What are the Line-Based Operations in Asio?

Internet Protocols

The Internet Protocol (IP) is a set of rules which are used for routing packets across various networks. It is also used for providing addresses to the packets of data so that they can be identified correctly. Examples of IP are- HTTP (Hyper Text Transfer Protocol), FTP (File Transfer Protocol), TCP (Transmission Control Protocol), etc. 

Whenever we use the internet to visit any website or communicate with another device, then these protocols are used to secure the data. Upon the arrival of the packets to their destination, they are treated in different ways according to the transport protocol, which is used in combination with IP.

Line-Based Operations

Line-Based operations are the actions that are performed on line-based protocols. Let’s first see what line-based protocols are:

💠 The most used internet protocols like HTTP, FTP, and SMTP are line-based protocols. 

💠 They are called line-based because they are delimited by the character sequence “\r\n.” 

💠 Simply, they use whitespace and syntax to format the elements of the fields like timestamp, tag set, single data point, fieldset, etc. 

💠 Asio consists of the functions read_until() and async_read_until() to implement the line-based protocols and other protocols using delimiters.

Let’s look at the functions used to implement the line-based protocols in detail:

read_until

The read_until() consists of operations that are used to read data into a streambuf or a dynamic buffer sequence until it matches a regular expression or contains delimiters or a function object matches. The streambuf is an input/output buffer that is used along with I/O streams.

The requirements for this function are the header file asio/read_until.hpp and the convenience header asio.hpp.

async_read_until

The async_read_until() consists of an asynchronous operation that is used to perform the same operation as read_until(), that is, to read data into a streambuf or a dynamic buffer sequence until it matches a regular expression or contains delimiters or a function object matches.

The requirements for this function are also the same, that is, the header file asio/read_until.hpp and the convenience header asio.hpp. The streambuf is used in both read_until and async_read_until. Let’s discuss in detail what streambuf refers to.

streambuf

The streambuf is a typedef to use basic_streambuf, which is an automatically resizable buffer class. It is used to match the streambuf’s output and input sequences with the character arrays. These character arrays are the basic_streambuf object which can be directly accessed by the array elements and can be used effectively with I/O operations. The following is the syntax:

typedef basic_streambuf streambuf;

Member Functions

The following are its member functions with their syntax and their description.

is_match_condition

The is_match_condition type trait is used to find if the type can be used as a match condition function with read_until and async_read_until. We need to include the header asio.read_until.hpp to use the same.

We can create the is_match_condition by writing the following statement.

template<
    typename T>
struct is_match_condition

The following is its data member, along with the syntax.

Let’s see an example to implement these.

Implementation of Line-Based Operation

We need to use Socket programming in order to use the function read_until. We have written both server-side and client-side codes for the same. Let’s understand both.

Server-Side Implementation

First, we need to accept the request coming from the client for a new connection, so we have used tcp::acceptor for the same. Now we need a streambuf class that represents a buffer of data to read data as a stream. We are storing the data in a string and displaying it. After reading, we performed a write operation to send the response to the client.

Code 

#include <iostream>
#include <asio.hpp>

using asio::ip::tcp;

int main() {
    asio::io_service io_service;
    // Listen for new connection
    tcp::acceptor acceptor_(io_service, tcp::endpoint(tcp::v4(), 8080));
    //socket creation
    tcp::socket socket_(io_service);
    // Waiting for connection
    acceptor_.accept(socket_);

    // Read operation
    asio::streambuf buf;
    asio::read_until(socket_, buf, "\n");
    std::string message = asio::buffer_cast<const char*>(buf.data());

    std::cout << message << std::endl;

    // Write operation
    const std::string msg = "Hello Ninjas! This message is sent from Server!\n";
    asio::write(socket_, asio::buffer(msg));
    std::cout << "Server has sent a message to the Client!" << std::endl;
    return 0;
}

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Output

Client-Side Implementation

In order to connect to the server, we need a socket object. The connection request is then made to the server. We have sent a message to the server using the write operation. In case of an error, we will print the error message. The streambuf is again used to read the response from the server. If there is no error, we will print the message received.

Code 

#include <iostream>
#include <asio.hpp>

using asio::ip::tcp;

int main() {
    asio::io_service io_service;
    tcp::socket socket(io_service);

    // Connect the socket
    socket.connect(tcp::endpoint(asio::ip::address::from_string("127.0.0.1"), 8080));
   
    const std::string msg = "Hello Ninjas! This message is from Client!\n";
    asio::error_code error;
    asio::write(socket, asio::buffer(msg), error);
    if (!error) {
        std::cout << "Client has sent a message to Server!" << std::endl;
    }
    else {
        std::cout << "send failed: " << error.message() << std::endl;
    }

    // Getting response from server
    asio::streambuf receive_buffer;
    asio::read(socket, receive_buffer, asio::transfer_all(), error);
    if (error && error != asio::error::eof) {
        std::cout << "receive failed: " << error.message() << std::endl;
    }
    else {
        const char* data = asio::buffer_cast<const char*>(receive_buffer.data());
        std::cout << data << std::endl;
    }

    return 0;
}

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Output

Also see, Application of Oops

Frequently Asked Questions

What is Asio?

Asio is a cross-platform, open-source C++ library. It is an underrated C++ library designed for input, output, and networking purposes. Asio stands for asynchronous input-output. Christopher M. Kohlhoff developed Asio in 2003.

How are asynchronous operations different from synchronous operations?

The operations and programs in asynchronous operations can run in parallel, while the programs in synchronous operations will run one at a time. The asynchronous operations are non-blocking, while the synchronous operation is blocking.

How do Internet Protocols protect data on the network?

The internet protocols help to determine the correct destination and deliver the packets accordingly. It checks the data with the use of a checksum mechanism. A packet is lost or undelivered if the destination Ip is not alive. 

What is the use of the Asio library?

Asio helps in doing network programming using C++ language. It allows the processing of data asynchronously by providing asynchronous I/O models.

Conclusion

This article was about Asio, which is a C++ library for networking and communication. We have discussed line-based operations in this article. We have also covered some important functions like read_until, async_read_until, etc., and class streambuf and its member functions. 

You can check out our other articles if you want to dive deep into other concepts related to Asio -

👉 Asio Timers 

👉 SSL Support in Asio

👉 TCP, UDP, and ICMP Networking
 

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