Complete the HTTP GET example

examples/http_get_bearssl/http_get_bearssl.c

@@ -1,13 +1,13 @@
-/* http_get_mbedtls - HTTPS version of the http_get example, using mbed TLS.
+/* http_get_bearssl - HTTPS version of the http_get example, using BearSSL.
  *
  * Retrieves a JSON response from the howsmyssl.com API via HTTPS over TLS v1.2.
  *
- * Validates the server's certificate using the root CA loaded (in PEM format) in cert.c.
+ * Validates the server's certificate using a hardcoded public key.
  *
- * Adapted from the ssl_client1 example in mbedtls.
+ * Adapted from the client_basic sample in BearSSL.
  *
- * Original Copyright (C) 2006-2015, ARM Limited, All Rights Reserved, Apache 2.0 License.
+ * Original Copyright (c) 2016 Thomas Pornin <pornin@bolet.org>, MIT License.
- * Additions Copyright (C) 2015 Angus Gratton, Apache 2.0 License.
+ * Additions Copyright (C) 2016 Stefan Schake, MIT License.
  */
 #include "espressif/esp_common.h"
 #include "esp/uart.h"
@@ -35,83 +35,47 @@
 
 #define GET_REQUEST "GET "WEB_URL" HTTP/1.1\nHost: "WEB_SERVER"\n\n"
 
-static const unsigned char TA0_DN[] = {
+/*
-        0x30, 0x1C, 0x31, 0x0B, 0x30, 0x09, 0x06, 0x03, 0x55, 0x04, 0x06, 0x13,
+ * howsmyssl.com public key
-        0x02, 0x43, 0x41, 0x31, 0x0D, 0x30, 0x0B, 0x06, 0x03, 0x55, 0x04, 0x03,
+ * BearSSL doesn't allow disabling validation and we don't have
-        0x13, 0x04, 0x52, 0x6F, 0x6F, 0x74
+ * a correct date/time on the ESP so it would always fail.
+ * Instead, we compare the server key against this static public key
+ * to validate the server.
+ */
+static const unsigned char SERVER_PKEY_RSA_N[] = {
+	0xA9, 0x11, 0x5C, 0xAF, 0x4F, 0xDD, 0xEB, 0x88, 0xCD, 0xF6, 0x47, 0x11,
+	0xB9, 0x7F, 0xFA, 0x08, 0xD7, 0x90, 0x01, 0x14, 0x36, 0x84, 0xBF, 0xE2,
+	0xD8, 0xC4, 0x26, 0xBF, 0xD3, 0x6B, 0xBA, 0x2E, 0x06, 0x9C, 0x23, 0x95,
+	0x98, 0x8E, 0xC0, 0xC5, 0x91, 0xF0, 0xC6, 0xC3, 0x39, 0x98, 0x04, 0xC6,
+	0x78, 0x14, 0x13, 0x08, 0xA7, 0x12, 0x3D, 0x86, 0x1A, 0x14, 0x71, 0x35,
+	0x7E, 0xFB, 0x8B, 0xF8, 0xA1, 0x52, 0x21, 0x5B, 0xDE, 0x51, 0x5A, 0x3A,
+	0x35, 0x6F, 0x8F, 0xDB, 0xF9, 0x6A, 0xA5, 0xF2, 0x74, 0x6E, 0xCA, 0xFC,
+	0xA4, 0x70, 0xCC, 0x70, 0x4D, 0x5E, 0x4E, 0x69, 0xA2, 0xFE, 0x42, 0x23,
+	0x8A, 0xC0, 0x01, 0x3B, 0xEF, 0x46, 0xB4, 0xC2, 0x6F, 0x48, 0x26, 0xDD,
+	0xF5, 0x05, 0x9B, 0x69, 0x88, 0xB0, 0x7D, 0x38, 0xA8, 0x49, 0x07, 0x11,
+	0xE5, 0xFE, 0x27, 0x0F, 0x4F, 0x28, 0x83, 0x18, 0xAB, 0x47, 0x1F, 0x72,
+	0x40, 0xEC, 0x67, 0x16, 0xBE, 0x45, 0x76, 0x0B, 0x83, 0x91, 0xE5, 0x42,
+	0xC2, 0xA2, 0x5B, 0xF2, 0xEB, 0xB1, 0x8C, 0x37, 0x0F, 0x4B, 0x5E, 0x0F,
+	0x05, 0x7D, 0x54, 0x48, 0x9F, 0x55, 0xAE, 0x41, 0xC9, 0x07, 0x6F, 0xD7,
+	0xB3, 0xF3, 0xE2, 0x61, 0x18, 0x03, 0x48, 0xA1, 0x3C, 0x8D, 0xBD, 0x5C,
+	0xCD, 0x3B, 0x55, 0xCD, 0x97, 0xE3, 0xD1, 0x80, 0x8A, 0x30, 0x88, 0x3A,
+	0xAC, 0xEE, 0x64, 0x08, 0xBD, 0x74, 0x82, 0x24, 0x82, 0x11, 0xD4, 0x93,
+	0xFA, 0xEF, 0x52, 0x5F, 0x2C, 0x51, 0x0C, 0x88, 0x09, 0xB9, 0x77, 0xA0,
+	0xFA, 0x6F, 0xAB, 0xEB, 0xE1, 0x08, 0x5C, 0xA5, 0x02, 0x53, 0xA1, 0x18,
+	0xFC, 0xB8, 0x06, 0x67, 0x7E, 0x80, 0xDF, 0xF1, 0xCD, 0xAE, 0x23, 0x58,
+	0xCD, 0xCE, 0x7C, 0x69, 0x2E, 0x4D, 0xD6, 0xB0, 0xD2, 0x6D, 0x11, 0x85,
+	0x5E, 0x36, 0x41, 0x27
 };
 
-static const unsigned char TA0_RSA_N[] = {
+static const unsigned char SERVER_PKEY_RSA_E[] = {
-        0xB6, 0xD9, 0x34, 0xD4, 0x50, 0xFD, 0xB3, 0xAF, 0x7A, 0x73, 0xF1, 0xCE,
+	0x01, 0x00, 0x01
-        0x38, 0xBF, 0x5D, 0x6F, 0x45, 0xE1, 0xFD, 0x4E, 0xB1, 0x98, 0xC6, 0x60,
-        0x83, 0x26, 0xD2, 0x17, 0xD1, 0xC5, 0xB7, 0x9A, 0xA3, 0xC1, 0xDE, 0x63,
-        0x39, 0x97, 0x9C, 0xF0, 0x5E, 0x5C, 0xC8, 0x1C, 0x17, 0xB9, 0x88, 0x19,
-        0x6D, 0xF0, 0xB6, 0x2E, 0x30, 0x50, 0xA1, 0x54, 0x6E, 0x93, 0xC0, 0xDB,
-        0xCF, 0x30, 0xCB, 0x9F, 0x1E, 0x27, 0x79, 0xF1, 0xC3, 0x99, 0x52, 0x35,
-        0xAA, 0x3D, 0xB6, 0xDF, 0xB0, 0xAD, 0x7C, 0xCB, 0x49, 0xCD, 0xC0, 0xED,
-        0xE7, 0x66, 0x10, 0x2A, 0xE9, 0xCE, 0x28, 0x1F, 0x21, 0x50, 0xFA, 0x77,
-        0x4C, 0x2D, 0xDA, 0xEF, 0x3C, 0x58, 0xEB, 0x4E, 0xBF, 0xCE, 0xE9, 0xFB,
-        0x1A, 0xDA, 0xA3, 0x83, 0xA3, 0xCD, 0xA3, 0xCA, 0x93, 0x80, 0xDC, 0xDA,
-        0xF3, 0x17, 0xCC, 0x7A, 0xAB, 0x33, 0x80, 0x9C, 0xB2, 0xD4, 0x7F, 0x46,
-        0x3F, 0xC5, 0x3C, 0xDC, 0x61, 0x94, 0xB7, 0x27, 0x29, 0x6E, 0x2A, 0xBC,
-        0x5B, 0x09, 0x36, 0xD4, 0xC6, 0x3B, 0x0D, 0xEB, 0xBE, 0xCE, 0xDB, 0x1D,
-        0x1C, 0xBC, 0x10, 0x6A, 0x71, 0x71, 0xB3, 0xF2, 0xCA, 0x28, 0x9A, 0x77,
-        0xF2, 0x8A, 0xEC, 0x42, 0xEF, 0xB1, 0x4A, 0x8E, 0xE2, 0xF2, 0x1A, 0x32,
-        0x2A, 0xCD, 0xC0, 0xA6, 0x46, 0x2C, 0x9A, 0xC2, 0x85, 0x37, 0x91, 0x7F,
-        0x46, 0xA1, 0x93, 0x81, 0xA1, 0x74, 0x66, 0xDF, 0xBA, 0xB3, 0x39, 0x20,
-        0x91, 0x93, 0xFA, 0x1D, 0xA1, 0xA8, 0x85, 0xE7, 0xE4, 0xF9, 0x07, 0xF6,
-        0x10, 0xF6, 0xA8, 0x27, 0x01, 0xB6, 0x7F, 0x12, 0xC3, 0x40, 0xC3, 0xC9,
-        0xE2, 0xB0, 0xAB, 0x49, 0x18, 0x3A, 0x64, 0xB6, 0x59, 0xB7, 0x95, 0xB5,
-        0x96, 0x36, 0xDF, 0x22, 0x69, 0xAA, 0x72, 0x6A, 0x54, 0x4E, 0x27, 0x29,
-        0xA3, 0x0E, 0x97, 0x15
 };
 
-static const unsigned char TA0_RSA_E[] = {
+static const br_rsa_public_key server_pkey = {
-        0x01, 0x00, 0x01
+    (unsigned char *)SERVER_PKEY_RSA_N, sizeof SERVER_PKEY_RSA_N,
+    (unsigned char *)SERVER_PKEY_RSA_E, sizeof SERVER_PKEY_RSA_E,
 };
 
-static const unsigned char TA1_DN[] = {
-        0x30, 0x1C, 0x31, 0x0B, 0x30, 0x09, 0x06, 0x03, 0x55, 0x04, 0x06, 0x13,
-        0x02, 0x43, 0x41, 0x31, 0x0D, 0x30, 0x0B, 0x06, 0x03, 0x55, 0x04, 0x03,
-        0x13, 0x04, 0x52, 0x6F, 0x6F, 0x74
-};
-
-static const unsigned char TA1_EC_Q[] = {
-        0x04, 0x71, 0x74, 0xBA, 0xAB, 0xB9, 0x30, 0x2E, 0x81, 0xD5, 0xE5, 0x57,
-        0xF9, 0xF3, 0x20, 0x68, 0x0C, 0x9C, 0xF9, 0x64, 0xDB, 0xB4, 0x20, 0x0D,
-        0x6D, 0xEA, 0x40, 0xD0, 0x4A, 0x6E, 0x42, 0xFD, 0xB6, 0x9A, 0x68, 0x25,
-        0x44, 0xF6, 0xDF, 0x7B, 0xC4, 0xFC, 0xDE, 0xDD, 0x7B, 0xBB, 0xC5, 0xDB,
-        0x7C, 0x76, 0x3F, 0x41, 0x66, 0x40, 0x6E, 0xDB, 0xA7, 0x87, 0xC2, 0xE5,
-        0xD8, 0xC5, 0xF3, 0x7F, 0x8D
-};
-
-static const br_x509_trust_anchor TAs[2] = {
-        {
-                (unsigned char *)TA0_DN, sizeof TA0_DN,
-                BR_X509_TA_CA,
-                {
-                        BR_KEYTYPE_RSA,
-                        { .rsa = {
-                                (unsigned char *)TA0_RSA_N, sizeof TA0_RSA_N,
-                                (unsigned char *)TA0_RSA_E, sizeof TA0_RSA_E,
-                        } }
-                }
-        },
-        {
-                (unsigned char *)TA1_DN, sizeof TA1_DN,
-                BR_X509_TA_CA,
-                {
-                        BR_KEYTYPE_EC,
-                        { .ec = {
-                                BR_EC_secp256r1,
-                                (unsigned char *)TA1_EC_Q, sizeof TA1_EC_Q,
-                        } }
-                }
-        }
-};
-
-#define TAs_NUM 2
-
 /*
  * Low-level data read callback for the simplified SSL I/O API.
  */
@@ -152,20 +116,27 @@ sock_write(void *ctx, const unsigned char *buf, size_t len)
     }
 }
 
-// In mono mode, BearSSL requires ~16k of buffer
+/*
-// TODO: investigate Maximum Fragment Length (RFC 6066) extension
+ * Buffer to store a record + BearSSL state
+ * We use MONO mode to save 16k of RAM.
+ * This could be even smaller by using max_fragment_len, but
+ * the howsmyssl.com server doesn't seem to support it.
+ */
 static unsigned char bearssl_buffer[BR_SSL_BUFSIZE_MONO];
+
 static br_ssl_client_context sc;
 static br_x509_minimal_context xc;
+static br_x509_knownkey_context kkc;
 static br_sslio_context ioc;
 
 void http_get_task(void *pvParameters)
 {
     int successes = 0, failures = 0;
     while (1) {
-        /* Wait until we can resolve the DNS for the server, as an indication
+        /*
-        our network is probably working...
+         * Wait until we can resolve the DNS for the server, as an indication
-        */
+         * our network is probably working...
+         */
         const struct addrinfo hints = {
             .ai_family = AF_INET,
             .ai_socktype = SOCK_STREAM,
@@ -188,15 +159,45 @@ void http_get_task(void *pvParameters)
         }
 
         printf("Initializing BearSSL... ");
-        br_ssl_client_init_full(&sc, &xc, TAs, TAs_NUM);
+        br_ssl_client_init_full(&sc, &xc, NULL, 0);
+
+        /*
+         * Overwrite the default X509 engine with a much simpler known key one
+         * This sidesteps validation failure in the default engine, as we have no date/time
+         * Instead, the servers key is compared to the hardcoded public key above
+         */
+        br_x509_knownkey_init_rsa(&kkc, &server_pkey);
+        br_ssl_engine_set_x509(&sc.eng, &kkc.vtable);
+
+        /*
+         * Set the I/O buffer to the provided array. We allocated a
+         * buffer large enough for full-duplex behaviour with all
+         * allowed sizes of SSL records, hence we set the last argument
+         * to 1 (which means "split the buffer into separate input and
+         * output areas").
+         */
         br_ssl_engine_set_buffer(&sc.eng, bearssl_buffer, sizeof bearssl_buffer, 0);
-        // Inject some entropy from the ESP hardware RNG
+
-        // This is necessary because we don't support any of the BearSSL methods
+        /*
+         * Inject some entropy from the ESP hardware RNG
+         * This is necessary because we don't support any of the BearSSL methods
+         */
         for (int i = 0; i < 10; i++) {
             int rand = hwrand();
             br_ssl_engine_inject_entropy(&sc.eng, &rand, 4);
         }
+
+        /*
+         * Reset the client context, for a new handshake. We provide the
+         * target host name: it will be used for the SNI extension. The
+         * last parameter is 0: we are not trying to resume a session.
+         */
         br_ssl_client_reset(&sc, WEB_SERVER, 0);
+
+        /*
+         * Initialise the simplified I/O wrapper context, to use our
+         * SSL client context, and the two callbacks for socket I/O.
+         */
         br_sslio_init(&ioc, &sc.eng, sock_read, &fd, sock_write, &fd);
         printf("done.\r\n");
 
@@ -210,16 +211,34 @@ void http_get_task(void *pvParameters)
         }
         printf("Connected\r\n");
 
-        if (br_sslio_write_all(&ioc, GET_REQUEST, strlen(GET_REQUEST)) != BR_ERR_OK)
+        /*
-        {
+         * Note that while the context has, at that point, already
+         * assembled the ClientHello to send, nothing happened on the
+         * network yet. Real I/O will occur only with the next call.
+         *
+         * We write our simple HTTP request. We test the call
+         * for an error (-1), but this is not strictly necessary, since
+         * the error state "sticks": if the context fails for any reason
+         * (e.g. bad server certificate), then it will remain in failed
+         * state and all subsequent calls will return -1 as well.
+         */
+        if (br_sslio_write_all(&ioc, GET_REQUEST, strlen(GET_REQUEST)) != BR_ERR_OK) {
             close(fd);
             freeaddrinfo(res);
             printf("br_sslio_write_all failed: %d\r\n", br_ssl_engine_last_error(&sc.eng));
             failures++;
             continue;
         }
+
+        /*
+         * SSL is a buffered protocol: we make sure that all our request
+         * bytes are sent onto the wire.
+         */
         br_sslio_flush(&ioc);
 
+        /*
+         * Read and print the server response
+         */
         for (;;)
         {
             int rlen;
@@ -237,15 +256,29 @@ void http_get_task(void *pvParameters)
             }
         }
 
+        /*
+         * If reading the response failed for any reason, we detect it here
+         */
+        if (br_ssl_engine_last_error(&sc.eng) != BR_ERR_OK) {
+            close(fd);
+            freeaddrinfo(res);
+            printf("failure, error = %d\r\n", br_ssl_engine_last_error(&sc.eng));
+            failures++;
+            continue;
+        }
+
+        /*
+         * Close the connection and start over after a delay
+         */
         close(fd);
         freeaddrinfo(res);
         successes++;
-        printf("successes = %d failures = %d\r\n", successes, failures);
+        printf("\r\n\r\nsuccesses = %d failures = %d\r\n", successes, failures);
         for(int countdown = 10; countdown >= 0; countdown--) {
-            printf("%d... ", countdown);
+            printf("%d...\n", countdown);
             vTaskDelay(1000 / portTICK_PERIOD_MS);
         }
-        printf("\r\nStarting again!\r\n");
+        printf("Starting again!\r\n\r\n");
     }
 }