cmake: Add `FindLibevent` module

cmake/bitcoin-config.h.in

@@ -61,6 +61,9 @@
    */
 #cmakedefine01 HAVE_DECL_SETSID
 
+/* Define this symbol if evhttp_connection_get_peer expects const char** */
+#cmakedefine HAVE_EVHTTP_CONNECTION_GET_PEER_CONST_CHAR 1
+
 /* Define to 1 if fdatasync is available. */
 #cmakedefine HAVE_FDATASYNC 1
 

cmake/module/FindLibevent.cmake

@@ -0,0 +1,80 @@
+# Copyright (c) 2024-present The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or https://opensource.org/license/mit/.
+
+#[=======================================================================[
+FindLibevent
+------------
+
+Finds the Libevent headers and libraries.
+
+This is a wrapper around find_package()/pkg_check_modules() commands that:
+ - facilitates searching in various build environments
+ - prints a standard log message
+
+#]=======================================================================]
+
+# Check whether evhttp_connection_get_peer expects const char**.
+# See https://github.com/libevent/libevent/commit/a18301a2bb160ff7c3ffaf5b7653c39ffe27b385
+function(check_evhttp_connection_get_peer target)
+  include(CMakePushCheckState)
+  cmake_push_check_state(RESET)
+  set(CMAKE_REQUIRED_LIBRARIES ${target})
+  include(CheckCXXSourceCompiles)
+  check_cxx_source_compiles("
+    #include <cstdint>
+    #include <event2/http.h>
+
+    int main()
+    {
+        evhttp_connection* conn = (evhttp_connection*)1;
+        const char* host;
+        uint16_t port;
+        evhttp_connection_get_peer(conn, &host, &port);
+    }
+    " HAVE_EVHTTP_CONNECTION_GET_PEER_CONST_CHAR
+  )
+  cmake_pop_check_state()
+  set(HAVE_EVHTTP_CONNECTION_GET_PEER_CONST_CHAR ${HAVE_EVHTTP_CONNECTION_GET_PEER_CONST_CHAR} PARENT_SCOPE)
+endfunction()
+
+
+include(FindPackageHandleStandardArgs)
+if(VCPKG_TARGET_TRIPLET)
+  find_package(Libevent ${Libevent_FIND_VERSION} NO_MODULE QUIET
+    COMPONENTS extra
+  )
+  find_package_handle_standard_args(Libevent
+    REQUIRED_VARS Libevent_DIR
+    VERSION_VAR Libevent_VERSION
+  )
+  check_evhttp_connection_get_peer(libevent::extra)
+  add_library(libevent::libevent ALIAS libevent::extra)
+  mark_as_advanced(Libevent_DIR)
+  mark_as_advanced(_event_h)
+  mark_as_advanced(_event_lib)
+else()
+  find_package(PkgConfig REQUIRED)
+  pkg_check_modules(libevent QUIET
+    IMPORTED_TARGET
+    libevent>=${Libevent_FIND_VERSION}
+  )
+  set(_libevent_required_vars libevent_LIBRARY_DIRS libevent_FOUND)
+  if(NOT WIN32)
+    pkg_check_modules(libevent_pthreads QUIET
+      IMPORTED_TARGET
+      libevent_pthreads>=${Libevent_FIND_VERSION}
+    )
+    list(APPEND _libevent_required_vars libevent_pthreads_FOUND)
+  endif()
+  find_package_handle_standard_args(Libevent
+    REQUIRED_VARS ${_libevent_required_vars}
+    VERSION_VAR libevent_VERSION
+  )
+  unset(_libevent_required_vars)
+  check_evhttp_connection_get_peer(PkgConfig::libevent)
+  add_library(libevent::libevent ALIAS PkgConfig::libevent)
+  if(NOT WIN32)
+    add_library(libevent::pthreads ALIAS PkgConfig::libevent_pthreads)
+  endif()
+endif()