Log error details via Display instead of Debug

src/error.rs

@@ -52,7 +52,7 @@ impl ErrorKind {
     /// A description of this error kind
     pub fn description(self) -> &'static str {
         match self {
-            ErrorKind::Unavailable => "permanent failure or unavailable",
+            ErrorKind::Unavailable => "permanent failure",
             ErrorKind::Transient => "transient failure",
             ErrorKind::NotReady => "not ready yet",
             ErrorKind::Other => "uncategorised",
@@ -123,7 +123,15 @@ impl Error {
 
 impl fmt::Display for Error {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "RNG error [{}]: {}", self.kind.description(), self.msg())
+        #[cfg(feature="std")] {
+            if let Some(ref cause) = self.cause {
+                return write!(f, "{} ({}); cause: {}",
+                        self.msg(),
+                        self.kind.description(),
+                        cause);
+            }
+        }
+        write!(f, "{} ({})", self.msg(), self.kind.description())
     }
 }
 

src/lib.rs

@@ -950,8 +950,8 @@ thread_local!(
     static THREAD_RNG_KEY: Rc<RefCell<ReseedingRng<StdRng, EntropyRng>>> = {
         const THREAD_RNG_RESEED_THRESHOLD: u64 = 32_768;
         let mut entropy_source = EntropyRng::new();
-        let r = StdRng::from_rng(&mut entropy_source)
-            .expect("could not initialize thread_rng");
+        let r = StdRng::from_rng(&mut entropy_source).unwrap_or_else(|err|
+                panic!("could not initialize thread_rng: {}", err));
         let rng = ReseedingRng::new(r,
                                     THREAD_RNG_RESEED_THRESHOLD,
                                     entropy_source);
@@ -1041,7 +1041,8 @@ impl Rng for EntropyRng {
     }
 
     fn fill_bytes(&mut self, dest: &mut [u8]) {
-        self.try_fill_bytes(dest).unwrap();
+        self.try_fill_bytes(dest).unwrap_or_else(|err|
+                panic!("all entropy sources failed; first error: {}", err))
     }
 
     fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> {
@@ -1065,13 +1066,15 @@ impl Rng for EntropyRng {
                 let os_rng_result = try_os_new(dest);
                 match os_rng_result {
                     Ok(os_rng) => {
+                        debug!("EntropyRng: using OsRng");
                         switch_rng = Some(EntropySource::Os(os_rng));
                     }
                     Err(os_rng_error) => {
                         warn!("EntropyRng: OsRng failed [falling back to JitterRng]: {}",
                               os_rng_error);
                         match try_jitter_new(dest) {
                             Ok(jitter_rng) => {
+                                debug!("EntropyRng: using JitterRng");
                                 switch_rng = Some(EntropySource::Jitter(jitter_rng));
                             }
                             Err(_jitter_error) => {
@@ -1090,6 +1093,7 @@ impl Rng for EntropyRng {
                           os_rng_error);
                     match try_jitter_new(dest) {
                         Ok(jitter_rng) => {
+                            debug!("EntropyRng: using JitterRng");
                             switch_rng = Some(EntropySource::Jitter(jitter_rng));
                         }
                         Err(_jitter_error) => {
@@ -1102,7 +1106,7 @@ impl Rng for EntropyRng {
             }
             EntropySource::Jitter(ref mut rng) => {
                 if let Ok(os_rng) = try_os_new(dest) {
-                    info!("EntropyRng: OsRng available [switching back from JitterRng]");
+                    debug!("EntropyRng: using OsRng");
                     switch_rng = Some(EntropySource::Os(os_rng));
                 } else {
                     return rng.try_fill_bytes(dest); // use JitterRng
@@ -1194,7 +1198,7 @@ pub fn sample<T, I, R>(rng: &mut R, iterable: I, amount: usize) -> Vec<T>
 mod test {
     use impls;
     #[cfg(feature="std")]
-    use super::{random, thread_rng};
+    use super::{random, thread_rng, EntropyRng};
     use super::{Rng, SeedableRng, StdRng};
     #[cfg(feature="alloc")]
     use alloc::boxed::Box;
@@ -1240,6 +1244,13 @@ mod test {
             impls::fill_bytes_via_u64(self, dest)
         }
     }
+
+    #[test]
+    #[cfg(feature="std")]
+    fn test_entropy() {
+        let mut rng = EntropyRng::new();
+        rng.next_u32();
+    }
 
     #[test]
     fn test_fill_bytes_default() {

src/os.rs

@@ -78,14 +78,14 @@ impl Rng for OsRng {
         loop {
             if let Err(e) = self.try_fill_bytes(dest) {
                 if err_count >= RETRY_LIMIT {
-                    error!("OsRng failed too many times; last error: {:?}", e);
-                    panic!("OsRng failed too many times; last error: {:?}", e);
+                    error!("OsRng failed too many times; last error: {}", e);
+                    panic!("OsRng failed too many times; last error: {}", e);
                 }
 
                 match e.kind() {
                     ErrorKind::Transient => {
                         if !error_logged {
-                            warn!("OsRng failed; retrying up to {} times. Error: {:?}",
+                            warn!("OsRng failed; retrying up to {} times. Error: {}",
                                     TRANSIENT_RETRIES, e);
                             error_logged = true;
                         }
@@ -95,7 +95,7 @@ impl Rng for OsRng {
                     }
                     ErrorKind::NotReady => {
                         if !error_logged {
-                            warn!("OsRng failed; waiting up to {}s and retrying. Error: {:?}",
+                            warn!("OsRng failed; waiting up to {}s and retrying. Error: {}",
                                     MAX_RETRY_PERIOD, e);
                             error_logged = true;
                         }
@@ -104,8 +104,8 @@ impl Rng for OsRng {
                         continue;
                     }
                     _ => {
-                        error!("OsRng failed: {:?}", e);
-                        panic!("OsRng fatal error: {:?}", e);
+                        error!("OsRng failed: {}", e);
+                        panic!("OsRng fatal error: {}", e);
                     }
                 }
             }

src/reseeding.rs

@@ -46,7 +46,8 @@ impl<R: Rng+SeedableRng, Rsdr: Rng> ReseedingRng<R, Rsdr> {
     pub fn reseed_if_necessary(&mut self) {
         if self.bytes_generated >= self.generation_threshold {
             trace!("Reseeding RNG after {} bytes", self.bytes_generated);
-            R::from_rng(&mut self.reseeder).map(|result| self.rng = result).unwrap();
+            R::from_rng(&mut self.reseeder).map(|result| self.rng = result)
+                    .unwrap_or_else(|err| panic!("reseeding failed: {}", err));
             self.bytes_generated = 0;
         }
     }