Set Variable from Content of Text File?

[Nick Pearson]

Hi John,

I've not done any module development myself, so I don't know the specific
capabilities, but I don't see why this wouldn't be possible to accomplish.
Perhaps a module that does exactly as you say and sets a variable using the
contents of a file, or a module that could read the contents of a file
containing one or more variable declarations.  It would be good to be able
to specify when the file should be reloaded.  This could be set to a number
of requests between reloads, amount of time between reloads, or reloads
based on some condition of a request.

Although I've not come across this need myself yet, I can see where it could
be quite useful.

Nick


On Fri, Jan 9, 2009 at 12:17 PM, Resicow <resicow at gmail.com> wrote:

> Hi Nick,
>
> Thanks for your thoughts, I really appreciate it!
>
> I know nginx is all about speed, and reading a file each time can be a
> waste of resources (hence no htaccess). I'm not skilled in module
> development, but do you think it would be possible either as a custom
> module, or using the embedded perl module to accomplish this?
>
> There are a few things that I want to do besides the maintenance page, and
> basically they require the ability of setting a variable to the contents of
> a text file, which allows nginx to make some decisions, instead of checking
> for the existence of lots of files. Lets say I have 10 things I want nginx
> to do... wouldn't checking for the existence of 10 different files have more
> overhead than just reading the contents of one?
>
> http://wiki.codemongers.com/NginxHttpAccessKeyModule
>
> For example the access key module. Right now the access key signature is
> defined in the config file, and supports variables. So instead of changing
> the config file to change the signature, I could set the signature to a
> variable, and have that variable read each time from a text file, that could
> change anytime I wanted (and be different for different directories),
> without having to edit the config file and reload from command line.
>
> Thanks,
>
> John
>
>
>
>
>
> Nick Pearson wrote:
>
>> Hi John,
>>
>> That's an interesting problem.  There's no way that I've seen that would
>> let you read the contents of a file from the nginx config.  Maybe someone
>> else can shed some light on this.
>>
>> In any case, I'm not sure you'd want the overhead of opening and reading a
>> file on every request.  However, you might be able to come up with a
>> solution using symlinks and/or a simple cron script that will make the
>> appropriate file available to nginx when necessary.  A command like this
>> might work...
>>
>> if [ -s maintenance_file.txt ]; then ln -s `cat maintenance_file.txt`
>> maintenance.html; elif [ -f maintenance.html ]; then rm maintenance.html; fi
>>
>> I tested this out locally, and it works.  If the maintenance_file.txt file
>> has text in it, it assumes the text is a filename and creates a symlink to
>> that filename (at a location where nginx would see the symlink and serve the
>> linked file as a maintenance page).  If the maintenance_file.txt is empty
>> and the symlink exists, then the symlink is deleted.  (This could be made
>> much more robust, but it works as is if the maintenance_file.txt is either
>> empty or contains a single line with no newline/return characters.)
>>
>> I realize this isn't exactly what you're going for, but it might
>> accomplish your goal.  And ultimately, this will be more performant than
>> having nginx read the contents of a file on each request.
>>
>> Nick
>>
>>
>> On Fri, Jan 9, 2009 at 11:12 AM, Resicow <resicow at gmail.com <mailto:
>> resicow at gmail.com>> wrote:
>>
>>    Hi Nick,
>>
>>    Thanks for your response... I understand the response below, but I
>>    was hoping for a way of doing this by reading the contents of the
>>    text file... So something like this...
>>
>>      if (-f $document_root/system/back_soon.txt) {
>>
>>              set $file_to_load read /$document_root/system/back_soon.txt
>>              rewrite  ^(.*)$  $file_to_load last;
>>              break;
>>
>>    }
>>
>>    So if the file exists read and set a variable based on the
>>    contents of the file, and then rewrite to the variable path.
>>
>>    Thanks,
>>
>>    John
>>
>>
>>
>>
>>
>>    Nick Pearson wrote:
>>
>>        John,
>>
>>        See Ezra's response in the thread here:
>>
>> http://thread.gmane.org/gmane.comp.web.nginx.english/8978/focus=8990
>>
>>        That explanation is just for a single downtime notice, but you
>>        can use a variation of his solution to accomplish what you
>>        want.  For example:
>>
>>        server {
>>           ...
>>           if (-f $document_root/system/back_soon.html) {
>>               rewrite  ^(.*)$  /system/back_soon.html last;
>>               break;
>>           }
>>           if (-f $document_root/system/down_for_a_while.html) {
>>               rewrite  ^(.*)$  /system/down_for_a_while.html last;
>>               break;
>>           }
>>           ...
>>        }
>>
>>        This will show the back_soon.html page if it exists.  If it
>>        doesn't exist and the down_for_a_while.html page does, then
>>        that will be displayed.  Otherwise, processing will continue
>>        normally.
>>
>>
>>        On Thu, Jan 8, 2009 at 2:05 PM, Resicow <resicow at gmail.com
>>        <mailto:resicow at gmail.com> <mailto:resicow at gmail.com
>>        <mailto:resicow at gmail.com>>> wrote:
>>
>>           Hello Nginx Community, and Happy New Year...
>>
>>           Is it possible to set the value of a variable based on the
>>           contents of a text file?
>>
>>           So if there is site downtime, I can place a file in a directory
>>           that nginx will see and will know to serve a downtime
>>        notice, but
>>           then can nginx read the contents of the file to determine which
>>           downtime notice to serve?
>>
>>           Thanks,
>>
>>           John
>>
>>
>>
>>
>>
>>
>
>
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