Multipart array index and data loss in HTTP client

[RomainMazB]

Laravel Version

13.7.0

PHP Version

8.4.1

Database Driver & Version

No response

Description

Passing nested array as multipart in the HTTP client results in an index loss.
This array:

Http::asMultipart()->post('http://foo.com/multipart', [
  'user' => [
    'name' => 'foo',
    'email' => 'bar@baz.com'
  ]
]);

results to this wrong body (the name and email index are lost)

--c88de6383a5ee47d40326eed35ccdff493bbb202
Content-Disposition: form-data; name="user[]"
Content-Length: 3

foo
--c88de6383a5ee47d40326eed35ccdff493bbb202
Content-Disposition: form-data; name="user[]"
Content-Length: 11

bar@baz.com
--c88de6383a5ee47d40326eed35ccdff493bbb202--

Also, when using two arrays containing the same index, only the second one is added to the data (in addition to the name index loss):

Http::asMultipart()->post('http://foo.com/multipart', [
  'user' => [
    'name' => 'foo',
  ],
  'admin' => [
    'name' => 'bar',
  ]
]);

results to this multipart body (the whole user entry data is lost):

-3832af0fa930d17bf9d26df6d6c948ec91c74edb
Content-Disposition: form-data; name="admin[]"
Content-Length: 3

bar
--3832af0fa930d17bf9d26df6d6c948ec91c74edb--

Steps To Reproduce

I created a repository with a branch containing two tests to demonstrate the issues.
The tests can be read here: RomainMazB@0029219

Way to fix

This PR: #59984 exists to upgrade guzzle/psr7 to ^2.9 and remove the HTTP Client implementation which causes the issue

[RomainMazB]

I just confirmed for the second use case that it was only the conflicting indexes that are lost.
This request:

Http::asMultipart()->post('http://foo.com/multipart', [
  'users' => ['a' => 3, 'b' => 7],
  'admins' => ['b' => 5, 'c' => 6],
]);

Ends up to this (the users.b key and data is lost because conflicting with admins.b):

--5e3e545961be4f87f13d7c7f1a71ac1b230c066a
Content-Disposition: form-data; name="users[]"
Content-Length: 1

3
--5e3e545961be4f87f13d7c7f1a71ac1b230c066a
Content-Disposition: form-data; name="admins[]"
Content-Length: 1

5
--5e3e545961be4f87f13d7c7f1a71ac1b230c066a
Content-Disposition: form-data; name="admins[]"
Content-Length: 1

6
--5e3e545961be4f87f13d7c7f1a71ac1b230c066a--

It's due to the flatMap method usage here:

framework/src/Illuminate/Http/Client/PendingRequest.php

Line 1158 in 5cbe7eb

->flatMap(function ($value, $key) {

This collection:

[
  'users' => ['a' => 3, 'b' => 7],
  'admins' => ['b' => 5, 'c' => 6],
]

becomes this after been flattened:

[
  "a" => [
    "name" => "users[]",
    "contents" => 3
  ],
  "b" => [
    "name" => "admins[]",
    "contents" => 5
  ],
  "c" => [
    "name" => "admins[]",
    "contents" => 6
  ]
]

[github-actions]

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If possible, please make a pull request fixing the issue you have described, along with corresponding tests. All pull requests are promptly reviewed by the Laravel team.

Thank you!

[RomainMazB]

Fixed by #59984