How to create named pipe (mkfifo) in Android?

Introduction

Named pipes, also known as FIFO (First In, First Out) pipes, are a mechanism for inter-process communication (IPC) in Unix-like operating systems. They allow processes to communicate by writing data to one end of the pipe and reading it from the other end. This article explains how to create and use named pipes in Android.

Understanding Named Pipes

What are Named Pipes?

Named pipes are special files that behave like pipes, but instead of being associated with specific processes, they are identified by a unique name in the filesystem.

Advantages of Named Pipes

• Unidirectional or Bidirectional Communication: They can be used for unidirectional communication (one-way) or bidirectional communication (two-way).
• Asynchronous Communication: Processes can read and write to the pipe independently, without waiting for each other.
• Easy to Use: They are relatively easy to create and use compared to other IPC mechanisms like sockets.

Creating a Named Pipe in Android

Unfortunately, Android’s standard Linux environment does not include the mkfifo command. Instead, you need to use a more powerful method of creating a named pipe directly within your application code.

Using Java (Android):

import java.io.File;
import java.io.IOException;
import android.util.Log;

public class NamedPipeExample {

    public static void main(String[] args) {
        try {
            // Create a directory for the named pipe
            File pipeDir = new File("/data/local/tmp");
            pipeDir.mkdirs();

            // Define the named pipe path
            String pipePath = "/data/local/tmp/my_pipe";
            File pipeFile = new File(pipePath);

            // Create the named pipe (if it doesn't already exist)
            if (!pipeFile.exists()) {
                if (pipeFile.createNewFile()) {
                    Log.i("NamedPipeExample", "Pipe created successfully!");
                } else {
                    Log.e("NamedPipeExample", "Failed to create pipe");
                }
            } else {
                Log.i("NamedPipeExample", "Pipe already exists.");
            }

        } catch (IOException e) {
            Log.e("NamedPipeExample", "Error creating named pipe: " + e.getMessage());
        }
    }
}

Explanation:

• File pipeDir = new File("/data/local/tmp");: Create a File object representing the directory where the named pipe will be created. The /data/local/tmp directory is a common location for temporary files in Android.
• pipeDir.mkdirs();: Create the directory if it doesn’t already exist.
• String pipePath = "/data/local/tmp/my_pipe";: Define the name and location of your named pipe file.
• if (!pipeFile.exists()) { ... }: Check if the named pipe file already exists. If it doesn’t, create it using pipeFile.createNewFile().
• if (pipeFile.createNewFile()) { ... }: Create the named pipe. Note that in Android, named pipes need to be created with read/write permissions for the application to work.
• Log.i("NamedPipeExample", "Pipe created successfully!");: Log a success message. You can use this for debugging.

Using the Named Pipe

Once the named pipe is created, you can use it for communication between processes.

Reading and Writing Data to the Pipe:

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.IOException;

public class PipeReadWriteExample {

    public static void main(String[] args) {
        try {
            // Define the pipe path
            String pipePath = "/data/local/tmp/my_pipe";

            // Open the pipe for writing (server side)
            BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(pipePath)));
            writer.write("Hello from the server!");
            writer.flush();
            writer.close();

            // Open the pipe for reading (client side)
            BufferedReader reader = new BufferedReader(new InputStreamReader(new FileInputStream(pipePath)));
            String message = reader.readLine();
            System.out.println("Received from the pipe: " + message);
            reader.close();

        } catch (IOException e) {
            System.out.println("Error reading/writing to the pipe: " + e.getMessage());
        }
    }
}

Explanation:

• BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(pipePath)));: Open the pipe for writing using a BufferedWriter. This side of the pipe will be referred to as the ‘server’ in this example.
• writer.write("Hello from the server!");: Write data to the pipe.
• writer.flush(); writer.close();: Flush the buffer and close the writer.
• BufferedReader reader = new BufferedReader(new InputStreamReader(new FileInputStream(pipePath)));: Open the pipe for reading using a BufferedReader. This side of the pipe will be referred to as the ‘client’ in this example.
• String message = reader.readLine();: Read data from the pipe.
• System.out.println("Received from the pipe: " + message);: Print the data read from the pipe.
• reader.close();: Close the reader.

Key Points

• Permissions: You will need to ensure that the process creating the named pipe has write permissions in the directory where the pipe is located.
• Concurrency: Multiple processes can read or write to a named pipe concurrently, but you need to handle synchronization to avoid race conditions.
• Cleanup: Remember to remove the named pipe when it is no longer needed using File.delete().

Conclusion

This article provided a comprehensive explanation of how to create and use named pipes in Android. While the mkfifo command is not available directly, you can create them through Java code. Named pipes offer a robust and efficient way for inter-process communication, making them valuable for developing complex Android applications.