Amp\Artax\Client::normalizeRequestBodyHeaders PHP Method

    private function normalizeRequestBodyHeaders(Request $request, array $options)
    {
        if ($request->hasHeader('Content-Length')) {
            // If the user manually assigned a Content-Length we don't need to do anything here.
            return;
        }
        $body = $request->getBody();
        $method = $request->getMethod();
        if (empty($body) && $body !== '0' && in_array($method, ['POST', 'PUT', 'PATCH'])) {
            $request->setHeader('Content-Length', '0');
            $request->removeHeader('Transfer-Encoding');
        } elseif (is_scalar($body) && $body !== '') {
            $body = (string) $body;
            $request->setBody($body);
            $request->setHeader('Content-Length', strlen($body));
            $request->removeHeader('Transfer-Encoding');
        } elseif ($body instanceof \Iterator) {
            $request->removeHeader('Content-Length');
            $request->setHeader('Transfer-Encoding', 'chunked');
            $chunkedBody = new ChunkingIterator($body);
            $request->setBody($chunkedBody);
        } elseif ($body !== null) {
            throw new \InvalidArgumentException('Request entity body must be a scalar or Iterator');
        }
        if ($body && $options[self::OP_EXPECT_CONTINUE] && !$request->hasHeader('Expect')) {
            $request->setHeader('Expect', '100-continue');
        }
        if ($method === 'TRACE' || $method === 'HEAD' || $method === 'OPTIONS') {
            $request->setBody(null);
        }
    }