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/*
* SMTP email client
*
* Adapted from the `ssl_mail_client` example in mbedtls.
*
* SPDX-FileCopyrightText: The Mbed TLS Contributors
*
* SPDX-License-Identifier: Apache-2.0
*
* SPDX-FileContributor: 2015-2021 Espressif Systems (Shanghai) CO LTD
*/
#include <string.h>
#include <stdlib.h>
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "esp_event.h"
#include "esp_log.h"
#include "esp_system.h"
#include "nvs_flash.h"
#include "protocol_examples_common.h"
#include "mbedtls/platform.h"
#include "mbedtls/net_sockets.h"
#include "mbedtls/esp_debug.h"
#include "mbedtls/ssl.h"
#include "mbedtls/entropy.h"
#include "mbedtls/ctr_drbg.h"
#include "mbedtls/error.h"
#include <mbedtls/base64.h>
#include <sys/param.h>
/* Constants that are configurable in menuconfig */
#define MAIL_SERVER CONFIG_SMTP_SERVER
#define MAIL_PORT CONFIG_SMTP_PORT_NUMBER
#define SENDER_MAIL CONFIG_SMTP_SENDER_MAIL
#define SENDER_PASSWORD CONFIG_SMTP_SENDER_PASSWORD
#define RECIPIENT_MAIL CONFIG_SMTP_RECIPIENT_MAIL
#define SERVER_USES_STARTSSL 1
static const char *TAG = "smtp_example";
#define TASK_STACK_SIZE (8 * 1024)
#define BUF_SIZE 512
#define VALIDATE_MBEDTLS_RETURN(ret, min_valid_ret, max_valid_ret, goto_label) \
do { \
if (ret < min_valid_ret || ret > max_valid_ret) { \
goto goto_label; \
} \
} while (0) \
/**
* Root cert for smtp.googlemail.com, taken from server_root_cert.pem
*
* The PEM file was extracted from the output of this command:
* openssl s_client -showcerts -connect smtp.googlemail.com:587 -starttls smtp
*
* The CA root cert is the last cert given in the chain of certs.
*
* To embed it in the app binary, the PEM file is named
* in the component.mk COMPONENT_EMBED_TXTFILES variable.
*/
extern const uint8_t server_root_cert_pem_start[] asm("_binary_server_root_cert_pem_start");
extern const uint8_t server_root_cert_pem_end[] asm("_binary_server_root_cert_pem_end");
extern const uint8_t esp_logo_png_start[] asm("_binary_esp_logo_png_start");
extern const uint8_t esp_logo_png_end[] asm("_binary_esp_logo_png_end");
static int write_and_get_response(mbedtls_net_context *sock_fd, unsigned char *buf, size_t len)
{
int ret;
const size_t DATA_SIZE = 128;
unsigned char data[DATA_SIZE];
char code[4];
size_t i, idx = 0;
if (len) {
ESP_LOGD(TAG, "%s", buf);
}
if (len && (ret = mbedtls_net_send(sock_fd, buf, len)) <= 0) {
ESP_LOGE(TAG, "mbedtls_net_send failed with error -0x%x", -ret);
return ret;
}
do {
len = DATA_SIZE - 1;
memset(data, 0, DATA_SIZE);
ret = mbedtls_net_recv(sock_fd, data, len);
if (ret <= 0) {
ESP_LOGE(TAG, "mbedtls_net_recv failed with error -0x%x", -ret);
goto exit;
}
data[len] = '\0';
printf("\n%s", data);
len = ret;
for (i = 0; i < len; i++) {
if (data[i] != '\n') {
if (idx < 4) {
code[idx++] = data[i];
}
continue;
}
if (idx == 4 && code[0] >= '0' && code[0] <= '9' && code[3] == ' ') {
code[3] = '\0';
ret = atoi(code);
goto exit;
}
idx = 0;
}
} while (1);
exit:
return ret;
}
static int write_ssl_and_get_response(mbedtls_ssl_context *ssl, unsigned char *buf, size_t len)
{
int ret;
const size_t DATA_SIZE = 128;
unsigned char data[DATA_SIZE];
char code[4];
size_t i, idx = 0;
if (len) {
ESP_LOGD(TAG, "%s", buf);
}
while (len && (ret = mbedtls_ssl_write(ssl, buf, len)) <= 0) {
if (ret != MBEDTLS_ERR_SSL_WANT_READ && ret != MBEDTLS_ERR_SSL_WANT_WRITE) {
ESP_LOGE(TAG, "mbedtls_ssl_write failed with error -0x%x", -ret);
goto exit;
}
}
do {
len = DATA_SIZE - 1;
memset(data, 0, DATA_SIZE);
ret = mbedtls_ssl_read(ssl, data, len);
if (ret == MBEDTLS_ERR_SSL_WANT_READ || ret == MBEDTLS_ERR_SSL_WANT_WRITE) {
continue;
}
if (ret <= 0) {
ESP_LOGE(TAG, "mbedtls_ssl_read failed with error -0x%x", -ret);
goto exit;
}
ESP_LOGD(TAG, "%s", data);
len = ret;
for (i = 0; i < len; i++) {
if (data[i] != '\n') {
if (idx < 4) {
code[idx++] = data[i];
}
continue;
}
if (idx == 4 && code[0] >= '0' && code[0] <= '9' && code[3] == ' ') {
code[3] = '\0';
ret = atoi(code);
goto exit;
}
idx = 0;
}
} while (1);
exit:
return ret;
}
static int write_ssl_data(mbedtls_ssl_context *ssl, unsigned char *buf, size_t len)
{
int ret;
if (len) {
ESP_LOGD(TAG, "%s", buf);
}
while (len && (ret = mbedtls_ssl_write(ssl, buf, len)) <= 0) {
if (ret != MBEDTLS_ERR_SSL_WANT_READ && ret != MBEDTLS_ERR_SSL_WANT_WRITE) {
ESP_LOGE(TAG, "mbedtls_ssl_write failed with error -0x%x", -ret);
return ret;
}
}
return 0;
}
static int perform_tls_handshake(mbedtls_ssl_context *ssl)
{
int ret = -1;
uint32_t flags;
char *buf = NULL;
buf = (char *) calloc(1, BUF_SIZE);
if (buf == NULL) {
ESP_LOGE(TAG, "calloc failed for size %d", BUF_SIZE);
goto exit;
}
ESP_LOGI(TAG, "Performing the SSL/TLS handshake...");
fflush(stdout);
while ((ret = mbedtls_ssl_handshake(ssl)) != 0) {
if (ret != MBEDTLS_ERR_SSL_WANT_READ && ret != MBEDTLS_ERR_SSL_WANT_WRITE) {
ESP_LOGE(TAG, "mbedtls_ssl_handshake returned -0x%x", -ret);
goto exit;
}
}
ESP_LOGI(TAG, "Verifying peer X.509 certificate...");
if ((flags = mbedtls_ssl_get_verify_result(ssl)) != 0) {
/* In real life, we probably want to close connection if ret != 0 */
ESP_LOGW(TAG, "Failed to verify peer certificate!");
mbedtls_x509_crt_verify_info(buf, BUF_SIZE, " ! ", flags);
ESP_LOGW(TAG, "verification info: %s", buf);
} else {
ESP_LOGI(TAG, "Certificate verified.");
}
ESP_LOGI(TAG, "Cipher suite is %s", mbedtls_ssl_get_ciphersuite(ssl));
ret = 0; /* No error */
exit:
if (buf) {
free(buf);
}
return ret;
}
static void smtp_client_task(void *pvParameters)
{
char *buf = NULL;
unsigned char base64_buffer[128];
int ret, len;
size_t base64_len;
mbedtls_entropy_context entropy;
mbedtls_ctr_drbg_context ctr_drbg;
mbedtls_ssl_context ssl;
mbedtls_x509_crt cacert;
mbedtls_ssl_config conf;
mbedtls_net_context server_fd;
mbedtls_ssl_init(&ssl);
mbedtls_x509_crt_init(&cacert);
mbedtls_ctr_drbg_init(&ctr_drbg);
ESP_LOGI(TAG, "Seeding the random number generator");
mbedtls_ssl_config_init(&conf);
mbedtls_entropy_init(&entropy);
if ((ret = mbedtls_ctr_drbg_seed(&ctr_drbg, mbedtls_entropy_func, &entropy,
NULL, 0)) != 0) {
ESP_LOGE(TAG, "mbedtls_ctr_drbg_seed returned -0x%x", -ret);
goto exit;
}
ESP_LOGI(TAG, "Loading the CA root certificate...");
ret = mbedtls_x509_crt_parse(&cacert, server_root_cert_pem_start,
server_root_cert_pem_end - server_root_cert_pem_start);
if (ret < 0) {
ESP_LOGE(TAG, "mbedtls_x509_crt_parse returned -0x%x", -ret);
goto exit;
}
ESP_LOGI(TAG, "Setting hostname for TLS session...");
/* Hostname set here should match CN in server certificate */
if ((ret = mbedtls_ssl_set_hostname(&ssl, MAIL_SERVER)) != 0) {
ESP_LOGE(TAG, "mbedtls_ssl_set_hostname returned -0x%x", -ret);
goto exit;
}
ESP_LOGI(TAG, "Setting up the SSL/TLS structure...");
if ((ret = mbedtls_ssl_config_defaults(&conf,
MBEDTLS_SSL_IS_CLIENT,
MBEDTLS_SSL_TRANSPORT_STREAM,
MBEDTLS_SSL_PRESET_DEFAULT)) != 0) {
ESP_LOGE(TAG, "mbedtls_ssl_config_defaults returned -0x%x", -ret);
goto exit;
}
mbedtls_ssl_conf_authmode(&conf, MBEDTLS_SSL_VERIFY_REQUIRED);
mbedtls_ssl_conf_ca_chain(&conf, &cacert, NULL);
mbedtls_ssl_conf_rng(&conf, mbedtls_ctr_drbg_random, &ctr_drbg);
#ifdef CONFIG_MBEDTLS_DEBUG
mbedtls_esp_enable_debug_log(&conf, 4);
#endif
if ((ret = mbedtls_ssl_setup(&ssl, &conf)) != 0) {
ESP_LOGE(TAG, "mbedtls_ssl_setup returned -0x%x", -ret);
goto exit;
}
mbedtls_net_init(&server_fd);
ESP_LOGI(TAG, "Connecting to %s:%s...", MAIL_SERVER, MAIL_PORT);
if ((ret = mbedtls_net_connect(&server_fd, MAIL_SERVER,
MAIL_PORT, MBEDTLS_NET_PROTO_TCP)) != 0) {
ESP_LOGE(TAG, "mbedtls_net_connect returned -0x%x", -ret);
goto exit;
}
ESP_LOGI(TAG, "Connected.");
mbedtls_ssl_set_bio(&ssl, &server_fd, mbedtls_net_send, mbedtls_net_recv, NULL);
buf = (char *) calloc(1, BUF_SIZE);
if (buf == NULL) {
ESP_LOGE(TAG, "calloc failed for size %d", BUF_SIZE);
goto exit;
}
#if SERVER_USES_STARTSSL
/* Get response */
ret = write_and_get_response(&server_fd, (unsigned char *) buf, 0);
VALIDATE_MBEDTLS_RETURN(ret, 200, 299, exit);
ESP_LOGI(TAG, "Writing EHLO to server...");
len = snprintf((char *) buf, BUF_SIZE, "EHLO %s\r\n", "ESP32");
ret = write_and_get_response(&server_fd, (unsigned char *) buf, len);
VALIDATE_MBEDTLS_RETURN(ret, 200, 299, exit);
ESP_LOGI(TAG, "Writing STARTTLS to server...");
len = snprintf((char *) buf, BUF_SIZE, "STARTTLS\r\n");
ret = write_and_get_response(&server_fd, (unsigned char *) buf, len);
VALIDATE_MBEDTLS_RETURN(ret, 200, 299, exit);
ret = perform_tls_handshake(&ssl);
if (ret != 0) {
goto exit;
}
#else /* SERVER_USES_STARTSSL */
ret = perform_tls_handshake(&ssl);
if (ret != 0) {
goto exit;
}
/* Get response */
ret = write_ssl_and_get_response(&ssl, (unsigned char *) buf, 0);
VALIDATE_MBEDTLS_RETURN(ret, 200, 299, exit);
ESP_LOGI(TAG, "Writing EHLO to server...");
len = snprintf((char *) buf, BUF_SIZE, "EHLO %s\r\n", "ESP32");
ret = write_ssl_and_get_response(&ssl, (unsigned char *) buf, len);
VALIDATE_MBEDTLS_RETURN(ret, 200, 299, exit);
#endif /* SERVER_USES_STARTSSL */
/* Authentication */
ESP_LOGI(TAG, "Authentication...");
ESP_LOGI(TAG, "Write AUTH LOGIN");
len = snprintf( (char *) buf, BUF_SIZE, "AUTH LOGIN\r\n" );
ret = write_ssl_and_get_response(&ssl, (unsigned char *) buf, len);
VALIDATE_MBEDTLS_RETURN(ret, 200, 399, exit);
ESP_LOGI(TAG, "Write USER NAME");
ret = mbedtls_base64_encode((unsigned char *) base64_buffer, sizeof(base64_buffer),
&base64_len, (unsigned char *) SENDER_MAIL, strlen(SENDER_MAIL));
if (ret != 0) {
ESP_LOGE(TAG, "Error in mbedtls encode! ret = -0x%x", -ret);
goto exit;
}
len = snprintf((char *) buf, BUF_SIZE, "%s\r\n", base64_buffer);
ret = write_ssl_and_get_response(&ssl, (unsigned char *) buf, len);
VALIDATE_MBEDTLS_RETURN(ret, 300, 399, exit);
ESP_LOGI(TAG, "Write PASSWORD");
ret = mbedtls_base64_encode((unsigned char *) base64_buffer, sizeof(base64_buffer),
&base64_len, (unsigned char *) SENDER_PASSWORD, strlen(SENDER_PASSWORD));
if (ret != 0) {
ESP_LOGE(TAG, "Error in mbedtls encode! ret = -0x%x", -ret);
goto exit;
}
len = snprintf((char *) buf, BUF_SIZE, "%s\r\n", base64_buffer);
ret = write_ssl_and_get_response(&ssl, (unsigned char *) buf, len);
VALIDATE_MBEDTLS_RETURN(ret, 200, 399, exit);
/* Compose email */
ESP_LOGI(TAG, "Write MAIL FROM");
len = snprintf((char *) buf, BUF_SIZE, "MAIL FROM:<%s>\r\n", SENDER_MAIL);
ret = write_ssl_and_get_response(&ssl, (unsigned char *) buf, len);
VALIDATE_MBEDTLS_RETURN(ret, 200, 299, exit);
ESP_LOGI(TAG, "Write RCPT");
len = snprintf((char *) buf, BUF_SIZE, "RCPT TO:<%s>\r\n", RECIPIENT_MAIL);
ret = write_ssl_and_get_response(&ssl, (unsigned char *) buf, len);
VALIDATE_MBEDTLS_RETURN(ret, 200, 299, exit);
ESP_LOGI(TAG, "Write DATA");
len = snprintf((char *) buf, BUF_SIZE, "DATA\r\n");
ret = write_ssl_and_get_response(&ssl, (unsigned char *) buf, len);
VALIDATE_MBEDTLS_RETURN(ret, 300, 399, exit);
ESP_LOGI(TAG, "Write Content");
/* We do not take action if message sending is partly failed. */
len = snprintf((char *) buf, BUF_SIZE,
"From: %s\r\nSubject: mbed TLS Test mail\r\n"
"To: %s\r\n"
"MIME-Version: 1.0 (mime-construct 1.9)\n",
"ESP32 SMTP Client", RECIPIENT_MAIL);
/**
* Note: We are not validating return for some ssl_writes.
* If by chance, it's failed; at worst email will be incomplete!
*/
ret = write_ssl_data(&ssl, (unsigned char *) buf, len);
/* Multipart boundary */
len = snprintf((char *) buf, BUF_SIZE,
"Content-Type: multipart/mixed;boundary=XYZabcd1234\n"
"--XYZabcd1234\n");
ret = write_ssl_data(&ssl, (unsigned char *) buf, len);
/* Text */
len = snprintf((char *) buf, BUF_SIZE,
"Content-Type: text/plain\n"
"This is a simple test mail from the SMTP client example.\r\n"
"\r\n"
"Enjoy!\n\n--XYZabcd1234\n");
ret = write_ssl_data(&ssl, (unsigned char *) buf, len);
/* Attachment */
len = snprintf((char *) buf, BUF_SIZE,
"Content-Type: image/png;name=esp_logo.png\n"
"Content-Transfer-Encoding: base64\n"
"Content-Disposition:attachment;filename=\"esp_logo.png\"\r\n\n");
ret = write_ssl_data(&ssl, (unsigned char *) buf, len);
/* Image contents... */
const uint8_t *offset = esp_logo_png_start;
while (offset < esp_logo_png_end - 1) {
int read_bytes = MIN(((sizeof (base64_buffer) - 1) / 4) * 3, esp_logo_png_end - offset - 1);
ret = mbedtls_base64_encode((unsigned char *) base64_buffer, sizeof(base64_buffer),
&base64_len, (unsigned char *) offset, read_bytes);
if (ret != 0) {
ESP_LOGE(TAG, "Error in mbedtls encode! ret = -0x%x", -ret);
goto exit;
}
offset += read_bytes;
len = snprintf((char *) buf, BUF_SIZE, "%s\r\n", base64_buffer);
ret = write_ssl_data(&ssl, (unsigned char *) buf, len);
}
len = snprintf((char *) buf, BUF_SIZE, "\n--XYZabcd1234\n");
ret = write_ssl_data(&ssl, (unsigned char *) buf, len);
len = snprintf((char *) buf, BUF_SIZE, "\r\n.\r\n");
ret = write_ssl_and_get_response(&ssl, (unsigned char *) buf, len);
VALIDATE_MBEDTLS_RETURN(ret, 200, 299, exit);
ESP_LOGI(TAG, "Email sent!");
/* Close connection */
mbedtls_ssl_close_notify(&ssl);
ret = 0; /* No errors */
exit:
mbedtls_net_free(&server_fd);
mbedtls_x509_crt_free(&cacert);
mbedtls_ssl_free(&ssl);
mbedtls_ssl_config_free(&conf);
mbedtls_ctr_drbg_free(&ctr_drbg);
mbedtls_entropy_free(&entropy);
if (ret != 0) {
mbedtls_strerror(ret, buf, 100);
ESP_LOGE(TAG, "Last error was: -0x%x - %s", -ret, buf);
}
putchar('\n'); /* Just a new line */
if (buf) {
free(buf);
}
vTaskDelete(NULL);
}
void app_main(void)
{
ESP_ERROR_CHECK(nvs_flash_init());
ESP_ERROR_CHECK(esp_netif_init());
ESP_ERROR_CHECK(esp_event_loop_create_default());
/**
* This helper function configures Wi-Fi or Ethernet, as selected in menuconfig.
* Read "Establishing Wi-Fi or Ethernet Connection" section in
* examples/protocols/README.md for more information about this function.
*/
ESP_ERROR_CHECK(example_connect());
xTaskCreate(&smtp_client_task, "smtp_client_task", TASK_STACK_SIZE, NULL, 5, NULL);
}
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