Use CStr as the type for symbol name

Cargo.toml

@@ -13,7 +13,7 @@ description = "Bindings around the platform's dynamic library loading primitives
 keywords = ["dlopen", "load", "shared", "dylib"]
 categories = ["api-bindings"]
 rust-version = "1.56.0"
-edition = "2015"
+edition = "2021"
 
 [target.'cfg(windows)'.dependencies.windows-targets]
 version = ">=0.48, <0.54"

src/lib.rs

@@ -27,7 +27,7 @@
 //! fn call_dynamic() -> Result<u32, Box<dyn std::error::Error>> {
 //!     unsafe {
 //!         let lib = libloading::Library::new("/path/to/liblibrary.so")?;
-//!         let func: libloading::Symbol<unsafe extern fn() -> u32> = lib.get(b"my_func")?;
+//!         let func: libloading::Symbol<unsafe extern fn() -> u32> = lib.get(c"my_func")?;
 //!         Ok(func())
 //!     }
 //! }

src/os/unix/consts.rs

@@ -54,8 +54,7 @@ mod posix {
 
 #[cfg(any(not(libloading_docs), unix))]
 mod posix {
-    extern crate cfg_if;
-    use self::cfg_if::cfg_if;
+    use cfg_if::cfg_if;
     use super::c_int;
     cfg_if! {
         if #[cfg(target_os = "haiku")] {

src/os/unix/mod.rs

@@ -8,11 +8,13 @@ mod unix_imports {
 }
 
 pub use self::consts::*;
+use crate::error::Error;
+use crate::util::ensure_compatible_types;
 use self::unix_imports::*;
-use std::ffi::{CStr, OsStr};
+use std::borrow::Cow;
+use std::ffi::{CStr, CString, OsStr};
 use std::os::raw;
 use std::{fmt, marker, mem, ptr};
-use util::{cstr_cow_from_bytes, ensure_compatible_types};
 
 mod consts;
 
@@ -181,6 +183,25 @@ impl Library {
     where
         P: AsRef<OsStr>,
     {
+        /// Checks for the last byte and avoids allocating if it is zero.
+        ///
+        /// Non-last null bytes still result in an error.
+        fn cstr_cow_from_bytes(slice: &[u8]) -> Result<Cow<'_, CStr>, Error> {
+            Ok(match slice.last() {
+                // Slice out of 0 elements
+                None => Cow::Borrowed(c""),
+                // Slice with trailing 0
+                Some(&0) => Cow::Borrowed(
+                    CStr::from_bytes_with_nul(slice)
+                        .map_err(|source| Error::CreateCStringWithTrailing { source })?,
+                ),
+                // Slice with no trailing 0
+                Some(_) => {
+                    Cow::Owned(CString::new(slice).map_err(|source| Error::CreateCString { source })?)
+                }
+            })
+        }
+
         let filename = match filename {
             None => None,
             Some(ref f) => Some(cstr_cow_from_bytes(f.as_ref().as_bytes())?),
@@ -207,12 +228,12 @@ impl Library {
         .map_err(|e| e.unwrap_or(crate::Error::DlOpenUnknown))
     }
 
-    unsafe fn get_impl<T, F>(&self, symbol: &[u8], on_null: F) -> Result<Symbol<T>, crate::Error>
+    unsafe fn get_impl<T, F>(&self, symbol: &CStr, on_null: F) -> Result<Symbol<T>, crate::Error>
     where
         F: FnOnce() -> Result<Symbol<T>, crate::Error>,
     {
         ensure_compatible_types::<T, *mut raw::c_void>()?;
-        let symbol = cstr_cow_from_bytes(symbol)?;
+
         // `dlsym` may return nullptr in two cases: when a symbol genuinely points to a null
         // pointer or the symbol cannot be found. In order to detect this case a double dlerror
         // pattern must be used, which is, sadly, a little bit racy.
@@ -243,9 +264,6 @@ impl Library {
 
     /// Get a pointer to a function or static variable by symbol name.
     ///
-    /// The `symbol` may not contain any null bytes, with the exception of the last byte. Providing a
-    /// null terminated `symbol` may help to avoid an allocation.
-    ///
     /// Symbol is interpreted as-is; no mangling is done. This means that symbols like `x::y` are
     /// most likely invalid.
     ///
@@ -265,8 +283,7 @@ impl Library {
     /// pointer without it being an error. If loading a null pointer is something you care about,
     /// consider using the [`Library::get_singlethreaded`] call.
     #[inline(always)]
-    pub unsafe fn get<T>(&self, symbol: &[u8]) -> Result<Symbol<T>, crate::Error> {
-        extern crate cfg_if;
+    pub unsafe fn get<T>(&self, symbol: &CStr) -> Result<Symbol<T>, crate::Error> {
         cfg_if::cfg_if! {
             // These targets are known to have MT-safe `dlerror`.
             if #[cfg(any(
@@ -290,9 +307,6 @@ impl Library {
 
     /// Get a pointer to function or static variable by symbol name.
     ///
-    /// The `symbol` may not contain any null bytes, with the exception of the last byte. Providing a
-    /// null terminated `symbol` may help to avoid an allocation.
-    ///
     /// Symbol is interpreted as-is; no mangling is done. This means that symbols like `x::y` are
     /// most likely invalid.
     ///
@@ -309,7 +323,7 @@ impl Library {
     /// The implementation of thread-local variables is extremely platform specific and uses of such
     /// variables that work on e.g. Linux may have unintended behaviour on other targets.
     #[inline(always)]
-    pub unsafe fn get_singlethreaded<T>(&self, symbol: &[u8]) -> Result<Symbol<T>, crate::Error> {
+    pub unsafe fn get_singlethreaded<T>(&self, symbol: &CStr) -> Result<Symbol<T>, crate::Error> {
         self.get_impl(symbol, || {
             Ok(Symbol {
                 pointer: ptr::null_mut(),

src/os/windows/mod.rs

@@ -15,9 +15,9 @@ mod windows_imports {
     windows_targets::link!("kernel32.dll" "system" fn GetProcAddress(module: HMODULE, procname: *const u8) -> FARPROC);
 }
 
+use crate::util::ensure_compatible_types;
 use self::windows_imports::*;
-use util::{ensure_compatible_types, cstr_cow_from_bytes};
-use std::ffi::{OsStr, OsString};
+use std::ffi::{CStr, OsStr, OsString};
 use std::{fmt, io, marker, mem, ptr};
 use std::os::raw;
 
@@ -173,18 +173,15 @@ impl Library {
 
     /// Get a pointer to a function or static variable by symbol name.
     ///
-    /// The `symbol` may not contain any null bytes, with the exception of the last byte. A null
-    /// terminated `symbol` may avoid a string allocation in some cases.
-    ///
     /// Symbol is interpreted as-is; no mangling is done. This means that symbols like `x::y` are
     /// most likely invalid.
     ///
     /// # Safety
     ///
     /// Users of this API must specify the correct type of the function or variable loaded.
-    pub unsafe fn get<T>(&self, symbol: &[u8]) -> Result<Symbol<T>, crate::Error> {
+    pub unsafe fn get<T>(&self, symbol: &CStr) -> Result<Symbol<T>, crate::Error> {
         ensure_compatible_types::<T, FARPROC>()?;
-        let symbol = cstr_cow_from_bytes(symbol)?;
+
         with_get_last_error(|source| crate::Error::GetProcAddress { source }, || {
             let symbol = GetProcAddress(self.0, symbol.as_ptr().cast());
             if symbol.is_none() {

src/safe.rs

@@ -5,7 +5,7 @@ use super::os::unix as imp;
 #[cfg(all(not(libloading_docs), windows))]
 use super::os::windows as imp;
 use super::Error;
-use std::ffi::OsStr;
+use std::ffi::{CStr, OsStr};
 use std::fmt;
 use std::marker;
 use std::ops;
@@ -87,9 +87,6 @@ impl Library {
 
     /// Get a pointer to a function or static variable by symbol name.
     ///
-    /// The `symbol` may not contain any null bytes, with the exception of the last byte. Providing a
-    /// null-terminated `symbol` may help to avoid an allocation.
-    ///
     /// The symbol is interpreted as-is; no mangling is done. This means that symbols like `x::y` are
     /// most likely invalid.
     ///
@@ -130,7 +127,7 @@ impl Library {
     /// # };
     /// unsafe {
     ///     let awesome_function: Symbol<unsafe extern fn(f64) -> f64> =
-    ///         lib.get(b"awesome_function\0").unwrap();
+    ///         lib.get(c"awesome_function").unwrap();
     ///     awesome_function(0.42);
     /// }
     /// ```
@@ -141,11 +138,11 @@ impl Library {
     /// # use ::libloading::{Library, Symbol};
     /// # let lib = unsafe { Library::new("/path/to/awesome.module").unwrap() };
     /// unsafe {
-    ///     let awesome_variable: Symbol<*mut f64> = lib.get(b"awesome_variable\0").unwrap();
+    ///     let awesome_variable: Symbol<*mut f64> = lib.get(c"awesome_variable").unwrap();
     ///     **awesome_variable = 42.0;
     /// };
     /// ```
-    pub unsafe fn get<T>(&self, symbol: &[u8]) -> Result<Symbol<T>, Error> {
+    pub unsafe fn get<T>(&self, symbol: &CStr) -> Result<Symbol<T>, Error> {
         self.0.get(symbol).map(|from| Symbol::from_raw(from, self))
     }
 
@@ -215,7 +212,7 @@ impl<'lib, T> Symbol<'lib, T> {
     /// # use ::libloading::{Library, Symbol};
     /// unsafe {
     ///     let lib = Library::new("/path/to/awesome.module").unwrap();
-    ///     let symbol: Symbol<*mut u32> = lib.get(b"symbol\0").unwrap();
+    ///     let symbol: Symbol<*mut u32> = lib.get(c"symbol").unwrap();
     ///     let symbol = symbol.into_raw();
     /// }
     /// ```
@@ -238,7 +235,7 @@ impl<'lib, T> Symbol<'lib, T> {
     /// # use ::libloading::{Library, Symbol};
     /// unsafe {
     ///     let lib = Library::new("/path/to/awesome.module").unwrap();
-    ///     let symbol: Symbol<*mut u32> = lib.get(b"symbol\0").unwrap();
+    ///     let symbol: Symbol<*mut u32> = lib.get(c"symbol").unwrap();
     ///     let symbol = symbol.into_raw();
     ///     let symbol = Symbol::from_raw(symbol, &lib);
     /// }
@@ -280,7 +277,7 @@ impl<'lib, T> Symbol<'lib, Option<T>> {
     /// # use ::libloading::{Library, Symbol};
     /// unsafe {
     ///     let lib = Library::new("/path/to/awesome.module").unwrap();
-    ///     let symbol: Symbol<Option<*mut u32>> = lib.get(b"symbol\0").unwrap();
+    ///     let symbol: Symbol<Option<*mut u32>> = lib.get(c"symbol").unwrap();
     ///     let symbol: Symbol<*mut u32> = symbol.lift_option().expect("static is not null");
     /// }
     /// ```

src/test_helpers.rs

@@ -33,5 +33,5 @@ pub unsafe extern "C" fn test_get_static_u32() -> u32 {
 
 #[no_mangle]
 pub unsafe extern "C" fn test_check_static_ptr() -> bool {
-    TEST_STATIC_PTR == (&mut TEST_STATIC_PTR as *mut *mut _ as *mut _)
+    TEST_STATIC_PTR == (&raw mut TEST_STATIC_PTR as *mut *mut _ as *mut _)
 }

src/util.rs

@@ -1,29 +1,5 @@
-use std::borrow::Cow;
-use std::ffi::{CStr, CString};
-use std::os::raw;
-
 use crate::Error;
 
-/// Checks for the last byte and avoids allocating if it is zero.
-///
-/// Non-last null bytes still result in an error.
-pub(crate) fn cstr_cow_from_bytes(slice: &[u8]) -> Result<Cow<'_, CStr>, Error> {
-    static ZERO: raw::c_char = 0;
-    Ok(match slice.last() {
-        // Slice out of 0 elements
-        None => unsafe { Cow::Borrowed(CStr::from_ptr(&ZERO)) },
-        // Slice with trailing 0
-        Some(&0) => Cow::Borrowed(
-            CStr::from_bytes_with_nul(slice)
-                .map_err(|source| Error::CreateCStringWithTrailing { source })?,
-        ),
-        // Slice with no trailing 0
-        Some(_) => {
-            Cow::Owned(CString::new(slice).map_err(|source| Error::CreateCString { source })?)
-        }
-    })
-}
-
 #[inline]
 pub(crate) fn ensure_compatible_types<T, E>() -> Result<(), Error> {
     if ::std::mem::size_of::<T>() != ::std::mem::size_of::<E>() {