caddyhttp: document CEL raw strings for regexp patterns (#8280)

Co-authored-by: hikmetba-bit <hikmetba-bit@users.noreply.github.com>

Francis Lavoie committed Oct 29, 2026 at 09:08 UTC 4fce7c8bbcf260f1dfdc10f9f7d4d1ca76885a24

1 file changed +16

modules/caddyhttp/matchers.go

+16

@@ -843,6 +843,13 @@ func (m MatchPathRE) MatchWithError(r *http.Request) (bool, error) {

843 // Example:

844 //

845 // expression path_regexp('^/bar')

846 +//

847 +// The pattern is a CEL string literal, so CEL's own escape sequences

848 +// (e.g. \b, \n, \t) are interpreted before the result reaches the regexp

849 +// engine. A pattern that needs a literal backslash escape meant for the

850 +// regexp engine, such as \b for a word boundary, should be written as a

851 +// CEL raw string (prefixed with r) so CEL passes the backslash through

852 +// unchanged: expression path_regexp(r'^/bar\b').

853 func (MatchPathRE) CELLibrary(ctx caddy.Context) (cel.Library, error) {

854 unnamedPattern, err := CELMatcherImpl(

855 "path_regexp",

@@ -1309,6 +1316,15 @@ func (m MatchHeaderRE) Validate() error {

1316 // Example:

1317 //

1318 // expression header_regexp('foo', 'Field', 'fo+')

1319 +//

1320 +// The pattern is a CEL string literal, so CEL's own escape sequences

1321 +// (e.g. \b, \n, \t) are interpreted before the result reaches the regexp

1322 +// engine. A pattern that needs a literal backslash escape meant for the

1323 +// regexp engine, such as \b for a word boundary, should be written as a

1324 +// CEL raw string (prefixed with r) so CEL passes the backslash through

1325 +// unchanged: expression header_regexp('foo', 'User-Agent', r'bot\b').

1326 +// Without the r prefix, \b is interpreted by CEL as a backspace

1327 +// character before the regexp engine ever sees the pattern.

1328 func (MatchHeaderRE) CELLibrary(ctx caddy.Context) (cel.Library, error) {

1329 unnamedPattern, err := CELMatcherImpl(

1330 "header_regexp",