Question

我正在尝试使用libmosquitto（在C中）连接到SSL / TLS中的MQTT代理。我确信它正在服务器端工作，因为我在命令行中使用mosquitto_sub（或mosquitto_pub）并使用我在代码中使用的相同证书成功连接到borker。

当我尝试使用我的C程序进行连接时，我总是会收到以下错误：“错误：无法创建TLS上下文。”

我在Linux上使用libmosquitto 1.4.8。这是我正在使用的代码：

#include <mosquitto.h>

static struct SomeStruct *data = NULL;
// The variable mosq is included in the struct
// The struct has been created somewhere else

void foo(void)
{
    // I usually check the return values but removed
    // it to make the code easier to read
    mosquitto_lib_init();
    data->mosq = mosquitto_new("foobar", true, data);

    // Connect the callbacks

    mosquitto_username_pw_set(data->mosq, "user", "pass");
    mosquitto_tls_set(data->mosq, "/path/to/ca/file.crt,
                        NULL, NULL, NULL, NULL);
    mosquitto_tls_insecure_set(data->mosq, 1)
    mosquitto_tls_opts_set(data->mosq,
                            1,    // also tried 0
                            NULL, // also tried "tlsv1.2"
                            NULL);

    // All the return values are correct up to here

    mosquitto_connect(data->mosq, "mqtt.example.com", 8883, 30); // Fails
    // Logs : Error: Unable to create TLS context.
    // A TLS error occurred.
}

有谁知道这可能是什么问题？

干杯，

安托

编辑：我忘了添加我没有使用mosquitto的主循环，因为我使用的另一个库已经有一个我需要非常有限的线程数。因此，每当文件描述符发生变化时，我都会调用mosquitto_loop()。

Answer 1

只有在SSL_CTX_new（）失败时才会出现此问题。如果mosquitto_sub在同一台机器上工作正常，这似乎不太可能。尝试＆＃34; tlsv1＆＃34;，＆＃34; tlsv1.1＆＃34;作为tls_opts_set的其他选项。您还可以尝试修补mosquitto客户端库以获取有关openssl不满意原因的更多信息：

diff --git a/lib/net_mosq.c b/lib/net_mosq.c
index 08f24d9..d4c57fd 100644
--- a/lib/net_mosq.c
+++ b/lib/net_mosq.c
@@ -409,6 +409,8 @@ int _mosquitto_socket_connect(struct mosquitto *mosq, const char *host, uint16_t
 #ifdef WITH_TLS
        int ret;
        BIO *bio;
+       int e;
+       char ebuf[256];
 #endif

        if(!mosq || !host || !port) return MOSQ_ERR_INVAL;
@@ -441,6 +443,11 @@ int _mosquitto_socket_connect(struct mosquitto *mosq, const char *host, uint16_t
 #endif
                if(!mosq->ssl_ctx){
                        _mosquitto_log_printf(mosq, MOSQ_LOG_ERR, "Error: Unable to create TLS context.");
+                       e = ERR_get_error();
+                       while(e){
+                               _mosquitto_log_printf(mosq, MOSQ_LOG_ERR, "OpenSSL Error: %s", ERR_error_string(e, ebuf));
+                               e = ERR_get_error();
+                       }
                        COMPAT_CLOSE(sock);
                        return MOSQ_ERR_TLS;
                }

重现问题的示例代码：

#include <stdio.h>

#include <mosquitto.h>

void my_log_callback(struct mosquitto *mosq, void *obj, int level, const char *str)
{
    printf("LOG: %s\n", str);
}


int main(int argc, char *argv[])
{
    struct mosquitto *mosq = NULL;
    int rc;

    printf("Calling connect before lib init, this should fail.\n");
    mosq = mosquitto_new(NULL, true, NULL);
    mosquitto_log_callback_set(mosq, my_log_callback);
    mosquitto_tls_set(mosq, "mosquitto.org.crt", NULL, NULL, NULL, NULL);
    rc = mosquitto_connect(mosq, "test.mosquitto.org", 8883, 60);
    printf("connect returned %d\n", rc);
    mosquitto_destroy(mosq);


    mosquitto_lib_init();


    printf("Calling connect after lib init, this should be fine.\n");
    mosq = mosquitto_new(NULL, true, NULL);
    mosquitto_log_callback_set(mosq, my_log_callback);
    mosquitto_tls_set(mosq, "mosquitto.org.crt", NULL, NULL, NULL, NULL);
    rc = mosquitto_connect(mosq, "test.mosquitto.org", 8883, 60);
    printf("connect returned %d\n", rc);
    mosquitto_destroy(mosq);


    mosquitto_lib_cleanup();


    printf("Calling connect after lib cleanup, this should fail.\n");
    mosq = mosquitto_new(NULL, true, NULL);
    mosquitto_log_callback_set(mosq, my_log_callback);
    mosquitto_tls_set(mosq, "mosquitto.org.crt", NULL, NULL, NULL, NULL);
    rc = mosquitto_connect(mosq, "test.mosquitto.org", 8883, 60);
    printf("connect returned %d\n", rc);
    mosquitto_destroy(mosq);

    return 0;
}

这会产生输出：

Calling connect before lib init, this should fail.
LOG: Error: Unable to create TLS context.
LOG: OpenSSL Error: error:140A90A1:lib(20):func(169):reason(161)
connect returned 8
Calling connect after lib init, this should be fine.
LOG: Client mosq/7v?>w@YfTKk\U=;sO] sending CONNECT
connect returned 0
Calling connect after lib cleanup, this should fail.
LOG: Error: Unable to create TLS context.
LOG: OpenSSL Error: error:140A90F1:lib(20):func(169):reason(241)
connect returned 8

最终的OpenSSL错误与您的错误相同，因此您需要检查是否已取消初始化openssl。这是mosquitto_lib_cleanup（）所做的事情，但它可能是你的代码完全独立于libmosquitto的东西。

C中的mosquitto和SSL / TLS

1 个答案: