Process image given multiple URL parameters in Go

Question

I would probably prefer to use pressly/chi, but I guess it makes no difference. I imagine given an input URL like this example.com/Jd8saD.jpg?resize=420x320&fit=crop&rotate=90, then it would go to the following GET function because of r.Get("/:image", ImageGET):

function ImageGET(w http.ResponseWriter, r *http.Request) {
  if r.URL.Query().Get("resize") != "" {
    // do something
  }
  if r.URL.Query().Get("crop") != "" {
    // do something
  }
  if r.URL.Query().Get("watermark") != "" {
    // do something
  }
  etc
}

Now, my question is, how should I design whatever function does the image processing so that it will process everything properly and efficiently? I don't expect you to write code that will handle the resizing, but how would these functions look like? Perhaps:

function Resize(size string) (imgfile?, error) {
  // the resize stuff
}

What would that returned imgfile even be? A struct containing some relevant img info?

Answer 1

Likely,

imgfile

will satisfy the image.Image interface and not the data saved on disk (ie. the actual jpg file)

Image is a finite rectangular grid of color.Color values taken from a color model.

Lots of 3rd party golang image libraries use image.Image to manipulate images.

---

I would use a standard image.Image interface retrieved (read to memory) by a filename in the imageGET function and modified according to the queries. You can see also the jpeg golang library from the standard lib.

function ImageGET(w http.ResponseWriter, r *http.Request) {
  // GetJPEGImageFromFileSystem must decode os.File content and 
  // return a golang image.Image interface
  img, _ := GetJPEGImageFromFileSystem(r.URL.Query().Get("filename"))
  if r.URL.Query().Get("resize") != "" {
      // If resizing, write over the image.Image in Memory, 
      // but not the image File on disk
      img, _ = Resize(img, r.URL.Query().GET("resize"))
  }
  // etc...
}

function Resize(img image.Image, size string) (image.Image, error) {
  // the resize stuff -- or, alternatively just call a dependency in the original handler to resize
  return resizedImage, nil
}