ref: 02ac617541ca1a7bf82b1615fb5a58235469b5d3
dir: /man/2/filter/
.TH FILTER 2 .SH NAME filter \- data processing interface .SH SYNOPSIS .B include "filter.m"; .br .BI "filter := load Filter " filterpath ";" .EX Rq: adt { pick { Start => pid: int; Fill or Result => buf: array of byte; reply: chan of int; Finished => buf: array of byte; Info => msg: string; Error => e: string; } }; init: fn(); start: fn(param: string): chan of ref Rq; .EE .SH DESCRIPTION .B Filter defines a general module interface for byte-stream processing. This manual page documents how to use the interface, and by implication how a .B Filter module should behave. There is a different implementation module for each filter type and algorithm (eg, for compression or line encoding). All implementations are instances of type .BR Filter , loaded from the Dis file .IR filterpath , given in the manual page for each standard filter (or you can write your own to match this specification). For details of each existing filter module, see .IR filter-deflate (2) and following manual pages. .PP .B Init must be called before any other operation of a filter module. .PP .B Start sets the filter going; .I param can be used to pass any filter-specific information to the processor. .B Start spawns a new thread to do the processing; it returns a channel that is used to receive requests from the filter. The first message sent is always .BR Rq.Start ; .I pid is the process id of the new process spawned. .PP Subsequent messages are: .TF Rq.Finished .PD .TP .B Rq.Fill A request by the filter to fill .I buf with data. The number of bytes that have actually been placed in the buffer should be sent on .IR reply . If \-1 is sent, the filter will terminate. If the value is 0, the filter will terminate once it has processed all its input. .TP .B Rq.Result .I Buf contains data from the filter. Receipt of the the data must be acknowledged by sending a value on .IR reply . If the value is \-1, the filter will terminate. .TP .B Rq.Finished The filter has finished processing. .I Buf contains any data that was not consumed by the filter. The filter terminates after sending this message. .TP .B Rq.Info This message is used to send a string of arbitrary information from the filter during the course of its processing. .TP .B Rq.Error The filter has encountered an error when processing. .I E is a string describing the error. The filter terminates after sending this message. .SH SOURCE .B /module/filter.m .SH SEE ALSO .IR gzip (1), .IR filter-deflate (2), .IR filter-slip (2)