Why does Axios trims JSON bodies?

[valeriangalliat]

Describe the issue

When the Content-Type is set to application/json, and when given an already stringified JSON data parameter, Axios trims the body.

This can be an issue e.g. when computing cryptographic signatures or hashes of the body: the signature of the data parameter we give Axios won't match the one for the payload received on the server side.

Example Code

require('http').createServer((req, res) => {
  process.stdout.write('BEFORE:')
  req.pipe(process.stdout)
  req.on('end', () => process.stdout.write(':AFTER'))
  res.end()
}).listen(9876)

require('axios')({
  method: 'POST',
  url: 'http://localhost:9876/',
  headers: {
    'content-type': 'application/json',
  },
  data: '   {\n  "foo":       "bar"\n\n    }   '
})

Expected behavior, if applicable

The server should log the unaltered body - with the before/after flags above:

BEFORE:   {
  "foo":       "bar"

    }   :AFTER

Instead, Axios trims the body, resulting in the server logging:

BEFORE:{
  "foo":       "bar"

    }:AFTER

Environment

• Axios Version 0.27.2
• Adapter HTTP
• Node.js Version 18.6.0
• OS: OSX 12.4

Additional notes

This happens because the stringifySafely function (which is called on application/json bodies) explicitly trims an already-stringified JSON body:

axios/lib/defaults/index.js

Line 48 in bdf493c

return utils.trim(rawValue);

It seems this comes from this PR #4020 but I don't find any explanation why trim was added there. If anybody knows the reason, I'd be curious to know! Otherwise I can submit a patch to remove the trim but I'm worried that might break other code relying on the trim to happen...

Otherwise I'm wondering how I could send an application/json request without running in this special case of preprocessing the data parameter - in a way where I can give a raw data string that is guaranteed to be sent unaltered. Thanks for the help!

[valeriangalliat]

It looks like I can bypass this body preprocessing behaviour by passing a stream or buffer instead of a string.

Even though I'm unclear why the trim happened in the first place, I'll close this issue. :)