feat: add sans-io TFTP protocol crate

Cargo.lock

@@ -5,3 +5,17 @@ version = 4
 [[package]]
 name = "pfs-tftp"
 version = "0.1.0"
+dependencies = [
+ "pfs-tftp-sync",
+]
+
+[[package]]
+name = "pfs-tftp-proto"
+version = "0.1.0"
+
+[[package]]
+name = "pfs-tftp-sync"
+version = "0.1.0"
+dependencies = [
+ "pfs-tftp-proto",
+]

Cargo.toml

@@ -3,6 +3,9 @@ name = "pfs-tftp"
 version = "0.1.0"
 edition = "2024"
 
+[workspace]
+members = ["crates/pfs-tftp-proto", "crates/pfs-tftp-sync"]
+
 [lints.rust]
 unsafe_code = "forbid"
 
@@ -12,3 +15,4 @@ todo = "warn"
 unwrap_used = "warn"
 
 [dependencies]
+pfs-tftp-sync = { path = "crates/pfs-tftp-sync" }

crates/pfs-tftp-proto/Cargo.toml

@@ -0,0 +1,14 @@
+[package]
+name = "pfs-tftp-proto"
+version = "0.1.0"
+edition = "2024"
+
+[lints.rust]
+unsafe_code = "forbid"
+
+[lints.clippy]
+pedantic = { level = "warn", priority = -1 }
+todo = "warn"
+unwrap_used = "warn"
+
+[dependencies]

crates/pfs-tftp-proto/src/lib.rs

@@ -0,0 +1,13 @@
+//! TFTP protocol types and codecs (sans I/O).
+//!
+//! This crate intentionally performs no network or filesystem I/O.
+//! It provides:
+//! - Encoding/decoding of RFC 1350 packet formats.
+//! - Netascii streaming translation helpers.
+//!
+//! Protocol reference: `rfc1350.txt` at the workspace root.
+
+#![forbid(unsafe_code)]
+
+pub mod netascii;
+pub mod packet;

crates/pfs-tftp-proto/src/netascii.rs

@@ -0,0 +1,149 @@
+//! Netascii translation helpers.
+//!
+//! RFC 1350, Section 1 defines *netascii* as ASCII with the newline / carriage-return
+//! conventions from the Telnet specification (RFC 764). In practice, this means:
+//! - Newline is transmitted as CR LF.
+//! - A literal carriage return is transmitted as CR NUL.
+//!
+//! The translation must work as a streaming transform because CR and LF can be
+//! split across TFTP DATA block boundaries (RFC 1350, Section 2: 512-byte blocks).
+
+#![forbid(unsafe_code)]
+
+/// Streaming encoder from local bytes into netascii bytes.
+///
+/// This implementation treats `\n` as the local newline and maps:
+/// - `\n` -> `\r\n`
+/// - `\r` -> `\r\0`
+///
+/// RFC reference: RFC 1350, Section 1 (netascii definition).
+#[derive(Debug, Default, Clone)]
+pub struct NetasciiEncoder;
+
+impl NetasciiEncoder {
+    #[must_use]
+    pub fn new() -> Self {
+        Self
+    }
+
+    pub fn encode_chunk(&mut self, input: &[u8], output: &mut Vec<u8>) {
+        for &b in input {
+            match b {
+                b'\n' => output.extend_from_slice(b"\r\n"),
+                b'\r' => output.extend_from_slice(b"\r\0"),
+                _ => output.push(b),
+            }
+        }
+    }
+}
+
+/// Streaming decoder from netascii bytes into local bytes.
+///
+/// This decoder maintains state for a pending CR at a chunk boundary.
+/// It maps:
+/// - `\r\n` -> `\n`
+/// - `\r\0` -> `\r`
+///
+/// RFC reference: RFC 1350, Section 1 (netascii definition).
+#[derive(Debug, Clone, Default)]
+pub struct NetasciiDecoder {
+    pending_cr: bool,
+}
+
+impl NetasciiDecoder {
+    #[must_use]
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Decodes a chunk of netascii bytes, appending the translated bytes to `output`.
+    ///
+    /// # Errors
+    /// Returns an error if an invalid CR sequence is encountered (anything other than
+    /// CR LF or CR NUL), per the netascii definition referenced by RFC 1350, Section 1.
+    pub fn decode_chunk(&mut self, input: &[u8], output: &mut Vec<u8>) -> Result<(), DecodeError> {
+        for &b in input {
+            if self.pending_cr {
+                self.pending_cr = false;
+                match b {
+                    b'\n' => output.push(b'\n'),
+                    0 => output.push(b'\r'),
+                    _ => return Err(DecodeError::InvalidCrSequence(b)),
+                }
+                continue;
+            }
+
+            if b == b'\r' {
+                self.pending_cr = true;
+            } else {
+                output.push(b);
+            }
+        }
+        Ok(())
+    }
+
+    /// Flushes any pending state at end-of-stream.
+    ///
+    /// A dangling CR is invalid netascii.
+    ///
+    /// # Errors
+    /// Returns an error if the stream ends with a dangling CR byte.
+    pub fn finish(self) -> Result<(), DecodeError> {
+        if self.pending_cr {
+            Err(DecodeError::DanglingCr)
+        } else {
+            Ok(())
+        }
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum DecodeError {
+    DanglingCr,
+    InvalidCrSequence(u8),
+}
+
+impl core::fmt::Display for DecodeError {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        match self {
+            Self::DanglingCr => write!(f, "dangling CR at end of stream"),
+            Self::InvalidCrSequence(b) => write!(f, "invalid netascii CR sequence: 0x{b:02x}"),
+        }
+    }
+}
+
+impl std::error::Error for DecodeError {}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[allow(clippy::unwrap_used)]
+    #[test]
+    fn encode_newlines_and_cr() {
+        let mut enc = NetasciiEncoder::new();
+        let mut out = Vec::new();
+        enc.encode_chunk(b"a\nb\rc", &mut out);
+        assert_eq!(out, b"a\r\nb\r\0c");
+    }
+
+    #[allow(clippy::unwrap_used)]
+    #[test]
+    fn decode_across_chunk_boundary() {
+        let mut dec = NetasciiDecoder::new();
+        let mut out = Vec::new();
+        dec.decode_chunk(b"a\r", &mut out).unwrap();
+        dec.decode_chunk(b"\nb", &mut out).unwrap();
+        dec.finish().unwrap();
+        assert_eq!(out, b"a\nb");
+    }
+
+    #[allow(clippy::unwrap_used)]
+    #[test]
+    fn decode_rejects_dangling_cr() {
+        let mut dec = NetasciiDecoder::new();
+        let mut out = Vec::new();
+        dec.decode_chunk(b"a\r", &mut out).unwrap();
+        assert!(matches!(dec.finish(), Err(DecodeError::DanglingCr)));
+    }
+}

crates/pfs-tftp-proto/src/packet.rs

@@ -0,0 +1,360 @@
+//! Packet encoding/decoding for TFTP (RFC 1350).
+//!
+//! RFC 1350, Section 5 ("TFTP Packets") defines the packet formats:
+//! - RRQ/WRQ: Figure 5-1
+//! - DATA: Figure 5-2
+//! - ACK: Figure 5-3
+//! - ERROR: Figure 5-4
+//!
+//! This module implements strict parsing/serialization of those formats.
+
+#![forbid(unsafe_code)]
+
+use core::fmt;
+
+/// RFC 1350, Section 2: data blocks are 512 bytes.
+pub const BLOCK_SIZE: usize = 512;
+
+/// Maximum packet size in RFC 1350 (DATA with 512 bytes).
+pub const MAX_PACKET_SIZE: usize = 4 + BLOCK_SIZE;
+
+/// TFTP opcode values (RFC 1350, Section 5).
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[repr(u16)]
+pub enum Opcode {
+    /// Read request (RRQ), RFC 1350 Figure 5-1.
+    Rrq = 1,
+    /// Write request (WRQ), RFC 1350 Figure 5-1.
+    Wrq = 2,
+    /// Data (DATA), RFC 1350 Figure 5-2.
+    Data = 3,
+    /// Acknowledgment (ACK), RFC 1350 Figure 5-3.
+    Ack = 4,
+    /// Error (ERROR), RFC 1350 Figure 5-4.
+    Error = 5,
+}
+
+impl Opcode {
+    #[must_use]
+    pub fn from_u16(value: u16) -> Option<Self> {
+        match value {
+            1 => Some(Self::Rrq),
+            2 => Some(Self::Wrq),
+            3 => Some(Self::Data),
+            4 => Some(Self::Ack),
+            5 => Some(Self::Error),
+            _ => None,
+        }
+    }
+}
+
+/// Transfer mode for RRQ/WRQ (RFC 1350, Section 5, Figure 5-1).
+///
+/// RFC 1350 lists: "netascii", "octet", "mail" (mail is obsolete; Section 1).
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Mode {
+    NetAscii,
+    Octet,
+    Mail,
+}
+
+impl Mode {
+    #[must_use]
+    pub fn as_str(self) -> &'static str {
+        match self {
+            Self::NetAscii => "netascii",
+            Self::Octet => "octet",
+            Self::Mail => "mail",
+        }
+    }
+
+    #[must_use]
+    pub fn parse_case_insensitive(s: &str) -> Option<Self> {
+        if s.eq_ignore_ascii_case("netascii") {
+            Some(Self::NetAscii)
+        } else if s.eq_ignore_ascii_case("octet") {
+            Some(Self::Octet)
+        } else if s.eq_ignore_ascii_case("mail") {
+            Some(Self::Mail)
+        } else {
+            None
+        }
+    }
+}
+
+/// Error codes (RFC 1350 Appendix, "Error Codes").
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[repr(u16)]
+pub enum ErrorCode {
+    NotDefined = 0,
+    FileNotFound = 1,
+    AccessViolation = 2,
+    DiskFull = 3,
+    IllegalOperation = 4,
+    UnknownTransferId = 5,
+    FileAlreadyExists = 6,
+    NoSuchUser = 7,
+}
+
+impl ErrorCode {
+    #[must_use]
+    pub fn from_u16(value: u16) -> Option<Self> {
+        match value {
+            0 => Some(Self::NotDefined),
+            1 => Some(Self::FileNotFound),
+            2 => Some(Self::AccessViolation),
+            3 => Some(Self::DiskFull),
+            4 => Some(Self::IllegalOperation),
+            5 => Some(Self::UnknownTransferId),
+            6 => Some(Self::FileAlreadyExists),
+            7 => Some(Self::NoSuchUser),
+            _ => None,
+        }
+    }
+}
+
+/// A RRQ/WRQ request (RFC 1350 Figure 5-1).
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Request {
+    pub filename: String,
+    pub mode: Mode,
+}
+
+/// A decoded TFTP packet (RFC 1350 Section 5).
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum Packet {
+    Rrq(Request),
+    Wrq(Request),
+    Data { block: u16, data: Vec<u8> },
+    Ack { block: u16 },
+    Error { code: ErrorCode, message: String },
+}
+
+impl Packet {
+    /// Encode a packet into a newly allocated buffer.
+    #[must_use]
+    pub fn encode(&self) -> Vec<u8> {
+        let mut out = Vec::with_capacity(MAX_PACKET_SIZE);
+        self.encode_into(&mut out);
+        out
+    }
+
+    /// Encode a packet by appending to `out`.
+    pub fn encode_into(&self, out: &mut Vec<u8>) {
+        match self {
+            Self::Rrq(req) => encode_request(out, Opcode::Rrq, req),
+            Self::Wrq(req) => encode_request(out, Opcode::Wrq, req),
+            Self::Data { block, data } => {
+                out.extend_from_slice(&(Opcode::Data as u16).to_be_bytes());
+                out.extend_from_slice(&block.to_be_bytes());
+                out.extend_from_slice(data);
+            }
+            Self::Ack { block } => {
+                out.extend_from_slice(&(Opcode::Ack as u16).to_be_bytes());
+                out.extend_from_slice(&block.to_be_bytes());
+            }
+            Self::Error { code, message } => {
+                out.extend_from_slice(&(Opcode::Error as u16).to_be_bytes());
+                out.extend_from_slice(&(*code as u16).to_be_bytes());
+                out.extend_from_slice(message.as_bytes());
+                out.push(0);
+            }
+        }
+    }
+
+    /// Decode a packet from UDP payload bytes.
+    ///
+    /// # Errors
+    /// Returns a [`DecodeError`] if the input does not match an RFC 1350 packet format.
+    pub fn decode(input: &[u8]) -> Result<Self, DecodeError> {
+        let (opcode, rest) = parse_opcode(input)?;
+        match opcode {
+            Opcode::Rrq | Opcode::Wrq => {
+                let (filename, rest) = parse_netascii_z(rest, "filename")?;
+                let (mode_str, rest) = parse_netascii_z(rest, "mode")?;
+                if !rest.is_empty() {
+                    return Err(DecodeError::TrailingBytes);
+                }
+                let Some(mode) = Mode::parse_case_insensitive(&mode_str) else {
+                    return Err(DecodeError::UnknownMode(mode_str));
+                };
+                let req = Request { filename, mode };
+                Ok(if opcode == Opcode::Rrq {
+                    Self::Rrq(req)
+                } else {
+                    Self::Wrq(req)
+                })
+            }
+            Opcode::Data => {
+                if rest.len() < 2 {
+                    return Err(DecodeError::Truncated("block"));
+                }
+                if rest.len() > 2 + BLOCK_SIZE {
+                    return Err(DecodeError::OversizeData(rest.len() - 2));
+                }
+                let block = u16::from_be_bytes([rest[0], rest[1]]);
+                let data = rest[2..].to_vec();
+                Ok(Self::Data { block, data })
+            }
+            Opcode::Ack => {
+                if rest.len() != 2 {
+                    return Err(DecodeError::InvalidLength {
+                        kind: "ACK",
+                        expected: 4,
+                        got: input.len(),
+                    });
+                }
+                let block = u16::from_be_bytes([rest[0], rest[1]]);
+                Ok(Self::Ack { block })
+            }
+            Opcode::Error => {
+                if rest.len() < 2 {
+                    return Err(DecodeError::Truncated("error code"));
+                }
+                let code_u16 = u16::from_be_bytes([rest[0], rest[1]]);
+                let Some(code) = ErrorCode::from_u16(code_u16) else {
+                    return Err(DecodeError::UnknownErrorCode(code_u16));
+                };
+                let (message, trailing) = parse_netascii_z(&rest[2..], "error message")?;
+                if !trailing.is_empty() {
+                    return Err(DecodeError::TrailingBytes);
+                }
+                Ok(Self::Error { code, message })
+            }
+        }
+    }
+}
+
+fn encode_request(out: &mut Vec<u8>, opcode: Opcode, req: &Request) {
+    out.extend_from_slice(&(opcode as u16).to_be_bytes());
+    out.extend_from_slice(req.filename.as_bytes());
+    out.push(0);
+    out.extend_from_slice(req.mode.as_str().as_bytes());
+    out.push(0);
+}
+
+fn parse_opcode(input: &[u8]) -> Result<(Opcode, &[u8]), DecodeError> {
+    if input.len() < 2 {
+        return Err(DecodeError::Truncated("opcode"));
+    }
+    let opcode_u16 = u16::from_be_bytes([input[0], input[1]]);
+    let Some(opcode) = Opcode::from_u16(opcode_u16) else {
+        return Err(DecodeError::UnknownOpcode(opcode_u16));
+    };
+    Ok((opcode, &input[2..]))
+}
+
+fn parse_netascii_z<'a>(
+    input: &'a [u8],
+    field: &'static str,
+) -> Result<(String, &'a [u8]), DecodeError> {
+    let Some(pos) = input.iter().position(|&b| b == 0) else {
+        return Err(DecodeError::MissingTerminator(field));
+    };
+    if pos == 0 {
+        return Err(DecodeError::EmptyField(field));
+    }
+    let bytes = &input[..pos];
+    if bytes.iter().any(|&b| b > 0x7F) {
+        return Err(DecodeError::NonNetascii(field));
+    }
+    let s = core::str::from_utf8(bytes).map_err(|_| DecodeError::NonUtf8(field))?;
+    Ok((s.to_owned(), &input[pos + 1..]))
+}
+
+/// A parse error for RFC 1350 packet formats.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum DecodeError {
+    Truncated(&'static str),
+    UnknownOpcode(u16),
+    MissingTerminator(&'static str),
+    EmptyField(&'static str),
+    NonNetascii(&'static str),
+    NonUtf8(&'static str),
+    UnknownMode(String),
+    UnknownErrorCode(u16),
+    OversizeData(usize),
+    InvalidLength {
+        kind: &'static str,
+        expected: usize,
+        got: usize,
+    },
+    TrailingBytes,
+}
+
+impl fmt::Display for DecodeError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::Truncated(what) => write!(f, "truncated packet ({what})"),
+            Self::UnknownOpcode(op) => write!(f, "unknown opcode {op}"),
+            Self::MissingTerminator(field) => write!(f, "missing NUL terminator for {field}"),
+            Self::EmptyField(field) => write!(f, "empty {field}"),
+            Self::NonNetascii(field) => write!(f, "{field} contains non-netascii bytes"),
+            Self::NonUtf8(field) => write!(f, "{field} is not valid UTF-8"),
+            Self::UnknownMode(mode) => write!(f, "unknown transfer mode {mode:?}"),
+            Self::UnknownErrorCode(code) => write!(f, "unknown error code {code}"),
+            Self::OversizeData(n) => write!(f, "DATA payload too large ({n} bytes)"),
+            Self::InvalidLength { kind, expected, got } => {
+                write!(f, "{kind} packet has invalid length (expected {expected}, got {got})")
+            }
+            Self::TrailingBytes => write!(f, "trailing bytes after packet"),
+        }
+    }
+}
+
+impl std::error::Error for DecodeError {}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[allow(clippy::unwrap_used)]
+    #[test]
+    fn rrq_roundtrip() {
+        let pkt = Packet::Rrq(Request {
+            filename: "hello.txt".to_string(),
+            mode: Mode::Octet,
+        });
+        let encoded = pkt.encode();
+        let decoded = Packet::decode(&encoded).unwrap();
+        assert_eq!(decoded, pkt);
+    }
+
+    #[allow(clippy::unwrap_used)]
+    #[test]
+    fn data_roundtrip_small() {
+        let pkt = Packet::Data {
+            block: 42,
+            data: b"abc".to_vec(),
+        };
+        let encoded = pkt.encode();
+        let decoded = Packet::decode(&encoded).unwrap();
+        assert_eq!(decoded, pkt);
+    }
+
+    #[allow(clippy::unwrap_used)]
+    #[test]
+    fn ack_requires_exact_length() {
+        let mut bytes = Vec::new();
+        Packet::Ack { block: 1 }.encode_into(&mut bytes);
+        bytes.push(0);
+        let err = Packet::decode(&bytes).unwrap_err();
+        assert!(matches!(err, DecodeError::InvalidLength { kind: "ACK", .. }));
+    }
+
+    #[allow(clippy::unwrap_used)]
+    #[test]
+    fn rejects_unknown_opcode() {
+        let err = Packet::decode(&[0, 9]).unwrap_err();
+        assert!(matches!(err, DecodeError::UnknownOpcode(9)));
+    }
+
+    #[allow(clippy::unwrap_used)]
+    #[test]
+    fn rejects_data_larger_than_512() {
+        let mut bytes = vec![0, 3, 0, 1];
+        bytes.extend(std::iter::repeat(0x61).take(BLOCK_SIZE + 1));
+        let err = Packet::decode(&bytes).unwrap_err();
+        assert!(matches!(err, DecodeError::OversizeData(513)));
+    }
+}

crates/pfs-tftp-sync/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+name = "pfs-tftp-sync"
+version = "0.1.0"
+edition = "2024"
+
+[lints.rust]
+unsafe_code = "forbid"
+
+[lints.clippy]
+pedantic = { level = "warn", priority = -1 }
+todo = "warn"
+unwrap_used = "warn"
+
+[dependencies]
+pfs-tftp-proto = { path = "../pfs-tftp-proto" }

crates/pfs-tftp-sync/src/client.rs

@@ -0,0 +1,44 @@
+#![forbid(unsafe_code)]
+
+use std::net::SocketAddr;
+use std::time::Duration;
+
+/// Configuration for a synchronous TFTP client.
+#[derive(Debug, Clone)]
+pub struct ClientConfig {
+    pub timeout: Duration,
+    pub retries: u32,
+}
+
+impl Default for ClientConfig {
+    fn default() -> Self {
+        Self {
+            timeout: Duration::from_secs(5),
+            retries: 5,
+        }
+    }
+}
+
+/// A synchronous TFTP client.
+#[derive(Debug)]
+pub struct Client {
+    pub(crate) server: SocketAddr,
+    pub(crate) config: ClientConfig,
+}
+
+impl Client {
+    #[must_use]
+    pub fn new(server: SocketAddr, config: ClientConfig) -> Self {
+        Self { server, config }
+    }
+
+    #[must_use]
+    pub fn server(&self) -> SocketAddr {
+        self.server
+    }
+
+    #[must_use]
+    pub fn config(&self) -> &ClientConfig {
+        &self.config
+    }
+}

crates/pfs-tftp-sync/src/lib.rs

@@ -0,0 +1,13 @@
+//! Synchronous TFTP client/server helpers built on `pfs-tftp-proto`.
+//!
+//! This crate provides small, blocking APIs built on `std::net::UdpSocket`.
+//! It intentionally avoids async runtimes for simplicity.
+
+#![forbid(unsafe_code)]
+
+pub mod client;
+pub mod server;
+pub mod util;
+
+pub use client::{Client, ClientConfig};
+pub use server::{Server, ServerConfig};

crates/pfs-tftp-sync/src/server.rs

@@ -0,0 +1,47 @@
+#![forbid(unsafe_code)]
+
+use std::net::SocketAddr;
+use std::path::PathBuf;
+use std::time::Duration;
+
+/// Configuration for a synchronous TFTP server.
+#[derive(Debug, Clone)]
+pub struct ServerConfig {
+    pub bind: SocketAddr,
+    pub root: PathBuf,
+    pub allow_write: bool,
+    pub overwrite: bool,
+    pub timeout: Duration,
+    pub retries: u32,
+}
+
+impl Default for ServerConfig {
+    fn default() -> Self {
+        Self {
+            bind: SocketAddr::from(([0, 0, 0, 0], 6969)),
+            root: PathBuf::from("."),
+            allow_write: false,
+            overwrite: false,
+            timeout: Duration::from_secs(5),
+            retries: 5,
+        }
+    }
+}
+
+/// A synchronous TFTP server.
+#[derive(Debug)]
+pub struct Server {
+    pub(crate) config: ServerConfig,
+}
+
+impl Server {
+    #[must_use]
+    pub fn new(config: ServerConfig) -> Self {
+        Self { config }
+    }
+
+    #[must_use]
+    pub fn config(&self) -> &ServerConfig {
+        &self.config
+    }
+}

crates/pfs-tftp-sync/src/util.rs

@@ -0,0 +1,4 @@
+#![forbid(unsafe_code)]
+
+// Misc sync helpers live here.
+