INTERNET-DRAFT Ken A L Coar draft-coar-cgi-v11-02.{html,txt} IBM Corporation D.R.T. Robinson ESI 2 April, 1999 The WWW Common Gateway Interface 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>. 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 [NCSA-CGI]. This document also defines the use of the CGI/1.1 interface on the Unix and AmigaDOS(tm) systems. Discussion of this draft occurs on the CGI-WG mailing list; see the project Web page at <URL:http://Web.Golux.Com/coar/cgi/> for details on the mailing list and the status of the project. Table of Contents 1 Introduction..............................................3 1.1 Purpose................................................3 1.2 Requirements...........................................3 1.3 Specifications.........................................4 Coar, et al. INTERNET-DRAFT [Page 1]
CGI/1.1 Expires: 14 October, 1999 1.4 Terminology............................................4 2 Notational Conventions and Generic Grammar................4 2.1 Augmented BNF..........................................4 2.2 Basic Rules............................................5 3 Protocol Parameters.......................................6 3.1 URL Encoding...........................................6 3.2 The Script URI.........................................6 4 Invoking the Script.......................................7 5 The CGI Script Command Line...............................7 6 Data Input to the CGI Script..............................7 6.1 Request Metadata (Metavariables).......................8 6.1.1 AUTH_TYPE...........................................8 6.1.2 CONTENT_LENGTH......................................9 6.1.3 CONTENT_TYPE........................................9 6.1.4 GATEWAY_INTERFACE...................................10 6.1.5 HTTP_*..............................................10 6.1.6 PATH_INFO...........................................11 6.1.7 PATH_TRANSLATED.....................................11 6.1.8 QUERY_STRING........................................12 6.1.9 REMOTE_ADDR.........................................12 6.1.10 REMOTE_HOST........................................13 6.1.11 REMOTE_IDENT.......................................13 6.1.12 REMOTE_USER........................................13 6.1.13 REQUEST_METHOD.....................................13 6.1.14 SCRIPT_NAME........................................14 6.1.15 SERVER_NAME........................................14 6.1.16 SERVER_PORT........................................14 6.1.17 SERVER_PROTOCOL....................................15 6.1.18 SERVER_SOFTWARE....................................15 6.2 Request Content-Bodies................................15 7 Data Output from the CGI Script...........................16 7.1 Non-Parsed Header Output...............................16 7.2 Parsed Header Output...................................16 7.2.1 CGI header fields...................................17 7.2.1.1 Content-Type.....................................17 7.2.1.2 Location.........................................17 7.2.1.3 Status...........................................18 7.2.1.4 Extension header fields..........................18 7.2.2 HTTP header fields..................................18 8 Server Implementation.....................................19 8.1 Requirements for Servers...............................19 8.1.1 Script-URI..........................................19 8.1.2 Request Content-body Handling.......................19 8.1.3 Required Metavariables..............................20 8.2 Recommendations for Servers............................20 8.3 Summary of Metavariables...............................21 9 Script Implementation.....................................22 9.1 Requirements for Scripts...............................22 9.2 Recommendations for Scripts............................22 10 System Specifications....................................23 10.1 AmigaDOS..............................................23 10.2 Unix..................................................23 11 Security Considerations..................................24 11.1 Safe Methods..........................................24 Coar, et al. INTERNET-DRAFT [Page 2]
CGI/1.1 Expires: 14 October, 1999 11.2 HTTP Header Fields Containing Sensitive Information...24 11.3 Script Interference with the Server...................24 12 Acknowledgments..........................................25 13 References...............................................25 14 Authors' Addresses.......................................26 1. Introduction 1.1. Purpose Together the HTTP [3],[8] server and the CGI script are responsible for servicing a client request by sending back responses. The client request comprises a Universal Resource Identifier (URI) [1], a request method, and various ancillary information about the request provided by the transport mechanism. The CGI defines the abstract parameters, known as metavariables, which describe the client's request. Together with a concrete programmer interface this specifies a platform-independent interface between the script and the HTTP server. 1.2. Requirements This specification uses the same words as RFC 1123 [5] to define the significance of each particular requirement. These are: MUST This word or the adjective 'required' means that the item is an absolute requirement of the specification. SHOULD This word or the adjective 'recommended' means that there may exist valid reasons in particular circumstances to ignore this item, but the full implications should be understood and the case carefully weighed before choosing a different course. MAY This word or the adjective 'optional' means that this item is truly optional. One vendor may choose to include the item because a particular marketplace requires it or because it enhances the product, for example; another vendor may omit the same item. An implementation is not compliant if it fails to satisfy one or more of the 'must' requirements for the protocols it implements. An implementation that satisfies all of the 'must' and all of the 'should' requirements for its features is said to be 'unconditionally compliant'; one that satisfies all of the 'must' requirements but not all of the 'should' requirements for its features is said to be 'conditionally Coar, et al. INTERNET-DRAFT [Page 3]
CGI/1.1 Expires: 14 October, 1999 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 12 of this document. New systems may be defined by new specifications without revision of this document. implementation defined The behaviour of the feature may vary from implementation to implementation, but a particular implementation must document its behaviour. 1.4. Terminology This specification uses many terms defined in the HTTP/1.1 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. metavariable A named parameter that carries information from the server to the script. It is not necessarily a variable in the operating-system's environment, although that is the most common implementation. script The software which is invoked by the server via this interface. It need not be a standalone program, but could be a dynamically-loaded or shared library, or even a subroutine in the server. server The application program which invokes the script in order to service requests. 2. Notational Conventions and Generic Grammar 2.1. Augmented BNF All of the mechanisms specified in this document are described in both prose and an augmented Backus-Naur Form (BNF) similar to that used by RFC 822 [6]. This augmented BNF contains the following constructs: name = definition Coar, et al. INTERNET-DRAFT [Page 4]
CGI/1.1 Expires: 14 October, 1999 The definition 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 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] An 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" hex = digit | "A" | "B" | "C" | "D" | "E" | "F" | "a" | "b" | "c" | "d" | "e" | "f" digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" OCTET = <any 8-bit byte> CHAR = <any character> CTL = <any control character> SP = <space character> HT = <horizontal tab character> NL = <newline> LWSP = SP | HT | NL tspecial = "(" | ")" | "@" | "," | ";" | ":" | "\" | <"> Coar, et al. INTERNET-DRAFT [Page 5]
CGI/1.1 Expires: 14 October, 1999 | "/" | "[" | "]" | "?" | "<" | ">" | "{" | "}" | SP | HT token = 1*<any CHAR except CTLs or tspecials> quoted-string = ( <"> *qdtext <"> ) | ( "<" *qatext ">") qdtext = <any CHAR except <"> and CTLs but including LWSP> qatext = <any CHAR except "<", ">" and CTLs but including LWSP> Note that newline (NL) need not be a single character, but can be a character sequence. 3. Protocol Parameters 3.1. URL Encoding Some variables and constructs used here are described as being 'URL-encoded'. This encoding is described in section 2 of RFC 2396 [4]. An alternate "shortcut" encoding for representing the space character exists and is in common use. Scripts MUST be prepared to recognise both '+' and '%20' as an encoded space in a URL-encoded value. Note that some unsafe characters may have different semantics if they are encoded. The definition of which characters are unsafe depends on the context. For example, the following two URLs do not necessarily refer to the same resource: http://somehost.com/somedir%2Fvalue http://somehost.com/somedir/value See section 2 of RFC 2396 [4] for authoritative treatment of this issue. 3.2. The Script URI The 'Script-URI' is defined as the URI of the resource identified by the metavariables. Often, this URI will be the same as the URI requested by the client (the 'Client-URI'); however, it need not be. Instead, it could be a URI invented by the server, and so it can only be used in the context of the server and its CGI interface. The Script-URI has the syntax of generic-RL as defined in section 2.1 of RFC 1808 [7], with the exception that object parameters and fragment identifiers are not permitted: <scheme>://<host><port>/<path>?<query> The various components of the script URI are defined by some of the metavariables (see section 4 below); Coar, et al. INTERNET-DRAFT [Page 6]
CGI/1.1 Expires: 14 October, 1999 script-uri = protocol "://" SERVER_NAME ":" SERVER_PORT enc-script enc-path-info "?" QUERY_STRING where 'protocol' is obtained from SERVER_PROTOCOL, 'enc-script' is a URL-encoded version of SCRIPT_NAME and 'enc-path-info' is a URL-encoded version of PATH_INFO. See section 4.6 for more information about the PATH_INFO metavariable. Note that the scheme and the protocol are not identical; for instance, a resource accessed via an SSL mechanism may have a Client-URI with a scheme of "https" rather than "http". CGI/1.1 provides no means for the script to reconstruct this, and therefore the Script-URI includes the base protocol used. 4. Invoking the Script The script is invoked in a system defined manner. Unless specified otherwise, this will be by treating the file containing the script as an executable program, and running it as a child process of the server. 5. The CGI 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' query. This is identified by a "GET" or "HEAD" HTTP request with a URL query string not containing any unencoded "=" characters. For such a request, servers SHOULD parse the search string into words, using the following rules: search-string = search-word *( "+" search-word ) search-word = 1*schar schar = xunreserved | escape | xreserved xunreserved = alpha | digit | xsafe | extra xsafe = "$" | "-" | "_" | "." xreserved = ";" | "/" | "?" | ":" | "@" | "&" After parsing, each word is URL-decoded, optionally encoded in a system defined manner, and then the argument list is set to the list of words. If the server cannot create any part of the argument list, then the server SHOULD NOT generate any command line information. For example, the number of arguments may be greater than operating system or server limitations permit, or one of the words may not be representable as an argument. Scripts SHOULD check to see if the QUERY_STRING value contains an unencoded "=" character, and SHOULD NOT use the command line arguments if it does. 6. Data Input to the CGI Script Coar, et al. INTERNET-DRAFT [Page 7]
CGI/1.1 Expires: 14 October, 1999 Information about a request comes from two different sources: the request header, and any associated content-body. Servers MUST make portions of this information available to scripts. 6.1. Request Metadata (Metavariables) Each CGI server implementation MUST define a mechanism to pass data about the request from the server to the script. The metavariables containing these data are accessed by the script in a system defined manner. In all cases, a missing metavariable is equivalent to a zero-length (NULL) value, and vice versa. The representation of the characters in the metavariables is system defined. Case is not significant in the metavariable names, in that there cannot be two different variables whose names differ in case only. Here they are shown using a canonical representation of capitals plus underscore ("_"). The actual representation of the names is system defined; for a particular system the representation MAY be defined differently than this. metavariable values MUST be considered case-sensitive except as noted otherwise. The canonical variables defined by this specification are: AUTH_TYPE CONTENT_LENGTH CONTENT_TYPE GATEWAY_INTERFACE HTTP_* PATH_INFO PATH_TRANSLATED QUERY_STRING REMOTE_ADDR REMOTE_HOST REMOTE_IDENT REMOTE_USER REQUEST_METHOD SCRIPT_NAME SERVER_NAME SERVER_PORT SERVER_PROTOCOL SERVER_SOFTWARE 6.1.1. AUTH_TYPE This variable is specific to requests made via the HTTP scheme. If the script-URI required access authentication for external access, then the server SHOULD set the value of this variable from the 'auth-scheme' token in the request's "Authorization" Coar, et al. INTERNET-DRAFT [Page 8]
CGI/1.1 Expires: 14 October, 1999 header field. therwise it is set to NULL. AUTH_TYPE = "" | auth-scheme auth-scheme = "Basic" | token HTTP access authentication schemes are described in section 11 of the HTTP/1.1 specification [8]. The auth-scheme is not case-sensitive. Servers SHOULD provide this metavariable to scripts if the request header included an "Authorization" field. 6.1.2. CONTENT_LENGTH This metavariable is set to the size of the content-body entity attached to the request, if any, in decimal number of octets. If no data are attached, then this metavariable is either NULL or not defined. The syntax is the same as for the HTTP "Content-Length" header field (section 14.14, HTTP/1.1 specification [8]). CONTENT_LENGTH = "" | 1*digit Servers MUST provide this metavariable to scripts if the request was accompanied by a content-body entity. 6.1.3. CONTENT_TYPE If the request includes a content-body, CONTENT_TYPE is set tothe Internet Media Type [9] of the attached entity if the type was provided via a "Content-type" field in the request header, or if the server can determine it in the absence of a supplied "Content-type" field. The syntax is the same as for the HTTP "Content-Type" header field. 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 in section 3.7 of the HTTP/1.1 specification [8]. Example: application/x-www-form-urlencoded There is no default value for this variable. If and only if it is unset, then the script MAY attempt to determine the media Coar, et al. INTERNET-DRAFT [Page 9]
CGI/1.1 Expires: 14 October, 1999 type from the data received. If the type remains unknown, then the script MAY choose to either assume a content-type of application/octet-stream or reject the request with a 415 ("Unsupported Media Type") error. See section 7.2.1.3 for more information about returning error status values. Servers MUST provide this metavariable to scripts if a "Content-Type" field was present in the original 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 datatype, or it MAY omit this metavariable when communicating the request information to the script. 6.1.4. GATEWAY_INTERFACE This metavariable is set to the dialect of CGI being used by the server to communicate with the script. Syntax: GATEWAY_INTERFACE = "CGI" "/" major "." minor major = 1*digit minor = 1*digit Note that the major and minor numbers are treated as separate integers and hence each may be more 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 in either the major or the minor number MUST be ignored by scripts and SHOULD NOT be generated by servers. This document defines the 1.1 version of the CGI interface ("CGI/1.1"). Servers MUST provide this metavariable to scripts. 6.1.5. HTTP_* These variables are specific to requests made via the HTTP scheme. Interpretation of these variables depends on the value of theSERVER_PROTOCOL metavariable (see section 6.1.17). metavariables with names beginning with "HTTP_" contain values from the request header, if the scheme used was HTTP. Each HTTP header field name is converted to upper case, has all occurrences of "-" replaced with "_", and has "HTTP_" prepended to form the metavariable name. The header data MAY be presented as sent by the client, or MAY be rewritten in ways which do not change its semantics. If multiple header fields with the same field-name are received then the server MUST rewrite them as though they had been received as a single header field having the same semantics before being represented in a metavariable. Similarly, a header field that is received on more than one line MUST be merged into a single line. The server MUST, if necessary, change the representation Coar, et al. INTERNET-DRAFT [Page 10]
CGI/1.1 Expires: 14 October, 1999 of the data (for example, the character set) to be appropriate for a CGI metavariable. Servers are not required to create metavariables for all the request header fields that they receive. In particular, they MAY decline to make available any header fields carrying authentication information, such as "Authorization"; and they MAY header fields the values of which are available to the script via other metavariables, such as "Content-Length" and "Content-Type". 6.1.6. PATH_INFO The PATH_INFO metavariable specifies a path to be interpreted by the CGI script. It identifies the source or sub-resource to be returned by the CGI script, and it is derived from the portion of the URI path following the script name but preceding any query data. The syntax and semantics are similar to a decoded HTTP URL 'path' token (defined in RFC 2396 [4]), with the exception that a PATH_INFO of "/" represents a single void path segment. PATH_INFO = "" | ( "/" path ) path = segment *( "/" segment ) segment = *pchar pchar = <any CHAR except "/"> The PATH_INFO string is the trailing part of the <path> component of the script-URI (see section 3.2) that follows the SCRIPT_NAME portion of the path. Servers MAY impose their own restrictions and limitations on what values they will accept for PATH_INFO, and MAY reject or edit any values they considers objectionable before passing them to the script. Servers MUST make this URI component available to CGI scripts. The PATH_INFO quantity is case-sensitive, and the server MUST preserve the case of the PATH_INFO element of the URI when making it available to scripts. 6.1.7. PATH_TRANSLATED PATH_TRANSLATED is derived by taking any path-info component of the request URI (see section 6.1.6), decoding it (see section 3.1), parsing it as a URI in its own right, and performing any virtual-to-physical filesystem translation. PATH_TRANSLATED = *CHAR For a request such as the following: http://somehost.com/cgi-bin/somescript/this%2eis%2epath%2einfo Coar, et al. INTERNET-DRAFT [Page 11]
CGI/1.1 Expires: 14 October, 1999 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.info This would then be translated to a filesystem location, perhaps something like this: /usr/local/www/htdocs/this.is.the.path.info This resulting filesystem path is the value of PATH_TRANSLATED. The value of PATH_TRANSLATED may or may not map to a valid filesystem location or file. Servers MUST preserve the case of the path-info segment if and only if the underlying filesystem supports case-sensitive names. If the filesystem is only case-aware, case-preserving, or case-blind with regard to filenames, servers are not required to preserve the case of the original segment through the translation. The filesystem translation algorithm the server uses to derive PATH_TRANSLATED is implementation defined; CGI scripts which use this variable may suffer limited portability. Servers SHOULD provide this metavariable to scripts. 6.1.8. QUERY_STRING A URL-encoded string; the <query> part of the script-URI. (See section 3.2.) QUERY_STRING = query-string query-string = *qchar qchar = unreserved | escape | reserved unreserved = alpha | digit | safe | extra reserved = ";" | "/" | "?" | ":" | "@" | "&" | "=" safe = "$" | "-" | "_" | "." | "+" extra = "!" | "*" | "'" | "(" | ")" | "," escape = "%" hex hex The URL syntax for a query string is described in section 3 of RFC 2396 [4]. Servers MUST supply this value to scripts. The QUERY_STRING value is case-sensitive. 6.1.9. REMOTE_ADDR The IP address of the agent sending the request to the server. This is not necessarily that of the client (such as if the request came through a proxy). REMOTE_ADDR = hostnumber Coar, et al. INTERNET-DRAFT [Page 12]
CGI/1.1 Expires: 14 October, 1999 hostnumber = ipv4-address | ipv6-address ipv4-address = digits "." digits "." digits "." digits ipv6-address = hexbit16 ":" hexbit16 ":" hexbit16 ":" hexbit16 ":" hexbit16 ":" hexbit16 ":" hexbit16 ":" hexbit16 digits = 1*digit hexbit16 = 1*hex Servers MUST supply this value to scripts. 6.1.10. REMOTE_HOST The fully qualified domain name of the agent sending the request to the server, if available, otherwise NULL. (See section 6.1.9.) Fully qualified domain names take the form as described in section 3.5 of RFC 1034 [10] and section 2.1 of RFC 1123 [5]. Domain names are not case sensitive. Servers SHOULD provide this information to scripts. 6.1.11. REMOTE_IDENT The identity information reported about the connection by a RFC 1413 [11] request to the remote agent, if available. Servers MAY choose not to support this feature, or not to request the data for efficiency reasons. REMOTE_IDENT = *CHAR The data returned may be used for authentication purposes, but the level of trust reposed in them should be minimal. Servers MAY supply this information to scripts if the RFC1413 [11] lookup is performed. 6.1.12. REMOTE_USER If the request required authentication using the "Basic" mechanism (i.e., the AUTH_TYPE metavariable is set to "Basic"), then the value of the REMOTE_USER metavariable is set to the user-ID supplied. In all other cases the value of this metavariable is undefined. REMOTE_USER = "" | userid | *OCTET userid = token This variable is specific to requests made via the HTTP protocol. Servers SHOULD provide this metavariable to scripts. 6.1.13. REQUEST_METHOD The REQUEST_METHOD metavariable is set to the method with Coar, et al. INTERNET-DRAFT [Page 13]
CGI/1.1 Expires: 14 October, 1999 which the request was made, as described in section 5.1.1 of the HTTP/1.0 specification [3] and section 5.1.1 of the HTTP/1.1 specification [8]. REQUEST_METHOD = http-method http-method = "GET" | "HEAD" | "POST" | "PUT" | "DELETE" | extension-method extension-method = token The method is case sensitive. Note that of the new methods defined by the HTTP/1.1 specification [8], OPTIONS and TRACE are not appropriate for the CGI/1.1 environment. This variable is specific to requests made with HTTP. Servers MUST provide this metavariable to scripts. 6.1.14. SCRIPT_NAME The SCRIPT_NAME metavariable is set to a URL path that could identify the CGI script (rather than the script's output). The syntax and semantics are identical to a decoded HTTP URL 'path' token (see RFC 2396 [4]). SCRIPT_NAME = "" | ( "/" [ path ] ) The SCRIPT_NAME string is some leading part of the <path> component of the script-URI derived in some implementation defined manner. No PATH_INFO or QUERY_STRING segments (see sections 6.1.6 and 6.1.8) are included in the SCRIPT_NAME value. Servers MUST provide this metavariable to scripts. 6.1.15. SERVER_NAME The SERVER_NAME metavariable is set to the name of the server, as derived from the <host> part of the script-URI (see section 3.2). SERVER_NAME = hostname | hostnumber Servers MUST provide this metavariable to scripts. 6.1.16. SERVER_PORT The SERVER_PORT metavariable is set to the port on which the request was received, as used in the <port> part of the script-URI. SERVER_PORT = 1*digit If the <port> portion of the script-URI is blank, the actual port number upon which the request was received MUST be Coar, et al. INTERNET-DRAFT [Page 14]
CGI/1.1 Expires: 14 October, 1999 supplied. Servers MUST provide this metavariable to scripts. 6.1.17. SERVER_PROTOCOL The SERVER_PROTOCOL metavariable iss set to the name and revision of the information protocol with which thLe request arrived. This is not necessarily the same as the protocol version used by the server in its response to the client. SERVER_PROTOCOL = HTTP-Version | extension-version | extension-token HTTP-Version = "HTTP" "/" 1*digit "." 1*digit extension-version = protocol "/" 1*digit "." 1*digit protocol = 1*( alpha | digit | "+" | "-" | "." ) extension-token = token 'protocol' is a version of the <scheme> part of the script-URI, but is not identical to it. For example, the scheme of a request may be "https" while the protocol remains "http". The protocol is not case sensitive, but by convention, 'protocol' is in upper case. A well-known extension token value 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. Servers MUST provide this metavariable to scripts. 6.1.18. SERVER_SOFTWARE The SERVER_SOFTWARE metavariable is set to the name and version of the information server software answering the request (and running the gateway). SERVER_SOFTWARE = *CHAR Servers MUST provide this metavariable to scripts. 6.2. Request Content-Bodies As there may be a data entity attached to the request, there MUST be a system defined method for the script to read these data. Unless defined otherwise, this will be via the 'standard input' file descriptor. If the CONTENT_LENGTH value (see section 6.1.2) is non-NULL, the server MUST supply at least that many bytes to scripts on the standard input stream. Scripts are not obliged to read the data. Servers MAY signal an EOF condition after CONTENT_LENGTH bytes have been read, but are are not obligated to do so. Therefore, scripts MUST NOT attempt to read more than Coar, et al. INTERNET-DRAFT [Page 15]
CGI/1.1 Expires: 14 October, 1999 CONTENT_LENGTH bytes, even if more data are available. For non-parsed header (NPH) scripts (see section 7.1 below), servers SHOULD attempt to ensure that the script input comes directly from the client, with minimal buffering. For all scripts the data will be as supplied by the client. Section 8.1.2 describes the requirements of servers with regard to requests that include content-bodies. 7. Data Output from the CGI Script There MUST be a system defined method for the script to send data back to the server or client; a script MUST always return some data. Unless defined otherwise, this will be via the 'standard output' file descriptor. There are two forms of output that scripts can supply to servers: non-parsed header (NPH) output, and parsed header output. Servers MUST support parsed header output and MAY support NPH output. The method of distinguishing between the two types of output (or scripts) is implementation defined. Servers MAY implement a timeout period within which data must be received from scripts. 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 and SHOULD abort the client request with a '500 Internal Server Error' response. 7.1. Non-Parsed Header Output Scripts using the NPH output form MUST return a complete HTTP response message, as described in Section 6 of the HTTP specifications [3],[8]. NPH scripts MUST use the SERVER_PROTOCOL variable to determine the appropriate format for a response. Servers SHOULD attempt to ensure that the script output is sent directly to the client, with minimal internal and no transport-visible buffering. 7.2. Parsed Header Output Scripts using the parsed header output form MUST supply a CGI response message to the server as follows: CGI-Response = *( CGI-field | HTTP-Field ) NL [ Entity-Body ] CGI-Field = Content-type | Location | Status | extension-header The response comprises a header and a body, separated by a Coar, et al. INTERNET-DRAFT [Page 16]
CGI/1.1 Expires: 14 October, 1999 blank line. The body may be NULL. The header fields are either CGI header fields to be interpreted by the server, or HTTP header fields to be included in the response returned to the client if the request method is HTTP. At least one CGI-Field MUST be supplied, but no CGI field name may be used more than once in a response. If a body is supplied, then a "Content-type" header field MUST be supplied by the script, otherwise the script MUST send a "Location" or "Status" header field. If a Location CGI-field is returned, then the script MUST NOT supply any HTTP-Fields. All header fields occurring in a CGI-Response MUST be specified one per line; CGI/1.1 makes no provision for continuation lines. 7.2.1. CGI header fields The CGI header fields have the generic syntax: generic-field = field-name ":" [ field-value ] NL field-name = 1*<any CHAR, excluding CTLs, SP and ":"> field-value = *( field-content | LWSP ) field-content = *( token | tspecial | quoted-string ) The field-name is not case sensitive; a NULL field value is equivalent to the header field not being sent. 7.2.1.1. Content-Type The Internet Media Type [9] of the entity body, which is to be sent unmodified to the client. Content-Type = "Content-Type" ":" media-type NL This is actually an HTTP-Field rather than a CGI-field, but it is listed here because of its importance in the CGI dialogue as a member of the "one of these is required" set of header fields. 7.2.1.2. Location This is used to specify to the server that the script is returning a reference to a document rather than an actual document. Location = "Location" ":" ( fragment-URI | rel-URL-abs-path ) NL fragment-URI = URI [ # fragmentid ] URI = scheme ":" *qchar fragmentid = *qchar rel-URL-abs-path = "/" [ hpath ] [ "?" query-string ] hpath = fpsegment *( "/" psegment ) fpsegment = 1*hchar psegment = *hchar Coar, et al. INTERNET-DRAFT [Page 17]
CGI/1.1 Expires: 14 October, 1999 hchar = alpha | digit | safe | extra | ":" | "@" | "& | "=" The Location value is either an absolute URI with optional fragment, as defined in RFC 1630 [1], or an absolute path within the server's URI space (i.e., omitting the scheme and network-related fields) and optional query-string. If an absolute URI is returned by the script, then the server MUST generate a '302 redirect' HTTP response message unless the script has supplied an explicit Status response header field, and if no entity body is supplied by the script, the server MUST produce one. If the Location value is a path, then the server MUST generate the response that it would have produced in response to a request containing the URL scheme "://" SERVER_NAME ":" SERVER_PORT rel-URL-abs-path Note: If the request was accompanied by a content-body (such as for a POST request), the content-body will be lost if the script redirects the request with a Location field. 7.2.1.3. 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" ":" digit digit digit SP reason-phrase NL reason-phrase = *<CHAR, excluding CTLs, NL> The valid status codes are listed in section 6.1.1 of the HTTP/1.0 specifications [3]. If the SERVER_PROTOCOL is "HTTP/1.1", then the status codes defined in the HTTP/1.1 specification [8] may be used. If the script does not return a "Status" header field, then "200 OK" SHOULD be assumed by the server. If a script is being used to handle a particular error or condition encountered by the server, such as a '404 Not Found' error, the script SHOULD use the "Status" CGI header field to propagate the error condition back to the client. E.g., in the example mentioned it SHOULD include a "Status: 404 Not Found" in the header data returned to the server. 7.2.1.4. Extension header fields Scripts MAY include in their CGI response header additional fields not defined in this or the HTTP specification. These are called "extension" fields, and have the syntax of a generic-field as defined in section 7.2.1. The name of an extension field MUST NOT conflict with a field name defined in this or any other specification; extension field names SHOULD begin with "X-CGI-" to ensure uniqueness. 7.2.2. HTTP header fields Coar, et al. INTERNET-DRAFT [Page 18]
CGI/1.1 Expires: 14 October, 1999 The script MAY return any other header fields defined by the specification for the SERVER_PROTOCOL (HTTP/1.0 [3] or HTTP/1.1 [8]). Servers MUST resolve conflicts beteen CGI header and HTTP header formats or names (see section 8). 8. Server Implementation This section defines the requirements that must be met by HTTP servers in order to provide a coherent and correct CGI/1.1 environment in which scripts may function. It is intended primarily for server implementors, but it is useful for script authors to be familiar with the information as well. 8.1. Requirements for Servers In order to be considered CGI/1.1-compliant, a server must meet certain basic criteria and provide certain minimal functionality. The details of these requirements are described in the following sections. 8.1.1. Script-URI Servers MUST support the standard mechanism (described below) which allows script authors to determine what URL to use in documents which reference the script; specifically, what URL to use in order to achieve particular settings of the metavariables. This mechanism is as follows: The server MUST translate the header data from the CGI header field syntax to the HTTP header field syntax if these differ. For example, the character sequence for newline (such as Unix's ASCII NL) used by CGI scripts may not be the same as that used by HTTP (ASCII CR followed by LF). The server MUST also resolve any conflicts between header fields returned by the script and header fields that it would otherwise send itself. The fields affected and the resolution method used SHOULD be documented as part of the server implementation. 8.1.2. Request Content-body Handling Because CGI/1.1 requires that the CONTENT_LENGTH metavariable be provided when a script is activated (see section 8.3), servers MUST take care to correctly process requests that include a content-body but do not specify a Content-Length field in the request header (such as a request with a Transfer-Encoding of "chunked"). Requests that require special treatment meet all of the following criteria: 1. The resource identified by the request-URI is a CGI/1.1 script, and 2. The request header does not include a Content-Length Coar, et al. INTERNET-DRAFT [Page 19]
CGI/1.1 Expires: 14 October, 1999 field, and 3. The request includes a content-body, and 4. The request header includes a Transfer-Encoding field that specifies a method (such as "chunked") which either does not require or prohibits a Content-Length field. If an HTTP/1.1 server determines that a request meets all of the above criteria, it MUST process the request in one of the two following ways: * The server may read (buffer) the entire request in order to determine the correct value of the CONTENT_LENGTH metavariable, and supply the buffered information to the script as though the content-body had not been transfer-encoded. The server MAY abort the request with a '413 Request Entity Too Large' status and close the connection if the size of the content-body is greater than the server is prepared to buffer. Or, * The server may reject the request with a '411 Length Required' status. 8.1.3. Required Metavariables Servers MUST provide scripts with certain information and metavariables as described in section 8.3. 8.2. Recommendations for Servers Servers SHOULD provide the "query" component of the script-URI as command-line arguments to scripts if it does not contain any unencoded '=' characters and the command-line arguments can be generated in an unambiguous manner. (See section 5.) Servers SHOULD set the AUTH_TYPE metavariable to the value of the 'auth-scheme' token of the "Authorization" field if it was supplied as part of the request header. (See section 6.1.1.) Where applicable, servers SHOULD set the current working directory to the directory in which the script is located before invoking it. 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: 1. define any restrictions on allowed characters, in Coar, et al. INTERNET-DRAFT [Page 20]
CGI/1.1 Expires: 14 October, 1999 particular whether ASCII NUL is permitted; 2. define any restrictions on allowed path segments, in particular whether non-terminal NULL segments are permitted; 3. define the behaviour for "." or ".." path segments; i.e., whether they are prohibited, treated as ordinary path segments or interpreted in accordance with the relative URL specification [7]; 4. define any limits of the implementation, including limits on path or search string lengths, and limits on the volume of header data 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). For non-parsed header (NPH) scripts (see section 7.1), servers SHOULD attempt to ensure that the script input comes directly from the client, with minimal buffering. For all scripts the data will be as supplied by the client. 8.3. Summary of MetaVariables Servers MUST provide the following metavariables to scripts. See the individual descriptions for exceptions and semantics. CONTENT_LENGTH (section 6.1.2) CONTENT_TYPE (section 6.1.3) GATEWAY_INTERFACE (section 6.1.4) PATH_INFO (section 6.1.6) QUERY_STRING (section 6.1.8) REMOTE_ADDR (section 6.1.9) REQUEST_METHOD (section 6.1.13) SCRIPT_NAME (section 6.1.14) SERVER_NAME (section 6.1.15) SERVER_PORT (section 6.1.16) SERVER_PROTOCOL (section 6.1.17) SERVER_SOFTWARE (section 6.1.18) Servers SHOULD define the following metavariables for scripts. See the individual descriptions for exceptions and semantics. AUTH_TYPE (section 6.1.1) REMOTE_HOST (section 6.1.10) In addition, servers SHOULD provide metavariables for all fields present in the HTTP request header, with the exception of those involved with access control. Servers MAY at their discretion provide metavariables for access control fields. Servers MAY define the following metavariables. See the individual descriptions for exceptions and semantics. PATH_TRANSLATED (section 6.1.7) Coar, et al. INTERNET-DRAFT [Page 21]
CGI/1.1 Expires: 14 October, 1999 REMOTE_IDENT (section 6.1.11) REMOTE_USER (section 6.1.12) Servers may at their discretion define additional implementation-specific extension metavariables provided their names do not conflict with defined header field names. Implementation-specific metavariable names SHOULD be prefixed with "X_" (e.g., "X_DBA") to avoid the potential for such conflicts. 9. Script Implementation This section defines the requirements and recommendations for scripts that are intended to function in a CGI/1.1 environment. It is intended primarily as a reference for script authors, but server implementors should be familiar with these issues as well. 9.1. Requirements for Scripts Scripts using the parsed-header method to communicate with servers MUST supply a response header to the server. (See section 7.) Scripts using the NPH method to communicate with servers MUST provide complete HTTP responses, and MUST use the value of the SERVER_PROTOCOL metavariable to determine the appropriate format. (See section 7.1.) Scripts MUST check the value of the REQUEST_METHOD metavariable in order to provide an appropriate response. (See section 6.1.13.) Scripts MUST be prepared to handled URL-encoded values in metavariables. In addition, they MUST recognise both "+" and "%20" in URL-encoded quantities as representing the space character. (See section 3.1.) Scripts MUST ignore leading zeros in the major and minor version numbers in the GATEWAY_INTERFACE metavariable value. (See section 6.1.4.) When processing requests that include a content-body, scripts MUST NOT read more than CONTENT_LENGTH bytes from the input stream. (See sections 6.1.2 and 6.2.) 9.2. Recommendations for Scripts Servers may interrupt or terminate script execution at any time and without warning, so scripts SHOULD be prepared to deal with abnormal termination. Scripts SHOULD reject unexpected methods (such as DELETE, etc.) with error '405 Method Not Allowed'. If the script does Coar, et al. INTERNET-DRAFT [Page 22]
CGI/1.1 Expires: 14 October, 1999 not intend processing the PATH_INFO data, then it SHOULD reject the request with '404 Not Found' if PATH_INFO is not NULL. If a script is processing the output of a form , it SHOULD verify that the CONTENT_TYPE is "application/x-www-form-urlencoded" [2] or whatever other media type is expected. Scripts parsing PATH_INFO, PATH_TRANSLATED, or SCRIPT_NAME 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'. As it is impossible for scripts to determine the client URI that initiated a request without knowledge of the specific server in use, the script SHOULD NOT return "text/html" documents containing relative URL links without including a "<BASE>" tag in the document. When returning header fields, scripts SHOULD try to send the CGI header fields (see section 7.2) as soon as possible, and preferably before any HTTP header fields. This may help reduce the server's memory requirements. 10. System Specifications 10.1. AmigaDOS The implementation of the CGI on an AmigaDOS operating system platform SHOULD use environment variables as the mechanism of providing request metadata to CGI scripts. 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 is used for the definition of environment variable names and header field names; the newline (NL) sequence is LF; servers SHOULD also accept CR LF as a newline. 10.2. Unix The implementation of the CGI on a UNIX operating system platform SHOULD use environment variables as the mechanism of Coar, et al. INTERNET-DRAFT [Page 23]
CGI/1.1 Expires: 14 October, 1999 providing request metadata to CGI scripts. For Unix compatible operating systems, the following are defined: Environment variables These are accessed by the C library routine getenv. The command line This is accessed using the the argc and argv arguments to main(). The words have any characters which are 'active' in the Bourne shell escaped with a backslash. If the value of the QUERY_STRING metavariable contains an unencoded equals-sign '=', then the command line SHOULD NOT be used by the script. 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 is used for the definition of environment variable names and header field names; the newline (NL) sequence is LF; servers SHOULD also accept CR LF as a newline. 11. Security Considerations 11.1. Safe Methods As discussed in the security considerations of the HTTP specifications [3],[8], the convention has been established that the GET and HEAD methods should be 'safe'; they should cause no side-effects and only have the significance of resource retrieval. 11.2. HTTP 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 using the "Basic" authentication scheme, then the client will send an "Authorization" header field containing a username and password. If the server, rather than the script, validates this information then the password SHOULD NOT be passed on to the script via the HTTP_AUTHORIZATION metavariable without careful consideration. This also applies to the Proxy-Authorization header field and the corresponding HTTP_PROXY_AUTHORIZATION metavariable. 11.3. 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 Coar, et al. INTERNET-DRAFT [Page 24]
CGI/1.1 Expires: 14 October, 1999 process. It SHOULD therefore be ensured that the script cannot interfere with the server process, its configuration, or documents. If the script is executed by calling a function linked in to the server software (either at compile-time or run-time) then precautions SHOULD be taken to protect the core memory of the server, or to ensure that untrusted code cannot be executed. 12. Acknowledgements This work is based on a draft published in 1997 by David R. Robinson in 1997, which in turn was 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 by Chris Adie, Dave Kristol, Mike Meyer, David Morris, and Harald Alvestrand. 13. References [1] Berners-Lee, T., 'Universal Resource Identifiers in WWW: A Unifying Syntax for the Expression of Names and Addresses of Objects on the Network as used in the World-Wide Web', RFC 1630, CERN, June 1994. [2] Berners-Lee, T. and Connolly, D., 'Hypertext Markup Language - 2.0', RFC 1866, MIT/W3C, November 1995. [3] Berners-Lee, T., Fielding, R. T. and Frystyk, H., 'Hypertext Transfer Protocol -- HTTP/1.0', RFC 1945, MIT/LCS, UC Irvine, May 1996. [4] Berners-Lee, T., Fielding, R., and Masinter, L., Editors, 'Uniform Resource Identifiers (URI): Generic Syntax', RFC 2396, MIT, U.C. Irvine, Xerox Corporation, August 1996. [5] Braden, R., Editor, 'Requirements for Internet Hosts -- Application and Support', STD 3, RFC 1123, IETF, October 1989. [6] Crocker, D.H., 'Standard for the Format of ARPA Internet Text Messages', STD 11, RFC 822, University of Delaware, August 1982. [7] Fielding, R., 'Relative Uniform Resource Locators', RFC 1808, UC Irvine, June 1995. [8] Coar, et al. INTERNET-DRAFT [Page 25]
CGI/1.1 Expires: 14 October, 1999 Fielding, R., Gettys, J., Mogul, J., Frystyk, H. and Berners-Lee, T., 'Hypertext Transfer Protocol -- HTTP/1.1', RFC 2068, UC Irvine, DEC, MIT/LCS, January 1997. [9] Freed, N. and Borenstein N., 'Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types', RFC 2046, Innosoft, First Virtual, November 1996. [10] Mockapetris, P., 'Domain Names - Concepts and Facilities', STD 13, RFC 1034, ISI, November 1987. [11] St. Johns, M., 'Identification Protocol', RFC 1431, US Department of Defense, February 1993. [12] 'Coded Character Set -- 7-bit American Standard Code for Information Interchange', ANSI X3.4-1986. 14. Authors' Addresses Ken A L Coar MeepZor Consulting 7824 Mayfaire Crest Lane, Suite 202 Raleigh, NC 27615-4875 U.S.A. Tel: +1 (919) 254.4237 Fax: +1 (919) 254.5250 Email: Ken.Coar@Golux.Com David Robinson Electronic Share Information Ltd Mount Pleasant House 2 Mount Pleasant Huntingdon Road Cambridge CB3 0RN UK Tel: +44 (1223) 566926 Fax: +44 (1223) 506288 Email: drtr@esi.co.uk Coar, et al. INTERNET-DRAFT [Page 26]