Last modified 22/09/92 by CTB

HTRESP

Response types

The syntax of the responses to HTTP requests are as follows:

Error

RESPONSE="ERROR" HTTPV=VersionNumber CrLf STATUS=String REASON=String [IDENTIFIER=String] CrLf [body section]

Forward

RESPONSE="FORWARD" HTTPV=VersionNumber CrLf UDI=String CrLf [body section]

Redirection

RESPONSE="REDIRECTION" HTTPV=VersionNumber CrLf UDI=String CrLf [body section]

Query

RESPONSE="QUERY" HTTPV=VersionNumber CrLf SERVER=String CrLf [body section] Algorithm

Index

RESPONSE="INDEX" HTTPV=VersionNumber CrLf [body section]

Data

RESPONSE="DATA" HTTPV=VersionNumber CrLf [body section]

Confirmation

RESPONSE="CONFIRMATION" HTTPV=VersionNumber CrLf [body section]

Body Section

The body section has the following syntax: NOTATION=String TOEOF|BYTES=Number [EDITABLE] CrLf [PROFILE KEY=String [DURATION=String]] CrLf [FETCHED=TimeStamp CrLf] ENDHEADER CrLf [data] where the NOTATION string is a list of format transformations which must be applied to the 'data' in order to reach the final format in the list, e.g.: NOTATION="UUDECODE,UNCOMPRESS,PLAINTEXT" BYTES=1000 means that if the following1000 bytes of data are UUDECODEd and then UNCOMPRESSed, the resulting data will be in PLAINTEXT format. Therefore the 'data' section may not necessarily be in ASCII.

The PROFILE KEY is an indication by the server that it has cached the client's profile (sent as part of the request), and that the client need only sent this key, instead of the complete profile. The DURATION is optionally sent by the server to indicate how long the key will be valid for. This will be an estimated relative time.

Note that the presence of the TOEOF indicator means that the data section is of indeterminate length, i.e. the length could not be calculated, either because it is the result of some translation process which does not allow the server to calculate the length, or because the data is being produced by a data sourcing process which may run for an indeterminate amount of time.

The FETCHED field is the data and time that the server retrieved the document. When the browser attempts to PUT a document, this is returned to prevent the erasure of any changes made to the document in the time between the document being retrieved and being returned. The format of the TimeStamp is DD MM YY HH:MM:SS, and is the local time of the server.

Where the RESPONSE is an ERROR, the STATUS and REASON fields may have a number of values, depending upon the situation encountered by the server. These are described below:

The following STATUS values are allowed:

SERVER_ERR: Fatal error at the server end, no retry (of the same request) possible.
CLIENT_ERR: Fatal error caused by the client, no retry (of the same request) possible.
TEMP_ERR: Temporary error at server end, retry of same request possible after some delay.

The meanings of the various REASON values change depending on the value of STATUS. Where the STATUS is CLIENT_ERR, the meanings are:

AUTH_FAIL: The user ID and password supplied do not match any pair used by the server. [Should always use AUTH_REFUSED - CTB]
AUTH_REFUSED: The user does not have authorisation to carry out that operation on that document. This is only used where a password and user ID have been supplied.
PWD_REQ: The operation can only be carried out by an authorised user, and no such authorisation was supplied by the client.
PROFILEKEY_FAIL: The profile key supplied is not valid or no longer valid for this server.
DOC_UNAVAIL: The UDI supplied does not match any file available to the server (note that the file could exist, but not be available to the server).
VERSION_ERR: The HTTP version number supplied by the client is higher than that being used by the server, and the server cannot handle that request.
INVALID_COMMAND: The user supplied a command which the server does not recognise (where the client's protocol version is higher than the server's, a VERSION_ERR should be sent instead)
FMT_FAIL: The document cannot be supplied in any of the formats supplied by the user.

Where the STATUS is SERVER_ERR, the meanings are:

AUTH_FAIL: The server was unable to authorise the user, even though a password and user ID have been supplied.
AUTH_REFUSED: The server has insufficient privilege to carry out that operation, even though the client does (this should only happen if the server has been incorrectly set up).
VERSION_ERR: The HTTP version number supplied by the client is lower than that being used by the server, and the server cannot handle that request.
INVALID_COMMAND: The client has sent the server a command which it cannot handle, even though it is specified in the protocol version that the server is using.

FWD_FAIL The server cannot access the information necessary to return the forwarding information. Where the STATUS is TEMP_ERR, the meanings are:

AUTH_FAIL: The server was unable to carry out the authorisation operation at the present time due to a temporary failure (such as password file being updated by someone else).
PROFILE_FAIL: The server was unable to access the stored profile information at the moment.
DOC_UNAVAIL: The document requested is temporarily unavailable.
SERVER_BUSY: The server is unable to process the request at the present time.

Other combinations of STATUS/REASON are undefined at the moment.

The field IDENTIFER may be included to identify the scope over which the error ranges. For example, for an authorisation error, the server may return a mask for all those files which will generate such an error.Implementation Note: Note that in theory the body of an error message may be in ANY acceptable format. However, in order to make the implementation of the new browser as simple as possible, it will assume only HTML will be contained in these messages. But since most of these will be generated by the server anyway, this isn't such a restriction. Note also that the browser will not allow any links in an error document to be followed.

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