6. Addresses
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## 6. Addresses

The low-level format of the addresses are different depending on the mode of communication you have chosen. A function is provided by each of the lower layers to map a user-friendly string-form address to the binary form required by the lower layers.

        void *cs_straddr(COMSTACK handle, const char *str);

The format for TCP/IP and SSL addresses is:

        <host> [ ':' <portnum> ]

The `hostname` can be either a domain name or an IP address. The port number, if omitted, defaults to 210.

For TCP/IP and SSL, the special hostnames `@`, maps to `IN6ADDR_ANY_INIT` with IPV4 binding as well (bindv6only=0), The special hostname `@4` binds to `INADDR_ANY` (IPV4 only listener). The special hostname `@6` binds to `IN6ADDR_ANY_INIT` with bindv6only=1 (IPV6 only listener).

For UNIX sockets, the format of an address is the socket filename.

When a connection has been established, you can use

        const char *cs_addrstr(COMSTACK h);

to retrieve the host name of the peer system. The function returns a pointer to a static area, which is overwritten on the next call to the function.

A fairly recent addition to the COMSTACK module is the utility function

        COMSTACK cs_create_host (const char *str, int blocking, void **vp);

which is just a wrapper for `cs_create` and `cs_straddr`. The `str` is similar to that described for `cs_straddr` but with a prefix denoting the COMSTACK type. Prefixes supported are `tcp:`, `unix:` and `ssl:` for TCP/IP, UNIX and SSL respectively. If no prefix is given, then TCP/IP is used. The `blocking` is passed to function `cs_create`. The third parameter `vp` is a pointer to COMSTACK stack type specific values. Parameter `vp` is reserved for future use. Set it to `NULL`.

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