map: Remove infinite recursion check (#5094)

It was not accurate. Placeholders could be used in outputs that are
defined in the same mapping as long as that placeholder does not do the
same.

A more general solution would be to detect it at run-time in the
replacer directly, but that's a bit tedious
and will require allocations I think.

A better implementation of this check could still be done, but I don't
know if it would always be accurate. Could be a "best-effort" thing?
But I've also never heard of an actual case where someone configured
infinite recursion...

1 files changed, 1 insertions, 10 deletions

diff --git a/modules/caddyhttp/map/map.go b/modules/caddyhttp/map/map.go
index b972534b0..fbd1e4058 100644
--- a/modules/caddyhttp/map/map.go
+++ b/modules/caddyhttp/map/map.go
@@ -109,22 +109,13 @@ func (h *Handler) Validate() error {
 		}
 		seen[input] = i
 
-		// prevent infinite recursion
-		for _, out := range m.Outputs {
-			for _, dest := range h.Destinations {
-				if strings.Contains(caddy.ToString(out), dest) ||
-					strings.Contains(m.Input, dest) {
-					return fmt.Errorf("mapping %d requires value of {%s} to define value of {%s}: infinite recursion", i, dest, dest)
-				}
-			}
-		}
-
 		// ensure mappings have 1:1 output-to-destination correspondence
 		nOut := len(m.Outputs)
 		if nOut != nDest {
 			return fmt.Errorf("mapping %d has %d outputs but there are %d destinations defined", i, nOut, nDest)
 		}
 	}
+
 	return nil
 }