IPv4 Sockets: Unveiling sockaddr_in
Understanding IPv4 Internet Domain Socket Addresses
sin_port and sin_addr in Network Byte Order
The sockaddr_in structure, commonly used in socket programming, plays a crucial role in describing an IPv4 Internet domain socket address. Two of its key members, sin_port and sin_addr, are stored in network byte order. This means that they are represented in a specific format that is suitable for transmission over the network.
Network byte order is a convention that ensures that data is transmitted in a consistent manner across different platforms. It specifies the order of bytes in multi-byte data types, such as integers and IP addresses. For sin_port, the port number is stored in big-endian format, where the most significant byte is placed first. For sin_addr, the IP address is stored as a 32-bit integer in network byte order.
Ancillary Message and IP_TOS
IP_RECVTOS Message in Linux 2.2 and Later
In Linux versions 2.2 and later, the ancillary message IP_RECVTOS is supported. This message allows the IP_TOS (Type of Service) field to be passed with incoming packets. When enabled, the IP_TOS ancillary message is included with incoming packets, providing information about the priority and throughput requirements of the data.
Generic Socket Address Type: sockaddr
Unifying Socket Addresses
The sockaddr type is defined to allow any type of socket address to be passed to interfaces in the sockets API. This type serves as a generic representation of socket addresses, regardless of their underlying protocol or address family. Its primary purpose is to enable seamless communication between applications and the operating system, regardless of the specific socket address format.
sockaddr_in and sockaddr_in6 Structures
First Member is a sockaddr Structure
Both sockaddr_in and sockaddr_in6 are structures that begin with a sockaddr structure as their first member. According to the C standard, this is permissible because a structure can contain itself as a member. This design allows sockaddr_in and sockaddr_in6 to inherit the common attributes of sockaddr, such as the sa_family field, which specifies the address family.
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