Added error handling for unknown ALSA device errors (#1)

Instead of taking the easy way out and killing the whole program by panicking, device enumeration and stream creation will now report the error variant 'Unknown'

src/alsa/mod.rs

@@ -92,7 +92,10 @@ impl Device {
         ) {
             -2 |
             -16 /* determined empirically */ => return Err(FormatsEnumerationError::DeviceNotAvailable),
-            e => check_errors(e).expect("device not available")
+            -22 => return Err(FormatsEnumerationError::InvalidArgument),
+            e => if check_errors(e).is_err() {
+                return Err(FormatsEnumerationError::Unknown)
+            }
         }
 
         let hw_params = HwParams::alloc();
@@ -271,6 +274,14 @@ impl Device {
                 Err(FormatsEnumerationError::DeviceNotAvailable) => {
                     return Err(DefaultFormatError::DeviceNotAvailable);
                 },
+                Err(FormatsEnumerationError::InvalidArgument) => {
+                    // this happens sometimes when querying for input and output capabilities but
+                    // the device supports only one
+                    return Err(DefaultFormatError::StreamTypeNotSupported);
+                }
+                Err(FormatsEnumerationError::Unknown) => {
+                    return Err(DefaultFormatError::DeviceNotAvailable);
+                }
                 Ok(fmts) => fmts.collect(),
             }
         };
@@ -633,7 +644,10 @@ impl EventLoop {
                 alsa::SND_PCM_NONBLOCK,
             ) {
                 -16 /* determined empirically */ => return Err(CreationError::DeviceNotAvailable),
-                e => check_errors(e).expect("Device unavailable")
+                -22 => return Err(CreationError::InvalidArgument),
+                e => if check_errors(e).is_err() {
+                    return Err(CreationError::Unknown);
+                }
             }
             let hw_params = HwParams::alloc();
 
@@ -693,7 +707,10 @@ impl EventLoop {
                 alsa::SND_PCM_NONBLOCK,
             ) {
                 -16 /* determined empirically */ => return Err(CreationError::DeviceNotAvailable),
-                e => check_errors(e).expect("Device unavailable")
+                -22 => return Err(CreationError::InvalidArgument),
+                e => if check_errors(e).is_err() {
+                    return Err(CreationError::Unknown);
+                }
             }
             let hw_params = HwParams::alloc();
 

src/lib.rs

@@ -289,6 +289,10 @@ pub enum FormatsEnumerationError {
     /// The device no longer exists. This can happen if the device is disconnected while the
     /// program is running.
     DeviceNotAvailable,
+    /// We called something the C-Layer did not understand
+    InvalidArgument,
+    /// The C-Layer returned an error we don't know about
+    Unknown
 }
 
 /// May occur when attempting to request the default input or output stream format from a `Device`.
@@ -309,6 +313,11 @@ pub enum CreationError {
     DeviceNotAvailable,
     /// The required format is not supported.
     FormatNotSupported,
+    /// An ALSA device function was called with a feature it does not support
+    /// (trying to use capture capabilities on an output only format yields this)
+    InvalidArgument,
+    /// The C-Layer returned an error we don't know about
+    Unknown,
 }
 
 /// An iterator yielding all `Device`s currently available to the system.
@@ -714,6 +723,12 @@ impl Error for FormatsEnumerationError {
             &FormatsEnumerationError::DeviceNotAvailable => {
                 "The requested device is no longer available (for example, it has been unplugged)."
             },
+            &FormatsEnumerationError::InvalidArgument => {
+                "Invalid argument passed to the Backend (This happens when trying to read for example capture capabilities but the device does not support it -> dmix on Linux)"
+            },
+            &FormatsEnumerationError::Unknown => {
+                "An unknown error in the Backend occured"
+            },
         }
     }
 }
@@ -736,6 +751,14 @@ impl Error for CreationError {
             &CreationError::FormatNotSupported => {
                 "The requested samples format is not supported by the device."
             },
+
+            &CreationError::InvalidArgument => {
+                "The requested device does not support this capability (invalid argument)"
+            }
+
+            &CreationError::Unknown => {
+                "An unknown error in the Backend occured"
+            },
         }
     }
 }