vlib: add a new dl.loader module, to simplify dynamic library loading, when the DLLs may be in multiple customisable locations (#17161)

vlib/dl/README.md

@@ -4,3 +4,6 @@
 It is a thin wrapper over `LoadLibrary` on Windows, and `dlopen` on Unix.
 
 Using it, you can implement a plugin system for your application.
+
+> NOTE: We highly recommend using `dl.loader` instead of `dl` directly.
+> It provides a more user-friendly API in the V way.

vlib/dl/loader/README.md

@@ -0,0 +1,36 @@
+## Description:
+
+`dl.loader` is an abstraction layer over `dl` that provides a more user-friendly API in the V way.
+It can be used to Dynamically Load a library during runtime in scenarios where the library to load
+does not have a determined path an can be located in different places.
+
+It also provides a way to load a library from a specific path, or from a list of paths, or from
+a custom environment variable that contains a list of paths.
+
+## Usage:
+
+```v
+import dl.loader
+
+// Load a library from a list of paths
+const default_paths = [
+	'not-existing-dynamic-link-library'
+	// 'C:\\Windows\\System32\\shell32.dll',
+	'shell32',
+]
+
+fn main() {
+	mut dl_loader := loader.get_or_create_dynamic_lib_loader(
+		key: 'LibExample'
+		env_path: 'LIB_PATH'
+		paths: default_paths
+	)!
+
+	defer {
+		dl_loader.unregister()
+	}
+
+	sym := dl_loader.get_sym('CommandLineToArgvW')!
+	assert !isnil(sym)
+}
+```

vlib/dl/loader/loader.v

@@ -0,0 +1,153 @@
+[has_globals]
+module loader
+
+import dl
+import os
+
+const (
+	dl_no_path_issue_msg  = 'no paths to dynamic library'
+	dl_open_issue_msg     = 'could not open dynamic library'
+	dl_sym_issue_msg      = 'could not get optional symbol from dynamic library'
+	dl_close_issue_msg    = 'could not close dynamic library'
+	dl_register_issue_msg = 'could not register dynamic library loader'
+)
+
+pub const (
+	dl_no_path_issue_code  = 1
+	dl_open_issue_code     = 1
+	dl_sym_issue_code      = 2
+	dl_close_issue_code    = 3
+	dl_register_issue_code = 4
+
+	dl_no_path_issue_err   = error_with_code(dl_no_path_issue_msg, dl_no_path_issue_code)
+	dl_open_issue_err      = error_with_code(dl_open_issue_msg, dl_open_issue_code)
+	dl_sym_issue_err       = error_with_code(dl_sym_issue_msg, dl_sym_issue_code)
+	dl_close_issue_err     = error_with_code(dl_close_issue_msg, dl_close_issue_code)
+	dl_register_issue_err  = error_with_code(dl_register_issue_msg, dl_register_issue_code)
+)
+
+__global (
+	registered_dl_loaders map[string]&DynamicLibLoader
+)
+
+fn register_dl_loader(dl_loader &DynamicLibLoader) ! {
+	if dl_loader.key in registered_dl_loaders {
+		return loader.dl_register_issue_err
+	}
+	registered_dl_loaders[dl_loader.key] = dl_loader
+}
+
+// registered_dl_loader_keys returns the keys of registered DynamicLibLoader.
+pub fn registered_dl_loader_keys() []string {
+	return registered_dl_loaders.keys()
+}
+
+// DynamicLibLoader is a wrapper around dlopen, dlsym and dlclose.
+[heap]
+pub struct DynamicLibLoader {
+pub:
+	key   string
+	flags int = dl.rtld_lazy
+	paths []string
+mut:
+	handle  voidptr
+	sym_map map[string]voidptr
+}
+
+// DynamicLibLoaderConfig is a configuration for DynamicLibLoader.
+[params]
+pub struct DynamicLibLoaderConfig {
+	// flags is the flags for dlopen.
+	flags int = dl.rtld_lazy
+	// key is the key to register the DynamicLibLoader.
+	key string
+	// env_path is the environment variable name that contains the path to the dynamic library.
+	env_path string
+	// paths is the list of paths to the dynamic library.
+	paths []string
+}
+
+// new_dynamic_lib_loader returns a new DynamicLibLoader.
+fn new_dynamic_lib_loader(conf DynamicLibLoaderConfig) !&DynamicLibLoader {
+	mut paths := []string{}
+
+	if conf.env_path.len > 0 {
+		if env_path := os.getenv_opt(conf.env_path) {
+			paths << env_path.split(os.path_delimiter)
+		}
+	}
+
+	paths << conf.paths
+
+	if paths.len == 0 {
+		return loader.dl_no_path_issue_err
+	}
+
+	mut dl_loader := &DynamicLibLoader{
+		key: conf.key
+		flags: conf.flags
+		paths: paths
+	}
+
+	register_dl_loader(dl_loader)!
+	return dl_loader
+}
+
+// get_or_create_dynamic_lib_loader returns a DynamicLibLoader.
+// If the DynamicLibLoader is not registered, it creates a new DynamicLibLoader.
+pub fn get_or_create_dynamic_lib_loader(conf DynamicLibLoaderConfig) !&DynamicLibLoader {
+	if dl_loader := registered_dl_loaders[conf.key] {
+		return dl_loader
+	}
+	return new_dynamic_lib_loader(conf)
+}
+
+// load loads the dynamic library.
+pub fn (mut dl_loader DynamicLibLoader) open() !voidptr {
+	if !isnil(dl_loader.handle) {
+		return dl_loader.handle
+	}
+
+	for path in dl_loader.paths {
+		if handle := dl.open_opt(path, dl_loader.flags) {
+			dl_loader.handle = handle
+			return handle
+		}
+	}
+
+	return loader.dl_open_issue_err
+}
+
+// close closes the dynamic library.
+pub fn (mut dl_loader DynamicLibLoader) close() ! {
+	if !isnil(dl_loader.handle) {
+		if dl.close(dl_loader.handle) {
+			dl_loader.handle = unsafe { nil }
+			return
+		}
+	}
+
+	return loader.dl_close_issue_err
+}
+
+// get_sym gets a symbol from the dynamic library.
+pub fn (mut dl_loader DynamicLibLoader) get_sym(name string) !voidptr {
+	if sym := dl_loader.sym_map[name] {
+		return sym
+	}
+
+	handle := dl_loader.open()!
+	if sym := dl.sym_opt(handle, name) {
+		dl_loader.sym_map[name] = sym
+		return sym
+	}
+
+	dl_loader.close()!
+	return loader.dl_sym_issue_err
+}
+
+// unregister unregisters the DynamicLibLoader.
+pub fn (mut dl_loader DynamicLibLoader) unregister() {
+	dl_loader.close() or {}
+	registered_dl_loaders.delete(dl_loader.key)
+}

vlib/dl/loader/loader_test.v

@@ -0,0 +1,83 @@
+import dl.loader
+import dl
+
+fn test_dl_loader() ! {
+	$if linux {
+		run_test_invalid_lib_linux()!
+		return
+	}
+	$if windows {
+		run_test_invalid_lib_windows()!
+		run_test_valid_lib_windows()!
+		run_test_invalid_sym_windows()!
+		run_test_valid_sym_windows()!
+		return
+	} $else {
+		eprint('currently not implemented on this platform')
+	}
+}
+
+fn get_or_create_loader(name string, paths []string) !&loader.DynamicLibLoader {
+	return loader.get_or_create_dynamic_lib_loader(
+		key: name
+		paths: paths
+		flags: dl.rtld_now
+	)
+}
+
+fn run_test_invalid_lib_linux() ! {
+	// ensure a not-existing dl won't be loaded
+	mut dl_loader := get_or_create_loader(@MOD + '.' + @FN + '.' + 'lib', [
+		'not-existing-dynamic-link-library',
+	])!
+	defer {
+		dl_loader.unregister()
+	}
+	h := dl_loader.open() or { unsafe { nil } }
+	assert isnil(h)
+}
+
+fn run_test_invalid_lib_windows() ! {
+	// ensure a not-existing dl won't be loaded
+	mut dl_loader := get_or_create_loader(@MOD + '.' + @FN + '.' + 'lib', [
+		'not-existing-dynamic-link-library',
+	])!
+	defer {
+		dl_loader.unregister()
+	}
+	h := dl_loader.open() or { unsafe { nil } }
+	assert isnil(h)
+}
+
+fn run_test_valid_lib_windows() ! {
+	mut dl_loader := get_or_create_loader(@MOD + '.' + @FN + '.' + 'lib', [
+		'not-existing-dynamic-link-library',
+		'shell32',
+	])!
+	defer {
+		dl_loader.unregister()
+	}
+	h := dl_loader.open() or { unsafe { nil } }
+	assert !isnil(h)
+}
+
+fn run_test_invalid_sym_windows() ! {
+	mut dl_loader := get_or_create_loader(@MOD + '.' + @FN + '.' + 'lib', ['shell32'])!
+	defer {
+		dl_loader.unregister()
+	}
+	proc := dl_loader.get_sym('CommandLineToArgvW2') or { unsafe { nil } }
+	assert isnil(proc)
+}
+
+fn run_test_valid_sym_windows() ! {
+	mut dl_loader := get_or_create_loader(@MOD + '.' + @FN + '.' + 'lib', [
+		'not-existing-dynamic-link-library',
+		'shell32',
+	])!
+	defer {
+		dl_loader.unregister()
+	}
+	proc := dl_loader.get_sym('CommandLineToArgvW') or { unsafe { nil } }
+	assert !isnil(proc)
+}