Encode & decode in same memory/execution produce empty message output

[scottleedavis]

During troubleshooting a failing test where this library is called by a plugin:
https://github.com/scottleedavis/mattermost-plugin-watermark/blob/master/server/plugin_test.go#L69-L78
I found what appears to be a bug where calling Encode & Decode during the same memory/execution of a program, produces an empty message. However, when an encode happens separately from a decode, everything seems to work as intended. (In my case running Encode via plugin inside mattermost, and later downloading the image and running Decode)

Two examples that fail on my system.

• in memory https://gist.github.com/scottleedavis/25f5e7d1b97dcb8964b74712cfbc6a29
• in files https://gist.github.com/scottleedavis/cf07abde16e15d7abde990282869471a
  Both examples above fail to set the message.

If there any glaring errors in any of the above code, please let me know!

Thank you for building this library! 👍

[auyer]

I ran and commented on both your gists. Go check them out!

Encoding and decoding happens in one single test in this package, and there is no reason it should not work elsewhere.
Give this Test a look:

steganography/steganography_test.go

Lines 77 to 118 in 1aa26d8

	func TestEncodeDecodeGeneratedSmallImage(t *testing.T) {
	// Creating image
	width := 30
	height := 1
	upLeft := image.Point{0, 0}
	lowRight := image.Point{width, height}
	newimg := image.NewRGBA(image.Rectangle{upLeft, lowRight})
	// Set color for each pixel.
	for x := 0; x < width; x++ {
	for y := 0; y < height; y++ {
	newimg.Set(x, y, color.White)
	}
	}
	w := new(bytes.Buffer)
	err := EncodeRGBA(w, newimg, []uint8{84, 84, 84}) // Encode the message into the image file
	if err != nil {
	log.Printf("Error Encoding file %v", err)
	t.FailNow()
	}
	decodeImg, _, err := image.Decode(w)
	if err != nil {
	log.Println("Failed to Decode Image")
	t.FailNow()
	}
	sizeOfMessage := GetMessageSizeFromImage(decodeImg)
	msg := Decode(sizeOfMessage, decodeImg) // Read the message from the picture file
	// otherwise, print the message to STDOUT
	if !bytes.Equal(msg, []uint8{84, 84, 84}) {
	log.Println(string(msg))
	log.Print("messages dont match")
	t.FailNow()
	}
	}

[scottleedavis]

Cool, thank you for the test reference.

Could anything in my environment be affecting this perhaps?

$ go version
go version go1.12.5 darwin/amd64

[scottleedavis]

it appears, the png I was testing against was corrupted. I can say every test/setup discussed works now, except the unit test for the plugin.

If you have desire you are welcome to check it out or contribute, however no pressure at all.

scottleedavis/mattermost-plugin-watermark#2
make test runs the test

Thanks for your help!