tcp_out.c File Reference

Transmission Control Protocol, outgoing traffic.

The output functions of TCP.

#include "lwip/opt.h"
#include "lwip/tcp_impl.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/snmp.h"
#include <string.h>

Macros
#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) More...
#define	TCP_DATA_COPY(dst, src, len, seg)   MEMCPY(dst, src, len)
#define	TCP_DATA_COPY2(dst, src, len, chksum, chksum_swapped)   MEMCPY(dst, src, len)

Functions
static struct tcp_seg *	tcp_create_segment (struct tcp_pcb *pcb, struct pbuf *p, u8_t flags, u32_t seqno, u8_t optflags)
	Create a TCP segment with prefilled header. More...
err_t	tcp_enqueue_flags (struct tcp_pcb *pcb, u8_t flags)
	Enqueue TCP options for transmission. More...
void	tcp_keepalive (struct tcp_pcb *pcb)
	Send keepalive packets to keep a connection active although no data is sent over it. More...
err_t	tcp_output (struct tcp_pcb *pcb)
	Find out what we can send and send it. More...
static struct pbuf *	tcp_output_alloc_header (struct tcp_pcb *pcb, u16_t optlen, u16_t datalen, u32_t seqno_be)
	Allocate a pbuf and create a tcphdr at p->payload, used for output functions other than the default tcp_output -> tcp_output_segment (e.g. More...
static void	tcp_output_segment (struct tcp_seg *seg, struct tcp_pcb *pcb)
	Called by tcp_output() to actually send a TCP segment over IP. More...
static struct pbuf *	tcp_pbuf_prealloc (pbuf_layer layer, u16_t length, u16_t max_length, u16_t *oversize, struct tcp_pcb *pcb, u8_t apiflags, u8_t first_seg)
	Allocate a PBUF_RAM pbuf, perhaps with extra space at the end. More...
void	tcp_rexmit (struct tcp_pcb *pcb)
	Requeue the first unacked segment for retransmission. More...
void	tcp_rexmit_fast (struct tcp_pcb *pcb)
	Handle retransmission after three dupacks received. More...
void	tcp_rexmit_rto (struct tcp_pcb *pcb)
	Requeue all unacked segments for retransmission. More...
void	tcp_rst (u32_t seqno, u32_t ackno, ip_addr_t *local_ip, 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. More...
err_t	tcp_send_empty_ack (struct tcp_pcb *pcb)
	Send an ACK without data. More...
err_t	tcp_send_fin (struct tcp_pcb *pcb)
	Called by tcp_close() to send a segment including FIN flag but not data. More...
err_t	tcp_write (struct tcp_pcb *pcb, const void *arg, u16_t len, u8_t apiflags)
	Write data for sending (but does not send it immediately). More...
static err_t	tcp_write_checks (struct tcp_pcb *pcb, u16_t len)
	Checks if tcp_write is allowed or not (checks state, snd_buf and snd_queuelen). More...
void	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. More...

#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)

#define TCP_DATA_COPY	(		dst,
			src,
			len,
			seg
	)		MEMCPY(dst, src, len)

Referenced by tcp_write().

#define TCP_DATA_COPY2	(		dst,
			src,
			len,
			chksum,
			chksum_swapped
	)		MEMCPY(dst, src, len)

Referenced by tcp_write().

static struct tcp_seg* tcp_create_segment ( struct tcp_pcb *  pcb, struct pbuf *  p, u8_t  flags, u32_t  seqno, u8_t  optflags  )

static

Create a TCP segment with prefilled header.

Called by tcp_write and tcp_enqueue_flags.

Parameters

pcb	Protocol control block for the TCP connection.
p	pbuf that is used to hold the TCP header.
flags	TCP flags for header.
seqno	TCP sequence number of this packet
optflags	options to include in TCP header

Returns

a new tcp_seg pointing to p, or NULL. The TCP header is filled in except ackno and wnd. p is freed on failure.

References tcp_seg::flags, htonl, htons, tcp_seg::len, LWIP_ASSERT, LWIP_DEBUGF, LWIP_TCP_OPT_LENGTH, memp_malloc(), tcp_seg::next, NULL, tcp_seg::p, pbuf::payload, pbuf_free(), pbuf_header(), tcp_pcb::remote_port, TCP_HLEN, TCP_OUTPUT_DEBUG, tcp_seg_free(), TCP_STATS_INC, TCPH_HDRLEN_FLAGS_SET, tcp_seg::tcphdr, TF_SEG_DATA_CHECKSUMMED, and pbuf::tot_len.

Referenced by tcp_enqueue_flags(), and tcp_write().

err_t tcp_enqueue_flags	(	struct tcp_pcb *	pcb,
		u8_t	flags
	)

Enqueue TCP options for transmission.

Called by tcp_connect(), tcp_listen_input(), and tcp_send_ctrl().

Parameters

pcb	Protocol control block for the TCP connection.
flags	TCP header flags to set in the outgoing segment.
optdata	pointer to TCP options, or NULL.
optlen	length of TCP options in bytes.

References ERR_MEM, ERR_OK, tcp_pcb::flags, pbuf::len, tcp_seg::len, LWIP_ASSERT, LWIP_DBG_TRACE, LWIP_DEBUGF, LWIP_TCP_OPT_LENGTH, MEM_ALIGNMENT, tcp_seg::next, ntohl, NULL, tcp_seg::p, pbuf_alloc(), pbuf_clen(), PBUF_RAM, PBUF_TRANSPORT, S16_F, tcp_pcb::snd_buf, tcp_pcb::snd_lbb, tcp_pcb::snd_queuelen, tcp_create_segment(), TCP_FIN, TCP_OUTPUT_DEBUG, TCP_QLEN_DEBUG, TCP_SNDQUEUELEN_OVERFLOW, TCP_STATS_INC, TCP_SYN, TCP_TCPLEN, tcp_seg::tcphdr, TF_FIN, TF_NAGLEMEMERR, TF_SEG_OPTS_MSS, TF_SEG_OPTS_TS, TF_TIMESTAMP, U16_F, U32_F, tcp_pcb::unacked, tcp_pcb::unsent, tcp_pcb::unsent_oversize, and X16_F.

Referenced by tcp_connect(), tcp_listen_input(), and tcp_send_fin().

void 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

References CHECKSUM_GEN_TCP, htonl, inet_chksum_pseudo(), ip4_addr1_16, ip4_addr2_16, ip4_addr3_16, ip4_addr4_16, ip_output(), IP_PROTO_TCP, tcp_pcb::keep_cnt_sent, LWIP_DEBUGF, NULL, pbuf::payload, pbuf_free(), tcp_pcb::rcv_nxt, tcp_pcb::snd_nxt, TCP_DEBUG, tcp_output_alloc_header(), TCP_STATS_INC, tcp_ticks, tcphdr, tcp_pcb::tmr, pbuf::tot_len, U16_F, and U32_F.

Referenced by tcp_slowtmr().

err_t tcp_output

(

struct tcp_pcb *

pcb

)

Find out what we can send and send it.

Parameters

pcb	Protocol control block for the TCP connection to send data

Returns

ERR_OK if data has been sent or nothing to send another err_t on error

References tcp_pcb::cwnd, ERR_OK, tcp_pcb::flags, tcp_pcb::lastack, tcp_seg::len, LISTEN, LWIP_ASSERT, LWIP_DEBUGF, LWIP_MIN, tcp_seg::next, ntohl, NULL, S16_F, tcp_pcb::snd_nxt, tcp_pcb::snd_wnd, SYN_SENT, TCP_ACK, TCP_CWND_DEBUG, tcp_do_output_nagle, tcp_input_pcb, TCP_OUTPUT_DEBUG, tcp_output_segment(), TCP_RST, tcp_seg_free(), tcp_send_empty_ack(), TCP_SEQ_LT, TCP_TCPLEN, TCPH_FLAGS, TCPH_SET_FLAG, tcp_seg::tcphdr, TF_ACK_DELAY, TF_ACK_NOW, TF_FIN, TF_NAGLEMEMERR, U16_F, U32_F, tcp_pcb::unacked, tcp_pcb::unsent, and tcp_pcb::unsent_oversize.

Referenced by tcp_close_shutdown(), tcp_connect(), tcp_fasttmr(), tcp_input(), tcp_listen_input(), tcp_pcb_remove(), tcp_recved(), tcp_rexmit_rto(), tcp_slowtmr(), and tcp_timewait_input().

static struct pbuf* tcp_output_alloc_header ( struct tcp_pcb *  pcb, u16_t  optlen, u16_t  datalen, u32_t  seqno_be  )

static

Allocate a pbuf and create a tcphdr at p->payload, used for output functions other than the default tcp_output -> tcp_output_segment (e.g.

tcp_send_empty_ack, etc.)

Parameters

pcb	tcp pcb for which to send a packet (used to initialize tcp_hdr)
optlen	length of header-options
datalen	length of tcp data to reserve in pbuf
seqno_be	seqno in network byte order (big-endian)

Returns

pbuf with p->payload being the tcp_hdr

References htonl, htons, pbuf::len, LWIP_ASSERT, NULL, pbuf::payload, pbuf_alloc(), PBUF_IP, PBUF_RAM, tcp_pcb::rcv_ann_right_edge, tcp_pcb::rcv_ann_wnd, tcp_pcb::rcv_nxt, tcp_pcb::remote_port, TCP_ACK, TCP_HLEN, TCPH_HDRLEN_FLAGS_SET, and tcphdr.

Referenced by tcp_keepalive(), tcp_send_empty_ack(), and tcp_zero_window_probe().

static void tcp_output_segment ( struct tcp_seg *  seg, struct tcp_pcb *  pcb  )

static

Called by tcp_output() to actually send a TCP segment over IP.

Parameters

seg	the tcp_seg to send
pcb	the tcp_pcb for the TCP connection used to send the segment

Bug:

Exclude retransmitted segments from this count.

References tcp_seg::flags, FOLD_U32T, htonl, htons, inet_chksum_pseudo(), inet_chksum_pseudo_partial(), netif::ip_addr, ip_addr_copy, ip_addr_isany, ip_output(), IP_PROTO_TCP, ip_route(), pbuf::len, tcp_seg::len, LWIP_ASSERT, LWIP_DBG_LEVEL_WARNING, LWIP_DEBUGF, ntohl, NULL, tcp_seg::p, pbuf::payload, tcp_pcb::rcv_ann_right_edge, tcp_pcb::rcv_ann_wnd, tcp_pcb::rcv_nxt, tcp_pcb::rtime, tcp_pcb::rtseq, tcp_pcb::rttest, snmp_inc_tcpoutsegs, SWAP_BYTES_IN_WORD, TCP_BUILD_MSS_OPTION, TCP_DEBUG, tcp_eff_send_mss(), TCP_MSS, TCP_OUTPUT_DEBUG, TCP_RTO_DEBUG, TCP_STATS_INC, tcp_ticks, TCPH_HDRLEN, tcp_seg::tcphdr, TF_SEG_DATA_CHECKSUMMED, TF_SEG_OPTS_MSS, TF_SEG_OPTS_TS, pbuf::tot_len, U32_F, and X16_F.

Referenced by tcp_output().

static struct pbuf* tcp_pbuf_prealloc ( pbuf_layer  layer, u16_t  length, u16_t  max_length, u16_t *  oversize, struct tcp_pcb *  pcb, u8_t  apiflags, u8_t  first_seg  )

static

Allocate a PBUF_RAM pbuf, perhaps with extra space at the end.

This function is like pbuf_alloc(layer, length, PBUF_RAM) except there may be extra bytes available at the end.

Parameters

layer	flag to define header size.
length	size of the pbuf's payload.
max_length	maximum usable size of payload+oversize.
oversize	pointer to a u16_t that will receive the number of usable tail bytes.
pcb	The TCP connection that willo enqueue the pbuf.
apiflags	API flags given to tcp_write.
first_seg	true when this pbuf will be used in the first enqueued segment.

References tcp_pcb::flags, pbuf::len, LWIP_ASSERT, LWIP_MEM_ALIGN_SIZE, LWIP_MIN, LWIP_UNUSED_ARG, pbuf::next, NULL, pbuf_alloc(), PBUF_RAM, TCP_WRITE_FLAG_MORE, TF_NODELAY, pbuf::tot_len, tcp_pcb::unacked, and tcp_pcb::unsent.

Referenced by tcp_write().

void tcp_rexmit

(

struct tcp_pcb *

pcb

)

Requeue the first unacked segment for retransmission.

Called by tcp_receive() for fast retramsmit.

Parameters

pcb	the tcp_pcb for which to retransmit the first unacked segment

References tcp_seg::next, tcp_pcb::nrtx, ntohl, NULL, tcp_pcb::rttest, snmp_inc_tcpretranssegs, TCP_SEQ_LT, tcp_seg::tcphdr, tcp_pcb::unacked, tcp_pcb::unsent, and tcp_pcb::unsent_oversize.

Referenced by tcp_process(), and 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

References tcp_pcb::cwnd, tcp_pcb::dupacks, tcp_pcb::flags, tcp_pcb::lastack, LWIP_DEBUGF, tcp_pcb::mss, ntohl, NULL, tcp_pcb::snd_wnd, tcp_pcb::ssthresh, TCP_FR_DEBUG, tcp_rexmit(), tcp_seg::tcphdr, TF_INFR, U16_F, U32_F, and tcp_pcb::unacked.

Referenced by tcp_receive().

void tcp_rexmit_rto

(

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

References tcp_seg::next, tcp_pcb::nrtx, NULL, tcp_pcb::rttest, tcp_output(), tcp_pcb::unacked, and tcp_pcb::unsent.

Referenced by tcp_slowtmr().

void tcp_rst	(	u32_t	seqno,
		u32_t	ackno,
		ip_addr_t *	local_ip,
		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

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

References htonl, htons, inet_chksum_pseudo(), ip_output(), IP_PROTO_TCP, pbuf::len, LWIP_ASSERT, LWIP_DEBUGF, NULL, pbuf::payload, pbuf_alloc(), pbuf_free(), PBUF_IP, PBUF_RAM, PP_HTONS, snmp_inc_tcpoutrsts, TCP_ACK, TCP_DEBUG, TCP_HLEN, TCP_RST, TCP_RST_DEBUG, TCP_STATS_INC, TCP_WND, TCPH_HDRLEN_FLAGS_SET, tcphdr, pbuf::tot_len, and U32_F.

Referenced by tcp_abandon(), tcp_close_shutdown(), tcp_input(), tcp_listen_input(), tcp_process(), tcp_slowtmr(), and tcp_timewait_input().

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

References ERR_BUF, ERR_OK, tcp_pcb::flags, htonl, inet_chksum_pseudo(), ip_output(), IP_PROTO_TCP, LWIP_DEBUGF, LWIP_TCP_OPT_LENGTH, NULL, pbuf::payload, pbuf_free(), tcp_pcb::rcv_nxt, tcp_pcb::snd_nxt, tcp_output_alloc_header(), TCP_OUTPUT_DEBUG, tcphdr, TF_ACK_DELAY, TF_ACK_NOW, TF_SEG_OPTS_TS, TF_TIMESTAMP, pbuf::tot_len, and U32_F.

Referenced by tcp_output(), and tcp_receive().

err_t tcp_send_fin

(

struct tcp_pcb *

pcb

)

Called by tcp_close() to send a segment including FIN flag but not data.

Parameters

pcb	the tcp_pcb over which to send a segment

Returns

ERR_OK if sent, another err_t otherwise

References ERR_OK, tcp_pcb::flags, tcp_seg::next, NULL, tcp_enqueue_flags(), TCP_FIN, TCP_RST, TCP_SYN, TCPH_FLAGS, TCPH_SET_FLAG, tcp_seg::tcphdr, TF_FIN, and tcp_pcb::unsent.

Referenced by tcp_close_shutdown().

err_t tcp_write	(	struct tcp_pcb *	pcb,
		const void *	arg,
		u16_t	len,
		u8_t	apiflags
	)

Write data for sending (but does not send it immediately).

It waits in the expectation of more data being sent soon (as it can send them more efficiently by combining them together). To prompt the system to send data now, call tcp_output() after calling tcp_write().

Parameters

pcb	Protocol control block for the TCP connection to enqueue data for.
arg	Pointer to the data to be enqueued for sending.
len	Data length in bytes
apiflags	combination of following flags : TCP_WRITE_FLAG_COPY (0x01) data will be copied into memory belonging to the stack TCP_WRITE_FLAG_MORE (0x02) for TCP connection, PSH flag will be set on last segment sent,

Returns

ERR_OK if enqueued, another err_t on error

References ERR_ARG, ERR_MEM, ERR_OK, tcp_pcb::flags, tcp_seg::flags, inet_chksum(), pbuf::len, tcp_seg::len, LWIP_ASSERT, LWIP_DBG_STATE, LWIP_DBG_TRACE, LWIP_DEBUGF, LWIP_ERROR(), LWIP_MIN, LWIP_TCP_OPT_LENGTH, tcp_pcb::mss, pbuf::next, tcp_seg::next, ntohl, NULL, tcp_seg::p, pbuf::payload, pbuf_alloc(), pbuf_cat(), pbuf_clen(), pbuf_free(), PBUF_RAM, PBUF_RAW, PBUF_ROM, PBUF_TRANSPORT, S16_F, tcp_pcb::snd_buf, tcp_pcb::snd_lbb, tcp_pcb::snd_queuelen, tcp_pcb::snd_wnd_max, tcp_create_segment(), TCP_DATA_COPY, TCP_DATA_COPY2, TCP_OUTPUT_DEBUG, tcp_pbuf_prealloc(), TCP_PSH, TCP_QLEN_DEBUG, tcp_segs_free(), TCP_SNDQUEUELEN_OVERFLOW, TCP_STATS_INC, TCP_TCPLEN, tcp_write_checks(), TCP_WRITE_FLAG_COPY, TCP_WRITE_FLAG_MORE, TCPH_SET_FLAG, TF_NAGLEMEMERR, TF_SEG_DATA_CHECKSUMMED, TF_SEG_OPTS_TS, TF_TIMESTAMP, pbuf::tot_len, U16_F, U32_F, tcp_pcb::unacked, tcp_pcb::unsent, and tcp_pcb::unsent_oversize.

Referenced by http_send_data().

static err_t tcp_write_checks ( struct tcp_pcb *  pcb, u16_t  len  )

static

Checks if tcp_write is allowed or not (checks state, snd_buf and snd_queuelen).

Parameters

pcb	the tcp pcb to check for
len	length of data to send (checked agains snd_buf)

Returns

ERR_OK if tcp_write is allowed to proceed, another err_t otherwise

References CLOSE_WAIT, ERR_CONN, ERR_MEM, ERR_OK, ESTABLISHED, tcp_pcb::flags, LWIP_ASSERT, LWIP_DBG_LEVEL_SEVERE, LWIP_DBG_STATE, LWIP_DEBUGF, NULL, tcp_pcb::snd_buf, tcp_pcb::snd_queuelen, SYN_RCVD, SYN_SENT, TCP_OUTPUT_DEBUG, TCP_QLEN_DEBUG, TCP_SNDQUEUELEN_OVERFLOW, TCP_STATS_INC, TF_NAGLEMEMERR, U16_F, tcp_pcb::unacked, and tcp_pcb::unsent.

Referenced by tcp_write().

void 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

References if(), inet_chksum_pseudo(), ip4_addr1_16, ip4_addr2_16, ip4_addr3_16, ip4_addr4_16, ip_output(), IP_PROTO_TCP, tcp_pcb::keep_cnt_sent, tcp_seg::len, LWIP_DEBUGF, NULL, tcp_seg::p, pbuf::payload, pbuf_copy_partial(), pbuf_free(), tcp_pcb::rcv_nxt, tcp_pcb::snd_nxt, TCP_ACK, TCP_DEBUG, TCP_FIN, TCP_HLEN, tcp_output_alloc_header(), TCP_STATS_INC, tcp_ticks, TCPH_FLAGS, TCPH_FLAGS_SET, tcphdr, tcp_seg::tcphdr, tcp_pcb::tmr, pbuf::tot_len, U16_F, U32_F, tcp_pcb::unacked, and tcp_pcb::unsent.

Referenced by tcp_slowtmr().