patch contrib/grpc: Fix bug in Tx0cp code path in posix endpoint. (#20962)

Author: ubyte

contrib/libs/grpc/patches/pr37696_code_path_in_posix_endpoint.patch

@@ -0,0 +1,13 @@
+diff --git a/src/core/lib/event_engine/posix_engine/posix_endpoint.cc b/src/core/lib/event_engine/posix_engine/posix_endpoint.cc
+index 7634bb1334b81..c5708db02c57a 100644
+--- a/src/core/lib/event_engine/posix_engine/posix_endpoint.cc
++++ b/src/core/lib/event_engine/posix_engine/posix_endpoint.cc
+@@ -236,7 +236,7 @@ msg_iovlen_type TcpZerocopySendRecord::PopulateIovs(size_t* unwind_slice_idx,
+        iov_size++) {
+     MutableSlice& slice = internal::SliceCast<MutableSlice>(
+         buf_.MutableSliceAt(out_offset_.slice_idx));
+-    iov[iov_size].iov_base = slice.begin();
++    iov[iov_size].iov_base = slice.begin() + out_offset_.byte_idx;
+     iov[iov_size].iov_len = slice.length() - out_offset_.byte_idx;
+     *sending_length += iov[iov_size].iov_len;
+     ++(out_offset_.slice_idx);

contrib/libs/grpc/src/core/lib/event_engine/posix_engine/posix_endpoint.cc

@@ -238,7 +238,7 @@ msg_iovlen_type TcpZerocopySendRecord::PopulateIovs(size_t* unwind_slice_idx,
        iov_size++) {
     MutableSlice& slice = internal::SliceCast<MutableSlice>(
         buf_.MutableSliceAt(out_offset_.slice_idx));
-    iov[iov_size].iov_base = slice.begin();
+    iov[iov_size].iov_base = slice.begin() + out_offset_.byte_idx;
     iov[iov_size].iov_len = slice.length() - out_offset_.byte_idx;
     *sending_length += iov[iov_size].iov_len;
     ++(out_offset_.slice_idx);