CDRIVER-4637 Remove ENABLE_SRV=AUTO, clean up SRV URI support

CMakeLists.txt

@@ -71,11 +71,9 @@ mongo_bool_setting(ENABLE_EXAMPLES "Build MongoDB C Driver examples")
 mongo_bool_setting(ENABLE_MAN_PAGES "Build the manual pages" DEFAULT VALUE OFF)
 mongo_bool_setting(ENABLE_HTML_DOCS "Build the HTML documentation" DEFAULT VALUE OFF)
 mongo_bool_setting(ENABLE_UNINSTALL "Generate an 'uninstall' script and an 'uninstall' build target")
+mongo_bool_setting(ENABLE_SRV "Enable support for mongodb+srv URIs.")
 
 # Optional features that are ENABLED when necessary dependencies are found:
-mongo_setting(ENABLE_SRV "Enable support for mongodb+srv URIs."
-              OPTIONS ON OFF AUTO
-              DEFAULT VALUE AUTO)
 mongo_setting(ENABLE_SNAPPY "Enable Snappy compression support"
               OPTIONS ON OFF AUTO
               DEFAULT VALUE AUTO)

build/cmake/CMakeLists.txt

@@ -2,7 +2,7 @@ add_subdirectory (make_dist)
 
 set (build_cmake_MODULES
    CheckSchedGetCPU.cmake
-   FindResSearch.cmake
+   ResSearch.cmake
    FindSASL2.cmake
    FindSnappy.cmake
    FindSphinx.cmake

build/cmake/ResSearch.cmake

@@ -0,0 +1,57 @@
+include(CheckSymbolExists)
+include(CMakePushCheckState)
+
+cmake_push_check_state(RESET)
+
+# The name of the library that performs name resolution, suitable for giving to the "-l" link flag
+set(RESOLVE_LIB_NAME)
+# If TRUE, then the C runtime provides the name resolution that we need
+set(resolve_is_libc FALSE)
+
+if(WIN32)
+    set(RESOLVE_LIB_NAME Dnsapi)
+    set(_MONGOC_HAVE_DNSAPI 1)
+else()
+    # Try to find the search functions for various configurations.
+    # Headers required by minimum on the strictest system: (Tested on FreeBSD 13)
+    set(resolve_headers netinet/in.h sys/types.h arpa/nameser.h resolv.h)
+    set(CMAKE_REQUIRED_LIBRARIES resolv)
+    check_symbol_exists(res_nsearch "${resolve_headers}" _MONGOC_HAVE_RES_NSEARCH_RESOLV)
+    check_symbol_exists(res_search "${resolve_headers}" _MONGOC_HAVE_RES_SEARCH_RESOLV)
+    check_symbol_exists(res_ndestroy "${resolve_headers}" _MONGOC_HAVE_RES_NDESTROY_RESOLV)
+    check_symbol_exists(res_nclose "${resolve_headers}" _MONGOC_HAVE_RES_NCLOSE_RESOLV)
+    if((_MONGOC_HAVE_RES_NSEARCH_RESOLV OR _MONGOC_HAVE_RES_SEARCH_RESOLV)
+        AND (_MONGOC_HAVE_RES_NDESTROY_RESOLV OR _MONGOC_HAVE_RES_NCLOSE_RESOLV))
+        set(RESOLVE_LIB_NAME resolv)
+    else()
+        # Can we use name resolution with just libc?
+        unset(CMAKE_REQUIRED_LIBRARIES)
+        check_symbol_exists(res_nsearch "${resolve_headers}" _MONGOC_HAVE_RES_NSEARCH_NOLINK)
+        check_symbol_exists(res_search "${resolve_headers}" _MONGOC_HAVE_RES_SEARCH_NOLINK)
+        check_symbol_exists(res_ndestroy "${resolve_headers}" _MONGOC_HAVE_RES_NDESTROY_NOLINK)
+        check_symbol_exists(res_nclose "${resolve_headers}" _MONGOC_HAVE_RES_NCLOSE_NOLINK)
+        if((_MONGOC_HAVE_RES_NSEARCH_NOLINK OR _MONGOC_HAVE_RES_SEARCH_NOLINK)
+            AND (_MONGOC_HAVE_RES_NDESTROY_NOLINK OR _MONGOC_HAVE_RES_NCLOSE_NOLINK))
+            set(resolve_is_libc TRUE)
+            message(VERBOSE "Name resolution is provided by the C runtime")
+        endif()
+    endif()
+endif()
+
+_mongo_pick(MONGOC_HAVE_DNSAPI 1 0 _MONGOC_HAVE_DNSAPI)
+_mongo_pick(MONGOC_HAVE_RES_NSEARCH 1 0 [[_MONGOC_HAVE_RES_NSEARCH_NOLINK OR _MONGOC_HAVE_RES_NSEARCH_RESOLV]])
+_mongo_pick(MONGOC_HAVE_RES_SEARCH 1 0 [[_MONGOC_HAVE_RES_SEARCH_NOLINK OR _MONGOC_HAVE_RES_SEARCH_RESOLV]])
+_mongo_pick(MONGOC_HAVE_RES_NDESTROY 1 0 [[_MONGOC_HAVE_RES_NDESTROY_NOLINK OR _MONGOC_HAVE_RES_NDESTROY_RESOLV]])
+_mongo_pick(MONGOC_HAVE_RES_NCLOSE 1 0 [[_MONGOC_HAVE_RES_NCLOSE_NOLINK OR _MONGOC_HAVE_RES_NCLOSE_RESOLV]])
+
+if(RESOLVE_LIB_NAME OR resolve_is_libc)
+    # Define the resolver interface:
+    add_library(_mongoc-resolve INTERFACE)
+    add_library(mongo::detail::c_resolve ALIAS _mongoc-resolve)
+    set_target_properties(_mongoc-resolve PROPERTIES
+        INTERFACE_LINK_LIBRARIES "${RESOLVE_LIB_NAME}"
+        EXPORT_NAME detail::c_resolve)
+    install(TARGETS _mongoc-resolve EXPORT mongoc-targets)
+endif()
+
+cmake_pop_check_state()