Update GetImageBlob/GetImagesBlob to return error as second element (#…

…322)

imagick/magick_wand_exception.go

@@ -29,13 +29,22 @@ func (mw *MagickWand) clearException() bool {
 	return 1 == C.int(C.MagickClearException(mw.mw))
 }
 
-// Returns the kind, reason and description of any error that occurs when using other methods in this API
+// GetLastError returns the kind, reason and description of any error that occurs when using other methods in this API.
+// The exception is cleared after this call.
 func (mw *MagickWand) GetLastError() error {
+	return mw.getLastError(true)
+}
+
+// Returns the kind, reason and description of any error that occurs when using other methods in this API.
+// Clears the exception, if clear is true.
+func (mw *MagickWand) getLastError(clear bool) error {
 	var et C.ExceptionType
 	csdescription := C.MagickGetException(mw.mw, &et)
 	defer relinquishMemory(unsafe.Pointer(csdescription))
 	if ExceptionType(et) != EXCEPTION_UNDEFINED {
-		mw.clearException()
+		if clear {
+			mw.clearException()
+		}
 		return &MagickWandException{ExceptionType(C.int(et)), C.GoString(csdescription)}
 	}
 	runtime.KeepAlive(mw)

imagick/magick_wand_image.go

@@ -937,16 +937,16 @@ func (mw *MagickWand) GetImageBackgroundColor() (bgColor *PixelWand, err error)
 // position in the image sequence. Use SetImageFormat() to set the format to
 // write to the blob (GIF, JPEG, PNG, etc.). Utilize ResetIterator() to ensure
 // the write is from the beginning of the image sequence.
-func (mw *MagickWand) GetImageBlob() []byte {
+func (mw *MagickWand) GetImageBlob() ([]byte, error) {
 	clen := C.size_t(0)
 	csblob := C.MagickGetImageBlob(mw.mw, &clen)
 	defer relinquishMemory(unsafe.Pointer(csblob))
 	if err := mw.GetLastError(); err != nil {
-		return nil
+		return nil, err
 	}
 	ret := C.GoBytes(unsafe.Pointer(csblob), C.int(clen))
 	runtime.KeepAlive(mw)
-	return ret
+	return ret, nil
 }
 
 // GetImagesBlob Implements direct to memory image formats. It returns the image sequence
@@ -955,15 +955,16 @@ func (mw *MagickWand) GetImageBlob() []byte {
 // format, use SetImageFormat(). Note, some image formats do not permit
 // multiple images to the same image stream (e.g. JPEG). in this instance,
 // just the first image of the sequence is returned as a blob.
-func (mw *MagickWand) GetImagesBlob() []byte {
+func (mw *MagickWand) GetImagesBlob() ([]byte, error) {
 	clen := C.size_t(0)
 	csblob := C.MagickGetImagesBlob(mw.mw, &clen)
 	defer relinquishMemory(unsafe.Pointer(csblob))
 	if err := mw.GetLastError(); err != nil {
-		return nil
+		return nil, err
 	}
+	ret := C.GoBytes(unsafe.Pointer(csblob), C.int(clen))
 	runtime.KeepAlive(mw)
-	return C.GoBytes(unsafe.Pointer(csblob), C.int(clen))
+	return ret, nil
 }
 
 // GetImageBluePrimary Returns the chromaticy blue primary point for the image.

imagick/magick_wand_test.go

@@ -234,7 +234,7 @@ func TestReadImageBlob(t *testing.T) {
 	mw := NewMagickWand()
 
 	// Try to read an empty wand
-	blob := mw.GetImageBlob()
+	blob, _ := mw.GetImageBlob()
 	if blob != nil {
 		t.Fatal("Expected nil blob on invalid wand")
 	}
@@ -246,7 +246,10 @@ func TestReadImageBlob(t *testing.T) {
 	}
 
 	mw.ReadImage(`logo:`)
-	blob = mw.GetImageBlob()
+	blob, err := mw.GetImageBlob()
+	if err != nil {
+		t.Fatal(err)
+	}
 
 	// Read a valid blob
 	if err := mw.ReadImageBlob(blob); err != nil {