rust: bssl-tls: Retract accidental datagram trait implementation

This DatagramSocket trait should never be implemented back on TlsConnection.

Update-Note: a reasonable application should have always used
`sync_recv` or `sync_send`.

Signed-off-by: Xiangfei Ding <xfding@google.com>
Change-Id: Ibc0cb059a814d1633d71533254b3e8a56a6a6964
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/102787
Presubmit-BoringSSL-Verified: boringssl-scoped@luci-project-accounts.iam.gserviceaccount.com <boringssl-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Benjamin <davidben@google.com>

rust/bssl-tls/src/connection/io/stdio.rs

diff --git a/rust/bssl-tls/src/connection/io/stdio.rs b/rust/bssl-tls/src/connection/io/stdio.rs
index e048bcc..43448ae 100644
--- a/rust/bssl-tls/src/connection/io/stdio.rs
+++ b/rust/bssl-tls/src/connection/io/stdio.rs
@@ -18,19 +18,12 @@
 use crate::{
     ReceiveBuffer,
     connection::TlsConnection,
-    context::{
-        DtlsMode, //
-        TlsMode,
-    },
+    context::TlsMode,
     errors::{
         IoError,
         TlsRetryReason, //
     },
-    io::{
-        AbstractSocketResult,
-        IoStatus,
-        stdio::DatagramSocket, //
-    }, //
+    io::IoStatus, //
 };
 
 fn translate_res_for_stdio(res: Result<IoStatus, Error>) -> Result<usize, io::Error> {
@@ -79,29 +72,3 @@
         translate_res_for_stdio(self.flush()).map(|_| ())
     }
 }
-
-fn translate_result_for_datagram(res: Result<IoStatus, Error>) -> AbstractSocketResult {
-    match res {
-        Ok(IoStatus::Ok(bytes)) => AbstractSocketResult::Ok(bytes),
-        Ok(IoStatus::EndOfStream) | Err(Error::Io(IoError::EndOfStream)) => {
-            AbstractSocketResult::EndOfStream
-        }
-        Ok(IoStatus::Retry(_)) => AbstractSocketResult::Retry,
-        Ok(IoStatus::Empty | IoStatus::Err) => AbstractSocketResult::Err(Box::new(io::Error::new(
-            io::ErrorKind::Other,
-            "transport failed or empty",
-        ))),
-        Err(e) => AbstractSocketResult::Err(Box::new(io::Error::new(io::ErrorKind::Other, e))),
-    }
-}
-
-impl<R> DatagramSocket for TlsConnection<R, DtlsMode> {
-    fn send(&mut self, datagram: &[u8]) -> AbstractSocketResult {
-        translate_result_for_datagram(self.sync_send(datagram))
-    }
-
-    fn recv(&mut self, datagram: &mut [u8]) -> AbstractSocketResult {
-        let mut datagram = ReceiveBuffer::new(datagram);
-        translate_result_for_datagram(self.sync_recv(&mut datagram))
-    }
-}

rust/bssl-tls/src/io/stdio.rs

diff --git a/rust/bssl-tls/src/io/stdio.rs b/rust/bssl-tls/src/io/stdio.rs
index 8da2071..535d5b1 100644
--- a/rust/bssl-tls/src/io/stdio.rs
+++ b/rust/bssl-tls/src/io/stdio.rs
@@ -21,7 +21,7 @@
 
 use super::AbstractSocketResult;
 
-/// A datagram socket protocol
+/// A datagram socket protocol as backing transport of TLS connection.
 pub trait DatagramSocket: Send {
     /// Send a complete datagram through the socket.
     ///