<?php
/**
 * Build multipart/form-data
 *
 * @param array @$data Data
 * @param array @$files 1-D array of files where key is field name and value if file contents
 * @param string &$contentType Retun variable for content type
 *
 * @return string Encoded data
 */
function buildMultipartFormData(array &$data, array &$files, &$contentType)
{
	$eol = "\r\n";

	// Build test string
	$testStr = '';
	array_walk_recursive($data, function($item, $key) use (&$testStr, &$eol) {
		$testStr .= $key . $eol . $item . $eol;
	});

	// Get file content type and content.  Add to test string
	$finfo = finfo_open(FILEINFO_MIME_TYPE);
	$fileContent = array();
	$fileContentTypes = array();
	foreach ($files as $key=>$filename)
	{
		$fileContent[$key] = file_get_contents($filename);
		$fileContentTypes[$key] = finfo_file($finfo, $filename);
		$testStr .= $key . $eol . $fileContentTypes[$key] . $eol. $fileContent[$key] . $eol;
	}
	finfo_close($finfo);

	// Find a boundary not present in the test string
	$boundaryLen = 6;
	$alpha = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';
	do {
		$boundary = '--';
		for ($i = 0; $i < $boundaryLen; $i++)
		{
			$c = rand(0, 61);
			$boundary .= $alpha[$c];
		}

		// Check test string
		if (strpos($testStr, $boundary) !== false)
		{
			$boundary = null;
			$boundaryLen++;
		}
	} while ($boundary === null);
	unset($testStr);

	// Set content type
	$contentType = 'multipart/form-data, boundary='.$boundary;

	// Build data
	$rtn = '';
	$func = function($data, $baseKey = null) use (&$func, &$boundary, &$eol)
	{
		$rtn = '';
		foreach ($data as $key=>&$value)
		{
			// Get key
			$key = $baseKey === null ? $key : ($baseKey . '[' . $key . ']');

			// Add data
			if (is_array($value))
				$rtn .= $func($value, $key);
			else
				$rtn .= '--' . $boundary . $eol . 'Content-Disposition: form-data; name="'.$key.'"' . $eol . $eol . $value . $eol;
		}

		return $rtn;
	};
	$rtn = $func($data);

	// Add files
	foreach ($files as $key=>$filename)
	{
		$rtn .= '--' . $boundary . $eol . 'Content-Disposition: file; name="'.$key.'"; filename="'.basename($filename).'"' . $eol
			. 'Content-Type: ' . $fileContentTypes[$key] . $eol
			. 'Content-Transfer-Encoding: binary' . $eol . $eol
			. $fileContent[$key] . $eol;
	}

	return $rtn . '--' . $boundary . '--' . $eol;
}