ljharb/qs

Different array parse behaviour of x-www-form-urlencoded between ExpressJS and rails

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#178 opened on Nov 11, 2016

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bughelp wantedparse

Description

I use content-type: application/x-www-form-urlencoded to send POST request to backend server. The post body as follow:

listing[pictures][files][][name]=9ADDD7B1-FCFF-4538-916A-1E63DFB43A72&
listing[pictures][files][][name]=EFFE67B2-5D41-4B74-A33E-5963F54FAEC7&
listing[pictures][files][][name]=BBC9CB38-FE01-4F1A-AE37-7ED71F4B2CB5

In backend server, if I use ruby on rails, the POST will be parsed as follow:

"pictures"=>{
    "files"=>[
        {"name"=>"9ADDD7B1-FCFF-4538-916A-1E63DFB43A72"}, 
        {"name"=>"EFFE67B2-5D41-4B74-A33E-5963F54FAEC7"}, 
        {"name"=>"BBC9CB38-FE01-4F1A-AE37-7ED71F4B2CB5"}
    ]
}

This result is what I expected to be.

But, If I use nodeJS express and body-parser:

// parse application/json
app.use(bodyParser.json());
// parse application/x-www-form-urlencoded
app.use(bodyParser.urlencoded({ extended: true }));

extended: true means that bodyParser will use qs to parse data.

The POST will be parsed as follow:

"pictures"=>{
    "files"=>[
        "name"=>[
            "9ADDD7B1-FCFF-4538-916A-1E63DFB43A72", 
            "EFFE67B2-5D41-4B74-A33E-5963F54FAEC7", 
            "BBC9CB38-FE01-4F1A-AE37-7ED71F4B2CB5"
        ]
    ]
}

Contributor guide

Tech stack
javascriptnodejsexpress
Domain
backendapi
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Understanding of query string parsingNode.js basics
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40
Research direction
The issue reports a discrepancy in how qs parses repeated square bracket notations like `listing[pictures][files][][name]`. The expected behavior is to create an array of objects with a 'name' key, but qs produces an object with an array of names. To fix, investigate the parsing logic in `lib/parse.js`, specifically how `[]` is handled for nested properties. Look for any existing options like 'arrayLimit' or 'parameterLimit' that may affect nesting. Check the test suite for similar parsing cases and consider adding a test for this scenario.