ESP32 WebServer Library – header()

/*
 * Author: Avant Maker
 * Date: June 16, 2025
 * Version: 1.0
 * License: MIT 
 * 
 * Description: 
 * This example demonstrates how to access specific headers by their names,
 * which is the most common usage pattern for header processing.
 * 
 * How to use this example: 
 * Upload this code to your ESP32 and replace the WiFi credentials. 
 * After connecting, test with curl commands like: 
 * curl -H "User-Agent: MyCustomAgent" -H "Accept: application/json" http://ESP32_IP.
 * The server will display the specific header values in a formatted response.
 *
 * Code Source:
 * This example code is sourced from the Comprehensive Guide
 * to the ESP32 Arduino Core Library, accessible on AvantMaker.com.
 * For additional code examples and in-depth documentation related to
 * the ESP32 Arduino Core Library, please visit:
 *
 * https://avantmaker.com/home/all-about-esp32-arduino-core-library/
 *
 * AvantMaker.com, your premier destination for all things
 * DIY, AI, IoT, Smart Home, and STEM projects. We are dedicated
 * to empowering makers, learners, and enthusiasts with
 * the resources they need to bring their nnovative ideas to life.
 */
 
#include <WiFi.h>
#include <WebServer.h>

const char* ssid = "your_wifi_ssid";
const char* password = "your_wifi_password";

WebServer server(80);

// Headers we want to collect and access
const char* headerKeys[] = {"User-Agent", "Accept", "Content-Type", "Authorization"};
const size_t headerKeysCount = sizeof(headerKeys) / sizeof(headerKeys[0]);

void handleRoot() {
  String message = "ESP32 Header Information\n\n";
  
  // Access headers by name
  String userAgent = server.header("User-Agent");
  if (userAgent.length() > 0) {
    message += "Browser/Client: " + userAgent + "\n";
  } else {
    message += "User-Agent: Not provided\n";
  }
  
  String acceptHeader = server.header("Accept");
  if (acceptHeader.length() > 0) {
    message += "Accepts: " + acceptHeader + "\n";
  }
  
  String contentType = server.header("Content-Type");
  if (contentType.length() > 0) {
    message += "Content-Type: " + contentType + "\n";
  }
  
  String authorization = server.header("Authorization");
  if (authorization.length() > 0) {
    message += "Authorization: " + authorization + "\n";
  } else {
    message += "Authorization: Not provided\n";
  }
  
  message += "\nRequest Method: " + String((server.method() == HTTP_GET) ? "GET" : 
                                           (server.method() == HTTP_POST) ? "POST" : "OTHER");
  message += "\nURI: " + server.uri();
  
  server.send(200, "text/plain", message);
}

void setup() {
  Serial.begin(115200);
  
  // Connect to WiFi
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(1000);
    Serial.println("Connecting to WiFi...");
  }
  
  // Configure headers to collect
  server.collectHeaders(headerKeys, headerKeysCount);
  
  // Set up route handler
  server.on("/", handleRoot);
  
  // Start server
  server.begin();
  Serial.println("HTTP server started");
  Serial.print("IP address: ");
  Serial.println(WiFi.localIP());
}

void loop() {
  server.handleClient();
}

/*
 * Author: Avant Maker
 * Date: June 16, 2025
 * Version: 1.0
 * License: MIT 
 * 
 * Description: 
 * This example shows how to access all collected headers using index-based
 * iteration, which is useful for debugging or when you need to process
 * all available headers.
 * 
 * How to use this example: 
 * After uploading and connecting to WiFi, visit the ESP32's IP address
 * in your browser. The /headers endpoint will display all collected headers
 * with their index positions. Try accessing from different browsers
 * or with different HTTP clients to see how header sets vary.
 *
 * Code Source:
 * This example code is sourced from the Comprehensive Guide
 * to the ESP32 Arduino Core Library, accessible on AvantMaker.com.
 * For additional code examples and in-depth documentation related to
 * the ESP32 Arduino Core Library, please visit:
 *
 * https://avantmaker.com/home/all-about-esp32-arduino-core-library/
 *
 * AvantMaker.com, your premier destination for all things
 * DIY, AI, IoT, Smart Home, and STEM projects. We are dedicated
 * to empowering makers, learners, and enthusiasts with
 * the resources they need to bring their nnovative ideas to life.
 */
 
#include <WiFi.h>
#include <WebServer.h>

#include <WiFi.h>
#include <WebServer.h>

const char* ssid = "your_wifi_ssid";
const char* password = "your_wifi_password";

WebServer server(80);

void handleHeaders() {
  String message = "All Collected Headers\n";
  message += "=====================\n\n";
  
  int headerCount = server.headers();
  message += "Total headers collected: " + String(headerCount) + "\n\n";
  
  // Iterate through headers by index
  for (int i = 0; i < headerCount; i++) {
    String headerName = server.headerName(i);
    String headerValue = server.header(i);
    
    message += "Header[" + String(i) + "]: ";
    message += headerName + " = " + headerValue + "\n";
  }
  
  if (headerCount == 0) {
    message += "No headers were collected.\n";
    message += "Make sure to call collectHeaders() or collectAllHeaders()!\n";
  }
  
  server.send(200, "text/plain", message);
}

void handleRoot() {
  String html = "<html><body>";
  html += "<h1>ESP32 Header Inspector</h1>";
  html += "<p><a href='/headers'>View All Headers</a></p>";
  html += "<p><a href='/specific'>View Specific Headers</a></p>";
  html += "</body></html>";
  
  server.send(200, "text/html", html);
}

void handleSpecific() {
  String message = "Specific Header Values\n";
  message += "======================\n\n";
  
  // Check for common headers
  if (server.hasHeader("Host")) {
    message += "Host: " + server.header("Host") + "\n";
  }
  
  if (server.hasHeader("Connection")) {
    message += "Connection: " + server.header("Connection") + "\n";
  }
  
  if (server.hasHeader("Cache-Control")) {
    message += "Cache-Control: " + server.header("Cache-Control") + "\n";
  }
  
  server.send(200, "text/plain", message);
}

void setup() {
  Serial.begin(115200);
  
  // Connect to WiFi
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(1000);
    Serial.println("Connecting to WiFi...");
  }
  
  // Collect all headers for comprehensive inspection
  server.collectAllHeaders();
  
  // Set up route handlers
  server.on("/", handleRoot);
  server.on("/headers", handleHeaders);
  server.on("/specific", handleSpecific);
  
  // Start server
  server.begin();
  Serial.println("HTTP server started");
  Serial.print("IP address: ");
  Serial.println(WiFi.localIP());
}

void loop() {
  server.handleClient();
}

/*
 * Author: Avant Maker
 * Date: June 16, 2025
 * Version: 1.0
 * License: MIT 
 * 
 * Description: 
 * This example demonstrates practical usage of headers for implementing
 * content negotiation and basic authentication, showing real-world applications
 * of the header() method.
 * 
 * How to use this example: 
 * curl -H "Accept: application/json" http://ESP32_IP/api for JSON response,
 * curl -H "Accept: text/xml" http://ESP32_IP/api for XML response,
 * and curl -H "Authorization: Bearer validtoken123" http://ESP32_IP/secure
 * for authenticated access. Default responses are in plain text.
 *
 * Code Source:
 * This example code is sourced from the Comprehensive Guide
 * to the ESP32 Arduino Core Library, accessible on AvantMaker.com.
 * For additional code examples and in-depth documentation related to
 * the ESP32 Arduino Core Library, please visit:
 *
 * https://avantmaker.com/home/all-about-esp32-arduino-core-library/
 *
 * AvantMaker.com, your premier destination for all things
 * DIY, AI, IoT, Smart Home, and STEM projects. We are dedicated
 * to empowering makers, learners, and enthusiasts with
 * the resources they need to bring their nnovative ideas to life.
 */

#include <WiFi.h>
#include <WebServer.h>

const char* ssid = "your_wifi_ssid";
const char* password = "your_wifi_password";

WebServer server(80);

// Valid API token for demonstration
const String validToken = "validtoken123";

void handleAPI() {
  String acceptHeader = server.header("Accept");
  String response;
  String contentType;
  
  // Content negotiation based on Accept header
  if (acceptHeader.indexOf("application/json") != -1) {
    response = "{\"message\":\"Hello from AvantMaker ESP32 Example\",\"status\":\"success\",\"timestamp\":" + String(millis()) + "}";
    contentType = "application/json";
  } else if (acceptHeader.indexOf("text/xml") != -1 || acceptHeader.indexOf("application/xml") != -1) {
    response = "<?xml version=\"1.0\"?><response><message>Hello from ESP32</message><status>success</status><timestamp>" + String(millis()) + "</timestamp></response>";
    contentType = "application/xml";
  } else {
    response = "Hello from ESP32\nStatus: success\nTimestamp: " + String(millis());
    contentType = "text/plain";
  }
  
  server.send(200, contentType, response);
}

void handleSecure() {
  String authHeader = server.header("Authorization");
  
  if (authHeader.length() == 0) {
    server.send(401, "text/plain", "Authorization header required");
    return;
  }
  
  // Simple Bearer token authentication
  if (authHeader.startsWith("Bearer ")) {
    String token = authHeader.substring(7); // Remove "Bearer " prefix
    if (token == validToken) {
      String response = "Access granted!\n";
      response += "User-Agent: " + server.header("User-Agent") + "\n";
      response += "Client IP: " + server.client().remoteIP().toString() + "\n";
      response += "Request time: " + String(millis()) + " ms";
      
      server.send(200, "text/plain", response);
    } else {
      server.send(403, "text/plain", "Invalid token");
    }
  } else {
    server.send(400, "text/plain", "Invalid authorization format. Use 'Bearer <token>'");
  }
}

void handleRoot() {
  String userAgent = server.header("User-Agent");
  String html = "<html><body>";
  html += "<h1>ESP32 Advanced Header Processing</h1>";
  html += "<p>Your browser: " + userAgent + "</p>";
  html += "<h2>Available Endpoints:</h2>";
  html += "<ul>";
  html += "<li><a href='/api'>/api</a> - Content negotiation demo</li>";
  html += "<li>/secure - Authentication demo (requires Bearer token)</li>";
  html += "</ul>";
  html += "</body></html>";
  
  server.send(200, "text/html", html);
}

void setup() {
  Serial.begin(115200);
  
  // Connect to WiFi
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(1000);
    Serial.println("Connecting to WiFi...");
  }
  
  // Collect headers needed for our functionality
  const char* requiredHeaders[] = {"Accept", "Authorization", "User-Agent", "Content-Type"};
  const size_t headerCount = sizeof(requiredHeaders) / sizeof(requiredHeaders[0]);
  
  server.collectHeaders(requiredHeaders, headerCount);
  
  // Set up route handlers
  server.on("/", handleRoot);
  server.on("/api", handleAPI);
  server.on("/secure", handleSecure);
  
  // Start server
  server.begin();
  Serial.println("HTTP server started");
  Serial.print("IP address: ");
  Serial.println(WiFi.localIP());
}

void loop() {
  server.handleClient();
}