From 76d9c5b23446328c26ecdbc180932979044613e6 Mon Sep 17 00:00:00 2001
From: Marc Alff <marc.alff@oracle.com>
Date: Tue, 10 Jan 2023 22:50:24 +0100
Subject: [PATCH 01/14] WIP

---
 CMakeLists.txt                                | 46 +++++++++++++---
 examples/CMakeLists.txt                       |  5 +-
 examples/http/CMakeLists.txt                  | 29 +++++------
 exporters/otlp/CMakeLists.txt                 |  4 +-
 exporters/zipkin/CMakeLists.txt               |  1 -
 ext/src/CMakeLists.txt                        |  4 +-
 ext/src/http/client/curl/CMakeLists.txt       | 52 +++++++++----------
 ext/test/http/CMakeLists.txt                  |  5 +-
 ext/test/w3c_tracecontext_test/CMakeLists.txt | 25 ++++-----
 9 files changed, 103 insertions(+), 68 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 9c010e6eea..732cf4b882 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,3 +1,6 @@
+# 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
@@ -148,6 +151,9 @@ 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"
@@ -194,6 +200,7 @@ option(
   "Only build the API (use as a header-only library). Overrides WITH_EXAMPLES and all options to enable exporters"
   OFF)
 option(WITH_EXAMPLES "Whether to build examples" ON)
+option(WITH_EXAMPLES_HTTP "Whether to build http client/server examples" ON)
 
 option(WITH_LOGS_PREVIEW "Whether to build logs preview" OFF)
 option(WITH_ASYNC_EXPORT_PREVIEW "Whether enable async export" OFF)
@@ -314,22 +321,47 @@ 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 CURL ?
+#
+
+if(WITH_ZIPKIN
+   OR WITH_OTLP_HTTP
+   OR WITH_EXAMPLES_HTTP
+   OR BUILD_W3CTRACECONTEXT_TEST)
+  set(USE_CURL ON)
+else()
+  set(USE_CURL OFF)
+endif()
+
+if((NOT WITH_API_ONLY) AND USE_CURL)
+  find_package(CURL REQUIRED)
+endif()
+
+#
+# Do we need HTTP CLIENT CURL ?
+#
+
+if(WITH_OTLP_HTTP
+  OR WITH_HTTP_EXAMPLES)
+  set(WITH_HTTP_CLIENT_CURL ON)
+else()
+  set(WITH_HTTP_CLIENT_CURL OFF)
+endif()
+
+#
+# Do we need NLOHMANN_JSON ?
+#
+
 if(WITH_ELASTICSEARCH
    OR WITH_ZIPKIN
    OR WITH_OTLP_HTTP
diff --git a/examples/CMakeLists.txt b/examples/CMakeLists.txt
index 1f891f412d..201b00f1ce 100644
--- a/examples/CMakeLists.txt
+++ b/examples/CMakeLists.txt
@@ -24,4 +24,7 @@ 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()
diff --git a/examples/http/CMakeLists.txt b/examples/http/CMakeLists.txt
index a1181c93a4..3aeb2624a1 100644
--- a/examples/http/CMakeLists.txt
+++ b/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)
diff --git a/exporters/otlp/CMakeLists.txt b/exporters/otlp/CMakeLists.txt
index 7cecab0eca..49db6058ae 100644
--- a/exporters/otlp/CMakeLists.txt
+++ b/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)
diff --git a/exporters/zipkin/CMakeLists.txt b/exporters/zipkin/CMakeLists.txt
index 0139a783e2..ce093f3e55 100644
--- a/exporters/zipkin/CMakeLists.txt
+++ b/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
diff --git a/ext/src/CMakeLists.txt b/ext/src/CMakeLists.txt
index 6d7a14be41..48389427cf 100644
--- a/ext/src/CMakeLists.txt
+++ b/ext/src/CMakeLists.txt
@@ -2,4 +2,6 @@ if(WITH_ZPAGES)
   add_subdirectory(zpages)
 endif()
 
-add_subdirectory(http/client/curl)
+if(WITH_HTTP_CLIENT_CURL)
+  add_subdirectory(http/client/curl)
+endif()
diff --git a/ext/src/http/client/curl/CMakeLists.txt b/ext/src/http/client/curl/CMakeLists.txt
index 836cd019b4..38fdad4030 100644
--- a/ext/src/http/client/curl/CMakeLists.txt
+++ b/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})
diff --git a/ext/test/http/CMakeLists.txt b/ext/test/http/CMakeLists.txt
index 341648085d..654e490376 100644
--- a/ext/test/http/CMakeLists.txt
+++ b/ext/test/http/CMakeLists.txt
@@ -1,4 +1,6 @@
-find_package(CURL)
+# Copyright The OpenTelemetry Authors
+# SPDX-License-Identifier: Apache-2.0
+
 if(CURL_FOUND)
   set(FILENAME curl_http_test)
   add_compile_definitions(WITH_CURL)
@@ -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} ${GTEST_BOTH_LIBRARIES}
diff --git a/ext/test/w3c_tracecontext_test/CMakeLists.txt b/ext/test/w3c_tracecontext_test/CMakeLists.txt
index ea74a8eeb0..cc2ae43b1c 100644
--- a/ext/test/w3c_tracecontext_test/CMakeLists.txt
+++ b/ext/test/w3c_tracecontext_test/CMakeLists.txt
@@ -1,17 +1,14 @@
-include_directories(${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()

From ccc880556c3bf5d7d5067d6f1e5487f5eb9ceaa9 Mon Sep 17 00:00:00 2001
From: Marc Alff <marc.alff@oracle.com>
Date: Tue, 10 Jan 2023 23:59:56 +0100
Subject: [PATCH 02/14] Format cleanup

Explicitly ask for OTLP_HTTP
---
 CMakeLists.txt | 6 +++---
 ci/do_ci.sh    | 5 +++++
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 4b5126e56b..d698939a5f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -152,7 +152,8 @@ 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_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)
 
@@ -351,8 +352,7 @@ endif()
 # Do we need HTTP CLIENT CURL ?
 #
 
-if(WITH_OTLP_HTTP
-  OR WITH_HTTP_EXAMPLES)
+if(WITH_OTLP_HTTP OR WITH_EXAMPLES_HTTP)
   set(WITH_HTTP_CLIENT_CURL ON)
 else()
   set(WITH_HTTP_CLIENT_CURL OFF)
diff --git a/ci/do_ci.sh b/ci/do_ci.sh
index 6c80c0efe6..3ffbbd42e5 100755
--- a/ci/do_ci.sh
+++ b/ci/do_ci.sh
@@ -94,6 +94,8 @@ elif [[ "$1" == "cmake.maintainer.test" ]]; then
   cd "${BUILD_DIR}"
   rm -rf *
   cmake -DCMAKE_BUILD_TYPE=Debug  \
+        -DWITH_OTLP=ON \
+        -DWITH_OTLP_HTTP=ON \
         -DWITH_PROMETHEUS=ON \
         -DWITH_ZIPKIN=ON \
         -DWITH_JAEGER=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`

From 36b78afba5cbcdf53d372e7cffe532e71e2881eb Mon Sep 17 00:00:00 2001
From: Marc Alff <marc.alff@oracle.com>
Date: Thu, 12 Jan 2023 11:15:49 +0100
Subject: [PATCH 03/14] Don't require CURL by default.

---
 CMakeLists.txt | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index d698939a5f..94050c1321 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -201,7 +201,9 @@ option(
   "Only build the API (use as a header-only library). Overrides WITH_EXAMPLES and all options to enable exporters"
   OFF)
 option(WITH_EXAMPLES "Whether to build examples" ON)
-option(WITH_EXAMPLES_HTTP "Whether to build http client/server examples" ON)
+
+# This requires CURL, OFF by default.
+option(WITH_EXAMPLES_HTTP "Whether to build http client/server examples" OFF)
 
 option(WITH_LOGS_PREVIEW "Whether to build logs preview" OFF)
 option(WITH_ASYNC_EXPORT_PREVIEW "Whether enable async export" OFF)
@@ -346,6 +348,7 @@ endif()
 
 if((NOT WITH_API_ONLY) AND USE_CURL)
   find_package(CURL REQUIRED)
+  message(STATUS "Found CURL ${CURL_VERSION}"
 endif()
 
 #

From 1da8230431b1a75928e98e34f37f3e29fb334d13 Mon Sep 17 00:00:00 2001
From: Marc Alff <marc.alff@oracle.com>
Date: Thu, 12 Jan 2023 11:18:41 +0100
Subject: [PATCH 04/14] Typo

---
 CMakeLists.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 94050c1321..85b4e11bea 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -348,7 +348,7 @@ endif()
 
 if((NOT WITH_API_ONLY) AND USE_CURL)
   find_package(CURL REQUIRED)
-  message(STATUS "Found CURL ${CURL_VERSION}"
+  message(STATUS "Found CURL ${CURL_VERSION}")
 endif()
 
 #

From 4557babefec1898cde146b3bd58f8e2224b75d13 Mon Sep 17 00:00:00 2001
From: Marc Alff <marc.alff@oracle.com>
Date: Thu, 12 Jan 2023 11:48:21 +0100
Subject: [PATCH 05/14] Cleanup

---
 ci/do_ci.sh                  | 2 --
 ext/test/http/CMakeLists.txt | 2 +-
 2 files changed, 1 insertion(+), 3 deletions(-)

diff --git a/ci/do_ci.sh b/ci/do_ci.sh
index 3ffbbd42e5..01a40ddfe7 100755
--- a/ci/do_ci.sh
+++ b/ci/do_ci.sh
@@ -94,8 +94,6 @@ elif [[ "$1" == "cmake.maintainer.test" ]]; then
   cd "${BUILD_DIR}"
   rm -rf *
   cmake -DCMAKE_BUILD_TYPE=Debug  \
-        -DWITH_OTLP=ON \
-        -DWITH_OTLP_HTTP=ON \
         -DWITH_PROMETHEUS=ON \
         -DWITH_ZIPKIN=ON \
         -DWITH_JAEGER=ON \
diff --git a/ext/test/http/CMakeLists.txt b/ext/test/http/CMakeLists.txt
index 654e490376..268c91cbf2 100644
--- a/ext/test/http/CMakeLists.txt
+++ b/ext/test/http/CMakeLists.txt
@@ -1,7 +1,7 @@
 # Copyright The OpenTelemetry Authors
 # SPDX-License-Identifier: Apache-2.0
 
-if(CURL_FOUND)
+if(WITH_HTTP_CLIENT_CURL)
   set(FILENAME curl_http_test)
   add_compile_definitions(WITH_CURL)
   add_executable(${FILENAME} ${FILENAME}.cc)

From 1dbd2208735b41955673653d7cf30e11742405b5 Mon Sep 17 00:00:00 2001
From: Marc Alff <marc.alff@oracle.com>
Date: Thu, 12 Jan 2023 12:13:46 +0100
Subject: [PATCH 06/14] Reordered dependencies, start from client curl

---
 CMakeLists.txt | 32 +++++++++++++++++---------------
 1 file changed, 17 insertions(+), 15 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 85b4e11bea..ea9ff1d9f8 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -333,14 +333,26 @@ if(WITH_OTLP)
   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(WITH_ZIPKIN
-   OR WITH_OTLP_HTTP
-   OR WITH_EXAMPLES_HTTP
-   OR BUILD_W3CTRACECONTEXT_TEST)
+if(WITH_HTTP_CLIENT_CURL)
   set(USE_CURL ON)
 else()
   set(USE_CURL OFF)
@@ -348,17 +360,7 @@ endif()
 
 if((NOT WITH_API_ONLY) AND USE_CURL)
   find_package(CURL REQUIRED)
-  message(STATUS "Found CURL ${CURL_VERSION}")
-endif()
-
-#
-# Do we need HTTP CLIENT CURL ?
-#
-
-if(WITH_OTLP_HTTP OR WITH_EXAMPLES_HTTP)
-  set(WITH_HTTP_CLIENT_CURL ON)
-else()
-  set(WITH_HTTP_CLIENT_CURL OFF)
+  message(STATUS "Found CURL: ${CURL_LIBRARIES}, version ${CURL_VERSION}")
 endif()
 
 #

From 270138ca6c75a064a1b75f71cbbb82a250d5e5be Mon Sep 17 00:00:00 2001
From: Marc Alff <marc.alff@oracle.com>
Date: Thu, 12 Jan 2023 14:30:02 +0100
Subject: [PATCH 07/14] Added CHANGELOG

---
 CHANGELOG.md | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index ee58553c3d..f8365c3da1 100644
--- a/CHANGELOG.md
+++ b/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
 

From 69d18613f6a05c6c140ff4567db9924ad554e272 Mon Sep 17 00:00:00 2001
From: Marc Alff <marc.alff@oracle.com>
Date: Thu, 12 Jan 2023 14:44:15 +0100
Subject: [PATCH 08/14] Fixed format.

---
 CMakeLists.txt | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index ea9ff1d9f8..19b9a3687a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -8,7 +8,7 @@ cmake_minimum_required(VERSION 3.1)
 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()
@@ -341,8 +341,8 @@ if(WITH_OTLP_HTTP
    OR WITH_ELASTICSEARCH
    OR WITH_JAEGER
    OR WITH_ZIPKIN
-  OR BUILD_W3CTRACECONTEXT_TEST
-  OR WITH_EXAMPLES_HTTP)
+   OR BUILD_W3CTRACECONTEXT_TEST
+   OR WITH_EXAMPLES_HTTP)
   set(WITH_HTTP_CLIENT_CURL ON)
 else()
   set(WITH_HTTP_CLIENT_CURL OFF)

From 4f2434a46fbe093e59cae00e27ba8142bd785029 Mon Sep 17 00:00:00 2001
From: Marc Alff <marc.alff@oracle.com>
Date: Fri, 13 Jan 2023 23:11:10 +0100
Subject: [PATCH 09/14] Test examples in maintainer mode

---
 ci/do_ci.sh | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/ci/do_ci.sh b/ci/do_ci.sh
index 01a40ddfe7..873c53b587 100755
--- a/ci/do_ci.sh
+++ b/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 \

From 2e03d763da858b1ea418114ecdd9a4b4125bf55d Mon Sep 17 00:00:00 2001
From: Marc Alff <marc.alff@oracle.com>
Date: Mon, 16 Jan 2023 11:22:31 +0100
Subject: [PATCH 10/14] Review comments

---
 CMakeLists.txt                 | 10 +++++++++-
 examples/CMakeLists.txt        |  3 +++
 examples/otlp/CMakeLists.txt   |  3 +++
 examples/zipkin/CMakeLists.txt |  3 +++
 ext/src/CMakeLists.txt         |  3 +++
 5 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 19b9a3687a..14823b8d13 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -203,7 +203,7 @@ option(
 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" OFF)
+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)
@@ -211,6 +211,14 @@ option(WITH_ASYNC_EXPORT_PREVIEW "Whether enable async export" OFF)
 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)
diff --git a/examples/CMakeLists.txt b/examples/CMakeLists.txt
index 201b00f1ce..f1a4ec20e5 100644
--- a/examples/CMakeLists.txt
+++ b/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)
diff --git a/examples/otlp/CMakeLists.txt b/examples/otlp/CMakeLists.txt
index 30ce3cab48..bcf387a108 100644
--- a/examples/otlp/CMakeLists.txt
+++ b/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
   ${CMAKE_SOURCE_DIR}/exporters/otlp/include)
diff --git a/examples/zipkin/CMakeLists.txt b/examples/zipkin/CMakeLists.txt
index f55f363d72..e3e3a5f55f 100644
--- a/examples/zipkin/CMakeLists.txt
+++ b/examples/zipkin/CMakeLists.txt
@@ -1,3 +1,6 @@
+# Copyright The OpenTelemetry Authors
+# SPDX-License-Identifier: Apache-2.0
+
 include_directories(${CMAKE_SOURCE_DIR}/exporters/zipkin/include)
 
 add_executable(example_zipkin main.cc)
diff --git a/ext/src/CMakeLists.txt b/ext/src/CMakeLists.txt
index 48389427cf..84f30dd906 100644
--- a/ext/src/CMakeLists.txt
+++ b/ext/src/CMakeLists.txt
@@ -1,3 +1,6 @@
+# Copyright The OpenTelemetry Authors
+# SPDX-License-Identifier: Apache-2.0
+
 if(WITH_ZPAGES)
   add_subdirectory(zpages)
 endif()

From b1b36d4c57e7cebc6fcbe6e94638e9bcc04d0940 Mon Sep 17 00:00:00 2001
From: Marc Alff <marc.alff@oracle.com>
Date: Mon, 16 Jan 2023 11:37:11 +0100
Subject: [PATCH 11/14] Review comments.

---
 CMakeLists.txt | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 14823b8d13..9d82f8d99c 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -360,13 +360,7 @@ endif()
 # Do we need CURL ?
 #
 
-if(WITH_HTTP_CLIENT_CURL)
-  set(USE_CURL ON)
-else()
-  set(USE_CURL OFF)
-endif()
-
-if((NOT WITH_API_ONLY) AND USE_CURL)
+if((NOT WITH_API_ONLY) AND WITH_HTTP_CLIENT_CURL)
   find_package(CURL REQUIRED)
   message(STATUS "Found CURL: ${CURL_LIBRARIES}, version ${CURL_VERSION}")
 endif()

From 2771103a822a8304391fc74340c3adae91385563 Mon Sep 17 00:00:00 2001
From: Marc Alff <marc.alff@oracle.com>
Date: Mon, 16 Jan 2023 14:27:27 +0100
Subject: [PATCH 12/14] Fixed format

---
 CMakeLists.txt | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 9d82f8d99c..857d5df3ab 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -203,7 +203,10 @@ option(
 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_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)

From 1301d221cf8f3c198600c8d1a5cb1b91d1ca33f2 Mon Sep 17 00:00:00 2001
From: Marc Alff <marc.alff@oracle.com>
Date: Tue, 17 Jan 2023 14:23:02 +0100
Subject: [PATCH 13/14] Added comments.

This is to force CI to rebuild in github,
stuck with no recovery in github UI.
---
 CMakeLists.txt | 1 +
 1 file changed, 1 insertion(+)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 857d5df3ab..f47a49ab79 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -364,6 +364,7 @@ endif()
 #
 
 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()

From 8e17b6c2e5b889389423700e35e9f3599fba5bc9 Mon Sep 17 00:00:00 2001
From: Marc Alff <marc.alff@oracle.com>
Date: Tue, 17 Jan 2023 14:25:46 +0100
Subject: [PATCH 14/14] Format.

---
 CMakeLists.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index f47a49ab79..6429162d05 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -206,7 +206,7 @@ option(WITH_EXAMPLES "Whether to build examples" ON)
 option(
   WITH_EXAMPLES_HTTP
   "Whether to build http client/server examples. Requires WITH_EXAMPLES and CURL"
-   OFF)
+  OFF)
 
 option(WITH_LOGS_PREVIEW "Whether to build logs preview" OFF)
 option(WITH_ASYNC_EXPORT_PREVIEW "Whether enable async export" OFF)