Hitesh Singh.N

PES1UG21CS233

Multithreaded TCP Server

HP Assignement: PThreads

Build a multi-threaded server in C++, make use of PThreads for parallel programming.

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Requirements

• g++
• GNU Make (4.2.1 or higher)
• ncat (7.80 or higher)

Protocol Definition

The protocol consists of a series of messages sent between the client and the server. Each message is a single line of text, terminated by a newline character. The client and server will exchange messages until the client sends an END message, at which point the server will close the connection.

The server will respond to each message with a single line of text, terminated by a newline character. The server will not send a response until it has received a complete message from the client.

The client will send one of the following messages to the server:

• READ <key> - Read the value of the given key from the database.
• WRITE <key>:<value> - Write the given key-value pair to the database.
• COUNT - Count the number of key-value pairs in the database.
• DELETE <key> - Delete the given key from the database.
• END - End the connection.

The database is a simple key-value store. Each key is a string, and each value is an string. The database is initialized to an empty state when the server starts. It may be implemented as a simple std::map<std::string, std::string> KV_DATASTORE, but the specifics are up to you.

Sample Input & Output

Write

Following is an example tests/inputs/WRITE.txt to write a key value pair to the database.

nc localhost 8080 < tests/inputs/WRITE.txt  # FIN

WRITE
Hello
:1234
END

Read

Following is an example tests/inputs/READ.txt to read a key value pair from the database.

nc localhost 8080 < tests/inputs/READ.txt  # NULL if does not exist

READ
Hello
END

Count

Following is an example tests/inputs/COUNT.txt where the client only sends the COUNT message to list the number of KV pairs in the database.

nc localhost 8080 < tests/inputs/COUNT.txt  # 0,1, etc.

COUNT
END

Delete

Following is an example tests/inputs/DELETE.txt where the client only sends the DELETE message to list the number of KV pairs in the database.

nc localhost 8080 < tests/inputs/DELETE.txt  # FIN if key present, NULL otherwise

DELETE
Hello
END

All Commands

Following is an example tests/inputs/ALL.txt. Consider we are starting from an empty database and this is the first client connecting to the server.

nc localhost 8080 < tests/inputs/ALL.txt  # 0,1, etc.

DELETE
Hello  # 1. Delete the Key Hello, (returns FIN because it was not present)
COUNT  # 2. Count the number of KV pairs (returns 0)
READ
Hello  # 3. Read the value of the Key Hello
WRITE
Hello
:1234  # 4. Write the KV pair Hello:1234
READ
Hello  # 5. Read the value of the Key Hello, (returns 1234)
COUNT  # 6. Count the number of KV pairs (returns 1)
END    # 7. End the connection

Anti-Example

Following is an anti-example tests/inputs/BROKEN.txt. Here, the client has forgotten to send the END message. The server will wait forever for the END message, and the client will wait forever for the server's response to the COUNT message.

DELETE
Hello  # 1. Delete the Key Hello, (returns FIN because it was not present)
COUNT  # 2. Count the number of KV pairs (returns 0)
READ
Hello  # 3. Read the value of the Key Hello; the server will wait forever for the END message

Running

To run serial version :

make serial
./bin/serial_server 8080

To run parallel version :

make parallel
./bin/parallel_server 8080

Testing

To connect to the server

ncat localhost 8080 < tests/inputs/ALL.txt

Run the test cases

make test_serial
make test_parallel

# To run with logging enabled
ENABLE_LOGGING=1 make test_serial
ENABLE_LOGGING=1 make test_parallel

FAQ

1. Port already in use. This may happen if the server was not closed properly and the port is still in use.

   Solution: Kill the process using the port

   sudo lsof -i :8080
   kill -9 <PID>

2. nc: HTTP/1.1 400 Bad Request Connection: close. This may happen if the server is not running or netcat is pointed at the wrong port.

    Solution: Start the server and make sure the port is correct.
    ```bash
    ./bin/serial_server 8080
    ```