1. Web Server Design Week 1 Old Dominion University Department of Computer Science CS 495/595 Spring 2006 Michael L. Nelson 1/09/06

2. Goals We will write a web (http) server from scratch –we will not use Apache, IIS, or other existing web servers –the point is to learn http and have a working server your server won’t be as “good” as Apache -- and that’s ok… We will focus on the hypertext transfer protocol (http) –we will not focus on the all the neat things you can do that are outside / on top of the protocol modules, servlets, WebDAV/DASL, etc.

3. Administrivia This is a programming class! –I assume you know how to: do network (socket) programming write a daemon –you can work in any environment you want to machines will be provided, deviate at your own risk –your grade will be determined solely on your server’s performance on 5 different checkpoints through the semester You will work in teams of: –2 grad –3 undergrad

4. Administrivia 2 Important URLs –http://www.cs.odu.edu/~mln/teaching/cs595-s06/http://www.cs.odu.edu/~mln/teaching/cs595-s06/ –http://list.odu.edu/listinfo/cs595-s06/http://list.odu.edu/listinfo/cs595-s06/ Class homepage: –Readings are listed under the day they are expected to be completed –assignments are listed under the day they will be demoed in class –each group will give a 3-4 minute status report the week before an assignment is due! See the syllabus for grading scale, other details

5. No WWW History If you want to know more, read a book (irony intentional)

6. How To Read RFCs (quoting from RFC 2119) The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119. 1. MUST This word, or the terms "REQUIRED" or "SHALL", mean that the definition is an absolute requirement of the specification. 2. MUST NOT This phrase, or the phrase "SHALL NOT", mean that the definition is an absolute prohibition of the specification. 3. SHOULD This word, or the adjective "RECOMMENDED", mean that there may exist valid reasons in particular circumstances to ignore a particular item, but the full implications must be understood and carefully weighed before choosing a different course. 4. SHOULD NOT This phrase, or the phrase "NOT RECOMMENDED" mean that there may exist valid reasons in particular circumstances when the particular behavior is acceptable or even useful, but the full implications should be understood and the case carefully weighed before implementing any behavior described with this label. 5. MAY This word, or the adjective "OPTIONAL", mean that an item is truly optional. One vendor may choose to include the item because a particular marketplace requires it or because the vendor feels that it enhances the product while another vendor may omit the same item. An implementation which does not include a particular option MUST be prepared to interoperate with another implementation which does include the option, though perhaps with reduced functionality. In the same vein an implementation which does include a particular option MUST be prepared to interoperate with another implementation which does not include the option (except, of course, for the feature the option provides.)

7. Uniform Resource Identifiers URI URL URN RFC 2396 RFC 2141 RFC 1738

8. Terminology Highlights (section 1.3) connection A transport layer virtual circuit established between two programs for the purpose of communication. message The basic unit of HTTP communication, consisting of a structured sequence of octets matching the syntax defined in section 4 and transmitted via the connection. request An HTTP request message, as defined in section 5. response An HTTP response message, as defined in section 6. resource A network data object or service that can be identified by a URI, as defined in section 3.2. Resources may be available in multiple representations (e.g. multiple languages, data formats, size, and resolutions) or vary in other ways. entity The information transferred as the payload of a request or response. An entity consists of metainformation in the form of entity-header fields and content in the form of an entity-body, as described in section 7. representation An entity included with a response that is subject to content negotiation, as described in section 12. There may exist multiple representations associated with a particular response status.

9. Terminology Highlights (section 1.3) content negotiation The mechanism for selecting the appropriate representation when servicing a request, as described in section 12. The representation of entities in any response can be negotiated (including error responses). variant A resource may have one, or more than one, representation(s) associated with it at any given instant. Each of these representations is termed a `variant'. Use of the term `variant' does not necessarily imply that the resource is subject to content negotiation. client A program that establishes connections for the purpose of sending requests. user agent The client which initiates a request. These are often browsers, editors, spiders (web-traversing robots), or other end user tools. server An application program that accepts connections in order to service requests by sending back responses. Any given program may be capable of being both a client and a server; our use of these terms refers only to the role being performed by the program for a particular connection, rather than to the program's capabilities in general. Likewise, any server may act as an origin server, proxy, gateway, or tunnel, switching behavior based on the nature of each request.

10. Terminology Highlights (section 1.3) origin server The server on which a given resource resides or is to be created. upstream/downstream Upstream and downstream describe the flow of a message: all messages flow from upstream to downstream. inbound/outbound Inbound and outbound refer to the request and response paths for messages: "inbound" means "traveling toward the origin server", and "outbound" means "traveling toward the user agent"

11. Intermediaries proxy –“a forwarding agent, receiving requests for a URI in its absolute form, rewriting all or part of the message, and forwarding the reformatted request toward the server identified by the URI” gateway –“a receiving agent, acting as a layer above some other server(s) and, if necessary, translating the requests to the underlying server's protocol” tunnel –“a relay point between two connections without changing the messages; tunnels are used when the communication needs to pass through an intermediary (such as a firewall) even when the intermediary cannot understand the contents of the messages.” definitions from section 1.4 of RFC 2616

12. No Intermediaries for Us For simplicity, we will ignore the possibility of intermediaries in our assignments No caching intermediaries –skip section 13 of RFC 2616 –any caching activities will be on the part of the client

13. HTTP Operation Client Origin Server request = (method, URI, version, “MIME-like” message) response = (version, success/error code, “MIME-like” message)

14. GET AIHT:~/Desktop/cs595-s06 mln$ telnet www.cs.odu.edu 80 | tee 1-1.out Trying 128.82.4.2... Connected to xenon.cs.odu.edu. Escape character is '^]'. GET /~mln/index.html HTTP/1.1 Connection: close Host: www.cs.odu.edu HTTP/1.1 200 OK Date: Mon, 09 Jan 2006 17:07:04 GMT Server: Apache/1.3.26 (Unix) ApacheJServ/1.1.2 PHP/4.3.4 Last-Modified: Sun, 29 May 2005 02:46:53 GMT ETag: "1c52-14ed-42992d1d" Accept-Ranges: bytes Content-Length: 5357 Connection: close Content-Type: text/html Home Page for Michael L. Nelson <!-- [lots of html deleted] Connection closed by foreign host. Request (ends w/ CRLF) Response

15. HEAD AIHT:~/Desktop/cs595-s06 mln$ telnet www.cs.odu.edu 80 | tee 1-2.out Trying 128.82.4.2... Connected to xenon.cs.odu.edu. Escape character is '^]'. HEAD /~mln/index.html HTTP/1.1 Connection: close Host: www.cs.odu.edu HTTP/1.1 200 OK Date: Mon, 09 Jan 2006 17:14:39 GMT Server: Apache/1.3.26 (Unix) ApacheJServ/1.1.2 PHP/4.3.4 Last-Modified: Sun, 29 May 2005 02:46:53 GMT ETag: "1c52-14ed-42992d1d" Accept-Ranges: bytes Content-Length: 5357 Connection: close Content-Type: text/html Connection closed by foreign host.

16. OPTIONS AIHT:~/Desktop/cs595-s06 mln$ telnet www.cs.odu.edu 80 | tee 1-3.out Trying 128.82.4.2... Connected to xenon.cs.odu.edu. Escape character is '^]'. OPTIONS /~mln/index.html HTTP/1.1 Connection: close Host: www.cs.odu.edu HTTP/1.1 200 OK Date: Mon, 09 Jan 2006 17:16:46 GMT Server: Apache/1.3.26 (Unix) ApacheJServ/1.1.2 PHP/4.3.4 Content-Length: 0 Allow: GET, HEAD, POST, PUT, DELETE, CONNECT, OPTIONS, PATCH, PROPFIND, PROPPATCH, MKCOL, COPY, MOVE, LOCK, UNLOCK, TRACE Connection: close Connection closed by foreign host.

17. Response Codes - 1xx: Informational - Request received, continuing process - 2xx: Success - The action was successfully received, understood, and accepted - 3xx: Redirection - Further action must be taken in order to complete the request - 4xx: Client Error - The request contains bad syntax or cannot be fulfilled - 5xx: Server Error - The server failed to fulfill an apparently valid request from section 6.1.1 of RFC 2616

18. Other Responses - ex. 501 AIHT:~/Desktop/cs595-s06 mln$ telnet www.cs.odu.edu 80 | tee 1-4.out Trying 128.82.4.2... Connected to xenon.cs.odu.edu. Escape character is '^]'. NOTAREALMETHOD /index.html HTTP/1.1 Connection: close Host: www.cs.odu.edu HTTP/1.1 501 Method Not Implemented Date: Mon, 09 Jan 2006 17:22:40 GMT Server: Apache/1.3.26 (Unix) ApacheJServ/1.1.2 PHP/4.3.4 Allow: GET, HEAD, POST, PUT, DELETE, CONNECT, OPTIONS, PATCH, PROPFIND, PROPPATCH, MKCOL, COPY, MOVE, LOCK, UNLOCK, TRACE Connection: close Transfer-Encoding: chunked Content-Type: text/html; charset=iso-8859-1 15f 501 Method Not Implemented Method Not Implemented NOTAREALMETHOD to /index.html not supported. Invalid method in request NOTAREALMETHOD /index.html HTTP/1.1 Apache/1.3.26 Server at www.cs.odu.edu Port 80 0 Connection closed by foreign host. come up with your own examples for: 400 403 404 505

19. Other Responses - ex. 301 AIHT:~/Desktop/cs595-s06 mln$ telnet www.cs.odu.edu 80 | tee 1-6.out Trying 128.82.4.2... Connected to xenon.cs.odu.edu. Escape character is '^]'. GET /~mln HTTP/1.1 Connection: close Host: www.cs.odu.edu Connection closed by foreign host. HTTP/1.1 301 Moved Permanently Date: Mon, 09 Jan 2006 19:32:24 GMT Server: Apache/1.3.26 (Unix) ApacheJServ/1.1.2 PHP/4.3.4 Location: http://www.cs.odu.edu/~mln/ Connection: close Transfer-Encoding: chunked Content-Type: text/html; charset=iso-8859-1 12e 301 Moved Permanently Moved Permanently The document has moved here. Apache/1.3.26 Server at www.cs.odu.edu Port 80 0

20. Things to Think About for Your Server Configuration files –should not have to recompile for trivial changes Logging –real http servers log their events –you’ll need logging for debugging consider concurrent logs with varying verbosity MIME types –most servers use a separate file (specified in your config file!) to map file extensions to MIME types Claim HTTP/1.1 –even though we’ll not fully satisfy all requirements What does it mean to GET a directory?

21. Date/Time Format from 3.3.1 RFC 2616 Sun, 06 Nov 1994 08:49:37 GMT ; RFC 822, updated by RFC 1123 Sunday, 06-Nov-94 08:49:37 GMT ; RFC 850, obsoleted by RFC 1036 Sun Nov 6 08:49:37 1994 ; ANSI C's asctime() format … HTTP/1.1 clients and servers that parse the date value MUST accept all three formats (for compatibility with HTTP/1.0), though they MUST only generate the RFC 1123 format for representing HTTP-date values in header fields. See section 19.3 for further information for simplicity, we’ll only do RFC 1123

22. To Do for Next Time… Subscribe to the class email list Submit group info to me –I’ll assign each group a unique port: 70XX xx = group # in the class Submit preferred development language / environment for your group –3 Unix development machines will be made available; we’ll try to get whatever languages you want