Cleanup CMake makefiles for CURL usage (#1916)

CHANGELOG.md

@@ -28,6 +28,34 @@ Increment the:
   to enable Bazel 6.0.0 compatibility [#1873](https://github.com/open-telemetry/opentelemetry-cpp/pull/1873)
 * [BUILD] Cleanup CMake makefiles for nlohmann_json
   [#1912](https://github.com/open-telemetry/opentelemetry-cpp/pull/1912)
+* [BUILD] Cleanup CMake makefiles for CURL usage
+  [#1916](https://github.com/open-telemetry/opentelemetry-cpp/pull/1916)
+
+Important changes:
+
+* [BUILD] Cleanup CMake makefiles for CURL usage
+  [#1916](https://github.com/open-telemetry/opentelemetry-cpp/pull/1916)
+  * CMake option `WITH_OTLP_HTTP`
+    * Before this change, the CMake option `WITH_OTLP_HTTP` was unpredictable,
+      sometime set to ON and sometime set to OFF by default,
+      depending on whether a CURL package was found or not.
+      The option `WITH_OTLP_HTTP` was sometime not displayed in the ccmake
+      UI, making it impossible to even discover there is an option of that name.
+    * With this change, CMake option `WITH_OTLP_HTTP` is always OFF by
+      default. WITH_OTLP_HTTP MUST be set to ON explicitly to build the
+      OTLP HTTP exporter. The option is always visible in the ccmake UI.
+  * CMake option `BUILD_W3CTRACECONTEXT_TEST`
+    * Before this change, the W3C trace context tests were built, or
+      not, in an unpredictable way, depending on the presence, or not, of a
+      CURL package. In particular, the build could ignore the W3C trace
+      context tests even when BUILD_W3CTRACECONTEXT_TEST=ON.
+    * With this change, option BUILD_W3CTRACECONTEXT_TEST is honored.
+  * HTTP client/server examples
+    * Before this change, the HTTP client/server examples were built, or
+      not, in an unpredictable way, depending on the presence, or not, of a
+      CURL package.
+    * With this change, a new option `WITH_EXAMPLES_HTTP` is used to
+      build the HTTP client/server examples.
 
 ## [1.8.1] 2022-12-04
 

CMakeLists.txt

@@ -1,11 +1,14 @@
+# Copyright The OpenTelemetry Authors
+# SPDX-License-Identifier: Apache-2.0
+
 cmake_minimum_required(VERSION 3.1)
 
 # See https://cmake.org/cmake/help/v3.3/policy/CMP0057.html required by certain
 # versions of gtest
 cmake_policy(SET CMP0057 NEW)
 
 # See https://cmake.org/cmake/help/v3.12/policy/CMP0074.html required by certain
-# version of zlib which is dependeded by cURL.
+# version of zlib which CURL depends on.
 if(${CMAKE_VERSION} VERSION_GREATER_EQUAL "3.12")
   cmake_policy(SET CMP0074 NEW)
 endif()
@@ -148,6 +151,10 @@ if(WITH_STL)
 endif()
 
 option(WITH_OTLP "Whether to include the OpenTelemetry Protocol in the SDK" OFF)
+
+option(WITH_OTLP_HTTP "Whether to include the OTLP http exporter in the SDK"
+       OFF)
+
 option(WITH_ZIPKIN "Whether to include the Zipkin exporter in the SDK" OFF)
 
 option(WITH_PROMETHEUS "Whether to include the Prometheus Client in the SDK"
@@ -195,12 +202,26 @@ option(
   OFF)
 option(WITH_EXAMPLES "Whether to build examples" ON)
 
+# This requires CURL, OFF by default.
+option(
+  WITH_EXAMPLES_HTTP
+  "Whether to build http client/server examples. Requires WITH_EXAMPLES and CURL"
+  OFF)
+
 option(WITH_LOGS_PREVIEW "Whether to build logs preview" OFF)
 option(WITH_ASYNC_EXPORT_PREVIEW "Whether enable async export" OFF)
 # Exemplar specs status is experimental, so behind feature flag by default
 option(WITH_METRICS_EXEMPLAR_PREVIEW
        "Whethere to enable exemplar within metrics" OFF)
 
+#
+# Verify options dependencies
+#
+
+if(WITH_EXAMPLES_HTTP AND NOT WITH_EXAMPLES)
+  message(FATAL_ERROR "WITH_EXAMPLES_HTTP=ON requires WITH_EXAMPLES=ON")
+endif()
+
 find_package(Threads)
 
 function(install_windows_deps)
@@ -314,22 +335,44 @@ if(WITH_OTLP)
     endif()
   endif()
   include(CMakeDependentOption)
-  if(WITH_OTLP_HTTP OR (NOT DEFINED WITH_OTLP_HTTP AND NOT DEFINED
-                                                       CACHE{WITH_OTLP_HTTP}))
-    find_package(CURL)
-  endif()
 
   cmake_dependent_option(
     WITH_OTLP_GRPC "Whether to include the OTLP gRPC exporter in the SDK" ON
     "gRPC_FOUND" OFF)
-  cmake_dependent_option(
-    WITH_OTLP_HTTP "Whether to include the OTLP http exporter in the SDK" ON
-    "CURL_FOUND" OFF)
 
   message(STATUS "PROTOBUF_PROTOC_EXECUTABLE=${PROTOBUF_PROTOC_EXECUTABLE}")
   include(cmake/opentelemetry-proto.cmake)
 endif()
 
+#
+# Do we need HTTP CLIENT CURL ?
+#
+
+if(WITH_OTLP_HTTP
+   OR WITH_ELASTICSEARCH
+   OR WITH_JAEGER
+   OR WITH_ZIPKIN
+   OR BUILD_W3CTRACECONTEXT_TEST
+   OR WITH_EXAMPLES_HTTP)
+  set(WITH_HTTP_CLIENT_CURL ON)
+else()
+  set(WITH_HTTP_CLIENT_CURL OFF)
+endif()
+
+#
+# Do we need CURL ?
+#
+
+if((NOT WITH_API_ONLY) AND WITH_HTTP_CLIENT_CURL)
+  # No specific version required.
+  find_package(CURL REQUIRED)
+  message(STATUS "Found CURL: ${CURL_LIBRARIES}, version ${CURL_VERSION}")
+endif()
+
+#
+# Do we need NLOHMANN_JSON ?
+#
+
 if(WITH_ELASTICSEARCH
    OR WITH_ZIPKIN
    OR WITH_OTLP_HTTP

ci/do_ci.sh

@@ -95,6 +95,8 @@ elif [[ "$1" == "cmake.maintainer.test" ]]; then
   rm -rf *
   cmake -DCMAKE_BUILD_TYPE=Debug  \
         -DWITH_PROMETHEUS=ON \
+        -DWITH_EXAMPLES=ON \
+        -DWITH_EXAMPLES_HTTP=ON \
         -DWITH_ZIPKIN=ON \
         -DWITH_JAEGER=ON \
         -DBUILD_W3CTRACECONTEXT_TEST=ON \
@@ -180,6 +182,7 @@ elif [[ "$1" == "cmake.legacy.exporter.otprotocol.test" ]]; then
   cmake -DCMAKE_BUILD_TYPE=Debug  \
         -DCMAKE_CXX_STANDARD=11 \
         -DWITH_OTLP=ON \
+        -DWITH_OTLP_HTTP=ON \
         -DWITH_ASYNC_EXPORT_PREVIEW=ON \
         "${SRC_DIR}"
   grpc_cpp_plugin=`which grpc_cpp_plugin`
@@ -193,6 +196,7 @@ elif [[ "$1" == "cmake.exporter.otprotocol.test" ]]; then
   rm -rf *
   cmake -DCMAKE_BUILD_TYPE=Debug  \
         -DWITH_OTLP=ON \
+        -DWITH_OTLP_HTTP=ON \
         "${SRC_DIR}"
   grpc_cpp_plugin=`which grpc_cpp_plugin`
   proto_make_file="CMakeFiles/opentelemetry_proto.dir/build.make"
@@ -205,6 +209,7 @@ elif [[ "$1" == "cmake.exporter.otprotocol.with_async_export.test" ]]; then
   rm -rf *
   cmake -DCMAKE_BUILD_TYPE=Debug  \
         -DWITH_OTLP=ON \
+        -DWITH_OTLP_HTTP=ON \
         -DWITH_ASYNC_EXPORT_PREVIEW=ON \
         "${SRC_DIR}"
   grpc_cpp_plugin=`which grpc_cpp_plugin`

examples/CMakeLists.txt

@@ -1,3 +1,6 @@
+# Copyright The OpenTelemetry Authors
+# SPDX-License-Identifier: Apache-2.0
+
 add_subdirectory(common)
 include_directories(common)
 if(WITH_OTLP_GRPC OR WITH_OTLP_HTTP)
@@ -24,4 +27,7 @@ add_subdirectory(batch)
 add_subdirectory(metrics_simple)
 add_subdirectory(multithreaded)
 add_subdirectory(multi_processor)
-add_subdirectory(http)
+
+if(WITH_EXAMPLES_HTTP)
+  add_subdirectory(http)
+endif()

examples/http/CMakeLists.txt

@@ -1,20 +1,17 @@
-find_package(CURL)
+# Copyright The OpenTelemetry Authors
+# SPDX-License-Identifier: Apache-2.0
 
-if(NOT CURL_FOUND)
-  message(WARNING "Skipping http client/server example build: CURL not found")
-else()
-  include_directories(${CMAKE_SOURCE_DIR}/exporters/ostream/include
-                      ${CMAKE_SOURCE_DIR}/ext/include ${CMAKE_SOURCE_DIR/})
+include_directories(${CMAKE_SOURCE_DIR}/exporters/ostream/include
+                    ${CMAKE_SOURCE_DIR}/ext/include ${CMAKE_SOURCE_DIR/})
 
-  add_executable(http_client client.cc)
-  add_executable(http_server server.cc)
+add_executable(http_client client.cc)
+add_executable(http_server server.cc)
 
-  target_link_libraries(
-    http_client ${CMAKE_THREAD_LIBS_INIT} opentelemetry_trace
-    opentelemetry_http_client_curl opentelemetry_exporter_ostream_span
-    ${CURL_LIBRARIES})
+target_link_libraries(
+  http_client ${CMAKE_THREAD_LIBS_INIT} opentelemetry_trace
+  opentelemetry_http_client_curl opentelemetry_exporter_ostream_span
+  ${CURL_LIBRARIES})
 
-  target_link_libraries(
-    http_server ${CMAKE_THREAD_LIBS_INIT} opentelemetry_trace
-    opentelemetry_http_client_curl opentelemetry_exporter_ostream_span)
-endif()
+target_link_libraries(
+  http_server ${CMAKE_THREAD_LIBS_INIT} opentelemetry_trace
+  opentelemetry_http_client_curl opentelemetry_exporter_ostream_span)

examples/otlp/CMakeLists.txt

@@ -1,3 +1,6 @@
+# Copyright The OpenTelemetry Authors
+# SPDX-License-Identifier: Apache-2.0
+
 include_directories(
   ${CMAKE_BINARY_DIR}/generated/third_party/opentelemetry-proto
   ${CMAKE_SOURCE_DIR}/exporters/otlp/include)

examples/zipkin/CMakeLists.txt

@@ -1,3 +1,6 @@
+# Copyright The OpenTelemetry Authors
+# SPDX-License-Identifier: Apache-2.0
+
 include_directories(${CMAKE_SOURCE_DIR}/exporters/zipkin/include)
 
 add_executable(example_zipkin main.cc)

exporters/otlp/CMakeLists.txt

@@ -1,3 +1,6 @@
+# Copyright The OpenTelemetry Authors
+# SPDX-License-Identifier: Apache-2.0
+
 add_library(
   opentelemetry_otlp_recordable
   src/otlp_log_recordable.cc src/otlp_recordable.cc
@@ -94,7 +97,6 @@ if(WITH_OTLP_GRPC)
 endif()
 
 if(WITH_OTLP_HTTP)
-  find_package(CURL REQUIRED)
   add_library(opentelemetry_exporter_otlp_http_client src/otlp_http_client.cc)
   set_target_properties(opentelemetry_exporter_otlp_http_client
                         PROPERTIES EXPORT_NAME otlp_http_client)

exporters/zipkin/CMakeLists.txt

@@ -13,7 +13,6 @@
 # limitations under the License.
 
 include_directories(include)
-find_package(CURL REQUIRED)
 add_definitions(-DWITH_CURL)
 add_library(
   opentelemetry_exporter_zipkin_trace

ext/src/CMakeLists.txt

@@ -1,5 +1,10 @@
+# Copyright The OpenTelemetry Authors
+# SPDX-License-Identifier: Apache-2.0
+
 if(WITH_ZPAGES)
   add_subdirectory(zpages)
 endif()
 
-add_subdirectory(http/client/curl)
+if(WITH_HTTP_CLIENT_CURL)
+  add_subdirectory(http/client/curl)
+endif()

ext/src/http/client/curl/CMakeLists.txt

@@ -1,30 +1,30 @@
-find_package(CURL)
-if(CURL_FOUND)
-  add_library(
-    opentelemetry_http_client_curl http_client_factory_curl.cc
-                                   http_client_curl.cc http_operation_curl.cc)
+# Copyright The OpenTelemetry Authors
+# SPDX-License-Identifier: Apache-2.0
 
-  set_target_properties(opentelemetry_http_client_curl
-                        PROPERTIES EXPORT_NAME http_client_curl)
+add_library(
+  opentelemetry_http_client_curl http_client_factory_curl.cc
+                                 http_client_curl.cc http_operation_curl.cc)
 
-  if(TARGET CURL::libcurl)
-    target_link_libraries(
-      opentelemetry_http_client_curl
-      PUBLIC opentelemetry_ext
-      PRIVATE CURL::libcurl)
-  else()
-    target_include_directories(opentelemetry_http_client_curl
-                               INTERFACE "${CURL_INCLUDE_DIRS}")
-    target_link_libraries(
-      opentelemetry_http_client_curl
-      PUBLIC opentelemetry_ext
-      PRIVATE ${CURL_LIBRARIES})
-  endif()
+set_target_properties(opentelemetry_http_client_curl
+                      PROPERTIES EXPORT_NAME http_client_curl)
 
-  install(
-    TARGETS opentelemetry_http_client_curl
-    EXPORT "${PROJECT_NAME}-target"
-    RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
-    LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
-    ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR})
+if(TARGET CURL::libcurl)
+  target_link_libraries(
+    opentelemetry_http_client_curl
+    PUBLIC opentelemetry_ext
+    PRIVATE CURL::libcurl)
+else()
+  target_include_directories(opentelemetry_http_client_curl
+                             INTERFACE "${CURL_INCLUDE_DIRS}")
+  target_link_libraries(
+    opentelemetry_http_client_curl
+    PUBLIC opentelemetry_ext
+    PRIVATE ${CURL_LIBRARIES})
 endif()
+
+install(
+  TARGETS opentelemetry_http_client_curl
+  EXPORT "${PROJECT_NAME}-target"
+  RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
+  LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
+  ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR})

ext/test/http/CMakeLists.txt

@@ -1,5 +1,7 @@
-find_package(CURL)
-if(CURL_FOUND)
+# Copyright The OpenTelemetry Authors
+# SPDX-License-Identifier: Apache-2.0
+
+if(WITH_HTTP_CLIENT_CURL)
   set(FILENAME curl_http_test)
   add_compile_definitions(WITH_CURL)
   add_executable(${FILENAME} ${FILENAME}.cc)
@@ -19,6 +21,7 @@ if(CURL_FOUND)
     TEST_PREFIX ext.http.curl.
     TEST_LIST ${FILENAME})
 endif()
+
 set(URL_PARSER_FILENAME url_parser_test)
 add_executable(${URL_PARSER_FILENAME} ${URL_PARSER_FILENAME}.cc)
 target_link_libraries(${URL_PARSER_FILENAME} ${GTEST_BOTH_LIBRARIES}

ext/test/w3c_tracecontext_test/CMakeLists.txt

@@ -1,17 +1,14 @@
-include_directories(${CMAKE_SOURCE_DIR}/exporters/ostream/include)
+# Copyright The OpenTelemetry Authors
+# SPDX-License-Identifier: Apache-2.0
 
-find_package(CURL)
-if(NOT CURL_FOUND)
-  message(WARNING "Skipping example_w3c_tracecontext_test: CURL not found")
-else()
-  add_executable(w3c_tracecontext_test main.cc)
-  target_link_libraries(
-    w3c_tracecontext_test
-    PRIVATE ${CMAKE_THREAD_LIBS_INIT} opentelemetry_trace
-            opentelemetry_http_client_curl opentelemetry_exporter_ostream_span
-            ${CURL_LIBRARIES} nlohmann_json::nlohmann_json)
-  if(nlohmann_json_clone)
-    add_dependencies(w3c_tracecontext_test nlohmann_json::nlohmann_json)
-  endif()
+include_directories(${CMAKE_SOURCE_DIR}/exporters/ostream/include)
 
+add_executable(w3c_tracecontext_test main.cc)
+target_link_libraries(
+  w3c_tracecontext_test
+  PRIVATE ${CMAKE_THREAD_LIBS_INIT} opentelemetry_trace
+          opentelemetry_http_client_curl opentelemetry_exporter_ostream_span
+          ${CURL_LIBRARIES} nlohmann_json::nlohmann_json)
+if(nlohmann_json_clone)
+  add_dependencies(w3c_tracecontext_test nlohmann_json::nlohmann_json)
 endif()