Struct Connection 

pub struct Connection<T>
where
    T: AsyncRead + AsyncWrite,
{ /* private fields */ }

A TDS connection with split I/O for cancellation safety.

This struct splits the underlying transport into read and write halves, allowing Attention packets to be sent even while blocked reading results.

Cancellation

SQL Server uses out-of-band “Attention” packets to cancel running queries. Without split I/O, the driver would be unable to send cancellation while blocked awaiting a read (e.g., processing a large result set).

Example

use mssql_codec::Connection;
use tokio::net::TcpStream;

let stream = TcpStream::connect("localhost:1433").await?;
let conn = Connection::new(stream);

// Can cancel from another task while reading
let cancel_handle = conn.cancel_handle();
tokio::spawn(async move {
    tokio::time::sleep(Duration::from_secs(5)).await;
    cancel_handle.cancel().await?;
});

Implementations

impl<T> Connection<T>

where T: AsyncRead + AsyncWrite,

pub fn new(transport: T) -> Self

Create a new connection from a transport.

The transport is immediately split into read and write halves.

pub fn with_codecs( transport: T, read_codec: TdsCodec, write_codec: TdsCodec, ) -> Self

Create a new connection with custom codecs.

pub fn cancel_handle(&self) -> CancelHandle<T>

Get a handle for cancelling queries on this connection.

The handle can be cloned and sent to other tasks.

pub fn is_cancelling(&self) -> bool

Check if a cancellation is currently in progress.

pub async fn read_message(&mut self) -> Result<Option<Message>, CodecError>

Read the next complete message from the connection.

This handles multi-packet message reassembly automatically.

pub async fn read_packet(&mut self) -> Result<Option<Packet>, CodecError>

Read a single packet from the connection.

This is lower-level than read_message and doesn’t perform reassembly.

pub async fn send_packet(&mut self, packet: Packet) -> Result<(), CodecError>

Send a packet on the connection.

pub async fn send_message( &mut self, packet_type: PacketType, payload: Bytes, max_packet_size: usize, ) -> Result<(), CodecError>

Send a complete message, splitting into multiple packets if needed.

If reset_connection is true, the RESETCONNECTION flag is set on the first packet. This causes SQL Server to reset connection state (temp tables, SET options, isolation level, etc.) before executing the command. Per TDS spec, this flag MUST only be set on the first packet of a message.

pub async fn send_message_with_reset( &mut self, packet_type: PacketType, payload: Bytes, max_packet_size: usize, reset_connection: bool, ) -> Result<(), CodecError>

Send a complete message with optional connection reset.

If reset_connection is true, the RESETCONNECTION flag is set on the first packet. This causes SQL Server to reset connection state (temp tables, SET options, isolation level, etc.) before executing the command. Per TDS spec, this flag MUST only be set on the first packet of a message.

pub async fn flush(&mut self) -> Result<(), CodecError>

Flush the write buffer.

pub fn read_codec(&self) -> &TdsCodec

Get a reference to the read codec.

pub fn read_codec_mut(&mut self) -> &mut TdsCodec

Get a mutable reference to the read codec.

Trait Implementations

impl<T> Debug for Connection<T>

where T: AsyncRead + AsyncWrite + Debug,

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.