templates: Propagate httpError to HTTP response

Now possible with Go 1.17.
See https://github.com/golang/go/issues/34201.

2 files changed, 9 insertions, 3 deletions

diff --git a/modules/caddyhttp/templates/templates.go b/modules/caddyhttp/templates/templates.go
index 33e5a70..6fed8c8 100644
--- a/modules/caddyhttp/templates/templates.go
+++ b/modules/caddyhttp/templates/templates.go
@@ -16,6 +16,7 @@ package templates
 
 import (
 	"bytes"
+	"errors"
 	"fmt"
 	"net/http"
 	"strconv"
@@ -312,6 +313,12 @@ func (t *Templates) executeTemplate(rr caddyhttp.ResponseRecorder, r *http.Reque
 
 	err := ctx.executeTemplateInBuffer(r.URL.Path, rr.Buffer())
 	if err != nil {
+		// templates may return a custom HTTP error to be propagated to the client,
+		// otherwise for any other error we assume the template is broken
+		var handlerErr caddyhttp.HandlerError
+		if errors.As(err, &handlerErr) {
+			return handlerErr
+		}
 		return caddyhttp.Error(http.StatusInternalServerError, err)
 	}
 
diff --git a/modules/caddyhttp/templates/tplcontext.go b/modules/caddyhttp/templates/tplcontext.go
index 1a145a2..14ac31b 100644
--- a/modules/caddyhttp/templates/tplcontext.go
+++ b/modules/caddyhttp/templates/tplcontext.go
@@ -350,9 +350,8 @@ func (c TemplateContext) funcFileExists(filename string) (bool, error) {
 	return false, nil
 }
 
-// funcHTTPError returns a structured HTTP handler error. EXPERIMENTAL.
-// TODO: Requires https://github.com/golang/go/issues/34201 to be fixed (Go 1.17).
-// Example usage might be: `{{if not (fileExists $includeFile)}}{{httpError 404}}{{end}}`
+// funcHTTPError returns a structured HTTP handler error. EXPERIMENTAL; SUBJECT TO CHANGE.
+// Example usage: `{{if not (fileExists $includeFile)}}{{httpError 404}}{{end}}`
 func (c TemplateContext) funcHTTPError(statusCode int) (bool, error) {
 	return false, caddyhttp.Error(statusCode, nil)
 }