add convenience error poster for GstBus that auto gathers go runtime debug info

examples/gif-encoder/main.go

@@ -3,7 +3,6 @@
 package main
 
 import (
-	"errors"
 	"flag"
 	"fmt"
 	"image"
@@ -62,9 +61,7 @@ func encodeGif(mainLoop *gst.MainLoop) error {
 		// Build out the rest of the elements for the pipeline pipeline.
 		elements, err := gst.NewElementMany("queue", "videoconvert", "videoscale", "videorate", "jpegenc")
 		if err != nil {
-			err := gst.NewGError(2, err)
+			pipeline.GetPipelineBus().PostError(self, "Failed to build elements for the linked pipeline", err)
-			pipeline.GetPipelineBus().
-				Post(gst.NewErrorMessage(self, err, "", nil))
 			return
 		}
 
@@ -97,9 +94,7 @@ func encodeGif(mainLoop *gst.MainLoop) error {
 		// use this value to calculate the total number of frames we expect to produce.
 		query := gst.NewDurationQuery(gst.FormatTime)
 		if ok := self.Query(query); !ok {
-			err := gst.NewGError(3, errors.New("Failed to query video duration from decodebin"))
+			pipeline.GetPipelineBus().PostError(self, "Failed to query video duration from decodebin", nil)
-			pipeline.GetPipelineBus().
-				Post(gst.NewErrorMessage(self, err, "", nil))
 			return
 		}
 
@@ -115,10 +110,6 @@ func encodeGif(mainLoop *gst.MainLoop) error {
 		var frameNum int
 		appSink.SetCallbacks(&app.SinkCallbacks{
 			NewSampleFunc: func(sink *app.Sink) gst.FlowReturn {
-				// We can retrieve a reader with the raw bytes of the image directly from the
-				// sink.
-				imgReader := sink.PullSample().GetBuffer().Reader()
-
 				// Increment the frame number counter
 				frameNum++
 
@@ -131,9 +122,13 @@ func encodeGif(mainLoop *gst.MainLoop) error {
 
 				fmt.Printf("\033[2K\rProcessing image frame %d/%d", frameNum, totalFrames)
 
+				// We can retrieve a reader with the raw bytes of the image directly from the
+				// sink.
+				imgReader := sink.PullSample().GetBuffer().Reader()
+
 				img, err := jpeg.Decode(imgReader)
 				if err != nil {
-					fmt.Println("Error decoding jpeg frame:", err)
+					pipeline.GetPipelineBus().PostError(sink, "Error decoding jpeg frame", err)
 					return gst.FlowError
 				}
 
@@ -170,7 +165,8 @@ func encodeGif(mainLoop *gst.MainLoop) error {
 			err := msg.ParseError()
 			fmt.Println("ERROR:", err.Error())
 			if debug := err.DebugString(); debug != "" {
-				fmt.Println("DEBUG:", debug)
+				fmt.Println("DEBUG")
+				fmt.Println(debug)
 			}
 			mainLoop.Quit()
 			isError = true

gst/gst_bus.go

@@ -20,7 +20,10 @@ GstBusSyncReply cgoBusSyncHandler (GstBus * bus, GstMessage * message, gpointer
 import "C"
 
 import (
+	"errors"
+	"fmt"
 	"reflect"
+	"runtime/debug"
 	"sync"
 	"time"
 	"unsafe"
@@ -315,6 +318,22 @@ func (b *Bus) Post(msg *Message) bool {
 	return gobool(C.gst_bus_post(b.Instance(), msg.Instance()))
 }
 
+// PostError is a wrapper for creating a new error mesesage and then posting it to the bus.
+// It gathers stack info from the caller and appends it to the debug info in the error. And optional
+// error object can be provided and will be added to the structure of the error.
+func (b *Bus) PostError(src interface{}, msg string, err error) bool {
+	gerr := NewGError(1, errors.New(msg))
+	var st *Structure
+	if err != nil {
+		st = NewStructure("go-error")
+		if addErr := st.SetValue("error", err.Error()); addErr != nil {
+			fmt.Println("go-gst-warning: failed to set error message to structure")
+		}
+	}
+	gstMsg := NewErrorMessage(src, gerr, string(debug.Stack()), st)
+	return b.Post(gstMsg)
+}
+
 // SetFlushing sets whether to flush out and unref any messages queued in the bus. Releases references to the message origin
 // objects. Will flush future messages until SetFlushing sets flushing to FALSE.
 func (b *Bus) SetFlushing(flushing bool) { C.gst_bus_set_flushing(b.Instance(), gboolean(flushing)) }