An example to emulate an HTML form POST request with file uploads

ABOUT_MULTIPART_UPLOAD.md

Multipart Upload with PHP

About

This is a simple example to do a "multipart/form-data" POST request in PHP without any fancy library.

Setup

You need to download all files into a folder. Then create an empty folder "uploads" in the same folder to store the uploaded files.

To serve the handle_upload.php file properly, run this command in the folder:

php -S 127.0.0.1:8080 -t .

The file handle_upload.php should be accessible at "http://localhost:8080/handle_upload.php".

When all the aboves are ready, run this:

php upload.php ./test_data.txt

You can try other files than "test_data.txt" to see the upload result.

The uploaded file should be available in the "./uploads" folder you created.

Inspiration

Inspired by the Stackoverflow question here.

functions.php

<?php

/**
 * A genertor that yields multipart form-data fragments (without the ending EOL).
 * Would encode all files with base64 to make the request binary-safe.
 *
 * @param iterable $vars
 *    Key-value iterable (e.g. assoc array) of string or integer.
 *    Keys represents the field name.
 * @param iterable $files
 *    Key-value iterable (e.g. assoc array) of file path string.
 *    Keys represents the field name of file upload.
 *
 * @return \Generator
 *    Generator of multipart form-data fragments (without the ending EOL) in assoc format,
 *    always contains 2 key-values:
 *    * header: An array of header for a key-value pair.
 *    * content: A value string (can contain binary content) of the key-value pair.
 */
function generate_multipart_data_parts(iterable $vars, iterable $files=[]): Generator {
    // handle normal variables
    foreach ($vars as $name => $value) {
        $name = urlencode($name);
        $value = urlencode($value);
        yield [
            'header' => ["Content-Disposition: form-data; name=\"{$name}\""],
            'content' => $value,
        ];
    }

    // handle file contents
    foreach ($files as $file_fieldname => $file_path) {
        $file_fieldname = urlencode($file_fieldname);
        $file_data = file_get_contents($file_path);
        yield [
            'header' => [
                "Content-Disposition: form-data; name=\"{$file_fieldname}\"; filename=\"".basename($file_path)."\"",
                "Content-Type: application/octet-stream", // for binary safety
            ],
            'content' => $file_data
        ];
    }
}

/**
 * Converts output of generate_multipart_data_parts() into form data.
 *
 * @param iterable $parts
 *    An iterator of form fragment arrays. See return data of
 *    generate_multipart_data_parts().
 * @param string|null $boundary
 *    An optional pre-generated boundary string to use for wrapping data.
 *    Please reference section 7.2 "The Multipart Content-Type" in RFC1341.
 *
 * @return array
 *    An assoc array with 2 items:
 *    * boundary: the multipart boundary string
 *    * data: the data string (can contain binary data)
 */
function wrap_multipart_data(iterable $parts, ?string $boundary = null): array {
    if (empty($boundary)) {
        $boundary = 'boundary' . time();
    }
    $data = '';
    foreach ($parts as $part) {
        list('header' => $header, 'content' => $content) = $part;
        // Check content for boundary.
        // Note: Won't check header and expect the program makes sense there.
        if (strstr($content, "\r\n$boundary") !== false) {
            throw new \Exception('Error: data contains the multipart boundary');
        }
        $data .= "--{$boundary}\r\n";
        $data .= implode("\r\n", $header) . "\r\n\r\n" . $content . "\r\n";
    }
    // signal end of request (note the trailing "--")
    $data .= "--{$boundary}--\r\n";
    return ['boundary' => $boundary, 'data' => $data];
}

handle_upload.php

<?php

echo "\$_POST ----------\n";
var_dump($_POST);
echo "\n";

echo "\$_FILES ---------\n";
$uploads_dir = __DIR__ . '/uploads';
foreach ($_FILES as $field => $file) {
    if ($file['error'] === UPLOAD_ERR_OK) {
        $now = sha1(microtime(true));
        $tmp_name = $file["tmp_name"];
        $pathinfo = pathinfo($file['name']);
        while (is_file("{$uploads_dir}/{$field}_{$pathinfo['basename']}_{$now}.{$pathinfo['extension']}")) {
            $now .= '(1)';
        }
        move_uploaded_file($tmp_name, "{$uploads_dir}/{$field}_{$pathinfo['basename']}_{$now}.{$pathinfo['extension']}");
        echo "successfully uploaded {$field} ({$file['name']})" . PHP_EOL;
    } else {
        echo "failed to upload {$field} ({$file['name']})" . PHP_EOL;
    }
}
echo "\n";

test_data.txt

This is a dummy text file
for upload test.

upload.php

<?php

require __DIR__ . '/functions.php';

$filepath = $argv[0] ?? __DIR__ . '/test_data.txt';

// build data for a multipart/form-data request
list('boundary' => $boundary, 'data' => $data) = wrap_multipart_data(generate_multipart_data_parts(
    // normal form variables
    [
        'hello' => 'world',
        'foo' => 'bar',
    ],
    // files
    [
        'uploaded_file_test' => $filepath,
    ]
));

// Send POST REQUEST
$context_options = array(
    'http' => array(
        'method' => 'POST',
        'header' => "Content-type: multipart/form-data; boundary={$boundary}\r\n"
            . "Content-Length: " . strlen($data) . "\r\n",
        'content' => $data,
        'timeout' => 10,
    )
);

$context = stream_context_create($context_options);
$result = fopen('http://localhost:8080/handle_upload.php', 'r', false, $context);
$response = stream_get_contents($result);
echo $response;