| Rfc | 3875 |
|---|
| Title | The Common Gateway Interface (CGI) Version 1.1 |
|---|
| Author | D. Robinson, K.
Coar |
|---|
| Date | October 2004 |
|---|
| Format: | TXT, PDF, HTML |
|---|
| Status: | INFORMATIONAL |
|---|
|
Network Working Group D. Robinson
Request for Comments: 3875 K. Coar
Category: Informational The Apache Software Foundation
October 2004
The Common Gateway Interface (CGI) Version 1.1
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2004).
IESG Note
This document is not a candidate for any level of Internet Standard.
The IETF disclaims any knowledge of the fitness of this document for
any purpose, and in particular notes that it has not had IETF review
for such things as security, congestion control or inappropriate
interaction with deployed protocols. The RFC Editor has chosen to
publish this document at its discretion. Readers of this document
should exercise caution in evaluating its value for implementation
and deployment.
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 (WWW) since 1993.
This specification defines the 'current practice' parameters of the
'CGI/1.1' interface developed and documented at the U.S. National
Centre for Supercomputing Applications. This document also defines
the use of the CGI/1.1 interface on UNIX(R) and other, similar
systems.
Table of Contents
1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Requirements . . . . . . . . . . . . . . . . . . . . . . 4
1.3. Specifications . . . . . . . . . . . . . . . . . . . . . 4
1.4. Terminology . . . . . . . . . . . . . . . . . . . . . . 5
2. Notational Conventions and Generic Grammar. . . . . . . . . . 5
2.1. Augmented BNF . . . . . . . . . . . . . . . . . . . . . 5
2.2. Basic Rules . . . . . . . . . . . . . . . . . . . . . . 6
2.3. URL Encoding . . . . . . . . . . . . . . . . . . . . . . 7
3. Invoking the Script . . . . . . . . . . . . . . . . . . . . . 8
3.1. Server Responsibilities . . . . . . . . . . . . . . . . 8
3.2. Script Selection . . . . . . . . . . . . . . . . . . . . 9
3.3. The Script-URI . . . . . . . . . . . . . . . . . . . . . 9
3.4. Execution . . . . . . . . . . . . . . . . . . . . . . . 10
4. The CGI Request . . . . . . . . . . . . . . . . . . . . . . . 10
4.1. Request Meta-Variables . . . . . . . . . . . . . . . . . 10
4.1.1. AUTH_TYPE. . . . . . . . . . . . . . . . . . . . 11
4.1.2. CONTENT_LENGTH . . . . . . . . . . . . . . . . . 12
4.1.3. CONTENT_TYPE . . . . . . . . . . . . . . . . . . 12
4.1.4. GATEWAY_INTERFACE. . . . . . . . . . . . . . . . 13
4.1.5. PATH_INFO. . . . . . . . . . . . . . . . . . . . 13
4.1.6. PATH_TRANSLATED. . . . . . . . . . . . . . . . . 14
4.1.7. QUERY_STRING . . . . . . . . . . . . . . . . . . 15
4.1.8. REMOTE_ADDR. . . . . . . . . . . . . . . . . . . 15
4.1.9. REMOTE_HOST. . . . . . . . . . . . . . . . . . . 16
4.1.10. REMOTE_IDENT . . . . . . . . . . . . . . . . . . 16
4.1.11. REMOTE_USER. . . . . . . . . . . . . . . . . . . 16
4.1.12. REQUEST_METHOD . . . . . . . . . . . . . . . . . 17
4.1.13. SCRIPT_NAME. . . . . . . . . . . . . . . . . . . 17
4.1.14. SERVER_NAME. . . . . . . . . . . . . . . . . . . 17
4.1.15. SERVER_PORT. . . . . . . . . . . . . . . . . . . 18
4.1.16. SERVER_PROTOCOL. . . . . . . . . . . . . . . . . 18
4.1.17. SERVER_SOFTWARE. . . . . . . . . . . . . . . . . 19
4.1.18. Protocol-Specific Meta-Variables . . . . . . . . 19
4.2. Request Message-Body . . . . . . . . . . . . . . . . . . 20
4.3. Request Methods . . . . . . . . . . . . . . . . . . . . 20
4.3.1. GET. . . . . . . . . . . . . . . . . . . . . . . 20
4.3.2. POST . . . . . . . . . . . . . . . . . . . . . . 21
4.3.3. HEAD . . . . . . . . . . . . . . . . . . . . . . 21
4.3.4. Protocol-Specific Methods. . . . . . . . . . . . 21
4.4. The Script Command Line. . . . . . . . . . . . . . . . . 21
5. NPH Scripts . . . . . . . . . . . . . . . . . . . . . . . . . 22
5.1. Identification . . . . . . . . . . . . . . . . . . . . . 22
5.2. NPH Response . . . . . . . . . . . . . . . . . . . . . . 22
6. CGI Response. . . . . . . . . . . . . . . . . . . . . . . . . 23
6.1. Response Handling. . . . . . . . . . . . . . . . . . . . 23
6.2. Response Types . . . . . . . . . . . . . . . . . . . . . 23
6.2.1. Document Response. . . . . . . . . . . . . . . . 23
6.2.2. Local Redirect Response. . . . . . . . . . . . . 24
6.2.3. Client Redirect Response . . . . . . . . . . . . 24
6.2.4. Client Redirect Response with Document . . . . . 24
6.3. Response Header Fields . . . . . . . . . . . . . . . . . 25
6.3.1. Content-Type . . . . . . . . . . . . . . . . . . 25
6.3.2. Location . . . . . . . . . . . . . . . . . . . . 26
6.3.3. Status . . . . . . . . . . . . . . . . . . . . . 26
6.3.4. Protocol-Specific Header Fields. . . . . . . . . 27
6.3.5. Extension Header Fields. . . . . . . . . . . . . 27
6.4. Response Message-Body. . . . . . . . . . . . . . . . . . 28
7. System Specifications . . . . . . . . . . . . . . . . . . . . 28
7.1. AmigaDOS . . . . . . . . . . . . . . . . . . . . . . . . 28
7.2. UNIX . . . . . . . . . . . . . . . . . . . . . . . . . . 28
7.3. EBCDIC/POSIX . . . . . . . . . . . . . . . . . . . . . . 29
8. Implementation. . . . . . . . . . . . . . . . . . . . . . . . 29
8.1. Recommendations for Servers. . . . . . . . . . . . . . . 29
8.2. Recommendations for Scripts. . . . . . . . . . . . . . . 30
9. Security Considerations . . . . . . . . . . . . . . . . . . . 30
9.1. Safe Methods . . . . . . . . . . . . . . . . . . . . . . 30
9.2. Header Fields Containing Sensitive Information . . . . . 31
9.3. Data Privacy . . . . . . . . . . . . . . . . . . . . . . 31
9.4. Information Security Model . . . . . . . . . . . . . . . 31
9.5. Script Interference with the Server. . . . . . . . . . . 31
9.6. Data Length and Buffering Considerations . . . . . . . . 32
9.7. Stateless Processing . . . . . . . . . . . . . . . . . . 32
9.8. Relative Paths . . . . . . . . . . . . . . . . . . . . . 33
9.9. Non-parsed Header Output . . . . . . . . . . . . . . . . 33
10. Acknowledgements. . . . . . . . . . . . . . . . . . . . . . . 33
11. References. . . . . . . . . . . . . . . . . . . . . . . . . . 33
11.1. Normative References. . . . . . . . . . . . . . . . . . 33
11.2. Informative References. . . . . . . . . . . . . . . . . 34
12. Authors' Addresses. . . . . . . . . . . . . . . . . . . . . . 35
13. Full Copyright Statement. . . . . . . . . . . . . . . . . . . 36
1. Introduction
1.1. Purpose
The Common Gateway Interface (CGI) [22] allows an HTTP [1], [4]
server and a CGI script to share responsibility for responding to
client requests. The client request comprises a Uniform Resource
Identifier (URI) [11], a request method and various ancillary
information about the request provided by the transport protocol.
The CGI defines the abstract parameters, known as meta-variables,
which describe a client's request. Together with a concrete
programmer interface this specifies a platform-independent interface
between the script and the HTTP server.
The server is responsible for managing connection, data transfer,
transport and network issues related to the client request, whereas
the CGI script handles the application issues, such as data access
and document processing.
1.2. Requirements
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 BCP 14, RFC 2119 [3].
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 that 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
defined in section 7 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; a particular implementation must document its
behaviour.
1.4. Terminology
This specification uses many terms defined in the HTTP/1.1
specification [4]; 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.
'meta-variable'
A named parameter which 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 that is invoked by the server according to 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. It might be a set of statements interpreted at run-time,
as the term 'script' is frequently understood, but that is not a
requirement and within the context of this specification the term
has the broader definition stated.
'server'
The application program that invokes the script in order to
service requests from the client.
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 [13]. Unless stated otherwise, the elements are
case-sensitive. This augmented BNF contains the following
constructs:
name = definition
The name of a rule and its definition are separated by the equals
character ('='). Whitespace is only significant in that
continuation lines of a definition are indented.
"literal"
Double quotation marks (") surround literal text, except for a
literal quotation mark, which is surrounded by angle-brackets ('<'
and '>').
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. The full form is 'n*m rule' indicating at least n
and at most m occurrences of the rule. n and m are optional
decimal values with default values of 0 and infinity respectively.
[rule]
An element enclosed in square brackets ('[' and ']') is optional,
and is equivalent to '*1 rule'.
N rule
A rule preceded by a decimal number represents exactly N
occurrences of the rule. It is equivalent to 'N*N rule'.
2.2. Basic Rules
This specification uses a BNF-like grammar defined in terms of
characters. Unlike many specifications which define the bytes
allowed by a protocol, here each literal in the grammar corresponds
to the character it represents. How these characters are represented
in terms of bits and bytes within a system are either system-defined
or specified in the particular context. The single exception is the
rule 'OCTET', defined below.
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"
alphanum = alpha | digit
OCTET = <any 8-bit byte>
CHAR = alpha | digit | separator | "!" | "#" | "$" |
"%" | "&" | "'" | "*" | "+" | "-" | "." | "`" |
"^" | "_" | "{" | "|" | "}" | "~" | CTL
CTL = <any control character>
SP = <space character>
HT = <horizontal tab character>
NL = <newline>
LWSP = SP | HT | NL
separator = "(" | ")" | "<" | ">" | "@" | "," | ";" | ":" |
"\" | <"> | "/" | "[" | "]" | "?" | "=" | "{" |
"}" | SP | HT
token = 1*<any CHAR except CTLs or separators>
quoted-string = <"> *qdtext <">
qdtext = <any CHAR except <"> and CTLs but including LWSP>
TEXT = <any printable character>
Note that newline (NL) need not be a single control character, but
can be a sequence of control characters. A system MAY define TEXT to
be a larger set of characters than <any CHAR excluding CTLs but
including LWSP>.
2.3. URL Encoding
Some variables and constructs used here are described as being
'URL-encoded'. This encoding is described in section 2 of RFC 2396
[2]. 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 that has the octet as its code within the
US-ASCII [9] coded character set, if it exists. Currently there is
no provision within the URI syntax to identify which character set
non-ASCII codes represent, so CGI handles this issue on an ad-hoc
basis.
Note that some unsafe (reserved) characters may have different
semantics when encoded. The definition of which characters are
unsafe depends on the context; see section 2 of RFC 2396 [2], updated
by RFC 2732 [7], for an authoritative treatment. These reserved
characters are generally used to provide syntactic structure to the
character string, for example as field separators. In all cases, the
string is first processed with regard to any reserved characters
present, and then the resulting data can be URL-decoded by replacing
"%" escape sequences by their character values.
To encode a character string, all reserved and forbidden characters
are replaced by the corresponding "%" escape sequences. The string
can then be used in assembling a URI. The reserved characters will
vary from context to context, but will always be drawn from this set:
reserved = ";" | "/" | "?" | ":" | "@" | "&" | "=" | "+" | "$" |
"," | "[" | "]"
The last two characters were added by RFC 2732 [7]. In any
particular context, a sub-set of these characters will be reserved;
the other characters from this set MUST NOT be encoded when a string
is URL-encoded in that context. Other basic rules used to describe
URI syntax are:
hex = digit | "A" | "B" | "C" | "D" | "E" | "F" | "a" | "b"
| "c" | "d" | "e" | "f"
escaped = "%" hex hex
unreserved = alpha | digit | mark
mark = "-" | "_" | "." | "!" | "~" | "*" | "'" | "(" | ")"
3. Invoking the Script
3.1. Server Responsibilities
The server acts as an application gateway. It receives the request
from the client, selects a CGI script to handle the request, converts
the client request to a CGI request, executes the script and converts
the CGI response into a response for the client. When processing the
client request, it is responsible for implementing any protocol or
transport level authentication and security. The server MAY also
function in a 'non-transparent' manner, modifying the request or
response in order to provide some additional service, such as media
type transformation or protocol reduction.
The server MUST perform translations and protocol conversions on the
client request data required by this specification. Furthermore, the
server retains its responsibility to the client to conform to the
relevant network protocol even if the CGI script fails to conform to
this specification.
If the server is applying authentication to the request, then it MUST
NOT execute the script unless the request passes all defined access
controls.
3.2. Script Selection
The server determines which CGI is script to be executed based on a
generic-form URI supplied by the client. This URI includes a
hierarchical path with components separated by "/". For any
particular request, the server will identify all or a leading part of
this path with an individual script, thus placing the script at a
particular point in the path hierarchy. The remainder of the path,
if any, is a resource or sub-resource identifier to be interpreted by
the script.
Information about this split of the path is available to the script
in the meta-variables, described below. Support for non-hierarchical
URI schemes is outside the scope of this specification.
3.3. The Script-URI
The mapping from client request URI to choice of script is defined by
the particular server implementation and its configuration. The
server may allow the script to be identified with a set of several
different URI path hierarchies, and therefore is permitted to replace
the URI by other members of this set during processing and generation
of the meta-variables. The server
1. MAY preserve the URI in the particular client request; or
2. it MAY select a canonical URI from the set of possible values
for each script; or
3. it can implement any other selection of URI from the set.
From the meta-variables thus generated, a URI, the 'Script-URI', can
be constructed. This MUST have the property that if the client had
accessed this URI instead, then the script would have been executed
with the same values for the SCRIPT_NAME, PATH_INFO and QUERY_STRING
meta-variables. The Script-URI has the structure of a generic URI as
defined in section 3 of RFC 2396 [2], with the exception that object
parameters and fragment identifiers are not permitted. The various
components of the Script-URI are defined by some of the
meta-variables (see below);
script-URI = <scheme> "://" <server-name> ":" <server-port>
<script-path> <extra-path> "?" <query-string>
where <scheme> is found from SERVER_PROTOCOL, <server-name>,
<server-port> and <query-string> are the values of the respective
meta-variables. The SCRIPT_NAME and PATH_INFO values, URL-encoded
with ";", "=" and "?" reserved, give <script-path> and <extra-path>.
See section 4.1.5 for more information about the PATH_INFO
meta-variable.
The scheme and the protocol are not identical as the scheme
identifies the access method in addition to the application protocol.
For example, a resource accessed using Transport Layer Security (TLS)
[14] would have a request URI with a scheme of https when using the
HTTP protocol [19]. CGI/1.1 provides no generic means for the script
to reconstruct this, and therefore the Script-URI as defined includes
the base protocol used. However, a script MAY make use of
scheme-specific meta-variables to better deduce the URI scheme.
Note that this definition also allows URIs to be constructed which
would invoke the script with any permitted values for the path-info
or query-string, by modifying the appropriate components.
3.4. Execution
The script is invoked in a system-defined manner. Unless specified
otherwise, the file containing the script will be invoked as an
executable program. The server prepares the CGI request as described
in section 4; this comprises the request meta-variables (immediately
available to the script on execution) and request message data. The
request data need not be immediately available to the script; the
script can be executed before all this data has been received by the
server from the client. The response from the script is returned to
the server as described in sections 5 and 6.
In the event of an error condition, the server can interrupt or
terminate script execution at any time and without warning. That
could occur, for example, in the event of a transport failure between
the server and the client; so the script SHOULD be prepared to handle
abnormal termination.
4. The CGI Request
Information about a request comes from two different sources; the
request meta-variables and any associated message-body.
4.1. Request Meta-Variables
Meta-variables contain data about the request passed from the server
to the script, and are accessed by the script in a system-defined
manner. Meta-variables are identified by case-insensitive names;
there cannot be two different variables whose names differ in case
only. Here they are shown using a canonical representation of
capitals plus underscore ("_"). A particular system can define a
different representation.
meta-variable-name = "AUTH_TYPE" | "CONTENT_LENGTH" |
"CONTENT_TYPE" | "GATEWAY_INTERFACE" |
"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" | scheme |
protocol-var-name | extension-var-name
protocol-var-name = ( protocol | scheme ) "_" var-name
scheme = alpha *( alpha | digit | "+" | "-" | "." )
var-name = token
extension-var-name = token
Meta-variables with the same name as a scheme, and names beginning
with the name of a protocol or scheme (e.g., HTTP_ACCEPT) are also
defined. The number and meaning of these variables may change
independently of this specification. (See also section 4.1.18.)
The server MAY set additional implementation-defined extension meta-
variables, whose names SHOULD be prefixed with "X_".
This specification does not distinguish between zero-length (NULL)
values and missing values. For example, a script cannot distinguish
between the two requests http://host/script and http://host/script?
as in both cases the QUERY_STRING meta-variable would be NULL.
meta-variable-value = "" | 1*<TEXT, CHAR or tokens of value>
An optional meta-variable may be omitted (left unset) if its value is
NULL. Meta-variable values MUST be considered case-sensitive except
as noted otherwise. The representation of the characters in the
meta-variables is system-defined; the server MUST convert values to
that representation.
4.1.1. AUTH_TYPE
The AUTH_TYPE variable identifies any mechanism used by the server to
authenticate the user. It contains a case-insensitive value defined
by the client protocol or server implementation.
For HTTP, if the client request required authentication for external
access, then the server MUST set the value of this variable from the
'auth-scheme' token in the request Authorization header field.
AUTH_TYPE = "" | auth-scheme
auth-scheme = "Basic" | "Digest" | extension-auth
extension-auth = token
HTTP access authentication schemes are described in RFC 2617 [5].
4.1.2. CONTENT_LENGTH
The CONTENT_LENGTH variable contains the size of the message-body
attached to the request, if any, in decimal number of octets. If no
data is attached, then NULL (or unset).
CONTENT_LENGTH = "" | 1*digit
The server MUST set this meta-variable if and only if the request is
accompanied by a message-body entity. The CONTENT_LENGTH value must
reflect the length of the message-body after the server has removed
any transfer-codings or content-codings.
4.1.3. CONTENT_TYPE
If the request includes a message-body, the CONTENT_TYPE variable is
set to the Internet Media Type [6] of the message-body.
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 3.7 of the HTTP/1.1
specification [4].
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 the script MAY
choose to assume a type of application/octet-stream or it may reject
the request with an error (as described in section 6.3.3).
Each media-type defines a set of optional and mandatory parameters.
This may include a charset parameter with a case-insensitive value
defining the coded character set for the message-body. If the
charset parameter is omitted, then the default value should be
derived according to whichever of the following rules is the first to
apply:
1. There MAY be a system-defined default charset for some
media-types.
2. The default for media-types of type "text" is ISO-8859-1 [4].
3. Any default defined in the media-type specification.
4. The default is US-ASCII.
The server MUST set this meta-variable if an HTTP Content-Type field
is present in the client request header. If the server receives a
request with an attached entity but no Content-Type header field, it
MAY attempt to determine the correct content type, otherwise it
should omit this meta-variable.
4.1.4. GATEWAY_INTERFACE
The GATEWAY_INTERFACE variable MUST be set to the dialect of CGI
being used by the server to communicate with the script. Syntax:
GATEWAY_INTERFACE = "CGI" "/" 1*digit "." 1*digit
Note that the major and minor numbers are treated as separate
integers and hence 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 the script
and MUST NOT be generated by the server.
This document defines the 1.1 version of the CGI interface.
4.1.5. PATH_INFO
The PATH_INFO variable specifies a path to be interpreted by the CGI
script. It identifies the resource or sub-resource to be returned by
the CGI script, and is derived from the portion of the URI path
hierarchy following the part that identifies the script itself.
Unlike a URI path, the PATH_INFO is not URL-encoded, and cannot
contain path-segment parameters. A PATH_INFO of "/" represents a
single void path segment.
PATH_INFO = "" | ( "/" path )
path = lsegment *( "/" lsegment )
lsegment = *lchar
lchar = <any TEXT or CTL except "/">
The value is considered case-sensitive and the server MUST preserve
the case of the path as presented in the request URI. The server MAY
impose restrictions and limitations on what values it permits for
PATH_INFO, and MAY reject the request with an error if it encounters
any values considered objectionable. That MAY include any requests
that would result in an encoded "/" being decoded into PATH_INFO, as
this might represent a loss of information to the script. Similarly,
treatment of non US-ASCII characters in the path is system-defined.
URL-encoded, the PATH_INFO string forms the extra-path component of
the Script-URI (see section 3.3) which follows the SCRIPT_NAME part
of that path.
4.1.6. PATH_TRANSLATED
The PATH_TRANSLATED variable is derived by taking the PATH_INFO
value, parsing it as a local URI in its own right, and performing any
virtual-to-physical translation appropriate to map it onto the
server's document repository structure. The set of characters
permitted in the result is system-defined.
PATH_TRANSLATED = *<any character>
This is the file location that would be accessed by a request for
<scheme> "://" <server-name> ":" <server-port> <extra-path>
where <scheme> is the scheme for the original client request and
<extra-path> is a URL-encoded version of PATH_INFO, with ";", "=" and
"?" reserved. For example, a request such as the following:
http://somehost.com/cgi-bin/somescript/this%2eis%2epath%3binfo
would result in a PATH_INFO value of
/this.is.the.path;info
An internal URI is constructed from the scheme, server location and
the URL-encoded PATH_INFO:
http://somehost.com/this.is.the.path%3binfo
This would then be translated to a location in the server's document
repository, perhaps a filesystem path something like this:
/usr/local/www/htdocs/this.is.the.path;info
The value of PATH_TRANSLATED is the result of the translation.
The value is derived in this way irrespective of whether it maps to a
valid repository location. The server MUST preserve the case of the
extra-path segment unless the underlying repository supports case-
insensitive names. If the repository is only case-aware, case-
preserving, or case-blind with regard to document names, the server
is not required to preserve the case of the original segment through
the translation.
The translation algorithm the server uses to derive PATH_TRANSLATED
is implementation-defined; CGI scripts which use this variable may
suffer limited portability.
The server SHOULD set this meta-variable if the request URI includes
a path-info component. If PATH_INFO is NULL, then the
PATH_TRANSLATED variable MUST be set to NULL (or unset).
4.1.7. QUERY_STRING
The QUERY_STRING variable contains a URL-encoded search or parameter
string; it provides information to the CGI script to affect or refine
the document to be returned by the script.
The URL syntax for a search string is described in section 3 of RFC
2396 [2]. The QUERY_STRING value is case-sensitive.
QUERY_STRING = query-string
query-string = *uric
uric = reserved | unreserved | escaped
When parsing and decoding the query string, the details of the
parsing, reserved characters and support for non US-ASCII characters
depends on the context. For example, form submission from an HTML
document [18] uses application/x-www-form-urlencoded encoding, in
which the characters "+", "&" and "=" are reserved, and the ISO
8859-1 encoding may be used for non US-ASCII characters.
The QUERY_STRING value provides the query-string part of the
Script-URI. (See section 3.3).
The server MUST set this variable; if the Script-URI does not include
a query component, the QUERY_STRING MUST be defined as an empty
string ("").
4.1.8. REMOTE_ADDR
The REMOTE_ADDR variable MUST be set to the network address of the
client sending the request to the server.
REMOTE_ADDR = hostnumber
hostnumber = ipv4-address | ipv6-address
ipv4-address = 1*3digit "." 1*3digit "." 1*3digit "." 1*3digit
ipv6-address = hexpart [ ":" ipv4-address ]
hexpart = hexseq | ( [ hexseq ] "::" [ hexseq ] )
hexseq = 1*4hex *( ":" 1*4hex )
The format of an IPv6 address is described in RFC 3513 [15].
4.1.9. REMOTE_HOST
The REMOTE_HOST variable contains the fully qualified domain name of
the client sending the request to the server, if available, otherwise
NULL. Fully qualified domain names take the form as described in
section 3.5 of RFC 1034 [17] and section 2.1 of RFC 1123 [12].
Domain names are not case sensitive.
REMOTE_HOST = "" | hostname | hostnumber
hostname = *( domainlabel "." ) toplabel [ "." ]
domainlabel = alphanum [ *alphahypdigit alphanum ]
toplabel = alpha [ *alphahypdigit alphanum ]
alphahypdigit = alphanum | "-"
The server SHOULD set this variable. If the hostname is not
available for performance reasons or otherwise, the server MAY
substitute the REMOTE_ADDR value.
4.1.10. REMOTE_IDENT
The REMOTE_IDENT variable MAY be used to provide identity information
reported about the connection by an RFC 1413 [20] 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, or
not to return available identity data.
REMOTE_IDENT = *TEXT
The data returned may be used for authentication purposes, but the
level of trust reposed in it should be minimal.
4.1.11. REMOTE_USER
The REMOTE_USER variable provides a user identification string
supplied by client as part of user authentication.
REMOTE_USER = *TEXT
If the client request required HTTP Authentication [5] (e.g., the
AUTH_TYPE meta-variable is set to "Basic" or "Digest"), then the
value of the REMOTE_USER meta-variable MUST be set to the user-ID
supplied.
4.1.12. REQUEST_METHOD
The REQUEST_METHOD meta-variable MUST be set to the method which
should be used by the script to process the request, as described in
section 4.3.
REQUEST_METHOD = method
method = "GET" | "POST" | "HEAD" | extension-method
extension-method = "PUT" | "DELETE" | token
The method is case sensitive. The HTTP methods are described in
section 5.1.1 of the HTTP/1.0 specification [1] and section 5.1.1 of
the HTTP/1.1 specification [4].
4.1.13. SCRIPT_NAME
The SCRIPT_NAME variable MUST be set to a URI path (not URL-encoded)
which could identify the CGI script (rather than the script's
output). The syntax is the same as for PATH_INFO (section 4.1.5)
SCRIPT_NAME = "" | ( "/" path )
The leading "/" is not part of the path. It is optional if the path
is NULL; however, the variable MUST still be set in that case.
The SCRIPT_NAME string forms some leading part of the path component
of the Script-URI derived in some implementation-defined manner. No
PATH_INFO segment (see section 4.1.5) is included in the SCRIPT_NAME
value.
4.1.14. SERVER_NAME
The SERVER_NAME variable MUST be set to the name of the server host
to which the client request is directed. It is a case-insensitive
hostname or network address. It forms the host part of the
Script-URI.
SERVER_NAME = server-name
server-name = hostname | ipv4-address | ( "[" ipv6-address "]" )
A deployed server can have more than one possible value for this
variable, where several HTTP virtual hosts share the same IP address.
In that case, the server would use the contents of the request's Host
header field to select the correct virtual host.
4.1.15. SERVER_PORT
The SERVER_PORT variable MUST be set to the TCP/IP port number on
which this request is received from the client. This value is used
in the port part of the Script-URI.
SERVER_PORT = server-port
server-port = 1*digit
Note that this variable MUST be set, even if the port is the default
port for the scheme and could otherwise be omitted from a URI.
4.1.16. SERVER_PROTOCOL
The SERVER_PROTOCOL variable MUST be set to the name and version of
the application protocol used for this CGI request. This MAY differ
from the protocol version used by the server in its communication
with the client.
SERVER_PROTOCOL = HTTP-Version | "INCLUDED" | extension-version
HTTP-Version = "HTTP" "/" 1*digit "." 1*digit
extension-version = protocol [ "/" 1*digit "." 1*digit ]
protocol = token
Here, 'protocol' defines the syntax of some of the information
passing between the server and the script (the 'protocol-specific'
features). It is not case sensitive and is usually presented in
upper case. The protocol is not the same as the scheme part of the
script URI, which defines the overall access mechanism used by the
client to communicate with the server. For example, a request that
reaches the script with a protocol of "HTTP" may have used an "https"
scheme.
A well-known value for SERVER_PROTOCOL which the server MAY use is
"INCLUDED", which signals that the current document is being included
as part of a composite document, rather than being the direct target
of the client request. The script should treat this as an HTTP/1.0
request.
4.1.17. SERVER_SOFTWARE
The SERVER_SOFTWARE meta-variable MUST be set to the name and version
of the information server software making the CGI request (and
running the gateway). It SHOULD be the same as the server
description reported to the client, if any.
SERVER_SOFTWARE = 1*( product | comment )
product = token [ "/" product-version ]
product-version = token
comment = "(" *( ctext | comment ) ")"
ctext = <any TEXT excluding "(" and ")">
4.1.18. Protocol-Specific Meta-Variables
The server SHOULD set meta-variables specific to the protocol and
scheme for the request. Interpretation of protocol-specific
variables depends on the protocol version in SERVER_PROTOCOL. The
server MAY set a meta-variable with the name of the scheme to a
non-NULL value if the scheme is not the same as the protocol. The
presence of such a variable indicates to a script which scheme is
used by the request.
Meta-variables with names beginning with "HTTP_" contain values read
from the client request header fields, if the protocol used is HTTP.
The HTTP header field name is converted to upper case, has all
occurrences of "-" replaced with "_" and has "HTTP_" prepended to
give the meta-variable name. The header data can be presented as
sent by the client, or can be rewritten in ways which do not change
its semantics. If multiple header fields with the same field-name
are received then the server MUST rewrite them as a single value
having the same semantics. Similarly, a header field that spans
multiple lines 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 meta-variable.
The server is not required to create meta-variables for all the
header fields that it receives. In particular, it SHOULD remove any
header fields carrying authentication information, such as
'Authorization'; or that are available to the script in other
variables, such as 'Content-Length' and 'Content-Type'. The server
MAY remove header fields that relate solely to client-side
communication issues, such as 'Connection'.
4.2. Request Message-Body
Request data is accessed by the script in a system-defined method;
unless defined otherwise, this will be by reading the 'standard
input' file descriptor or file handle.
Request-Data = [ request-body ] [ extension-data ]
request-body = <CONTENT_LENGTH>OCTET
extension-data = *OCTET
A request-body is supplied with the request if the CONTENT_LENGTH is
not NULL. The server MUST make at least that many bytes available
for the script to read. The server MAY signal an end-of-file
condition after CONTENT_LENGTH bytes have been read or it MAY supply
extension data. Therefore, the script MUST NOT attempt to read more
than CONTENT_LENGTH bytes, even if more data is available. However,
it is not obliged to read any of the data.
For non-parsed header (NPH) scripts (section 5), the server SHOULD
attempt to ensure that the data supplied to the script is precisely
as supplied by the client and is unaltered by the server.
As transfer-codings are not supported on the request-body, the server
MUST remove any such codings from the message-body, and recalculate
the CONTENT_LENGTH. If this is not possible (for example, because of
large buffering requirements), the server SHOULD reject the client
request. It MAY also remove content-codings from the message-body.
4.3. Request Methods
The Request Method, as supplied in the REQUEST_METHOD meta-variable,
identifies the processing method to be applied by the script in
producing a response. The script author can choose to implement the
methods most appropriate for the particular application. If the
script receives a request with a method it does not support it SHOULD
reject it with an error (see section 6.3.3).
4.3.1. GET
The GET method indicates that the script should produce a document
based on the meta-variable values. By convention, the GET method is
'safe' and 'idempotent' and SHOULD NOT have the significance of
taking an action other than producing a document.
The meaning of the GET method may be modified and refined by
protocol-specific meta-variables.
4.3.2. POST
The POST method is used to request the script perform processing and
produce a document based on the data in the request message-body, in
addition to meta-variable values. A common use is form submission in
HTML [18], intended to initiate processing by the script that has a
permanent affect, such a change in a database.
The script MUST check the value of the CONTENT_LENGTH variable before
reading the attached message-body, and SHOULD check the CONTENT_TYPE
value before processing it.
4.3.3. HEAD
The HEAD method requests the script to do sufficient processing to
return the response header fields, without providing a response
message-body. The script MUST NOT provide a response message-body
for a HEAD request. If it does, then the server MUST discard the
message-body when reading the response from the script.
4.3.4. Protocol-Specific Methods
The script MAY implement any protocol-specific method, such as
HTTP/1.1 PUT and DELETE; it SHOULD check the value of SERVER_PROTOCOL
when doing so.
The server MAY decide that some methods are not appropriate or
permitted for a script, and may handle the methods itself or return
an error to the client.
4.4. The Script Command Line
Some systems support a method for supplying an array of strings to
the CGI script. This is only used in the case of an 'indexed' HTTP
query, which is identified by a 'GET' or 'HEAD' request with a URI
query string that does not contain any unencoded "=" characters. For
such a request, the server SHOULD treat the query-string as a
search-string and parse it into words, using the rules
search-string = search-word *( "+" search-word )
search-word = 1*schar
schar = unreserved | escaped | xreserved
xreserved = ";" | "/" | "?" | ":" | "@" | "&" | "=" | "," |
"$"
After parsing, each search-word is URL-decoded, optionally encoded in
a system-defined manner and then added to the command line argument
list.
If the server cannot create any part of the argument list, then the
server MUST NOT generate any command line information. For example,
the number of arguments may be greater than operating system or
server limits, or one of the words may not be representable as an
argument.
The script SHOULD check to see if the QUERY_STRING value contains an
unencoded "=" character, and SHOULD NOT use the command line
arguments if it does.
5. NPH Scripts
5.1. Identification
The server MAY support NPH (Non-Parsed Header) scripts; these are
scripts to which the server passes all responsibility for response
processing.
This specification provides no mechanism for an NPH script to be
identified on the basis of its output data alone. By convention,
therefore, any particular script can only ever provide output of one
type (NPH or CGI) and hence the script itself is described as an 'NPH
script'. A server with NPH support MUST provide an implementation-
defined mechanism for identifying NPH scripts, perhaps based on the
name or location of the script.
5.2. NPH Response
There MUST be a system-defined method for the script to send data
back to the server or client; a script MUST always return some data.
Unless defined otherwise, this will be the same as for conventional
CGI scripts.
Currently, NPH scripts are only defined for HTTP client requests. An
(HTTP) NPH script MUST return a complete HTTP response message,
currently described in section 6 of the HTTP specifications [1], [4].
The script MUST use the SERVER_PROTOCOL variable to determine the
appropriate format for a response. It MUST also take account of any
generic or protocol-specific meta-variables in the request as might
be mandated by the particular protocol specification.
The server MUST ensure that the script output is sent to the client
unmodified. Note that this requires the script to use the correct
character set (US-ASCII [9] and ISO 8859-1 [10] for HTTP) in the
header fields. The server SHOULD attempt to ensure that the script
output is sent directly to the client, with minimal internal and no
transport-visible buffering.
Unless the implementation defines otherwise, the script MUST NOT
indicate in its response that the client can send further requests
over the same connection.
6. CGI Response
6.1. Response Handling
A script MUST always provide a non-empty response, and so there is a
system-defined method for it to send this data back to the server.
Unless defined otherwise, this will be via the 'standard output' file
descriptor.
The script MUST check the REQUEST_METHOD variable when processing the
request and preparing its response.
The server MAY implement a timeout period within which data must be
received from the script. If a server implementation defines such a
timeout and receives no data from a script within the timeout period,
the server MAY terminate the script process.
6.2. Response Types
The response comprises a message-header and a message-body, separated
by a blank line. The message-header contains one or more header
fields. The body may be NULL.
generic-response = 1*header-field NL [ response-body ]
The script MUST return one of either a document response, a local
redirect response or a client redirect (with optional document)
response. In the response definitions below, the order of header
fields in a response is not significant (despite appearing so in the
BNF). The header fields are defined in section 6.3.
CGI-Response = document-response | local-redir-response |
client-redir-response | client-redirdoc-response
6.2.1. Document Response
The CGI script can return a document to the user in a document
response, with an optional error code indicating the success status
of the response.
document-response = Content-Type [ Status ] *other-field NL
response-body
The script MUST return a Content-Type header field. A Status header
field is optional, and status 200 'OK' is assumed if it is omitted.
The server MUST make any appropriate modifications to the script's
output to ensure that the response to the client complies with the
response protocol version.
6.2.2. Local Redirect Response
The CGI script can return a URI path and query-string
('local-pathquery') for a local resource in a Location header field.
This indicates to the server that it should reprocess the request
using the path specified.
local-redir-response = local-Location NL
The script MUST NOT return any other header fields or a message-body,
and the server MUST generate the response that it would have produced
in response to a request containing the URL
scheme "://" server-name ":" server-port local-pathquery
6.2.3. Client Redirect Response
The CGI script can return an absolute URI path in a Location header
field, to indicate to the client that it should reprocess the request
using the URI specified.
client-redir-response = client-Location *extension-field NL
The script MUST not provide any other header fields, except for
server-defined CGI extension fields. For an HTTP client request, the
server MUST generate a 302 'Found' HTTP response message.
6.2.4. Client Redirect Response with Document
The CGI script can return an absolute URI path in a Location header
field together with an attached document, to indicate to the client
that it should reprocess the request using the URI specified.
client-redirdoc-response = client-Location Status Content-Type
*other-field NL response-body
The Status header field MUST be supplied and MUST contain a status
value of 302 'Found', or it MAY contain an extension-code, that is,
another valid status code that means client redirection. The server
MUST make any appropriate modifications to the script's output to
ensure that the response to the client complies with the response
protocol version.
6.3. Response Header Fields
The response header fields are either CGI or extension header fields
to be interpreted by the server, or protocol-specific header fields
to be included in the response returned to the client. At least one
CGI field MUST be supplied; each CGI field MUST NOT appear more than
once in the response. The response header fields have the syntax:
header-field = CGI-field | other-field
CGI-field = Content-Type | Location | Status
other-field = protocol-field | extension-field
protocol-field = generic-field
extension-field = generic-field
generic-field = field-name ":" [ field-value ] NL
field-name = token
field-value = *( field-content | LWSP )
field-content = *( token | separator | quoted-string )
The field-name is not case sensitive. A NULL field value is
equivalent to a field not being sent. Note that each header field in
a CGI-Response MUST be specified on a single line; CGI/1.1 does not
support continuation lines. Whitespace is permitted between the ":"
and the field-value (but not between the field-name and the ":"), and
also between tokens in the field-value.
6.3.1. Content-Type
The Content-Type response field sets the Internet Media Type [6] of
the entity body.
Content-Type = "Content-Type:" media-type NL
If an entity body is returned, the script MUST supply a Content-Type
field in the response. If it fails to do so, the server SHOULD NOT
attempt to determine the correct content type. The value SHOULD be
sent unmodified to the client, except for any charset parameter
changes.
Unless it is otherwise system-defined, the default charset assumed by
the client for text media-types is ISO-8859-1 if the protocol is HTTP
and US-ASCII otherwise. Hence the script SHOULD include a charset
parameter. See section 3.4.1 of the HTTP/1.1 specification [4] for a
discussion of this issue.
6.3.2. Location
The Location header field is used to specify to the server that the
script is returning a reference to a document rather than an actual
document (see sections 6.2.3 and 6.2.4). It is either an absolute
URI (optionally with a fragment identifier), indicating that the
client is to fetch the referenced document, or a local URI path
(optionally with a query string), indicating that the server is to
fetch the referenced document and return it to the client as the
response.
Location = local-Location | client-Location
client-Location = "Location:" fragment-URI NL
local-Location = "Location:" local-pathquery NL
fragment-URI = absoluteURI [ "#" fragment ]
fragment = *uric
local-pathquery = abs-path [ "?" query-string ]
abs-path = "/" path-segments
path-segments = segment *( "/" segment )
segment = *pchar
pchar = unreserved | escaped | extra
extra = ":" | "@" | "&" | "=" | "+" | "$" | ","
The syntax of an absoluteURI is incorporated into this document from
that specified in RFC 2396 [2] and RFC 2732 [7]. A valid absoluteURI
always starts with the name of scheme followed by ":"; scheme names
start with a letter and continue with alphanumerics, "+", "-" or ".".
The local URI path and query must be an absolute path, and not a
relative path or NULL, and hence must start with a "/".
Note that any message-body attached to the request (such as for a
POST request) may not be available to the resource that is the target
of the redirect.
6.3.3. Status
The Status header field contains a 3-digit integer result code that
indicates the level of success of the script's attempt to handle the
request.
Status = "Status:" status-code SP reason-phrase NL
status-code = "200" | "302" | "400" | "501" | extension-code
extension-code = 3digit
reason-phrase = *TEXT
Status code 200 'OK' indicates success, and is the default value
assumed for a document response. Status code 302 'Found' is used
with a Location header field and response message-body. Status code
400 'Bad Request' may be used for an unknown request format, such as
a missing CONTENT_TYPE. Status code 501 'Not Implemented' may be
returned by a script if it receives an unsupported REQUEST_METHOD.
Other valid status codes are listed in section 6.1.1 of the HTTP
specifications [1], [4], and also the IANA HTTP Status Code Registry
[8] and MAY be used in addition to or instead of the ones listed
above. The script SHOULD check the value of SERVER_PROTOCOL before
using HTTP/1.1 status codes. The script MAY reject with error 405
'Method Not Allowed' HTTP/1.1 requests made using a method it does
not support.
Note that returning an error status code does not have to mean an
error condition with the script itself. For example, a script that
is invoked as an error handler by the server should return the code
appropriate to the server's error condition.
The reason-phrase is a textual description of the error to be
returned to the client for human consumption.
6.3.4. Protocol-Specific Header Fields
The script MAY return any other header fields that relate to the
response message defined by the specification for the SERVER_PROTOCOL
(HTTP/1.0 [1] or HTTP/1.1 [4]). 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 US-ASCII LF) used by CGI scripts may not be the same as that
used by HTTP (US-ASCII CR followed by LF).
The script MUST NOT return any header fields that relate to
client-side communication issues and could affect the server's
ability to send the response to the client. The server MAY remove
any such header fields returned by the client. It SHOULD resolve any
conflicts between header fields returned by the script and header
fields that it would otherwise send itself.
6.3.5. Extension Header Fields
There may be additional implementation-defined CGI header fields,
whose field names SHOULD begin with "X-CGI-". The server MAY ignore
(and delete) any unrecognised header fields with names beginning "X-
CGI-" that are received from the script.
6.4. Response Message-Body
The response message-body is an attached document to be returned to
the client by the server. The server MUST read all the data provided
by the script, until the script signals the end of the message-body
by way of an end-of-file condition. The message-body SHOULD be sent
unmodified to the client, except for HEAD requests or any required
transfer-codings, content-codings or charset conversions.
response-body = *OCTET
7. System Specifications
7.1. AmigaDOS
Meta-Variables
Meta-variables are passed to the script in identically named
environment variables. 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.
Character set
The US-ASCII character set [9] is used for the definition of
meta-variables, header fields and values; the newline (NL)
sequence is LF; servers SHOULD also accept CR LF as a newline.
7.2. UNIX
For UNIX compatible operating systems, the following are defined:
Meta-Variables
Meta-variables are passed to the script in identically named
environment variables. These are accessed by the C library
routine getenv() or variable environ.
The command line
This is accessed using the argc and argv arguments to main(). The
words 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 SHOULD be set to the
directory containing the script.
Character set
The US-ASCII character set [9], excluding NUL, is used for the
definition of meta-variables, header fields and CHAR values; TEXT
values use ISO-8859-1. The PATH_TRANSLATED value can contain any
8-bit byte except NUL. The newline (NL) sequence is LF; servers
should also accept CR LF as a newline.
7.3. EBCDIC/POSIX
For POSIX compatible operating systems using the EBCDIC character
set, the following are defined:
Meta-Variables
Meta-variables are passed to the script in identically named
environment variables. These are accessed by the C library
routine getenv().
The command line
This is accessed using the argc and argv arguments to main(). The
words 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 SHOULD be set to the
directory containing the script.
Character set
The IBM1047 character set [21], excluding NUL, is used for the
definition of meta-variables, header fields, values, TEXT strings
and the PATH_TRANSLATED value. The newline (NL) sequence is LF;
servers should also accept CR LF as a newline.
media-type charset default
The default charset value for text (and other implementation-
defined) media types is IBM1047.
8. Implementation
8.1. Recommendations for Servers
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 specify its behaviour for the following
cases:
1. define any restrictions on allowed path segments, in particular
whether non-terminal NULL segments are permitted;
2. 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 [2];
3. define any limits of the implementation, including limits on
path or search string lengths, and limits on the volume of
header fields the server will parse.
8.2. Recommendations for Scripts
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" [18] or "multipart/form-data"
[16]. If CONTENT_TYPE is blank, the script can reject the request
with a 415 'Unsupported Media Type' error, where supported by the
protocol.
When parsing PATH_INFO, PATH_TRANSLATED or SCRIPT_NAME the script
should 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'.
When returning header fields, the script should try to send the CGI
header fields as soon as possible, and should send them before any
HTTP header fields. This may help reduce the server's memory
requirements.
Script authors should be aware that the REMOTE_ADDR and REMOTE_HOST
meta-variables (see sections 4.1.8 and 4.1.9) may not identify the
ultimate source of the request. They identify the client for the
immediate request to the server; that client may be a proxy, gateway,
or other intermediary acting on behalf of the actual source client.
9. Security Considerations
9.1. Safe Methods
As discussed in the security considerations of the HTTP
specifications [1], [4], the convention has been established that the
GET and HEAD methods should be 'safe' and 'idempotent' (repeated
requests have the same effect as a single request). See section 9.1
of RFC 2616 [4] for a full discussion.
9.2. Header Fields Containing Sensitive Information
Some HTTP header fields 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 by using
the Basic authentication scheme, then the client will send an
Authorization header field containing a username and password. The
server validates this information and so it should not pass on the
password via the HTTP_AUTHORIZATION meta-variable without careful
consideration. This also applies to the Proxy-Authorization header
field and the corresponding HTTP_PROXY_AUTHORIZATION meta-variable.
9.3. Data Privacy
Confidential data in a request should be placed in a message-body as
part of a POST request, and not placed in the URI or message headers.
On some systems, the environment used to pass meta-variables to a
script may be visible to other scripts or users. In addition, many
existing servers, proxies and clients will permanently record the URI
where it might be visible to third parties.
9.4. Information Security Model
For a client connection using TLS, the security model applies between
the client and the server, and not between the client and the script.
It is the server's responsibility to handle the TLS session, and thus
it is the server which is authenticated to the client, not the CGI
script.
This specification provides no mechanism for the script to
authenticate the server which invoked it. There is no enforced
integrity on the CGI request and response messages.
9.5. Script Interference with the Server
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, documents or log files.
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.
9.6. Data Length and Buffering Considerations
This specification places no limits on the length of the message-body
presented to the script. The script should not assume that
statically allocated buffers of any size are sufficient to contain
the entire submission at one time. Use of a fixed length buffer
without careful overflow checking may result in an attacker
exploiting 'stack-smashing' or 'stack-overflow' vulnerabilities of
the operating system. The script may spool large submissions to disk
or other buffering media, but a rapid succession of large submissions
may result in denial of service conditions. If the CONTENT_LENGTH of
a message-body is larger than resource considerations allow, scripts
should respond with an error status appropriate for the protocol
version; potentially applicable status codes include 503 'Service
Unavailable' (HTTP/1.0 and HTTP/1.1), 413 'Request Entity Too Large'
(HTTP/1.1), and 414 'Request-URI Too Large' (HTTP/1.1).
Similar considerations apply to the server's handling of the CGI
response from the script. There is no limit on the length of the
header or message-body returned by the script; the server should not
assume that statically allocated buffers of any size are sufficient
to contain the entire response.
9.7. Stateless Processing
The stateless nature of the Web makes each script execution and
resource retrieval independent of all others even when multiple
requests constitute a single conceptual Web transaction. Because of
this, a script should not make any assumptions about the context of
the user-agent submitting a request. In particular, scripts should
examine data obtained from the client and verify that they are valid,
both in form and content, before allowing them to be used for
sensitive purposes such as input to other applications, commands, or
operating system services. These uses include (but are not limited
to) system call arguments, database writes, dynamically evaluated
source code, and input to billing or other secure processes. It is
important that applications be protected from invalid input
regardless of whether the invalidity is the result of user error,
logic error, or malicious action.
Authors of scripts involved in multi-request transactions should be
particularly cautious about validating the state information;
undesirable effects may result from the substitution of dangerous
values for portions of the submission which might otherwise be
presumed safe. Subversion of this type occurs when alterations are
made to data from a prior stage of the transaction that were not
meant to be controlled by the client (e.g., hidden HTML form
elements, cookies, embedded URLs, etc.).
9.8. Relative Paths
The server should be careful of ".." path segments in the request
URI. These should be removed or resolved in the request URI before
it is split into the script-path and extra-path. Alternatively, when
the extra-path is used to find the PATH_TRANSLATED, care should be
taken to avoid the path resolution from providing translated paths
outside an expected path hierarchy.
9.9. Non-parsed Header Output
If a script returns a non-parsed header output, to be interpreted by
the client in its native protocol, then the script must address all
security considerations relating to that protocol.
10. 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; also David
Morris, Jeremy Madea, Patrick McManus, Adam Donahue, Ross Patterson
and Harald Alvestrand.
11. References
11.1 Normative References
[1] Berners-Lee, T., Fielding, R. and H. Frystyk, "Hypertext
Transfer Protocol -- HTTP/1.0", RFC 1945, May 1996.
[2] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource
Identifiers (URI) : Generic Syntax", RFC 2396, August 1998.
[3] Bradner, S., "Key words for use in RFCs to Indicate Requirements
Levels", BCP 14, RFC 2119, March 1997.
[4] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L.,
Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol --
HTTP/1.1", RFC 2616, June 1999.
[5] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
Leach, P., Luotonen, A., and L. Stewart, "HTTP Authentication:
Basic and Digest Access Authentication", RFC 2617, June 1999.
[6] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046, November
1996.
[7] Hinden, R., Carpenter, B., and L. Masinter, "Format for Literal
IPv6 Addresses in URL's", RFC 2732, December 1999.
[8] "HTTP Status Code Registry",
http://www.iana.org/assignments/http-status-codes, IANA.
[9] "Information Systems -- Coded Character Sets -- 7-bit American
Standard Code for Information Interchange (7-Bit ASCII)", ANSI
INCITS.4-1986 (R2002).
[10] "Information technology -- 8-bit single-byte coded graphic
character sets -- Part 1: Latin alphabet No. 1", ISO/IEC
8859-1:1998.
11.2. Informative References
[11] 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,
June 1994.
[12] Braden, R., Ed., "Requirements for Internet Hosts -- Application
and Support", STD 3, RFC 1123, October 1989.
[13] Crocker, D., "Standard for the Format of ARPA Internet Text
Messages", STD 11, RFC 822, August 1982.
[14] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC
2246, January 1999.
[15] Hinden R. and S. Deering, "Internet Protocol Version 6 (IPv6)
Addressing Architecture", RFC 3513, April 2003.
[16] Masinter, L., "Returning Values from Forms:
multipart/form-data", RFC 2388, August 1998.
[17] Mockapetris, P., "Domain Names - Concepts and Facilities", STD
13, RFC 1034, November 1987.
[18] Raggett, D., Le Hors, A., and I. Jacobs, Eds., "HTML 4.01
Specification", W3C Recommendation December 1999,
http://www.w3.org/TR/html401/.
[19] Rescola, E. "HTTP Over TLS", RFC 2818, May 2000.
[20] St. Johns, M., "Identification Protocol", RFC 1413, February
1993.
[21] IBM National Language Support Reference Manual Volume 2,
SE09-8002-01, March 1990.
[22] "The Common Gateway Interface",
http://hoohoo.ncsa.uiuc.edu/cgi/, NCSA, University of Illinois.
12. Authors' Addresses
David Robinson
The Apache Software Foundation
EMail: drtr@apache.org
Ken A. L. Coar
The Apache Software Foundation
EMail: coar@apache.org
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