.TH "tcp" 3 "Thu Jan 28 2021" "Version 1.0.5" "libnetfilter_queue" \" -*- nroff -*-
.ad l
.nh
.SH NAME
tcp \- TCP helper functions
.SH SYNOPSIS
.br
.PP
.SS "Modules"

.in +1c
.ti -1c
.RI "\fBInternal TCP functions\fP"
.br
.in -1c
.SS "Functions"

.in +1c
.ti -1c
.RI "struct tcphdr * \fBnfq_tcp_get_hdr\fP (struct pkt_buff *pktb)"
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.RI "void * \fBnfq_tcp_get_payload\fP (struct tcphdr *tcph, struct pkt_buff *pktb)"
.br
.ti -1c
.RI "unsigned int \fBnfq_tcp_get_payload_len\fP (struct tcphdr *tcph, struct pkt_buff *pktb)"
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.ti -1c
.RI "int \fBnfq_tcp_snprintf\fP (char *buf, size_t size, const struct tcphdr *tcph)"
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.ti -1c
.RI "int \fBnfq_tcp_mangle_ipv4\fP (struct pkt_buff *pktb, unsigned int match_offset, unsigned int match_len, const char *rep_buffer, unsigned int rep_len)"
.br
.ti -1c
.RI "int \fBnfq_tcp_mangle_ipv6\fP (struct pkt_buff *pktb, unsigned int match_offset, unsigned int match_len, const char *rep_buffer, unsigned int rep_len)"
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.in -1c
.SH "Detailed Description"
.PP 

.SH "Function Documentation"
.PP 
.SS "struct tcphdr* nfq_tcp_get_hdr (struct pkt_buff * pktb)"
nfq_tcp_get_hdr - get the TCP header 
.PP
\fBParameters\fP
.RS 4
\fIpktb\fP pointer to user-space network packet buffer 
.RE
.PP
\fBReturns\fP
.RS 4
validated pointer to the TCP header or NULL if the TCP header was not set or if a minimal length check fails\&. 
.RE
.PP
\fBNote\fP
.RS 4
You have to call \fBnfq_ip_set_transport_header()\fP or \fBnfq_ip6_set_transport_header()\fP first to set the TCP header\&. 
.RE
.PP

.PP
Definition at line 43 of file tcp\&.c\&.
.SS "void* nfq_tcp_get_payload (struct tcphdr * tcph, struct pkt_buff * pktb)"
nfq_tcp_get_payload - get the TCP packet payload 
.PP
\fBParameters\fP
.RS 4
\fItcph\fP pointer to the TCP header 
.br
\fIpktb\fP pointer to user-space network packet buffer 
.RE
.PP
\fBReturns\fP
.RS 4
Pointer to the TCP payload, or NULL if malformed TCP packet\&. 
.RE
.PP

.PP
Definition at line 62 of file tcp\&.c\&.
.SS "unsigned int nfq_tcp_get_payload_len (struct tcphdr * tcph, struct pkt_buff * pktb)"
nfq_tcp_get_payload_len - get the tcp packet payload 
.PP
\fBParameters\fP
.RS 4
\fItcph\fP pointer to the TCP header 
.br
\fIpktb\fP pointer to user-space network packet buffer 
.RE
.PP
\fBReturns\fP
.RS 4
Length of TCP payload (user data) 
.RE
.PP

.PP
Definition at line 84 of file tcp\&.c\&.
.SS "int nfq_tcp_mangle_ipv4 (struct pkt_buff * pktb, unsigned int match_offset, unsigned int match_len, const char * rep_buffer, unsigned int rep_len)"
nfq_tcp_mangle_ipv4 - mangle TCP/IPv4 packet buffer 
.PP
\fBParameters\fP
.RS 4
\fIpktb\fP pointer to network packet buffer 
.br
\fImatch_offset\fP offset to content that you want to mangle 
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\fImatch_len\fP length of the existing content you want to mangle 
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\fIrep_buffer\fP pointer to data you want to use to replace current content 
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\fIrep_len\fP length of data you want to use to replace current content 
.RE
.PP
\fBReturns\fP
.RS 4
1 for success and 0 for failure\&. See \fBpktb_mangle()\fP for failure case 
.RE
.PP
\fBNote\fP
.RS 4
This function updates the IPv4 length and recalculates the IPv4 & TCP checksums for you\&. 
.RE
.PP
\fBWarning\fP
.RS 4
After changing the length of a TCP message, the application will need to mangle sequence numbers in both directions until another change puts them in sync again 
.RE
.PP

.PP
Definition at line 219 of file tcp\&.c\&.
.SS "int nfq_tcp_mangle_ipv6 (struct pkt_buff * pktb, unsigned int match_offset, unsigned int match_len, const char * rep_buffer, unsigned int rep_len)"
nfq_tcp_mangle_ipv6 - Mangle TCP/IPv6 packet buffer 
.PP
\fBParameters\fP
.RS 4
\fIpktb\fP Pointer to network packet buffer 
.br
\fImatch_offset\fP Offset from start of TCP data of content that you want to mangle 
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\fImatch_len\fP Length of the existing content you want to mangle 
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\fIrep_buffer\fP Pointer to data you want to use to replace current content 
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\fIrep_len\fP Length of data you want to use to replace current content 
.RE
.PP
\fBReturns\fP
.RS 4
1 for success and 0 for failure\&. See \fBpktb_mangle()\fP for failure case 
.RE
.PP
\fBNote\fP
.RS 4
This function updates the IPv6 length and recalculates the TCP checksum for you\&. 
.RE
.PP
\fBWarning\fP
.RS 4
After changing the length of a TCP message, the application will need to mangle sequence numbers in both directions until another change puts them in sync again 
.RE
.PP

.PP
Definition at line 254 of file tcp\&.c\&.
.SS "int nfq_tcp_snprintf (char * buf, size_t size, const struct tcphdr * tcph)"
nfq_pkt_snprintf_tcp_hdr - print tcp header into one buffer in a humnan readable way 
.PP
\fBParameters\fP
.RS 4
\fIbuf\fP pointer to buffer that is used to print the object 
.br
\fIsize\fP size of the buffer (or remaining room in it)\&. 
.br
\fItcph\fP pointer to a valid tcp header\&. 
.RE
.PP
\fBReturns\fP
.RS 4
Same as \fBsnprintf\fP 
.RE
.PP
\fBSee also\fP
.RS 4
\fBsnprintf\fP(3) 
.RE
.PP

.PP
Definition at line 160 of file tcp\&.c\&.
.SH "Author"
.PP 
Generated automatically by Doxygen for libnetfilter_queue from the source code\&.