fix: Use request URL path instead of route pattern in BaseURL middleware

The BaseURL function was using c.Path() which returns the route pattern
(e.g., '/app/*') instead of the actual request path. This caused the
X-Forwarded-Prefix header to not be properly detected when calculating
the base URL for reverse proxy scenarios.

Fixed by using c.Request().URL.Path which contains the actual stripped
path after StripPathPrefix middleware processes the request.

Fixes #9145

Author: Team Coding Agent 1

core/http/middleware/baseurl.go

@@ -11,8 +11,12 @@ import (
 // The returned URL is guaranteed to end with `/`.
 // The method should be used in conjunction with the StripPathPrefix middleware.
 func BaseURL(c echo.Context) string {
-	path := c.Path()
-	origPath := c.Request().URL.Path
+	// Use the current request path (after StripPathPrefix has stripped the prefix)
+	// NOT c.Path() which returns the route pattern (e.g., '/app/*')
+	currentPath := c.Request().URL.Path
+	
+	// Get the original path before stripping
+	origPath := currentPath
 
 	// Check if StripPathPrefix middleware stored the original path
 	if storedPath, ok := c.Get("_original_path").(string); ok && storedPath != "" {
@@ -33,15 +37,14 @@ func BaseURL(c echo.Context) string {
 		host = forwardedHost
 	}
 
-	if path != origPath && strings.HasSuffix(origPath, path) && len(path) > 0 {
-		prefixLen := len(origPath) - len(path)
-		if prefixLen > 0 && prefixLen <= len(origPath) {
-			pathPrefix := origPath[:prefixLen]
-			if !strings.HasSuffix(pathPrefix, "/") {
-				pathPrefix += "/"
-			}
-			return scheme + "://" + host + pathPrefix
+	// Calculate the prefix by comparing original path with current (stripped) path
+	// The prefix is what was stripped from the beginning of origPath to get currentPath
+	if origPath != currentPath && strings.HasSuffix(origPath, currentPath) && len(origPath) > len(currentPath) {
+		pathPrefix := origPath[:len(origPath)-len(currentPath)]
+		if !strings.HasSuffix(pathPrefix, "/") {
+			pathPrefix += "/"
 		}
+		return scheme + "://" + host + pathPrefix
 	}
 
 	return scheme + "://" + host + "/"