50 lines
1.7 KiB
C
50 lines
1.7 KiB
C
/*
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Calculates Internet checksums for protocols like TCP/IP.
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Author: Robert David Graham
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Copyright: 2020
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License: The MIT License (MIT)
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Dependencies: none
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*/
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#ifndef UTIL_CHECKSUM_H
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#define UTIL_CHECKSUM_H
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#include <stddef.h>
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/**
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* Calculate a checksum for IPv4 packets.
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* @param ip_src
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* The source IPv4 address, represented a standard way,
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* as a 32-bit integer in host byte order.
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* @param ip_dst
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* The destination IPv4 address, represented as a 32-bit integer in host byte order.
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* @param ip_proto
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* A value of 6 for TCP or 17 for UDP.
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* @param payload_length
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* The length of the IP packet payload, meaning, everything after the IPv4 header.
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* In other words, it's the "total length" field of the IP packet minus the
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* length of the IP header.
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* @param payload
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* A pointer to the aforementioned payload (a pointer to the first byte past the
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* IP header). Note that the calculation skips the checksum field, so the payload
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* we use is everything but the 2 bytes in the checksum field. Thus, due to the
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* quirkiness of Internet protocols, the result of this calculation should end
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* up equally the value of the checksum field.
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* @return
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* the calculated checksum, which should equal the checksum found in the payload
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*/
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unsigned
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checksum_ipv4(unsigned ip_src, unsigned ip_dst, unsigned ip_proto, size_t payload_length, const void *payload);
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unsigned
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checksum_ipv6(const unsigned char *ip_src, const unsigned char *ip_dst, unsigned ip_proto, size_t payload_length, const void *payload);
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/**
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* Simple unit tests.
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* @return
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* 1 if failure, 0 if success
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*/
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int checksum_selftest(void);
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#endif
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