System Calls

Below are the system calls that can be used to access network functionality.

getaddrinfo() :

Purpose :

It helps set up the structs, specifically struct addrinfo. It does all the dirty work like DNS and service name lookup and fill up the structs with all the relevant information based on the parameters passed.
Function prototye
```
int getaddrinfo(const char *node,  // e.g. "www.example.com" or IP
                const char *service, // e.g. "http" or port number
                const struct addrinfo *hints,
                struct addrinfo **res);
```
1. node :
  
  Type : const char *
  
  Value : Domain name or IP in form of string.
  
  Purpose : To help find the host computer IP address for connection.
2. service :
  
  Type : const char *
  
  Value : Service/Protocol or Port in form of string.
  
  Purpose : To help specify the port number in the host computer.
3. hints :
  
  Type : const struct addrinfo *
  
  Value : Pointer to struct addrinfo.
  
  Purpose : To guide how it should fetch relevent data and store it to struct addrinfo **res.
4. res :
  
  Type : struct addrinfo **
  
  Value : Pointer to linked list of struct addrinfo *

Return Type :

Non-zero value in case of error or zero, otherwise.

Code Snippet

int status;
struct addrinfo hints;
struct addrinfo *servinfo; // will point to the results

memset(&hints, 0, sizeof hints); // make sure the struct is 
                                 // garbage free


hints.ai_family = AF_UNSPEC;     // don't care IPv4 or IPv6
hints.ai_socktype = SOCK_STREAM; // TCP stream sockets
hints.ai_flags = AI_PASSIVE;     // fill in my IP(my host) for me

if ((status = getaddrinfo(NULL, "3490", &hints, &servinfo)) != 0){
    fprintf(stderr, "getaddrinfo erro: %s\n", gai_strerror(status));
    exit(1);
}

// servinfo now  points to a linked list of 1 or more struct 
// addrinfos


// ... do everything until you don't need servinfo anymore ...

freeaddrinfo(servinfo); // free the linked list

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System Calls

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