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92 lines
2.4 KiB
Markdown
92 lines
2.4 KiB
Markdown
# System Calls
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Below are the system calls that can be used to access network functionality.
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* **getaddrinfo()** :
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* Purpose :
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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.
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* Function prototye
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```
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int getaddrinfo(const char *node, // e.g. "www.example.com" or IP
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const char *service, // e.g. "http" or port number
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const struct addrinfo *hints,
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struct addrinfo **res);
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```
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1. node :
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Type : `const char *`
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Value : Domain name or IP in form of string.
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Purpose : To help find the host computer IP address for connection.
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2. service :
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Type : `const char *`
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Value : Service/Protocol or Port in form of string.
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Purpose : To help specify the port number in the host computer.
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3. hints :
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Type : `const struct addrinfo *`
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Value : Pointer to *struct addrinfo*.
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Purpose : To guide how it should fetch relevent data and store it to `struct addrinfo **res`.
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4. res :
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Type : `struct addrinfo **`
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Value : Pointer to linked list of *struct addrinfo \**
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* Return Type :
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Non-zero value in case of error or zero, otherwise.
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**Code Snippet**
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```
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int status;
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struct addrinfo hints;
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struct addrinfo *servinfo; // will point to the results
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memset(&hints, 0, sizeof hints); // make sure the struct is
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// garbage free
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hints.ai_family = AF_UNSPEC; // don't care IPv4 or IPv6
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hints.ai_socktype = SOCK_STREAM; // TCP stream sockets
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hints.ai_flags = AI_PASSIVE; // fill in my IP(my host) for me
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if ((status = getaddrinfo(NULL, "3490", &hints, &servinfo)) != 0){
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fprintf(stderr, "getaddrinfo erro: %s\n", gai_strerror(status));
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exit(1);
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}
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// servinfo now points to a linked list of 1 or more struct
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// addrinfos
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// ... do everything until you don't need servinfo anymore ...
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freeaddrinfo(servinfo); // free the linked list
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```
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* **socket() :**
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* Purpose :
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Assign a *file descriptor* for accessing OS resources to access network. Defines the type connection it would make to other host.
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* Function Prototype :
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