Add automatic versioning to Cmake (#505)

It pulls the version from the user-agent string in the header, so it
will not need to be manually adjusted. This version file is installed so
that you can check for a specific version with find_package(httplib)

Also added HTTPLIB_INCLUDE_DIR (root path without header name), and
HTTPLIB_LIBRARY (only if compiled).

Added HTTPLIB_VERSION, and HTTPLIB_FOUND (although it's recommended
to check if the target exists).

Updated CMakeLists documentation for all this.

CMakeLists.txt

@@ -32,11 +32,15 @@
 
 	-------------------------------------------------------------------------------
 
-	These three variables are available after you run find_package(httplib)
+	These variables are available after you run find_package(httplib)
-	* HTTPLIB_HEADER_PATH - this is the full path to the installed header.
+	* HTTPLIB_HEADER_PATH - this is the full path to the installed header (e.g. /usr/include/httplib.h).
 	* HTTPLIB_IS_USING_OPENSSL - a bool for if OpenSSL support is enabled.
 	* HTTPLIB_IS_USING_ZLIB - a bool for if ZLIB support is enabled.
-	* HTTPLIB_IS_COMPILED - a bool for if the library is header-only or compiled.
+	* HTTPLIB_IS_COMPILED - a bool for if the library is compiled, or otherwise header-only.
+	* HTTPLIB_INCLUDE_DIR - the root path to httplib's header (e.g. /usr/include).
+	* HTTPLIB_LIBRARY - the full path to the library if compiled (e.g. /usr/lib/libhttplib.so).
+	* HTTPLIB_VERSION - the project's version string.
+	* HTTPLIB_FOUND - a bool for if the target was found.
 
 	Want to use precompiled headers (Cmake feature since v3.16)?
 	It's as simple as doing the following (before linking):
@@ -48,7 +52,15 @@
 	FindPython3 requires Cmake v3.12
 ]]
 cmake_minimum_required(VERSION 3.12.0 FATAL_ERROR)
-project(httplib LANGUAGES CXX)
+
+# Get the user agent and use it as a version
+# This gets the string with the user agent from the header.
+# This is so the maintainer doesn't actually need to update this manually.
+file(STRINGS httplib.h _user_agent_match REGEX "User\-Agent.*cpp\-httplib/([0-9]+\.?)+")
+# Need to pull out just the version for use
+string(REGEX MATCH "([0-9]+\\.?)+" _httplib_version "${_user_agent_match}")
+
+project(httplib VERSION ${_httplib_version} LANGUAGES CXX)
 
 # Change as needed to set an OpenSSL minimum version.
 # This is used in the installed Cmake config file.
@@ -205,6 +217,23 @@ configure_package_config_file("${PROJECT_NAME}Config.cmake.in"
 	NO_CHECK_REQUIRED_COMPONENTS_MACRO
 )
 
+if(HTTPLIB_COMPILE)
+	write_basic_package_version_file("${PROJECT_NAME}ConfigVersion.cmake"
+		# Example: if you find_package(httplib 0.5.4)
+		# then anything >= 0.5 and <= 1.0 is accepted
+		COMPATIBILITY SameMajorVersion
+	)
+else()
+	write_basic_package_version_file("${PROJECT_NAME}ConfigVersion.cmake"
+		# Example: if you find_package(httplib 0.5.4)
+		# then anything >= 0.5 and <= 1.0 is accepted
+		COMPATIBILITY SameMajorVersion
+		# Tells Cmake that it's a header-only lib
+		# Mildly useful for end-users :)
+		ARCH_INDEPENDENT
+	)
+endif()
+
 # Creates the export httplibTargets.cmake
 # This is strictly what holds compilation requirements
 # and linkage information (doesn't find deps though).
@@ -218,6 +247,7 @@ install(FILES "${_httplib_build_includedir}/httplib.h" DESTINATION ${CMAKE_INSTA
 
 install(FILES
 		"${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}Config.cmake"
+		"${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}ConfigVersion.cmake"
 	DESTINATION ${_TARGET_INSTALL_CMAKEDIR}
 )
 

httplibConfig.cmake.in

@@ -6,6 +6,7 @@
 set(HTTPLIB_IS_USING_OPENSSL @HTTPLIB_IS_USING_OPENSSL@)
 set(HTTPLIB_IS_USING_ZLIB @HTTPLIB_IS_USING_ZLIB@)
 set(HTTPLIB_IS_COMPILED @HTTPLIB_COMPILE@)
+set(HTTPLIB_VERSION @PROJECT_VERSION@)
 
 include(CMakeFindDependencyMacro)
 
@@ -25,9 +26,41 @@ if(@HTTPLIB_IS_USING_ZLIB@)
 	find_dependency(ZLIB REQUIRED)
 endif()
 
-# Lets the end-user find the header path if needed
+# Mildly useful for end-users
+# Not really recommended to be used though
+set_and_check(HTTPLIB_INCLUDE_DIR "@PACKAGE_CMAKE_INSTALL_FULL_INCLUDEDIR@")
+# Lets the end-user find the header path with the header appended
 # This is helpful if you're using Cmake's pre-compiled header feature
 set_and_check(HTTPLIB_HEADER_PATH "@PACKAGE_CMAKE_INSTALL_FULL_INCLUDEDIR@/httplib.h")
 
 # Brings in the target library
 include("${CMAKE_CURRENT_LIST_DIR}/httplibTargets.cmake")
+
+# Ouputs a "found httplib /usr/include/httplib.h" message when using find_package(httplib)
+include(FindPackageMessage)
+if(TARGET httplib::httplib)
+	set(HTTPLIB_FOUND TRUE)
+
+	# Since the compiled version has a lib, show that in the message
+	if(@HTTPLIB_COMPILE@)
+		# The list of configurations is most likely just 1 unless they installed a debug & release
+		get_target_property(_httplib_configs httplib::httplib "IMPORTED_CONFIGURATIONS")
+		# Need to loop since the "IMPORTED_LOCATION" property isn't want we want.
+		# Instead, we need to find the IMPORTED_LOCATION_RELEASE or IMPORTED_LOCATION_DEBUG which has the lib path.
+		foreach(_httplib_conf "${_httplib_configs}")
+			# Grab the path to the lib and sets it to HTTPLIB_LIBRARY
+			get_target_property(HTTPLIB_LIBRARY httplib::httplib "IMPORTED_LOCATION_${_httplib_conf}")
+			# Check if we found it
+			if(HTTPLIB_LIBRARY)
+				break()
+			endif()
+		endforeach()
+
+		unset(_httplib_configs)
+		unset(_httplib_conf)
+
+		find_package_message(httplib "Found httplib: ${HTTPLIB_LIBRARY} (found version \"${HTTPLIB_VERSION}\")" "[${HTTPLIB_LIBRARY}][${HTTPLIB_HEADER_PATH}]")
+	else()
+		find_package_message(httplib "Found httplib: ${HTTPLIB_HEADER_PATH} (found version \"${HTTPLIB_VERSION}\")" "[${HTTPLIB_HEADER_PATH}]")
+	endif()
+endif()