refactor(proto): make echo_packet_len return Result to handle negative lengths

crates/irtt-proto/src/echo.rs

@@ -1,7 +1,7 @@
 use crate::{
     flags::{has, FLAG_HMAC, FLAG_OPEN, FLAG_REPLY},
     hmac,
-    layout::{try_echo_packet_len, PacketLayout},
+    layout::{echo_packet_len, PacketLayout},
     open::{check_hmac_presence, reject},
     params::Params,
     validate_header, write_header, ProtoError, Result, HEADER_SIZE, HMAC_SIZE, RECV_COUNT_SIZE,
@@ -43,7 +43,7 @@ pub fn encode_echo_request(request: &EchoRequest, hmac_key: Option<&[u8]>) -> Re
         flags |= FLAG_HMAC;
     }
     let layout = PacketLayout::echo(hmac_key.is_some(), &request.params);
-    let len = try_echo_packet_len(hmac_key.is_some(), &request.params)?;
+    let len = echo_packet_len(hmac_key.is_some(), &request.params)?;
     let payload_offset = layout.header_len();
     let available_payload_len = len.saturating_sub(payload_offset);
     if request.payload.len() > available_payload_len {
@@ -87,7 +87,7 @@ pub fn decode_echo_reply(
             actual: packet.len(),
         });
     }
-    let expected_len = try_echo_packet_len(has(flags, FLAG_HMAC), params)?;
+    let expected_len = echo_packet_len(has(flags, FLAG_HMAC), params)?;
     if packet.len() != expected_len {
         return Err(ProtoError::PacketLengthMismatch {
             expected: expected_len,
@@ -371,7 +371,7 @@ mod tests {
         };
         params.received_stats = ReceivedStats::Both;
         let layout = PacketLayout::echo(true, &params);
-        let mut packet = Vec::with_capacity(try_echo_packet_len(true, &params).unwrap());
+        let mut packet = Vec::with_capacity(echo_packet_len(true, &params).unwrap());
         write_header(&mut packet, FLAG_REPLY | FLAG_HMAC);
         packet.extend_from_slice(&[0; HMAC_SIZE]);
         packet.extend_from_slice(&0x7896_b6ab_8771_5213u64.to_le_bytes());

crates/irtt-proto/src/layout.rs

@@ -111,13 +111,7 @@ pub fn echo_header_len(hmac: bool, params: &Params) -> usize {
     PacketLayout::echo(hmac, params).header_len()
 }
 
-pub fn echo_packet_len(hmac: bool, params: &Params) -> usize {
+pub fn echo_packet_len(hmac: bool, params: &Params) -> Result<usize> {
-    let header_len = echo_header_len(hmac, params);
-    let requested = usize::try_from(params.length).unwrap_or(0);
-    header_len.max(requested)
-}
-
-pub fn try_echo_packet_len(hmac: bool, params: &Params) -> Result<usize> {
     let header_len = echo_header_len(hmac, params);
     let requested =
         usize::try_from(params.length).map_err(|_| ProtoError::NegativePacketLength {
@@ -300,9 +294,9 @@ mod tests {
     fn negotiated_length_never_smaller_than_header() {
         let mut p = params(ReceivedStats::Both, StampAt::Both, Clock::Both);
         p.length = 20;
-        assert_eq!(echo_packet_len(false, &p), 60);
+        assert_eq!(echo_packet_len(false, &p).unwrap(), 60);
         p.length = 92;
-        assert_eq!(echo_packet_len(false, &p), 92);
+        assert_eq!(echo_packet_len(false, &p).unwrap(), 92);
     }
 
     #[test]
@@ -311,7 +305,7 @@ mod tests {
         p.length = -1;
 
         assert_eq!(
-            try_echo_packet_len(false, &p),
+            echo_packet_len(false, &p),
             Err(ProtoError::NegativePacketLength { length: -1 })
         );
     }
@@ -320,9 +314,9 @@ mod tests {
     fn checked_packet_len_preserves_non_negative_header_floor() {
         let mut p = params(ReceivedStats::Both, StampAt::Both, Clock::Both);
         p.length = 0;
-        assert_eq!(try_echo_packet_len(false, &p), Ok(60));
+        assert_eq!(echo_packet_len(false, &p), Ok(60));
 
         p.length = 92;
-        assert_eq!(try_echo_packet_len(false, &p), Ok(92));
+        assert_eq!(echo_packet_len(false, &p), Ok(92));
     }
 }

crates/irtt-proto/src/lib.rs

@@ -15,7 +15,7 @@ pub use echo::{decode_echo_reply, encode_echo_request, EchoReply, EchoRequest, T
 pub use error::{ProtoError, Result};
 pub use flags::*;
 pub use hmac::{compute_hmac, compute_hmac_in_place, verify_hmac};
-pub use layout::{echo_header_len, echo_packet_len, try_echo_packet_len, PacketLayout};
+pub use layout::{echo_header_len, echo_packet_len, PacketLayout};
 pub use open::{decode_open_reply, encode_open_request, OpenReply, OpenRequest};
 pub use params::{Clock, Params, ReceivedStats, ServerFill, StampAt};