May 12, 1993
typerules - HylaFAX file type identification and conversion rules
Only three types of files are accepted by the HylaFAX server for transmission as facsimile: POSTSCRIPT® files, PDF files, and TIFF Class F (bilevel Group 3-encoded) files. All other types of files must be converted to one of these three formats. The facsimile submission program applies a set of rules against the contents of each input file to identify the file’s type and to figure out how to convert the file to a format that is suitable for transmission. These rules are stored in the file /etc/hylafax/typerules, an ASCII file that is patterned after the /etc/magic file used by the System V file(1) program. However, there are significant differences, noted below.
Type rules work by matching data patterns in a file; typically patterns that appear in the first few bytes of the file (i.e. magic numbers). There are two types of rules, primary rules and secondary rules. Secondary rules specify additional rules to apply after a primary rule has been matched. When secondary rules are used, rule scanning continues up to the next primary type rule in the file.
Each rule consists of a set of whitespace-separated fields:
If an line is terminated wth a backslash character, the entry is continued on the next line with any leading whitespace characters compressed to a single space. Comments are marked with the ‘‘#’’ character; everything from to the end of the line is discarded. Secondary rules have a ‘‘>’’ character in the first column of the line; primary rules do not.
offset datatype match result command
The fields in each rule entry are:
|offset||The byte offset in the file at which data should be extracted and compared to a matching string or value.|
|datatype||The type of data value to extract at the specified offset for comparison purposes; one of: ‘‘byte’’ (8 bit unsigned number), ‘‘short’’ (16 bit unsigned number), ‘‘long’’ (32 bit unsigned number), ‘‘filename’’ (the name of the file), ‘‘string’’ (an array of bytes), ‘‘istring’’ (a case-insensitive array of bytes), or ‘‘ascii’’ (an array of ASCII-only bytes).|
|match||The value and operation to use in matching; the value used is based on the datatype field. If value is ‘‘x’’, then it is interpreted to mean match anything; otherwise the following operators are supported (where data is the value extracted from the file and value is specified in the match field) except for types ‘‘filename’’, ‘‘string’’, ‘‘istring’’, and ‘‘ascii’’:
For ‘‘string’’, ‘‘istring’’, and ‘‘ascii’’ no operator is allowed; the implicit operation is always ‘‘=’’. In these cases, the field is terminated by a tab or end of line, not by ‘‘#’’ or ‘‘ ’’. Characters in the field have their literal value; there are no C-style character escapes. For ‘‘filename’’ no operator is allowed; the operation expects that the value is a regular expression to positively match the supplied data.
|result||One of ‘‘ps’’, ‘‘tiff’’, or ‘‘error’’ (case insensitive). The first two results specify whether the rule generates a POSTSCRIPT file or a TIFF/F file (Group 3-encoded bilevel data), respectively. The ‘‘error’’ result indicates that a file is unsuitable for transmission and, if supplied for transmission, should cause the job to be aborted with the command field used in an error message.|
|command||A command description that is expanded and passed to the shell to convert the input file to the result format (suitable for sending as facsimile). Before the string is passed to the shell, it is scanned and the following ‘‘%’’ escape codes are substituted for:
See below for example uses of these codes.
The following rules are used to match the formats that are handled directly by the server:
#offset datatype match result command 0 string %! ps # POSTSCRIPT 0 string %PDF ps # POSTSCRIPT by Ghostscript 0 short 0x4d4d tiff # big-endian TIFF 0 short 0x4949 tiff # little-endian TIFF
These rules are used to process the ASCII version of IRIS Inventor database files while blocking the transmission of the binary format variant:
#offset datatype match result command 0 string #Inventor V error IRIS Inventor file >15 string binary error binary IRIS Inventor file >15 string ascii ps %F/textfmt -fCourier-Bold -p11bp\ -U -q >%o <%i
This rule is typically the last entry in the file and is used to convert all unmatched ASCII data files to POSTSCRIPT:
#offset datatype match result command 0 ascii x ps %F/textfmt -fCourier-Bold -p11bp -U -q >%o <%i
It is much better to convert data that is to be transmitted to POSTSCRIPT because this data format permits the facsimile server to do the final imaging according to the optimal transfer parameters (resolution, binary encoding, etc.).
It might be better to allow secondary rules to augment a primary rule rather than just replace them. This would allow, for example, command line options to be selected based on file type.