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ESP32 WiFiClientSecure Library – available

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Description

The available method in the WiFiClientSecure library checks if there are any bytes available to read from the secure connection. It is used after establishing a TLS connection to determine if the server has sent data that can be processed, making it essential for reading responses in IoT applications.

Syntax and Usage

The available method has a single, straightforward usage without arguments. Below is the syntax with an example:

Checking Available Data

client.available()

Returns the number of bytes available to read from the secure connection, typically used in a loop to process incoming data.

For practical applications and examples of this method, please consult the “Example Code” section on this page. This section provides comprehensive guidance to help you better understand and apply the method effectively.

Argument(s)

This method does not require any arguments. It operates on the current state of the WiFiClientSecure object, checking the buffer for incoming data from the secure connection.

Return Value

The available method returns an int value:

  • Positive integer: The number of bytes available to read from the connection.
  • 0: No data is available to read, indicating either the buffer is empty or the connection has no new data.

Example Codes

Below is an example code demonstrating the usage of the available method, adapted from the reference code provided.

Example: Reading Server Response with available

This example connects to www.howsmyssl.com securely, sends an HTTPS GET request, and uses available to check for and read the server’s response, printing it to the Serial Monitor.

ATTENTION: The Root CA certificate has an expiration date. If the code fails to execute, it may be due to the Root CA certificate has expired. Try obtaining the latest Root CA certificate and replacing the expired one in this code. For detailed instructions on acquiring a website’s Root CA certificate, check out the link below:
How to Acquire the Root CA Certificate

/*
 * Author: Avant Maker
 * Date: February 24, 2025
 * Version: 1.0
 *
 * Description: Below is an example code demonstrating how
 * to use the ESP32 WiFiClientSecure Library's available method. 
 * 
 * ATTENTION: The Root CA certificate has an expiration date.
 * If this code fails to execute, acquire the most up-to-date
 * Root CA certificate.
 * To find out more details about how to acquire the Root CA
 * certificate of www.howsmyssl.com, please check out this link below:
 *
 * https://avantmaker.com/references/esp32-arduino-core-index/esp32-wificlientsecure-library/how-to-acquire-the-root-ca-certificate/
 *
 * License: MIT 
 * 
 * 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/references/esp32-arduino-core-index/
 *
 * 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 innovative ideas to life.
 */

#include <WiFi.h>
#include <NetworkClientSecure.h>

// WiFi credentials
const char* wifiName = "Your-WiFi-SSID";         // Your WiFi SSID
const char* wifiPass = "Your-WiFi-Password";     // Your WiFi password
// Server details
const char* targetServer = "www.howsmyssl.com";  // Target server URL

// Root CA certificate for www.howsmyssl.com
const char* rootCACert = R"literal(
-----BEGIN CERTIFICATE-----
MIIFBTCCAu2gAwIBAgIQS6hSk/eaL6JzBkuoBI110DANBgkqhkiG9w0BAQsFADBP
MQswCQYDVQQGEwJVUzEpMCcGA1UEChMgSW50ZXJuZXQgU2VjdXJpdHkgUmVzZWFy
Y2hhG3JvdXAxFTATBgNVBAMTDElTUkcgUm9vdCBYMTAeFw0yNDAzMTMwMDAwMDBa
Fw0yNzAzMTIyMzU5NTlaMDMxCzAJBgNVBAYTAlVTMRYwFAYDVQQKEw1MZXQncyBF
bmNyeXB0MQwwCgYDVQQDEwNSMTAwggEiMA0GCSqGSIb3DQEBAQUAA4IBDwAwggEK
AoIBAQDPV+XmxFQS7bRH/sknWHZGUCiMHT6I3wWd1bUYKb3dtVq/+vbOo76vACFL
YlpaPAEvxVgD9on/jhFD68G14BQHlo9vH9fnuoE5CXVlt8KvGFs3Jijno/QHK20a
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FpOUurDTazgGzRYSespSdcitdrLCnF2YRVxvYXvGLe48E1KGAdlX5jgc3421H5KR
mudKHMxFqHJV8LDmowfs/acbZp4/SItxhHFYyTr6717yW0QrPHTnj7JHwQdqzZq3
DZb3EoEmUVQK7GH29/Xi8orIlQ2NAgMBAAGjgfgwgfUwDgYDVR0PAQH/BAQDAgGG
MB0GA1UdJQQWMBQGCCsGAQUFBwMCBggrBgEFBQcDATASBgNVHRMBAf8ECDAGAQH/
AgEAMB0GA1UdDgQWBBS7vMNHpeS8qcbDpHIMEI2iNeHI6DAfBgNVHSMEGDAWgBR5
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1n5PJKBLBX9eb9LU6l8zSxPWV7bK3lG4XaMJgnT9x3ies7msFtpKK5bDtotij/l0
GaKeA97pb5uwD9KgWvaFXMIEt8jVTjLEvwRdvCn294GPDF08U8lAkIv7tghluaQh
1QnlE4SEN4LOECj8dsIGJXpGUk3aU3KkJz9icKy+aUgA+2cP21uh6NcDIS3XyfaZ
QjmDQ993ChII8SXWupQZVBiIpcWO4RqZk3lr7Bz5MUCwzDIA359e57SSq5CCkY0N
4B6Vulk7LktfwrdGNVI5BsC9qqxSwSKgRJeZ9wygIaehbHFHFhcBaMDKpiZlBHyz
rsnnlFXCb5s8HKn5LsUgGvB24L7sGNZP2CX7dhHov+YhD+jozLW2p9W4959Bz2Ei
RmqDtmiXLnzqTpXbI+suyCsohKRg6Un0RC47+cpiVwHiXZAW+cn8eiNIjqbVgXLx
KPpdzvvtTnOPlC7SQZSYmdunr3Bf9b77AiC/ZidstK36dRILKz7OA54=
-----END CERTIFICATE-----
)literal";

NetworkClientSecure secureClient;

void setup() {
  Serial.begin(115200);
  delay(200);

  WiFi.begin(wifiName, wifiPass);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.println("\nConnected to WiFi");

  secureClient.setCACert(rootCACert);
  if (!secureClient.connect(targetServer, 443)) {
    Serial.println("Connection failed. Check code description for solution.");
    return;
  }

  Serial.println("Connected to server!");
  secureClient.println("GET /a/check HTTP/1.1");
  secureClient.println("Host: www.howsmyssl.com");
  secureClient.println("Connection: close");
  secureClient.println();

  // Wait for server response
  while (secureClient.connected()) {
    String line = secureClient.readStringUntil('\n');
    if (line == "\r") {
      Serial.println("Headers received");
      break;
    }
  }

  // Check and read available data
  while (secureClient.available()) {
    char c = secureClient.read();
    Serial.print(c);
  }

  secureClient.stop();
  Serial.println("\nConnection closed");
}

void loop() {
}

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