diff --git a/src/convert.rs b/src/convert.rs
index 715f14a..c535b17 100644
--- a/src/convert.rs
+++ b/src/convert.rs
@@ -11,12 +11,61 @@ impl Convert {
         }
     }
 
-    pub fn to_string(buf: &[u8]) -> Result<(String, usize), Box<dyn Error>> {
-        let zero_index = match buf[2..].iter().position(|&b| b == 0x00) {
-            Some(index) => index,
+    pub fn to_string(buf: &[u8], start: usize) -> Result<(String, usize), Box<dyn Error>> {
+        match buf[start..].iter().position(|&b| b == 0x00) {
+            Some(index) => Ok((
+                String::from_utf8(buf[start..start + index].to_vec())?,
+                index + start,
+            )),
             None => return Err("invalid string".into()),
-        };
-
-        Ok((String::from_utf8(buf[2..zero_index].to_vec())?, zero_index))
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn converts_to_u16() {
+        assert_eq!(Convert::to_u16(&[0x01, 0x02]).unwrap(), 0x0102);
+        assert_eq!(Convert::to_u16(&[0x00, 0x02]).unwrap(), 0x0002);
+        assert_eq!(Convert::to_u16(&[0xfe, 0xdc, 0xba]).unwrap(), 0xfedc);
+    }
+
+    #[test]
+    fn returns_error_on_short_array() {
+        assert!(Convert::to_u16(&[0x01]).is_err());
+        assert!(Convert::to_u16(&[]).is_err());
+    }
+
+    #[test]
+    fn converts_to_string() {
+        let (result, index) = Convert::to_string(b"hello world\0", 0).unwrap();
+        assert_eq!(result, "hello world");
+        assert_eq!(index, 11);
+
+        let (result, index) = Convert::to_string(b"hello\0world", 0).unwrap();
+        assert_eq!(result, "hello");
+        assert_eq!(index, 5);
+
+        let (result, index) = Convert::to_string(b"\0hello world", 0).unwrap();
+        assert_eq!(result, "");
+        assert_eq!(index, 0);
+    }
+
+    #[test]
+    fn converts_to_string_with_index() {
+        let (result, index) = Convert::to_string(b"hello\0world\0", 0).unwrap();
+        assert_eq!(result, "hello");
+        assert_eq!(index, 5);
+
+        let (result, index) = Convert::to_string(b"hello\0world\0", 5).unwrap();
+        assert_eq!(result, "");
+        assert_eq!(index, 5);
+
+        let (result, index) = Convert::to_string(b"hello\0world\0", 6).unwrap();
+        assert_eq!(result, "world");
+        assert_eq!(index, 11);
     }
 }
diff --git a/src/lib.rs b/src/lib.rs
index b3f8e16..ec561cf 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,8 +1,12 @@
 mod config;
 mod convert;
+mod message;
 mod packet;
 mod server;
+mod worker;
 
 pub use config::Config;
 pub use convert::Convert;
+pub use message::Message;
 pub use server::Server;
+pub use worker::Worker;
diff --git a/src/message.rs b/src/message.rs
new file mode 100644
index 0000000..85ae55d
--- /dev/null
+++ b/src/message.rs
@@ -0,0 +1,65 @@
+use std::{
+    error::Error,
+    net::{SocketAddr, UdpSocket},
+};
+
+use crate::packet::{ErrorCode, Opcode, Option};
+
+pub struct Message;
+
+impl Message {
+    pub fn send_data(socket: &UdpSocket, data: &[u8]) -> Result<(), Box<dyn Error>> {
+        let buf = [&[0x00, Opcode::Data as u8], data].concat();
+
+        socket.send(&buf)?;
+
+        Ok(())
+    }
+
+    pub fn send_ack(socket: &UdpSocket, block: u16) -> Result<(), Box<dyn Error>> {
+        let buf = [&[0x00, Opcode::Ack as u8], &block.to_be_bytes()[..]].concat();
+
+        socket.send(&buf)?;
+
+        Ok(())
+    }
+
+    pub fn send_error(
+        socket: &UdpSocket,
+        code: ErrorCode,
+        msg: &str,
+    ) -> Result<(), Box<dyn Error>> {
+        socket.send(&get_error_buf(code, msg))?;
+
+        Ok(())
+    }
+
+    pub fn send_error_to(socket: &UdpSocket, to: &SocketAddr, code: ErrorCode, msg: &str) {
+        if socket.send_to(&get_error_buf(code, msg), to).is_err() {
+            eprintln!("could not send an error message");
+        }
+    }
+
+    pub fn send_oack_to(
+        socket: &UdpSocket,
+        to: &SocketAddr,
+        options: Vec<Option>,
+    ) -> Result<(), Box<dyn Error>> {
+        todo!();
+
+        let buf = [];
+
+        socket.send_to(&buf, to)?;
+
+        Ok(())
+    }
+}
+
+fn get_error_buf(code: ErrorCode, msg: &str) -> Vec<u8> {
+    [
+        &[0x00, Opcode::Error as u8, 0x00, code as u8],
+        msg.as_bytes(),
+        &[0x00],
+    ]
+    .concat()
+}
diff --git a/src/packet.rs b/src/packet.rs
index 7085710..6b32b8f 100644
--- a/src/packet.rs
+++ b/src/packet.rs
@@ -97,14 +97,14 @@ fn parse_rq(buf: &[u8], opcode: Opcode) -> Result<Packet, Box<dyn Error>> {
     let mode: String;
     let mut zero_index: usize;
 
-    (filename, zero_index) = Convert::to_string(&buf[2..])?;
-    (mode, zero_index) = Convert::to_string(&buf[zero_index + 1..])?;
+    (filename, zero_index) = Convert::to_string(buf, 2)?;
+    (mode, zero_index) = Convert::to_string(buf, zero_index + 1)?;
 
     let mut value: String;
     let mut option;
     while zero_index < buf.len() - 1 {
-        (option, zero_index) = Convert::to_string(&buf[zero_index + 1..])?;
-        (value, zero_index) = Convert::to_string(&buf[zero_index + 1..])?;
+        (option, zero_index) = Convert::to_string(buf, zero_index + 1)?;
+        (value, zero_index) = Convert::to_string(buf, zero_index + 1)?;
         options.push(Option { option, value });
     }
 
@@ -136,6 +136,6 @@ fn parse_ack(buf: &[u8]) -> Result<Packet, Box<dyn Error>> {
 
 fn parse_error(buf: &[u8]) -> Result<Packet, Box<dyn Error>> {
     let code = ErrorCode::from_u16(Convert::to_u16(&buf[2..])?)?;
-    let (msg, _) = Convert::to_string(&buf[4..])?;
+    let (msg, _) = Convert::to_string(buf, 4)?;
     Ok(Packet::Error { code, msg })
 }
diff --git a/src/server.rs b/src/server.rs
index 58b5f0d..a1cb84d 100644
--- a/src/server.rs
+++ b/src/server.rs
@@ -1,19 +1,24 @@
-use crate::packet::{ErrorCode, Opcode, Packet};
-use crate::Config;
+use crate::packet::{ErrorCode, Packet};
+use crate::{Config, Message, Worker};
 use std::error::Error;
 use std::net::{SocketAddr, UdpSocket};
+use std::path::{Path, PathBuf};
 
 const MAX_REQUEST_PACKET_SIZE: usize = 512;
 
 pub struct Server {
     socket: UdpSocket,
+    directory: PathBuf,
 }
 
 impl Server {
     pub fn new(config: &Config) -> Result<Server, Box<dyn Error>> {
         let socket = UdpSocket::bind(SocketAddr::from((config.ip_address, config.port)))?;
 
-        let server = Server { socket };
+        let server = Server {
+            socket,
+            directory: config.directory.clone(),
+        };
 
         Ok(server)
     }
@@ -23,32 +28,117 @@ impl Server {
             let mut buf = [0; MAX_REQUEST_PACKET_SIZE];
             if let Ok((number_of_bytes, from)) = self.socket.recv_from(&mut buf) {
                 if let Ok(packet) = Packet::deserialize(&buf[..number_of_bytes]) {
-                    match packet {
-                        Packet::Rrq {
-                            filename,
-                            mode,
-                            options,
-                        } => todo!(),
-                        Packet::Wrq {
-                            filename,
-                            mode,
-                            options,
-                        } => todo!(),
-                        _ => self.send_error_msg(from),
+                    match &packet {
+                        Packet::Rrq { filename, .. } => {
+                            match self.check_file_exists(&Path::new(&filename)) {
+                                ErrorCode::FileNotFound => {
+                                    eprintln!("requested file does not exist");
+                                    Message::send_error_to(
+                                        &self.socket,
+                                        &from,
+                                        ErrorCode::FileNotFound,
+                                        "requested file does not exist",
+                                    );
+                                }
+                                ErrorCode::AccessViolation => {
+                                    eprintln!("requested file is not in the directory");
+                                    Message::send_error_to(
+                                        &self.socket,
+                                        &from,
+                                        ErrorCode::AccessViolation,
+                                        "requested file is not in the directory",
+                                    );
+                                }
+                                ErrorCode::FileExists => self
+                                    .handle_rrq(&packet, from)
+                                    .unwrap_or_else(|_| eprintln!("could not handle read request")),
+                                _ => {}
+                            }
+                        }
+                        Packet::Wrq { filename, .. } => {
+                            match self.check_file_exists(&Path::new(&filename)) {
+                                ErrorCode::FileExists => {
+                                    eprintln!("requested file already exists");
+                                    Message::send_error_to(
+                                        &self.socket,
+                                        &from,
+                                        ErrorCode::FileExists,
+                                        "requested file already exists",
+                                    );
+                                }
+                                ErrorCode::AccessViolation => {
+                                    eprintln!("requested file is not in the directory");
+                                    Message::send_error_to(
+                                        &self.socket,
+                                        &from,
+                                        ErrorCode::AccessViolation,
+                                        "requested file is not in the directory",
+                                    );
+                                }
+                                ErrorCode::FileNotFound => {
+                                    self.handle_wrq(&packet, from).unwrap_or_else(|_| {
+                                        eprintln!("could not handle write request")
+                                    })
+                                }
+                                _ => {}
+                            }
+                        }
+                        _ => {
+                            eprintln!("invalid request packet received");
+                            Message::send_error_to(
+                                &self.socket,
+                                &from,
+                                ErrorCode::IllegalOperation,
+                                "invalid request",
+                            );
+                        }
                     }
                 };
             }
         }
     }
 
-    fn send_error_msg(&self, to: SocketAddr) {
-        let buf = [
-            0x00,
-            Opcode::Error as u8,
-            0x00,
-            ErrorCode::IllegalOperation as u8,
-            0x00,
-        ];
-        self.socket.send_to(&buf, to);
+    fn handle_rrq(&self, packet: &Packet, to: SocketAddr) -> Result<(), Box<dyn Error>> {
+        if let Packet::Rrq {
+            filename,
+            mode: _,
+            options,
+        } = packet
+        {
+            let worker = Worker::new(self.socket.local_addr().unwrap(), to)?;
+            worker.send_file(Path::new(&filename), options)?;
+        } else {
+            return Err("invalid read request packet".into());
+        }
+
+        Ok(())
+    }
+
+    fn handle_wrq(&self, packet: &Packet, to: SocketAddr) -> Result<(), Box<dyn Error>> {
+        if let Packet::Wrq {
+            filename,
+            mode: _,
+            options,
+        } = packet
+        {
+            let worker = Worker::new(self.socket.local_addr().unwrap(), to)?;
+            worker.receive_file(Path::new(&filename), options)?;
+        } else {
+            return Err("invalid write request packet".into());
+        }
+
+        Ok(())
+    }
+
+    fn check_file_exists(&self, file: &Path) -> ErrorCode {
+        if !file.ancestors().any(|a| a == &self.directory) {
+            return ErrorCode::AccessViolation;
+        }
+
+        if !file.exists() {
+            return ErrorCode::FileNotFound;
+        }
+
+        ErrorCode::FileExists
     }
 }
diff --git a/src/worker.rs b/src/worker.rs
new file mode 100644
index 0000000..7353364
--- /dev/null
+++ b/src/worker.rs
@@ -0,0 +1,27 @@
+use std::{
+    error::Error,
+    net::{SocketAddr, UdpSocket},
+    path::Path,
+};
+
+use crate::packet::Option;
+
+pub struct Worker {
+    socket: UdpSocket,
+}
+
+impl Worker {
+    pub fn new(addr: SocketAddr, remote: SocketAddr) -> Result<Worker, Box<dyn Error>> {
+        let socket = UdpSocket::bind(SocketAddr::from((addr.ip(), 0)))?;
+        socket.connect(remote)?;
+        Ok(Worker { socket })
+    }
+
+    pub fn send_file(&self, file: &Path, options: &Vec<Option>) -> Result<(), Box<dyn Error>> {
+        Ok(())
+    }
+
+    pub fn receive_file(&self, file: &Path, options: &Vec<Option>) -> Result<(), Box<dyn Error>> {
+        Ok(())
+    }
+}