How to pass and parse nested object with postman multipart/form-data

Question

I have a route which works with multipart/form-data. All was good before I tried to pass nested objects via postman. There are a lot of code in this function but I removed it for this question because it does not matter.

func (h *handler) SubmitFormNewPark(w http.ResponseWriter, r *http.Request) {
    ctx := context.InitFromHTTP(w, r, "submit_form_new_park")
    defer ctx.OnExit(nil)

    err := r.ParseMultipartForm(0)
    if err != nil {
        logger.Get().Warn(ctx, "can't parse new park form", zap.Error(err))
        h.writeResponse(ctx, w, models.FormParkResponse{Success: false})
        return
    }

    multipartForm := make(map[string]interface{})
    for key, value := range r.MultipartForm.Value {
        multipartForm[key] = value
    }
}

Firstly all was good because I had not nested object

But after I added nested object there are different keys in r.MultipartForm.Value

If I print the r.MultipartForm.Value I get next map

map[city:[city] entity_name:[entity_name] ip_info[ip_address]:[ip_address] ip_info[ip_fio]:[ip_fio] name:[Name] office_address:[office address] office_phone:[74954954949]]

But I expect get "ip_info" key as map with keys ip_address and ip_fio

I also tried to use keys such as ip_info[0][ip_fio] and ip_info[0][ip_address].

I think that golang parameter parsing just takes the literal name ( as you can see the key in your map). I have only been able to read an array of params on the same key like this. Eg.req.GetParameters("ip_info[ip_fio]"). What I did was send multiple values on the same key and GetParameters will return a string slice with the values from that key. — Alex Efimov
– Alex Efimov, Commented Jan 20, 2021 at 9:28
Unlike with JSON, for example, there is no standard way of nesting objects in multipart/form-data. There are several (incompatible) ways of marshaling complex/nested structures into this type of data. I'm not sure which format postman uses (and maybe it supports multiple ones), but you'll need to find a Go library that's compatible with that format. Or if it's an option, maybe use JSON, or some other more flexible data type instead. — Jonathan Hall
– Jonathan Hall, Commented Jan 20, 2021 at 10:11

derv-dice · Accepted Answer · 2021-01-21 06:08:36Z

You can parse nested objects with this code:

Note: You can improove this example to recursively parse nested objects in nested objects

package main

import (
    "fmt"
    "log"
    "net/http"
    "regexp"
)

var rxNestedKey = regexp.MustCompile(`^(?P<key>[A-Za-z0-9_]+)\[(?P<n_key>[A-Za-z0-9_]+)\]$`)

func Handler(w http.ResponseWriter, r *http.Request) {
    err := r.ParseMultipartForm(0)
    if err != nil {

        return
    }

    multipartForm := map[string]interface{}{}
    nestedBuf := map[string]map[string]interface{}{}

    for key, value := range r.MultipartForm.Value {
        // check key has nested key
        if rxNestedKey.MatchString(key) {
            // parse nested key (nK) and key (k)
            k := rxNestedKey.FindStringSubmatch(key)[1]
            nK := rxNestedKey.FindStringSubmatch(key)[2]

            if nestedBuf[k] == nil {
                nestedBuf[k] = map[string]interface{}{}
            }
            nestedBuf[k][nK] = value
        } else {
            multipartForm[key] = value
        }
    }

    // collect all nested data from buff
    for k, v := range nestedBuf {
        multipartForm[k] = v
    }

    fmt.Printf("%+v\n", multipartForm)
}

func main() {
    http.HandleFunc("/", Handler)
    log.Fatal(http.ListenAndServe("localhost:8080", nil))
}

Parsed as:

map[ip:map[address:[127.0.0.1] port:[8080]] office_city:[Moscow] office_phone:[7845612349879]]

Jonathan Picazo · Accepted Answer · 2023-09-18 15:56:30Z

0

This helped me figure out how to pass nested data. Thank you.

answered Sep 18, 2023 at 15:56

Jonathan Picazo

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