Golang how to create file from nodejs array of bytes

Question

My go server recieves a JS array by post request, getting data like this

How do I write this to an a file?

In node.js I can do it like this:

fs.writeFile(`${dir}/${body.file_name}`, Buffer.from(body.file), { flag: "w" }, function (err) {
        if (err) {
            console.log(err);
            return res.status(200).json({ 'status': 'error' });
        }
        console.log(`file sucessfully saved to "${dir}${body.file_name}"`);
        return res.status(200).json({ 'status': 'ok' });
    });

As per the How to Ask, please do not post images of code, data, error message, etc. Instead, copy or type the text into your question, formatted as code. Reserve the use of images for diagrams or demonstrating rendering bugs; things that are impossible to describe accurately via text. — Bohemian
– Bohemian ♦, Commented Nov 26, 2022 at 23:55

wakumaku · Accepted Answer · 2022-11-27 00:46:12Z

Translating line by line to go would result into something like this:

func handleIncommingFile() http.HandlerFunc {
    return func(w http.ResponseWriter, r *http.Request) {
        if r.Body == nil {
            log.Println("body is empty")
            w.WriteHeader(http.StatusBadRequest)
            w.Write([]byte(`{ 'status': 'error' }`))
            return
        }

        body, err := io.ReadAll(r.Body)
        if err != nil {
            log.Printf("reading body: %v", err)
            w.WriteHeader(http.StatusInternalServerError)
            w.Write([]byte(`{ 'status': 'error' }`))
            return
        }
        defer r.Body.Close()

        if err := os.WriteFile("path/to/filename.ext", body, 0644); err != nil {
            log.Printf("writting content: %v", err)
            w.WriteHeader(http.StatusInternalServerError)
            w.Write([]byte(`{ 'status': 'error' }`))
            return
        }

        w.WriteHeader(http.StatusOK)
        w.Write([]byte(`{ 'status': 'ok' }`))
    }
}

Note that I'm returning different HTTP Status Code depending on the error context and that there are missing checks, for example, if the file already exist.

Also I would recommend to inject an storage service to the handler to simplify it and move the file creation logic to another package.

func handleIncommingFile(store storage.Manager)  http.HandlerFunc {
    return func(w http.ResponseWriter, r *http.Request) {
        if err := store.Save(r.Body); err != nil {
            w.WriteHeader(http.StatusInternalServerError)
            return
        }
        w.WriteHeader(http.StatusOK)
// ...

This will help you to test thandler and storage testing :)

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