1. Web Server Design Week 2 Old Dominion University
Department of Computer Science
CS 495/595 Spring 2008
Michael L. Nelson
1/17/12

2. 19.6.1.1 Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses
Both clients and servers MUST support the Host request-header.
A client that sends an HTTP/1.1 request MUST send a Host header.
Servers MUST report a 400 (Bad Request) error if an HTTP/1.1 request does not include a Host request-header.
Servers MUST accept absolute URIs.

3. Absolute & Relative URIs
% telnet 80 | tee 3-1.out
Trying
Connected to xenon.cs.odu.edu.
Escape character is '^]'.
GET /~mln/index.html HTTP/1.1
Connection: close
Host:
[deletia]
% telnet 80 | tee 3-2.out
GET HTTP/1.1
[AIHT:~/Desktop/cs595-s06] mln% diff 3-1.out 3-2.out
5c5
< Date: Mon, 23 Jan :54:49 GMT
---
> Date: Mon, 23 Jan :55:02 GMT

4. 5.2 The Resource Identified by a Request
The exact resource identified by an Internet request is determined by
examining both the Request-URI and the Host header field.
An origin server that does not allow resources to differ by the
requested host MAY ignore the Host header field value when
determining the resource identified by an HTTP/1.1 request. (But see
section for other requirements on Host support in HTTP/1.1.)
An origin server that does differentiate resources based on the host
requested (sometimes referred to as virtual hosts or vanity host
names) MUST use the following rules for determining the requested
resource on an HTTP/1.1 request:
1. If Request-URI is an absoluteURI, the host is part of the
Request-URI. Any Host header field value in the request MUST be
ignored.
2. If the Request-URI is not an absoluteURI, and the request includes
a Host header field, the host is determined by the Host header
field value.
3. If the host as determined by rule 1 or 2 is not a valid host on
the server, the response MUST be a 400 (Bad Request) error message.
[AIHT:~/Desktop/cs595-s06] mln% telnet 80 | tee 3-4.out
Trying
Connected to xenon.cs.odu.edu.
Escape character is '^]'.
GET /~mln/index.html HTTP/1.1
Connection: close
Host: foo.bar.edu
HTTP/ OK
Date: Mon, 23 Jan :59:19 GMT
Server: Apache/ (Unix) ApacheJServ/1.1.2 PHP/4.3.4
Last-Modified: Sun, 29 May :46:53 GMT
ETag: "1c52-14ed-42992d1d"
Accept-Ranges: bytes
Content-Length: 5357
Content-Type: text/html
[deletia]

5. Is This RFC-2616 Compliant? % telnet www.cs.odu.edu 80
Trying
Connected to xenon.cs.odu.edu.
Escape character is '^]'.
HEAD HTTP/1.1
Host:
Connection: close
HTTP/ OK
Date: Fri, 30 Jan :17:46 GMT
Server: Apache/2.2.0
Last-Modified: Wed, 14 Jan :45:46 GMT
ETag: " cfe-1247a280"
Accept-Ranges: bytes
Content-Length: 7422
Content-Type: text/html

6. Is This RFC-2616 Compliant? % telnet www.google.com 80
Trying
Connected to
Escape character is '^]'.
HEAD / HTTP/1.1
Connection: close
HTTP/ OK
Cache-Control: private
Content-Type: text/html
Set-Cookie: PREF=ID=d ae:TM= :LM= :S=L0vxDxm20siPrfQi;
expires=Sun, 17-Jan :14:07 GMT; path=/; domain=.google.com
Server: GWS/2.1
Content-Length: 0
Date: Mon, 22 Jan :53:39 GMT
Connection closed by foreign host.

7. This is Compliant… % telnet www.cs.odu.edu 80 Trying 128.82.4.2...
Connected to xenon.cs.odu.edu.
Escape character is '^]'.
HEAD / HTTP/1.1
Connection: close
HTTP/ Bad Request
Date: Mon, 22 Jan :56:07 GMT
Server: Apache/2.2.0
Content-Type: text/html; charset=iso
Connection closed by foreign host.

8. Host: Matters… % telnet www.cs.odu.edu 80 % telnet www.cs.odu.edu 80
Trying
Connected to xenon.cs.odu.edu.
Escape character is '^]'.
HEAD / HTTP/1.1
Host:
Connection: close
HTTP/ OK
Date: Mon, 16 Jan :45:56 GMT
Server: Apache/ (Unix) PHP/5.3.5 mod_ssl/ OpenSSL/0.9.8q
Accept-Ranges: bytes
Content-Type: text/html
Connection closed by foreign host.
% telnet 80
Trying
Connected to xenon.cs.odu.edu.
Escape character is '^]'.
HEAD / HTTP/1.1
Connection: close
Host:
HTTP/ OK
Date: Mon, 16 Jan :46:11 GMT
Server: Apache/ (Unix) PHP/5.3.5 mod_ssl/ OpenSSL/0.9.8q
Last-Modified: Sun, 23 Nov :22:06 GMT
ETag: "19f2-45c638bee2380"
Accept-Ranges: bytes
Content-Length: 6642
Content-Type: text/html
Connection closed by foreign host.

9. 3.2.2 http URL (RFC 2616)
The "http" scheme is used to locate network resources via the HTTP
protocol. This section defines the scheme-specific syntax and
semantics for http URLs.
http_URL = " "//" host [ ":" port ] [ abs_path [ "?" query ]]
If the port is empty or not given, port 80 is assumed. The semantics
are that the identified resource is located at the server listening
for TCP connections on that port of that host, and the Request-URI
for the resource is abs_path (section 5.1.2). The use of IP addresses
in URLs SHOULD be avoided whenever possible (see RFC 1900 [24]). If
the abs_path is not present in the URL, it MUST be given as "/" when
used as a Request-URI for a resource (section 5.1.2).

10. 3.2.3 URI Comparison (RFC 2616) http://abc.com:80/~smith/home.html
When comparing two URIs to decide if they match or not, a client
SHOULD use a case-sensitive octet-by-octet comparison of the entire
URIs, with these exceptions:
- A port that is empty or not given is equivalent to the default
port for that URI-reference;
- Comparisons of host names MUST be case-insensitive;
- Comparisons of scheme names MUST be case-insensitive;
- An empty abs_path is equivalent to an abs_path of "/".
Characters other than those in the "reserved" and "unsafe" sets (see
RFC 2396 [42]) are equivalent to their ""%" HEX HEX" encoding.
For example, the following three URIs are equivalent:

11. What can be in a URI? (or: “Learning to Love BNF”) (RFC 2396)
uric = reserved | unreserved | escaped
unreserved = alphanum | mark
mark = "-" | "_" | "." | "!" | "~" | "*" | "'" | "(" | ")"
alphanum = alpha | digit

12. alphanum alpha = lowalpha | upalpha
lowalpha = "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" | "i" |
"j" | "k" | "l" | "m" | "n" | "o" | "p" | "q" | "r" |
"s" | "t" | "u" | "v" | "w" | "x" | "y" | "z"
upalpha = "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" | "I" |
"J" | "K" | "L" | "M" | "N" | "O" | "P" | "Q" | "R" |
"S" | "T" | "U" | "V" | "W" | "X" | "Y" | "Z"
digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" |
"8" | "9"

13. reserved
Many URI include components consisting of or delimited by, certain
special characters. These characters are called "reserved", since
their usage within the URI component is limited to their reserved
purpose. If the data for a URI component would conflict with the
reserved purpose, then the conflicting data must be escaped before
forming the URI.
reserved = ";" | "/" | "?" | ":" | | "&" | "=" | "+" |
"$" | ","
The "reserved" syntax class above refers to those characters that are
allowed within a URI, but which may not be allowed within a
particular component of the generic URI syntax; they are used as
delimiters of the components described in Section 3.
Characters in the "reserved" set are not reserved in all contexts.
The set of characters actually reserved within any given URI
component is defined by that component. In general, a character is
reserved if the semantics of the URI changes if the character is
replaced with its escaped US-ASCII encoding.

14. escaped
An escaped octet is encoded as a character triplet, consisting of the
percent character "%" followed by the two hexadecimal digits
representing the octet code. For example, "%20" is the escaped
encoding for the US-ASCII space character.
escaped = "%" hex hex
hex = digit | "A" | "B" | "C" | "D" | "E" | "F" |
"a" | "b" | "c" | "d" | "e" | "f"

15. Encoding Cheat Sheet
from:

16. excluded
Although they are disallowed within the URI syntax, we include here a
description of those US-ASCII characters that have been excluded and
the reasons for their exclusion.
The control characters in the US-ASCII coded character set are not
used within a URI, both because they are non-printable and because
they are likely to be misinterpreted by some control mechanisms.
control = <US-ASCII coded characters 00-1F and 7F hexadecimal>
The space character is excluded because significant spaces may
disappear and insignificant spaces may be introduced when URI are
transcribed or typeset or subjected to the treatment of word-
processing programs. Whitespace is also used to delimit URI in many
contexts.
space = <US-ASCII coded character 20 hexadecimal>

17. excluded
The angle-bracket "<" and ">" and double-quote (") characters are
excluded because they are often used as the delimiters around URI in
text documents and protocol fields. The character "#" is excluded
because it is used to delimit a URI from a fragment identifier in URI
references (Section 4). The percent character "%" is excluded because
it is used for the encoding of escaped characters.
delims = "<" | ">" | "#" | "%" | <">
Other characters are excluded because gateways and other transport
agents are known to sometimes modify such characters, or they are
used as delimiters.
unwise = "{" | "}" | "|" | "\" | "^" | "[" | "]" | "`"

18. Clients Hide Details! % telnet www.cs.odu.edu 80 Trying 128.82.4.2...
Connected to xenon.cs.odu.edu.
Escape character is '^]'.
HEAD world.txt HTTP/1.1
Host:
Connection: close
HTTP/ Not Found
Date: Tue, 17 Jan :27:17 GMT
Server: Apache/ (Unix) PHP/5.3.5 mod_ssl/ OpenSSL/0.9.8q
Content-Type: text/html; charset=iso

19. Spaces Are Encoded % telnet www.cs.odu.edu 80 Trying 128.82.4.2...
Connected to xenon.cs.odu.edu.
Escape character is '^]'.
HEAD HTTP/1.1
Host:
Connection: close
HTTP/ OK
Date: Tue, 17 Jan :27:54 GMT
Server: Apache/ (Unix) PHP/5.3.5 mod_ssl/ OpenSSL/0.9.8q
Last-Modified: Tue, 17 Jan :25:55 GMT
ETag: "c-4b6b00cf932d2"
Accept-Ranges: bytes
Content-Length: 12
Content-Type: text/plain

20. Fragments (from RFC-1630)
This represents a part of, fragment of, or a sub-function within, an
object. Its syntax and semantics are defined by the application
responsible for the object, or the specification of the content type
of the object. …
The fragment-id follows the URL of the whole object from which it is
separated by a hash sign (#). If the fragment-id is void, the hash
sign may be omitted: A void fragment-id with or without the hash sign
means that the URL refers to the whole object.
A reference to a particular part of a document may, including the
fragment identifier, look like
in which case the string "#andy" is not sent to the server, but is
retained by the client and used when the whole object had been
retrieved.
stated less clearly in section 4.1, RFC 2396

21. URLs & Filenames? HIERARCHICAL FORMS
The slash ("/", ASCII 2F hex) character is reserved for the
delimiting of substrings whose relationship is hierarchical. This
enables partial forms of the URI. Substrings consisting of single
or double dots ("." or "..") are similarly reserved.
The significance of the slash between two segments is that the
segment of the path to the left is more significant than the
segment of the path to the right. ("Significance" in this case
refers solely to closeness to the root of the hierarchical
structure and makes no value judgement!)
Note
The similarity to unix and other disk operating system filename
conventions should be taken as purely coincidental, and should
not be taken to indicate that URIs should be interpreted as
file names.
RFC-1630; restated in various ways in other RFCs

22. MIME Types Multipurpose Internet Mail Extensions
RFCs 2045, 2046
used to populate http “Content-Type” response headers
Although not part of http, web servers generally have a configurable method of mapping file extensions to MIME types, e.g.:
.jpeg, .jpg image/jpeg
.pdf application/pdf
.ppt application/vnd.ms-powerpoint

23. TRACE Method ignore for now % telnet www.cs.vt.edu 80
Trying
Connected to cs.vt.edu.
Escape character is '^]'.
TRACE / HTTP/1.1
Testing-1: Hello, Sailor!
Testing-2: 69,105
Host:
Connection: close
HTTP/ OK
Date: Mon, 16 Jan :23:32 GMT
Server: Apache/2.2.3 (CentOS)
Transfer-Encoding: chunked
Content-Type: message/http 77
ignore for now

24. TRACE no longer on www.cs.odu.edu
% telnet 80
Trying
Connected to xenon.cs.odu.edu.
Escape character is '^]'.
TRACE / HTTP/1.1
Testing-1: Hello, Sailor!
Testing-2: 69,105
Host:
Connection: close
HTTP/ Method Not Allowed
Date: Mon, 16 Jan :23:14 GMT
Server: Apache/ (Unix) PHP/5.3.5 mod_ssl/ OpenSSL/0.9.8q
Allow:
Content-Length: 353
Content-Type: text/html; charset=iso
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<html><head>
<title>405 Method Not Allowed</title>

25. OPTIONS to verify… % telnet www.cs.odu.edu 80 Trying 128.82.4.2...
Connected to xenon.cs.odu.edu.
Escape character is '^]'.
OPTIONS / HTTP/1.1
Testing-1: Hello, Sailor!
Testing-2: 69,105
Host:
Connection: close
HTTP/ OK
Date: Mon, 16 Jan :54:43 GMT
Server: Apache/ (Unix) PHP/5.3.5 mod_ssl/ OpenSSL/0.9.8q
Allow: GET,HEAD,POST,OPTIONS
Content-Length: 0
Content-Type: text/html
Connection closed by foreign host.

26. Parsing Lines 2.2 Basic Rules …
CR = <US-ASCII CR, carriage return (13)>
LF = <US-ASCII LF, linefeed (10)>
HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
protocol elements except the entity-body (see appendix 19.3 for
tolerant applications). The end-of-line marker within an entity-body
is defined by its associated media type, as described in section 3.7.
CRLF = CR LF
HTTP/1.1 header field values can be folded onto multiple lines if the
continuation line begins with a space or horizontal tab.
OK:
Line1: xyz
Line2: ab c
Line3: pdq
not OK:
19.3 Tolerant Applications …
The line terminator for message-header fields is the sequence CRLF.
However, we recommend that applications, when parsing such headers,
recognize a single LF as a line terminator and ignore the leading CR.

27. Common Log Format see: http://en.wikipedia.org/wiki/Common_Log_Format
frank [10/Oct/2000:13:55: ] "GET /apache_pb.gif HTTP/1.0"
[16/Jan/2012:18:18: ] "GET /~mln/ HTTP/1.1"
[16/Jan/2012:18:18: ] "HEAD /~mln/ HTTP/1.1"
see:

28. Good things to have in a config file(s)…
MIME types (including default type)
document root
your server name (version, assignment, etc.)
location of your access log, debugging log(s)
resolve IP addrs --> hostnames (y/n)
default port # your server will run on
templates (or pointers to templates) for directory listings, dynamically created entities (e.g., for non-200 responses), log formats
default timeout (seconds)
virtual URIs
redirects (code, URI1, URI2)