fix: assure we don't stop early on NAK if READY was sent to handle V1 specialty (#882).

Seeing READY means a pack will follow, which is exactly the kind of knowledge we want.
Thus we now either listen to the client OR to what the server says.

Note that this remedy relies on `multi-ack-detailed`, which some very old servers might
not support. For those we would be out-of-luck, but that seems acceptable.

Author: Byron

gix-protocol/src/fetch/response/async_io.rs

@@ -47,6 +47,7 @@ impl Response {
                 let mut line = String::new();
                 let mut acks = Vec::<Acknowledgement>::new();
                 let mut shallows = Vec::<ShallowUpdate>::new();
+                let mut saw_ready = false;
                 let has_pack = 'lines: loop {
                     line.clear();
                     let peeked_line = match reader.peek_data_line().await {
@@ -81,14 +82,16 @@ impl Response {
                     if Response::parse_v1_ack_or_shallow_or_assume_pack(&mut acks, &mut shallows, &peeked_line) {
                         break 'lines true;
                     }
-                    if let Some(Acknowledgement::Nak) = acks.last().filter(|_| !client_expects_pack) {
-                        break 'lines false;
-                    }
                     assert_ne!(
                         reader.readline_str(&mut line).await?,
                         0,
                         "consuming a peeked line works"
                     );
+                    // When the server sends ready, we know there is going to be a pack so no need to stop early.
+                    saw_ready |= matches!(acks.last(), Some(Acknowledgement::Ready));
+                    if let Some(Acknowledgement::Nak) = acks.last().filter(|_| !client_expects_pack && !saw_ready) {
+                        break 'lines false;
+                    }
                 };
                 Ok(Response {
                     acks,

gix-protocol/src/fetch/response/blocking_io.rs

@@ -47,6 +47,7 @@ impl Response {
                 let mut line = String::new();
                 let mut acks = Vec::<Acknowledgement>::new();
                 let mut shallows = Vec::<ShallowUpdate>::new();
+                let mut saw_ready = false;
                 let has_pack = 'lines: loop {
                     line.clear();
                     let peeked_line = match reader.peek_data_line() {
@@ -81,10 +82,12 @@ impl Response {
                     if Response::parse_v1_ack_or_shallow_or_assume_pack(&mut acks, &mut shallows, &peeked_line) {
                         break 'lines true;
                     }
-                    if let Some(Acknowledgement::Nak) = acks.last().filter(|_| !client_expects_pack) {
+                    assert_ne!(reader.readline_str(&mut line)?, 0, "consuming a peeked line works");
+                    // When the server sends ready, we know there is going to be a pack so no need to stop early.
+                    saw_ready |= matches!(acks.last(), Some(Acknowledgement::Ready));
+                    if let Some(Acknowledgement::Nak) = acks.last().filter(|_| !client_expects_pack && !saw_ready) {
                         break 'lines false;
                     }
-                    assert_ne!(reader.readline_str(&mut line)?, 0, "consuming a peeked line works");
                 };
                 Ok(Response {
                     acks,