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mod_zeroconf

mod_zeroconf. A Zero Configuration Registration Module for Apache 2.0. Sander Temme. sander@temme.net. Agenda. Technology Overview Zeroconf Applications mod_zeroconf for Apache 2.0 Design Demo Code Walkthrough Q&A. What is Zeroconf?. IETF Working Group Formed in Sept. 1999

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mod_zeroconf

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  1. mod_zeroconf A Zero Configuration Registration Module for Apache 2.0

  2. Sander Temme sander@temme.net

  3. Agenda • Technology Overview • Zeroconf Applications • mod_zeroconf for Apache 2.0 • Design • Demo • Code Walkthrough • Q&A

  4. What is Zeroconf? • IETF Working Group • Formed in Sept. 1999 • Usability of TCP/IP • Enhancements to Existing Protocols • Not SLP, …

  5. What is Zeroconf?

  6. What is Zeroconf? • TCP/IP Autoconfiguration • Network naming • Service Browsing

  7. Technology Overview • Link-local addressing • multicast DNS • DNS Service-Discovery

  8. Link-local Addressing • No Central Address Server • Pick a Random Address • In 169.254.0.0/16 range • Address Defense • Can Work With Centrally Assigned Addresses

  9. Link-local Addressing 169.254.1.219 Printer 169.254.10.29 Network 169.254.4.51 169.254.4.51

  10. mDNS • DNS-like Protocol • Every Host Runs Responder • Hosts Pick Own Names • Communication over IP Multicast • Link-local • Resolves to Link-local or Regular Address

  11. mDNS PC_BILL 169.254.1.219 Printer 169.254.10.29 lj21569478 Network Mac_Steve PC_LARRY 169.254.4.51 169.254.4.51

  12. DNS-SD • Service Publishing and Browsing • Uses Existing DNS Record types • User Sees Only Service Names • Works With mDNS or Regular DNS

  13. DNS-SD Laserjet, Closet Under the Stairs PC_BILL 169.254.1.219 Printer 169.254.10.29 Bill’s Files lj21569478 Network Mac_Steve PC_LARRY 169.254.4.51 169.254.4.51 Steve’s Movies Larry’s Tunes

  14. Applications • Printer Configuration • Music/Photo/Document Sharing • Distributed Compilation • Network gaming • … (the sky is the limit)

  15. Peer to Peer Chat

  16. Sharing Tunes

  17. Sharing Sites

  18. Platform support • MacOSX 10.2 and up • Linux: several initiatives • Mandrake put it in the distribution • No one else so far • Windows… • Link-local addressing works • Third-party mDNSResponder

  19. Windows and Rendezvous

  20. Zeroconf on Linux • May need Link-local address • http://zeroconf.sourceforge.net/?selected=zcip • http://www.zeroconf.org/AVH-IPv4LL.c • Need mDNSResponder • tmdns or • Apple’s mDNSResponder or • http://developer.apple.com/darwin/projects/rendezvous/ • zmdns, openmdns (search SourceForge) or • Howl or • Embeddable: mdnsd http://www.dotlocal.org/mdnsd/ • Running Java? Try http://jmdns.sourceforge.net/

  21. Zeroconf and Apache • Goals • Publish Apache http services • Work with external mDNSResponder • Support Apache 2.0 • ASF Licensed • Existing initiatives • mod_rendezvous: Apache 1.3, Mac only • mod_rendezvous_apple: ditto • mdnsmod: No code on SF, in ‘planning stage’

  22. External mDNSResponder • Apple mDNSResponder • No client libraries • zmdns • Wrapper around Apple code • Mixed BSD, APSL • Alpha stage • openmdns, tmdns • GPL

  23. Howl • Based on Apple code • Modified BSD license • At version 0.9.3, API should be stable • Linux, Windows, MacOSX, … • Plugin for Windows Internet Explorer http://www.porchdogsoft.com/products/

  24. Configuration # En/disable Zeroconf server-wide. Default: off Zeroconf {on|off} # Register main server or virtualhost container. ZeroconfRegister “service name” [/partialpath] # This is part of the core ServerName hostname:port

  25. Demo

  26. mod_zeroconf Design Apache 2.0 Core Virtual Host Config Info mod_zeroconf mDNS Callbacks Howl mDNSResponder mDNS Registration

  27. What Gets Registered? • Service Name • SRV information: port, hostname, partial URI • Hostname/IP (if different) • Callback function

  28. mod_zeroconf Design Apache Core Virtual Host Config Info mod_zeroconf Callback Process mDNS Callbacks Howl mDNSResponder mDNS Registration

  29. Registration Callbacks • Network can be very dynamic • Service name, Hostname conflicts • Apache needs to respond • Can’t block parent process: • fork a child

  30. mod_zeroconf.c: post_config static int zc_post_config(apr_pool_t * pconf, apr_pool_t * plog, apr_pool_t * ptemp, server_rec *s) { void *data; const char *userdata_key = "zeroconf_init_module"; apr_pool_userdata_get(&data, userdata_key, s->process->pool); if (!data) { apr_pool_userdata_set((const void *) 1, userdata_key, apr_pool_cleanup_null, s->process->pool); } else { . . . } return OK; }

  31. mod_zeroconf.c: config check /* Check if Zeroconf has been enabled globally. If not, bail here */ cfg = our_sconfig(s); if (cfg->enabled == 0) { return OK; } /* Still here? Let's go. */ TESTORBAIL(sw_rendezvous_init(&howl_session)); /* Get System Hostname (not shown) */ for (ws = s; ws; ws = ws->next) { cfg = our_sconfig(ws); if (cfg->serviceName) { . . . } }

  32. mod_zeroconf.c: TEXT Record if (cfg->partialURI) { TESTORBAIL(sw_text_record_init(&text_record)); TESTORBAIL(sw_text_record_add_key_and_string_value(text_record, "path", cfg->partialURI)); pathinfo = sw_text_record_bytes(text_record); pilength = sw_text_record_len(text_record); } else { pathinfo = NULL; pilength = 0; } serverport = ws->port == 0 ? 80 : ws->port; if (apr_strnatcasecmp(thehostname, ws->server_hostname) != 0) { zc_register_host(ws); }

  33. mod_zeroconf.c: Publish! howl_result = sw_rendezvous_publish(howl_session, cfg->serviceName, "_http._tcp", NULL, ws->server_hostname, serverport, pathinfo, pilength, NULL, howl_publish_reply, (sw_opaque) ws, &howl_id); pubidPtr = apr_palloc(s->process->pool, sizeof(sw_rendezvous_publish_id)); *pubidPtr = howl_id; apr_pool_userdata_set(howl_id, cfg->serviceName, apr_pool_cleanup_null, ws->process->pool);

  34. mod_zeroconf.c: Fork callback #if APR_HAS_FORK callbackchild = apr_palloc(s->process->pool, sizeof(apr_proc_t)); switch(forkstatus = apr_proc_fork(callbackchild, s->process->pool)) { case APR_INCHILD: sw_rendezvous_run(howl_session); break; /* Not reached */ case APR_INPARENT: apr_pool_note_subprocess(s->process->pool, callbackchild, APR_KILL_AFTER_TIMEOUT); break; default: ap_log_error(APLOG_MARK, APLOG_ERR, forkstatus, s, "Failed to fork callback child"); return HTTP_INTERNAL_SERVER_ERROR; } #endif /* APR_HAS_FORK */

  35. mod_zeroconf: To-Dos • Learn about https protocol • Learn about DAV, … • Port to MacOSX? Apache 1.3? • Alternative mDNS implementations • IPv6 compatibility • More solid hostname registration • Better callback code • etc…

  36. mod_zeroconf: Where? • Project home page: • http://www.temme.net/sander/mod_zeroconf/ • Contact: • sander@temme.net • About Apache server: • http://httpd.apache.org/ • Apache modules: • apache-modules@covalent.net

  37. Conclusion • Zeroconf is great • Will make networks more usable • Platform support needed across vendors • Applications will follow • mod_zeroconf is cool • Patches are welcome

  38. Q&A

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