I've decided to create separate issue disregarding that we have already ZBX-3783 because I'll mention server side, maybe there also will be something to change/fix - all is up to you.

I'm creating this issue based on a real case happened.
My perl script resolved a host name to IP and mistakenly added one line break at the end of IP address. Then the script updates host's IP using zabbix API.

By API method "hostinterface.update" I was able to successfully put these params:

{
   "interfaceid": "11",
   "ip": "10.20.0.71\n"
}

As it look then (note here the line break):

mysql> select * from interface where hostid=10094;
+-------------+--------+------+------+-------+-------------+----------------+-------+
| interfaceid | hostid | main | type | useip | ip          | dns            | port  |
+-------------+--------+------+------+-------+-------------+----------------+-------+
|          11 |  10094 |    1 |    1 |     0 | 10.20.0.71
 | 2008serverNEW2 | 10050 |
+-------------+--------+------+------+-------+-------------+----------------+-------+

As it should look if there no line break:

mysql> select * from interface where hostid=10094;
+-------------+--------+------+------+-------+------------+----------------+-------+
| interfaceid | hostid | main | type | useip | ip         | dns            | port  |
+-------------+--------+------+------+-------+------------+----------------+-------+
|          11 |  10094 |    1 |    1 |     0 | 10.20.0.71 | 2008serverNEW2 | 10050 |
+-------------+--------+------+------+-------+------------+----------------+-------+

This line break of course is not visible in frontend.

So it's bad that API allows to do that -> has to be fixed.

Server side:
IF server/proxy compiled with IPv6 support then it is able to process the IP address with a line break(s) at the end.

But without IPv6 support an agent goes to unavailable. Error message text in frontend is (the line break preserved here !):

"Get value from agent failed: gethostbyname() failed for '10.20.0.71
': [1] Unknown host"

Such problem becomes very unclear - what is bad actually.

Difference is that with IPv6 server/proxy uses "getaddrinfo()" system call, but without IPv6 - another system call - "gethostbyname()".
See comms.c lines 282 and 348
I don't know why it is so.

"# man gethostbyname" says that, quote:

" The gethostbyname*() and gethostbyaddr*() functions are obsolete. Applications should use getaddrinfo(3) and getnameinfo(3) instead.

...
This page is part of release 3.27 of the Linux man-pages project."

As we see the getaddrinfo() (used with IPv6) is more, say, "robust" in our case
So question to C devs - is this good/required to use namely gethostbyname() there in zabbix code ?