Move `sys::pal::os::Env` into `sys::env`

Although `Env` (as `Vars`), `Args`, path functions, and OS constants are
publicly exposed via `std::env`, their implementations are each
self-contained. Keep them separate in `std::sys` and make a new module,
`sys::env`, for `Env`.

1 files changed, 146 insertions, 0 deletions

diff --git a/library/std/src/sys/env/wasi.rs b/library/std/src/sys/env/wasi.rs
new file mode 100644
index 00000000000..6bdb2d5a547
--- /dev/null
+++ b/library/std/src/sys/env/wasi.rs
@@ -0,0 +1,146 @@
+use core::slice::memchr;
+
+use crate::ffi::{CStr, OsStr, OsString};
+use crate::os::wasi::prelude::*;
+use crate::sys::common::small_c_string::run_with_cstr;
+use crate::sys::pal::os::{cvt, libc};
+use crate::{fmt, io, vec};
+
+pub struct Env {
+    iter: vec::IntoIter<(OsString, OsString)>,
+}
+
+// FIXME(https://github.com/rust-lang/rust/issues/114583): Remove this when <OsStr as Debug>::fmt matches <str as Debug>::fmt.
+pub struct EnvStrDebug<'a> {
+    slice: &'a [(OsString, OsString)],
+}
+
+impl fmt::Debug for EnvStrDebug<'_> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let Self { slice } = self;
+        f.debug_list()
+            .entries(slice.iter().map(|(a, b)| (a.to_str().unwrap(), b.to_str().unwrap())))
+            .finish()
+    }
+}
+
+impl Env {
+    pub fn str_debug(&self) -> impl fmt::Debug + '_ {
+        let Self { iter } = self;
+        EnvStrDebug { slice: iter.as_slice() }
+    }
+}
+
+impl fmt::Debug for Env {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let Self { iter } = self;
+        f.debug_list().entries(iter.as_slice()).finish()
+    }
+}
+
+impl !Send for Env {}
+impl !Sync for Env {}
+
+impl Iterator for Env {
+    type Item = (OsString, OsString);
+    fn next(&mut self) -> Option<(OsString, OsString)> {
+        self.iter.next()
+    }
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+}
+
+cfg_if::cfg_if! {
+    if #[cfg(target_feature = "atomics")] {
+        // Access to the environment must be protected by a lock in multi-threaded scenarios.
+        use crate::sync::{PoisonError, RwLock};
+        static ENV_LOCK: RwLock<()> = RwLock::new(());
+        pub fn env_read_lock() -> impl Drop {
+            ENV_LOCK.read().unwrap_or_else(PoisonError::into_inner)
+        }
+        pub fn env_write_lock() -> impl Drop {
+            ENV_LOCK.write().unwrap_or_else(PoisonError::into_inner)
+        }
+    } else {
+        // No need for a lock if we are single-threaded.
+        pub fn env_read_lock() -> impl Drop {
+            Box::new(())
+        }
+        pub fn env_write_lock() -> impl Drop {
+            Box::new(())
+        }
+    }
+}
+
+pub fn env() -> Env {
+    unsafe {
+        let _guard = env_read_lock();
+
+        // Use `__wasilibc_get_environ` instead of `environ` here so that we
+        // don't require wasi-libc to eagerly initialize the environment
+        // variables.
+        let mut environ = libc::__wasilibc_get_environ();
+
+        let mut result = Vec::new();
+        if !environ.is_null() {
+            while !(*environ).is_null() {
+                if let Some(key_value) = parse(CStr::from_ptr(*environ).to_bytes()) {
+                    result.push(key_value);
+                }
+                environ = environ.add(1);
+            }
+        }
+        return Env { iter: result.into_iter() };
+    }
+
+    // See src/libstd/sys/pal/unix/os.rs, same as that
+    fn parse(input: &[u8]) -> Option<(OsString, OsString)> {
+        if input.is_empty() {
+            return None;
+        }
+        let pos = memchr::memchr(b'=', &input[1..]).map(|p| p + 1);
+        pos.map(|p| {
+            (
+                OsStringExt::from_vec(input[..p].to_vec()),
+                OsStringExt::from_vec(input[p + 1..].to_vec()),
+            )
+        })
+    }
+}
+
+pub fn getenv(k: &OsStr) -> Option<OsString> {
+    // environment variables with a nul byte can't be set, so their value is
+    // always None as well
+    run_with_cstr(k.as_bytes(), &|k| {
+        let _guard = env_read_lock();
+        let v = unsafe { libc::getenv(k.as_ptr()) } as *const libc::c_char;
+
+        if v.is_null() {
+            Ok(None)
+        } else {
+            // SAFETY: `v` cannot be mutated while executing this line since we've a read lock
+            let bytes = unsafe { CStr::from_ptr(v) }.to_bytes().to_vec();
+
+            Ok(Some(OsStringExt::from_vec(bytes)))
+        }
+    })
+    .ok()
+    .flatten()
+}
+
+pub unsafe fn setenv(k: &OsStr, v: &OsStr) -> io::Result<()> {
+    run_with_cstr(k.as_bytes(), &|k| {
+        run_with_cstr(v.as_bytes(), &|v| unsafe {
+            let _guard = env_write_lock();
+            cvt(libc::setenv(k.as_ptr(), v.as_ptr(), 1)).map(drop)
+        })
+    })
+}
+
+pub unsafe fn unsetenv(n: &OsStr) -> io::Result<()> {
+    run_with_cstr(n.as_bytes(), &|nbuf| unsafe {
+        let _guard = env_write_lock();
+        cvt(libc::unsetenv(nbuf.as_ptr())).map(drop)
+    })
+}