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conn: reduce initial memory in Receive() #215

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30 changes: 11 additions & 19 deletions conn_linux.go
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Original file line number Diff line number Diff line change
Expand Up @@ -121,28 +121,20 @@ func (c *conn) Send(m Message) error {

// Receive receives one or more Messages from netlink.
func (c *conn) Receive() ([]Message, error) {
b := make([]byte, os.Getpagesize())
for {
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@nickgarlis nickgarlis Nov 5, 2025

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I wonder whether the reason for the loop here was to make sure we are not falling behind the kernel in an async scenario. Perhaps @mdlayher wanted to avoid setting the buffer to the exact number of available bytes.

Is it possible for more bytes come in before the next recvmsg call ? I think that shouldn't happen but have you confirmed that @florianl ?

If it's indeed safe then it'd be nice to have this.

// Peek at the buffer to see how many bytes are available.
//
// TODO(mdlayher): deal with OOB message data if available, such as
// when PacketInfo ConnOption is true.
n, _, _, _, err := c.s.Recvmsg(context.Background(), b, nil, unix.MSG_PEEK)
if err != nil {
return nil, err
}

// Break when we can read all messages
if n < len(b) {
break
}

// Double in size if not enough bytes
b = make([]byte, len(b)*2)
b := make([]byte, unix.SizeofNlMsghdr)
// Peek at the buffer to see how many bytes are available.
//
// TODO(mdlayher): deal with OOB message data if available, such as
// when PacketInfo ConnOption is true.
n, _, _, _, err := c.s.Recvmsg(context.Background(), b, nil, unix.MSG_PEEK|unix.MSG_TRUNC)
if err != nil {
return nil, err
}
// Resize buffer to the expected size.
b = make([]byte, nlmsgAlign(n))

// Read out all available messages
n, _, _, _, err := c.s.Recvmsg(context.Background(), b, nil, 0)
n, _, _, _, err = c.s.Recvmsg(context.Background(), b, nil, 0)
if err != nil {
return nil, err
}
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