Remove std dependancy for error handling

src/cloudabi.rs

@@ -8,23 +8,22 @@
 
 //! Implementation for CloudABI
 use crate::Error;
-use core::num::NonZeroU32;
 
 extern "C" {
     fn cloudabi_sys_random_get(buf: *mut u8, buf_len: usize) -> u16;
 }
 
 pub fn getrandom_inner(dest: &mut [u8]) -> Result<(), Error> {
     let errno = unsafe { cloudabi_sys_random_get(dest.as_mut_ptr(), dest.len()) };
-    if let Some(code) = NonZeroU32::new(errno as u32) {
-        error!("cloudabi_sys_random_get failed with code {}", code);
-        Err(Error::from(code))
+    if errno != 0 {
+        error!("cloudabi_sys_random_get: failed with {}", errno);
+        Err(Error::from_os_error(errno.into()))
     } else {
         Ok(()) // Zero means success for CloudABI
     }
 }
 
 #[inline(always)]
-pub fn error_msg_inner(_: NonZeroU32) -> Option<&'static str> {
+pub fn custom_description(_: u16) -> Option<&'static str> {
     None
 }

src/dummy.rs

@@ -6,17 +6,14 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-//! A dummy implementation for unsupported targets which always returns
-//! `Err(Error::UNAVAILABLE)`
+//! A dummy implementation for unsupported targets which always fails
 use crate::Error;
-use core::num::NonZeroU32;
 
 pub fn getrandom_inner(_: &mut [u8]) -> Result<(), Error> {
-    error!("no support for this platform");
-    Err(Error::UNAVAILABLE)
+    Err(Error::from_custom_error(0))
 }
 
 #[inline(always)]
-pub fn error_msg_inner(_: NonZeroU32) -> Option<&'static str> {
-    None
+pub fn custom_description(_: u16) -> Option<&'static str> {
+    Some("getrandom: this target is not supported")
 }

src/error.rs

@@ -5,78 +5,119 @@
 // <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
-use core::convert::From;
 use core::fmt;
 use core::num::NonZeroU32;
 
-// A randomly-chosen 24-bit prefix for our codes
-pub(crate) const CODE_PREFIX: u32 = 0x57f4c500;
-const CODE_UNKNOWN: u32 = CODE_PREFIX | 0x00;
-const CODE_UNAVAILABLE: u32 = CODE_PREFIX | 0x01;
-
-/// The error type.
+/// A small and `no_std` compatible error type. It can indicate failure from
+/// either the underlying OS or a custom error reason.
 ///
-/// This type is small and no-std compatible.
+/// The [`Error::raw_os_error()`] will indicate if the error is from the OS, and
+/// if so, which error code the OS gave the application. If such an error is
+/// encountered, please consult with your system documentation.
 #[derive(Copy, Clone, Eq, PartialEq)]
-pub struct Error(pub(crate) NonZeroU32);
+pub struct Error(NonZeroU32);
 
+// This NonZeroU32 has enough room to store 3 types of values:
+//   - OS Errors:         in range [1, 1 << 31) (i.e. positive i32 values)
+//   - Custom u16 Errors: in range [1 << 31, 1 << 31 + 1 << 16)
+//   - Unknown Errors:    currently just (1 << 32) - 1
+// TODO simplify impls with try_from when version >= 1.34
 impl Error {
     /// An unknown error.
-    pub const UNKNOWN: Error = Error(unsafe { NonZeroU32::new_unchecked(CODE_UNKNOWN) });
+    pub(crate) const UNKNOWN: Error = Self(unsafe { NonZeroU32::new_unchecked(u32::max_value()) });
+    const CUSTOM_START: u32 = 1 << 31;
 
-    /// No generator is available.
-    pub const UNAVAILABLE: Error = Error(unsafe { NonZeroU32::new_unchecked(CODE_UNAVAILABLE) });
+    pub(crate) fn from_os_error(errno: i32) -> Self {
+        if errno > 0 {
+            Self(NonZeroU32::new(errno as u32).unwrap())
+        } else {
+            Self::UNKNOWN
+        }
+    }
 
-    /// Extract the error code.
-    ///
-    /// This may equal one of the codes defined in this library or may be a
-    /// system error code.
-    ///
-    /// One may attempt to format this error via the `Display` implementation.
-    pub fn code(&self) -> NonZeroU32 {
-        self.0
+    pub(crate) fn from_custom_error(custom: u16) -> Self {
+        Self(NonZeroU32::new(custom as u32 + Self::CUSTOM_START).unwrap())
     }
 
-    pub(crate) fn msg(&self) -> Option<&'static str> {
-        if let Some(msg) = crate::imp::error_msg_inner(self.0) {
-            Some(msg)
+    /// Extract the raw OS error code (if this error came from the OS)
+    ///
+    /// This method is identical to `std::io::Error::raw_os_error()`, except
+    /// that it works in `no_std` contexts. If this method returns `None`, the
+    /// error value can still be formatted via the `Diplay` implementation.
+    pub fn raw_os_error(&self) -> Option<i32> {
+        if self.0.get() < Self::CUSTOM_START {
+            Some(self.0.get() as i32)
         } else {
-            match *self {
-                Error::UNKNOWN => Some("getrandom: unknown error"),
-                Error::UNAVAILABLE => Some("getrandom: unavailable"),
-                _ => None,
-            }
+            None
         }
     }
-}
 
-impl fmt::Debug for Error {
-    fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
-        match self.msg() {
-            Some(msg) => write!(f, "Error(\"{}\")", msg),
-            None => write!(f, "Error(0x{:08X})", self.0),
+    pub fn custom_code(&self) -> Option<u16> {
+        let custom = self.0.get().checked_sub(Self::CUSTOM_START)?;
+        if custom <= u16::max_value() as u32 {
+            Some(custom as u16)
+        } else {
+            None
         }
     }
 }
 
-impl fmt::Display for Error {
-    fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
-        match self.msg() {
-            Some(msg) => write!(f, "{}", msg),
-            None => write!(f, "getrandom: unknown code 0x{:08X}", self.0),
-        }
+#[cfg(any(unix, target_os = "redox"))]
+fn os_err_desc(errno: i32, buf: &mut [u8]) -> Option<&str> {
+    let buf_ptr = buf.as_mut_ptr() as *mut libc::c_char;
+    if unsafe { libc::strerror_r(errno, buf_ptr, buf.len()) } != 0 {
+        return None;
     }
+
+    // Take up to trailing null byte
+    let idx = buf.iter().position(|&b| b == 0).unwrap_or(buf.len());
+    core::str::from_utf8(&buf[..idx]).ok()
+}
+
+#[cfg(not(any(unix, target_os = "redox")))]
+fn os_err_desc(_errno: i32, _buf: &mut [u8]) -> Option<&str> {
+    None
 }
 
-impl From<NonZeroU32> for Error {
-    fn from(code: NonZeroU32) -> Self {
-        Error(code)
+impl fmt::Debug for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let mut dbg = f.debug_struct("Error");
+        if let Some(errno) = self.raw_os_error() {
+            dbg.field("os_error", &errno);
+            let mut buf = [0u8; 128];
+            if let Some(desc) = os_err_desc(errno, &mut buf) {
+                dbg.field("description", &desc);
+            }
+        } else if let Some(custom) = self.custom_code() {
+            dbg.field("custom_error", &custom);
+            if let Some(desc) = crate::imp::custom_description(custom) {
+                dbg.field("description", &desc);
+            }
+        } else {
+            dbg.field("unknown_error", &self.0);
+        }
+        dbg.finish()
     }
 }
 
-impl From<&Error> for Error {
-    fn from(error: &Error) -> Self {
-        *error
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        if let Some(errno) = self.raw_os_error() {
+            let mut buf = [0u8; 128];
+            if let Some(desc) = os_err_desc(errno, &mut buf) {
+                f.write_str(desc)
+            } else {
+                write!(f, "OS Error: {}", errno)
+            }
+        } else if let Some(custom) = self.custom_code() {
+            if let Some(desc) = crate::imp::custom_description(custom) {
+                f.write_str(desc)
+            } else {
+                write!(f, "Custom Error: {}", custom)
+            }
+        } else {
+            write!(f, "Unknown Error: {}", self.0)
+        }
     }
 }
 

src/error_impls.rs

@@ -9,24 +9,22 @@ extern crate std;
 
 use crate::error::Error;
 use core::convert::From;
-use core::num::NonZeroU32;
 use std::{error, io};
 
 impl From<io::Error> for Error {
     fn from(err: io::Error) -> Self {
-        err.raw_os_error()
-            .and_then(|code| NonZeroU32::new(code as u32))
-            .map(|code| Error(code))
-            // in practice this should never happen
-            .unwrap_or(Error::UNKNOWN)
+        match err.raw_os_error() {
+            Some(errno) => Error::from_os_error(errno),
+            None => Error::UNKNOWN,
+        }
     }
 }
 
 impl From<Error> for io::Error {
     fn from(err: Error) -> Self {
-        match err.msg() {
-            Some(msg) => io::Error::new(io::ErrorKind::Other, msg),
-            None => io::Error::from_raw_os_error(err.0.get() as i32),
+        match err.raw_os_error() {
+            Some(errno) => io::Error::from_raw_os_error(errno),
+            None => io::Error::new(io::ErrorKind::Other, err),
         }
     }
 }

src/freebsd.rs

@@ -7,14 +7,11 @@
 // except according to those terms.
 
 //! Implementation for FreeBSD
-extern crate std;
-
+use crate::util_libc::fill_exact;
 use crate::Error;
-use core::num::NonZeroU32;
 use core::ptr;
-use std::io;
 
-fn kern_arnd(buf: &mut [u8]) -> Result<usize, Error> {
+fn kern_arnd(buf: &mut [u8]) -> libc::ssize_t {
     static MIB: [libc::c_int; 2] = [libc::CTL_KERN, libc::KERN_ARND];
     let mut len = buf.len();
     let ret = unsafe {
@@ -28,21 +25,17 @@ fn kern_arnd(buf: &mut [u8]) -> Result<usize, Error> {
         )
     };
     if ret == -1 {
-        error!("freebsd: kern.arandom syscall failed");
-        return Err(io::Error::last_os_error().into());
+        -1
+    } else {
+        len as libc::ssize_t
     }
-    Ok(len)
 }
 
 pub fn getrandom_inner(dest: &mut [u8]) -> Result<(), Error> {
-    let mut start = 0;
-    while start < dest.len() {
-        start += kern_arnd(&mut dest[start..])?;
-    }
-    Ok(())
+    fill_exact(dest, kern_arnd)
 }
 
 #[inline(always)]
-pub fn error_msg_inner(_: NonZeroU32) -> Option<&'static str> {
+pub fn custom_description(_: u16) -> Option<&'static str> {
     None
 }

src/fuchsia.rs

@@ -8,7 +8,6 @@
 
 //! Implementation for Fuchsia Zircon
 use crate::Error;
-use core::num::NonZeroU32;
 
 #[link(name = "zircon")]
 extern "C" {
@@ -21,6 +20,6 @@ pub fn getrandom_inner(dest: &mut [u8]) -> Result<(), Error> {
 }
 
 #[inline(always)]
-pub fn error_msg_inner(_: NonZeroU32) -> Option<&'static str> {
+pub fn custom_description(_: u16) -> Option<&'static str> {
     None
 }

src/ios.rs

@@ -7,10 +7,9 @@
 // except according to those terms.
 
 //! Implementation for iOS
-extern crate std;
-
 use crate::Error;
-use core::num::NonZeroU32;
+
+const CALL_FAILED: u16 = 0;
 
 // TODO: Make extern once extern_types feature is stabilized. See:
 //   https://github.com/rust-lang/rust/issues/43467
@@ -27,14 +26,16 @@ extern "C" {
 pub fn getrandom_inner(dest: &mut [u8]) -> Result<(), Error> {
     let ret = unsafe { SecRandomCopyBytes(kSecRandomDefault, dest.len(), dest.as_mut_ptr()) };
     if ret == -1 {
-        error!("SecRandomCopyBytes call failed");
-        Err(Error::UNKNOWN)
+        Err(Error::from_custom_error(CALL_FAILED))
     } else {
         Ok(())
     }
 }
 
 #[inline(always)]
-pub fn error_msg_inner(_: NonZeroU32) -> Option<&'static str> {
-    None
+pub fn custom_description(custom: u16) -> Option<&'static str> {
+    match custom {
+        CALL_FAILED => Some("SecRandomCopyBytes: call failed"),
+        _ => None,
+    }
 }