From b59e494ae7d90e58a9d476098fb96b5d26c73066 Mon Sep 17 00:00:00 2001
From: d2weber <29163905+d2weber@users.noreply.github.com>
Date: Tue, 10 Sep 2024 18:06:09 +0200
Subject: [PATCH] Fixes #982

---
 .github/workflows/test.yml |  8 ++++++++
 ci.sh                      | 14 ++++++++++++++
 src/socket/tcp.rs          | 16 +++++++---------
 3 files changed, 29 insertions(+), 9 deletions(-)

diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 4a13ca959..a3e79ec6e 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -47,3 +47,11 @@ jobs:
       - uses: actions/checkout@v4
       - name: Run Tests nightly
         run: ./ci.sh test nightly
+
+  test-build-16bit:
+    runs-on: ubuntu-22.04
+    continue-on-error: true
+    steps:
+      - uses: actions/checkout@v4
+      - name: Build for target with 16 bit pointer
+        run: ./ci.sh build_16bit
diff --git a/ci.sh b/ci.sh
index 109047719..eb9235f7e 100755
--- a/ci.sh
+++ b/ci.sh
@@ -82,6 +82,16 @@ clippy() {
     cargo +$MSRV clippy --tests --examples -- -D warnings
 }
 
+build_16bit() {
+    rustup toolchain install nightly
+    rustup +nightly component add rust-src
+
+    TARGET_WITH_16BIT_POINTER=msp430-none-elf
+    for features in ${FEATURES_CHECK[@]}; do
+        cargo +nightly build -Z build-std=core,alloc --target $TARGET_WITH_16BIT_POINTER --no-default-features --features=$features
+    done
+}
+
 coverage() {
     for features in ${FEATURES_TEST[@]}; do
         cargo llvm-cov --no-report --no-default-features --features "$features"
@@ -121,6 +131,10 @@ if [[ $1 == "clippy" || $1 == "all" ]]; then
     clippy
 fi
 
+if [[ $1 == "build_16bit" || $1 == "all" ]]; then
+    build_16bit
+fi
+
 if [[ $1 == "coverage" || $1 == "all" ]]; then
     coverage
 fi
diff --git a/src/socket/tcp.rs b/src/socket/tcp.rs
index 46f1b36f9..9460fa5c0 100644
--- a/src/socket/tcp.rs
+++ b/src/socket/tcp.rs
@@ -5,7 +5,7 @@
 use core::fmt::Display;
 #[cfg(feature = "async")]
 use core::task::Waker;
-use core::{cmp, fmt, mem};
+use core::{fmt, mem};
 
 #[cfg(feature = "async")]
 use crate::socket::WakerRegistration;
@@ -510,6 +510,7 @@ impl<'a> Socket<'a> {
         // [...] the above constraints imply that 2 * the max window size must be less
         // than 2**31 [...] Thus, the shift count must be limited to 14 (which allows
         // windows of 2**30 = 1 Gbyte).
+        #[cfg(not(target_pointer_width = "16"))] // Prevent overflow
         if rx_capacity > (1 << 30) {
             panic!("receiving buffer too large, cannot exceed 1 GiB")
         }
@@ -676,10 +677,7 @@ impl<'a> Socket<'a> {
     /// Used in internal calculations as well as packet generation.
     #[inline]
     fn scaled_window(&self) -> u16 {
-        cmp::min(
-            self.rx_buffer.window() >> self.remote_win_shift as usize,
-            (1 << 16) - 1,
-        ) as u16
+        u16::try_from(self.rx_buffer.window() >> self.remote_win_shift).unwrap_or(u16::MAX)
     }
 
     /// Return the last window field value, including scaling according to RFC 1323.
@@ -698,7 +696,7 @@ impl<'a> Socket<'a> {
         let last_win = (self.remote_last_win as usize) << self.remote_win_shift;
         let last_win_adjusted = last_ack + last_win - next_ack;
 
-        Some(cmp::min(last_win_adjusted >> self.remote_win_shift, (1 << 16) - 1) as u16)
+        Some(u16::try_from(last_win_adjusted >> self.remote_win_shift).unwrap_or(u16::MAX))
     }
 
     /// Set the timeout duration.
@@ -2335,7 +2333,7 @@ impl<'a> Socket<'a> {
             State::SynSent | State::SynReceived => {
                 repr.control = TcpControl::Syn;
                 // window len must NOT be scaled in SYNs.
-                repr.window_len = self.rx_buffer.window().min((1 << 16) - 1) as u16;
+                repr.window_len = u16::try_from(self.rx_buffer.window()).unwrap_or(u16::MAX);
                 if self.state == State::SynSent {
                     repr.ack_number = None;
                     repr.window_scale = Some(self.remote_win_shift);
@@ -3075,7 +3073,7 @@ mod test {
                     ack_number: Some(REMOTE_SEQ + 1),
                     max_seg_size: Some(BASE_MSS),
                     window_scale: Some(*shift_amt),
-                    window_len: cmp::min(*buffer_size, 65535) as u16,
+                    window_len: u16::try_from(*buffer_size).unwrap_or(u16::MAX),
                     ..RECV_TEMPL
                 }]
             );
@@ -3810,7 +3808,7 @@ mod test {
                     ack_number: None,
                     max_seg_size: Some(BASE_MSS),
                     window_scale: Some(*shift_amt),
-                    window_len: cmp::min(*buffer_size, 65535) as u16,
+                    window_len: u16::try_from(*buffer_size).unwrap_or(u16::MAX),
                     sack_permitted: true,
                     ..RECV_TEMPL
                 }]