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https://issues.apache.org/jira/browse/COUCHDB-393?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12730159#action_12730159
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Paul Joseph Davis commented on COUCHDB-393:
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The way I implemented this uses Erlang's RPC calls to query the value of a
running CouchDB node. To simply switch the -p flag back to couchdb would
probably require dropping the entire implementation and going with writing a
file after the server socket is opened etc etc. Going to a file based system
would also mean that it wouldn't make any sense to keep around the -n flag.
So basically, if you think we should do file writing then that's cool, but if
we want the RPC style so that we can add different types of introspection for
sysadmins then the current system would probably be more future proof.
For reference, I was pulling this pattern from rabbitmq's rabbitmqctl command
that does similar things.
> Cannot discover currently running http port if ini file specifies port 0
> ------------------------------------------------------------------------
>
> Key: COUCHDB-393
> URL: https://issues.apache.org/jira/browse/COUCHDB-393
> Project: CouchDB
> Issue Type: Improvement
> Components: HTTP Interface
> Affects Versions: 0.9
> Environment: Ubuntu 9.04
> Reporter: Stuart Langridge
> Assignee: Noah Slater
> Attachments: couchctl.patch
>
>
> It is currently not possible, if the ini file specifies port 0 as the http
> port (so that the OS chooses a random port) to discover which port the OS
> actually chose.
> It would be nice if the currently running port was made available in the
> statusline output (couchdb -s), but a log statement would be adequate; some
> way that an external script can discover which port a running CouchDB is
> listening on.
> Edited discussion from #couchdb:
> <bitdiddle> aquarius: well at a glance it appears couch_http passes the 0 to
> mochiweb_http which passes it to the mochiweb_socket_server, which passes it
> to gen_tcp, an erlang module that lets the underlying OS assign it.
> mochiweb_socket_server then grabs that port and stores it. It has a get
> method to retrieve properties but that needs to be exposed to mochiweb_http
> so it would take a little work to do it. It's probably a JIRA ticket, unless
> someone else sees a quicker approach
> <davisp> bitdiddle: you got that far and didn't find it?
> <aquarius> davisp: is there a better way to find the port?
> <davisp> oh, is that not the bind port?
> I was just thinking a log statement
> <aquarius> davisp: the problem is if you specify 0 as the bind port (so the
> OS chooses a port), how do you find out what was chosen?
> <davisp> aquarius: you have to look at the port returned by the socket
> aquarius: in other words, CouchDB was never written to do that
> <davisp> AFAIK
> <bitdiddle> davisp: I found it, just needs some work to expose it
> <davisp> aquarius: and by do that, I mean, we never put in a statement to log
> that
> <bitdiddle> mochiweb_http is the module that needs to bubble it up
> <aquarius> davisp: I don't really mind whether it's a log statement or it's
> exposed to couchdb -s (the latter seems tidier to me, but whichever), I just
> want to be able to start couch on port 0 and then later find out which port
> got chosen :)
> <davisp> aquarius: for the time being you can use something like netstat or
> lsof, but we'll get a log statement in there or something
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