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# netconn_new_with_callback()

## Name

netconn_new_with_callback() -- Create a new connection structure with a callback

## Synopsis

``struct netconn *netconn_new_with_callback`(enum netconn_type type, void (*callback) (struct netconn *conn, enum netconn_evt evt, u16_t len));`

## Description

This function is similar to `netconn_new()` except that an additional function pointer callback is passed. The function pointed to by callback will be called when data is sent or received. Specifically, the netconn_evt parameter to the callback is used to indicate the event type. This enum can have the following values:

NETCONN_EVT_RCVPLUS

  Used when new incoming data from a remote peer arrives. The amount of data received is passed in len. If len is 0 then a connection event has occurred: this may be an error, the acceptance of a connection for a listening connection (called for the listening connection), or deletion of the connection.

NETCONN_EVT_RCVMINUS

  Used when new incoming data from a remote peer has been received and accepted by higher layers. The amount of data accepted is passed in len. If len is 0 then this indicates the acceptance of a connection as a result of a listening port (called for the newly created accepted connection).

NETCONN_EVT_SENDPLUS

  Used when data has been sent to a remote peer and received by it. This only occurs for TCP connections, and specifically is only triggered when, as a consequence of TCP acknowledgements from the remote peer, the free TCP send buffer size now exceeds the configured send buffer low water mark (configured with the CYGNUM_LWIP_TCP_SNDLOWAT CDL configuration option). The amount of data sent in the most recent transaction is passed in len. If len is 0 then this indicates the connection has been deleted.

NETCONN_EVT_SENDMINUS

  This is only used for TCP connections, and is triggered when a sufficient amount of data has been sent on the connection that the amount of free send buffer space is now under the send buffer low water mark (configured with the CYGNUM_LWIP_TCP_SNDLOWAT CDL configuration option). The amount of data sent in the most recent transaction is passed in len.

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