Add options to allow for strictly requiring OpenSSL/ZLIB

HTTPLIB_REQUIRE_OPENSSL & HTTPLIB_REQUIRE_ZLIB require the libs be found, or the build fails.

HTTPLIB_USE_OPENSSL_IF_AVAILABLE & HTTPLIB_USE_ZLIB_IF_AVAILABLE silently search for the libs.
If they aren't found, the build still continues, but shuts off support for those features.

Author: sum01

CMakeLists.txt

@@ -5,14 +5,30 @@ project(httplib VERSION 0.5.12 LANGUAGES CXX)
 # This is used in the installed Cmake config file.
 set(_HTTPLIB_OPENSSL_MIN_VER "1.1.1")
 
+# Allow for a build to require OpenSSL to pass, instead of just being optional
+option(HTTPLIB_REQUIRE_OPENSSL "Requires OpenSSL to be found & linked, or fails build." OFF)
+option(HTTPLIB_REQUIRE_ZLIB "Requires ZLIB to be found & linked, or fails build." OFF)
+# Allow for a build to casually enable OpenSSL/ZLIB support, but silenty continue if not found.
+# Make these options so their automatic use can be specifically disabled (as needed)
+option(HTTPLIB_USE_OPENSSL_IF_AVAILABLE "Uses OpenSSL (if available) to enable HTTPS support." ON)
+option(HTTPLIB_USE_ZLIB_IF_AVAILABLE "Uses ZLIB (if available) to enable compression support." ON)
+
 # TODO: implement the option of option to correctly split, building, and export with the split.py script.
 # option(HTTPLIB_SPLIT "Uses a Python script to split the header into a header & source file." OFF)
 
 # Threads needed for <thread> on some systems, and for <pthread.h> on Linux
 find_package(Threads REQUIRED)
-# Look quietly since these are optional
-find_package(OpenSSL ${_HTTPLIB_OPENSSL_MIN_VER} QUIET)
-find_package(ZLIB QUIET)
+if(HTTPLIB_REQUIRE_OPENSSL)
+	find_package(OpenSSL ${_HTTPLIB_OPENSSL_MIN_VER} REQUIRED)
+elseif(HTTPLIB_USE_OPENSSL_IF_AVAILABLE)
+	# Look quietly since it's optional are optional
+	find_package(OpenSSL ${_HTTPLIB_OPENSSL_MIN_VER} QUIET)
+endif()
+if(HTTPLIB_REQUIRE_ZLIB)
+	find_package(ZLIB REQUIRED)
+elseif(HTTPLIB_USE_ZLIB_IF_AVAILABLE)
+	find_package(ZLIB QUIET)
+endif()
 
 # Used for default, common dirs that the end-user can change (if needed)
 # like CMAKE_INSTALL_INCLUDEDIR or CMAKE_INSTALL_DATADIR

README.md

@@ -515,6 +515,12 @@ res = cli.Post("/resource/foo", "...", "text/plain");
 Building & Installation (Cmake)
 -------------------------------
 
+Build options:
+* `HTTPLIB_USE_OPENSSL_IF_AVAILABLE` (default on)
+* `HTTPLIB_USE_ZLIB_IF_AVAILABLE` (default on)
+* `HTTPLIB_REQUIRE_OPENSSL` (default off)
+* `HTTPLIB_REQUIRE_ZLIB` (default off)
+
 After installation with Cmake, a `find_package(httplib)` is available.  
 This creates a `httplib::httplib` target (if found).  
 It can be linked like so: 

httplibConfig.cmake.in

@@ -5,8 +5,17 @@ include(CMakeFindDependencyMacro)
 
 # We add find_dependency calls here to not make the end-user have to call them.
 find_dependency(Threads REQUIRED)
-find_dependency(OpenSSL @_HTTPLIB_OPENSSL_MIN_VER@ QUIET)
-find_dependency(ZLIB QUIET)
+if(@HTTPLIB_REQUIRE_OPENSSL@)
+	find_dependency(OpenSSL @_HTTPLIB_OPENSSL_MIN_VER@ REQUIRED)
+elseif(@HTTPLIB_USE_OPENSSL_IF_AVAILABLE@)
+	# Look quietly since it's optional are optional
+	find_dependency(OpenSSL @_HTTPLIB_OPENSSL_MIN_VER@ QUIET)
+endif()
+if(@HTTPLIB_REQUIRE_ZLIB@)
+	find_dependency(ZLIB REQUIRED)
+elseif(@HTTPLIB_USE_ZLIB_IF_AVAILABLE@)
+	find_dependency(ZLIB QUIET)
+endif()
 
 # Lets the end-user find the header path if needed
 # This is helpful if you're using Cmake's pre-compiled header feature