Passing IM error up the stack

img/processor/imagemagick.go

@@ -8,6 +8,7 @@ import (
 	"io"
 	"os/exec"
 	"strconv"
+	"strings"
 )
 
 type ImageMagick struct {
@@ -266,7 +267,7 @@ func (p *ImageMagick) execImagemagick(in *bytes.Reader, args []string, imgId str
 	if err != nil {
 		img.Log.Printf("[%s] Error executing convert command: %s\n", imgId, err.Error())
 		img.Log.Printf("[%s] ERROR: %s\n", imgId, cmderr.String())
-		return nil, err
+		return nil, fmt.Errorf("Error executing convert command: %w\nStderr: [%s]", err, strings.TrimSpace(cmderr.String()))
 	}
 
 	return out.Bytes(), nil
@@ -308,7 +309,7 @@ func (p *ImageMagick) LoadImageInfo(src *img.Image) (*img.Info, error) {
 	if err != nil {
 		img.Log.Printf("[%s] Error executing identify command: %s\n", err.Error(), imgId)
 		img.Log.Printf("[%s] ERROR: %s\n", cmderr.String(), imgId)
-		return nil, err
+		return nil, fmt.Errorf("Error executing identify command: %w\nStderr: [%s]", err, strings.TrimSpace(cmderr.String()))
 	}
 
 	imageInfo := &img.Info{

img/processor/imagemagick_test.go

@@ -692,3 +692,57 @@ func testImages(t *testing.T, fn transform, files []*testTransformation) {
 		fmt.Printf("%60s | %10d | %10d | %.2f\n", r.file, r.optSize, r.origSize, 1.0-(float32(r.optSize)/float32(r.origSize)))
 	}
 }
+
+func TestOptimise_ErrorIdentify(t *testing.T) {
+	_, err := proc.Optimise(&img.TransformationConfig{
+		Src: &img.Image{
+			Id:       "",
+			Data:     []byte("This is not an image!"),
+			MimeType: "image/jpeg",
+		},
+	})
+
+	if err == nil {
+		t.Error("expected error but got none")
+	}
+
+	expectedError := "Error executing identify command: exit status 1\nStderr: [identify: no decode delegate for this image format `' @ error/constitute.c/ReadImage/746.]"
+	if err.Error() != expectedError {
+		t.Errorf("expected error %s, but got %s", expectedError, err.Error())
+	}
+}
+
+func TestOptimise_ErrorConvert(t *testing.T) {
+	f := fmt.Sprintf("%s/%s", "./test_files/transformations", "medium-jpeg.jpg")
+
+	orig, err := ioutil.ReadFile(f)
+	if err != nil {
+		t.Errorf("Can't read file %s: %+v", f, err)
+	}
+
+	proc.GetAdditionalArgs = func(op string, image []byte, source *img.Info, target *img.Info) []string {
+		return []string{"-i_dont_know", "this"}
+	}
+
+	_, err = proc.Resize(&img.TransformationConfig{
+		Src: &img.Image{
+			Id:       "",
+			Data:     orig,
+			MimeType: "image/jpeg",
+		},
+		Config: &img.ResizeConfig{
+			Size: "300x300",
+		},
+	})
+
+	proc.GetAdditionalArgs = nil
+
+	if err == nil {
+		t.Error("expected error but got none")
+	}
+
+	expectedError := "Error executing convert command: exit status 1\nStderr: [convert: unrecognized option `-i_dont_know' @ error/convert.c/ConvertImageCommand/1965.]"
+	if err.Error() != expectedError {
+		t.Errorf("expected error %s, but got %s", expectedError, err.Error())
+	}
+}