_C_API void dd_span_set_error(dd_span_t* span_handle, int error_value);
+
+// Set an error message on a span. No-op if any argument is NULL.
+//
+// @param span_handle   Span handle
+// @param error_message Error message string
+DD_TRACE_C_API void dd_span_set_error_message(dd_span_t* span_handle,
+                                              const char* error_message);
+
+// Inject trace context into outgoing headers via callback.
+// No-op if any argument is NULL.
+//
+// @param span_handle       Span handle
+// @param on_context_write  Callback invoked per propagation header
+DD_TRACE_C_API void dd_span_inject(dd_span_t* span_handle,
+                                   dd_context_write_callback on_context_write);
+
+// Create a child span. Returns NULL if any required argument is NULL.
+//
+// @param span_handle Parent span handle
+// @param options     Span options (name must not be NULL)
+//
+// @return Child span handle, or NULL
+DD_TRACE_C_API dd_span_t* dd_span_create_child(
+    dd_span_t* span_handle, const dd_span_options_t* options);
+
+// Finish a span by recording its end time. No-op if span_handle is NULL.
+// After finishing, the span should be freed with dd_span_free.
+//
+// @param span_handle Span handle
+DD_TRACE_C_API void dd_span_finish(dd_span_t* span_handle);
+
+// Get the trace ID as a zero-padded hex string.
+//
+// @param span_handle  Span handle
+// @param buffer       Output buffer (at least 33 bytes for 128-bit IDs)
+// @param buffer_size  Size of the buffer
+// @return             Number of characters written, or -1 on error
+DD_TRACE_C_API int dd_span_get_trace_id(dd_span_t* span_handle, char* buffer,
+                                        size_t buffer_size);
+
+// Get the span ID as a zero-padded hex string.
+//
+// @param span_handle  Span handle
+// @param buffer       Output buffer (at least 17 bytes)
+// @param buffer_size  Size of the buffer
+// @return             Number of characters written (16), or -1 on error
+DD_TRACE_C_API int dd_span_get_span_id(dd_span_t* span_handle, char* buffer,
+                                       size_t buffer_size);
+
+// Set the resource name on a span. No-op if any argument is NULL.
+//
+// @param span_handle Span handle
+// @param resource    Resource name
+DD_TRACE_C_API void dd_span_set_resource(dd_span_t* span_handle,
+                                         const char* resource);
+
+// Set the service name on a span. No-op if any argument is NULL.
+//
+// @param span_handle Span handle
+// @param service     Service name
+DD_TRACE_C_API void dd_span_set_service(dd_span_t* span_handle,
+                                        const char* service);
+
+#if defined(__cplusplus)
+}
+#endif