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INTERNET-DRAFT                                               D. Robinson
<draft-robinson-www-interface-00.txt>            University of Cambridge
Expires 8 July 1996                                       8 January 1996

              The WWW Common Gateway Interface Version 1.1

Status of this memo

   This document is an Internet-Draft. Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas
   and its working groups. Note that other groups may also distribute
   working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced or obsoleted by other documents at any
   time. It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as `work in progress'.

   To learn the current status of any Internet-Draft, please check the
   `1id-abstracts.txt' listing contained in the Internet-Drafts Shadow
   Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe),
   munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or
   ftp.isi.edu (US West Coast).

   Distribution of this document is unlimited. Please send comments to
   the author; general discussion about CGI should take place on the
   <www-talk@w3.org> mailing list.

Abstract

   The Common Gateway Interface (CGI) is a simple interface for running
   external programs, software or gateways under an information server
   in a platform-independent manner. Currently, the supported
   information servers are HTTP servers.

   The interface has been in use by the World-Wide Web since 1993. This
   specification defines the interface known as `CGI/1.1', and its use
   on the Unix(R) and AmigaDOS(tm) systems.

1. Introduction

1.1. Purpose

   Together the HTTP [3] server and the CGI script are responsible for
   servicing a client request by sending back responses. The client
   request comprises a Universal Resource Identifier (URI) [1], a
   request method and various ancillary information about the request
   provided by the transport mechanism.



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   The CGI defines the abstract parameters, known as environment
   variables, which describe the client's request. Together with a
   concrete programmer interface this specifies a platform-independent
   interface between the script and the HTTP server.

1.2. Requirements

   This specification uses the same words as RFC 1123 [5] to define the
   significance of each particular requirement. These are:

   must

      This word or the adjective `required' means that the item is an
      absolute requirement of the specification.

   should

      This word or the adjective `recommended' means that there may
      exist valid reasons in particular circumstances to ignore this
      item, but the full implications should be understood and the case
      carefully weighed before choosing a different course.

   may

      This word or the adjective `optional' means that this item is
      truly optional. One vendor may choose to include the item because
      a particular marketplace requires it or because it enhances the
      product, for example; another vendor may omit the same item.

   An implementation is not compliant if it fails to satisfy one or more
   of the `must' requirements for the protocols it implements. An
   implementation that satisfies all of the `must' and all of the
   `should' requirements for its features is said to be `unconditionally
   compliant'; one that satisfies all of the `must' requirements but not
   all of the `should' requirements for its features is said to be
   `conditionally compliant'.

1.3. Specifications

   Not all of the functions and features of the CGI are defined in the
   main part of this specification. The following phrases are used to
   describe the features which are not specified:

   system defined

      The feature may differ between systems, but must be the same for
      different implementations using the same system. A system will
      usually identify a class of operating-systems. Some systems are



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      defined in section 12 of this document. New systems may be defined
      by new specifications without revision of this document.

   implementation defined

      The behaviour of the feature may vary from implementation to
      implementation, but a particular implementation must document its
      behaviour.

1.4. Terminology

   This specification uses many terms defined in the HTTP/1.0
   specification [3]; however, the following terms are used here in a
   sense which may not accord with their definitions in that document,
   or with their common meaning.

   environment variable

      A named parameter that carries information from the server to the
      script. It is not necessarily a variable in the operating-system's
      environment, although that is the most common implementation.

   script

      The software which is invoked by the server via this interface. It
      need not be a standalone program, but could be a
      dynamically-loaded or shared library, or even a subroutine in the
      server.

   server

      The application program which invokes the script in order to
      service requests.

2. Notational Conventions and Generic Grammar

2.1. Augmented BNF

   All of the mechanisms specified in this document are described in
   both prose and an augmented Backus-Naur Form (BNF) similar to that
   used by RFC 822 [6]. This augmented BNF contains the following
   constructs:

   name = definition

      The name of a rule is simply the name itself; it is separated from
      the definition by the equal character ("="). Whitespace is only
      significant in that continuation lines of a definition are



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      indented.

   "literal"

      Quotation marks (") or angle-brackets ("<" and ">") surround
      literal text. Unless stated otherwise, the text is case-sensitive.

   rule1 | rule2

      Alternative rules are separated by a vertical bar ("|").

   (rule1 rule2 rule3)

      Elements enclosed in parentheses are treated as a single element.

   *rule

      A rule preceded by an asterisk ("*") may have zero or more
      occurrences. A rule preceded by an integer followed by an asterisk
      must occur at least the specified number of times.

   [rule]

      A element enclosed in square brackets ("[" and "]") is optional.

2.2. Basic Rules

   The following rules are used throughout this specification to
   describe basic parsing constructs.

      alpha         = lowalpha | hialpha
      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"
      hialpha       = "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"
      OCTET         = <any 8-bit byte>
      CHAR          = <any character>
      CTL           = <any control character>
      SP            = <space character>
      NL            = <newline>
      LWSP          = SP | NL | <horizontal-tab>
      tspecial      = "(" | ")" | "@" | "," | ";" | ":" | "\" | <">



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                    | "/" | "[" | "]" | "?" | SP
      token         = 1*<any CHAR except CTLs or tspecials>
      quoted-string = ( <"> *qdtext <"> ) | ( "<" *qatext ">")
      qdtext        = <any CHAR except <"> and CTLs but including LWSP>
      qatext        = <any CHAR except "<", ">" and CTLs but
                      including LWSP>

   Note that newline (NL) need not be a single character, but can be a
   character sequence.

3. URL Encoding

   Some variables and constructs used here are described as being
   `URL-encoded'. This encoding is described in section 2.2 of RFC 1738
   [4]. In a URL encoded string an escape sequence consists of a percent
   character ("%") followed by two hexadecimal digits, where the two
   hexadecimal digits form an octet. An escape sequence represents the
   graphic character which has the octet as its code within the US-ASCII
   [11] coded character set, if it exists. If no such graphic character
   exists, then the escape sequence represents the octet value itself.

   Note that some unsafe characters may have different semantics if they
   are encoded. The definition of which characters are unsafe depends on
   the context.

4. The Script URI

   A `Script URI' can be defined; this describes the resource identified
   by the environment variables. Often, this URI will be the same as the
   URI requested by the client (the `Client URI'); however, it need not
   be. Instead, it could be a URI invented by the server, and so it can
   only be used in the context of the server and its CGI interface.

   The script URI has the syntax of generic-RL as defined in section 2.1
   of RFC 1808 [7], with the exception that object parameters and
   fragment identifiers are not permitted:

      <scheme>://<host>:<port>/<path>?<query>

   The various components of the script URI are defined by some of the
   environment variables (see below);

      script-uri = protocol "://" SERVER_NAME ":" SERVER_PORT enc-script
                   enc-path-info "?" QUERY_STRING

   where `protocol' is found from SERVER_PROTOCOL, `enc-script' is a
   URL-encoded version of SCRIPT_NAME and `enc-path-info' is a
   URL-encoded version of PATH_INFO.



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5. Environment variables

   Environment variables are used to pass data about the request from
   the server to the script. They are accessed by the script in a system
   defined manner. In all cases, a missing environment variable is
   equivalent to a zero-length (NULL) value, and vice versa. The
   representation of the characters in the environment variables is
   system defined.

   Case is not significant in the names, in that there cannot be two
   different variable whose names differ in case only. Here they are
   shown using a canonical representation of capitals plus underscore
   ("_"). The actual representation of the names is system defined; for
   a particular system the representation may be defined differently to
   this.

   The variables are:

      AUTH_TYPE
      CONTENT_LENGTH
      CONTENT_TYPE
      GATEWAY_INTERFACE
      HTTP_*
      PATH_INFO
      PATH_TRANSLATED
      QUERY_STRING
      REMOTE_ADDR
      REMOTE_HOST
      REMOTE_IDENT
      REMOTE_USER
      REQUEST_METHOD
      SCRIPT_NAME
      SERVER_NAME
      SERVER_PORT
      SERVER_PROTOCOL
      SERVER_SOFTWARE

   AUTH_TYPE

      The variable is specific to requests made with HTTP.

      If the script URI would require access authentication for external
      access, then this variable is found from the `auth-scheme' token
      in the request, otherwise NULL.

         auth-scheme = "Basic" | token

      HTTP access authentication schemes are described in section 11 of



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      the HTTP/1.0 specification [3]. The auth-scheme is not
      case-sensitive.

   CONTENT_LENGTH

      The size of the entity attached to the request, if any, in decimal
      number of octets. If no data is attached, then NULL. The syntax is
      the same as the HTTP Content-Length header (section 10, HTTP/1.0
      specification [3]).

         CONTENT_LENGTH = "" | [ 1*digit ]

   CONTENT_TYPE

      The Internet Media Type [9] of the attached entity. The syntax is
      the same as the HTTP Content-Type header.

         CONTENT_TYPE = "" | media-type
         media-type   = type "/" subtype *( ";" parameter)
         type         = token
         subtype      = token
         parameter    = attribute "=" value
         attribute    = token
         value        = token | quoted-string

      The type, subtype and parameter attribute names are not
      case-sensitive. Parameter values may be case sensitive.  Media
      types and their use in HTTP are described section 3.6 of the
      HTTP/1.0 specification [3]. Example:

         application/x-www-form-urlencoded

      There is no default value for this variable. If and only if it is
      unset, then the script may attempt to determine the media type
      from the data received. If the type remains unknown, then
      application/octet-stream should be assumed.

   GATEWAY_INTERFACE

      The version of the CGI specification to which this server
      complies.  Syntax:

         GATEWAY_INTERFACE =  "CGI" "/" 1*digit "." 1*digit

      Note that the major and minor numbers are treated as separate
      integers and that each may be incremented higher than a single
      digit.  Thus CGI/2.4 is a lower version than CGI/2.13 which in
      turn is lower than CGI/12.3. Leading zeros must be ignored by



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      scripts and should never be generated by servers.

      This document defines the 1.1 version of the CGI interface.

   HTTP_*

      These variables are specific to requests made with HTTP.
      Interpretation of these variables may depend on the value of
      SERVER_PROTOCOL.

      Environment variables with names beginning with "HTTP_" contain
      header data read from the client, if the protocol used was HTTP.
      The HTTP header name is converted to upper case, has all
      occurrences of "-" replaced with "_" and has "HTTP_" prepended to
      give the environment variable name. The header data may be
      presented as sent by the client, or may be rewritten in ways which
      do not change its semantics. If multiple headers with the same
      field-name are received then they must be rewritten as a single
      header having the same semantics. Similarly, a header that is
      received on more than one line must be merged onto a single line.
      The server must, if necessary, change the representation of the
      data (for example, the character set) to be appropriate for a CGI
      environment variable.

      The server is not required to create environment variables for all
      the headers that it receives. In particular, it may remove any
      headers carrying authentication information, such as
      "Authorization"; it may remove headers whose value is available to
      the script via other variables, such as "Content-Length" and
      "Content-Type".

   PATH_INFO

      A path to be interpreted by the CGI script. It identifies the
      resource or sub-resource to be returned by the CGI script. The
      syntax and semantics are similar to a decoded HTTP URL `hpath'
      token (defined in RFC 1738 [4]), with the exception that a
      PATH_INFO of "/" represents a single void path segment. Otherwise,
      the leading "/" character is not part of the path.

         PATH_INFO = "" | "/" path
         path      = segment *( "/" segment )
         segment   = *pchar
         pchar     = <any CHAR except "/">

      The PATH_INFO string is the trailing part of the <path> component
      of the script URI that follows the SCRIPT_NAME part of the path.




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   PATH_TRANSLATED

      The OS path to the file that the server would attempt to access
      were the client to request the absolute URL containing the path
      PATH_INFO.  i.e for a request of

         protocol "://" SERVER_NAME ":" SERVER_PORT enc-path-info

      where `enc-path-info' is a URL-encoded version of PATH_INFO. If
      PATH_INFO is NULL then PATH_TRANSLATED is set to NULL.

         PATH_TRANSLATED = *CHAR

      PATH_TRANSLATED need not be supported by the server. The server
      may choose to set PATH_TRANSLATED to NULL for reasons of security,
      or because the path would not be interpretable by a CGI script;
      such as the object it represented was internal to the server and
      not visible in the file-system; or for any other reason.

      The algorithm the server uses to derive PATH_TRANSLATED is
      obviously implementation defined; CGI scripts which use this
      variable may suffer limited portability.

   QUERY_STRING

      A URL-encoded search string; the <query> part of the script URI.

         QUERY_STRING = query-string
         query-string = *qchar
         qchar        = unreserved | escape | reserved
         unreserved   = alpha | digit | safe | extra
         reserved     = ";" | "/" | "?" | ":" | "@" | "&" | "="
         safe         = "$" | "-" | "_" | "." | "+"
         extra        = "!" | "*" | "'" | "(" | ")" | ","
         escape       = "%" hex hex
         hex          = digit | "A" | "B" | "C" | "D" | "E" | "F" | "a"
                      | "b" | "c" | "d" | "e" | "f"

      The URL syntax for a search string is described in RFC 1738 [4].

   REMOTE_ADDR

      The IP address of the agent sending the request to the server. Not
      necessarily that of the client.

         REMOTE_ADDR = hostnumber
         hostnumber  = digits "." digits "." digits "." digits
         digits      = 1*digit



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   REMOTE_HOST

      The fully qualified domain name of the agent sending the request
      to the server, if available, otherwise NULL. Not necessarily that
      of the client. Fully qualified domain names take the form as
      described in section 3.5 of RFC 1034 [8] and section 2.1 of RFC
      1123 [5]; a sequence of domain labels separated by ".", each
      domain label starting and ending with an alphanumerical character
      and possibly also containing "-" characters. The rightmost domain
      label will never start with a digit. Domain names are not case
      sensitive.

         REMOTE_HOST   = "" | hostname
         hostname      = *( domainlabel ".") toplabel
         domainlabel   = alphadigit [ *alphahypdigit alphadigit ]
         toplabel      = alpha [ *alphahypdigit alphadigit ]
         alphahypdigit = alphadigit | "-"
         alphadigit    = alpha | digit

   REMOTE_IDENT

      The identity information reported about the connection by a RFC
      931 [10] request to the remote agent, if available. The server may
      choose not to support this feature, or not to request the data for
      efficiency reasons.

         REMOTE_IDENT = *CHAR

      The data returned is not appropriate for use as authentication
      information.

   REMOTE_USER

      This variable is specific to requests made with HTTP.

      If AUTH_TYPE is "Basic", then the user-ID sent by the client. If
      AUTH_TYPE is NULL, then NULL, otherwise undefined.

         userid      = token

   REQUEST_METHOD

      This variable is specific to requests made with HTTP.

      The method with which the request was made, as described in
      section 5.1.1 of the HTTP/1.0 specification [3].

         http-method      = "GET" | "HEAD" | "POST" | extension-method



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         extension-method = token

      The method is case sensitive.

   SCRIPT_NAME

      A URL path that could identify the CGI script (rather then the
      particular CGI output). The syntax and semantics are identical to
      a decoded HTTP URL `hpath' token [4].

         SCRIPT_NAME = "" | "/" [ path ]

      The leading "/" is not part of the path. It is optional if the
      path is NULL.

      The SCRIPT_NAME string is some leading part of the <path>
      component of the script URI derived in some implementation defined
      manner.

   SERVER_NAME

      The name for this server, as used in the <host> part of the script
      URI. Thus either a fully qualified domain name, or an IP address.

         SERVER_NAME = hostname | hostnumber

   SERVER_PORT

      The port on which this request was received, as used in the <port>
      part of the script URI.

         SERVER_PORT = 1*digit

   SERVER_PROTOCOL

      The name and revision of the information protocol this request
      came in with.

         SERVER_PROTOCOL   = HTTP-Version | extension-version
         HTTP-Version      = "HTTP" "/" 1*digit "." 1*digit
         extension-version = protocol "/" 1*digit "." 1*digit
         protocol          = 1*( alpha | digit | "+" | "-" | "." )

      `protocol' is a version of the <scheme> part of the script URI,
      and is not case sensitive. By convention, `protocol' is in upper
      case.

   SERVER_SOFTWARE



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      The name and version of the information server software answering
      the request (and running the gateway).

         SERVER_SOFTWARE = *CHAR

6. Invoking the script

   This script is invoked in a system defined manner. Unless specified
   otherwise, this will be by treating the file containing the script as
   an executable, and running it as a child process of the server.

7. The CGI script command line

   Some systems support a method for supplying a array of strings to the
   CGI script. This is only used in the case of an `indexed' query. This
   is identified by a "GET" or "HEAD" HTTP request with a URL search
   string not containing any unencoded "=" characters. For such a
   request, the server should parse the search string into words, using
   the rule:

      search-string = search-word *( "+" search-word )
      search-word   = 1*schar
      schar         = xunreserved | escape | xreserved
      xunreserved   = alpha | digit | xsafe | extra
      xsafe         = "$" | "-" | "_" | "."
      xreserved     = ";" | "/" | "?" | ":" | "@" | "&"

   After parsing, each word is URL-decoded, optionally encoded in a
   system defined manner and then the argument list is set to the list
   of words.

   If the server cannot create any part of the argument list, then the
   server should generate no command line information. For example, the
   number of arguments may be greater than operating system or server
   limitations, or one of the words may not be representable as an
   argument.

8. Data input to the CGI script

   As there may be a data entity attached to the request, there must be
   a system defined method for the script to read this data. Unless
   defined otherwise, this will be via the `standard input' file
   descriptor.

   There will be at least CONTENT_LENGTH bytes available for the script
   to read. The script is not obliged to read the data, but it must not
   attempt to read more than CONTENT_LENGTH bytes, even if more data is
   available.



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   For non-parsed header (NPH) scripts (see below), the server should
   attempt to ensure that the script input comes directly from the
   client, with minimal buffering.

9. Data output from the CGI script

   There must be a system defined method for the script to send data
   back to the server or client; a script will always return some data.
   Unless defined otherwise, this will be via the `standard output' file
   descriptor.

   There are two forms of output that the script can give; non-parsed
   header (NPH) output, and parsed header output. A server is only
   required to support the latter; distinguishing between the two types
   of output (or scripts) is implementation defined.

9.1. Non-Parsed Header Output

   The script must return a complete HTTP response message, as described
   in Section 6 of the HTTP specification [3]. Note that this allows an
   HTTP/0.9 response to an HTTP/1.0 request.

   The server should attempt to ensure that the script output is sent
   directly to the client, with minimal buffering.

9.2. Parsed Header Output

   The script returns a CGI response message.

      CGI-Response = *( CGI-Header | HTTP-Header ) NL [ Entity-Body ]
      CGI-Header   = Content-type
                   | Location
                   | Status
                   | extension-header

   The response comprises headers and a body, separated by a blank line.
   The headers are either CGI headers to be interpreted by the server,
   or HTTP headers to be included in the response returned to the client
   if the request method is HTTP. At least one CGI-Header must be
   supplied, but no CGI header can be repeated with the same field-name.
   If a body is supplied, then a Content-type header is required,
   otherwise the script must send a Location or Status header.

   The CGI headers have the generic syntax:

      generic-header = field-name ":" [ field-value ] NL
      field-name     = 1*<any CHAR, excluding CTLs, SP and ":">
      field-value    = *( field-content | LWSP )



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      field-content  = *( token | tspecial | quoted-string)

   The field-name is not case sensitive; a NULL field value is
   equivalent to the header not being sent.

   Content-Type

      The Internet Media Type [9] of the entity body.

         Content-Type = "Content-Type" ":" media-type NL

   Location

      This is used to specify to the server that the script is returning
      a reference to a document rather than an actual document.

         Location         = "Location" ":"
                            ( fragment-URI | rel-URL-abs-path ) NL
         fragment-URI     = URI [ # fragmentid ]
         URI              = scheme ":" *qchar
         fragmentid       = *qchar

         rel-URL-abs-path = "/" [ hpath ] [ "?" query-string ]
         hpath            = fpsegment *( "/" psegment )
         fpsegment        = 1*hchar
         psegment         = *hchar
         hchar            = alpha | digit | safe | extra
                          | ":" | "@" | "& | "="

      The location value is either an absolute URI with optional
      fragment, as defined in RFC 1630 [1], or an absolute path and
      optional query-string. If an absolute URI is returned by the
      script, then the server will generate a redirect HTTP response
      message, and if no entity body is supplied by the script, then the
      server will produce one. If the Location value is a path, then the
      server will generate the response that it would have produced in
      response to a request containing the URL

         protocol "://" SERVER_NAME ":" SERVER_PORT rel-URL-abs-path

      The location header may only be sent if the REQUEST_METHOD is HEAD
      or GET.

   Status

      The Status header is used to indicate to the server what status
      code it will use in the response message. It should not be sent if
      the script returns a Location header.



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         Status        = "Status" ":" 3digit SP reason-phrase NL
         reason-phrase = *<CHAR, excluding CTLs, NL>

      The valid status codes are listed in section 6.1.1 of the HTTP/1.0
      specification [3]. If the script does not return a Status header,
      then "200 OK" should be assumed.

   HTTP headers

      The script may return any other headers defined by the HTTP/1.0
      specification [3]. The server must translate the header data from
      the CGI header syntax to the HTTP header syntax if these differ.
      For example, the character sequence for newline (such as Unix's
      ASCII NL) used by CGI scripts may not be the same as that used by
      HTTP (ASCII CR followed by LF).

10. Requirements for servers

   Servers must support the standard mechanism (described below) which
   allows the script author to determine what URL to use in documents
   which reference the script. Specifically, what URL to use in order to
   achieve particular settings of the environment variables. This
   mechanism is as follows:

   The value for SCRIPT_NAME is governed by the server configuration and
   the location of the script in the OS file-system. Given this, any
   access to the partial URL

      SCRIPT_NAME extra-path ? query-information

   where extra-path is either NULL or begins with a "/" and satisfies
   any other server requirements, will cause the CGI script to be
   executed with PATH_INFO set to the decoded extra-path, and
   QUERY_STRING set to query-information (not decoded).

   Servers may reject with error 404 any requests that would result in
   an encoded "/" being decoded into PATH_INFO or SCRIPT_NAME, as this
   might represent a loss of information to the script.

   Although the server and the CGI script need not be consistent in
   their handling of URL paths (client URLs and the PATH_INFO data,
   respectively), server authors may wish to impose consistency.  So the
   server implementation should define its behaviour for the following
   cases:

      o define any restrictions on allowed characters, in particular
        whether ASCII NULL is permitted;




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      o define any restrictions on allowed path segments, in particular
        whether non-terminal NULL segments are permitted;

      o define the behaviour for "." or ".." path segments; i.e. whether
        they are prohibited, treated as ordinary path segments or
        interpreted in accordance with the relative URL specification
        [7];

      o define any limits of the implementation, including limits on
        path or search string lengths, and limits on the volume of
        headers the server will parse.

   Servers may generate the script URI in any way from the client URI,
   or from any other data (but the behaviour should be documented).

11. Recommendations for scripts

   Scripts should reject unexpected methods (such as DELETE etc.) with
   error 405 Method Not Allowed. If the script does not intend
   processing the PATH_INFO data, then it should reject the request with
   404 Not Found if PATH_INFO is not NULL.

   If the output of a form is being processed, check that CONTENT_TYPE
   is "application/x-www-form-urlencoded" [2].

      Note: presumably 400 is the appropriate error code in this case.

   If parsing PATH_INFO, PATH_TRANSLATED or SCRIPT_NAME then be careful
   of void path segments ("//") and special path segments ("." and
   ".."). They should either be removed from the path before use in OS
   system calls, or the request should be rejected with 404 Not Found.
   It is very unlikely that any other use could be made of these.

   As it is impossible for the script to determine the client URI that
   initiated this request without knowledge of the specific server in
   use, the script should not return text/html documents containing
   relative URL links without including a <BASE> tag in the document.

   When returning headers, the script should try to send the CGI headers
   as soon as possible, and preferably before any HTTP headers. This may
   help reduce the server's memory requirements.

12. System specifications

12.1. AmigaDOS

   Environment variables




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      These are accessed by the DOS library routine GetVar. The flags
      argument should be 0. Case is ignored, but upper case is
      recommended for compatibility with case-sensitive systems.

   The current working directory

      The current working directory for the script is set to the
      directory containing the script.

12.2. Unix

   For Unix compatible operating systems, the following are defined:

   Environment variables

      These are accessed by the C library routine getenv.

   The command line

      This is accessed using the the argc and argv arguments to main().
      The words are have any characters which are `active' in the Bourne
      shell escaped with a backslash.

   The current working directory

      The current working directory for the script is set to the
      directory containing the script.

13. Security Considerations

13.1. Safe Methods

   As discussed in the security considerations of the HTTP specification
   [3], the convention has been established that the GET and HEAD
   methods should be `safe'; they should cause no side-effects and only
   have the significance of resource retrieval.

13.2. HTTP headers containing sensitive information

   Some HTTP headers may carry sensitive information which the server
   should not pass on to the script unless explicitly configured to do
   so. For example, if the server protects the script using the Basic
   authentication scheme, then the client will send an Authorization
   header containing a username and password. If the server, rather than
   the script, validates this information then it should not pass on the
   password via the HTTP_AUTHORIZATION environment variable.

13.3. Script interference with the server



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   The most common implementation of CGI invokes the script as a child
   process using the same user and group as the server process. It
   should therefore be ensured that the script cannot interfere with the
   server process, its configuration or documents.

   If the script is executed by calling a function linked in to the
   server software (either at compile-time or run-time) then precautions
   should be taken to protect the core memory of the server, or to
   ensure that untrusted code cannot be executed.

14. Acknowledgements

   This work is based on the original CGI interface that arose out of
   discussions on the www-talk mailing list. In particular, Rob McCool,
   John Franks, Ari Luotonen, George Phillips and Tony Sanders deserve
   special recognition for their efforts in defining and implementing
   the early versions of this interface.

   This document has also greatly benefited from the comments and
   suggestions made Chris Adie, Dave Kristol and Mike Meyer.

15. References

   [1]  Berners-Lee, T., `Universal Resource Identifiers in WWW: A
        Unifying Syntax for the Expression of Names and Addresses of
        Objects on the Network as used in the World-Wide Web', RFC 1630,
        CERN, June 1994.

   [2]  Berners-Lee, T. and Connolly, D., `Hypertext Markup Language -
        2.0', RFC 1866, MIT/W3C, November 1995.

   [3]  Berners-Lee, T., Fielding, R. T. and Frystyk Nielsen, H.,
        `Hypertext Transfer Protocol -- HTTP/1.0', Work in progress
        (draft-ietf-http-v10-spec-04.txt), MIT/LCS, UC Irvine, October
        1995.

   [4]  Berners-Lee, T., Masinter, L. and McCahill, M., Editors,
        `Uniform Resource Locators (URL)', RFC 1738, CERN, Xerox
        Corporation, University of Minnesota, December 1994.

   [5]  Braden, R., Editor, `Requirements for Internet Hosts --
        Application and Support', STD 3, RFC 1123, IETF, October 1989.

   [6]  Crocker, D.H., `Standard for the Format of ARPA Internet Text
        Messages', STD 11, RFC 822, University of Delaware, August 1982.

   [7]  Fielding, R., `Relative Uniform Resource Locators', RFC 1808, UC
        Irving, June 1995.



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   [8]  Mockapetris, P., `Domain Names - Concepts and Facilities', STD
        13, RFC 1034, ISI, November 1987.

   [9]  Postel, J., `Media Type Registration Procedure', RFC 1590, ISI,
        March 1994.

   [10] StJohns, M., `Authentication Server', RFC 931, TPSC, January
        1985.

   [11] `Coded Character Set -- 7-bit American Standard Code for
        Information Interchange', ANSI X3.4-1986.

16. Author's Address

      David Robinson
      Institute of Astronomy
      University of Cambridge
      Madingley Road
      Cambridge CB3 0HA
      UK

      Tel: +44 (1223) 337528
      Fax: +44 (1223) 337523
      EMail: drtr@ast.cam.ac.uk



























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