From 0fdece68c07836a566909d75a7f3836f229334b5 Mon Sep 17 00:00:00 2001
From: Brian Picciano <mediocregopher@gmail.com>
Date: Tue, 17 May 2022 13:29:12 -0600
Subject: Add /v2/assets/ handler, with resizing

---
 srv/src/api/assets.go | 113 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 113 insertions(+)
 create mode 100644 srv/src/api/assets.go

(limited to 'srv/src/api/assets.go')

diff --git a/srv/src/api/assets.go b/srv/src/api/assets.go
new file mode 100644
index 0000000..e94d324
--- /dev/null
+++ b/srv/src/api/assets.go
@@ -0,0 +1,113 @@
+package api
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"image"
+	"image/jpeg"
+	"image/png"
+	"io"
+	"net/http"
+	"path/filepath"
+	"strings"
+
+	"github.com/mediocregopher/blog.mediocregopher.com/srv/api/apiutil"
+	"github.com/mediocregopher/blog.mediocregopher.com/srv/post"
+	"golang.org/x/image/draw"
+)
+
+func resizeImage(out io.Writer, in io.Reader, maxWidth float64) error {
+
+	img, format, err := image.Decode(in)
+	if err != nil {
+		return fmt.Errorf("decoding image: %w", err)
+	}
+
+	imgRect := img.Bounds()
+	imgW, imgH := float64(imgRect.Dx()), float64(imgRect.Dy())
+
+	if imgW > maxWidth {
+
+		newH := imgH * maxWidth / imgW
+		newImg := image.NewRGBA(image.Rect(0, 0, int(maxWidth), int(newH)))
+
+		// Resize
+		draw.BiLinear.Scale(
+			newImg, newImg.Bounds(), img, img.Bounds(), draw.Over, nil,
+		)
+
+		img = newImg
+	}
+
+	switch format {
+	case "jpeg":
+		return jpeg.Encode(out, img, nil)
+	case "png":
+		return png.Encode(out, img)
+	default:
+		return fmt.Errorf("unknown image format %q", format)
+	}
+}
+
+func (a *api) servePostAssetHandler() http.Handler {
+
+	return http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {
+
+		id := filepath.Base(r.URL.Path)
+
+		maxWidth, err := apiutil.StrToInt(r.FormValue("w"), 0)
+		if err != nil {
+			apiutil.BadRequest(rw, r, fmt.Errorf("invalid w parameter: %w", err))
+			return
+		}
+
+		buf := new(bytes.Buffer)
+
+		err = a.params.PostAssetStore.Get(id, buf)
+
+		if errors.Is(err, post.ErrAssetNotFound) {
+			http.Error(rw, "Asset not found", 404)
+			return
+		} else if err != nil {
+			apiutil.InternalServerError(
+				rw, r, fmt.Errorf("fetching asset with id %q: %w", id, err),
+			)
+			return
+		}
+
+		if maxWidth == 0 {
+
+			if _, err := io.Copy(rw, buf); err != nil {
+				apiutil.InternalServerError(
+					rw, r,
+					fmt.Errorf(
+						"copying asset with id %q to response writer: %w",
+						id, err,
+					),
+				)
+			}
+
+			return
+		}
+
+		switch ext := strings.ToLower(strings.TrimPrefix(filepath.Ext(id), ".")); ext {
+		case "jpg", "jpeg", "png":
+
+			if err := resizeImage(rw, buf, float64(maxWidth)); err != nil {
+				apiutil.InternalServerError(
+					rw, r,
+					fmt.Errorf(
+						"resizing image with id %q to size %d: %w",
+						id, maxWidth, err,
+					),
+				)
+			}
+
+		default:
+			apiutil.BadRequest(rw, r, fmt.Errorf("cannot resize file with extension %q", ext))
+			return
+		}
+
+	})
+}
-- 
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