Adding errname as a linter.

Checks that sentinel errors are prefixed with the Err and error types are suffixed with the Error.

Also fixing one case in reverse proxy and exporting the error to allow error matching against it.

Signed-off-by: Yolan Romailler <[email protected]>

.golangci.yml

@@ -31,6 +31,7 @@ linters:
     - dupword
     - durationcheck
     - errcheck
+    - errname
     - exhaustive
     - exportloopref
     - gci

modules/caddyhttp/reverseproxy/reverseproxy.go

@@ -487,7 +487,7 @@ func (h *Handler) proxyLoopIteration(r *http.Request, origReq *http.Request, w h
 	upstream := h.LoadBalancing.SelectionPolicy.Select(upstreams, r, w)
 	if upstream == nil {
 		if proxyErr == nil {
-			proxyErr = caddyhttp.Error(http.StatusServiceUnavailable, noUpstreamsAvailable)
+			proxyErr = caddyhttp.Error(http.StatusServiceUnavailable, ErrNoUpstream)
 		}
 		if !h.LoadBalancing.tryAgain(h.ctx, start, retries, proxyErr, r) {
 			return true, proxyErr
@@ -1037,7 +1037,7 @@ func (lb LoadBalancing) tryAgain(ctx caddy.Context, start time.Time, retries int
 		// we have to assume the upstream received the request, and
 		// retries need to be carefully decided, because some requests
 		// are not idempotent
-		if !isDialError && !(isHandlerError && errors.Is(herr, noUpstreamsAvailable)) {
+		if !isDialError && !(isHandlerError && errors.Is(herr, ErrNoUpstream)) {
 			if lb.RetryMatch == nil && req.Method != "GET" {
 				// by default, don't retry requests if they aren't GET
 				return false
@@ -1446,7 +1446,8 @@ func (c ignoreClientGoneContext) Err() error {
 // from the proxy handler.
 const proxyHandleResponseContextCtxKey caddy.CtxKey = "reverse_proxy_handle_response_context"
 
-var noUpstreamsAvailable = fmt.Errorf("no upstreams available")
+// ErrNoUpstream occurs when there are no upstream available.
+var ErrNoUpstream = fmt.Errorf("no upstreams available")
 
 // Interface guards
 var (