rabbitmq-c 发送 nlohmann json

Question

想通过 RabbitMQ-C 发送图像，但图像文件太大。接收方无法检索图像。因此，我将图像转换为 base64，然后将其放入 JSON。

const char *msg;


FILE *image1;
    if (image1 = fopen(path, "rb")) {
        fseek(image1, 0, SEEK_END); //used to move file pointer to a specific position
                                    // if fseek(0 success, return 0; not successful, return non-zero value
                                    //SEEK_END: end of file
        
        length = ftell(image1); //ftell(): used to get total size of file after moving the file pointer at the end of the file
        sprintf(tmp, "size of file: %d  bytes", length);

//convert image to base64
        std::string line;
        std::ifstream myfile;
        myfile.open(path, std::ifstream::binary);
        std::vector<char> data((std::istreambuf_iterator<char>(myfile)), std::istreambuf_iterator<char>() );
        std::string base64_encode(unsigned char const* bytes_to_encode, unsigned int in_len);
        std::string code = base64_encode((unsigned char*)&data[0], (unsigned int)data.size());
        
//convert std::string to const char 
        const char* base64_Image = code.c_str();
        

        
        json j ;
    
        
        j.push_back("Title");
        j.push_back("content");
        j.push_back(base64_Image);
        
        std::string sa = j.dump();

        msg = sa.c_str();       //convert std::string to const char*
        
    }
    else {
        return;
    }

使用 RabbitMQ-C 向接收者发送消息（msg）但失败 [错误指向这里]

是 const char* 不能使用 amqp_cstring_bytes(msg) 转换为 amqp_bytes_t 吗？？

    respo = amqp_basic_publish(conn, 1, amqp_cstring_bytes(exchange), amqp_cstring_bytes(routing_key),0, 0, NULL, amqp_cstring_bytes(msg));

得到这个错误

If there is a handler for this exception, the program may be safely continued.```


Anyone know how to send image as JSON using RabbitMQ-C & C++ ?

Answer 1

amqp_cstring_bytes 需要一个 C 字符串，通常以 NUL 字节结束。您的 PNG 文件几乎可以保证包含一个 NUL 字节，这就解释了为什么您的消息在中途被截断了。

至于您粘贴中的代码：sa.c_str() 返回的指针仅在sa 处于活动状态且未修改时才有效。一旦退出包含sa 定义的块，变量就死了。

相反，使用amqp_bytes_alloc 获取适当大小的缓冲区并返回：

amqp_bytes_t bytes = amqp_bytes_malloc(sa.length());
strncpy((char *)bytes.bytes, sa.c_str(), sa.length());

然后将bytes 对象传递给amqp_basic_publish。完成后别忘了ampqp_bytes_free。