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    // Copyright 2013-2015 The Rust Project Developers. See the COPYRIGHT
    // file at the top-level directory of this distribution and at
    // http://rust-lang.org/COPYRIGHT.
    //
    // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
    // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
    // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
    // option. This file may not be copied, modified, or distributed
    // except according to those terms.

    //! Dynamic library facilities.
    //!
    //! A simple wrapper over the platform's dynamic library facilities

    #![unstable(feature = "dynamic_lib",
                reason = "API has not been scrutinized and is highly likely to \
                          either disappear or change",
                issue = "27810")]
    #![rustc_deprecated(since = "1.5.0", reason = "replaced with 'dylib' on crates.io")]
    #![allow(missing_docs)]
    #![allow(deprecated)]

    use prelude::v1::*;

    use env;
    use ffi::{CString, OsString};
    use path::{Path, PathBuf};

    pub struct DynamicLibrary {
        handle: *mut u8
    }

    impl Drop for DynamicLibrary {
        fn drop(&mut self) {
            match dl::check_for_errors_in(|| {
                unsafe {
                    dl::close(self.handle)
                }
            }) {
                Ok(()) => {},
                Err(str) => panic!("{}", str)
            }
        }
    }

    impl DynamicLibrary {
        /// Lazily open a dynamic library. When passed None it gives a
        /// handle to the calling process
        pub fn open(filename: Option<&Path>) -> Result<DynamicLibrary, String> {
            let maybe_library = dl::open(filename.map(|path| path.as_os_str()));

            // The dynamic library must not be constructed if there is
            // an error opening the library so the destructor does not
            // run.
            match maybe_library {
                Err(err) => Err(err),
                Ok(handle) => Ok(DynamicLibrary { handle: handle })
            }
        }

        /// Prepends a path to this process's search path for dynamic libraries
        pub fn prepend_search_path(path: &Path) {
            let mut search_path = DynamicLibrary::search_path();
            search_path.insert(0, path.to_path_buf());
            env::set_var(DynamicLibrary::envvar(), &DynamicLibrary::create_path(&search_path));
        }

        /// From a slice of paths, create a new vector which is suitable to be an
        /// environment variable for this platforms dylib search path.
        pub fn create_path(path: &[PathBuf]) -> OsString {
            let mut newvar = OsString::new();
            for (i, path) in path.iter().enumerate() {
                if i > 0 { newvar.push(DynamicLibrary::separator()); }
                newvar.push(path);
            }
            return newvar;
        }

        /// Returns the environment variable for this process's dynamic library
        /// search path
        pub fn envvar() -> &'static str {
            if cfg!(windows) {
                "PATH"
            } else if cfg!(target_os = "macos") {
                "DYLD_LIBRARY_PATH"
            } else {
                "LD_LIBRARY_PATH"
            }
        }

        fn separator() -> &'static str {
            if cfg!(windows) { ";" } else { ":" }
        }

        /// Returns the current search path for dynamic libraries being used by this
        /// process
        pub fn search_path() -> Vec<PathBuf> {
            match env::var_os(DynamicLibrary::envvar()) {
                Some(var) => env::split_paths(&var).collect(),
                None => Vec::new(),
            }
        }

        /// Accesses the value at the symbol of the dynamic library.
        pub unsafe fn symbol<T>(&self, symbol: &str) -> Result<*mut T, String> {
            // This function should have a lifetime constraint of 'a on
            // T but that feature is still unimplemented

            let raw_string = CString::new(symbol).unwrap();
            let maybe_symbol_value = dl::check_for_errors_in(|| {
                dl::symbol(self.handle, raw_string.as_ptr())
            });

            // The value must not be constructed if there is an error so
            // the destructor does not run.
            match maybe_symbol_value {
                Err(err) => Err(err),
                Ok(symbol_value) => Ok(symbol_value as *mut T)
            }
        }
    }

    #[cfg(all(test, not(target_os = "ios"), not(target_os = "nacl")))]
    mod tests {
        use super::*;
        use prelude::v1::*;
        use libc;
        use mem;
        use path::Path;

        #[test]
        #[cfg_attr(any(windows,
                       target_os = "android",  // FIXME #10379
                       target_env = "musl"), ignore)]
        #[allow(deprecated)]
        fn test_loading_cosine() {
            // The math library does not need to be loaded since it is already
            // statically linked in
            let libm = match DynamicLibrary::open(None) {
                Err(error) => panic!("Could not load self as module: {}", error),
                Ok(libm) => libm
            };

            let cosine: extern fn(libc::c_double) -> libc::c_double = unsafe {
                match libm.symbol("cos") {
                    Err(error) => panic!("Could not load function cos: {}", error),
                    Ok(cosine) => mem::transmute::<*mut u8, _>(cosine)
                }
            };

            let argument = 0.0;
            let expected_result = 1.0;
            let result = cosine(argument);
            if result != expected_result {
                panic!("cos({}) != {} but equaled {} instead", argument,
                       expected_result, result)
            }
        }

        #[test]
        #[cfg(any(target_os = "linux",
                  target_os = "macos",
                  target_os = "freebsd",
                  target_os = "dragonfly",
                  target_os = "bitrig",
                  target_os = "netbsd",
                  target_os = "openbsd"))]
        #[allow(deprecated)]
        fn test_errors_do_not_crash() {
            // Open /dev/null as a library to get an error, and make sure
            // that only causes an error, and not a crash.
            let path = Path::new("/dev/null");
            match DynamicLibrary::open(Some(&path)) {
                Err(_) => {}
                Ok(_) => panic!("Successfully opened the empty library.")
            }
        }
    }

    #[cfg(any(target_os = "linux",
              target_os = "android",
              target_os = "macos",
              target_os = "ios",
              target_os = "freebsd",
              target_os = "dragonfly",
              target_os = "bitrig",
              target_os = "netbsd",
              target_os = "openbsd"))]
    mod dl {
        use prelude::v1::*;

        use ffi::{CStr, OsStr};
        use str;
        use libc;
        use ptr;

        pub fn open(filename: Option<&OsStr>) -> Result<*mut u8, String> {
            check_for_errors_in(|| {
                unsafe {
                    match filename {
                        Some(filename) => open_external(filename),
                        None => open_internal(),
                    }
                }
            })
        }

        const LAZY: libc::c_int = 1;

        unsafe fn open_external(filename: &OsStr) -> *mut u8 {
            let s = filename.to_cstring().unwrap();
            libc::dlopen(s.as_ptr(), LAZY) as *mut u8
        }

        unsafe fn open_internal() -> *mut u8 {
            libc::dlopen(ptr::null(), LAZY) as *mut u8
        }

        pub fn check_for_errors_in<T, F>(f: F) -> Result<T, String> where
            F: FnOnce() -> T,
        {
            use sync::StaticMutex;
            static LOCK: StaticMutex = StaticMutex::new();
            unsafe {
                // dlerror isn't thread safe, so we need to lock around this entire
                // sequence
                let _guard = LOCK.lock();
                let _old_error = libc::dlerror();

                let result = f();

                let last_error = libc::dlerror() as *const _;
                let ret = if ptr::null() == last_error {
                    Ok(result)
                } else {
                    let s = CStr::from_ptr(last_error).to_bytes();
                    Err(str::from_utf8(s).unwrap().to_owned())
                };

                ret
            }
        }

        pub unsafe fn symbol(handle: *mut u8,
                             symbol: *const libc::c_char) -> *mut u8 {
            libc::dlsym(handle as *mut libc::c_void, symbol) as *mut u8
        }
        pub unsafe fn close(handle: *mut u8) {
            libc::dlclose(handle as *mut libc::c_void); ()
        }
    }

    #[cfg(target_os = "windows")]
    mod dl {
        use prelude::v1::*;

        use ffi::OsStr;
        use libc;
        use os::windows::prelude::*;
        use ptr;
        use sys::c;
        use sys::os;

        pub fn open(filename: Option<&OsStr>) -> Result<*mut u8, String> {
            // disable "dll load failed" error dialog.
            let mut use_thread_mode = true;
            let prev_error_mode = unsafe {
                // SEM_FAILCRITICALERRORS 0x01
                let new_error_mode = 1;
                let mut prev_error_mode = 0;
                // Windows >= 7 supports thread error mode.
                let result = c::SetThreadErrorMode(new_error_mode,
                                                   &mut prev_error_mode);
                if result == 0 {
                    let err = os::errno();
                    if err == c::ERROR_CALL_NOT_IMPLEMENTED as i32 {
                        use_thread_mode = false;
                        // SetThreadErrorMode not found. use fallback solution:
                        // SetErrorMode() Note that SetErrorMode is process-wide so
                        // this can cause race condition!  However, since even
                        // Windows APIs do not care of such problem (#20650), we
                        // just assume SetErrorMode race is not a great deal.
                        prev_error_mode = c::SetErrorMode(new_error_mode);
                    }
                }
                prev_error_mode
            };

            unsafe {
                c::SetLastError(0);
            }

            let result = match filename {
                Some(filename) => {
                    let filename_str: Vec<_> =
                        filename.encode_wide().chain(Some(0)).collect();
                    let result = unsafe {
                        c::LoadLibraryW(filename_str.as_ptr())
                    };
                    // beware: Vec/String may change errno during drop!
                    // so we get error here.
                    if result == ptr::null_mut() {
                        let errno = os::errno();
                        Err(os::error_string(errno))
                    } else {
                        Ok(result as *mut u8)
                    }
                }
                None => {
                    let mut handle = ptr::null_mut();
                    let succeeded = unsafe {
                        c::GetModuleHandleExW(0 as c::DWORD, ptr::null(),
                                              &mut handle)
                    };
                    if succeeded == c::FALSE {
                        let errno = os::errno();
                        Err(os::error_string(errno))
                    } else {
                        Ok(handle as *mut u8)
                    }
                }
            };

            unsafe {
                if use_thread_mode {
                    c::SetThreadErrorMode(prev_error_mode, ptr::null_mut());
                } else {
                    c::SetErrorMode(prev_error_mode);
                }
            }

            result
        }

        pub fn check_for_errors_in<T, F>(f: F) -> Result<T, String> where
            F: FnOnce() -> T,
        {
            unsafe {
                c::SetLastError(0);

                let result = f();

                let error = os::errno();
                if 0 == error {
                    Ok(result)
                } else {
                    Err(format!("Error code {}", error))
                }
            }
        }

        pub unsafe fn symbol(handle: *mut u8, symbol: *const libc::c_char) -> *mut u8 {
            c::GetProcAddress(handle as c::HMODULE, symbol) as *mut u8
        }
        pub unsafe fn close(handle: *mut u8) {
            c::FreeLibrary(handle as c::HMODULE);
        }
    }

    #[cfg(target_os = "nacl")]
    pub mod dl {
        use ffi::OsStr;
        use ptr;
        use result::Result;
        use result::Result::Err;
        use libc;
        use string::String;
        use ops::FnOnce;
        use option::Option;

        pub fn open(_filename: Option<&OsStr>) -> Result<*mut u8, String> {
            Err(format!("NaCl + Newlib doesn't impl loading shared objects"))
        }

        pub fn check_for_errors_in<T, F>(_f: F) -> Result<T, String>
            where F: FnOnce() -> T,
        {
            Err(format!("NaCl doesn't support shared objects"))
        }

        pub unsafe fn symbol(_handle: *mut u8, _symbol: *const libc::c_char) -> *mut u8 {
            ptr::null_mut()
        }
        pub unsafe fn close(_handle: *mut u8) { }
    }

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