feat: add page processing option.

Author: SupertigerDev

options/processing_options.go

@@ -74,6 +74,7 @@ type ProcessingOptions struct {
 	ZoomWidth         float64
 	ZoomHeight        float64
 	Dpr               float64
+	Page              int
 	Gravity           GravityOptions
 	Enlarge           bool
 	Extend            ExtendOptions
@@ -159,6 +160,7 @@ func NewProcessingOptions() *ProcessingOptions {
 		UsedPresets:           make([]string, 0, len(config.Presets)),
 
 		SecurityOptions: security.DefaultOptions(),
+		Page:            -1,
 
 		// Basically, we need this to update ETag when `IMGPROXY_QUALITY` is changed
 		defaultQuality: config.Quality,
@@ -807,6 +809,20 @@ func applySkipProcessingFormatsOption(po *ProcessingOptions, args []string) erro
 	return nil
 }
 
+func applyPageOption(po *ProcessingOptions, args []string) error {
+	if len(args) > 1 {
+		return newOptionArgumentError("Invalid page arguments: %v", args)
+	}
+
+	if p, err := strconv.Atoi(args[0]); err == nil && p >= 0 {
+		po.Page = p
+	} else {
+		return newOptionArgumentError("Invalid page: %s", args[0])
+	}
+
+	return nil
+}
+
 func applyRawOption(po *ProcessingOptions, args []string) error {
 	if len(args) > 1 {
 		return newOptionArgumentError("Invalid return_attachment arguments: %v", args)
@@ -1100,6 +1116,8 @@ func applyURLOption(po *ProcessingOptions, name string, args []string, usedPrese
 		return applyMaxAnimationFrameResolutionOption(po, args)
 	case "max_result_dimension", "mrd":
 		return applyMaxResultDimensionOption(po, args)
+	case "page":
+		return applyPageOption(po, args)
 	}
 
 	return newUnknownOptionError("processing", name)

processing/processing.go

@@ -283,6 +283,27 @@ func ProcessImage(ctx context.Context, imgdata *imagedata.ImageData, po *options
 	originWidth, originHeight := getImageSize(img)
 
 	animated := img.IsAnimated()
+
+	if po.Page >= 0 && animated {
+		if po.Page >= img.Pages() {
+			po.Page = img.Pages() - 1
+		}
+
+		frameHeight := img.PageHeight()
+		imgWidth := img.Width()
+
+		frame := new(vips.Image)
+		if err := img.Extract(frame, 0, po.Page*frameHeight, imgWidth, frameHeight); err != nil {
+			return nil, err
+		}
+
+		// Swap extracted frame into `img` so deferred Clear() will free it,
+		// and clear the temporary holder which now contains the original image.
+		img.Swap(frame)
+		frame.Clear()
+		animated = false
+	}
+
 	expectAlpha := !po.Flatten && (img.HasAlpha() || po.Padding.Enabled || po.Extend.Enabled)
 
 	switch {