4 files changed, 666 insertions, 1 deletions

diff --git a/src/dhcp.rs b/src/dhcp.rs
new file mode 100644
index 0000000..b53ee92
--- /dev/null
+++ b/src/dhcp.rs
@@ -0,0 +1,214 @@
+use std::{
+    io::{Result, Write},
+    net::Ipv4Addr,
+};
+
+use crate::wire;
+
+const MAGIC_COOKIE: [u8; 4] = [0x63, 0x82, 0x53, 0x63];
+
+#[derive(Debug, Default, Clone, Copy, PartialEq, Eq, Hash)]
+pub enum BootOp {
+    #[default]
+    Request,
+    Reply,
+}
+
+impl BootOp {
+    pub const OP_REQUEST: u8 = 1;
+    pub const OP_REPLY: u8 = 2;
+}
+
+impl From<BootOp> for u8 {
+    fn from(value: BootOp) -> Self {
+        match value {
+            BootOp::Request => BootOp::OP_REQUEST,
+            BootOp::Reply => BootOp::OP_REPLY,
+        }
+    }
+}
+
+#[derive(Debug, Default, Clone, Copy, PartialEq, Eq, Hash)]
+pub enum HardwareType {
+    #[default]
+    Ethernet,
+}
+
+impl HardwareType {
+    pub const TYPE_ETHER: u8 = 1;
+    pub const LEN_ETHER: u8 = 6;
+
+    pub fn hardware_len(&self) -> u8 {
+        match self {
+            HardwareType::Ethernet => Self::LEN_ETHER,
+        }
+    }
+}
+
+impl From<HardwareType> for u8 {
+    fn from(value: HardwareType) -> Self {
+        match value {
+            HardwareType::Ethernet => HardwareType::TYPE_ETHER,
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub enum DhcpMessageType {
+    Ack,
+}
+
+impl DhcpMessageType {
+    pub const CODE_ACK: u8 = 5;
+
+    pub fn code(&self) -> u8 {
+        match self {
+            DhcpMessageType::Ack => Self::CODE_ACK,
+        }
+    }
+}
+
+#[derive(Debug, Clone)]
+pub enum DhcpOption {
+    Pad,
+    End,
+    MessageType(DhcpMessageType),
+    ServerIdentifier(Ipv4Addr),
+    VendorClassIdentifier(String),
+    TftpServerName(String),
+    TftpFileName(String),
+    UserClassInformation(String),
+    ClientMachineIdentifier(String),
+    Unknown { code: u8, data: Vec<u8> },
+}
+
+impl DhcpOption {
+    pub const CODE_PAD: u8 = 0;
+    pub const CODE_END: u8 = 255;
+    pub const CODE_DHCP_MESSAGE_TYPE: u8 = 53;
+    pub const CODE_DHCP_SERVER_IDENTIFIER: u8 = 54;
+    pub const CODE_VENDOR_CLASS_IDENTIFIER: u8 = 60;
+    pub const CODE_TFTP_SERVER_NAME: u8 = 66;
+    pub const CODE_TFTP_FILE_NAME: u8 = 67;
+    pub const CODE_USER_CLASS_INFORMATION: u8 = 77;
+    pub const CODE_CLIENT_MACHINE_IDENTIFIER: u8 = 97;
+
+    pub fn code(&self) -> u8 {
+        match self {
+            DhcpOption::Pad => Self::CODE_PAD,
+            DhcpOption::End => Self::CODE_END,
+            DhcpOption::MessageType(_) => Self::CODE_DHCP_MESSAGE_TYPE,
+            DhcpOption::ServerIdentifier(_) => Self::CODE_DHCP_SERVER_IDENTIFIER,
+            DhcpOption::VendorClassIdentifier(_) => Self::CODE_VENDOR_CLASS_IDENTIFIER,
+            DhcpOption::TftpServerName(_) => Self::CODE_TFTP_SERVER_NAME,
+            DhcpOption::TftpFileName(_) => Self::CODE_TFTP_FILE_NAME,
+            DhcpOption::UserClassInformation(_) => Self::CODE_USER_CLASS_INFORMATION,
+            DhcpOption::ClientMachineIdentifier(_) => Self::CODE_CLIENT_MACHINE_IDENTIFIER,
+            DhcpOption::Unknown { code, .. } => *code,
+        }
+    }
+}
+
+#[derive(Debug)]
+pub struct DhcpPacket {
+    pub op: BootOp,
+    pub htype: HardwareType,
+    pub xid: u32,
+    pub secs: u16,
+    pub flags: u16,
+    pub ciaddr: Ipv4Addr,
+    pub yiaddr: Ipv4Addr,
+    pub siaddr: Ipv4Addr,
+    pub giaddr: Ipv4Addr,
+    pub chaddr: [u8; 16],
+    // server host name
+    pub sname: Option<String>,
+    // boot file name
+    pub file: Option<String>,
+    pub options: Vec<DhcpOption>,
+}
+
+impl Default for DhcpPacket {
+    fn default() -> Self {
+        Self {
+            op: Default::default(),
+            htype: Default::default(),
+            xid: Default::default(),
+            secs: Default::default(),
+            flags: Default::default(),
+            ciaddr: Ipv4Addr::UNSPECIFIED,
+            yiaddr: Ipv4Addr::UNSPECIFIED,
+            siaddr: Ipv4Addr::UNSPECIFIED,
+            giaddr: Ipv4Addr::UNSPECIFIED,
+            chaddr: Default::default(),
+            sname: Default::default(),
+            file: Default::default(),
+            options: Default::default(),
+        }
+    }
+}
+
+pub fn write_packet<W: Write>(mut writer: W, packet: &DhcpPacket) -> Result<()> {
+    wire::write_u8(&mut writer, u8::from(packet.op))?;
+    wire::write_u8(&mut writer, u8::from(packet.htype))?;
+    wire::write_u8(&mut writer, packet.htype.hardware_len())?;
+    wire::write_u8(&mut writer, 0)?; // hops
+    wire::write_u32(&mut writer, packet.xid)?;
+    wire::write_u16(&mut writer, packet.secs)?;
+    wire::write_u16(&mut writer, packet.flags)?;
+    wire::write_ipv4(&mut writer, packet.ciaddr)?;
+    wire::write_ipv4(&mut writer, packet.yiaddr)?;
+    wire::write_ipv4(&mut writer, packet.siaddr)?;
+    wire::write_ipv4(&mut writer, packet.giaddr)?;
+    wire::write(&mut writer, &packet.chaddr)?;
+    match &packet.sname {
+        Some(name) => wire::write_null_terminated_string(&mut writer, &name)?,
+        None => wire::write_null_terminated_string(&mut writer, "")?,
+    };
+    match &packet.file {
+        Some(name) => wire::write_null_terminated_string(&mut writer, &name)?,
+        None => wire::write_null_terminated_string(&mut writer, "")?,
+    };
+    wire::write(&mut writer, &MAGIC_COOKIE)?;
+    for option in &packet.options {
+        write_option(&mut writer, option)?;
+    }
+    write_option(&mut writer, &DhcpOption::End)?;
+    Ok(())
+}
+
+pub fn write_option<W: Write>(mut writer: W, option: &DhcpOption) -> Result<()> {
+    wire::write_u8(&mut writer, option.code())?;
+    match option {
+        DhcpOption::Pad | DhcpOption::End => {}
+        DhcpOption::MessageType(t) => {
+            wire::write_u8(&mut writer, 1)?;
+            wire::write_u8(&mut writer, t.code())?;
+        }
+        DhcpOption::ServerIdentifier(ip) => {
+            wire::write_u8(&mut writer, 4)?;
+            wire::write_ipv4(&mut writer, *ip)?;
+        }
+        DhcpOption::VendorClassIdentifier(vendor_class) => {
+            write_option_len_prefixed_string(&mut writer, &vendor_class)?
+        }
+        DhcpOption::TftpServerName(name) => write_option_len_prefixed_string(&mut writer, &name)?,
+        DhcpOption::TftpFileName(name) => write_option_len_prefixed_string(&mut writer, &name)?,
+        DhcpOption::UserClassInformation(user_class) => {
+            write_option_len_prefixed_string(&mut writer, &user_class)?
+        }
+        DhcpOption::ClientMachineIdentifier(identifier) => {
+            write_option_len_prefixed_string(&mut writer, &identifier)?
+        }
+        DhcpOption::Unknown { data, .. } => {
+            wire::write_u8(&mut writer, u8::try_from(data.len()).unwrap())?;
+            wire::write(&mut writer, &data)?;
+        }
+    }
+    Ok(())
+}
+
+fn write_option_len_prefixed_string<W: Write>(mut writer: W, s: &str) -> Result<()> {
+    wire::write_u8(&mut writer, u8::try_from(s.len()).unwrap())?;
+    wire::write(&mut writer, s.as_bytes())
+}
diff --git a/src/main.rs b/src/main.rs
index 87ea283..3d86a8e 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,3 +1,8 @@
+#![feature(cursor_split)]
+pub mod dhcp;
+pub mod tftp;
+pub mod wire;
+
 use std::io::{BufRead, Cursor, Read, Result, Write};
 use std::net::{Ipv4Addr, SocketAddr, SocketAddrV4, UdpSocket};
 
@@ -15,7 +20,7 @@ const MAGIC_COOKIE: [u8; 4] = [0x63, 0x82, 0x53, 0x63];
 const BOOT_FILE_NAME: &[u8] = b"ipxe.efi";
 const BOOT_FILE_NAME_IPXE: &[u8] = b"test.ipxe";
 
-const LOCAL_IPV4: Ipv4Addr = Ipv4Addr::new(192, 168, 2, 184);
+const LOCAL_IPV4: Ipv4Addr = Ipv4Addr::new(192, 168, 1, 100);
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 enum BootOp {
diff --git a/src/tftp.rs b/src/tftp.rs
new file mode 100644
index 0000000..becaa65
--- /dev/null
+++ b/src/tftp.rs
@@ -0,0 +1,365 @@
+use std::{
+    io::{Cursor, Read as _, Result, Write},
+    net::UdpSocket,
+    path::{Path, PathBuf},
+    str::FromStr,
+};
+
+use crate::wire;
+
+pub const PORT: u16 = 69;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub struct InvalidTftpOp(u16);
+
+impl std::fmt::Display for InvalidTftpOp {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "invalid tftp opcode '{}'", self.0)
+    }
+}
+
+impl std::error::Error for InvalidTftpOp {}
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub enum TftpOp {
+    ReadRequest,
+    WriteRequest,
+    Data,
+    Ack,
+    Error,
+    Oack,
+}
+
+impl Into<u16> for TftpOp {
+    fn into(self) -> u16 {
+        match self {
+            TftpOp::ReadRequest => 1,
+            TftpOp::WriteRequest => 2,
+            TftpOp::Data => 3,
+            TftpOp::Ack => 4,
+            TftpOp::Error => 5,
+            TftpOp::Oack => 6,
+        }
+    }
+}
+
+impl TryFrom<u16> for TftpOp {
+    type Error = InvalidTftpOp;
+
+    fn try_from(value: u16) -> std::result::Result<Self, InvalidTftpOp> {
+        match value {
+            1 => Ok(Self::ReadRequest),
+            2 => Ok(Self::WriteRequest),
+            3 => Ok(Self::Data),
+            4 => Ok(Self::Ack),
+            5 => Ok(Self::Error),
+            6 => Ok(Self::Oack),
+            unknown => Err(InvalidTftpOp(unknown)),
+        }
+    }
+}
+
+#[derive(Debug)]
+pub struct InvalidTftpMode(String);
+
+impl std::fmt::Display for InvalidTftpMode {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "invalid tftp mode '{}'", self.0)
+    }
+}
+
+impl std::error::Error for InvalidTftpMode {}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub enum TftpMode {
+    NetAscii,
+    Octet,
+    Mail,
+}
+
+impl FromStr for TftpMode {
+    type Err = InvalidTftpMode;
+
+    fn from_str(s: &str) -> std::result::Result<Self, Self::Err> {
+        match s.to_lowercase().as_str() {
+            "netascii" => Ok(Self::NetAscii),
+            "octet" => Ok(Self::Octet),
+            "mail" => Ok(Self::Mail),
+            _ => Err(InvalidTftpMode(s.to_string())),
+        }
+    }
+}
+
+#[derive(Debug)]
+pub enum TftpPacket {
+    Request(TftpRequestPacket),
+    Data(TftpDataPacket),
+    Ack(TftpAckPacket),
+    OAck(TftpOAckPacket),
+    Error(TftpErrorPacket),
+}
+
+impl TftpPacket {
+    pub fn write<W: Write>(&self, writer: W) -> Result<()> {
+        match self {
+            TftpPacket::Request(p) => p.write(writer),
+            TftpPacket::Data(p) => p.write(writer),
+            TftpPacket::Ack(p) => p.write(writer),
+            TftpPacket::OAck(p) => p.write(writer),
+            TftpPacket::Error(p) => p.write(writer),
+        }
+    }
+}
+
+#[derive(Debug)]
+pub struct TftpRequestPacket {
+    pub filename: String,
+    pub mode: TftpMode,
+    pub tsize: Option<u64>,
+    pub blksize: Option<u64>,
+}
+
+impl TftpRequestPacket {
+    pub fn write<W: Write>(&self, mut writer: W) -> Result<()> {
+        todo!()
+    }
+}
+
+#[derive(Debug)]
+pub struct TftpDataPacket {
+    pub block: u16,
+    pub data: Vec<u8>,
+}
+
+impl TftpDataPacket {
+    pub fn write<W: Write>(&self, mut writer: W) -> Result<()> {
+        wire::write_u16(&mut writer, TftpOp::Data.into())?;
+        wire::write_u16(&mut writer, self.block)?;
+        wire::write(&mut writer, &self.data)?;
+        Ok(())
+    }
+}
+
+#[derive(Debug)]
+pub struct TftpAckPacket {
+    pub block: u16,
+}
+
+impl TftpAckPacket {
+    pub fn write<W: Write>(&self, mut writer: W) -> Result<()> {
+        wire::write_u16(&mut writer, TftpOp::Data.into())?;
+        wire::write_u16(&mut writer, self.block)?;
+        Ok(())
+    }
+}
+
+#[derive(Debug)]
+pub struct TftpOAckPacket {
+    pub tsize: Option<u64>,
+    pub blksize: Option<u64>,
+}
+
+impl TftpOAckPacket {
+    pub fn write<W: Write>(&self, mut writer: W) -> Result<()> {
+        wire::write_u16(&mut writer, TftpOp::Oack.into())?;
+
+        // Only include options that were requested by the client
+        if let Some(blksize_val) = self.blksize {
+            wire::write(&mut writer, b"blksize")?;
+            wire::write_u8(&mut writer, 0)?; // null terminator
+            let blksize_str = blksize_val.to_string();
+            wire::write(&mut writer, blksize_str.as_bytes())?;
+            wire::write_u8(&mut writer, 0)?; // null terminator
+        }
+
+        if let Some(tsize_val) = self.tsize {
+            wire::write(&mut writer, b"tsize")?;
+            wire::write_u8(&mut writer, 0)?; // null terminator
+            let tsize_str = tsize_val.to_string();
+            wire::write(&mut writer, tsize_str.as_bytes())?;
+            wire::write_u8(&mut writer, 0)?; // null terminator
+        }
+
+        Ok(())
+    }
+}
+
+#[derive(Debug)]
+pub struct TftpErrorPacket {
+    pub code: u16,
+    pub message: String,
+}
+
+impl TftpErrorPacket {
+    pub fn write<W: Write>(&self, mut writer: W) -> Result<()> {
+        wire::write_u16(&mut writer, TftpOp::Error.into())?;
+        wire::write_u16(&mut writer, self.code)?;
+        wire::write_null_terminated_string(&mut writer, &self.message)?;
+        Ok(())
+    }
+}
+
+pub fn parse_packet(buf: &[u8]) -> Result<TftpPacket> {
+    let mut cursor = Cursor::new(buf);
+    let op = TftpOp::try_from(wire::read_u16(&mut cursor)?).unwrap();
+
+    match op {
+        TftpOp::ReadRequest => {
+            let filename = wire::read_null_terminated_string(&mut cursor)?;
+            let mode = wire::read_null_terminated_string(&mut cursor)?
+                .parse::<TftpMode>()
+                .unwrap();
+
+            let mut tsize = None;
+            let mut blksize = None;
+
+            while let Ok(opt_name) = wire::read_null_terminated_string(&mut cursor) {
+                if opt_name.is_empty() {
+                    break;
+                }
+                let opt_data = wire::read_null_terminated_string(&mut cursor)?;
+                match opt_name.as_str() {
+                    "tsize" => tsize = Some(opt_data.parse::<u64>().unwrap()),
+                    "blksize" => blksize = Some(opt_data.parse::<u64>().unwrap()),
+                    _ => eprintln!("unknown tftp request option '{opt_name}'"),
+                }
+            }
+
+            Ok(TftpPacket::Request(TftpRequestPacket {
+                filename,
+                mode,
+                tsize,
+                blksize,
+            }))
+        }
+        TftpOp::WriteRequest => unimplemented!(),
+        TftpOp::Data => {
+            let block = wire::read_u16(&mut cursor)?;
+            let mut data = Vec::new();
+            cursor.read_to_end(&mut data)?;
+            Ok(TftpPacket::Data(TftpDataPacket { block, data }))
+        }
+        TftpOp::Ack => {
+            let block = wire::read_u16(&mut cursor)?;
+            Ok(TftpPacket::Ack(TftpAckPacket { block }))
+        }
+        TftpOp::Error => {
+            let code = wire::read_u16(&mut cursor)?;
+            let message = wire::read_null_terminated_string(&mut cursor)?;
+            Ok(TftpPacket::Error(TftpErrorPacket { code, message }))
+        }
+        TftpOp::Oack => {
+            let mut tsize = None;
+            let mut blksize = None;
+
+            while let Ok(opt_name) = wire::read_null_terminated_string(&mut cursor) {
+                if opt_name.is_empty() {
+                    break;
+                }
+                let opt_data = wire::read_null_terminated_string(&mut cursor)?;
+                match opt_name.as_str() {
+                    "tsize" => tsize = Some(opt_data.parse::<u64>().unwrap()),
+                    "blksize" => blksize = Some(opt_data.parse::<u64>().unwrap()),
+                    _ => eprintln!("unknown tftp ack option '{opt_name}'"),
+                }
+            }
+            Ok(TftpPacket::OAck(TftpOAckPacket { tsize, blksize }))
+        }
+    }
+}
+
+pub fn serve(dir: &Path) -> Result<()> {
+    let socket = UdpSocket::bind(format!("0.0.0.0:{PORT}"))?;
+
+    // TODO: this needs to be done per addr
+    let mut last_blksize = 512u64;
+    let mut current_file = PathBuf::default();
+
+    loop {
+        let mut buf = [0u8; 1500];
+        let (n, addr) = socket.recv_from(&mut buf)?;
+        let packet = parse_packet(&buf[..n]).unwrap();
+
+        let response = match packet {
+            TftpPacket::Request(req) => {
+                println!(
+                    "Request options: tsize={:?}, blksize={:?}",
+                    req.tsize, req.blksize
+                );
+
+                let filepath = dir.join(req.filename);
+                current_file = filepath.clone();
+                let meta = std::fs::metadata(&filepath).unwrap();
+                let actual_file_size = meta.len();
+
+                // Only send OACK if client sent options
+                if req.tsize.is_some() || req.blksize.is_some() {
+                    if let Some(blksize) = req.blksize {
+                        last_blksize = blksize;
+                    }
+
+                    let tsize_response = if req.tsize.is_some() {
+                        Some(actual_file_size)
+                    } else {
+                        None
+                    };
+
+                    Some(TftpPacket::OAck(TftpOAckPacket {
+                        tsize: req.tsize,
+                        blksize: req.blksize,
+                    }))
+                } else {
+                    // No options, send first data block directly
+                    let contents = std::fs::read(&filepath).unwrap();
+                    let block_size = 512;
+                    let first_block = if contents.len() > block_size {
+                        contents[..block_size].to_vec()
+                    } else {
+                        contents
+                    };
+
+                    Some(TftpPacket::Data(TftpDataPacket {
+                        block: 1,
+                        data: first_block,
+                    }))
+                }
+            }
+            TftpPacket::Data(dat) => unimplemented!(),
+            TftpPacket::Ack(ack) => {
+                println!("Received ACK packet: block {}", ack.block);
+
+                let contents = std::fs::read(&current_file).unwrap();
+                let next_block = ack.block + 1;
+                let start_offset = (next_block - 1) as u64 * last_blksize;
+                let end_offset = next_block as u64 * last_blksize;
+                let prev_start_offset = (next_block.saturating_sub(2)) as u64 * last_blksize;
+                let prev_remain = contents.len() - prev_start_offset as usize;
+                if prev_remain as u64 >= last_blksize || ack.block == 0 {
+                    let end = std::cmp::min(end_offset as usize, contents.len());
+                    let block_data = contents[start_offset as usize..end].to_vec();
+                    println!("sending tftp data packet with {} bytes", block_data.len());
+                    Some(TftpPacket::Data(TftpDataPacket {
+                        block: next_block,
+                        data: block_data,
+                    }))
+                } else {
+                    None
+                }
+            }
+            TftpPacket::OAck(ack) => todo!(),
+            TftpPacket::Error(err) => {
+                println!(
+                    "Received ERROR packet: code {}, message: {}",
+                    err.code, err.message
+                );
+                None
+            }
+        };
+
+        if let Some(response) = response {
+            let mut writer = Cursor::new(&mut buf[..]);
+            response.write(&mut writer).unwrap();
+            let (response, _) = writer.split();
+            socket.send_to(&response, addr).unwrap();
+        }
+    }
+}
diff --git a/src/wire.rs b/src/wire.rs
new file mode 100644
index 0000000..dda7690
--- /dev/null
+++ b/src/wire.rs
@@ -0,0 +1,81 @@
+use std::{
+    io::{BufRead, Read, Result, Write},
+    net::Ipv4Addr,
+};
+
+pub fn write<W: Write>(mut writer: W, v: &[u8]) -> Result<()> {
+    writer.write_all(v)
+}
+
+pub fn write_u8<W: Write>(mut writer: W, v: u8) -> Result<()> {
+    writer.write_all(&[v])
+}
+
+pub fn write_u16<W: Write>(mut writer: W, v: u16) -> Result<()> {
+    writer.write_all(&u16::to_be_bytes(v))
+}
+
+pub fn write_u32<W: Write>(mut writer: W, v: u32) -> Result<()> {
+    writer.write_all(&u32::to_be_bytes(v))
+}
+
+pub fn write_ipv4<W: Write>(mut writer: W, v: Ipv4Addr) -> Result<()> {
+    writer.write_all(&v.octets())
+}
+
+pub fn write_null_terminated_string<W: Write>(mut writer: W, v: &str) -> Result<()> {
+    writer.write_all(v.as_bytes())?;
+    writer.write_all(&[0u8])
+}
+
+pub fn read_u8<R: Read>(mut reader: R) -> Result<u8> {
+    let mut buf = [0u8; 1];
+    reader.read_exact(&mut buf)?;
+    Ok(buf[0])
+}
+
+pub fn read_u16<R: Read>(mut reader: R) -> Result<u16> {
+    let mut buf = [0u8; 2];
+    reader.read_exact(&mut buf)?;
+    Ok(u16::from_be_bytes(buf))
+}
+
+pub fn read_u32<R: Read>(mut reader: R) -> Result<u32> {
+    let mut buf = [0u8; 4];
+    reader.read_exact(&mut buf)?;
+    Ok(u32::from_be_bytes(buf))
+}
+
+pub fn read_arr<const N: usize, R: Read>(mut reader: R) -> Result<[u8; N]> {
+    let mut buf = [0u8; N];
+    reader.read_exact(&mut buf)?;
+    Ok(buf)
+}
+
+pub fn read_null_terminated_vec<R: BufRead>(mut reader: R) -> Result<Vec<u8>> {
+    let mut buf = Vec::default();
+    reader.read_until(0, &mut buf)?;
+    buf.pop();
+    Ok(buf)
+}
+
+pub fn read_null_terminated_string<R: BufRead>(reader: R) -> Result<String> {
+    let buf = read_null_terminated_vec(reader)?;
+    Ok(String::from_utf8(buf).unwrap())
+}
+
+pub fn read_len8_prefixed_vec<R: BufRead>(mut reader: R) -> Result<Vec<u8>> {
+    let len = read_u8(&mut reader)?;
+    let mut buf = vec![0u8; len as usize];
+    reader.read_exact(&mut buf)?;
+    Ok(buf)
+}
+
+pub fn read_len8_prefixed_string<R: BufRead>(reader: R) -> Result<String> {
+    let buf = read_len8_prefixed_vec(reader)?;
+    Ok(String::from_utf8(buf).unwrap())
+}
+
+pub fn read_ipv4<R: BufRead>(reader: R) -> Result<Ipv4Addr> {
+    Ok(Ipv4Addr::from_octets(read_arr(reader)?))
+}