From: Eric Anderson <eric@...>
Date: 2004-12-12T02:07:24+09:00
Subject: Re: fsync on stdout for mod_rewrite

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Glenn Parker wrote:
> fsync is only meaningful for files in a file system.  You probably want 
> to use $stdout.flush, but if you set $stdout.sync = true then 
> $stdout.flush is already being done implicitly.

I first had $stdout.flush. Then I switched to sync when I found out 
about it. But according to the docs the operating system might no flush 
it. I wasn't sure if it applied to $stdout but I wanted to issue the 
command just in case.

> Maybe describing a little bit more about the connection between Apache 
> and your script would help, too.  Is a new script process created for 
> every URL?  If so, then this is likely not a buffering issue.  If not, 
> then you might be failing to reset some lingering state in the Ruby 
> interpreter between "calls" from Apache.

I have looked through the script 100 times and from I can tell 
everything should be ok for each request. The protocol between Apache 
and the script is:

Apache send the key followed by a newline character to the stdin of the 
script. In this case I am telling Apache to send the HTTP Host header. 
My script then does some logic to determine what to return. It usually 
is a path to the website being requested. The script is started when 
Apache starts up and continues to run as long as Apache runs. The path 
returned is followed by a newline character (the spec says you can also 
send it the characters NULL). The docs give it an example in perl with 
the following script:

My script is as follows. Any suggestions or improve or fix the problem 
are greatly appreciated. You can probably guess the structure of the 
database from the SQL statement. The idea is that it is supposed to 
return the name that is the closest to what was passed in. So if you get 
a request for foo.bar.com and you have a site called bar.com it returns 
bar.com. If you get a request from www.baz.bar.com and you have a site 
called baz.bar.com it will return baz.bar.com instead of just bar.com. 
There are a couple exceptions. For example account.<any domain>.com 
should return account.realsimplehosting.com. Also anything with svn in 
it should just return domain name and not the entire path. Also there is 
an effort to retry requests after failure. After 10 failures it will 
just return error.realsimplehosting.com. The script is attached to this 
email. I attached it so the lines won't get wrapped.

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#!/usr/bin/ruby

require 'dbi'

# CONSTANTS
RSH_VIRTUAL = 1
RSH_WEB_PATH = "/virtual/#{RSH_VIRTUAL}/web/"
NOT_FOUND_PATH = "#{RSH_WEB_PATH}notfound.realsimplehosting.com"
ERROR_PATH = "#{RSH_WEB_PATH}error.realsimplehosting.com"
PORTAL_PATH = "#{RSH_WEB_PATH}?.realsimplehosting.com"
PORTAL_SPECIFIERS = ['webreports', 'database', 'email', 'account', 'cp']

# Put these in the global context
$database = nil
$stmt = nil

# For caching the most recent answer. We may start caching more than this so
# that popular websites get a quicker response but I figured at a min we need
# to cache the most recent since each request calls this lookup several times.
last_request = '';
last_answer = '';

# To protect against infinate retries
loop_protect = 10

def init_database
	$database = DBI.connect 'DBI:Mysql:rsh', 'username', 'password'
	sql = <<-SQL
		SELECT
			accounts.id AS account,
			primary_domain.name AS path,
			LENGTH( aliases.name ) AS size
		FROM
			accounts INNER JOIN
			sites
				ON accounts.id = sites.account INNER JOIN
			domains AS primary_domain
				ON sites.primary_domain = primary_domain.id
				INNER JOIN
			domains AS aliases
				ON sites.id = aliases.site
		WHERE
			(? LIKE CONCAT( '%', aliases.name )) AND
			((sites.expire_date IS NULL) OR
			(sites.expire_date <= CURRENT_DATE()))
		ORDER BY size DESC
		SQL
	$stmt = $database.prepare sql
end

init_database
$stdout.sync = true
$stdin.each do | request |
	request.chomp!
	catch (:done) do
		if request == last_request
			throw :done
		end
		last_request = request
		last_answer = nil

		# Does DBI think we are good to go?
		init_database unless !$database.nil? && $database.connected? &&
			$database.ping

		begin
			$stmt.execute request
			if $stmt.rows == 0
				$stmt.cancel
				last_answer = NOT_FOUND_PATH
				throw :done
			end
			row = $stmt.fetch
			if request =~ /svn/i
				last_answer = row[1]
				$stmt.cancel
				throw :done
			end
			PORTAL_SPECIFIERS.each do |key|
				dev_key = "#{key}-dev"
				re = Regexp.new key, true
				dev_re = Regexp.new dev_key, true
				last_answer = PORTAL_PATH.sub '?', key if
					request =~ re
				last_answer = PORTAL_PATH.sub '?', dev_key if
					request =~ dev_re
			end
			last_answer = "/virtual/#{row[0]}/web/#{row[1]}" if 
				last_answer.nil? or request =~ /bypass/
			$stmt.cancel
		rescue	# In case the library gives us an error
			# Try reiniting the connection a couple of times.
			# Then just start directing to the error site
			unless loop_protect
				last_request = ''
				last_answer = ERROR_PATH
			end
			loop_protect -= 1 unless loop_protect == 0
			init_database
			retry
		end
	end
	puts last_answer
end
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