From d3e2076ea5b04411ea34094005756768787a4951 Mon Sep 17 00:00:00 2001
From: Bruce Leidl <bruce@subgraph.com>
Date: Wed, 11 Sep 2019 11:10:27 -0400
Subject: [PATCH] An error class which wraps errno results

---
 rust/src/system/errno.rs | 70 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 70 insertions(+)
 create mode 100644 rust/src/system/errno.rs

diff --git a/rust/src/system/errno.rs b/rust/src/system/errno.rs
new file mode 100644
index 0000000..5db0750
--- /dev/null
+++ b/rust/src/system/errno.rs
@@ -0,0 +1,70 @@
+use std::fmt::{self, Display};
+use std::io;
+use std::result;
+
+use libc::__errno_location;
+
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub struct Error(i32);
+pub type Result<T> = result::Result<T, Error>;
+
+impl Error {
+    pub fn from_raw_os_error(e: i32) -> Error {
+        Error(e)
+    }
+
+    pub fn last_os_error() -> Error {
+        Error(unsafe { *__errno_location() })
+    }
+
+    pub fn errno(self) -> i32 {
+        self.0
+    }
+}
+
+impl From<io::Error> for Error {
+    fn from(e: io::Error) -> Self {
+        Error::from_raw_os_error(e.raw_os_error().unwrap_or_default())
+    }
+}
+
+impl std::error::Error for Error {}
+
+impl Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        io::Error::from_raw_os_error(self.0).fmt(f)
+    }
+}
+
+pub fn errno_result<T>() -> Result<T> {
+    Err(Error::last_os_error())
+}
+
+pub fn cvt<T: IsMinusOne>(t: T) -> io::Result<T> {
+    if t.is_minus_one() {
+        Err(io::Error::last_os_error())
+    } else {
+        Ok(t)
+    }
+}
+
+pub trait IsMinusOne {
+    fn is_minus_one(&self) -> bool;
+}
+
+impl IsMinusOne for i32 {
+    fn is_minus_one(&self) -> bool {
+        *self == -1
+    }
+}
+impl IsMinusOne for i64 {
+    fn is_minus_one(&self) -> bool {
+        *self == -1
+    }
+}
+
+impl IsMinusOne for isize {
+    fn is_minus_one(&self) -> bool {
+        *self == -1
+    }
+}