# Regex matcher¶

## type.matcher.RegexMatcher¶

[type.matcher.RegexMatcher proto]

A regex matcher designed for safety when used with untrusted input.

{
"regex": "..."
}


regex

(string, REQUIRED) The regex match string. The string must be supported by the configured engine.

Google’s RE2 regex engine. The regex string must adhere to the documented syntax. The engine is designed to complete execution in linear time as well as limit the amount of memory used.

Envoy supports program size checking via runtime. The runtime keys re2.max_program_size.error_level and re2.max_program_size.warn_level can be set to integers as the maximum program size or complexity that a compiled regex can have before an exception is thrown or a warning is logged, respectively. re2.max_program_size.error_level defaults to 100, and re2.max_program_size.warn_level has no default if unset (will not check/log a warning).

Envoy emits two stats for tracking the program size of regexes: the histogram re2.program_size, which records the program size, and the counter re2.exceeded_warn_level, which is incremented each time the program size exceeds the warn level threshold.

{
"max_program_size": "{...}"
}

max_program_size

(UInt32Value) This field controls the RE2 “program size” which is a rough estimate of how complex a compiled regex is to evaluate. A regex that has a program size greater than the configured value will fail to compile. In this case, the configured max program size can be increased or the regex can be simplified. If not specified, the default is 100.

This field is deprecated; regexp validation should be performed on the management server instead of being done by each individual client.

## type.matcher.RegexMatchAndSubstitute¶

[type.matcher.RegexMatchAndSubstitute proto]

Describes how to match a string and then produce a new string using a regular expression and a substitution string.

{
"pattern": "{...}",
"substitution": "..."
}

pattern

(type.matcher.RegexMatcher) The regular expression used to find portions of a string (hereafter called the “subject string”) that should be replaced. When a new string is produced during the substitution operation, the new string is initially the same as the subject string, but then all matches in the subject string are replaced by the substitution string. If replacing all matches isn’t desired, regular expression anchors can be used to ensure a single match, so as to replace just one occurrence of a pattern. Capture groups can be used in the pattern to extract portions of the subject string, and then referenced in the substitution string.

substitution

(string) The string that should be substituted into matching portions of the subject string during a substitution operation to produce a new string. Capture groups in the pattern can be referenced in the substitution string. Note, however, that the syntax for referring to capture groups is defined by the chosen regular expression engine. Google’s RE2 regular expression engine uses a backslash followed by the capture group number to denote a numbered capture group. E.g., \1 refers to capture group 1, and \2 refers to capture group 2.