[WiFiServer/WiFiClient] client.available() exhibits blocking behavior

[redelacruz]

Boards

AMB82-Mini

External Hardware

Other than included JXF37 camera, none.

Hardware Configuration

None

Version

latest main (checkout manually)

IDE Name

VSCode w/ Arduino extension

Operating System

Windows 11

Auto Flash Mode

Disable

Erase All Flash Memory (16MB)

Disable

Standard Lib

Arduino_STD_PRINTF

Upload Speed

2000000

Description

This issue was created in order to create a reference issue for a PR.

---

When client.stop() is called and then a new client is created soon after, client.connected() == true due to still pending socket close.

In the very commonly used context

while (client.connected()) {
    if (client.available()) {
        // other stuff happens
    }
}

this causes client.available() to block, which it should not do. When writing asynchronous programs, this can cause major issues in timing-sensitive tasks.

Sketch

Requires fix for issue #257 to be applied because of WiFiClient copy assignment.

#include <WiFi.h>

char ssid[] = "";    // your network SSID (name)
char pass[] = "";        // your network password
int status = WL_IDLE_STATUS;
WiFiServer server(80);
WiFiClient client;

void setup()
{
    Serial.begin(115200);
    while (status != WL_CONNECTED) {
        status = WiFi.begin(ssid, pass);
        delay(5000);
    }
  
    server.setNonBlockingMode(); // server is set to NonBlockingMode();
    server.begin();
}

void loop()
{
    client = server.available();
    if (client) {
        Serial.println("new client connected");
        String currentLine = "";
        while (client.connected()) {
            if (client.available()) {
                char c = client.read();
                Serial.write(c);
                if (c == '\n') {
                    if (currentLine.length() == 0) {
                        //do something
                    } else {
                        currentLine = "";
                    }
                } else if (c != '\r') {
                    currentLine += c;
                }
            }
        }
        client.stop();
        Serial.println("client disconnected");
    } else {
        Serial.println("waiting for client connection");
        delay(1000);
    }
}

Error/Debug Message

// ... repeats while no client in non-blocking mode

[ERROR] get_available Accept connection failed
new client connected
client disconnected

[ERROR] get_available Accept connection failed
new client connected
client disconnected

[ERROR] get_available Accept connection failed
new client connected
client disconnected

[INFO] A client connected to this server :
[PORT]: 55775
[IP]:192.168.2.36

new client connected
GET / HTTP/1.1
Host: 192.168.2.172
Connection: keep-alive
Cache-Control: max-age=0
Upgrade-Insecure-Requests: 1
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/126.0.0.0 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.7
Accept-Encoding: gzip, deflate
Accept-Language: en-US,en;q=0.9,fil;q=0.8
Cookie: __guid=259319114.1308697201864418800.1719734660203.9114

client disconnected

[INFO] A client connected to this server :
[PORT]: 55776
[IP]:192.168.2.36

new client connected

// blocked here by client.available()

Reproduce remarks

Since the client does nothing in the sketch above, the socket can sometimes be closed quickly. But I was able to reproduce this issue reliably on first try or with one or two browser refreshes.

I have checked online documentation, FAQ, GitHub Wiki and existing/closed issues.

• I confirm I have checked online documentation, FAQ, GitHub Wiki and existing/closed issues.

[github-actions]

This issue is stale because it has been open for 14 days with no activity.