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Basic foilset Setting the Stage for CGI Programming: HTTP, URL, CGI, MIME, HTTPD and many other acronyms

Given by Nancy J. McCracken at ECS400 Senior Undergraduate Course on Spring Semester 1997. Foils prepared 11 May 1997
Outside Index Summary of Material

MIME stands for Multipart Internet Mail Extensions and is the developing standard for the contents of all messages passed over the Internet.
HTTP is Hypertext Transport Protocol and is the protocol that provides the basis of the World Wide Web: transmitting multimedia documents across the Internet. HTTPD is the daemon running the HTTP Web server.
URL stands for Uniform Resource Locator and is the universal addressing scheme for all documents (multimedia) on the WWW.
CGI is the Common Gateway Interface and is the scheme to interface other programs and systems to the HTTP Web protocol, using the same data protocols as the HTTP clients and servers.
References:
  • HTML and CGI Unleashed, John December and Mark GInsburg, chapters 19 and 20.
  • Innumerable web documents.

Table of Contents for full HTML of Setting the Stage for CGI Programming: HTTP, URL, CGI, MIME, HTTPD and many other acronyms

Denote Foils where Image Critical
Denote Foils where HTML is sufficient
1 Setting the Stage for CGI Programming:
HTTP, URL, CGI, MIME, HTTPD, and many other acronyms
too numerous to mention
2 In a Nutshell
3 Internet Documents: Drafts, Memos and Standards
4 Internet Documents - Examples
5 Internet E-Mail (RFC-822)
6 Multipurpose Internet Mail Extension (MIME)
7 MIME - Extension Model
8 MIME - "Content-Type" Header Field
9 MIME - Base Content Types
10 MIME - Base Content Types, continued
11 MIME - Implementation Status
12 HTTP - Hypertext Transport Protocol
13 HTTPD - HTTP Daemon
14 URL - Uniform Resource Locator
15 HTTP - How does it work?
16 HTTP - GET Request Example
17 HTTP - Reply Example
18 HTTP - POST Request Example
19 Common Gateway Interface (CGI) - an introduction

Outside Index Summary of Material

HTML version of Basic Foils prepared 11 May 1997

Foil 1 Setting the Stage for CGI Programming:
HTTP, URL, CGI, MIME, HTTPD, and many other acronyms
too numerous to mention

From Setting the Stage for CGI Programming: HTTP, URL, CGI, MIME, HTTPD and many other acronyms ECS400 Senior Undergraduate Course -- Spring Semester 1997. *
Full HTML Index
Wojtek Furmanski, Nancy McCracken
NPAC
Syracuse University
111 College Place
Syracuse NY 13244-4100
January 31, 1996
updated September 1996
Click here for body text
HTML version of Basic Foils prepared 11 May 1997

Foil 2 In a Nutshell

From Setting the Stage for CGI Programming: HTTP, URL, CGI, MIME, HTTPD and many other acronyms ECS400 Senior Undergraduate Course -- Spring Semester 1997. *
Full HTML Index
MIME stands for Multipart Internet Mail Extensions and is the developing standard for the contents of all messages passed over the Internet.
HTTP is Hypertext Transport Protocol and is the protocol that provides the basis of the World Wide Web: transmitting multimedia documents across the Internet. HTTPD is the daemon running the HTTP Web server.
URL stands for Uniform Resource Locator and is the universal addressing scheme for all documents (multimedia) on the WWW.
CGI is the Common Gateway Interface and is the scheme to interface other programs and systems to the HTTP Web protocol, using the same data protocols as the HTTP clients and servers.
References:
  • HTML and CGI Unleashed, John December and Mark GInsburg, chapters 19 and 20.
  • Innumerable web documents.
HTML version of Basic Foils prepared 11 May 1997

Foil 3 Internet Documents: Drafts, Memos and Standards

From Setting the Stage for CGI Programming: HTTP, URL, CGI, MIME, HTTPD and many other acronyms ECS400 Senior Undergraduate Course -- Spring Semester 1997. *
Full HTML Index
Some material presented here comes from Internet documents. Here is a summary of various document formats you may find.
Internet Drafts
  • Working documents of the Internet Engineering Task Force (IETF), its Area and Working Groups.
  • Other groups may also distribute Internet Drafts.
  • Some of these IDs are labelled by IETF-#.
  • IDs are valid for a maximum of 6 months and may be updated, replaced or obsoleted by other documents at any time.
Internet Memos
  • Referred to as RFC-# (Request for Comments)
  • More formal and complete than Internet Drafts, usually represent standard proposals/candidates.
  • Some RFCs become obsolete by subsequent RFCs, some others make it as standards
Internet Standards
  • Labelled by STD-# and often associated with the RFC-# specs (e.g. Internet E-Mail is referred to as FRC-822 or STD-11)
HTML version of Basic Foils prepared 11 May 1997

Foil 4 Internet Documents - Examples

From Setting the Stage for CGI Programming: HTTP, URL, CGI, MIME, HTTPD and many other acronyms ECS400 Senior Undergraduate Course -- Spring Semester 1997. *
Full HTML Index
Here are a few sample Internet documents relevant for this part of the course.
RFC-822: Crocker, D., "Standard for the Format of ARPA Internet Text Messages", SRD 11, RFC 822, UDEL, 1982.
RFC-1036: R. Horton and R. Adams, "Standard for Interchange of USENET Messages", RFC 850, AT&T, December 1987.
RFC-1521: Borenstein, N. and Freed, N., "MIME (Multipurpose Internet Mail Extension) Part One: Mechanisms for Specifying and Describing the Format of Internet Message Bodies", RFC 1521, Bellcore, September 1993.
RFC-1524: Borenstein, N. "A User Agent Configuration Mechanism for Multimedia Mail Format Information", RFC 1524, Bellcore, September 1993.
Internet Draft: Tim Berners-Lee, "Basic HTTP", CERN, 1992/3.
HTML version of Basic Foils prepared 11 May 1997

Foil 5 Internet E-Mail (RFC-822)

From Setting the Stage for CGI Programming: HTTP, URL, CGI, MIME, HTTPD and many other acronyms ECS400 Senior Undergraduate Course -- Spring Semester 1997. *
Full HTML Index
We all know and use it, but here is a formal specification.
Each message is a stream of 7-bit ASCII chars which contains a header and optional (newline separated) body.
Header consists of a set of entries with one entry per line given by a colon separated key:value pair.
Key contains no spaces or tabs and cannot exceed 63 chars.
Body is a fully unstructured sequence of ASCII chars.
There is a finite set of standard keys and an extension mechanism via the "X"-prefix. The standard set (as used by MH) is:
Date Bcc Resent-Date Resent-Fcc
From Fcc Resent-From resent-
Sender Message-ID Resent-To Message-Id
To Subject Resent-cc Forwarded
cc In-Reply-To Resent-Bcc Replied
HTML version of Basic Foils prepared 11 May 1997

Foil 6 Multipurpose Internet Mail Extension (MIME)

From Setting the Stage for CGI Programming: HTTP, URL, CGI, MIME, HTTPD and many other acronyms ECS400 Senior Undergraduate Course -- Spring Semester 1997. *
Full HTML Index
Goals
  • Multimedia, multi-language, multi-component extension of RFC-822
  • Full backward compatibility with RFC-822 (e.g. retain 7-bit ASCII encoding)
  • Open design to incorporate multiple well-known formats
  • Easy extension to new types and formats
History:
  • Working Group formed in fall 90 (Bellcore as lead)
  • First Internet Draft 1991
  • Internet Standard proposed in June 92 (RFC-1341)
  • Revised Version in September 93 (RFC-1521)
  • Now - many implementations in place/progress, also strong (and confusing?) coupling with the WWW/HTTP protocol
HTML version of Basic Foils prepared 11 May 1997

Foil 7 MIME - Extension Model

From Setting the Stage for CGI Programming: HTTP, URL, CGI, MIME, HTTPD and many other acronyms ECS400 Senior Undergraduate Course -- Spring Semester 1997. *
Full HTML Index
Retain RFC-822 header+body format
Add new header fields
Allow for multipart multimedia bodies
Include media type and encoding information in new header fields such as: Content-Type, Content-Description, Content-Transfer-Encoding, Content-ID
Retain 7-bit ASCII for all valid encoding schemes
Implement multi-component bodies via a special 'magic type' Content-Type: multipart
Provide natural support required for large multimedia message files such as remote references (similar to hyperlinks but NOT the URL model) and file fragmentation by further specification of the 'multipart' type.
HTML version of Basic Foils prepared 11 May 1997

Foil 8 MIME - "Content-Type" Header Field

From Setting the Stage for CGI Programming: HTTP, URL, CGI, MIME, HTTPD and many other acronyms ECS400 Senior Undergraduate Course -- Spring Semester 1997. *
Full HTML Index
Two level hierarchical typing scheme adopted of the form: basetype/subtype
Seven base media types are defined this minimal set is enforced, i.e. all extensions must pass the whole ID->RFC->STD process.
Allow for less restrictive subtyping the base types, for example:
  • Content-Type: text/plain
  • Content-Type: text/richtext
Some standard subtypes are specified and many more are expected. New subtypes must be registered with the IANA (Internet Assigned Numbers Authority).
Private experimental subtypes prefixed with "X-" may be used freely and without registration.
Seven base types are: text, image, audio, video, multipart, message, application.
HTML version of Basic Foils prepared 11 May 1997

Foil 9 MIME - Base Content Types

From Setting the Stage for CGI Programming: HTTP, URL, CGI, MIME, HTTPD and many other acronyms ECS400 Senior Undergraduate Course -- Spring Semester 1997. *
Full HTML Index
text
  • subtypes: plain (just ASCII) and richtext (a simple markup extension including <bold>, <italic> etc. tags)
  • character sets can be further specified in the header value field as follows:
    • Content-type: text/plain; charset=us-ascii
  • Other charsets can be used to support other languages such as iso-8859-1 (French) or iso-2022-JP (Japanese). These charsets need to be encoded in one of two encoding modes: base64 or quoted-printable. The latter retains ASCII subset and is more natural for non-ASCII extensions.
image
  • Standard subtypes: gif, jpeg. Others expected.
  • base64 is a natural encoding scheme for binary media - it packs three 8-bit chars into four 7-bit chars.
audio
  • Standard subtype: single-channel 8KHz u-law. Others expected.
video
  • Standard subtype: mpeg. Others plausible.
HTML version of Basic Foils prepared 11 May 1997

Foil 10 MIME - Base Content Types, continued

From Setting the Stage for CGI Programming: HTTP, URL, CGI, MIME, HTTPD and many other acronyms ECS400 Senior Undergraduate Course -- Spring Semester 1997. *
Full HTML Index
multipart
  • Specifies a MIME message composed of several parts with possible different Content-Type fields.
  • Parts are separated by a boundary string, specified in the multipart header entry
  • Subtypes: mixed (serial combination of media), parallel (for parallel presentation if possible), alternative (multiple representations of the same data) and digest (all parts are messages)
message
  • Subtypes: rfc822 (standard ARPA e-mail format), partial (a single chunk of a larger message, chopped into pieces for transmission and then reassembled), external-body (pointer to a remote data - similar to typerlink/URL but different representation)
application
  • Current subtypes: postscript, ODA
  • Placeholder for "anything else" - several interactive/custom/creative extensions expected here
  • Already registered: Andrew-inset,t ATOMICMAIL (Bellcore)
HTML version of Basic Foils prepared 11 May 1997

Foil 11 MIME - Implementation Status

From Setting the Stage for CGI Programming: HTTP, URL, CGI, MIME, HTTPD and many other acronyms ECS400 Senior Undergraduate Course -- Spring Semester 1997. *
Full HTML Index
3+ public domain implementations available
The most popular - Metamail (Bellcore) is a MIME transition (backward compatible with most current mailing systems)
Some existin implementations: PMDF, IMAP2, C-Client, Mail-Manager, MH-MIME, Z-Mail, Andrew, Pine, Elm, Unix Sytem 5 4.3, STI Document Browser, Servicemail, MIXMH
MIME support in progress by key vendors on most platforms
ATOMICMAIL (also called "computational mail" or "active mail") project at Bellcore towards interactive extensions of MIME
HTML version of Basic Foils prepared 11 May 1997

Foil 12 HTTP - Hypertext Transport Protocol

From Setting the Stage for CGI Programming: HTTP, URL, CGI, MIME, HTTPD and many other acronyms ECS400 Senior Undergraduate Course -- Spring Semester 1997. *
Full HTML Index
HTTP provides an upper level to the Internet, that is, it is built on top of a back-bone network with all the packets flowing from client to server and vice versa using the standard TCP/IP protocol.
It uses MIME formats and concepts, but does not fully conform to MIME as the WWW is not a mail system.
HTTP protocol is compatible with other network services such as FTP (File Transfer Protocol), NNTP (Network News Transport Protocol).
  • On a UNIX-based machine, the basic services are enumerated in the file /etc/services. Each service cooresponds to a standard port. For example, telnet is mapped to port 43, and FTP is mapped to port 21. All ports below 1024 are privileged - only the system administrator can determine port use.
The HTTP service is standardly assigned to port 80 - it provides a much shorter service connection than the other services.
HTML version of Basic Foils prepared 11 May 1997

Foil 13 HTTPD - HTTP Daemon

From Setting the Stage for CGI Programming: HTTP, URL, CGI, MIME, HTTPD and many other acronyms ECS400 Senior Undergraduate Course -- Spring Semester 1997. *
Full HTML Index
The HTTP daemon is the server which responds to the Internet service requests on standard port 80 (or on another custom port). The server program is available from NCSA and is easily installed by editing a set of configuration files which give directory locations for documents, cgi scripts, error messages and icons, and which allows for options regarding path names, domain access, and so on.
HTML version of Basic Foils prepared 11 May 1997

Foil 14 URL - Uniform Resource Locator

From Setting the Stage for CGI Programming: HTTP, URL, CGI, MIME, HTTPD and many other acronyms ECS400 Senior Undergraduate Course -- Spring Semester 1997. *
Full HTML Index
A URL has the standard form
  • service://machine:port/file.file-extension
HTML hyperlinks typically use the service http for linking to other documents and media files. Some other internet services can also be used such as
  • ftp://machine/file.file-extension.
In this way, a Web server can provide other Internet services through the browser interface.
The machine is an Internet address and can either be a symbolic name provided by the Domain Name Service (DNS) or the IP numbers.
If the port is not specified, it defaults to 80.
The file.file-extension is given by any Unix path name starting from the directory known to the server as "document root". Which path names are valid is one of the options of the server - whether "public_html" is automatically put into the path name and whether paths starting with "~username" are allowed.
In the http service, the file-extension is used to tell the browser what helper application to use to view the file. Typical file extensions are html, gif, jpeg, mpeg, au, ram, etc.
HTML version of Basic Foils prepared 11 May 1997

Foil 15 HTTP - How does it work?

From Setting the Stage for CGI Programming: HTTP, URL, CGI, MIME, HTTPD and many other acronyms ECS400 Senior Undergraduate Course -- Spring Semester 1997. *
Full HTML Index
On each hyperlink click, the browser (client) initiates a connection with the server at the "machine" (e.g. using UNIX BSD connect call on the default port 80, or a custom user-defined port)
A request is sent to the server, formatted as a MIME-like message.
The server replies with another MIME-like message which is received by the browser and either formatted in the browser window or viewed with a helper application.
The connection is closed on both sides. (The exception to this is the "server push" connection.)
HTML version of Basic Foils prepared 11 May 1997

Foil 16 HTTP - GET Request Example

From Setting the Stage for CGI Programming: HTTP, URL, CGI, MIME, HTTPD and many other acronyms ECS400 Senior Undergraduate Course -- Spring Semester 1997. *
Full HTML Index
GET /document.html HTTP/1.0
Accept: www/source
Accept: text/html
Accept: image/gif
User-Agent: Lynx/2.2 libww/2.14
From: mnotulli@ukonaix.cc.ukans.edu
  • -- blank-line-terminating-the-request --
First line syntax is always: METHOD URL ProtocolVersion
The following lines form a header of an (extended) MIME message
"User-Agent" specifies the browser type
"Accept" specifies MIME types recognized by the browser
The server is expected to provide the requested data in one of these acceptable formats.
HTML version of Basic Foils prepared 11 May 1997

Foil 17 HTTP - Reply Example

From Setting the Stage for CGI Programming: HTTP, URL, CGI, MIME, HTTPD and many other acronyms ECS400 Senior Undergraduate Course -- Spring Semester 1997. *
Full HTML Index
HTTP/1.0 200 OK
Date: Wednesday, 02-Feb-95 23:04:12 GMT
Server: NCSA/1.1
MIME-version: 1.0
Last-modified: Monday, 15-Nov-94 23:33:16 GMT
Content-type: text/html
Content-length: 2345 --
  • -- blank-line-separating-header-and-body--
<HTML><HEAD>
<TITLE> Document Title </TITLE>
. . .
This message contains both header and body
Some replies contain only header (e.g. error reports, such as HTTP/1.0 404 Not Found)
GET request also contained header only, whereas POST request (see next example) contains both header and body
HTML version of Basic Foils prepared 11 May 1997

Foil 18 HTTP - POST Request Example

From Setting the Stage for CGI Programming: HTTP, URL, CGI, MIME, HTTPD and many other acronyms ECS400 Senior Undergraduate Course -- Spring Semester 1997. *
Full HTML Index
POST /cgi-bin/post-query HTTP/1.0
Accept: www/source
Accept: text/html
Accept: video/mpeg
Accept: image/x-rgb
Accept: application/postscript
User-Agent: Lynx/2.2 libwww/2.14
From: grobe@unanaix.cc.ukans.edu
Content-type: application/x-www-form-urlencoded
Content-length: 150
  • --blank-line-separating-header-and-body---
org=Academic%20Computing%20Services
&users=10000
&browser=lynx
&contact=Michael%20Grobe%20grobe@kuhbuh.cc.ukans.edu
Both header and body present in POST requests - the body is typically used to pass a form contents to the server.
HTML version of Basic Foils prepared 11 May 1997

Foil 19 Common Gateway Interface (CGI) - an introduction

From Setting the Stage for CGI Programming: HTTP, URL, CGI, MIME, HTTPD and many other acronyms ECS400 Senior Undergraduate Course -- Spring Semester 1997. *
Full HTML Index
CGI is an interface for running programs on the server at the request of the client.
The client look-and-feel for accessing CGI programs is identical to conventional static HTML, but the server side implementation is different. When the user clicks on a CGI link, the server calls the corresponding process and returns its output, not the data/file/code associated with the process.
Typical Applications
  • Support for dynamic generation of HTML documents, such as on-the-fly conversions from other formats.
  • Interfacing with other (non-HTTP) remote services such as databases (WAIS, RDMS), video-on-demand, simulations, etc.
  • Support for the two-way interactivity between clients and servers ( to be achieved by building some intelligence and multiple choice/response capabilities into the CGI programs)
  • Interface to and integration with Forms/GUI area of HTML - submitted forms are handled by suitable CGI processes.
Look at a simple example of an HTML form with its CGI Perl program.
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