portability: implement skeleton with memrchr function

meson.build

@@ -33,6 +33,7 @@ add_project_arguments('-D_FILE_OFFSET_BITS=64', language: 'c')
 subproject = meson.is_subproject()
 
 subdir('doc')
+subdir('portability')
 subdir('libfetch')
 subdir('src')
 subdir('tests')

portability/memrchr.c

@@ -0,0 +1,9 @@
+#include <stddef.h>
+
+void *memrchr(const void *m, int c, size_t n)
+{
+	const unsigned char *s = m;
+	c = (unsigned char)c;
+	while (n--) if (s[n]==c) return (void *)(s+n);
+	return 0;
+}

portability/meson.build

@@ -0,0 +1,35 @@
+cc = meson.get_compiler('c')
+
+
+libportability_src = []
+
+
+check_functions = [
+	['memrchr', 'memrchr.c', 'NEED_MEMRCHR', 'string.h'],
+]
+
+
+foreach f : check_functions
+	if not cc.has_function(f.get(0), prefix: '#include <' + f.get(3) + '>', args: ['-D_GNU_SOURCE']) or not cc.has_header_symbol(f.get(3), f.get(0), args: ['-D_GNU_SOURCE'])
+		add_project_arguments('-D' + f.get(2), language: 'c')
+		libportability_src += [f.get(1)]
+	endif
+endforeach
+
+
+if libportability_src.length() > 0
+	libportability = static_library(
+		'portability',
+		libportability_src,
+		dependencies: static_deps,
+	)
+
+	libportability_dep = declare_dependency(
+		link_whole: libportability,
+		include_directories: include_directories('.'),
+	)
+else
+	libportability_dep = declare_dependency(
+		include_directories: include_directories('.'),
+	)
+endif

portability/string.h

@@ -0,0 +1,5 @@
+#include_next <string.h>
+
+#ifdef NEED_MEMRCHR
+extern void *memrchr(const void *m, int c, size_t n);
+#endif

src/meson.build

@@ -117,6 +117,7 @@ libapk_shared = shared_library(
 	install: not subproject,
 	dependencies: [
 		libfetch_dep,
+		libportability_dep,
 		shared_deps,
 	],
 	c_args: apk_cargs,
@@ -128,6 +129,7 @@ libapk_static = static_library(
 	install: not subproject,
 	dependencies: [
 		libfetch_dep,
+		libportability_dep,
 		static_deps,
 	],
 	c_args: [apk_cargs, '-DOPENSSL_NO_ENGINE'],
@@ -158,7 +160,12 @@ if(lua_dep.found())
 	libluaapk = library(
 		'luaapk',
 		luaapk_src,
-		dependencies: [lua_dep, libapk_dep, shared_deps],
+		dependencies: [
+			lua_dep,
+			libapk_dep,
+			shared_deps,
+			libportability_dep.partial_dependency(includes: true),
+		],
 		install: true,
 		install_dir: lua_dep.get_pkgconfig_variable('libdir'),
 		c_args: apk_cargs,
@@ -173,6 +180,7 @@ apk_exe = executable(
 		libapk_dep,
 		shared_deps,
 		libfetch_dep.partial_dependency(includes: true),
+		libportability_dep.partial_dependency(includes: true),
 	],
 	c_args: apk_cargs,
 )
@@ -185,6 +193,7 @@ if get_option('static_apk')
 		dependencies: [
 			static_deps,
 			libfetch_dep.partial_dependency(includes: true),
+			libportability_dep.partial_dependency(includes: true),
 		],
 		link_with: libapk_static,
 		c_args: [apk_cargs, '-DOPENSSL_NO_ENGINE'],