Socket API

1. Byte order

The network protocol uses "big-end byte order" (the high-order byte of the starting address store) to transmit these multi-byte integers.

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Uint16_t htons (uint16_t host16bitvalue)

Uint32_t htonl (uint32_t host32bitvalue)

Uint16_t ntohs (uint16_t net16bitvalue)

Uint32_t ntohl (uint32_t net32bitvalue)

two。 Translating IPv4 addresses between dotted decimal ASCII code strings and 32-bit network byte-ordered binary values

[/ / the following two functions are eliminated and written to help transition memory

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/ / return 1 if the string is valid, otherwise 0

/ / insufficient: addrptr returns INADDR_NONE (32-bit 1) when there is an error, and some manual says it returns-1

Int inet_aton (const char * strptr, struct in_addr * addrptr)

Char* inet_ntoa (struct in_addr inaddr); / / insufficient: non-reentrant

]

/ / advantages: both ipv4 and ipv6 are suitable

/ / p:presentation n:numeric

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/ / Note: 1 is returned for success, 0 for invalid input format, and-1 for error EAFNOSUPPORT

Int inet_pton (int family, const char * strptr, void * addrptr)

/ / A pointer to the result is returned successfully, and NULL; ENOSPC is returned if an error occurs.

Const char* inet_ntop (int family, const void * addrptr, char* strptr, size_t len)

3. Socket

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Int socket (int family, int type, int protocol)

Int connect (int sockfd, const struct sockaddr* servaddr, socklen_t addrlen)

/ / bind can specify an IP address or port, or both, or neither.

/ / bind system reserved port, root permission is required

Int bind (int sockfd, const struct sockaddr* myaddr, socklen_t addrlen)

/ / return the local protocol address associated with the socket

Int getsockname (int sockfd, struct sockaddr* localaddr, socklen_t * addrlen)

/ / return the remote protocol address associated with the socket, such as the corresponding address of the customer sockfd returned by accept

Int getpeername (itn sockfd, struct sockaddr* peeraddr, socklen_t addrlen)

Int listen (int sockfd, int backlog); / / still don't understand what value backlog specifies is better?

The listening socket maintains two queues: the incomplete connection queue (SYN_RCVD) and the completed connection queue (ESTABLISHED).

Int accept (int listenfd, struct sockaddr* cliaddr, socklen_t * addrlen)

4. After the connection is established

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Int close (int sockfd)

/ *

Fork is called once and returned twice: the calling process returns the child process ID number, and the child process returns 0

There are two uses of fork: one is that a process creates a copy of itself, and the other is that a process wants to execute another program, and the copy calls exec to replace itself with a new program.

, /

Pid_t fork (void)

Pid_t getppid (void); / / get the parent process ID