Tweet
Tweet

Slide 1

Slide 1 text

Getting started with PHP core development @arnoutboks Arnout Boks #phpce17 04 nov 2017

Slide 2

Slide 2 text

@arnoutboks #phpce17 PHP Open Source projects

Slide 3

Slide 3 text

@arnoutboks #phpce17 PHP Open Source projects 4175 contributors 418 contributors 689 contributors 1497 contributors

Slide 4

Slide 4 text

@arnoutboks #phpce17 PHP Open Source projects 4175 contributors 418 contributors 689 contributors 1497 contributors

Slide 5

Slide 5 text

@arnoutboks #phpce17 PHP Open Source projects 4175 contributors 418 contributors 689 contributors 1497 contributors 497 contributors?

Slide 6

Slide 6 text

@arnoutboks #phpce17 We all use PHP intensively Why not contribute something back?

Slide 7

Slide 7 text

@arnoutboks #phpce17 The catch

Slide 8

Slide 8 text

@arnoutboks #phpce17 The core

Slide 9

Slide 9 text

@arnoutboks #phpce17 The core

Slide 10

Slide 10 text

@arnoutboks #phpce17 My own journey to the core

Slide 11

Slide 11 text

@arnoutboks #phpce17 Once upon a time… getElementsByTagName( "bar" )->length;

Slide 12

Slide 12 text

@arnoutboks #phpce17 Once upon a time… getElementsByTagName( "bar" )->length; // returns 2

Slide 13

Slide 13 text

@arnoutboks #phpce17 Once upon a time… getElementsByTagNameNS( "http://www.example.com", "bar" )->length;

Slide 14

Slide 14 text

@arnoutboks #phpce17 Once upon a time… getElementsByTagNameNS( "http://www.example.com", "bar" )->length; // returns 1

Slide 15

Slide 15 text

@arnoutboks #phpce17 Once upon a time… getElementsByTagNameNS( "", "bar" )->length;

Slide 16

Slide 16 text

@arnoutboks #phpce17 Once upon a time… getElementsByTagNameNS( "", "bar" )->length; // returns 0!

Slide 17

Slide 17 text

@arnoutboks #phpce17 Once upon a time…

Slide 18

Slide 18 text

Reporting bugs Gotta squash them all

Slide 19

Slide 19 text

@arnoutboks #phpce17 bugs.php.net PHP bug tracker

Slide 20

Slide 20 text

@arnoutboks #phpce17 Write good bug reports https://bugs.php.net/how-to-report.php

Slide 21

Slide 21 text

@arnoutboks #phpce17 Search for existing bugs

Slide 22

Slide 22 text

@arnoutboks #phpce17 Sharpen bug details Report different platform/version: Don’t post “me too” comments – Do post other relevant details

Slide 23

Slide 23 text

@arnoutboks #phpce17 Help triaging bugs! https://bugs.php.net/random

Slide 24

Slide 24 text

Building PHP from git Living on the edge

Slide 25

Slide 25 text

@arnoutboks #phpce17 1. Install dependencies • git • build-essential • autoconf • automake • libtool • re2c • bison • libxml2-dev Using apt-get, yum or similar

Slide 26

Slide 26 text

@arnoutboks #phpce17 2. Clone php-src $ git clone https://github.com/php/php- src.git

Slide 27

Slide 27 text

@arnoutboks #phpce17 3. Generate ./configure script $ ./buildconf Uses autoconf to build ./configure from: • configure.ac • acinclude.m4 • sapi/*/config.m4 • ext/*/config.m4

Slide 28

Slide 28 text

@arnoutboks #phpce17 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

Slide 29

Slide 29 text

@arnoutboks #phpce17 5. Compile $ make $ make –j`nproc` To use all available cores (faster):

Slide 30

Slide 30 text

@arnoutboks #phpce17 6. Run! $ sapi/cli/php --version Binaries are in sapi/cli/php and sapi/cgi/php-cgi:

Slide 31

Slide 31 text

@arnoutboks #phpce17 Subsequent builds $ make Just run Recompiles only files that have changed

Slide 32

Slide 32 text

@arnoutboks #phpce17 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

Slide 33

Slide 33 text

@arnoutboks #phpce17 https://wiki.php.net/ internals/windows/stepbystepbuild Building for Windows

Slide 34

Slide 34 text

@arnoutboks #phpce17

Slide 35

Slide 35 text

@arnoutboks #phpce17 Vagrant boxes for compiling PHP core

Slide 36

Slide 36 text

@arnoutboks #phpce17 ramsey/vagrant-php-src-dev

Slide 37

Slide 37 text

@arnoutboks #phpce17 rlerdorf/php7dev

Slide 38

Slide 38 text

Running tests for PHP Human-driven CI

Slide 39

Slide 39 text

@arnoutboks #phpce17 Running tests $ sapi/cli/php run-tests.php –p `pwd`/sapi/cli/php

Slide 40

Slide 40 text

@arnoutboks #phpce17 Running tests $ sapi/cli/php run-tests.php –p `pwd`/sapi/cli/php $ sapi/cli/php run-tests.php -P

Slide 41

Slide 41 text

@arnoutboks #phpce17 Running tests $ sapi/cli/php run-tests.php –p `pwd`/sapi/cli/php $ sapi/cli/php run-tests.php -P $ make test

Slide 42

Slide 42 text

@arnoutboks #phpce17 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…]

Slide 43

Slide 43 text

@arnoutboks #phpce17 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

Slide 44

Slide 44 text

@arnoutboks #phpce17 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- [email protected] later. Do you want to send this report now? [Yns]:|

Slide 45

Slide 45 text

@arnoutboks #phpce17 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

Slide 46

Slide 46 text

Writing tests for PHP “the best bug report”

Slide 47

Slide 47 text

@arnoutboks #phpce17 Steps to reproduce for bug #67474 Test script: --------------- $doc = new DOMDocument(); $doc->loadXML(''); $list = $doc->getElementsByTagNameNS('', 'a'); echo $list->length; Expected result: ---------------- 1 Actual result: -------------- 0

Slide 48

Slide 48 text

@arnoutboks #phpce17 Testing tools My PHP projects: • Written in PHP • Tests written in PHP (PHPUnit, PHPSpec, CodeCeption) The PHP core: • Written in C • Tests written in …

Slide 49

Slide 49 text

@arnoutboks #phpce17 PHP is tested using PHPT tests No C skills required

Slide 50

Slide 50 text

@arnoutboks #phpce17 PHPT tests • Basically plaintext with sections • Some sections (can) contain PHP code • Let PHP print some output… • …and check against expected output

Slide 51

Slide 51 text

@arnoutboks #phpce17 Very simple PHPT test --TEST-- Basic arithmetic - addition --FILE-- --EXPECT-- int(43)

Slide 52

Slide 52 text

@arnoutboks #phpce17 Very simple PHPT test --TEST-- Basic arithmetic - addition --FILE-- --EXPECT-- int(43)

Slide 53

Slide 53 text

@arnoutboks #phpce17 Folder structure tests/ and Zend/tests/ tests for the Zend engine ext/standard/tests // tests for ‘standard’ extension (array, string, filesystem functions, etc.) ext//tests/ tests for extensions sapi//tests/ tests for specific SAPI’s (CGI, CLI, PHP-FPM, etc.)

Slide 54

Slide 54 text

@arnoutboks #phpce17 Naming PHPT files bug.phpt tests for bugs _basic[].phpt _variation[].phpt _error[].phpt tests for specific function: basic behavior, variations (edge cases, etc.) and errors .phpt general tests for extension

Slide 55

Slide 55 text

@arnoutboks #phpce17 PHPT test for bug #67474 --TEST-- Bug #67474 getElementsByTagNameNS and default namespace --FILE-- loadXML(''); $list = $doc->getElementsByTagNameNS('', 'a'); var_dump($list->length); ?> --EXPECT-- int(1)

Slide 56

Slide 56 text

@arnoutboks #phpce17 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] =============================================

Slide 57

Slide 57 text

@arnoutboks #phpce17 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

Slide 58

Slide 58 text

@arnoutboks #phpce17 Running our PHPT test $ cat ext/dom/tests/bug67474.log ---- EXPECTED OUTPUT int(1) ---- ACTUAL OUTPUT int(0) ---- FAILED

Slide 59

Slide 59 text

@arnoutboks #phpce17 Running our PHPT test

Slide 60

Slide 60 text

@arnoutboks #phpce17 Sections in PHPT files SKIPIF: Skips the test if the code in SKIPIF generates output containing ‘skip’ somewhere --SKIPIF--

Slide 61

Slide 61 text

@arnoutboks #phpce17 Sections in PHPT files Tip: Extensions usually have a skipif.inc shared between tests: --SKIPIF--

Slide 62

Slide 62 text

@arnoutboks #phpce17 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-- --EXPECT-- string(6) "barbar"

Slide 63

Slide 63 text

@arnoutboks #phpce17 Sections in PHPT files EXPECTF, EXPECTREGEX: Expect the output to match a certain format --FILE-- --EXPECTF-- resource(%d) of type (stream)

Slide 64

Slide 64 text

@arnoutboks #phpce17 Sections in PHPT files CLEAN: Cleans up after the test --FILE-- --EXPECT-- bool(true) --CLEAN--

Slide 65

Slide 65 text

@arnoutboks #phpce17 Sections in PHPT files INI: Specifies custom php.ini directives for the test --INI-- precision=7 --FILE-- --EXPECT-- float(3.141593)

Slide 66

Slide 66 text

@arnoutboks #phpce17 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

Slide 67

Slide 67 text

@arnoutboks #phpce17 Easy way to get started without C skills

Slide 68

Slide 68 text

@arnoutboks #phpce17 Finding untested code gcov.php.net

Slide 69

Slide 69 text

@arnoutboks #phpce17 PHP TestFest 2017 • September-December 2017 • Participate through a local User Group or by yourself • Write tests for PHP core • Win prizes! See phptestfest.org

Slide 70

Slide 70 text

@arnoutboks #phpce17 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/herdphp/docker-phpqa • https://gist.github.com/SammyK/4a5cf70d0973731d0c 85b151a323ea2d

Slide 71

Slide 71 text

Editing the PHP source Your own custom PHP

Slide 72

Slide 72 text

@arnoutboks #phpce17 A shot at fixing #67474: recap getElementsByTagNameNS( "", "bar" )->length; // returns 0!

Slide 73

Slide 73 text

@arnoutboks #phpce17 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 • …

Slide 74

Slide 74 text

@arnoutboks #phpce17 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 };

Slide 75

Slide 75 text

@arnoutboks #phpce17 A shot at fixing #67474

Slide 76

Slide 76 text

@arnoutboks #phpce17 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 };

Slide 77

Slide 77 text

@arnoutboks #phpce17 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); }

Slide 78

Slide 78 text

@arnoutboks #phpce17 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

Slide 79

Slide 79 text

@arnoutboks #phpce17 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

Slide 80

Slide 80 text

@arnoutboks #phpce17 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

Slide 81

Slide 81 text

@arnoutboks #phpce17 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); }

Slide 82

Slide 82 text

@arnoutboks #phpce17 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) ))) { { } // ... } Eventually:

Slide 83

Slide 83 text

@arnoutboks #phpce17 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) ))) { { } // ... } Eventually: element to ‘test’ filter namespace and local name

Slide 84

Slide 84 text

@arnoutboks #phpce17 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) ))) { { } // ... } Eventually: “no namespace filter”

Slide 85

Slide 85 text

@arnoutboks #phpce17 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) ))) { { } // ... } Eventually: “node has a namespace”, and “it matches the filter” or “filter is a wildcard”

Slide 86

Slide 86 text

@arnoutboks #phpce17 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) ))) { { } // ... } Fix: “node has empty namespace”, and “filter is empty namespace”

Slide 87

Slide 87 text

@arnoutboks #phpce17 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%)

Slide 88

Slide 88 text

@arnoutboks #phpce17 PR for #67474 Submit bug fixes to the oldest supported branch: http://php.net/supported-versions.php

Slide 89

Slide 89 text

@arnoutboks #phpce17 PR for #67474: 2 hours later…

Slide 90

Slide 90 text

@arnoutboks #phpce17 It’s not THAT difficult • Read past the C details • See where variables come from and go to • Try and see what happens • Rely on the tests

Slide 91

Slide 91 text

@arnoutboks #phpce17 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

Slide 92

Slide 92 text

@arnoutboks #phpce17 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/

Slide 93

Slide 93 text

@arnoutboks #phpce17 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

Slide 94

Slide 94 text

@arnoutboks #phpce17 Some time later…

Slide 95

Slide 95 text

Documentation for PHP Contributing to the manual

Slide 96

Slide 96 text

@arnoutboks #phpce17 edit.php.net PHP Docbook Online Editor ‘Easiest’ way to get started (if you can figure out how it works)

Slide 97

Slide 97 text

@arnoutboks #phpce17 edit.php.net

Slide 98

Slide 98 text

@arnoutboks #phpce17 edit.php.net

Slide 99

Slide 99 text

@arnoutboks #phpce17 edit.php.net

Slide 100

Slide 100 text

@arnoutboks #phpce17 1. Find the correct file Under “All files” in the left menu Top-level directory per language • reference// • functions/.xml • .xml • /.xml • language/.xml

Slide 101

Slide 101 text

@arnoutboks #phpce17 1. Find the correct file Tip: Use the “edit” link from the documentation itself

Slide 102

Slide 102 text

@arnoutboks #phpce17 2. Make your changes Documentation is written using DocBook XML http://tdg.docbook.org/tdg/5.2/

Slide 103

Slide 103 text

@arnoutboks #phpce17 2. Make your changes Documentation is written using DocBook XML (or just peek in other docs)

Slide 104

Slide 104 text

@arnoutboks #phpce17 3. Preview changes Seems broken at the moment

Slide 105

Slide 105 text

@arnoutboks #phpce17 4. Submit as patch

Slide 106

Slide 106 text

@arnoutboks #phpce17 Tip: submit a docs patch instead of user note

Slide 107

Slide 107 text

@arnoutboks #phpce17 Documentation karma Commit changes yourself? Apply for docs karma! http://doc.php.net/tutorial/ joining.php

Slide 108

Slide 108 text

@arnoutboks #phpce17 Don’t like edit.php.net? Make it better!

Slide 109

Slide 109 text

@arnoutboks #phpce17 Don’t like edit.php.net? Or set up your own development environment: https://www.sammyk.me/how-to-contribute-to-php- documentation

Slide 110

Slide 110 text

@arnoutboks #phpce17 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

Slide 111

Slide 111 text

@arnoutboks #phpce17 Where to help?

Slide 112

Slide 112 text

Recap Ways to contribute to PHP

Slide 113

Slide 113 text

@arnoutboks #phpce17 Numerous ways to contribute • Bug reports • Bug triaging • Running tests • Writing tests • Bug fixes • New features • Documentation patches • Documentation translations • Tools

Slide 114

Slide 114 text

@arnoutboks #phpce17 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

Slide 115

Slide 115 text

@arnoutboks #phpce17 You don’t have to be an expert to contribute to the PHP core

Slide 116

Slide 116 text

@arnoutboks #phpce17 Feedback & Questions @arnoutboks @arnoutboks @aboks Arnout Boks Please leave your feedback on joind.in: https://joind.in/talk/3e087

Slide 117

Slide 117 text

@arnoutboks #phpce17 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