Getaddrinfo() Function In Python

Function Name:

getaddrinfo

 

Function Signature:

socket.getaddrinfo(host, port, family=0, type=0, proto=0, flags=0)

 

Function Overview:

  • If we know a network service by host name like example.org or the IP address of the network service either in form of IPv4 or IPv6 along with the port number of the network service, getaddrinfo() will return a list of tuples containing information about socket(s) that can be created with the service.

For example, by specifying example.org, 80 as values for the hostname and port number parameters, getaddrinfo() queries what kind of client sockets need to be created to connect to example.org.

 

  • Remember, all the socket tuples returned may not be fully supported.

For instance, querying to example.org provides one of the tuples containing information required for creating datagram socket to it - <SocketKind.SOCK_DGRAM: 2>.

 

However, we do not know any web server is fully supporting HTTP over UDP.  The returned value could be on a future note and in accordance to the specifications rather than practically support the whole HTTP on UDP.

 

  • Examining other tuples returned in the example below reveals that there are tuples with <SocketKind.SOCK_STREAM: 1>.

It means TCP sockets can be created to connect to the service at example.org.

 

  • Also the tuples returned convey that both IPv4(AddressFamily.AF_INET: 2)  and IPv6(AddressFamily.AF_INET6 ) address families are supported.

 

Parameters:

host:     The host parameter takes either an ip address or a host name.

                           The ip address can be either an ipv4 address or an ipv6 address.

                           When a host name is used the Domain Name Service(DNS)         

                           will be used for resolving the name into an IP address.

 

port:    The port number of the service. If zero, information is returned for

                    all supported socket types.

 

family, type,

proto, flags -        These parameters act like a filter so that the

                                    getaddrinfo()returns the tuples pertaining only to the      

                                    types specifiedin them. For example if family=AF_INET only          

                                    the tuples corresponding to sockets supporting IPv4 address

                                    family will be returned provided they are supported by the

                                    service.

 

Example 1:

import socket

 

# Query for socket information to connect to example.com

addrInfo = socket.getaddrinfo("example.com",80)

 

# print socket tuples

print(addrInfo)

 

Output:

[(<AddressFamily.AF_INET: 2>, <SocketKind.SOCK_DGRAM: 2>, 17, '', ('93.184.216.34', 80)),

 

(<AddressFamily.AF_INET: 2>, <SocketKind.SOCK_STREAM: 1>, 6, '', ('93.184.216.34', 80)),

 

(<AddressFamily.AF_INET6: 30>, <SocketKind.SOCK_DGRAM: 2>, 17, '', ('2606:2800:220:1:248:1893:25c8:1946', 80, 0, 0)),

 

(<AddressFamily.AF_INET6: 30>, <SocketKind.SOCK_STREAM: 1>, 6, '', ('2606:2800:220:1:248:1893:25c8:1946', 80, 0, 0))]

 

The output above lists all the tuples as returned by getaddrinfo().

The tuples convey that the service example.org at port number 80 supports both Datagram Sockets (UDP) as well as connection oriented sockets (TCP).

They also reveal that the sockets can be created either using AF_INET or AF_INET6 address families.

Example 2:

import socket

 

# Query for socket info - Criteria is IPv4, TCP

addressInfo = socket.getaddrinfo("example.com", 80, family=socket.AF_INET, proto=socket.IPPROTO_TCP)

 

# Print socket info

print(addressInfo)

 

# Query for socket info - Criteria is IPv6, TCP

addressInfo = socket.getaddrinfo("example.com", 80, family=socket.AF_INET6, proto=socket.IPPROTO_TCP)

 

# Print socket info

print(addressInfo)

Output:

[(<AddressFamily.AF_INET: 2>, <SocketKind.SOCK_STREAM: 1>, 6, '', ('93.184.216.34', 80))]

[(<AddressFamily.AF_INET6: 30>, <SocketKind.SOCK_STREAM: 1>, 6, '', ('::ffff:93.184.216.34', 80, 0, 0))]

 

The Python Example 2 uses various criteria like Address Family and the Protocol while querying example.com for socket information. The first call to getaddrinfo() returns only the socket information corresponding to IPv4 and TCP. The second call to getaddrinfo() returns tuple(s) corresponding to IPv6 and TCP.


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