Minimum supported curl version 7.64.0

This is the libcurl version available in debian 10 and ubuntu 20.04

CMakeLists.txt

@@ -183,6 +183,7 @@ if(CPR_USE_SYSTEM_CURL)
         find_package(CURL COMPONENTS HTTP HTTPS)
         if(CURL_FOUND)
             message(STATUS "Curl ${CURL_VERSION_STRING} found on this system.")
+
             # To be able to load certificates under Windows when using OpenSSL:
             if(CMAKE_USE_OPENSSL AND WIN32 AND (NOT (CURL_VERSION_STRING VERSION_GREATER_EQUAL "7.71.0")))
                 message(FATAL_ERROR "Your system curl version (${CURL_VERSION_STRING}) is too old to support OpenSSL on Windows which requires curl >= 7.71.0. Update your curl version, use WinSSL, disable SSL or use the built-in version of curl.")
@@ -203,6 +204,11 @@ if(CPR_USE_SYSTEM_CURL)
             message(FATAL_ERROR "Curl not found on this system. To use the built-in version set CPR_USE_SYSTEM_CURL to OFF.")
         endif()
     endif()
+
+    # Check for the minimum supported curl version 
+    if(NOT (CURL_VERSION_STRING VERSION_GREATER_EQUAL "7.64.0"))
+        message(FATAL_ERROR "Your system curl version (${CURL_VERSION_STRING}) is too old! curl >= 7.64.0 is required. Update your curl version, or use the build in curl version e.g. via `cmake .. -DCPR_USE_SYSTEM_CURL=OFF` during CMake configure.")
+    endif()
 else()
     message(STATUS "Configuring built-in curl...")
 
@@ -287,6 +293,15 @@ else()
     restore_variable(DESTINATION CMAKE_CXX_CLANG_TIDY BACKUP CMAKE_CXX_CLANG_TIDY_BKP)
 endif()
 
+# Depending on which version of libcurl we are using the CMake target is called differently
+if(TARGET libcurl)
+    # Old curl CMake target name
+    set(CURL_LIB libcurl)
+else()
+    # New curl CMake target name
+    set(CURL_LIB CURL::libcurl)
+endif()
+
 # GTest configuration
 if(CPR_BUILD_TESTS)
     if(CPR_USE_SYSTEM_GTEST)

README.md

@@ -177,6 +177,7 @@ The only explicit requirements are:
 * a `C++17` compatible compiler such as Clang or GCC. The minimum required version of GCC is unknown, so if anyone has trouble building this library with a specific version of GCC, do let us know
 * in case you only have a `C++11` compatible compiler available, all versions below cpr 1.9.x are for you. The 1.10.0 release of cpr switches to `C++17` as a requirement.
 * If you would like to perform https requests `OpenSSL` and its development libraries are required.
+* If you do not use the build in version of [curl](https://github.com/curl/curl) but instead use your systems version, make sure you use a version `>= 7.64.0`. Lower versions are not supported. This means you need Debian `>= 10` or Ubuntu `>= 20.04 LTS`.
 
 ## Building cpr - Using vcpkg
 

cpr/CMakeLists.txt

@@ -32,7 +32,7 @@ add_library(cpr
 
 add_library(cpr::cpr ALIAS cpr)
 
-target_link_libraries(cpr PUBLIC CURL::libcurl) # todo should be private, but first dependencies in ssl_options need to be removed
+target_link_libraries(cpr PUBLIC ${CURL_LIB}) # todo should be private, but first dependencies in ssl_options need to be removed
 
 # Fix missing OpenSSL includes for Windows since in 'ssl_ctx.cpp' we include OpenSSL directly
 if(SSL_BACKEND_USED STREQUAL "OpenSSL")

test/CMakeLists.txt

@@ -26,7 +26,7 @@ macro(add_cpr_test _TEST_NAME)
         test_server
         GTest::GTest
         cpr::cpr
-        CURL::libcurl)
+        ${CURL_LIB})
     add_test(NAME cpr_${_TEST_NAME}_tests COMMAND ${_TEST_NAME}_tests)
     # Group under the "tests" project folder in IDEs such as Visual Studio.
     set_property(TARGET ${_TEST_NAME}_tests PROPERTY FOLDER "tests")