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TDMQ for MQTT

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ドキュメントTDMQ for MQTT

C SDK

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最終更新日: 2026-04-01 16:37:51

Feature Overview

Eclipse Paho C and Eclipse Paho Embedded C are C-language client libraries (MQTT C clients) under the Eclipse Paho project, each being a full-featured MQTT client written in ANSI C.
Eclipse Paho Embedded C can be used on desktop operating systems, but is mainly for embedded environments such as Mbed, Arduino, and FreeRTOS.
It provides two API types, synchronous and asynchronous, starting with MQTTClient and MQTTAsync respectively:
Synchronous APIs aim to be easier and more useful. Specific calls will block until the operation completes, making programming simpler.
The asynchronous API contains only one blocking call, API-waitForCompletion, which performs result notification via callback and is more suitable for non-main thread environments.

Cloud Resource Preparation

Please refer to the operation step of creating a resource to complete cloud resource preparation.

Environment Preparation

Note:
Paho MQTT C SDK requires CMake version 3.5+.

Example of Installing the Paho MQTT C SDK

 cd paho.mqtt.c && cmake .
 make && make install
 echo '/usr/local/lib64' > /etc/ld.so.conf.d/paho.conf
 echo '/usr/local/lib' >> /etc/ld.so.conf.d/paho.conf
 ldconfig

Sample Code

Copy the content below to /root/mqtt-example.c
#include "stdio.h"
#include "stdlib.h"
#include "string.h"

#include "MQTTClient.h"

#define ADDRESS     "tcp://mqtt-********.mqtt.tencenttdmq.com:1883"
#define CLIENTID    "sample_client"
#define TOPIC       "testtopic/1"
#define PAYLOAD     "Hello World!"
#define QOS         1
#define TIMEOUT     10000L
#define USERNAME    "your-username"
#define PASSWORD    "your-password"

int main(int argc, char* argv[])
{
    MQTTClient client;
    MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer;
    MQTTClient_message pubmsg = MQTTClient_message_initializer;
    MQTTClient_deliveryToken token;
    int rc;

    MQTTClient_create(&client, ADDRESS, CLIENTID,
        MQTTCLIENT_PERSISTENCE_NONE, NULL);
  
    // MQTT connection parameters
    conn_opts.keepAliveInterval = 20;
    conn_opts.cleansession = 1;
    conn_opts.MQTTVersion = MQTTVERSION_3_1_1;
    conn_opts.username = USERNAME;
    conn_opts.password = PASSWORD;

    if ((rc = MQTTClient_connect(client, &conn_opts)) != MQTTCLIENT_SUCCESS)
    {
        printf("Failed to connect, return code %d\\n", rc);
        exit(-1);
    }
  
    // Publish a message.
    pubmsg.payload = PAYLOAD;
    pubmsg.payloadlen = strlen(PAYLOAD);
    pubmsg.qos = QOS;
    pubmsg.retained = 0;
    MQTTClient_publishMessage(client, TOPIC, &pubmsg, &token);
    printf("Waiting for up to %d seconds for publication of %s\\n"
            "on topic %s for client with ClientID: %s\\n",
            (int)(TIMEOUT/1000), PAYLOAD, TOPIC, CLIENTID);
    rc = MQTTClient_waitForCompletion(client, token, TIMEOUT);
    printf("Message with delivery token %d delivered\\n", token);
  
    // Disconnect.
    MQTTClient_disconnect(client, 10000);
    MQTTClient_destroy(&client);
    return rc;
}

Parameter Description

Parameter
Description
ADDRESS
Broker connection address, copied from the Basic Information > Access Information section of the target cluster in the console, as shown below. Format: mqtt-xxx-gz.mqtt.qcloud.tencenttdmq.com:1883.

CLIENTID
Client ID, obtained from the Client Management page on the cluster details page in the console.
USERNAME
User name, obtained on the Authentication Management page in the console.
PASSWORD
Password, obtained on the Authentication Management page in the console.

Compilation Example

cd /root
gcc mqtt-example.c -lpaho-mqtt3c -o mqtt-example

Paho C MQTT 5.0 Support 

Paho C currently has complete support for MQTT 5.0.



Example of One-Device-One-Certificate

Scenario Introduction

For high-value devices with high security requirements, "one-device-one-certificate" is recommended for client authentication, which is an enhancement of mutual authentication (mTLS). On the basis of mutual authentication, the cloud performs management of the status of client certificates, including activating, deactivating, and revoking operations.


Generating a Certificate

Generating a CA Certificate

ECDSA
RSA
openssl ecparam -genkey -name prime256v1 -out CA.key
openssl req -new -x509 -key CA.key -sha256 -subj "/C=CN/ST=ZheJiang/L=HangZhou/O=TencentCloud/CN=MQTT-CA" -days 3650 -out CA.crt
openssl genrsa -out CA.key 4096
openssl req -new -x509 -key CA.key -sha256 -subj "/C=CN/ST=ZheJiang/L=HangZhou/O=TencentCloud/CN=MQTT-CA" -days 3650 -out CA.crt


Issuing a Server Certificate

Create a configuration file server.conf
[req]
distinguished_name = req_distinguished_name
req_extensions = v3_req
prompt = no

[req_distinguished_name]
C = CN
ST = ZheJiang
L = HangZhou
O = Example
CN = mqtt.example.com

[v3_req]
basicConstraints = critical, CA:FALSE
# Common Key Usage Combinations
#   TLS Server: keyUsage=digitalSignature,keyEncipherment + extendedKeyUsage=serverAuth
#   TLS Client: keyUsage=digitalSignature + extendedKeyUsage=clientAuth
#   Code Signing: keyUsage=digitalSignature + extendedKeyUsage=codeSigning
keyUsage = critical, digitalSignature, keyEncipherment
extendedKeyUsage = serverAuth
subjectAltName = @alt_names

[alt_names]
DNS.1 = mqtt.example.com
DNS.2 = www.example.com
DNS.3 = api.example.com
DNS.4 = *.example.com
IP.1 = 192.168.1.100
IP.2 = 10.0.0.50

ECDSA
RSA
openssl ecparam -genkey -name prime256v1 -out server.key
openssl req -new -key server.key -out server.csr -config server.conf
openssl x509 -req -in server.csr -CA CA.crt -CAkey CA.key -CAcreateserial -out server.crt -days 365 -sha256 -extensions v3_req -extfile server.conf
openssl genrsa -out server.key 4096
openssl req -new -key server.key -out server.csr -config server.conf
openssl x509 -req -in server.csr -CA CA.crt -CAkey CA.key -CAcreateserial -out server.crt -days 365 -sha256 -extensions v3_req -extfile server.conf

Verifying the Server Certificate

openssl x509 -in server.crt -text -noout
openssl verify -CAfile CA.crt server.crt
openssl x509 -in server.crt -text -noout | grep -A 10 "Subject Alternative Name"
Create a complete server certificate chain file.
cat server.crt > server.chain.crt
cat CA.crt >> server.chain.crt

Issuing a Client Certificate

Create a configuration file client.conf.
[v3_req]
basicConstraints = critical, CA:FALSE
keyUsage = critical, digitalSignature
extendedKeyUsage = clientAuth

ECDSA
RSA
openssl ecparam -genkey -name prime256v1 -out client.key
openssl req -new -key client.key -out client.csr -subj "/C=CN/ST=ZheJiang/L=HangZhou/O=IoV/CN=SN0001"
openssl x509 -req -in client.csr -CA CA.crt -CAkey CA.key -CAcreateserial -out client.crt -days 365 -sha256 -extfile client.conf -extensions v3_req
openssl genrsa -out client.key 4096
openssl req -new -key client.key -out client.csr -subj "/C=CN/ST=ZheJiang/L=HangZhou/O=IoV/CN=SN0001"
openssl x509 -req -in client.csr -CA CA.crt -CAkey CA.key -CAcreateserial -out client.crt -days 365 -sha256 -extfile client.conf -extensions v3_req









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