Add ZeekBundle for integrating third-party components into our builds

This provides an experimental alternative configuration & build approach for
third-party submodules. It introduces a small CMake abstraction that will build
the library separately at configuration time to isolate it from other
targets. Then, we use `find_package` to pick up the (static) library from our
build directory.

For an example of its use, see Broker's CMakeLists.txt.

Co-authored-by: Christian Kreibich <[email protected]>

ZeekBundle.cmake

@@ -0,0 +1,138 @@
+# CMake dependencies.
+include(FetchContent)
+
+# Users may override this path to place the compiled packages elsewhere.
+set(ZEEK_BUNDLE_PREFIX "${PROJECT_BINARY_DIR}/zeek-bundle"
+    CACHE STRING "Path to the Zeek packages cache directory")
+
+# Opt-in to changed CMake behavior for fetching ZIP files.
+if (POLICY CMP0135)
+    cmake_policy(SET CMP0135 NEW)
+endif ()
+
+# Tries to find a package in the Zeek package cache.
+function (ZeekBundle_Find name)
+    find_package(${name} CONFIG QUIET NO_DEFAULT_PATH HINTS ${ZEEK_BUNDLE_PREFIX})
+    if (${name}_FOUND)
+        set(ZeekBundle_FOUND ON PARENT_SCOPE)
+    else ()
+        set(ZeekBundle_FOUND OFF PARENT_SCOPE)
+    endif ()
+endfunction ()
+
+# Runs the build and install steps for an external project.
+function (ZeekBundle_BuildStep name type binDir)
+    # Build the external project.
+    message(STATUS "Building bundled project: ${name} as ${type}")
+    execute_process(
+        COMMAND "${CMAKE_COMMAND}" --build "${binDir}" --config ${type}
+        OUTPUT_FILE "${binDir}/build${type}.out"
+        ERROR_FILE "${binDir}/build${type}.err"
+        RESULT_VARIABLE buildResult)
+    if (NOT buildResult EQUAL 0)
+        file(READ "${binDir}/build${type}.err" cmakeErr)
+        message(FATAL_ERROR "Failed to build ${name}:\n\n${cmakeErr}")
+    endif ()
+    # Install the external project.
+    message(STATUS "Installing bundled project: ${name} as ${type}")
+    execute_process(
+        COMMAND "${CMAKE_COMMAND}" --build "${binDir}" --config ${type} --target install
+        OUTPUT_FILE "${binDir}/install${type}.out"
+        ERROR_FILE "${binDir}/install${type}.err"
+        RESULT_VARIABLE installResult)
+    if (NOT installResult EQUAL 0)
+        file(READ "${binDir}/install${type}.err" cmakeErr)
+        message(FATAL_ERROR "Failed to install ${name}:\n\n${cmakeErr}")
+    endif ()
+endfunction ()
+
+# Builds an external project at configure time.
+function (ZeekBundle_Build name srcDir binDir)
+    # Extra arguments are passed as CMake options to the external project.
+    set(cmakeArgs "")
+    foreach (arg IN LISTS ARGN)
+        list(APPEND cmakeArgs "-D${arg}")
+    endforeach ()
+    # Make sure we can build debug and release versions of the project separately.
+    list(APPEND cmakeArgs "-DCMAKE_DEBUG_POSTFIX=d")
+    # Run CMake for the external project.
+    message(STATUS "Configuring bundled project: ${name}")
+    execute_process(
+        COMMAND
+            "${CMAKE_COMMAND}" -G "${CMAKE_GENERATOR}" ${cmakeArgs} -DBUILD_SHARED_LIBS=OFF
+            -DCMAKE_POSITION_INDEPENDENT_CODE=ON -DENABLE_TESTING=OFF
+            "-DCMAKE_INSTALL_PREFIX=${ZEEK_BUNDLE_PREFIX}" "${srcDir}"
+        WORKING_DIRECTORY "${binDir}"
+        OUTPUT_FILE "${binDir}/cmake.out"
+        ERROR_FILE "${binDir}/cmake.err"
+        RESULT_VARIABLE cmakeResult)
+    if (NOT cmakeResult EQUAL 0)
+        file(READ "${binDir}/cmake.err" cmakeErr)
+        message(FATAL_ERROR "Failed to configure external project ${name}:\n\n${cmakeErr}")
+    endif ()
+    get_property(isMultiConfig GLOBAL PROPERTY GENERATOR_IS_MULTI_CONFIG)
+    if (isMultiConfig)
+        zeekbundle_buildstep(${name} Debug ${binDir})
+        zeekbundle_buildstep(${name} Release ${binDir})
+    else ()
+        # On Windows, we cannot mix debug and release libraries.
+        if (WIN32)
+            zeekbundle_buildstep(${name} ${CMAKE_BUILD_TYPE} ${binDir})
+        else ()
+            zeekbundle_buildstep(${name} Release ${binDir})
+        endif ()
+    endif ()
+
+endfunction ()
+
+# Adds a bundled package to Zeek.
+#
+# Usage:
+# ZeekBundle_Add(
+#   NAME <name>
+#   FETCH (URL <url> | GIT_REPOSITORY <repo> GIT_TAG <tag> | SOURCE_DIR <path>)
+#   [CONFIGURE <args>]
+# )
+function (ZeekBundle_Add)
+    # Parse the function arguments.
+    cmake_parse_arguments(arg "" "NAME" "FETCH;CONFIGURE" ${ARGN})
+    if (NOT arg_NAME)
+        message(FATAL_ERROR "ZeekBundle_Add: mandatory argument NAME is missing!")
+    endif ()
+    if (NOT arg_FETCH)
+        message(FATAL_ERROR "ZeekBundle_Add: mandatory argument FETCH is missing!")
+    endif ()
+    # Use find_package if the user explicitly requested the package.
+    if (DEFINED ${arg_NAME}_ROOT)
+        message(STATUS "ZeekBundle: use system library for ${arg_NAME}")
+        find_package(
+            ${arg_NAME}
+            CONFIG
+            QUIET
+            REQUIRED
+            NO_DEFAULT_PATH
+            PATHS
+            ${${arg_NAME}_ROOT})
+        return()
+    endif ()
+    # Check if we already have the package.
+    zeekbundle_find(${arg_NAME})
+    if (ZeekBundle_FOUND)
+        return()
+    endif ()
+    # Fetch the package by delegating to FetchContent.
+    FetchContent_Declare(dl_${arg_NAME} ${arg_FETCH})
+    string(TOLOWER "dl_${arg_NAME}" internalName)
+    FetchContent_Populate(${internalName})
+    # Build the package and verify that it was found.
+    zeekbundle_build(${arg_NAME} "${${internalName}_SOURCE_DIR}" "${${internalName}_BINARY_DIR}"
+                     ${arg_CONFIGURE})
+    find_package(
+        ${arg_NAME}
+        CONFIG
+        QUIET
+        REQUIRED
+        NO_DEFAULT_PATH
+        PATHS
+        ${ZEEK_BUNDLE_PREFIX})
+endfunction ()