<?php

namespace OpenTracing\Formats;

/**
 * Used a (single) arbitrary binary blob representing a SpanContext
 *
 * For both Tracer::inject() and Tracer::extract() the carrier must be a `string`.
 */
const BINARY = 'binary';

/**
 * Used for an arbitrary string-to-string map with an unrestricted character set for both keys and values
 *
 * Unlike `HTTP_HEADERS`, the `TEXT_MAP` format does not restrict the key or
 * value character sets in any way.
 *
 * For both Tracer::inject() and Tracer::extract() the carrier must be a `array|ArrayObject`.
 */
const TEXT_MAP = 'text_map';

/**
 * Used for a string-to-string map with keys and values that are suitable for use in HTTP headers (a la RFC 7230.
 * In practice, since there is such "diversity" in the way that HTTP headers are treated in the wild, it is strongly
 * recommended that Tracer implementations use a limited HTTP header key space and escape values conservatively.
 *
 * Unlike `TEXT_MAP`, the `HTTP_HEADERS` format requires that the keys and values be valid as HTTP headers as-is
 * (i.e., character casing may be unstable and special characters are disallowed in keys, values should be
 * URL-escaped, etc).
 *
 * For both Tracer::inject() and Tracer::extract() the carrier must be a `array|ArrayObject`.
 *
 * For example, Tracer::inject():
 *
 *    $headers = []
 *    $tracer->inject($span->getContext(), Formats\HTTP_HEADERS, $headers)
 *    $request = new GuzzleHttp\Psr7\Request($uri, $body, $headers);
 *
 * Or Tracer::extract():
 *
 *    $headers = $request->getHeaders()
 *    $clientContext = $tracer->extract(Formats\HTTP_HEADERS, $headers)
 *
 * @see http://www.php-fig.org/psr/psr-7/#12-http-headers
 * @see http://php.net/manual/en/function.getallheaders.php
 */
const HTTP_HEADERS = 'http_headers';
