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Posted to bugs@httpd.apache.org by bu...@apache.org on 2018/06/21 08:15:27 UTC
[Bug 62477] New: ProxyPassInterpolateEnv causes config syntax
failures at startup
https://bz.apache.org/bugzilla/show_bug.cgi?id=62477
Bug ID: 62477
Summary: ProxyPassInterpolateEnv causes config syntax failures
at startup
Product: Apache httpd-2
Version: 2.5-HEAD
Hardware: PC
OS: Mac OS X 10.1
Status: NEW
Severity: normal
Priority: P2
Component: mod_proxy
Assignee: bugs@httpd.apache.org
Reporter: toscano.luca@gmail.com
Target Milestone: ---
While playing with the following config (in httpd trunk) I got:
ProxyPassInterpolateEnv On
SetEnvIf "Test" "bla" proxy_port=8000
<Location /test>
ProxyPass "http://localhost:${proxy_port}/test" interpolate
</Location>
[Thu Jun 21 08:11:29.304425 2018] [core:warn] [pid 21013:tid 140441193370688]
AH00111: Config variable ${proxy_port} is not defined
AH00526: Syntax error on line 224 of /usr/local/apache2/conf/httpd.conf:
ProxyPass Unable to parse URL: http://localhost:${proxy_port}/test
httpd: abnormal exit 1
But if I move the ${proxy_port} outside scheme://host:port then httpd starts up
as expected.
https://httpd.apache.org/docs/2.4/mod/mod_proxy.html#proxypass says:
"""
The optional interpolate keyword, in combination with ProxyPassInterpolateEnv,
causes the ProxyPass to interpolate environment variables, using the syntax
${VARNAME}. Note that many of the standard CGI-derived environment variables
will not exist when this interpolation happens, so you may still have to resort
to mod_rewrite for complex rules. Also note that interpolation is not supported
within the scheme portion of a URL. Dynamic determination of the scheme can be
accomplished with mod_rewrite as in the following example.
"""
Didn't check in the code why this is the behavior, but either the code or the
docs are a bit misleading/wrong.
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[Bug 62477] ProxyPassInterpolateEnv causes config syntax failures at
startup
Posted by bu...@apache.org.
https://bz.apache.org/bugzilla/show_bug.cgi?id=62477
--- Comment #7 from Yann Ylavic <yl...@gmail.com> ---
Yes, a better error message and doc looks sensible, +1.
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[Bug 62477] ProxyPassInterpolateEnv causes config syntax failures at
startup
Posted by bu...@apache.org.
https://bz.apache.org/bugzilla/show_bug.cgi?id=62477
--- Comment #5 from Luca Toscano <to...@gmail.com> ---
Hi Yann!
I agree 100%, my question is (and this is me not familiar enough with the
worker workflow) if the proxy definition can be deferred to later on when the
proxy variable will be available, since I saw in various pieces of code that if
the worker is not found it can be defined and then used. Or is it necessary to
create/define it when the ProxyPass directive is parsed (so during httpd's
startup) ?
In any case, the error message is misleading in my opinion.. If we want to
restrict variable usage with interpolate then a trace of this restriction
should be found by a user when httpd logs the error, not in the docs :)
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[Bug 62477] ProxyPassInterpolateEnv causes config syntax failures at
startup
Posted by bu...@apache.org.
https://bz.apache.org/bugzilla/show_bug.cgi?id=62477
--- Comment #2 from Luca Toscano <to...@gmail.com> ---
As a quick test, commenting apr_uri_parse seems to make everything work fine
(of course not a solution, but the fix might be trivial).
ap_proxy_define_worker, afaics, is called when ProxyPass is parsed but also
during runtime if a (proxy) worker is not found, so the comment above simply
delays the whole process to runtime. So a possible solution is to not be strict
in URI parsing when the interpolate flag is used, since there may be variables
not yet resolved, but need to check a bit more the code before being sure.
Feedback welcome!
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[Bug 62477] ProxyPassInterpolateEnv causes config syntax failures at
startup
Posted by bu...@apache.org.
https://bz.apache.org/bugzilla/show_bug.cgi?id=62477
--- Comment #1 from Luca Toscano <to...@gmail.com> ---
The issue to me seems that ap_proxy_define_worker uses apr_uri_parse that fails
to parse things like ${variable}, and since it happens as a consequence of
ProxyPass directives getting parsed it can be effectively usable only by
variables already present at early startup, like the ones set by Define (that
indeed work fine).
It might be possible to delay this operation but not sure if it is worth. As
far as I understand ProxyPassInterpolateEnv seems not really usable at the
moment, but I might miss something. Feedback welcome :)
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[Bug 62477] ProxyPassInterpolateEnv causes config syntax failures at
startup
Posted by bu...@apache.org.
https://bz.apache.org/bugzilla/show_bug.cgi?id=62477
--- Comment #4 from Yann Ylavic <yl...@gmail.com> ---
If the scheme and hostname part of the URI can't be parsed, there is really no
point to define a worker, no load time characteristic allowing connections
management (e.g. reuse) for the same origin server, hence every connection will
be handled by the default "reverse-proxy" worker.
So the real hostname has to be declared somehow (e.g. <Proxy
scheme://realhostname>), and at this point as the doc you pointed to says: "If
you require a more flexible reverse-proxy configuration, see the RewriteRule
directive with the [P] flag".
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[Bug 62477] ProxyPassInterpolateEnv causes config syntax failures at
startup
Posted by bu...@apache.org.
https://bz.apache.org/bugzilla/show_bug.cgi?id=62477
--- Comment #6 from Luca Toscano <to...@gmail.com> ---
Sorry now I get what you were saying. If you have to defer the creation of the
worker based on a per request variable, then there is no point in defining a
"one off" worker / connection-pool. My naive view of the conn pool / worker was
that it would have been defined the first time by the first request value
populating the variable, and then re-used across requests, this is why I was
asking the question about deferring the worker initialization.
IIUC, either a worker is well defined at "startup" time, or the default worker
will be used. I am wondering if a more precise error message for the user when
apr_uri_parse fails and 'interpolate' is set might help (like "hey there,
please remember that you are not allowed to add variables for
scheme/hostname/port"). If my understanding is right I'd also like to add an
explanation in the docs, from my point of view it is not really clear.
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[Bug 62477] ProxyPassInterpolateEnv causes config syntax failures at
startup
Posted by bu...@apache.org.
https://bz.apache.org/bugzilla/show_bug.cgi?id=62477
--- Comment #3 from Luca Toscano <to...@gmail.com> ---
(In reply to Luca Toscano from comment #2)
> As a quick test, commenting apr_uri_parse seems to make everything work fine
> (of course not a solution, but the fix might be trivial).
Better: commenting the check for the return value of apr_uri_parse:
rv = apr_uri_parse(p, url, &uri);
/*if (rv != APR_SUCCESS) {
return apr_pstrcat(p, "Unable to parse URL: ", url, NULL);
}*/
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