How to Parse Files and JSON from HTTP Requests in Go

Parsing Files and JSON from HTTP Requests in Go

When constructing an HTTP request from an AngularJS front end, you may encounter the need to parse both a file and JSON data. This can be challenging, especially when attempting to parse the JSON data from the request body.

Consider the following HTTP request payload:

Content-Disposition: form-data; name="file"; filename="Parent Handbook.pdf"
Content-Type: application/pdf

Content-Disposition: form-data; name="doc"
{"title":"test","cat":"test cat","date":20142323}

In this scenario, "file" represents the PDF document, while "doc" contains the JSON data you wish to parse.

For parsing both the file and JSON data effectively, Go provides a suitable solution. Here's how you can achieve this:

Instead of assuming that r.Body contains the JSON data, you should utilize r.MultipartReader() to process both the PDF and JSON parts separately. This function provides a mime/multipart.Reader object that enables you to iterate through the different parts of the request using r.NextPart().

Here's an example of a revised handler function:

<code class="go">func (s *Server) PostFileHandler(w http.ResponseWriter, r *http.Request) {
    mr, err := r.MultipartReader()
    if err != nil {
        http.Error(w, err.Error(), http.StatusInternalServerError)
        return
    }

    doc := Doc{}
    for {
        part, err := mr.NextPart()

        // No more parts
        if err == io.EOF {
            break
        }

        // Error occurred
        if err != nil {
            http.Error(w, err.Error(), http.StatusInternalServerError)
            return
        }

        // PDF 'file' part
        if part.FormName() == "file" {
            doc.Url = part.FileName()
            outfile, err := os.Create("./docs/" + part.FileName())
            if err != nil {
                http.Error(w, err.Error(), http.StatusInternalServerError)
                return
            }
            defer outfile.Close()

            _, err = io.Copy(outfile, part)
            if err != nil {
                http.Error(w, err.Error(), http.StatusInternalServerError)
                return
            }
        }

        // JSON 'doc' part
        if part.FormName() == "doc" {
            jsonDecoder := json.NewDecoder(part)
            err = jsonDecoder.Decode(&doc)
            if err != nil {
                http.Error(w, err.Error(), http.StatusInternalServerError)
                return
            }</code>

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