Getting started with PHP core development - PHP Serbia 2018

Video recording: https://youtu.be/DNAJXROxQ8g
Joind.in: https://joind.in/talk/7d50f

While PHP’s open source community is thriving, only a relatively small number of PHP developers contribute to the number one tool they use on a daily basis: PHP itself. Although it may seem daunting to help out on a project written in C, requiring compilation and linking, getting started is actually pretty easy. In this talk I would like to share my own recent experiences of beginning to contribute to PHP itself. We will see different ways to contribute and cover some practical tips, workflows and resources, so you can start giving back to your programming language straight away!

Transcript

1. Getting started with PHP core development @arnoutboks Arnout Boks #phpsrb 27-05-2018
2. @arnoutboks #phpsrb PHP Open Source projects
3. @arnoutboks #phpsrb PHP Open Source projects 4175 contributors 418 contributors 689 contributors 1497 contributors
4. @arnoutboks #phpsrb PHP Open Source projects 4175 contributors 418 contributors 689 contributors 1497 contributors
5. @arnoutboks #phpsrb PHP Open Source projects 4175 contributors 418 contributors 689 contributors 1497 contributors 497 contributors?
6. @arnoutboks #phpsrb We all use PHP intensively Why not contribute something back?
7. @arnoutboks #phpsrb The catch
8. @arnoutboks #phpsrb The catch
9. @arnoutboks #phpsrb The core
10. @arnoutboks #phpsrb The core
11. @arnoutboks #phpsrb My own journey to the core
12. @arnoutboks #phpsrb Once upon a time… <something xmlns:foo="http://www.example.com"> <foo:bar /> <bar /> </something> <?php $doc = /* … (DOMDocument) */; $doc->getElementsByTagName( "bar" )->length;
13. @arnoutboks #phpsrb Once upon a time… <something xmlns:foo="http://www.example.com"> <foo:bar /> <bar /> </something> <?php $doc = /* … (DOMDocument) */; $doc->getElementsByTagName( "bar" )->length; // returns 2
14. @arnoutboks #phpsrb Once upon a time… <something xmlns:foo="http://www.example.com"> <foo:bar /> <bar /> </something> <?php $doc = /* … (DOMDocument) */; $doc->getElementsByTagNameNS( "http://www.example.com", "bar" )->length;
15. @arnoutboks #phpsrb Once upon a time… <something xmlns:foo="http://www.example.com"> <foo:bar /> <bar /> </something> <?php $doc = /* … (DOMDocument) */; $doc->getElementsByTagNameNS( "http://www.example.com", "bar" )->length; // returns 1
16. @arnoutboks #phpsrb Once upon a time… <something xmlns:foo="http://www.example.com"> <foo:bar /> <bar /> </something> <?php $doc = /* … (DOMDocument) */; $doc->getElementsByTagNameNS( "", "bar" )->length;
17. @arnoutboks #phpsrb Once upon a time… <something xmlns:foo="http://www.example.com"> <foo:bar /> <bar /> </something> <?php $doc = /* … (DOMDocument) */; $doc->getElementsByTagNameNS( "", "bar" )->length; // returns 0!
18. @arnoutboks #phpsrb Once upon a time…
19. Reporting bugs Gotta squash them all
20. @arnoutboks #phpsrb bugs.php.net PHP bug tracker
21. @arnoutboks #phpsrb Write good bug reports https://bugs.php.net/how-to-report.php
22. @arnoutboks #phpsrb Search for existing bugs
23. @arnoutboks #phpsrb Sharpen bug details Report different platform/version: Don’t post “me too” comments – Do post other relevant details
24. @arnoutboks #phpsrb Help triaging bugs! https://bugs.php.net/random
25. Building PHP from git Living on the edge
26. @arnoutboks #phpsrb 1. Install dependencies • git • build-essential • autoconf • automake • libtool • re2c • bison • libxml2-dev Using apt-get, yum or similar
27. @arnoutboks #phpsrb 2. Clone php-src $ git clone https://github.com/php/php- src.git
28. @arnoutboks #phpsrb 3. Generate ./configure script $ ./buildconf Uses autoconf to build ./configure from: • configure.ac • acinclude.m4 • sapi/*/config.m4 • ext/*/config.m4
29. @arnoutboks #phpsrb 4. Run ./configure script $ ./configure Configure a default PHP build: $ ./configure --disable-cgi --disable-dom --enable-opcache --with-sqlite3=/path /to/sqlite3 Customize extensions/SAPIs: $ ./configure --help See all options
30. @arnoutboks #phpsrb 5. Compile $ make $ make –j`nproc` To use all available cores (faster):
31. @arnoutboks #phpsrb 6. Run! $ sapi/cli/php --version Binaries are in sapi/cli/php and sapi/cgi/php-cgi:
32. @arnoutboks #phpsrb Subsequent builds $ make Just run Recompiles only files that have changed
33. @arnoutboks #phpsrb Cleanup scripts $ make clean # try again $ make distclean # try again $ ./buildconf –force $ ./configure # try again If compilation fails, try (subsequently): Might be needed after git pull/git checkout
34. @arnoutboks #phpsrb https://wiki.php.net/ internals/windows/stepbystepbuild Building for Windows
35. @arnoutboks #phpsrb
36. @arnoutboks #phpsrb • ramsey/vagrant-php-src- dev • rlerdorf/php7dev Vagrant boxes for compiling PHP
37. @arnoutboks #phpsrb Or use Docker: aboks/php-src-devtools
38. @arnoutboks #phpsrb Using php-src-devtools $ composer global require aboks/php-src- devtools $ git clone https://github.com/php/php- src.git && cd php-src $ php-src-devtools build
39. Running tests for PHP Human-driven CI
40. @arnoutboks #phpsrb Running tests $ sapi/cli/php run-tests.php –p `pwd`/sapi/cli/php
41. @arnoutboks #phpsrb Running tests $ sapi/cli/php run-tests.php –p `pwd`/sapi/cli/php $ sapi/cli/php run-tests.php -P
42. @arnoutboks #phpsrb Running tests $ sapi/cli/php run-tests.php –p `pwd`/sapi/cli/php $ sapi/cli/php run-tests.php -P $ make test # (or, with php-src-devtools) $ php-src-devtools test
43. @arnoutboks #phpsrb Running tests $ make test […] PASS Trivial "Hello World" test [tests/basic/001.phpt] SKIP Check libcurl config on windows [ext/curl/tests/check_win_config.phpt] reason: for windows only FAIL Compiled regex cache limit [ext/pcre/tests/cache_limit.phpt] XFAIL Inconsistencies when accessing protected members [Zend/tests/access_modifiers_008.phpt] XFAIL REASON: Discussion: http://marc.info/?l=php- internals&m=120221184420957&w=2 […10000 more lines of output…]
44. @arnoutboks #phpsrb Running tests $ make test […] ========================================= TEST RESULT SUMMARY ----------------------------------------- Number of tests : 14896 12520 Tests skipped : 2376 ( 16.0%) -------- Tests warned : 2 ( 0.0%) ( 0.0%) Tests failed : 175 ( 1.2%) ( 1.4%) Expected fail : 44 ( 0.3%) ( 0.4%) Tests passed : 12299 ( 82.6%) ( 98.2%) ----------------------------------------- Time taken : 2937 seconds
45. @arnoutboks #phpsrb Running tests $ make test […] You may have found a problem in PHP. This report can be automatically sent to the PHP QA team at http://qa.php.net/reports and http://news.php.net/php.qa.reports This gives us a better understanding of PHP's behavior. If you don't want to send the report immediately you can choose option "s" to save it. You can then email it to qa- reports@lists.php.net later. Do you want to send this report now? [Yns]:|
46. @arnoutboks #phpsrb Options for running tests $ make test TESTS=path/to/my/test.phpt $ make test TESTS=ext/dom $ make test TESTS="--verbose ext/dom" $ make test TESTS=--help
47. Writing tests for PHP “the best bug report”
48. @arnoutboks #phpsrb Steps to reproduce for bug #67474 Test script: --------------- $doc = new DOMDocument(); $doc->loadXML('<root xmlns:x="x"><a/><x:a/></root>'); $list = $doc->getElementsByTagNameNS('', 'a'); echo $list->length; Expected result: ---------------- 1 Actual result: -------------- 0
49. @arnoutboks #phpsrb Testing tools Typical PHP project: • Written in PHP • Tests written in PHP (PHPUnit, PHPSpec, CodeCeption) The PHP core: • Written in C • Tests written in …
50. @arnoutboks #phpsrb PHP is tested using PHPT tests No C skills required
51. @arnoutboks #phpsrb PHPT tests • Basically plaintext with sections • Some sections (can) contain PHP code • Let PHP print some output… • …and check against expected output
52. @arnoutboks #phpsrb Very simple PHPT test --TEST-- Basic arithmetic - addition --FILE-- <?php var_dump(42 + 1); ?> --EXPECT-- int(43)
53. @arnoutboks #phpsrb Very simple PHPT test --TEST-- Basic arithmetic - addition --FILE-- <?php var_dump(42 + 1); ?> --EXPECT-- int(43)
54. @arnoutboks #phpsrb Folder structure tests/ and Zend/tests/ tests for the Zend engine ext/standard/tests /<group>/ tests for ‘standard’ extension (array, string, filesystem functions, etc.) ext/<name>/tests/ tests for extensions sapi/<name>/tests/ tests for specific SAPI’s (CGI, CLI, PHP-FPM, etc.)
55. @arnoutboks #phpsrb Naming PHPT files bug<bugid>.phpt tests for bugs <func>_basic[<no>].phpt <func>_variation[<no>].phpt <func>_error[<no>].phpt tests for specific function: basic behavior, variations (edge cases, etc.) and errors <extname><no>.phpt general tests for extension
56. @arnoutboks #phpsrb PHPT test for bug #67474 --TEST-- Bug #67474 getElementsByTagNameNS and default namespace --FILE-- <?php $doc = new DOMDocument(); $doc->loadXML('<root xmlns:x="x"><a/><x:a/></root>'); $list = $doc->getElementsByTagNameNS('', 'a'); var_dump($list->length); ?> --EXPECT-- int(1)
57. @arnoutboks #phpsrb Running our PHPT test $ make test TESTS=ext/dom/tests/bug67474.phpt […] ============================================= FAILED TEST SUMMARY --------------------------------------------- Bug #67474 getElementsByTagNameNS and default namespace [ext/dom/tests/bug67474.phpt] =============================================
58. @arnoutboks #phpsrb Running our PHPT test Files generated for our failing test: bug67474.php contents of the FILE section bug67474.sh shell script for running the .php file bug67474.exp expected output bug67474.out actual output bug67474.diff diff between expected and actual bug67474.log log file, including the expected and actual output
59. @arnoutboks #phpsrb Running our PHPT test $ cat ext/dom/tests/bug67474.log ---- EXPECTED OUTPUT int(1) ---- ACTUAL OUTPUT int(0) ---- FAILED
60. @arnoutboks #phpsrb Running our PHPT test
61. @arnoutboks #phpsrb Sections in PHPT files SKIPIF: Skips the test if the code in SKIPIF generates output containing ‘skip’ somewhere --SKIPIF-- <?php if(!extension_loaded('dom')) { die('skip dom extension not available'); } ?>
62. @arnoutboks #phpsrb Sections in PHPT files Tip: Extensions usually have a skipif.inc shared between tests: --SKIPIF-- <?php require_once('skipif.inc'); ?>
63. @arnoutboks #phpsrb Sections in PHPT files GET, POST, PUT, COOKIE, HEADERS: Simulate HTTP input to the PHP script in FILE --GET-- foo=bar&baz=qux --COOKIE-- foo=bar;baz=qux --FILE-- <?php var_dump($_GET['foo'] . $_COOKIE['foo']); ?> --EXPECT-- string(6) "barbar"
64. @arnoutboks #phpsrb Sections in PHPT files EXPECTF, EXPECTREGEX: Expect the output to match a certain format --FILE-- <?php $fp = fopen(__FILE__, 'r'); var_dump($fp); ?> --EXPECTF-- resource(%d) of type (stream)
65. @arnoutboks #phpsrb Sections in PHPT files CLEAN: Cleans up after the test --FILE-- <?php touch(__DIR__ . '/foo.tmp'); var_dump(file_exists(__DIR__ . '/foo.tmp')); ?> --EXPECT-- bool(true) --CLEAN-- <?php unlink(__DIR__ . '/foo.tmp'); ?>
66. @arnoutboks #phpsrb Sections in PHPT files INI: Specifies custom php.ini directives for the test --INI-- precision=7 --FILE-- <?php var_dump(pi()); ?> --EXPECT-- float(3.141593)
67. @arnoutboks #phpsrb Sections in PHPT files XFAIL: Indicates the test is expected to fail, and gives an explanation why This is usually used for hard-to-fix bugs or bugs in upstream code. --XFAIL-- See bug #xxxx
68. @arnoutboks #phpsrb Easy way to get started without C skills
69. @arnoutboks #phpsrb Finding untested code gcov.php.net
70. @arnoutboks #phpsrb Resources • https://qa.php.net/write-test.php • https://www.sammyk.me/compiling-php-from-source- writing-tests-for-php-source • https://phptestfest.org/tutorials/ • http://www.phpinternalsbook.com/#testing-php- source • https://github.com/PHPTestFestBrasil/phptt • https://gist.github.com/SammyK/4a5cf70d0973731d0c 85b151a323ea2d
71. Editing the PHP source Your own custom PHP
72. @arnoutboks #phpsrb A shot at fixing #67474: recap <something xmlns:foo="http://www.example.com"> <foo:bar /> <bar /> </something> <?php $doc = /* … (DOMDocument) */; $doc->getElementsByTagNameNS( "", "bar" )->length; // returns 0!
73. @arnoutboks #phpsrb A shot at fixing #67474 php-src/ext/dom/ • attr.c • document.c • dom_ce.h • dom_fe.h • element.c • node.c • php_dom.c • xpath.c • …
74. @arnoutboks #phpsrb A shot at fixing #67474 const zend_function_entry php_dom_document_class_functions[] = { // ... PHP_FALIAS(createAttributeNS, dom_document_create_attribute_ns, arginfo_dom_document_create_attribute_ns) PHP_FALIAS(getElementsByTagNameNS, dom_document_get_elements_by_tag_name_ns, arginfo_dom_document_get_elements_by_tag_name_ns) PHP_FALIAS(getElementById, dom_document_get_element_by_id, arginfo_dom_document_get_element_by_id) // ... PHP_ME(domdocument, __construct, arginfo_dom_document_construct, ZEND_ACC_PUBLIC) PHP_FE_END };
75. @arnoutboks #phpsrb C macros
76. @arnoutboks #phpsrb C macros
77. @arnoutboks #phpsrb C macros #define MIN(a,b) a < b ? a : b int c = MIN(42,7) // ^ is converted into // int c = 42 < 7 ? 42 : 7
78. @arnoutboks #phpsrb A shot at fixing #67474 const zend_function_entry php_dom_document_class_functions[] = { // ... PHP_FALIAS(createAttributeNS, dom_document_create_attribute_ns, arginfo_dom_document_create_attribute_ns) PHP_FALIAS(getElementsByTagNameNS, dom_document_get_elements_by_tag_name_ns, arginfo_dom_document_get_elements_by_tag_name_ns) PHP_FALIAS(getElementById, dom_document_get_element_by_id, arginfo_dom_document_get_element_by_id) // ... PHP_ME(domdocument, __construct, arginfo_dom_document_construct, ZEND_ACC_PUBLIC) PHP_FE_END };
79. @arnoutboks #phpsrb A shot at fixing #67474 PHP_FUNCTION(dom_document_get_elements_by_tag_name_ns) { // ... if (zend_parse_method_parameters(ZEND_NUM_ARGS(), getThis(), "Oss", &id, dom_document_class_entry, &uri, &uri_len, &name, &name_len) == FAILURE) { return; } // ... local = xmlCharStrndup(name, name_len); nsuri = xmlCharStrndup(uri, uri_len); dom_namednode_iter(intern, 0, namednode, NULL, local, nsuri); }
80. @arnoutboks #phpsrb zend_parse_parameters (‘ZPP’) PHP_FUNCTION(dom_document_get_elements_by_tag_name_ns) { // ... if (zend_parse_method_parameters(ZEND_NUM_ARGS(), getThis(), "Oss", &id, dom_document_class_entry, &uri, &uri_len, &name, &name_len) == FAILURE) { return; } // ... local = xmlCharStrndup(name, name_len); nsuri = xmlCharStrndup(uri, uri_len); dom_namednode_iter(intern, 0, namednode, NULL, local, nsuri); } s: string s: string O: object of given class
81. @arnoutboks #phpsrb zend_parse_parameters (‘ZPP’) Specifier Type a array b boolean d double/float l long/int o object (any type) O object (specific type) r resource s string z mixed
82. @arnoutboks #phpsrb zend_parse_parameters (‘ZPP’) Modifier Effect * variable number of arguments (0 or more) + variable number of arguments (1 or more) ! optional argument | remaining arguments are optional See README.PARAMETER_PARSING_API
83. @arnoutboks #phpsrb A shot at fixing #67474 PHP_FUNCTION(dom_document_get_elements_by_tag_name_ns) { // ... if (zend_parse_method_parameters(ZEND_NUM_ARGS(), getThis(), "Oss", &id, dom_document_class_entry, &uri, &uri_len, &name, &name_len) == FAILURE) { return; } // ... local = xmlCharStrndup(name, name_len); nsuri = xmlCharStrndup(uri, uri_len); dom_namednode_iter(intern, 0, namednode, NULL, local, nsuri); }
84. @arnoutboks #phpsrb A shot at fixing #67474 xmlNode *dom_get_elements_by_tag_name_ns_raw( xmlNodePtr nodep, char *ns, char *local /* ... */ ) { // ... if ( ns == NULL || (nodep->ns != NULL && ( xmlStrEqual(nodep->ns->href, (xmlChar *)ns) || xmlStrEqual((xmlChar *)"*", (xmlChar *)ns) )) ) { /* namespace matches */ } // ... } Eventually:
85. @arnoutboks #phpsrb A shot at fixing #67474 xmlNode *dom_get_elements_by_tag_name_ns_raw( xmlNodePtr nodep, char *ns, char *local /* ... */ ) { // ... if ( ns == NULL || (nodep->ns != NULL && ( xmlStrEqual(nodep->ns->href, (xmlChar *)ns) || xmlStrEqual((xmlChar *)"*", (xmlChar *)ns) )) ) { /* namespace matches */ } // ... } Eventually: element to ‘test’ filter namespace and local name
86. @arnoutboks #phpsrb A shot at fixing #67474 xmlNode *dom_get_elements_by_tag_name_ns_raw( xmlNodePtr nodep, char *ns, char *local /* ... */ ) { // ... if ( ns == NULL || (nodep->ns != NULL && ( xmlStrEqual(nodep->ns->href, (xmlChar *)ns) || xmlStrEqual((xmlChar *)"*", (xmlChar *)ns) )) ) { /* namespace matches */ } // ... } Eventually: “no namespace filter”
87. @arnoutboks #phpsrb A shot at fixing #67474 xmlNode *dom_get_elements_by_tag_name_ns_raw( xmlNodePtr nodep, char *ns, char *local /* ... */ ) { // ... if ( ns == NULL || (nodep->ns != NULL && ( xmlStrEqual(nodep->ns->href, (xmlChar *)ns) || xmlStrEqual((xmlChar *)"*", (xmlChar *)ns) )) ) { /* namespace matches */ } // ... } Eventually: “node has a namespace”, and “it matches the filter” or “filter is a wildcard”
88. @arnoutboks #phpsrb A shot at fixing #67474 xmlNode *dom_get_elements_by_tag_name_ns_raw( xmlNodePtr nodep, char *ns, char *local /* ... */ ) { // ... if ( ns == NULL || (nodep->ns == NULL && !strcmp(ns, "")) || (nodep->ns != NULL && ( xmlStrEqual(nodep->ns->href, (xmlChar *)ns) || xmlStrEqual((xmlChar *)"*", (xmlChar *)ns) )) ) { /* namespace matches */ } // ... } Fix: “node has empty namespace”, and “filter is empty namespace”
89. @arnoutboks #phpsrb A shot at fixing #67474 $ make test TESTS=ext/dom/tests/bug67474.phpt […] ============================================= Running selected tests. PASS Bug #67474 getElementsByTagNameNS and default namespace [ext/dom/tests/bug67474.phpt] ============================================= Number of tests : 1 1 Tests passed : 1 (100.0%) (100.0%)
90. @arnoutboks #phpsrb PR for #67474 Submit bug fixes to the oldest supported branch: http://php.net/supported-versions.php
91. @arnoutboks #phpsrb The Release Managers PHP 7.1 Davey Shafik @dshafik Joe Watkins @krakjoe PHP 7.2 Remi Collet @RemiCollet Sara Golemon @SaraMG PHP 7.3 Christoph M. Becker @cmbecker69 Stanislav Malyshev @smalyshev
92. @arnoutboks #phpsrb PR for #67474: 2 hours later…
93. @arnoutboks #phpsrb It’s not THAT difficult • Read past the C details and macros • Focus on the logic • See where variables come from and go to • Try and see what happens • Rely on the tests
94. @arnoutboks #phpsrb You can do this!
95. @arnoutboks #phpsrb Bug fixes vs. features • Bug fixes • PR against oldest supported branch • No RFC needed • Refer to bug in bug tracker • Features • PR against master • Formal RFC needed
96. @arnoutboks #phpsrb RFC Process • Introduce idea, measure initial reaction • Formal proposal • Discussion period • Voting See https://wiki.php.net/rfc/howto & https://benramsey.com/talks/2015/06/dpc-contributing-core/
97. @arnoutboks #phpsrb Resources • http://php.net/internals • https://wiki.php.net/internals • https://wiki.php.net/internals/references • http://www.phpinternalsbook.com/ • http://blog.jpauli.tech/ • https://nikic.github.io/ • https://blog.ircmaxell.com/search/label/PHP-Internals • https://www.sammyk.me/how-to-find-and-patch-a- bug-in-php-source-php-internals • https://externals.io
98. @arnoutboks #phpsrb Some time later…
99. Documentation for PHP Contributing to the manual
100. @arnoutboks #phpsrb edit.php.net PHP Docbook Online Editor ‘Easiest’ way to get started (if you can figure out how it works)
101. @arnoutboks #phpsrb edit.php.net
102. @arnoutboks #phpsrb edit.php.net
103. @arnoutboks #phpsrb edit.php.net
104. @arnoutboks #phpsrb 1. Find the correct file Under “All files” in the left menu Top-level directory per language • reference/<ext|group>/ • functions/<function>.xml • <class>.xml • <class>/<method>.xml • language/<feature>.xml
105. @arnoutboks #phpsrb 1. Find the correct file Tip: Use the “edit” link from the documentation itself
106. @arnoutboks #phpsrb 2. Make your changes Documentation is written using DocBook XML http://tdg.docbook.org/tdg/5.2/
107. @arnoutboks #phpsrb 2. Make your changes Documentation is written using DocBook XML (or just peek in other docs)
108. @arnoutboks #phpsrb 3. Preview changes Seems broken at the moment
109. @arnoutboks #phpsrb 4. Submit as patch
110. @arnoutboks #phpsrb Tip: submit a docs patch instead of user note
111. @arnoutboks #phpsrb Documentation karma Commit changes yourself? Apply for docs karma! http://doc.php.net/tutorial/ joining.php
112. @arnoutboks #phpsrb Don’t like edit.php.net? Make it better!
113. @arnoutboks #phpsrb Don’t like edit.php.net? Or set up your own development environment: https://www.sammyk.me/how-to-contribute-to-php- documentation
114. @arnoutboks #phpsrb Where to help? • Bugs of type “Doc” in bug tracker • check-missing-docs.php • “Failures to meet strict standards” (in edit.php.net sidebar) • Translations • Missing translations • Out-of-date translations • Translations needing review • Translations with errors
115. @arnoutboks #phpsrb Where to help?
116. Recap Ways to contribute to PHP
117. @arnoutboks #phpsrb Numerous ways to contribute • Bug reports • Bug triaging • Running tests • Writing tests • Bug fixes • New features • Documentation patches • Documentation translations • Tools
118. @arnoutboks #phpsrb Why contribute? • Get ‘own’ bugs fixed • Fix ‘own’ bugs • Make PHP better • Make PHP more popular • Learn PHP • Learn C • Give back to the community
119. @arnoutboks #phpsrb You don’t have to be an expert to contribute to the PHP core
120. @arnoutboks #phpsrb Feedback & Questions @arnoutboks @arnoutboks @aboks Arnout Boks Please leave your feedback on joind.in: https://joind.in/talk/7d50f
121. @arnoutboks #phpsrb Image Credits • https://photojournal.jpl.nasa.gov/jpeg/PIA19058.jpg • https://www.flickr.com/photos/vivianejl/22990832 • https://www.flickr.com/photos/dhuiz/13609080315/ • https://www.flickr.com/photos/gotovan/8671348572 • https://www.flickr.com/photos/sidelong/246816211 • https://www.flickr.com/photos/pezon64/23764268828 • https://www.flickr.com/photos/crdot/6855538268/ • https://www.flickr.com/photos/borkurdotnet/9682277597