examples: appsink: improved error handling

The program should now exit gracefully with human readable messages.

examples/src/bin/appsink.rs

@@ -3,21 +3,63 @@ use gst::*;
 extern crate gstreamer_app as gst_app;
 use gst_app::*;
 
+extern crate glib;
+
+use std::fmt;
 use std::u64;
 use std::i16;
 use std::i32;
 
-fn main() {
-    gst::init().unwrap();
+#[derive(Debug)]
+enum AppSinkExError {
+    InitFailed(glib::Error),
+    ElementNotFound(&'static str),
+    ElementLinkFailed(&'static str, &'static str),
+    SetStateError(&'static str),
+    ElementError(std::string::String, glib::Error, std::string::String),
+}
 
+impl fmt::Display for AppSinkExError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match *self {
+            AppSinkExError::InitFailed(ref e) => {
+                write!(f, "GStreamer initialization failed: {:?}", e)
+            }
+            AppSinkExError::ElementNotFound(ref e) => write!(f, "Element {} not found", e),
+            AppSinkExError::ElementLinkFailed(ref e1, ref e2) => {
+                write!(f, "Link failed between {} and {}", e1, e2)
+            }
+            AppSinkExError::SetStateError(ref state) => {
+                write!(f, "Pipeline failed to switch to state {}", state)
+            }
+            AppSinkExError::ElementError(ref element, ref err, ref debug) => {
+                write!(f, "Error from {}: {} ({:?})", element, err, debug)
+            }
+        }
+    }
+}
+
+fn create_pipeline() -> Result<Pipeline, AppSinkExError> {
+    gst::init().map_err(|e| AppSinkExError::InitFailed(e))?;
     let pipeline = gst::Pipeline::new(None);
-    let src = gst::ElementFactory::make("audiotestsrc", None).unwrap();
-    let sink = gst::ElementFactory::make("appsink", None).unwrap();
+    let src = gst::ElementFactory::make("audiotestsrc", None)
+        .ok_or(AppSinkExError::ElementNotFound("audiotestsrc"))?;
+    let sink = gst::ElementFactory::make("appsink", None)
+        .ok_or(AppSinkExError::ElementNotFound("appsink"))?;
 
-    pipeline.add_many(&[&src, &sink]).unwrap();
-    gst::Element::link_many(&[&src, &sink]).unwrap();
+    pipeline
+        .add_many(&[&src, &sink])
+        .expect("Unable to add elements in the pipeline");
+
+    gst::Element::link(&src, &sink)
+        .map_err(|_| {
+            AppSinkExError::ElementLinkFailed("audiotestsrc", "appsink")
+        })?;
+
+    let appsink = sink.clone()
+        .dynamic_cast::<AppSink>()
+        .expect("Sink element is expected to be an appsink!");
 
-    let appsink = sink.clone().dynamic_cast::<AppSink>().unwrap();
     appsink.set_caps(&Caps::new_simple(
         "audio/x-raw",
         &[
@@ -40,9 +82,11 @@ fn main() {
                 Some(sample) => sample,
             };
 
-            let buffer = sample.get_buffer().unwrap();
+            let buffer = sample
+                .get_buffer()
+                .expect("Unable to extract buffer from the sample");
             assert_eq!(buffer.get_size() % 2, 0);
-            let map = buffer.map_read().unwrap();
+            let map = buffer.map_read().expect("Unable to map buffer for reading");
             let data = map.as_slice();
             let sum: f64 = data.chunks(2)
                 .map(|sample| {
@@ -58,12 +102,19 @@ fn main() {
         },
     ));
 
-    assert_ne!(
-        pipeline.set_state(gst::State::Playing),
-        gst::StateChangeReturn::Failure
-    );
+    Ok(pipeline)
+}
 
-    let bus = pipeline.get_bus().unwrap();
+fn main_loop() -> Result<(), AppSinkExError> {
+    let pipeline = create_pipeline()?;
+
+    if let gst::StateChangeReturn::Failure = pipeline.set_state(gst::State::Playing) {
+        return Err(AppSinkExError::SetStateError("playing"));
+    }
+
+    let bus = pipeline
+        .get_bus()
+        .expect("Pipeline without bus. Shouldn't happen!");
 
     loop {
         let msg = match bus.timed_pop(u64::MAX) {
@@ -74,20 +125,29 @@ fn main() {
         match msg.view() {
             MessageView::Eos(..) => break,
             MessageView::Error(err) => {
-                println!(
-                    "Error from {}: {} ({:?})",
+                if let gst::StateChangeReturn::Failure = pipeline.set_state(gst::State::Null) {
+                    return Err(AppSinkExError::SetStateError("null"));
+                }
+                return Err(AppSinkExError::ElementError(
                     msg.get_src().get_path_string(),
                     err.get_error(),
-                    err.get_debug()
-                );
-                break;
+                    err.get_debug().unwrap(),
+                ));
             }
             _ => (),
         }
     }
 
-    assert_ne!(
-        pipeline.set_state(gst::State::Null),
-        gst::StateChangeReturn::Failure
-    );
+    if let gst::StateChangeReturn::Failure = pipeline.set_state(gst::State::Null) {
+        return Err(AppSinkExError::SetStateError("null"));
+    }
+
+    Ok(())
+}
+
+fn main() {
+    match main_loop() {
+        Ok(r) => r,
+        Err(e) => eprintln!("Error! {}", e),
+    }
 }