feat: implement TFTP client and server binaries

Add command-line programs for TFTP operations:

tftpd - TFTP server daemon:
- Configurable root directory for serving files
- Optional write support with --writable flag
- Optional file overwriting with --overwrite flag
- Custom port binding (default: 69)
- Path traversal protection for security

tftp - TFTP client:
- get command for downloading files
- put command for uploading files
- Support for both octet and netascii modes
- Verbose mode for debugging

Also adds comprehensive integration tests that verify client-server
communication with real network I/O.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

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

@@ -17,5 +17,5 @@ mod packet;
 mod state;
 
 pub use error::{Error, ErrorCode, Result};
-pub use packet::{Mode, Opcode, Packet, MAX_DATA_SIZE, TFTP_PORT};
+pub use packet::{MAX_DATA_SIZE, Mode, Opcode, Packet, TFTP_PORT};
 pub use state::{ClientState, Event, ServerState, TransferDirection};

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

@@ -244,12 +244,11 @@ impl Packet {
             .position(|&b| b == 0)
             .ok_or(Error::MissingNullTerminator { field: "filename" })?;
 
-        let filename = std::str::from_utf8(&payload[..filename_end]).map_err(|e| {
-            Error::InvalidUtf8 {
+        let filename =
+            std::str::from_utf8(&payload[..filename_end]).map_err(|e| Error::InvalidUtf8 {
                 field: "filename",
                 source: e,
-            }
-        })?;
+            })?;
 
         // Find the mode string after the filename null terminator
         let mode_start = filename_end + 1;
@@ -263,11 +262,12 @@ impl Packet {
             .ok_or(Error::MissingNullTerminator { field: "mode" })?
             + mode_start;
 
-        let mode_str =
-            std::str::from_utf8(&payload[mode_start..mode_end]).map_err(|e| Error::InvalidUtf8 {
+        let mode_str = std::str::from_utf8(&payload[mode_start..mode_end]).map_err(|e| {
+            Error::InvalidUtf8 {
                 field: "mode",
                 source: e,
-            })?;
+            }
+        })?;
 
         let mode = Mode::parse(mode_str)?;
 
@@ -594,10 +594,7 @@ mod tests {
 
     #[test]
     fn test_invalid_mode() {
-        assert!(matches!(
-            Mode::parse("binary"),
-            Err(Error::InvalidMode(_))
-        ));
+        assert!(matches!(Mode::parse("binary"), Err(Error::InvalidMode(_))));
         assert!(matches!(Mode::parse("mail"), Err(Error::InvalidMode(_))));
     }
 

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

@@ -25,7 +25,7 @@
 //! ... (continues until final DATA with < 512 bytes)
 //! ```
 
-use crate::{Error, Mode, Packet, Result, MAX_DATA_SIZE};
+use crate::{Error, MAX_DATA_SIZE, Mode, Packet, Result};
 
 /// Direction of data transfer.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]