Written Assignment 9

Question 1

See image below

Question 2

There are 6 different possible outputs

abcdab
abcdef

abcdcd
ababef

abcdef
ababcd

abcdef
abcdab

ababef
abcdcd

ababcd
abcdef

Question 3

The type of getaddrinfo is:

int getaddrinfo(const char *node, const char *service,
                       const struct addrinfo *hints,
                       struct addrinfo **res);

Observe that the output argument of the function: struct addrinfo **res is a linked list of addrinfo struct containing sockaddr struct that is itself protocol-independent (unlike non-generic sockaddr_in struct that has fields like sin_port, sin_addr, and sin_zero[8]):

The structures mentioned are shown below and the all-caped texts are for further explanations.

struct addrinfo {
  int ai_flags; /* Hints argument flags */
  int ai_family; /* First arg to socket function */
  int ai_socktype; /* Second arg to socket function */
  int ai_protocol; /* Third arg to socket function */
  char *ai_canonname; /* Canonical host name */
  size_t ai_addrlen; /* Size of ai_addr struct */

  // LOOK AT THIS LINE. THE TYPE IS `sockaddr`, NOT `sockaddr_in`
  // WHICH MEANS IT IS GENERIC
  struct sockaddr *ai_addr; /* Ptr to socket address structure */

  struct addrinfo *ai_next; /* Ptr to next item in linked list */
};

// THIS IS GENERIC
struct sockaddr {
  uint16_t sa_family; /* Protocol family */
  char sa_data[14];   /* Address data */
};

// THIS IS NOT GENERIC
struct sockaddr_in {
  uint16_t sin_family; /* Protocol family (always AF_INET) */
  uint16_t sin_port; /* Port num in network byte order */
  struct in_addr sin_addr; /* IP addr in network byte order */
  unsigned char sin_zero[8]; /* Pad to sizeof(struct sockaddr) */
};

Because sockaddr is generic, the returning argument struct addrinfo **res from function getaddrinfo is protocol-independent (support any protocol including IPv4 and IPv6). Therefore getaddrinfo can be used with any protocol.