ESP32 HTTP Server request interrupts Telnet session #4399
Description
I have an ESP32 application that uses a web server as a user interface. For auditing and debugging during development I use Serial; however, that is impractical in the installed system. So, I decided to use Telnet (TCP/IP) to monitor what is happening when Serial is impractical.
The issue is that once a TCP/IP session has been established, when a HTTP request is received, the TCP/IP session is aborted.
I have reproduced the issue in a minimal sketch here:
#include "Arduino.h"
#include <WiFi.h>
#include <WiFiClient.h>
#include <WebServer.h>
WiFiClient telnetClient;
WebServer server(80);
WiFiServer telnetServer(23);
void telnetPrint(const char* text)
{
if (telnetClient)
{
telnetClient.print(text);
}
}
void telnetPrintln(const char *text)
{
telnetPrint(text);
telnetPrint("\r\n");
}
void _print(const char* text)
{
Serial.print(text);
telnetPrint(text);
}
void _println(const char* text)
{
Serial.println(text);
telnetPrintln(text);
}
void _println(IPAddress myIP)
{
char rgIPTxt[32];
sprintf(rgIPTxt,"%u.%u.%u.%u",myIP[0],myIP[1],myIP[2],myIP[3]);
_println(rgIPTxt);
}
const char *rootFmt="\
<html>\
<head>\
<title>Test</title>\
</head>\
<body>\
<h1>Test</h1>\
<div>\
<h2>Heap size=%d<br><br>\
</div>\
</body>\
</html>\
";
char rootMessage[1024];
void updateRootMessage()
{
_println("updateRoot");
snprintf(rootMessage, sizeof(rootMessage), rootFmt,
heap_caps_get_free_size(MALLOC_CAP_8BIT)
);
}
void handleRoot()
{
_println("Entered handleRoot");
updateRootMessage();
server.send(200, "text/html", rootMessage);
_println("Leaving handleRoot");
}
void wifiSTASetup(const char*ssid, const char*password)
{
WiFi.mode(WIFI_AP_STA);
WiFi.begin(ssid, password);
telnetServer.begin();
telnetClient=telnetServer.available();
_println("");
// Wait for connection
while (WiFi.status() != WL_CONNECTED)
{
delay(500);
_print(".");
}
_println("");
_print("Connected to ");
_println(ssid);
_print("IP address: ");
_println(WiFi.localIP());
server.on("/", handleRoot);
server.begin();
}
#define BAND 915E6
void setup()
{
Serial.begin(115200);
wifiSTASetup("yourssid", "yourpass");
}
void loop()
{
server.handleClient();
if (!telnetClient)
{
telnetClient=telnetServer.available();
if (telnetClient)
{
_println("telnetClient obtained");
}
}
}
This is the observed behavior:
When this sketch is running, before establishing a Telnet session, HTTP requests are processed as expected and Serial output is as expected. When a Telnet session is established, "telnetClient obtained" appears on the terminal (and via Serial) but when an HTTP request is processed, the Telnet terminal receives "Entered handleRoot" and MAY receive "updateRoot" and "Leaving handleRoot" but then the telnet session is aborted.
My actual application logs quite a bit of information, reacting to messages received via LoRa and on I/O pins. Everything there works as expected until an HTTP request is served which results in the connection abort.