Bug 52884

On my computer (Ubuntu 10.04), when listening to "localhost:port" like

Listen localhost:80

Apache-httpd will report the following error and fail to start with the following error messages:

(98)Address already in use: AH00072: make_sock: could not bind to address 127.0.0.1:80
no listening sockets available, shutting down
AH00015: Unable to open logs

This error message is very confusing because 127.0.0.1:80 is not being used at all. Interestingly, if you directly change localhost to 127.0.0.1, i.e., 

Listen 127.0.0.1:80

Then, everything is fine.

By tracing the code, I find the root cause is that the bind() operation is done for two times. And, of course, it failed at the 2nd time because the 1st time it had successed.

Further tracing why it bind() two times, I finally find that it's because of the function call getaddrinfo() in the function: call_resolver() in srclib/apr/network_io/unix/sockaddr.c

When fed with "localhost", the result set, i.e., ai_list will have two elements. Thus, Apache tries to bind() based on these two elements and leads to the failure. However, it only has one element when fed with "127.0.0.1". I have to say this is really a strange behavior.

I don't know whether this problem happens on the other platform. But if it happens, it really confuses users a lot and takes a lot of time and efforts.

One simple solution is to add a patch that transfer "localhost" to "127.0.0.1" directly in ap_set_listener() in server/listen.c

Thanks!