Panic: repeated read on failed websocket connection

by

The error message “panic: repeated read on failed websocket connection” usually indicates a panic or fatal error occurring while attempting to read data from a WebSocket connection that has already failed or been closed.

WebSockets are a communication protocol that allows for full-duplex communication between a client (typically a browser) and a server over a single, long-lived connection. This enables real-time, bidirectional data transfer.

There can be several reasons for the occurrence of the “panic: repeated read on failed websocket connection” error. Let’s explore some possible explanations:

  1. Connection closure: If the WebSocket connection is closed unexpectedly by either the client or the server, any subsequent attempts to read data from that connection will result in an error. This could be due to various factors, such as network issues, manual closure of connections, or server-side restrictions.
  2. Concurrency issues: If there are multiple goroutines or threads concurrently accessing and reading from the same WebSocket connection, it can lead to race conditions or conflicting read operations, resulting in the panic. Proper synchronization mechanisms, like channels or locks, should be used to ensure safe access to the connection.
  3. Incorrect usage: Improper implementation of WebSocket reading logic can also trigger this error. For instance, attempting to read from a connection that has already been closed, or trying to read without properly establishing a connection first.

Here’s an example illustrating a scenario where the “panic: repeated read on failed websocket connection” error might occur in Go: 

    
package main

import (
	"log"
	"net/http"
	"time"

	"github.com/gorilla/websocket"
)

func main() {
	upgrader := websocket.Upgrader{}
	http.HandleFunc("/ws", func(w http.ResponseWriter, r *http.Request) {
		// Upgrade HTTP connection to a WebSocket connection
		conn, err := upgrader.Upgrade(w, r, nil)
		if err != nil {
			log.Println("Failed to upgrade connection:", err)
			return
		}
		defer conn.Close()

		// Simulate a closed connection
		if err := conn.Close(); err != nil {
			log.Println("Failed to close connection:", err)
		}

		// Attempt to read from the closed connection
		_, _, err = conn.ReadMessage()
		if err != nil {
			log.Fatal("panic: repeated read on failed websocket connection")
		}
	})

	log.Fatal(http.ListenAndServe(":8080", nil))
}

In this example, we create a simple HTTP server using Go’s `net/http` package. When a client connects to the “/ws” endpoint, we upgrade the connection to a WebSocket connection. However, immediately after upgrading, we manually close the connection using `conn.Close()`. Finally, we attempt to read from the closed connection using `conn.ReadMessage()`, which results in the “panic: repeated read on failed websocket connection” error.

To prevent this error, it’s crucial to handle WebSocket connections properly, ensuring that they are established successfully, not closed unexpectedly, and accessed safely in concurrent scenarios.

Leave a comment