lalitb · pull · Jul 15, 2025 · Jul 15, 2025
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
@@ -73,7 +73,7 @@ jobs:
     - name: install dependencies
       run: |
         sudo -E apt-get update
-        sudo -E apt-get install -y zlib1g-dev libcurl4-openssl-dev libabsl-dev libprotobuf-dev libgrpc++-dev protobuf-compiler protobuf-compiler-grpc
+        sudo -E apt-get install -y zlib1g-dev libabsl-dev libprotobuf-dev libgrpc++-dev protobuf-compiler protobuf-compiler-grpc
     - name: run fetch content cmake test
       run: |
         ./ci/do_ci.sh cmake.fetch_content.test

diff --git a/CMakeLists.txt b/CMakeLists.txt
@@ -304,6 +304,42 @@ endif()
 # GNUInstallDirs.
 include(GNUInstallDirs)
 
+#
+# Do we need HTTP CLIENT CURL ?
+#
+
+if(WITH_OTLP_HTTP
+   OR WITH_ELASTICSEARCH
+   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 ZLIB ?
+#
+
+if((NOT WITH_API_ONLY)
+   AND WITH_HTTP_CLIENT_CURL
+   AND WITH_OTLP_HTTP_COMPRESSION)
+  include("${opentelemetry-cpp_SOURCE_DIR}/cmake/zlib.cmake")
+endif()
+
+#
+# Do we need CURL ?
+#
+
+if((NOT WITH_API_ONLY) AND WITH_HTTP_CLIENT_CURL)
+  include("${opentelemetry-cpp_SOURCE_DIR}/cmake/curl.cmake")
+endif()
+
+#
+# Do we need prometheus-cpp ?
+#
+
 if(WITH_PROMETHEUS)
   include("${opentelemetry-cpp_SOURCE_DIR}/cmake/prometheus-cpp.cmake")
 endif()
@@ -387,50 +423,6 @@ if(WITH_OTLP_GRPC
   set(CMAKE_CXX_CLANG_TIDY ${SAVED_CMAKE_CXX_CLANG_TIDY})
 endif()
 
-#
-# Do we need HTTP CLIENT CURL ?
-#
-
-if(WITH_OTLP_HTTP
-   OR WITH_ELASTICSEARCH
-   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)
-  # Set the CURL_VERSION from the legacy CURL_VERSION_STRING Required for CMake
-  # versions below 4.0
-  if(NOT DEFINED CURL_VERSION AND DEFINED CURL_VERSION_STRING)
-    set(CURL_VERSION ${CURL_VERSION_STRING})
-  endif()
-endif()
-
-#
-# Do we need ZLIB ?
-#
-
-if((NOT WITH_API_ONLY)
-   AND WITH_HTTP_CLIENT_CURL
-   AND WITH_OTLP_HTTP_COMPRESSION)
-  # No specific version required.
-  find_package(ZLIB REQUIRED)
-  # Set the ZLIB_VERSION from the legacy ZLIB_VERSION_STRING Required for CMake
-  # versions below 3.26
-  if(NOT DEFINED ZLIB_VERSION AND DEFINED ZLIB_VERSION_STRING)
-    set(ZLIB_VERSION ${ZLIB_VERSION_STRING})
-  endif()
-endif()
-
 #
 # Do we need NLOHMANN_JSON ?
 #
@@ -658,11 +650,11 @@ endif()
 if(gRPC_FOUND)
   message(STATUS "gRPC: ${gRPC_VERSION}")
 endif()
-if(CURL_FOUND)
-  message(STATUS "CURL: ${CURL_VERSION}")
+if(CURL_VERSION)
+  message(STATUS "CURL: ${CURL_VERSION} (${CURL_PROVIDER})")
 endif()
-if(ZLIB_FOUND)
-  message(STATUS "ZLIB: ${ZLIB_VERSION}")
+if(ZLIB_VERSION)
+  message(STATUS "ZLIB: ${ZLIB_VERSION} (${ZLIB_PROVIDER})")
 endif()
 if(USE_NLOHMANN_JSON)
   message(

diff --git a/cmake/curl.cmake b/cmake/curl.cmake
@@ -0,0 +1,76 @@
+# Copyright The OpenTelemetry Authors
+# SPDX-License-Identifier: Apache-2.0
+
+# Import the curl target (CURL::libcurl).
+# 1. Find an installed curl package
+# 2. Use FetchContent to fetch and build curl from GitHub
+
+# Find the curl package with the default search mode
+find_package(CURL QUIET)
+set(CURL_PROVIDER "find_package")
+
+if(NOT CURL_FOUND)
+  FetchContent_Declare(
+    "curl"
+    GIT_REPOSITORY "https://github.com/curl/curl.git"
+    GIT_TAG "${curl_GIT_TAG}"
+    )
+  set(CURL_PROVIDER "fetch_repository")
+
+  if(OPENTELEMETRY_INSTALL)
+    set(_CURL_DISABLE_INSTALL OFF)
+  else()
+    set(_CURL_DISABLE_INSTALL ON)
+  endif()
+
+  if(DEFINED BUILD_SHARED_LIBS)
+    set(_SAVED_BUILD_SHARED_LIBS ${BUILD_SHARED_LIBS})
+  endif()
+
+  set(CURL_DISABLE_INSTALL ${_CURL_DISABLE_INSTALL} CACHE BOOL "" FORCE)
+  set(CURL_USE_LIBPSL OFF CACHE BOOL "" FORCE)
+  set(BUILD_CURL_EXE OFF CACHE BOOL "" FORCE)
+  set(BUILD_LIBCURL_DOCS OFF CACHE BOOL "" FORCE)
+  set(BUILD_MISC_DOCS OFF CACHE BOOL "" FORCE)
+  set(ENABLE_CURL_MANUAL OFF CACHE BOOL "" FORCE)
+  set(BUILD_SHARED_LIBS ON CACHE BOOL "" FORCE)
+
+  FetchContent_MakeAvailable(curl)
+
+  # Restore BUILD_SHARED_LIBS
+  if(DEFINED _SAVED_BUILD_SHARED_LIBS)
+    set(BUILD_SHARED_LIBS ${_SAVED_BUILD_SHARED_LIBS} CACHE BOOL "" FORCE)
+  else()
+    unset(BUILD_SHARED_LIBS CACHE)
+  endif()
+
+  # Set the CURL_VERSION variable from the git tag.
+  string(REGEX REPLACE "^curl-([0-9]+)_([0-9]+)_([0-9]+)$" "\\1.\\2.\\3" CURL_VERSION "${curl_GIT_TAG}")
+
+  # disable iwyu and clang-tidy
+  foreach(_curl_target libcurl_shared libcurl_static)
+    if(TARGET ${_curl_target})
+      set_target_properties(${_curl_target} PROPERTIES CXX_INCLUDE_WHAT_YOU_USE ""
+                                                     CXX_CLANG_TIDY "")
+    endif()
+  endforeach()
+endif()
+
+# Set the CURL_VERSION from the legacy CURL_VERSION_STRING Required for CMake
+# versions below 4.0
+if(NOT CURL_VERSION AND CURL_VERSION_STRING)
+  set(CURL_VERSION ${CURL_VERSION_STRING})
+endif()
+
+# Add the main CURL::libcurl alias target if missing. Prefer the shared target followed by the static target
+if(NOT TARGET CURL::libcurl)
+  if(TARGET libcurl_shared)
+    add_library(CURL::libcurl ALIAS libcurl_shared)
+  elseif(TARGET libcurl_static)
+    add_library(CURL::libcurl ALIAS libcurl_static)
+  endif()
+endif()
+
+if(NOT TARGET CURL::libcurl)
+  message(FATAL_ERROR "The required curl target (CURL::libcurl) was not imported.")
+endif()
diff --git a/cmake/zlib.cmake b/cmake/zlib.cmake
@@ -0,0 +1,20 @@
+# Copyright The OpenTelemetry Authors
+# SPDX-License-Identifier: Apache-2.0
+
+# ZLIB must be found as an installed package for now.
+# Fetching ZLIB and building in-tree is not supported.
+# Protobuf, gRPC, prometheus-cpp, civetweb, CURL, and other dependencies require ZLIB and import its target.
+# When ZLIB::ZLIB is an alias of the shared library then inconsistent linking may occur.
+
+find_package(ZLIB REQUIRED)
+set(ZLIB_PROVIDER "find_package")
+
+# Set the ZLIB_VERSION from the legacy ZLIB_VERSION_STRING Required for CMake
+# versions below 3.26
+if(NOT ZLIB_VERSION AND ZLIB_VERSION_STRING)
+  set(ZLIB_VERSION ${ZLIB_VERSION_STRING})
+endif()
+
+if(NOT TARGET ZLIB::ZLIB)
+  message(FATAL_ERROR "The required zlib target (ZLIB::ZLIB) was not imported.")
+endif()
diff --git a/examples/http/CMakeLists.txt b/examples/http/CMakeLists.txt
@@ -7,7 +7,7 @@ add_executable(http_server server.cc)
 target_link_libraries(
   http_client
   PRIVATE opentelemetry-cpp::trace opentelemetry-cpp::http_client_curl
-          opentelemetry-cpp::ostream_span_exporter ${CURL_LIBRARIES})
+          opentelemetry-cpp::ostream_span_exporter CURL::libcurl)
 
 target_link_libraries(
   http_server

diff --git a/exporters/zipkin/CMakeLists.txt b/exporters/zipkin/CMakeLists.txt
@@ -59,7 +59,7 @@ if(BUILD_TESTING)
     ${GMOCK_LIB}
     opentelemetry_exporter_zipkin_trace
     opentelemetry_resources
-    ${CURL_LIBRARIES})
+    CURL::libcurl)
 
   gtest_add_tests(
     TARGET zipkin_exporter_test

diff --git a/ext/src/http/client/curl/CMakeLists.txt b/ext/src/http/client/curl/CMakeLists.txt
@@ -11,60 +11,21 @@ set_target_version(opentelemetry_http_client_curl)
 target_link_libraries(opentelemetry_http_client_curl
                       PUBLIC opentelemetry_common)
 
-unset(CURL_IMPORTED_TARGET_NAME)
-
-foreach(FIND_CURL_IMPORTED_TARGET CURL::libcurl CURL::libcurl_shared
-                                  CURL::libcurl_static)
-  if(TARGET ${FIND_CURL_IMPORTED_TARGET})
-    set(CURL_IMPORTED_TARGET_NAME ${FIND_CURL_IMPORTED_TARGET})
-    break()
-  endif()
-endforeach()
-
-if(TARGET ${CURL_IMPORTED_TARGET_NAME})
-  target_link_libraries(
-    opentelemetry_http_client_curl
-    PUBLIC opentelemetry_ext
-    PRIVATE ${CURL_IMPORTED_TARGET_NAME})
-
-  # Some versions of libcurl do not export the link directories, which may cause
-  # link errors
-  project_build_tools_get_imported_location(CURL_LIB_FILE_PATH
-                                            ${CURL_IMPORTED_TARGET_NAME})
-  get_filename_component(CURL_LIB_DIR_PATH "${CURL_LIB_FILE_PATH}" DIRECTORY)
-
-  if(CURL_LIB_DIR_PATH)
-    target_link_directories(opentelemetry_http_client_curl PUBLIC
-                            "$<BUILD_INTERFACE:${CURL_LIB_DIR_PATH}>")
-  endif()
-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()
+target_link_libraries(
+  opentelemetry_http_client_curl
+  PUBLIC opentelemetry_ext
+  PRIVATE CURL::libcurl)
 
 if(WITH_CURL_LOGGING)
   target_compile_definitions(opentelemetry_http_client_curl
                              PRIVATE ENABLE_CURL_LOGGING)
 endif()
 
 if(WITH_OTLP_HTTP_COMPRESSION)
-  if(TARGET ZLIB::ZLIB)
-    target_link_libraries(
-      opentelemetry_http_client_curl
-      PUBLIC opentelemetry_ext
-      PRIVATE ZLIB::ZLIB)
-  else()
-    target_include_directories(opentelemetry_http_client_curl
-                               INTERFACE "${ZLIB_INCLUDE_DIRS}")
-    target_link_libraries(
-      opentelemetry_http_client_curl
-      PUBLIC opentelemetry_ext
-      PRIVATE ${ZLIB_LIBRARIES})
-  endif()
+  target_link_libraries(
+    opentelemetry_http_client_curl
+    PUBLIC opentelemetry_ext
+    PRIVATE ZLIB::ZLIB)
 endif()
 
 otel_add_component(COMPONENT ext_http_curl TARGETS

diff --git a/ext/test/http/CMakeLists.txt b/ext/test/http/CMakeLists.txt
@@ -4,28 +4,10 @@
 if(WITH_HTTP_CLIENT_CURL)
   set(FILENAME curl_http_test)
   add_executable(${FILENAME} ${FILENAME}.cc)
-  target_link_libraries(${FILENAME} ${GMOCK_LIB} ${GTEST_BOTH_LIBRARIES}
-                        ${CMAKE_THREAD_LIBS_INIT})
-
-  unset(CURL_IMPORTED_TARGET_NAME)
-
-  foreach(FIND_CURL_IMPORTED_TARGET CURL::libcurl CURL::libcurl_shared
-                                    CURL::libcurl_static)
-    if(TARGET ${FIND_CURL_IMPORTED_TARGET})
-      set(CURL_IMPORTED_TARGET_NAME ${FIND_CURL_IMPORTED_TARGET})
-      break()
-    endif()
-  endforeach()
-
-  if(TARGET ${CURL_IMPORTED_TARGET_NAME})
-    target_link_libraries(${FILENAME} opentelemetry_http_client_curl
-                          opentelemetry_common ${CURL_IMPORTED_TARGET_NAME})
-  else()
-    target_include_directories(${FILENAME} PRIVATE ${CURL_INCLUDE_DIRS})
-    target_link_libraries(${FILENAME} ${CURL_LIBRARIES}
-                          opentelemetry_http_client_curl opentelemetry_common)
-  endif()
-
+  target_link_libraries(
+    ${FILENAME}
+    PRIVATE ${GMOCK_LIB} ${GTEST_BOTH_LIBRARIES} opentelemetry_http_client_curl
+            opentelemetry_common CURL::libcurl)
   gtest_add_tests(
     TARGET ${FILENAME}
     TEST_PREFIX ext.http.curl.

diff --git a/ext/test/w3c_tracecontext_http_test_server/CMakeLists.txt b/ext/test/w3c_tracecontext_http_test_server/CMakeLists.txt
@@ -6,4 +6,4 @@ target_link_libraries(
   w3c_tracecontext_http_test_server
   PRIVATE ${CMAKE_THREAD_LIBS_INIT} opentelemetry_trace
           opentelemetry_http_client_curl opentelemetry_exporter_ostream_span
-          ${CURL_LIBRARIES} nlohmann_json::nlohmann_json)
+          CURL::libcurl nlohmann_json::nlohmann_json)