fix automatic json response handling

runner/runner.go

@@ -11,6 +11,7 @@ import (
 	"path/filepath"
 	"runtime"
 	"strconv"
+	"strings"
 	"sync"
 	"sync/atomic"
 	"time"
@@ -589,6 +590,15 @@ func ApplyResponse(resp *Response, ctx *fasthttp.RequestCtx) {
 		return
 	}
 
+	// Check if Content-Type was manually set
+	contentTypeSet := false
+	for name := range resp.Headers {
+		if strings.ToLower(name) == "content-type" {
+			contentTypeSet = true
+			break
+		}
+	}
+
 	// Get a buffer from the pool
 	buf := bytebufferpool.Get()
 	defer bytebufferpool.Put(buf)
@@ -596,23 +606,50 @@ func ApplyResponse(resp *Response, ctx *fasthttp.RequestCtx) {
 	// Set body based on type
 	switch body := resp.Body.(type) {
 	case string:
+		if !contentTypeSet {
+			ctx.Response.Header.SetContentType("text/plain; charset=utf-8")
+		}
 		ctx.SetBodyString(body)
 	case []byte:
+		if !contentTypeSet {
+			ctx.Response.Header.SetContentType("text/plain; charset=utf-8")
+		}
 		ctx.SetBody(body)
-	case map[string]any, []any, []float64, []string, []int:
+	case map[string]any, map[any]any, []any, []float64, []string, []int, []map[string]any:
 		// Marshal JSON
 		if err := json.NewEncoder(buf).Encode(body); err == nil {
-			// Set content type if not already set
+			if !contentTypeSet {
-			if len(ctx.Response.Header.ContentType()) == 0 {
 				ctx.Response.Header.SetContentType("application/json")
 			}
 			ctx.SetBody(buf.Bytes())
 		} else {
-			// Fallback
+			// Fallback to string representation
+			if !contentTypeSet {
+				ctx.Response.Header.SetContentType("text/plain; charset=utf-8")
+			}
 			ctx.SetBodyString(fmt.Sprintf("%v", body))
 		}
 	default:
-		// Default to string representation
+		// Check if it's any other map or slice type
-		ctx.SetBodyString(fmt.Sprintf("%v", body))
+		typeStr := fmt.Sprintf("%T", body)
+		if typeStr[0] == '[' || (len(typeStr) > 3 && typeStr[:3] == "map") {
+			if err := json.NewEncoder(buf).Encode(body); err == nil {
+				if !contentTypeSet {
+					ctx.Response.Header.SetContentType("application/json")
+				}
+				ctx.SetBody(buf.Bytes())
+			} else {
+				if !contentTypeSet {
+					ctx.Response.Header.SetContentType("text/plain; charset=utf-8")
+				}
+				ctx.SetBodyString(fmt.Sprintf("%v", body))
+			}
+		} else {
+			// Default to string representation
+			if !contentTypeSet {
+				ctx.Response.Header.SetContentType("text/plain; charset=utf-8")
+			}
+			ctx.SetBodyString(fmt.Sprintf("%v", body))
+		}
 	}
 }