Filter Files

Filter configuration (ctrl/*.cfg) and trash can (text/*.can) files allow the sysop to specify words (or any sequence of characters) that will be used to disallow clients, users, or their content.

Each line in a filter file may contain a comparison pattern. Blank lines and lines beginning with a semicolon character (;) are ignored. Lines may contain up to 1000 characters.

A tab (ASCII 9) character or a new-line (CR or CRLF) sequence will terminate (signify the end of) each comparison pattern. All characters between the first tab character and the new-line sequence may be considered metadata for the comparison pattern.

To support the correct auto-addition of filters, it's important that all comparison patterns end in a new-line sequence (i.e. a non-empty file must end with an LF character).

• Leading white-space characters are ignored
• Alphabetic character are compared case-insensitively
• C-style string-literal backslash (\) escape sequences are supported in patterns (as of v3.17c)
• Patterns beginning with an exclamation mark (!) negate the match logic for that pattern
• Patterns ending with a caret (^) match only if the preceding (left most) characters are found at the beginning of the comparison string ¹⁾
• Patterns ending with a tilde (~) match when the preceding string of characters are found anywhere within the comparison string
• Patterns including an asterisk (*) will match when both the left and right string fragments (on either/both sides of the *) match the comparison string (as of v3.19a) ²⁾
• All other patterns are “exact match” string comparisons

Note:
There's no effective difference between the patterns “word^” and “word*”.

• sysop in the name.can file would mean new users could not use the name “sysop”.
• sysop* would mean new users could not use names beginning with the word “sysop”, like “sysop the” or “sysops”.
• sysop~ would mean new users could not use names that have the word “sysop” anywhere in them, like “imthesysop” or “Joe Sysop”.

viagra~

[adv]*

\ *

administrator  

!the *

An additional comparison format was introduced in v3.17 (Feb-9-2017) specifically for partial (ranges of) IPv4 address matching following standard Classless_Inter-Domain_Routing (CIDR) notation. For example, rather than using the comparison string “192.168.1.*” to match all IP addresses that begin with the first 3 octets of 192, 168, and 1, you could specify the same thing using CIDR notation:

192.168.1.0/24

This enables the flexibility of filtering ranges of IP addresses based on sub-networks that are not multiples of 8-bits (e.g. “192.168.1.33/30”) and the format is compatible with commonly available regional block lists.

All 4 octets of the IPv4 address must be specified in the CIDR comparison string (i.e. “192.168.1/24” is not a valid CIDR comparison string).

CIDR comparisons beginning with the negation prefix (!) are supported (reverses the IP address comparison logic).

IPv6 CIDR notation is not supported at this time.

The following table lists the supported trash can files, a description of their use, and optional rejection message (.msg) files that may be displayed to users that are (or have their content) filtered. Trash can files and their respective optional rejection message files are located in the text directory:

New in Synchronet v3.20:
Comparison patterns in .can files may contain metadata as tab-delimited key=value pairs. The keys supported are:

The following table lists other supported filter files and a description of their use. These filter files are located in the ctrl directory and do not have a respective response message file:

The following table lists supported filter exemption files and a description of their use. These filter exemption files are located in the ctrl directory:

• Configuration