Initial Marktplaats SDK scaffold

Clone the twdehands SDK into mrktplaats and retarget naming and defaults for app.marktplaats.nl while keeping the same request/response bodies and endpoint behavior.

imageutil.go

@@ -0,0 +1,79 @@
+package mrktplaats
+
+import (
+	"bytes"
+	"image"
+	"image/jpeg"
+	_ "image/jpeg" // register JPEG decoder for image.Decode
+	"io"
+)
+
+// maxImageUploadBytes is the threshold above which we attempt to compress an
+// image before sending it to the API. The marktplaats endpoints reject payloads
+// that are too large (HTTP 413 / LIMIT_UNEXPECTED_FILE).
+const maxImageUploadBytes = 900 * 1024 // 900 KB
+
+// autoCompressImage reads all bytes from r and, if the result exceeds
+// maxImageUploadBytes, decodes it as an image and re-encodes it as a JPEG at
+// progressively smaller dimensions until it fits. If the data cannot be decoded
+// as a recognised image format it is returned unchanged (the server will then
+// return whatever error it normally would). The original data is also returned
+// unchanged if it is already within the size limit.
+func autoCompressImage(r io.Reader) ([]byte, error) {
+	data, err := io.ReadAll(r)
+	if err != nil {
+		return nil, err
+	}
+	if len(data) <= maxImageUploadBytes {
+		return data, nil
+	}
+
+	src, _, err := image.Decode(bytes.NewReader(data))
+	if err != nil {
+		// Not a format we can handle — return as-is.
+		return data, nil
+	}
+
+	for maxDim := 1200; maxDim >= 300; maxDim = maxDim * 3 / 4 {
+		scaled := scaleImageNN(src, maxDim)
+		var buf bytes.Buffer
+		if err := jpeg.Encode(&buf, scaled, &jpeg.Options{Quality: 80}); err != nil {
+			return data, nil // encoding failed, return original
+		}
+		if buf.Len() <= maxImageUploadBytes {
+			return buf.Bytes(), nil
+		}
+	}
+	return data, nil // could not get small enough, let the server handle it
+}
+
+// scaleImageNN scales src down so that neither dimension exceeds maxDim,
+// preserving the aspect ratio using nearest-neighbour sampling.
+// Returns src unchanged if it already fits within maxDim×maxDim.
+func scaleImageNN(src image.Image, maxDim int) image.Image {
+	bounds := src.Bounds()
+	w, h := bounds.Dx(), bounds.Dy()
+	dstW, dstH := w, h
+
+	if dstW > maxDim {
+		dstH = dstH * maxDim / dstW
+		dstW = maxDim
+	}
+	if dstH > maxDim {
+		dstW = dstW * maxDim / dstH
+		dstH = maxDim
+	}
+	if dstW == w && dstH == h {
+		return src
+	}
+
+	dst := image.NewRGBA(image.Rect(0, 0, dstW, dstH))
+	for y := 0; y < dstH; y++ {
+		srcY := bounds.Min.Y + y*h/dstH
+		for x := 0; x < dstW; x++ {
+			srcX := bounds.Min.X + x*w/dstW
+			dst.Set(x, y, src.At(srcX, srcY))
+		}
+	}
+	return dst
+}