Provide clearenv()

1 files changed, 52 insertions, 0 deletions

diff --git a/src/env.rs b/src/env.rs
new file mode 100644
index 00000000..0d815be9
--- /dev/null
+++ b/src/env.rs
@@ -0,0 +1,52 @@
+use {Error, Result};
+
+/// Clear the environment of all name-value pairs.
+///
+/// On platforms where libc provides `clearenv()`, it will be used. libc's
+/// `clearenv()` is documented to return an error code but not set errno; if the
+/// return value indicates a failure, this function will return
+/// `Error::UnsupportedOperation`.
+///
+/// On platforms where libc does not provide `clearenv()`, a fallback
+/// implementation will be used that iterates over all environment variables and
+/// removes them one-by-one.
+///
+/// # Safety
+///
+/// This function is not threadsafe and can cause undefined behavior in
+/// combination with `std::env` or other program components that access the
+/// environment. See, for example, the discussion on `std::env::remove_var`; this
+/// function is a case of an "inherently unsafe non-threadsafe API" dealing with
+/// the environment.
+///
+///  The caller must ensure no other threads access the process environment while
+///  this function executes and that no raw pointers to an element of libc's
+///  `environ` is currently held. The latter is not an issue if the only other
+///  environment access in the program is via `std::env`, but the requirement on
+///  thread safety must still be upheld.
+pub unsafe fn clearenv() -> Result<()> {
+    let ret;
+    cfg_if! {
+        if #[cfg(any(target_os = "fuchsia",
+                     target_os = "wasi",
+                     target_env = "wasi",
+                     target_env = "uclibc",
+                     target_os = "linux",
+                     target_os = "android",
+                     target_os = "emscripten"))] {
+            ret = libc::clearenv();
+        } else {
+            use std::env;
+            for (name, _) in env::vars_os() {
+                env::remove_var(name);
+            }
+            ret = 0;
+        }
+    }
+
+    if ret == 0 {
+        Ok(())
+    } else {
+        Err(Error::UnsupportedOperation)
+    }
+}