ESP32 Arduino HTTP server: external and internal redirects

The objective of this ESP32 exemple code is to explain how to perform redirects using the async HTTP web server libraries on the Arduino core. The tests of this ESP32 tutorial were performed using a DFRobot’s ESP32 device integrated in a ESP32 development board.

Introduction

The objective of this ESP32 exemple code is to explain how to perform redirects using the async HTTP web server libraries on the Arduino core. If you haven’t yet installed them, please check here how to do it.

We will check both how to redirect to an internal and to an external URL.

The tests of this ESP32 tutorial were performed using a DFRobot’s ESP-WROOM-32 device integrated in a ESP32 FireBeetle board.

For more tutorials on the HTTP async server, please consult the related posts section.

The code

The first part of the code is similar to what we have been covering in the previous tutorial posts about the async HTTP web server. So, as usual, we started by including the libraries needed to setup everything.

Next, we declare two global variables that will hold the credentials needed to connect to the WiFi network. To finalize the global variables declaration, we will also need an instance of class AsyncWebServer, which we will use to setup the HTTP server.

#include <WiFi.h>
#include <FS.h>
#include <AsyncTCP.h>
#include <ESPAsyncWebServer.h>
 
const char* ssid = "yourNetworkName";
const char* password = "yourNetworkPassword";
 
AsyncWebServer server(80);

In the setup function, we will start by opening a serial connection and then connect the ESP32 to the WiFi network. After the connection, we will print the local IP assigned to it.

Serial.begin(115200);
 
WiFi.begin(ssid, password);
 
while (WiFi.status() != WL_CONNECTED) {
    delay(1000);
    Serial.println("Connecting to WiFi..");
}
 
Serial.println(WiFi.localIP());

Now we will configure the routes of our server. First, we will need a simple route to be the destination of the internal redirect. The handling function of this route will return a textual message to the client. We will call this route “/hello“.

server.on("/hello", HTTP_GET, [](AsyncWebServerRequest *request){
    request->send(200, "text/plain", "Hello from ESP32 server route");
});

Now that we have a working route, we will configure a second one to perform the internal redirect.

The declaration of the route and the binding to a handling function is performed the same way as in the previous one. Nonetheless, in the implementation of the handling function, we will call a different method of the request object to perform the redirect.

Thus, to perform the redirect, we call the redirect method of the request object, passing as input a string with the route to which we want to redirect the client.

Note that since the redirect will be internal, we simply need to specify the path (“/hello“), we don’t need to specify the whole URL (the http://{serverIp} should not be used).

We will call this route “/redirect/internal“.

server.on("/redirect/internal", HTTP_GET, [](AsyncWebServerRequest *request){
    request->redirect("/hello");
});

The third and last route we will specify will do an external redirect. The configuration is exactly the same but now we will pass the URL of the website to the redirect method. Since now we are going to redirect to an external location, we need to use the whole URL of the website, which includes the domain name (or the IP).

We will call this route “/redirect/external“.

server.on("/redirect/external", HTTP_GET, [](AsyncWebServerRequest *request){
    request->redirect("https://techtutorialsx.com/");
});

Finally, after setting all the routes, we need to call the begin method on the server object, so it starts listening to incoming HTTP requests. You can check the whole source code below.

#include <WiFi.h>
#include <FS.h>
#include <AsyncTCP.h>
#include <ESPAsyncWebServer.h>
 
const char* ssid = "yourNetworkName";
const char* password =  "yourNetworkPassword";
 
AsyncWebServer server(80);
 
void setup(){
 
  Serial.begin(115200);
 
  WiFi.begin(ssid, password);
 
  while (WiFi.status() != WL_CONNECTED) {
    delay(1000);
    Serial.println("Connecting to WiFi..");
  }
 
  Serial.println(WiFi.localIP());
 
  server.on("/hello", HTTP_GET, [](AsyncWebServerRequest *request){
    request->send(200, "text/plain", "Hello from ESP32 server route");
  });
 
  server.on("/redirect/internal", HTTP_GET, [](AsyncWebServerRequest *request){
    request->redirect("/hello");
  });
 
  server.on("/redirect/external", HTTP_GET, [](AsyncWebServerRequest *request){
    request->redirect("https://techtutorialsx.com/");
  });
 
  server.begin();
}
 
void loop(){}

Figure 1 – Internal redirect.

For the external redirect, the browser should be directed to the website specified, as shown in figure 2. In this case, we have opened the request information on the developers console in order to confirm that the server is returning a 302 HTTP response, alongside with the destination URL in the response headers.

Figure 2 – External redirect.

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