added image compression api

api/utils.go

+///////////////////////////////////////////////////////////////////////////////
+// Copyright © 2020 xx network SEZC                                          //
+//                                                                           //
+// Use of this source code is governed by a license that can be found in the //
+// LICENSE file                                                              //
+///////////////////////////////////////////////////////////////////////////////
+
+// Provides various utility functions for access over the bindings
+
+package api
+
+import (
+	"bytes"
+	"github.com/nfnt/resize"
+	"github.com/pkg/errors"
+	"image/jpeg"
+	"math"
+)
+
+const (
+	// Maximum input image size (in bytes)
+	maxSize int64 = 12000000
+	// Desired number of pixels in output image
+	desiredSize = 307200
+)
+
+// CompressJpeg takes a JPEG image in byte format
+// and compresses it based on the above consts
+func CompressJpeg(imgBytes []byte) ([]byte, error) {
+	// Convert bytes to a reader
+	imgBuf := bytes.NewReader(imgBytes)
+
+	// Ensure the size of the image is under the limit
+	if imgSize := imgBuf.Size(); imgSize > maxSize {
+		return nil, errors.Errorf("Image is too large: %d/%d", imgSize, maxSize)
+	}
+
+	// Decode the image information
+	imgInfo, err := jpeg.DecodeConfig(imgBuf)
+	if err != nil {
+		return nil, errors.Errorf("Unable to decode image config: %+v", err)
+	}
+
+	// If the dimensions of the image are below desiredSize, no compression is required
+	if imgInfo.Width*imgInfo.Height < desiredSize {
+		return imgBytes, nil
+	}
+
+	// Reset the buffer to the beginning to begin decoding the image
+	_, err = imgBuf.Seek(0, 0)
+	if err != nil {
+		return nil, errors.Errorf("Unable to reset image buffer: %+v", err)
+	}
+
+	// Decode image into image.Image object
+	img, err := jpeg.Decode(imgBuf)
+	if err != nil {
+		return nil, errors.Errorf("Unable to decode image: %+v", err)
+	}
+
+	// Determine the new width of the image based on desiredSize
+	newWidth := uint(math.Sqrt(float64(desiredSize * (imgInfo.Width / imgInfo.Height))))
+
+	// Resize the image based on newWidth while preserving aspect ratio
+	newImg := resize.Resize(newWidth, 0, img, resize.Bicubic)
+
+	// Encode the new image to a buffer
+	var newImgBuf *bytes.Buffer
+	err = jpeg.Encode(newImgBuf, newImg, nil)
+	if err != nil {
+		return nil, errors.Errorf("Unable to encode image: %+v", err)
+	}
+
+	// Return the compressed image in byte form
+	return newImgBuf.Bytes(), nil
+}

go.mod

@@ -8,6 +8,7 @@ require (
 	github.com/gopherjs/gopherjs v0.0.0-20200217142428-fce0ec30dd00 // indirect
 	github.com/magiconair/properties v1.8.4 // indirect
 	github.com/mitchellh/mapstructure v1.4.0 // indirect
+	github.com/nfnt/resize v0.0.0-20180221191011-83c6a9932646
 	github.com/pelletier/go-toml v1.8.1 // indirect
 	github.com/pkg/errors v0.9.1
 	github.com/smartystreets/assertions v1.0.1 // indirect

go.sum

@@ -167,6 +167,8 @@ github.com/mitchellh/mapstructure v1.4.0/go.mod h1:bFUtVrKA4DC2yAKiSyO/QUcy7e+RR
 github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd/go.mod h1:6dJC0mAP4ikYIbvyc7fijjWJddQyLn8Ig3JB5CqoB9Q=
 github.com/modern-go/reflect2 v1.0.1/go.mod h1:bx2lNnkwVCuqBIxFjflWJWanXIb3RllmbCylyMrvgv0=
 github.com/mwitkow/go-conntrack v0.0.0-20161129095857-cc309e4a2223/go.mod h1:qRWi+5nqEBWmkhHvq77mSJWrCKwh8bxhgT7d/eI7P4U=
+github.com/nfnt/resize v0.0.0-20180221191011-83c6a9932646 h1:zYyBkD/k9seD2A7fsi6Oo2LfFZAehjjQMERAvZLEDnQ=
+github.com/nfnt/resize v0.0.0-20180221191011-83c6a9932646/go.mod h1:jpp1/29i3P1S/RLdc7JQKbRpFeM1dOBd8T9ki5s+AY8=
 github.com/niemeyer/pretty v0.0.0-20200227124842-a10e7caefd8e/go.mod h1:zD1mROLANZcx1PVRCS0qkT7pwLkGfwJo4zjcN/Tysno=
 github.com/oklog/ulid v1.3.1/go.mod h1:CirwcVhetQ6Lv90oh/F+FBtV6XMibvdAFo93nm5qn4U=
 github.com/pascaldekloe/goe v0.0.0-20180627143212-57f6aae5913c/go.mod h1:lzWF7FIEvWOWxwDKqyGYQf6ZUaNfKdP144TG7ZOy1lc=