tcp_out.c File Reference

#include "lwip/opt.h"
#include "lwip/priv/tcp_priv.h"
#include "lwip/def.h"
#include "lwip/mem.h"
#include "lwip/memp.h"
#include "lwip/ip_addr.h"
#include "lwip/netif.h"
#include "lwip/inet_chksum.h"
#include "lwip/stats.h"
#include "lwip/ip6.h"
#include "lwip/ip6_addr.h"
#include <string.h>
#include "path/to/my/lwip_hooks.h"

Macros
#define	TCP_CHECKSUM_ON_COPY_SANITY_CHECK   0
#define	TCP_OVERSIZE_CALC_LENGTH(length)   ((length) + TCP_OVERSIZE)

Functions
err_t	tcp_write (struct tcp_pcb *pcb, const void *arg, u16_t len, u8_t apiflags)
err_t	tcp_split_unsent_seg (struct tcp_pcb *pcb, u16_t split)
err_t	tcp_send_fin (struct tcp_pcb *pcb)
err_t	tcp_enqueue_flags (struct tcp_pcb *pcb, u8_t flags)
err_t	tcp_output (struct tcp_pcb *pcb)
err_t	tcp_rexmit_rto_prepare (struct tcp_pcb *pcb)
void	tcp_rexmit_rto_commit (struct tcp_pcb *pcb)
void	tcp_rexmit_rto (struct tcp_pcb *pcb)
err_t	tcp_rexmit (struct tcp_pcb *pcb)
void	tcp_rexmit_fast (struct tcp_pcb *pcb)
void	tcp_rst (const struct tcp_pcb *pcb, u32_t seqno, u32_t ackno, const ip_addr_t *local_ip, const ip_addr_t *remote_ip, u16_t local_port, u16_t remote_port)
err_t	tcp_send_empty_ack (struct tcp_pcb *pcb)
err_t	tcp_keepalive (struct tcp_pcb *pcb)
err_t	tcp_zero_window_probe (struct tcp_pcb *pcb)

Detailed Description

Transmission Control Protocol, outgoing traffic

The output functions of TCP.

There are two distinct ways for TCP segments to get sent:

• queued data: these are segments transferring data or segments containing SYN or FIN (which both count as one sequence number). They are created as struct Packet buffers (PBUF) together with a struct tcp_seg and enqueue to the unsent list of the pcb. They are sent by tcp_output:
  • tcp_write : creates data segments
  • tcp_split_unsent_seg : splits a data segment
  • tcp_enqueue_flags : creates SYN-only or FIN-only segments
  • tcp_output / tcp_output_segment : finalize the tcp header (e.g. sequence numbers, options, checksum) and output to IP
  • the various tcp_rexmit functions shuffle around segments between the unsent an unacked lists to retransmit them
  • tcp_create_segment and tcp_pbuf_prealloc allocate pbuf and segment for these functions
• direct send: these segments don't contain data but control the connection behaviour. They are created as pbuf only and sent directly without enqueueing them:
  • tcp_send_empty_ack sends an ACK-only segment
  • tcp_rst sends a RST segment
  • tcp_keepalive sends a keepalive segment
  • tcp_zero_window_probe sends a window probe segment
  • tcp_output_alloc_header allocates a header-only pbuf for these functions

Macro Definition Documentation

TCP_CHECKSUM_ON_COPY_SANITY_CHECK

#define TCP_CHECKSUM_ON_COPY_SANITY_CHECK   0

Define this to 1 for an extra check that the output checksum is valid (usefule when the checksum is generated by the application, not the stack)

TCP_OVERSIZE_CALC_LENGTH

#define TCP_OVERSIZE_CALC_LENGTH

(

length

)

((length) + TCP_OVERSIZE)

The size of segment pbufs created when TCP_OVERSIZE is enabled

Function Documentation

tcp_enqueue_flags()

err_t tcp_enqueue_flags	(	struct tcp_pcb *	pcb,
		u8_t	flags
	)

Enqueue SYN or FIN for transmission.

Called by tcp_connect, tcp_listen_input, and tcp_close (via tcp_send_fin)

Parameters

pcb	Protocol control block for the TCP connection.
flags	TCP header flags to set in the outgoing segment.

tcp_keepalive()

err_t tcp_keepalive

(

struct tcp_pcb *

pcb

)

Send keepalive packets to keep a connection active although no data is sent over it.

Called by tcp_slowtmr()

Parameters

pcb	the tcp_pcb for which to send a keepalive packet

tcp_rexmit()

err_t tcp_rexmit

(

struct tcp_pcb *

pcb

)

Requeue the first unacked segment for retransmission

Called by tcp_receive() for fast retransmit.

Parameters

pcb	the tcp_pcb for which to retransmit the first unacked segment

tcp_rexmit_fast()

void tcp_rexmit_fast

(

struct tcp_pcb *

pcb

)

Handle retransmission after three dupacks received

Parameters

pcb	the tcp_pcb for which to retransmit the first unacked segment

tcp_rexmit_rto()

void tcp_rexmit_rto

(

struct tcp_pcb *

pcb

)

Requeue all unacked segments for retransmission

Called by tcp_process() only, tcp_slowtmr() needs to do some things between "prepare" and "commit".

Parameters

pcb	the tcp_pcb for which to re-enqueue all unacked segments

tcp_rexmit_rto_commit()

void tcp_rexmit_rto_commit

(

struct tcp_pcb *

pcb

)

Requeue all unacked segments for retransmission

Called by tcp_slowtmr() for slow retransmission.

Parameters

pcb	the tcp_pcb for which to re-enqueue all unacked segments

tcp_rexmit_rto_prepare()

err_t tcp_rexmit_rto_prepare

(

struct tcp_pcb *

pcb

)

Requeue all unacked segments for retransmission

Called by tcp_slowtmr() for slow retransmission.

Parameters

pcb	the tcp_pcb for which to re-enqueue all unacked segments

tcp_rst()

void tcp_rst	(	const struct tcp_pcb *	pcb,
		u32_t	seqno,
		u32_t	ackno,
		const ip_addr_t *	local_ip,
		const ip_addr_t *	remote_ip,
		u16_t	local_port,
		u16_t	remote_port
	)

Send a TCP RESET packet (empty segment with RST flag set) either to abort a connection or to show that there is no matching local connection for a received segment.

Called by tcp_abort() (to abort a local connection), tcp_input() (if no matching local pcb was found), tcp_listen_input() (if incoming segment has ACK flag set) and tcp_process() (received segment in the wrong state)

Since a RST segment is in most cases not sent for an active connection, tcp_rst() has a number of arguments that are taken from a tcp_pcb for most other segment output functions.

Parameters

pcb	TCP pcb (may be NULL if no pcb is available)
seqno	the sequence number to use for the outgoing segment
ackno	the acknowledge number to use for the outgoing segment
local_ip	the local IP address to send the segment from
remote_ip	the remote IP address to send the segment to
local_port	the local TCP port to send the segment from
remote_port	the remote TCP port to send the segment to

tcp_send_empty_ack()

err_t tcp_send_empty_ack

(

struct tcp_pcb *

pcb

)

Send an ACK without data.

Parameters

pcb	Protocol control block for the TCP connection to send the ACK

tcp_send_fin()

err_t tcp_send_fin

(

struct tcp_pcb *

pcb

)

Called by tcp_close() to send a segment including FIN flag but not data. This FIN may be added to an existing segment or a new, otherwise empty segment is enqueued.

Parameters

pcb	the tcp_pcb over which to send a segment

Returns

ERR_OK if sent, another err_t otherwise

tcp_split_unsent_seg()

err_t tcp_split_unsent_seg	(	struct tcp_pcb *	pcb,
		u16_t	split
	)

Split segment on the head of the unsent queue. If return is not ERR_OK, existing head remains intact

The split is accomplished by creating a new TCP segment and pbuf which holds the remainder payload after the split. The original pbuf is trimmed to new length. This allows splitting of read-only pbufs

Parameters

pcb	the tcp_pcb for which to split the unsent head
split	the amount of payload to remain in the head

tcp_zero_window_probe()

err_t tcp_zero_window_probe

(

struct tcp_pcb *

pcb

)

Send persist timer zero-window probes to keep a connection active when a window update is lost.

Called by tcp_slowtmr()

Parameters

pcb	the tcp_pcb for which to send a zero-window probe packet