add header checker

server.go

@@ -4,7 +4,6 @@ import (
 	"bytes"
 	"context"
 	"errors"
-	"fmt"
 	"io"
 	"log/slog"
 	"net"
@@ -618,18 +617,54 @@ func (server *Server) tryUpstream(ctx context.Context, upstreamIdx, priority int
 	if err != nil {
 		return nil, nil, err
 	}
+	streaming := false
+	defer func() {
+		if !streaming {
+			response.Body.Close()
+		}
+	}()
+
 	if response.StatusCode == http.StatusNotModified {
 		return response, nil, nil
 	}
-	if response.StatusCode >= 400 && response.StatusCode < 500 {
-		return nil, nil, nil
+
+	responseCheckers := upstream.Checkers
+	if len(responseCheckers) == 0 {
+		responseCheckers = append(responseCheckers, Checker{})
 	}
-	if response.StatusCode < 200 || response.StatusCode >= 500 {
-		logger.With(
-			"url", newurl,
-			"status", response.StatusCode,
-		).Warn("unexpected status")
-		return response, nil, fmt.Errorf("unexpected status(url=%v): %v: %v", newurl, response.StatusCode, response)
+
+	for _, checker := range responseCheckers {
+		if len(checker.StatusCodes) == 0 {
+			checker.StatusCodes = append(checker.StatusCodes, http.StatusOK)
+		}
+
+		if !slices.Contains(checker.StatusCodes, response.StatusCode) {
+			return nil, nil, err
+		}
+
+		for _, headerChecker := range checker.Headers {
+			if headerChecker.Match == nil {
+				// check header exists
+				if _, ok := response.Header[headerChecker.Name]; !ok {
+					logger.Debug("missing header", "header", headerChecker.Name)
+					return nil, nil, nil
+				}
+			} else {
+				// check header match
+				value := response.Header.Get(headerChecker.Name)
+				if matched, err := regexp.MatchString(*headerChecker.Match, value); err != nil {
+					return nil, nil, err
+				} else if !matched {
+					logger.Debug("invalid header value",
+						"header", headerChecker.Name,
+						"value", value,
+						"matcher", *headerChecker.Match,
+					)
+
+					return nil, nil, nil
+				}
+			}
+		}
 	}
 
 	var currentOffset int64
@@ -646,6 +681,7 @@ func (server *Server) tryUpstream(ctx context.Context, upstreamIdx, priority int
 	}
 	ch <- Chunk{buffer: buffer[:n]}
 
+	streaming = true
 	go func() {
 		defer close(ch)