Report the backend host as the source fact value

source.go

@@ -13,6 +13,8 @@ import (
 // callers need no branch.
 type sourceInjector struct {
 	name string
+	// hosts maps backend name to the value emitted; an unmapped name is emitted as-is.
+	hosts map[string]string
 	// inject is false when the query shape rules synthesis out. Suppression of an
 	// upstream fact of the same name does not depend on it.
 	inject     bool
@@ -25,7 +27,7 @@ func (s *Server) newSourceInjector(query string, factEntity bool) *sourceInjecto
 	if !s.cfg.SourceFactEnabled || s.cfg.SourceFact == "" {
 		return nil
 	}
-	return &sourceInjector{name: s.cfg.SourceFact, inject: injectable(query, factEntity)}
+	return &sourceInjector{name: s.cfg.SourceFact, hosts: s.hosts, inject: injectable(query, factEntity)}
 }
 
 // claims reports whether an upstream record carries the name pdbmux owns, and is
@@ -36,6 +38,13 @@ func (si *sourceInjector) claims(factName string) bool {
 	return si != nil && factName != "" && factName == si.name
 }
 
+func (si *sourceInjector) value(backend string) string {
+	if h, ok := si.hosts[backend]; ok {
+		return h
+	}
+	return backend
+}
+
 // injects reports whether this response may carry the synthetic record.
 func (si *sourceInjector) injects() bool {
 	return si != nil && si.inject
@@ -70,7 +79,7 @@ func (si *sourceInjector) factRecord(certname, backend, environment string) json
 		Environment string `json:"environment"`
 		Name        string `json:"name"`
 		Value       string `json:"value"`
-	}{Certname: certname, Environment: environment, Name: si.name, Value: backend})
+	}{Certname: certname, Environment: environment, Name: si.name, Value: si.value(backend)})
 	if err != nil {
 		return nil
 	}
@@ -87,7 +96,7 @@ func (si *sourceInjector) stamp(raw json.RawMessage, backend string) json.RawMes
 	if json.Unmarshal(raw, &obj) != nil || obj == nil {
 		return raw
 	}
-	value, err := json.Marshal(backend)
+	value, err := json.Marshal(si.value(backend))
 	if err != nil {
 		return raw
 	}