caddyhttp: Add support for triggering errors from `try_files` (#4346)

* caddyhttp: Add support for triggering errors from `try_files`

* caddyhttp: Use vars instead of placeholders/replacer for matcher errors

* caddyhttp: Add comment for matcher error var key

1 files changed, 6 insertions, 0 deletions

diff --git a/modules/caddyhttp/matchers.go b/modules/caddyhttp/matchers.go
index b452d48..a22a3f1 100644
--- a/modules/caddyhttp/matchers.go
+++ b/modules/caddyhttp/matchers.go
@@ -987,6 +987,12 @@ var wordRE = regexp.MustCompile(`\w+`)
 
 const regexpPlaceholderPrefix = "http.regexp"
 
+// MatcherErrorVarKey is the key used for the variable that
+// holds an optional error emitted from a request matcher,
+// to short-circuit the handler chain, since matchers cannot
+// return errors via the RequestMatcher interface.
+const MatcherErrorVarKey = "matchers.error"
+
 // Interface guards
 var (
 	_ RequestMatcher    = (*MatchHost)(nil)