Overhaul Nix's error types

CHANGELOG.md

@@ -14,6 +14,16 @@ This project adheres to [Semantic Versioning](https://semver.org/).
   (#[1457](https://github.com/nix-rust/nix/pull/1457))
 
 ### Changed
+- `ptsname_r` now returns a lossily-converted string in the event of bad UTF,
+  just like `ptsname`.
+  ([#1446](https://github.com/nix-rust/nix/pull/1446))
+- Nix's error type is now a simple wrapper around the platform's Errno.  This
+  means it is now `Into<std::io::Error>`.  It's also `Clone`, `Copy`, `Eq`, and
+  has a small fixed size.  It also requires less typing.  For example, the old
+  enum variant `nix::Error::Sys(nix::errno::Errno::EINVAL)` is now simply
+  `nix::Error::EINVAL`.
+  ([#1446](https://github.com/nix-rust/nix/pull/1446))
+
 ### Fixed
 ### Removed
 

src/dir.rs

@@ -84,7 +84,7 @@ impl AsRawFd for Dir {
 impl Drop for Dir {
     fn drop(&mut self) {
         let e = Errno::result(unsafe { libc::closedir(self.0.as_ptr()) });
-        if !std::thread::panicking() && e == Err(Error::Sys(Errno::EBADF)) {
+        if !std::thread::panicking() && e == Err(Error::from(Errno::EBADF)) {
             panic!("Closing an invalid file descriptor!");
         };
     }

src/env.rs

@@ -1,12 +1,24 @@
 use cfg_if::cfg_if;
-use crate::{Error, Result};
+use std::fmt;
+
+/// Indicates that [`clearenv`] failed for some unknown reason
+#[derive(Clone, Copy, Debug)]
+pub struct ClearEnvError;
+
+impl fmt::Display for ClearEnvError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "clearenv failed")
+    }
+}
+
+impl std::error::Error for ClearEnvError {}
 
 /// 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`.
+/// [`ClearEnvError`].
 ///
 /// On platforms where libc does not provide `clearenv()`, a fallback
 /// implementation will be used that iterates over all environment variables and
@@ -25,7 +37,7 @@ use crate::{Error, Result};
 ///  `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<()> {
+pub unsafe fn clearenv() -> std::result::Result<(), ClearEnvError> {
     let ret;
     cfg_if! {
         if #[cfg(any(target_os = "fuchsia",
@@ -48,6 +60,6 @@ pub unsafe fn clearenv() -> Result<()> {
     if ret == 0 {
         Ok(())
     } else {
-        Err(Error::UnsupportedOperation)
+        Err(ClearEnvError)
     }
 }

src/errno.rs

@@ -1,5 +1,6 @@
 use cfg_if::cfg_if;
 use libc::{c_int, c_void};
+use std::convert::TryFrom;
 use std::{fmt, io, error};
 use crate::{Error, Result};
 
@@ -48,6 +49,42 @@ pub fn errno() -> i32 {
 }
 
 impl Errno {
+    /// Convert this `Error` to an [`Errno`](enum.Errno.html).
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # use nix::Error;
+    /// # use nix::errno::Errno;
+    /// let e = Error::from(Errno::EPERM);
+    /// assert_eq!(Some(Errno::EPERM), e.as_errno());
+    /// ```
+    #[deprecated(
+        since = "0.22.0",
+        note = "It's a no-op now; just delete it."
+    )]
+    pub fn as_errno(self) -> Option<Self> {
+        Some(self)
+    }
+
+    /// Create a nix Error from a given errno
+    #[deprecated(
+        since = "0.22.0",
+        note = "It's a no-op now; just delete it."
+    )]
+    pub fn from_errno(errno: Errno) -> Error {
+        Error::from(errno)
+    }
+
+    /// Create a new invalid argument error (`EINVAL`)
+    #[deprecated(
+        since = "0.22.0",
+        note = "Use Errno::EINVAL instead"
+    )]
+    pub fn invalid_argument() -> Error {
+        Errno::EINVAL
+    }
+
     pub fn last() -> Self {
         last()
     }
@@ -68,11 +105,26 @@ impl Errno {
     /// should not be used when `-1` is not the errno sentinel value.
     pub fn result<S: ErrnoSentinel + PartialEq<S>>(value: S) -> Result<S> {
         if value == S::sentinel() {
-            Err(Error::Sys(Self::last()))
+            Err(Self::last())
         } else {
             Ok(value)
         }
     }
+
+    /// Backwards compatibility hack for Nix <= 0.21.0 users
+    ///
+    /// In older versions of Nix, `Error::Sys` was an enum variant.  Now it's a
+    /// function, which is compatible with most of the former use cases of the
+    /// enum variant.  But you should use `Error(Errno::...)` instead.
+    #[deprecated(
+        since = "0.22.0",
+        note = "Use Errno::... instead"
+    )]
+    #[allow(non_snake_case)]
+    #[inline]
+    pub fn Sys(errno: Errno) -> Error {
+        errno
+    }
 }
 
 /// The sentinel value indicates that a function failed and more detailed
@@ -115,6 +167,16 @@ impl From<Errno> for io::Error {
     }
 }
 
+impl TryFrom<io::Error> for Errno {
+    type Error = io::Error;
+
+    fn try_from(ioerror: io::Error) -> std::result::Result<Self, io::Error> {
+        ioerror.raw_os_error()
+            .map(Errno::from_i32)
+            .ok_or(ioerror)
+    }
+}
+
 fn last() -> Errno {
     Errno::from_i32(errno())
 }

src/fcntl.rs

@@ -288,7 +288,7 @@ fn inner_readlink<P: ?Sized + NixPath>(dirfd: Option<RawFd>, path: &P) -> Result
                 Some(next_size) => try_size = next_size,
                 // It's absurd that this would happen, but handle it sanely
                 // anyway.
-                None => break Err(super::Error::Sys(Errno::ENAMETOOLONG)),
+                None => break Err(super::Error::from(Errno::ENAMETOOLONG)),
             }
         }
     }
@@ -646,6 +646,6 @@ pub fn posix_fallocate(fd: RawFd, offset: libc::off_t, len: libc::off_t) -> Resu
     match Errno::result(res) {
         Err(err) => Err(err),
         Ok(0) => Ok(()),
-        Ok(errno) => Err(crate::Error::Sys(Errno::from_i32(errno))),
+        Ok(errno) => Err(crate::Error::from(Errno::from_i32(errno))),
     }
 }

src/lib.rs

@@ -79,91 +79,27 @@ pub mod unistd;
 
 use libc::{c_char, PATH_MAX};
 
-use std::{error, fmt, ptr, result};
+use std::{ptr, result};
 use std::ffi::{CStr, OsStr};
 use std::os::unix::ffi::OsStrExt;
 use std::path::{Path, PathBuf};
 
 use errno::Errno;
 
 /// Nix Result Type
-pub type Result<T> = result::Result<T, Error>;
+pub type Result<T> = result::Result<T, Errno>;
 
-/// Nix Error Type
+/// Nix's main error type.
 ///
-/// The nix error type provides a common way of dealing with
-/// various system system/libc calls that might fail.  Each
-/// error has a corresponding errno (usually the one from the
-/// underlying OS) to which it can be mapped in addition to
-/// implementing other common traits.
-#[derive(Clone, Copy, Debug, Eq, PartialEq)]
-pub enum Error {
-    Sys(Errno),
-    InvalidPath,
-    /// The operation involved a conversion to Rust's native String type, which failed because the
-    /// string did not contain all valid UTF-8.
-    InvalidUtf8,
-    /// The operation is not supported by Nix, in this instance either use the libc bindings or
-    /// consult the module documentation to see if there is a more appropriate interface available.
-    UnsupportedOperation,
-}
-
-impl Error {
-    /// Convert this `Error` to an [`Errno`](enum.Errno.html).
-    ///
-    /// # Example
-    ///
-    /// ```
-    /// # use nix::Error;
-    /// # use nix::errno::Errno;
-    /// let e = Error::from(Errno::EPERM);
-    /// assert_eq!(Some(Errno::EPERM), e.as_errno());
-    /// ```
-    pub fn as_errno(self) -> Option<Errno> {
-        if let Error::Sys(e) = self {
-            Some(e)
-        } else {
-            None
-        }
-    }
-
-    /// Create a nix Error from a given errno
-    pub fn from_errno(errno: Errno) -> Error {
-        Error::Sys(errno)
-    }
-
-    /// Get the current errno and convert it to a nix Error
-    pub fn last() -> Error {
-        Error::Sys(Errno::last())
-    }
-
-    /// Create a new invalid argument error (`EINVAL`)
-    pub fn invalid_argument() -> Error {
-        Error::Sys(Errno::EINVAL)
-    }
-
-}
-
-impl From<Errno> for Error {
-    fn from(errno: Errno) -> Error { Error::from_errno(errno) }
-}
-
-impl From<std::string::FromUtf8Error> for Error {
-    fn from(_: std::string::FromUtf8Error) -> Error { Error::InvalidUtf8 }
-}
-
-impl error::Error for Error {}
-
-impl fmt::Display for Error {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match *self {
-            Error::InvalidPath => write!(f, "Invalid path"),
-            Error::InvalidUtf8 => write!(f, "Invalid UTF-8 string"),
-            Error::UnsupportedOperation => write!(f, "Unsupported Operation"),
-            Error::Sys(errno) => write!(f, "{:?}: {}", errno, errno.desc()),
-        }
-    }
-}
+/// It's a wrapper around Errno.  As such, it's very interoperable with
+/// [`std::io::Error`], but it has the advantages of:
+/// * `Clone`
+/// * `Copy`
+/// * `Eq`
+/// * Small size
+/// * Represents all of the system's errnos, instead of just the most common
+/// ones.
+pub type Error = Errno;
 
 pub trait NixPath {
     fn is_empty(&self) -> bool;
@@ -217,7 +153,7 @@ impl NixPath for CStr {
             where F: FnOnce(&CStr) -> T {
         // Equivalence with the [u8] impl.
         if self.len() >= PATH_MAX as usize {
-            return Err(Error::InvalidPath);
+            return Err(Error::from(Errno::ENAMETOOLONG))
         }
 
         Ok(f(self))
@@ -238,11 +174,11 @@ impl NixPath for [u8] {
         let mut buf = [0u8; PATH_MAX as usize];
 
         if self.len() >= PATH_MAX as usize {
-            return Err(Error::InvalidPath);
+            return Err(Error::from(Errno::ENAMETOOLONG))
         }
 
         match self.iter().position(|b| *b == 0) {
-            Some(_) => Err(Error::InvalidPath),
+            Some(_) => Err(Error::from(Errno::EINVAL)),
             None => {
                 unsafe {
                     // TODO: Replace with bytes::copy_memory. rust-lang/rust#24028

src/mount/bsd.rs

@@ -1,4 +1,5 @@
 use crate::{
+    Error,
     Errno,
     NixPath,
     Result,
@@ -99,7 +100,7 @@ libc_bitflags!(
 /// by `nmount(2)`.
 #[derive(Debug)]
 pub struct NmountError {
-    errno: Errno,
+    errno: Error,
     errmsg: Option<String>
 }
 
@@ -109,14 +110,14 @@ impl NmountError {
         self.errmsg.as_deref()
     }
 
-    /// Returns the inner [`Errno`]
-    pub fn errno(&self) -> Errno {
+    /// Returns the inner [`Error`]
+    pub fn error(&self) -> Error {
         self.errno
     }
 
-    fn new(errno: Errno, errmsg: Option<&CStr>) -> Self {
+    fn new(error: Error, errmsg: Option<&CStr>) -> Self {
         Self {
-            errno,
+            errno: error,
             errmsg: errmsg.map(CStr::to_string_lossy).map(Cow::into_owned)
         }
     }
@@ -136,7 +137,7 @@ impl fmt::Display for NmountError {
 
 impl From<NmountError> for io::Error {
     fn from(err: NmountError) -> Self {
-        io::Error::from_raw_os_error(err.errno as i32)
+        err.errno.into()
     }
 }
 
@@ -381,7 +382,7 @@ impl<'a> Nmount<'a> {
                         Some(CStr::from_bytes_with_nul(sl).unwrap())
                     }
                 };
-                Err(NmountError::new(error.as_errno().unwrap(), errmsg))
+                Err(NmountError::new(error.into(), errmsg))
             }
         }
     }