Struct MessageReader 

pub struct MessageReader { /* private fields */ }

Cancellation-safe backend message reader.

PostgreSQL backend messages span multiple read operations (5-byte header, then a variable payload). A naive implementation using read_exact is not cancellation-safe: if the future is dropped between reads (e.g. by tokio::select! or tokio::time::timeout), bytes already pulled from the underlying stream are lost and the next read mis-parses the wire stream.

MessageReader externalizes the partial-read state so it survives across dropped futures. Each call to read uses one-shot AsyncReadExt::read (which is cancel-safe) and accumulates progress on self. If the returned future is dropped, no bytes are lost; the next invocation resumes from where the previous one left off.

Implementations

impl MessageReader

pub fn new() -> Self

pub fn with_capacity(capacity: usize) -> Self

pub fn with_max_message_size(self, max: usize) -> Self

Refuse any message whose payload is larger than max bytes.

max is compared against the message’s length field minus 4, so it excludes the tag and the length field itself. The payload buffer is sized from the length the server announces, so this bounds the memory one message can take. It can only lower the limit: a value above MAX_MESSAGE_SIZE, the default, is capped to it.

A refused message is terminal. Its payload is left on the wire, so the reader cannot resynchronize and every later read returns the same PgWireError::MessageTooLarge. Discard the reader and the connection.

pub async fn read<R: AsyncRead + Unpin>( &mut self, rd: &mut R, ) -> Result<BackendMessage>

Read the next complete backend message.

Cancellation-safe: dropping the returned future preserves all progress so far on self. Re-call to resume.

Trait Implementations

impl Default for MessageReader

fn default() -> Self

Returns the “default value” for a type.