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bubble up the mime type

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This commit is contained in:
Steve Dudenhoeffer
2025-07-21 23:14:55 -04:00
parent e0adc40661
commit 31766134ef
2 changed files with 21 additions and 35 deletions
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53
utils/compress_image.go
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@@ -7,7 +7,6 @@ import (
"image"
"image/gif"
"image/jpeg"
"image/png"
"net/http"
"golang.org/x/image/draw"
@@ -15,18 +14,21 @@ import (
// CompressImage takes a base‑64‑encoded image (JPEG, PNG or GIF) and returns
// a base‑64‑encoded version that is at most maxLength in size, or an error.
func CompressImage(b64 string, maxLength int) (string, error) {
func CompressImage(b64 string, maxLength int) (string, string, error) {
raw, err := base64.StdEncoding.DecodeString(b64)
if err != nil {
return "", fmt.Errorf("base64 decode: %w", err)
}
if len(raw) <= maxLength {
return b64, nil // small enough already
return "", "", fmt.Errorf("base64 decode: %w", err)
}
switch mime := http.DetectContentType(raw); mime {
mime := http.DetectContentType(raw)
if len(raw) <= maxLength {
return b64, mime, nil // small enough already
}
switch mime {
case "image/gif":
return compressGIF(raw, maxLength)
default: // jpeg, png, webp, etc. → treat as raster
return compressRaster(raw, maxLength)
}
@@ -34,20 +36,20 @@ func CompressImage(b64 string, maxLength int) (string, error) {
// ---------- Raster path (jpeg / png / single‑frame gif) ----------
func compressRaster(src []byte, maxLength int) (string, error) {
func compressRaster(src []byte, maxLength int) (string, string, error) {
img, _, err := image.Decode(bytes.NewReader(src))
if err != nil {
return "", fmt.Errorf("decode raster: %w", err)
return "", "", fmt.Errorf("decode raster: %w", err)
}
quality := 95
for {
var buf bytes.Buffer
if err := jpeg.Encode(&buf, img, &jpeg.Options{Quality: quality}); err != nil {
return "", fmt.Errorf("jpeg encode: %w", err)
return "", "", fmt.Errorf("jpeg encode: %w", err)
}
if buf.Len() <= maxLength {
return base64.StdEncoding.EncodeToString(buf.Bytes()), nil
return base64.StdEncoding.EncodeToString(buf.Bytes()), "image/jpeg", nil
}
if quality > 20 {
@@ -58,7 +60,7 @@ func compressRaster(src []byte, maxLength int) (string, error) {
// down‑scale 80%
b := img.Bounds()
if b.Dx() < 100 || b.Dy() < 100 {
return "", fmt.Errorf("cannot compress below %.02fMiB without destroying image", float64(maxLength)/1048576.0)
return "", "", fmt.Errorf("cannot compress below %.02fMiB without destroying image", float64(maxLength)/1048576.0)
}
dst := image.NewRGBA(image.Rect(0, 0, int(float64(b.Dx())*0.8), int(float64(b.Dy())*0.8)))
draw.ApproxBiLinear.Scale(dst, dst.Bounds(), img, b, draw.Over, nil)
@@ -69,25 +71,25 @@ func compressRaster(src []byte, maxLength int) (string, error) {
// ---------- Animated GIF path ----------
func compressGIF(src []byte, maxLength int) (string, error) {
func compressGIF(src []byte, maxLength int) (string, string, error) {
g, err := gif.DecodeAll(bytes.NewReader(src))
if err != nil {
return "", fmt.Errorf("gif decode: %w", err)
return "", "", fmt.Errorf("gif decode: %w", err)
}
for {
var buf bytes.Buffer
if err := gif.EncodeAll(&buf, g); err != nil {
return "", fmt.Errorf("gif encode: %w", err)
return "", "", fmt.Errorf("gif encode: %w", err)
}
if buf.Len() <= maxLength {
return base64.StdEncoding.EncodeToString(buf.Bytes()), nil
return base64.StdEncoding.EncodeToString(buf.Bytes()), "image/gif", nil
}
// down‑scale every frame by 80%
w, h := g.Config.Width, g.Config.Height
if w < 100 || h < 100 {
return "", fmt.Errorf("cannot compress animated GIF below 5 MiB without excessive quality loss")
return "", "", fmt.Errorf("cannot compress animated GIF below 5 MiB without excessive quality loss")
}
nw, nh := int(float64(w)*0.8), int(float64(h)*0.8)
@@ -110,20 +112,3 @@ func compressGIF(src []byte, maxLength int) (string, error) {
// loop back and test size again …
}
}
// ---------- Helpers for precise MIME decodes (optional) ----------
func decode(r *bytes.Reader, mime string) (image.Image, error) {
switch mime {
case "image/jpeg":
return jpeg.Decode(r)
case "image/png":
return png.Decode(r)
case "image/gif":
// for single‑frame GIFs only – call DecodeAll in caller if animated
return gif.Decode(r)
default:
i, _, err := image.Decode(r)
return i, err // let the stdlib guess the format
}
}