INTERNET-DRAFT David Robinson draft-coar-cgi-v11-03.txt Apache Software Foundation Expires 15 October 2003 Ken A.L. Coar IBM Corporation 16 April 2003 The Common Gateway Interface (CGI) Version 1.1 Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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'. The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Distribution of this document is unlimited. Please send comments to the authors, or via the CGI-WG mailing list; see the project Web page at . 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 `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. Robinson & Coar Expires 15 October 2003 [Page 1] INTERNET-DRAFT Common Gateway Interface -- 1.1 16 April 2003 Contents 1 Introduction.....................................................3 1.1 Purpose......................................................3 1.2 Requirements.................................................4 1.3 Specifications...............................................4 1.4 Terminology..................................................4 2 Notational Conventions and Generic Grammar.......................5 2.1 Augmented BNF................................................5 2.2 Basic Rules..................................................6 2.3 URL Encoding.................................................6 3 Invoking the Script..............................................7 3.1 Server Responsibilities......................................7 3.2 Script Selection.............................................8 3.3 The Script-URI...............................................8 3.4 Execution....................................................9 4 The CGI Request..................................................9 4.1 Request Meta-Variables.......................................9 4.1.1 AUTH_TYPE............................................10 4.1.2 CONTENT_LENGTH.......................................11 4.1.3 CONTENT_TYPE.........................................11 4.1.4 GATEWAY_INTERFACE....................................12 4.1.5 PATH_INFO............................................12 4.1.6 PATH_TRANSLATED......................................13 4.1.7 QUERY_STRING.........................................14 4.1.8 REMOTE_ADDR..........................................14 4.1.9 REMOTE_HOST..........................................15 4.1.10 REMOTE_IDENT.........................................15 4.1.11 REMOTE_USER..........................................15 4.1.12 REQUEST_METHOD.......................................15 4.1.13 SCRIPT_NAME..........................................16 4.1.14 SERVER_NAME..........................................16 4.1.15 SERVER_PORT..........................................16 4.1.16 SERVER_PROTOCOL......................................17 4.1.17 SERVER_SOFTWARE......................................17 4.1.18 Protocol-Specific Meta-Variables.....................17 4.2 Request Message-Body........................................18 4.3 Request Methods.............................................18 4.3.1 GET..................................................19 4.3.2 POST.................................................19 4.3.3 HEAD.................................................19 4.3.4 Protocol-Specific Methods............................19 4.4 The Script Command Line.....................................19 5 NPH Scripts.....................................................20 5.1 Indentification.............................................20 Robinson & Coar Expires 15 October 2003 [Page 2] INTERNET-DRAFT Common Gateway Interface -- 1.1 16 April 2003 5.2 NPH Response................................................20 6 CGI Response....................................................21 6.1 Response Handling...........................................21 6.2 Response Types..............................................21 6.2.1 Document Response....................................22 6.2.2 Local Redirect Response..............................22 6.2.3 Client Redirect Response.............................22 6.2.4 Client Redirect Response with Document...............22 6.3 Response Header Fields......................................23 6.3.1 Content-Type.........................................23 6.3.2 Location.............................................24 6.3.3 Status...............................................24 6.3.4 Protocol-Specific Header Fields......................25 6.3.5 Extension Header Fields..............................25 6.4 Response Message Body.......................................25 7 System Specifications...........................................25 7.1 AmigaDOS....................................................26 7.2 UNIX........................................................26 7.3 EBCDIC/POSIX................................................26 8 Implementation..................................................27 8.1 Recommendations for Servers.................................27 8.2 Recommendations for Scripts.................................28 9 Security Considerations.........................................28 9.1 Safe Methods................................................28 9.2 HTTP Headers Containing Sensitive Information...............28 9.3 Data Privacy................................................29 9.4 TLS Connection Endpoint.....................................29 9.5 Server/Script Authentication................................29 9.6 Script Interference with the Server.........................29 9.7 Data Length and Buffering Considerations....................29 9.8 Stateless Processing........................................30 9.9 Non-parsed Header Output....................................30 10 Acknowledgements................................................30 11 References......................................................31 12 Authors' Addresses..............................................32 1 Introduction 1.1 Purpose The Common Gateway Interface (CGI) [21] allows an HTTP [2], [8] server and a CGI script to share responsiblity for servicing client Robinson & Coar Expires 15 October 2003 [Page 3] INTERNET-DRAFT Common Gateway Interface -- 1.1 16 April 2003 requests 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. The CGI defines the abstract parameters, known as meta-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. The server is responsible for managing connection, data transfer, transport and network issues related to the request, whilst the CGI script is 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 RFC 2119 [5]. 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 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, but a particular implementation must document its behaviour. 1.4 Terminology Robinson & Coar Expires 15 October 2003 [Page 4] INTERNET-DRAFT Common Gateway Interface -- 1.1 16 April 2003 This specification uses many terms defined in the HTTP/1.1 specification [8]; 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 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. 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 which invokes the script in order to service requests from the cleint. 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 and its definition separated by the equal character ("="). Whitespace is only significant in that continuation lines of a definition are indented. "literal" Quotation marks (") surround literal text, except for a literal quotation mark, which is surrounded by angle-brackets ("<" and ">"). 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 Robinson & Coar Expires 15 October 2003 [Page 5] INTERNET-DRAFT Common Gateway Interface -- 1.1 16 April 2003 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 = CHAR = alpha | digit | separator | "!" | "#" | "$" | "%" | "&" | "'" | "*" | "+" | "-" | "." | "`" | "^" | "_" | "{" | "|" | "}" | "~" | CTL CTL = SP = HT = NL = LWSP = SP | HT | NL separator = "(" | ")" | "<" | ">" | "@" | "," | ";" | ":" | "\" | <"> | "/" | "[" | "]" | "?" | "=" | "{" | "}" | SP | HT token = 1* quoted-string = <"> *qdtext <"> qdtext = and CTLs but including LWSP> TEXT = 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 . 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 [3]. In Robinson & Coar Expires 15 October 2003 [Page 6] INTERNET-DRAFT Common Gateway Interface -- 1.1 16 April 2003 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 [20] 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 for each case. 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 [3], updated by RFC 2732 [11], for an authoritative treatment. These reserved characters are generally used to provide syntatic 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 "%" escapes by their character values. To encode a character string, all reseved and forbidden characters are replaced by the corresponding "%" escapes. 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 [11]. 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, select a CGI script to handle the request, convert the request to a CGI request, execute the script and convert 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 Robinson & Coar Expires 15 October 2003 [Page 7] INTERNET-DRAFT Common Gateway Interface -- 1.1 16 April 2003 `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 request data required by this specification. Futhermore, the server retains is responsibility to the client to conform to the 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 the CGI 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, identifies 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 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 heierarchies, and therefore is permitted to replace the URI by other members of this set during processing and generation of the meta-variables. The server - MAY preserve the URI in the particular request; or - MAY select a canonical URI from the set of possible values for each script; or - 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 PATH_INFO and QUERY_STRING meta- Robinson & Coar Expires 15 October 2003 [Page 8] INTERNET-DRAFT Common Gateway Interface -- 1.1 16 April 2003 variables. The Script-URI has the syntax of a generic URI as defined in section 3 of RFC 2396 [3], 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] ] ] script-path = abs-path extra-path = abs-path abs-path = "/" path-segments path-segments = segment *( "/" segment) segment = *lchar lchar = unreserved | escaped | extra extra = ":" | "@" | "&" | "=" | "+" | "$" | "," where `scheme' is found from SERVER_PROTOCOL, and script-path and extra-path are URL-encoded versions of SCRIPT_NAME and PATH_INFO, respectively, with ";", "=" and "?" reserved. 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 an access method in addition to a protocol. For instance, a resource accessed using Transport Layer Security (TLS) [7] may have a request URI with a scheme of https whilst using the HTTP protocol [16]. 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 permissable 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. 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 Robinson & Coar Expires 15 October 2003 [Page 9] INTERNET-DRAFT Common Gateway Interface -- 1.1 16 April 2003 manner. Meta-variables are identified by case-insensitive names; there cannot be two different variable whose names differ in case only. Here they are shown using a canonical representation of capitals plus underscore ("_"). A particular system can defined 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 var-name = token extension-var-name = token Meta-variables with the name of a scheme, and names beginning with the name of a protocol or scheme (e.g. HTTP_ACCEPT) are also be specified. The number and meaning of these variables may change independently of this specification. (See also section 4.1.18.) The server MAY define additional implementation-specific 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 requests http://host/script and http://host/script? ; in both cases the QUERY_STRING meta-variable would be NULL. An optional meta-variable may be ommitted (left unset) if its value is NULL. meta-variable-value = "" | 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 character set. 4.1.1 AUTH_TYPE The AUTH_TYPE variable identifies any mechanism used by the server to authenticate the user. Currently defined values are specific to requests made via the HTTP protocol. If the client request required authentication for external access, then the server MUST set the value of this variable from the `auth- Robinson & Coar Expires 15 October 2003 [Page 10] INTERNET-DRAFT Common Gateway Interface -- 1.1 16 April 2003 scheme' token in the request Authorization HTTP header field. Otherwise the variable is set to NULL. The syntax is for this variable is described in RFC 2617 [9]: AUTH_TYPE = "" | auth-scheme auth-scheme = "Basic" | "Digest" | token HTTP access authentication schemes are described in section 11 of the HTTP/1.1 specification [8]. The auth-scheme is not case-sensitive. 4.1.2 CONTENT_LENGTH The CONTENT_LENGTH variable contains the size of the message-body entity 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 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 [10] of the attached entity. 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 [8]. 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 Robinson & Coar Expires 15 October 2003 [Page 11] INTERNET-DRAFT Common Gateway Interface -- 1.1 16 April 2003 defining the coded character set for the attached entity. 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: - There MAY be a system-defined default charset for some media- types. - The default for media-types of type `text' is ISO-8859-1 [8]. - Any default defined in the media-type specification. - The default is US-ASCII. The server MUST set this meta-variable if an HTTP Content-Type field is present in the original request header. If the server receives a request with an attached entity but no Cotent-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 MUST be derived from the the portion of the URI path heirarchy following that 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 = psegment *( "/" psegment ) psegment = *pchar pchar = Robinson & Coar Expires 15 October 2003 [Page 12] INTERNET-DRAFT Common Gateway Interface -- 1.1 16 April 2003 The value is considered case-sensitive and the server MUST preseve 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. 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 3.2) that follows the SCRIPT_NAME part of that path. 4.1.6 PATH_TRANSLATED The PATH_TRANSLATED variable is derived by taking the PATH_INFO, parsing it as a URI in its own right, and performing any virtual-to- physical translation appropriate to map it onto the server's document repository structure. PATH_TRANSLATED = *TEXT This is the file location that would be accessed by a request for scheme "://" server-name ":" server-port enc(PATH_INFO) where `scheme' is found from SERVER_PROTOCOL (as described in section 3.2) and `enc(PATH_INFO)' 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 the PATH_INFO component would be decoded, and the result parsed as though it were a request for the following: 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 result of the translation is the value of PATH_TRANSLATED. The value of PATH_TRANSLATED may or may not map to a valid repository location. The server MUST preserve the case of the path-info segment if and only if the underlying repository supports case-sensitive 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. Robinson & Coar Expires 15 October 2003 [Page 13] INTERNET-DRAFT Common Gateway Interface -- 1.1 16 April 2003 The set of characters permitted in the repository location are system defined. 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 te script. The URL syntax for a search string is described in section 3 of RFC 2396 [3]. 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 detail of the parsing, reserved characters and non US-ASCII characters depends on the context. For example, form submission from an HTML document [15] uses application/x-www-form-urlencoded encoding, in which the characters "+", "&" and "=" are reserved, and the ISO 8859-1 encoding may used for non US-ASCII characters. The QUERY_STRING value provides the query-string part of the Script- URI. (See section 3.2). 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 ) Robinson & Coar Expires 15 October 2003 [Page 14] INTERNET-DRAFT Common Gateway Interface -- 1.1 16 April 2003 The format of IPv6 addresses is defined in RFC 2373 [12]. 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 [14] and section 2.1 of RFC 1123 [4]. 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 provides identity information reported about the connection by an RFC 1413 [17] 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. The server should 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 request required HTTP Authentication [9] (i.e. 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 that should be used by the script to process the request, as described in section 5.1.1 of the HTTP/1.0 specification [2] and section 5.1.1 of Robinson & Coar Expires 15 October 2003 [Page 15] INTERNET-DRAFT Common Gateway Interface -- 1.1 16 April 2003 the HTTP/1.1 specification [8]. REQUEST_METHOD = method method = "GET" | "POST" | "HEAD" | extension-method extension-method = "PUT" | "DELETE" | token The method is case sensitive. The methods are described in section 4.3. 4.1.13 SCRIPT_NAME The SCRIPT_NAME variable MUST be set to a URI path that could identify the CGI script (rather then 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 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. The syntax for an IPv6 address in a URI is defined in RFC 2373 [12]. 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 uses the contents of the Host header 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 Robinson & Coar Expires 15 October 2003 [Page 16] INTERNET-DRAFT Common Gateway Interface -- 1.1 16 April 2003 server-port = 1*digit Note that this variable MUST be set to the port number, 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 revision of the application protocol used for this CGI request. This is not necessarily the same as the protocol version used by the server in its response to 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 `protocol' is a version of the scheme part of the Script-URI, and is not case sensitive. By convention, `protocol' is in upper case. The protocol may not be identical to the scheme of the request; for example, the request may have scheme `https', whilst the protocol is `HTTP'. A well-known value for SERVER_PROTCOL 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 MAY treat this as an HTTP/1.0 request. The server MUST set this meta-variable. 4.1.17 SERVER_SOFTWARE The SERVER_SOFTWARE meta-variable MUST be set to the name and version of the information server software answering the 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 = 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 Robinson & Coar Expires 15 October 2003 [Page 17] INTERNET-DRAFT Common Gateway Interface -- 1.1 16 April 2003 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 different to 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 they the server MUST rewrite them as a value having the same semantics. Similarly, a header field 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 meta-variable. The server is not required to create meta-variables for all the headers that it receives. In particular, it SHOULD remove any headers carrying authentication information, such as `Authorization'; or which are available to the script via other variables, such as `Content-Length' and `Content-Type'. The server MAY remove headers which relate solely to client-side communication issues, such as `Connection'. 4.2 Request Message-Body 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. If the CONTENT_LENGTH is not NULL, the server MUST make at least that many bytes available for the script to read. The script is not obliged to read the data. The server MAY signal an end-of-file condition after CONTENT_LENGTH bytes have been read, but is not obliged to do so. Therefore, the script MUST NOT attempt to read more than CONTENT_LENGTH bytes, even if more data is available. 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 to by the client and is unaltered by the server. For a regular parsed-header script, the server MUST remove any transfer-codings from the message-body (and re-caclcuate the CONTENT_LENGTH), and it MAY remove any content-codings. 4.3 Request Methods Robinson & Coar Expires 15 October 2003 [Page 18] INTERNET-DRAFT Common Gateway Interface -- 1.1 16 April 2003 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 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 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 [15], intended to initate 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 the 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 conformance to the HTTP standard would REQUIRE a server to remove the response message body when returning the request to the client. 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 for 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 Robinson & Coar Expires 15 October 2003 [Page 19] INTERNET-DRAFT Common Gateway Interface -- 1.1 16 April 2003 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. This is identified by a `GET' or `HEAD' request with a URI query string not containing 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 | escape | xreserved xreserved = ";" | "/" | "?" | ":" | "@" | "&" | "=" | "," | "$" After parsing, each search-word is URL-decoded, optionally encoded in a system defined manner and then added to the 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 limitations, 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 Indentification The server MAY support NPH (Non-Parsed Header) scripts; these are scripts to which the server passes all responsbility 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 implemenation- 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. Robinson & Coar Expires 15 October 2003 [Page 20] INTERNET-DRAFT Common Gateway Interface -- 1.1 16 April 2003 Currently, NPH scripts are only defined for HTTP client requests. An (HTTP) NPH script MUST return a complete HTTP response message, as described in section 6 of the HTTP specifications [2], [8], as revised from time to time. 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 manadated 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 correct character set (US-ASCII [20] and ISO-Latin-1 [21] for HTTP) in the headers. 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 MUST be a system defined method for it to send this data back to the server or client. 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 header and a body, separated by a blank line. The body may be NULL. generic-response = 1*header-field NL [Entity-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 repsonse definitions below, the order of header fields in a response is not signficant (despite appearing so in the BNF). The header fields are defined in section 6.3. Robinson & Coar Expires 15 October 2003 [Page 21] INTERNET-DRAFT Common Gateway Interface -- 1.1 16 April 2003 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 Entity-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 ommitted. 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. This indicates to the server that it should re-process the request using the path specified. local-redir-response = local-Location NL The script MUST NOT return any other head fields or an entity 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, to indicate to the client that it should re-process the request using the URI specified. client-redir-response = client-Location *other-field NL The script MUST not provide any other header 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 together with an attached document, to indicate to the client that it Robinson & Coar Expires 15 October 2003 [Page 22] INTERNET-DRAFT Common Gateway Interface -- 1.1 16 April 2003 should re-process the request using the URI specified. client-redirdoc-response = client-Location Status Content-Type *other-field NL Entity-Body The Status header field MUST be supplied and MUST contain a status value of 302 `Found'. 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 header fields are either CGI or extension header fields to be interpreted by the server, or protocol-specific headers to be included in the response returned to the client. At least one CGI field MUST be supplied, and no CGI field can be used more than once in a response. The response headers 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 Internet Media Type [10] of the entity body, which SHOULD be sent unmodified to the client, except for any required transfer-codings or content-codings. Content-Type = "Content-Type:" media-type NL If a 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. This field MUST NOT appear more than once in the repsonse. Unless it is otherwise system-defined, the default charset assumed by Robinson & Coar Expires 15 October 2003 [Page 23] INTERNET-DRAFT Common Gateway Interface -- 1.1 16 April 2003 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 [8] for a discussion of this. 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. It is either an absolute URI (with fragment), indicating that the client is to fetch the referenced document, or a local path (with query string), indicating that the server is to fetch the referenced document. 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 ] The syntax of an absoluteURI is incorporated into this document from that specified in RFC 2396 [3] and RFC 2732 [11]. The two forms can be distingished as a local-pathquery must start with a "/" character, whereas an absoluteURI must start with a scheme; scheme names cannot contain "/" characters. 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. This field MUST NOT appear more than once in the repsonse. 6.3.3 Status The Status header field is used to indicate to the server what status code the server MUST use in the response message. Status = "Status:" status-code SP reason-phrase NL status-code = 200 | 302 | 400 | 501 | 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 entity body. Status code 400 `Bad Request' may be used for an unknown request format, such as a missing COTENT_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 Robinson & Coar Expires 15 October 2003 [Page 24] INTERNET-DRAFT Common Gateway Interface -- 1.1 16 April 2003 specifications [2], [8], and also the IANA HTTP Status Code Registry [18], and can 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. 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. This field MUST NOT appear more than once in the repsonse. 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 headers that relate to the response message defined by the specification for the SERVER_PROTOCOL (HTTP/1.0 [2] or HTTP/1.1 [8]). 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 communcation 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 headers returned by the script and headers that it would otherwise send itself. 6.3.5 Extension Header Fields The server may define additional implementation-specific CGI header fields, whoses field names SHOULD begin with `X-CGI-'. It MAY ignore (and delete) any unrecognised header-fields with names beginning `X- CGI-'. 6.4 Response Message Body The response entity body is a message body 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 entity body by way of an end of file condition. Entity-Body = *OCTET 7 System Specifications Robinson & Coar Expires 15 October 2003 [Page 25] INTERNET-DRAFT Common Gateway Interface -- 1.1 16 April 2003 7.1 AmigaDOS Meta-Variables The server SHOULD use environment variables as the mechanism of providing request meta-data to the CGI script. 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 [20] is used for the definition of meta-variables, headers 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 The server MUST use environment variables as the mechanism of providing request meta-data to the CGI script. 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 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 [20], excluding NUL, is used for the definition of meta-variables, headers and CHAR values; TEXT values are ISO-8859-1. 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 The server MUST use environment variables as the mechanism of Robinson & Coar Expires 15 October 2003 [Page 26] INTERNET-DRAFT Common Gateway Interface -- 1.1 16 April 2003 providing request meta-data to the CGI script. 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 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 EBCDIC-CP-US character set [19], excluding NUL, is used for the definition of meta-variables, headers all values. 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 EBCDIC-CP-US. 8 Implementation 8.1 Recommendations for Servers Servers may reject with error 404 `Not Found' 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: - define any restrictions on allowed path segments, in particular whether non-terminal NULL segments are permitted; - 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 [3]; - 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). Robinson & Coar Expires 15 October 2003 [Page 27] INTERNET-DRAFT Common Gateway Interface -- 1.1 16 April 2003 8.2 Recommendations for Scripts The server might interrupt or terminate script execution at any time and without warning, so the script SHOULD be prepared to handle abnormal termination. The script MAY reject with error 405 `Method Not Allowed' HTTP/1.1 requests made using a method it does not support. 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' [15] or `multipart/form-data' [13]. 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 headers, the script SHOULD try to send the CGI headers as soon as possible, and SHOULD send them before any HTTP headers. This may help reduce the server's memory requirements. 9 Security Considerations 9.1 Safe Methods As discussed in the security considerations of the HTTP specifications [2], [8], the convention has been established that the GET and HEAD methods should be `safe' and `idempotent'; they should cause no side-effects and only have the significance of resource retrieval. An idempotent request may be repeated an arbitrary number of times and produce side effects identical to a single request. 9.2 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 meta-variable without careful consideration. This also applies to the Proxy-Authorization header field and the corresponding HTTP_PROXY_AUTHORIZATION meta-variable. Robinson & Coar Expires 15 October 2003 [Page 28] INTERNET-DRAFT Common Gateway Interface -- 1.1 16 April 2003 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 client will log the URI where it might be visible to third parties. 9.4 TLS Connection Endpoint For a connection using TLS, the security 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 that is authenticated to the client, not the CGI script. 9.5 Server/Script Authentication This specification provides no mechanism for the script to authenticate the server that invoked it. There is no enforced integrity on the CGI request and response messages. 9.6 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. 9.7 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' Robinson & Coar Expires 15 October 2003 [Page 29] INTERNET-DRAFT Common Gateway Interface -- 1.1 16 April 2003 (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 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. 9.8 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 cautios 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.). 9.9 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 Robinson & Coar Expires 15 October 2003 [Page 30] INTERNET-DRAFT Common Gateway Interface -- 1.1 16 April 2003 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 [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., Fielding, R. T. and Frystyk, H., `Hypertext Transfer Protocol -- HTTP/1.0', RFC 1945, MIT/LCS, UC Irvine, May 1996. [3] Berners-Lee, T., Fielding, R. and Masinter, L., `Uniform Resource Identifiers (URI) : Generic Syntax', RFC 2396, MIT/LC, U.C. Irvine, Xerox Corporation, August 1998. [4] Braden, R., Editor, `Requirements for Internet Hosts -- Application and Support', STD 3, RFC 1123, IETF, October 1989. [5] Bradner, S., `Key words for use in RFCs to Indicate Requirements Levels', BCP 14, RFC 2119, Harvard University, March 1997. [6] Crocker, D.H., `Standard for the Format of ARPA Internet Text Messages', STD 11, RFC 822, University of Delaware, August 1982. [7] Dierks, T. and Allen, C., `The TLS Protocol Version 1.0', RFC 2246, Certicom, January 1999. [8] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P. and Berners-Lee, T., `Hypertext Transfer Protocol -- HTTP/1.1', RFC 2616, UC Irving, Compaq/W3C, Compaq, W3C/MIT, Xerox, Microsoft, W3C/MIT, June 1999. [9] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S., Leach, P., Luotonen, A. and Stewart L. `HTTP Authentication: Basic and Digest Access Authentication', RFC 2617, Northwestern University, Verisign Inc., AbiSource, Inc., Agranat Systems, Inc., Microsoft Corporation, Netscape Communications Corporation, Open Market, Inc., June 1999. [10] Freed, N. and Borenstein N., `Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types', RFC 2046, Innosoft, First Virtual, November 1996. [11] Hinden, R., Carpenter, B. and Masinter, L., `Format for Literal IPv6 Addresses in URL's', RFC 2732, Nokia, IBM, AT&T, December Robinson & Coar Expires 15 October 2003 [Page 31] INTERNET-DRAFT Common Gateway Interface -- 1.1 16 April 2003 1999. [12] Hinden R. and Deering S., `IP Version 6 Addressing Architecture', RFC 2373, Nokia, Cisco Systems, July 1998. [13] Masinter, L., `Returning Values from Forms: multipart/form- data', RFC 2388, Xerox Corporation, August 1998. [14] Mockapetris, P., `Domain Names - Concepts and Facilities', STD 13, RFC 1034, ISI, November 1987. [15] Raggett, Dave, Le Hors, Arnaud and Jacobs, Ian (eds) `HTML 4.01 Specification', W3C Recommendation December 1999, http://www.w3.org/TR/html401/. [16] Rescola, E. `HTTP Over TLS', RFC 2818, RTFM, May 2000. [17] St. Johns, M., `Identification Protocol', RFC 1413, US Department of Defense, February 1993. [18] `HTTP Status Code Registry', http://www.iana.org/assignments/http-status-codes, IANA [19] IBM National Language Support Reference Manual Volume 2, SE09-8002-01, March 1990. [20] `Information Systems -- Coded Character Sets -- 7-bit American Standard Code for Information Interchange (7-Bit ASCII)', ANSI INCITS.4-1986 (R2002). [21] `Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1', ISO/IEC 8859-1:1998. [22] `The Common Gateway Interface', http://hoohoo.ncsa.uiuc.edu/cgi/, NCSA, University of Illinois. 12 Authors' Addresses David Robinson Apache Software Foundation Email: drtr@apache.org Ken A. L. Coar MeepZor Consulting 7824 Mayfaire Crest Lane, Suite 202 Raleigh, NC 27615-4875 Robinson & Coar Expires 15 October 2003 [Page 32] INTERNET-DRAFT Common Gateway Interface -- 1.1 16 April 2003 USA Tel: +1 (919) 254 4237 Fax: +1 (919) 254 5420 Email: Ken.Coar@Golux.com Robinson & Coar Expires 15 October 2003 [Page 33]