Double Content-Type headers added to request if context->http->header is a multiline string

Description

When using file_get_contents to post an HTTP/HTTPS request, context->http->header can either be a string or an array of strings. If a string, it may ignore the header containing a Content-Type line and add an additional one.

The following code:

<?php
$header = "Authentication: Bearer XYZ" . PHP_EOL;
$header .= 'Content-Type: application/json' . PHP_EOL;

$httpoptions = [
 'method' => 'POST',
 'ignore_errors' => true,
 'content' => json_encode(["message" => "Hello world"]),
 'header' => $header,
];

$context = stream_context_create(['http' => $httpoptions]);

$result = file_get_contents("http://some-test-url/", false, $context);

Resulted in this request (captured using netcat):

POST / HTTP/1.1
Host: some-test-url
Connection: close
Content-Length: 25
Authentication: Bearer XYZ
Content-Type: application/json
Content-Type: application/x-www-form-urlencoded

{"message":"Hello world"}

But I expected this output instead:

POST / HTTP/1.1
Host: some-test-url
Connection: close
Content-Length: 25
Authentication: Bearer XYZ
Content-Type: application/json

{"message":"Hello world"}

Commentary:

There is a warning, "file_get_contents(): Content-type not specified assuming application/x-www-form-urlencoded", that is on some occasions issued (although not, oddly enough, for the code we tracked down this issue as applying to.)

The issue goes away if you build context->http->header as an array.

While arguably building the header as a multiline string seems (always seemed) odd to me, it's frequently quoted in examples across the Internet (which is probably how we ended up doing it) - several examples here: https://www.php.net/manual/en/function.stream-context-create.php

I doubt there are any backward compatibility issues that would be caused by a straight fix to this.

PHP Version

PHP 8.1.2

Operating System

Ubuntu 22.04

Comienza reproduciendo la solicitud con file_get_contents, stream_context_create y el encabezado multilínea mostrado en el issue, capturando el resultado con netcat. Rastrea el manejo de streams HTTP de PHP para encabezados de tipo string y compáralo con los encabezados de tipo array. Se considera terminado cuando el Content-Type proporcionado se conserva sin un encabezado application/x-www-form-urlencoded adicional.