twilio.cpp

#include "twilio.hpp"

/*
 * Send a SMS or MMS with the Twilio REST API
 *
 * Inputs:
 *  - to_number : Number to send the message to
 *  - from_number : Number to send the message from
 *  - message_body : Text to send in the message (max 1600 characters)
 *  - picture_url : (Optional) URL to an image
 *
 * Outputs:
 *  - response : Connection messages and Twilio responses returned to caller
 *  - bool (method) : Whether the message send was successful
 */
bool Twilio::send_message(
        const String& to_number,
        const String& from_number,
        const String& message_body,
        String& response,
        const String& picture_url)
{
        // Check the body is less than 1600 characters in length.  see:
        // https://support.twilio.com/hc/en-us/articles/223181508-Does-Twilio-support-concatenated-SMS-messages-or-messages-over-160-characters-
        // Note this is only checking ASCII length, not UCS-2 encoding; your
        // application may need to enhance this.
        if (message_body.length() > 1600) {
                response += "Message body must be 1600 or fewer characters.";
                response += "  You are attempting to send ";
                response += message_body.length();
                response += ".\r\n";
                return false;
        }

        // URL encode our message body & picture URL to escape special chars
        // such as '&' and '='
        String encoded_body = urlencode(message_body);

        // Use WiFiClientSecure class to create TLS 1.2 connection
        WiFiClientSecure client;
        client.setFingerprint(fingerprint.c_str());
        const char* host = "api.twilio.com";
        const int   httpsPort = 443;

        // Use WiFiClientSecure class to create TLS connection
        Serial.print("connecting to ");
        Serial.println(host);
        
        Serial.printf("Using fingerprint '%s'\n", fingerprint.c_str());

        // Connect to Twilio's REST API
        response += ("Connecting to host ");
        response += host;
        response += "\r\n";
        if (!client.connect(host, httpsPort)) {
                response += ("Connection failed!\r\n");
                return false;
        }

        // Check the SHA1 Fingerprint (We will watch for CA verification)
        if (client.verify(fingerprint.c_str(), host)) {
                response += ("Certificate fingerprints match.\r\n");
        } else {
                response += ("Certificate fingerprints don't match.\r\n");
                return false;
        }

        // Attempt to send an SMS or MMS, depending on picture URL
        String post_data = "To=" + urlencode(to_number) + "&From=" + urlencode(from_number) + \
        "&Body=" + encoded_body;
        if (picture_url.length() > 0) {
                String encoded_image = urlencode(picture_url);
                post_data += "&MediaUrl=" + encoded_image;
        }

        // Construct headers and post body manually
        String auth_header = _get_auth_header(account_sid, auth_token);
        String http_request = "POST /2010-04-01/Accounts/" +
                              String(account_sid) + "/Messages HTTP/1.1\r\n" +
                              auth_header + "\r\n" + "Host: " + host + "\r\n" +
                              "Cache-control: no-cache\r\n" +
                              "User-Agent: ESP8266 Twilio Example\r\n" +
                              "Content-Type: " +
                              "application/x-www-form-urlencoded\r\n" +
                              "Content-Length: " + post_data.length() +"\r\n" +
                              "Connection: close\r\n" +
                              "\r\n" + post_data + "\r\n";

        response += ("Sending http POST: \r\n"+http_request);
        client.println(http_request);

        // Read the response into the 'response' string
        response += ("request sent");
        while (client.connected()) {
        String line = client.readStringUntil('\n');
        response += (line);
        response += ("\r\n");
        }
        response += ("closing connection");
        return true;
}

/* Private function to create a Basic Auth field and parameter */
String Twilio::_get_auth_header(const String& user, const String& password) {
        size_t toencodeLen = user.length() + password.length() + 2;
        char toencode[toencodeLen];
        memset(toencode, 0, toencodeLen);
        snprintf(
                toencode,
                toencodeLen,
                "%s:%s",
                user.c_str(),
                password.c_str()
        );

        String encoded = base64::encode((uint8_t*)toencode, toencodeLen-1);
        String encoded_string = String(encoded);
        std::string::size_type i = 0;

        // Strip newlines (after every 72 characters in spec)
        while (i < encoded_string.length()) {
                i = encoded_string.indexOf('\n', i);
                if (i == -1) {
                        break;
                }
                encoded_string.remove(i, 1);
        }
        return "Authorization: Basic " + encoded_string;
}