HTTP and Apache Roy T. Fielding eBuilt, Inc. The Apache Software Foundation

Overview HTTP Basics Apache httpd architecture Connection management (listening) Request Reading Finding a representation Conditional request evaluation Response Writing Connection management (closing) Future Improvements waka/2.0

Web architecture Layered-client-server Uniform resource interface –Simple, but powerful –Semantics are visible to intermediaries HTTP extends interface across network HTTP Basics

HTTP Message Syntax GET /Test/hello.html HTTP/1.1 \r\n Host: kiwi.ics.uci.edu:8080 \r\n User-Agent: GET/7 libwww-perl/5.40 \r\n \r\n HTTP/ OK \r\n Date: Thu, 09 Mar :40:09 GMT \r\n Server: Apache/ \r\n Content-Type: text/html \r\n Content-Language: en \r\n Transfer-Encoding: chunked \r\n Etag: a797cd-465af \r\n Cache-control: max-age=3600 \r\n Vary: Accept-Language \r\n \r\n 4090 \r\n …

Request Envelope GET /Test/hello.html HTTP/1.1 \r\n Host: kiwi.ics.uci.edu:8080 \r\n User-Agent: GET/7 libwww-perl/5.40 \r\n \r\n

Request Control Data GET /Test/hello.html HTTP/1.1 \r\n Host: kiwi.ics.uci.edu:8080 \r\n User-Agent: GET/7 libwww-perl/5.40 \r\n \r\n

Request Metadata GET /Test/hello.html HTTP/1.1 \r\n Host: kiwi.ics.uci.edu:8080 \r\n User-Agent: GET/7 libwww-perl/5.40 \r\n \r\n

Request Metadata POST /nasdaq/trade.php HTTP/1.1 \r\n Host: \r\n User-Agent: poseur/1.0 libwww/3.1 \r\n Content-type: www/x-urlencoded \r\n Content-length: 58 \r\n \r\n Ticker=LNUX&quantity=140&action=sell &type=limit&amt=298.00

Request Data POST /nasdaq/trade.php HTTP/1.1 \r\n Host: \r\n User-Agent: poseur/1.0 libwww/3.1 \r\n Content-type: www/x-urlencoded \r\n Content-length: 58 \r\n \r\n Ticker=LNUX&quantity=140&action=sell &type=limit&amt=298.00

Request Data GET /Test/hello.html HTTP/1.1 \r\n Host: kiwi.ics.uci.edu:8080 \r\n User-Agent: GET/7 libwww-perl/5.40 \r\n \r\n

Response Envelope GET /Test/hello.html HTTP/1.1 \r\n Host: kiwi.ics.uci.edu:8080 \r\n User-Agent: GET/7 libwww-perl/5.40 \r\n \r\n HTTP/ OK \r\n Date: Thu, 09 Mar :40:09 GMT \r\n Server: Apache/ \r\n Content-Type: text/html \r\n Content-Language: en \r\n Transfer-Encoding: chunked \r\n Etag: a797cd-465af \r\n Cache-control: max-age=3600 \r\n Vary: Accept-Language \r\n \r\n 4090 \r\n …

Response Control Data GET /Test/hello.html HTTP/1.1 \r\n Host: kiwi.ics.uci.edu:8080 \r\n User-Agent: GET/7 libwww-perl/5.40 \r\n \r\n HTTP/ OK \r\n Date: Thu, 09 Mar :40:09 GMT \r\n Server: Apache/ \r\n Content-Type: text/html \r\n Content-Language: en \r\n Transfer-Encoding: chunked \r\n Etag: a797cd-465af \r\n Cache-control: max-age=3600 \r\n Vary: Accept-Language \r\n \r\n 4090 \r\n …

Response Metadata GET /Test/hello.html HTTP/1.1 \r\n Host: kiwi.ics.uci.edu:8080 \r\n User-Agent: GET/7 libwww-perl/5.40 \r\n \r\n HTTP/ OK \r\n Date: Thu, 09 Mar :40:09 GMT \r\n Server: Apache/ \r\n Content-Type: text/html \r\n Content-Language: en \r\n Transfer-Encoding: chunked \r\n Etag: a797cd-465af \r\n Cache-control: max-age=3600 \r\n Vary: Accept-Language \r\n \r\n 4090 \r\n …

Response Data GET /Test/hello.html HTTP/1.1 \r\n Host: kiwi.ics.uci.edu:8080 \r\n User-Agent: GET/7 libwww-perl/5.40 \r\n \r\n HTTP/ OK \r\n Date: Thu, 09 Mar :40:09 GMT \r\n Server: Apache/ \r\n Content-Type: text/html \r\n Content-Language: en \r\n Transfer-Encoding: chunked \r\n Etag: a797cd-465af \r\n Cache-control: max-age=3600 \r\n Vary: Accept-Language \r\n \r\n 4090 \r\n …

Overview HTTP Basics Apache httpd architecture Connection management (listening) Request Reading Finding a representation Conditional request evaluation Response Writing Connection management (closing) Future Improvements waka/2.0

httpd Initialization httpd core apache-2.0/src/main/*.c Initiate program http_main.c Read configuration files http_config.c, http_core.c Start logging http_log.c Start server listeners (MPM) apache-2.0/src/modules/mpm/*

Connection management Listening and Accept mpm/prefork/prefork.c mpm/mpmt_pthread.c … Connection set-up src/main/http_connection.c Modular hooks for protocol independence ap_process_http_connection() –Calls ap_read_request() and we are finally at the level of HTTP

Request Reading src/main/http_protocol.c GET /Test/hello.html HTTP/1.1 \r\n Host: kiwi.ics.uci.edu:8080 \r\n User-Agent: GET/7 libwww-perl/5.40 \r\n \r\n Request Line read_request_line(r) Header fields get_mime_headers(r) Host determination http_vhost.c

Request Processing src/main/http_request.c Access control Directory walk Location walk File walk Handler selection Field pre-processing Content Handler

Request Body src/main/http_protocol.c Declaration ap_setup_client_block(r, policy) Test ap_should_client_block(r) Read until done ap_get_client_block(r, …) Shortcut ap_discard_request_body(r)

Finding a representation Each content handler is responsible for associating the URI with a resource and applying the method, returning a representation as the response Redirection Negotiation Subrequests Errors

Conditional request evaluation Conditional requests modify method processing depending on the current state of the resource representation Last-Modified Etag Cache validation If-Modified-Since If-Nonematch Prerequisites If-Match If-Unmodified-Since Range-If If

Response Writing HTTP/ OK \r\n Date: Thu, 09 Mar :40:09 GMT \r\n Server: Apache/ \r\n Content-Type: text/html \r\n Content-Language: en \r\n Transfer-Encoding: chunked \r\n Etag: a797cd-465af \r\n Cache-control: max-age=3600 \r\n Vary: Accept-Language \r\n \r\n 4090 \r\n … Status code and reason phrase Header fields Body

Response Writing Status code and reason phrase r->status r->status_line || status_lines[idx] Header fields r->headers_out r->err_headers_out Headers set by modules mod_expires.c mod_headers.c –Header set Author John Q. Public

Send Body Body File Buffer IO-layer Transfer-encoding Length delimited Chunked Connection terminated

Connection management Persistent connections The big hairy if ap_set_keepalive(r) Connection tear-down Lingering close

Overview HTTP Basics Apache httpd architecture Connection management (listening) Request Reading Finding a representation Conditional request evaluation Response Writing Connection management (closing) Future Improvements waka/2.0

Future Improvements Configurable protocol elements Methods, status codes, field names Tokenized field manipulation Field name -> token Field value -> linked list Streaming IO Layers Stacked protocol manipulation Separate streams for data and metadata –Token streams Bucket brigades –Strings, Files, Cache handles

waka/2.0 A replacement for HTTP/1.x Emphasizes the REST architectural style Ideas from Speros HTTP-ng and W3C HTTP-NG Packet streams Control, meta-metadata, metadata, data Prioritized bandwidth usage Self-descriptive All syntax an extensible standard All cache rules in response Simple quality of service indicators Transport independent Tokenized Optimized for memory transfer

Questions? Where to go for more information Places to see: Front Doorwww.apache.org Developer Notesdev.apache.org PR Databasebugs.apache.org Apache Weekwww.apacheweek.com OReilly Netwww.oreilly.net/apache/