Enable optional logging support

Cargo.toml

@@ -14,6 +14,9 @@ members = [
     "tests/wasm_bindgen",
 ]
 
+[dependencies]
+log = { version = "0.4", optional = true }
+
 [target.'cfg(unix)'.dependencies]
 libc = "0.2.27"
 

README.md

@@ -38,6 +38,9 @@ fn get_random_buf() -> Result<[u8; 32], getrandom::Error> {
 
 This library is `no_std` compatible on SGX but requires `std` on most platforms.
 
+The `log` library is supported as an optional dependency. If enabled, error
+reporting will be improved on some platforms.
+
 For WebAssembly (`wasm32`), Enscripten targets are supported directly; otherwise
 one of the following features must be enabled:
 

src/error.rs

@@ -65,7 +65,7 @@ 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({:08X})", self.0),
+            None => write!(f, "Error(0x{:08X})", self.0),
         }
     }
 }
@@ -74,7 +74,7 @@ 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 {:08X}", self.0),
+            None => write!(f, "getrandom: unknown code 0x{:08X}", self.0),
         }
     }
 }

src/lib.rs

@@ -111,6 +111,10 @@ extern crate wasm_bindgen;
           feature = "stdweb"))]
 #[macro_use] extern crate stdweb;
 
+#[cfg(feature = "log")] #[macro_use] extern crate log;
+#[allow(unused)]
+#[cfg(not(feature = "log"))] macro_rules! warn { ($($x:tt)*) => () }
+
 #[cfg(any(
     target_os = "android",
     target_os = "netbsd",

src/wasm32_stdweb.rs

@@ -66,7 +66,8 @@ fn getrandom_init() -> Result<RngSource, Error> {
         else { unreachable!() }
     } else {
         let err: WebError = js!{ return @{ result }.error }.try_into().unwrap();
-        Err(ERROR_UNAVAILABLE)  // TODO: forward err
+        warn!("getrandom unavailable: {}", err);
+        Err(ERROR_UNAVAILABLE)
     }
 }
 
@@ -101,7 +102,8 @@ fn getrandom_fill(source: &mut RngSource, dest: &mut [u8]) -> Result<(), Error>
 
         if js!{ return @{ result.as_ref() }.success } != true {
             let err: WebError = js!{ return @{ result }.error }.try_into().unwrap();
-            return Err(ERROR_UNKNOWN)  // TODO: forward err
+            warn!("getrandom failed: {}", err);
+            return Err(ERROR_UNKNOWN)
         }
     }
     Ok(())