refactor(proto): reuse code in handshakes

proto/src/handshake/client.rs

@@ -0,0 +1,34 @@
+use crate::handshake::errors::ClientHandshakeError;
+use crate::handshake::request::HandshakeRequest;
+use crate::handshake::response::HandshakeResponse;
+use crate::message::backend::{AuthenticationOkData, BackendMessage};
+use crate::message::special::StartupMessageData;
+use crate::reader::backend::BackendProtoReader;
+use crate::writer::frontend::FrontendProtoWriter;
+use crate::writer::protowriter::ProtoFlush;
+
+pub async fn do_client_handshake(
+    writer: &mut (impl FrontendProtoWriter + ProtoFlush),
+    reader: &mut impl BackendProtoReader,
+    request: HandshakeRequest,
+) -> Result<HandshakeResponse, ClientHandshakeError> {
+    let startup_message: StartupMessageData = request.into();
+    writer.write_startup_message(startup_message).await?;
+
+    let auth = reader.read_proto().await?;
+    if !matches!(auth, BackendMessage::AuthenticationOk(AuthenticationOkData { status: 0 })) {
+        return Err(ClientHandshakeError::UnexpectedAuthResponse(auth));
+    }
+
+    let mut messages = Vec::new();
+    loop {
+        let msg = reader.read_proto().await?;
+        if matches!(msg, BackendMessage::ReadyForQuery(_)) {
+            break;
+        }
+
+        messages.push(msg);
+    }
+
+    HandshakeResponse::try_from(messages.as_slice())
+}