What

Instead of binding of a UNIX filepath, the socket binds to the localhost address space. The client does not need to be implemented, it can be a web browser.

Resources

The man pages for ip and its related functions were used. I consulted Wikipedia for some basic information about IP addresses:

• IP Address
• localhost
• Port number

You can see the errno and enums assocations in the errno.h source code.

Dev Comments

The sequence of events to achieve connection is nearly identical to the echo server. The only difference is that I need to bind the socket to a local IP address (localhost). The other operations of the socket API are the same.

I first consider implementing for ipv6, however the address structure has some fields that don’t have a clear value for them (e.g. scope_id). The Bugs section of the man page says that the API for ipv6 isn’t fully implemented, so I decided to reduce the implementation to ip (IPv4).

I had some trouble creating the address. My first approach was to have a constant struct in common.h like in Basic Echo, however it has a compile error because initializers cannot be constant. The initializers (htons, htonl) could not be assign to the struct member fields since they are not constant. I had to search on Stack Overflow for some help. The final solution that worked was to put it in dynamic memory. The INADDR_LOOPBACK address is created in an anonymous struct. Since the addresses should be in network order (big endian - the high order bits are in the lower addresses), the address and port have to be passed into htonl and htons respectively.

I tried to do some checking with getsockname, but the actual printing of the address is hard to do with its structure. There I used gdb to look at the variable and confirmed that it had 80 and 127.0.0.1.

The socket needs to be set to listening in order for the client to be able to connect (binding isn’t enough).