Weblog

How to handle "connection already closed" errors

Created by Gustaf Neumann, last modified by Gustaf Neumann 21 Aug 2020, at 12:47 PM

Newer versions of NaviServer produce by default an error, when a script tries to write a connection, which as already closed by the server (e.g. doing two ad_returndirect in a sequence). Such program code does not make sense and indicates an error that should be fixed.

In general, one can silence the behavior or fix it. To silence the behavior, on can alter the NaviServer config file to silently swallow these error conditions named "rejectalreadyclosedconn". See e.g. Sample configuration file

Recent version of OpenACS (oacs-5-10) have such error conditions already fixed in all the actively maintained packages in the oacs-5-10 branch. In order to fix custom packages, one has to watch out for the following situations:

• Request pages: all after every command that finishes a request a call to "ad_script_abort" is required. Such commands are essentially all "ns_return*" commands and the "ad_*" counterparts.
• Filters: in case, an application handles such commands in filters, the filter has to return with "filter_return" to stop the filter chain (i.e. not to call further filters). Notice that the documentation of ns_register states that the request page is as well handled to trigger e.g. the access log entry. So, in rare conditions, one has to check as well for additional closed cases by using "ns_conn isconnected".

Sometimes, it might be still tricky to find such occurrences. On recent versions of OpenACS one can use the xo* machinery to activate/deactivate Tcl command traces for such commands via ds/shell, like e.g. in:

xo::broadcast send {
  set traced_cmds [info commands ::ns_return*]
  foreach cmd $traced_cmds {trace add execution $cmd  enter {::tcltrace::before}}
}

"xo::broadcast" sends the command to every tcl based thread that executes the provided command. Tracing can be deactivated by replacing "trace add" by "trace remove" in this command.

Plain OpenACS (in oacs-5-10) has as well some support for this via acs-tcl/tcl/tcltrace-init.tcl.

Handling out of memory on "exec" calls

Created by Gustaf Neumann, last modified by Gustaf Neumann 13 Jul 2020, at 02:24 PM

On sites with high number of configured threads and high number of activated packages, the VM size of nsd might become large. One measures is to compile NaviServer and Tcl with the flag SYSTEM_MALLOC, and to run it with a memory efficient malloc library such as TCMalloc (using in the service file LD_PRELOAD=/usr/lib/libtcmalloc.so").

However, even then memory might become short, when "exec" is performed, even via the nsproxy module. The nsproxy module was developed to reduce memory consumption by running a separate process which communicates via pipes to nsd. The nsproxy module is designed to run multiple worker processes (the number can be configured), but when this number runs out (more such worker processes are needed) a new nsproxy worker process has to be created. This happens via a fork() system call under Linux, which can result in an out-of-memory message like the following:

 Error: exec: ns_fork() failed: Cannot allocate memory
 Error: exec failed: not enough memory

What should one do in such cases? In general, the first rule is to reduce the "exec" calls as far as possible, since these are relative slow and resource intensive, and NaviServer/Tcl provide a large number of built-ins or library functions, which should be used if possible.

Secondly, it is preferable to start many nsproxy workers rather soon in the live-time of nsd (e.g. at startup, when it has a small footprint) and ensure that the nsproxy module keeps these worker process alive a long time (by setting "idletimeout" to a high value)

ns_section ns/server/${server}/module/nsproxy {
     # ns_param recvtimeout        5000
     # ns_param waittimeout        1000
     # ns_param idletimeout        300000
     ns_param idletimeout  700000000
 }

When all configured nsproxy worker processes are running all the time, there is not need to fork later, and the error above will not occur anymore. The following snippet shows, how to start all nsproxy worker processes by creatin an ns_job queue with sufficient threads, and start a simple command executed by via nsproxy asynchronously (using the "-detached" flag) in parallel.

set concurrency [ns_proxy configure ExecPool -maxslaves]
if {"q1" ni [ns_job queues]} {
    ns_job create q1 $concurrency
}
#
# Queue a sufficient number of jobs to be executed in parallel
#
time {ns_job queue -detached q1 {exec sleep 1}} [expr {$concurrency * 2}]

Additionally, versions of NaviServer beyond 4.99.20 show via

ns_proxy stats ExecPool

the number of running worker processes of the ExecPool (also included in the process page of nsstats).

How to configure a Network Place under Windows XP to access file-storage via WebDAV

Created by Robert Taylor, last modified by Gustaf Neumann 01 May 2020, at 11:33 AM

Topic:

How to configure a Network Place under Windows XP to access a WebDAV folder in file storage. 

Overview: 

Creating a Network Place will allow you to drag and drop multiple files and even folders from your machine to your OpenACS or .LRN  website. Once you have done these eleven (arguably ten) simple (really!) steps to create a permanent connection on your computer to your file storage location. The Network Place will be accessible through My Network Places.

Once you have established a Network Place to your File Storage documents, you can transfer multiple files, create/delete/edit folders, delete files. Creating and modifying files and folders through the Network Place is the same as you would do using Explorer. You can also open, edit and save files without the hassle of downloading, saving and uploading them on your machine!

Instructions: 

	Step 1: To create a Network Place, open Windows Explorer. Then, right click on "My Network Places" and select Open.
	Step 2: Under Network Tasks, Select "Add a Network Place."
	Step 3: Click "Next" to start the Wizard.
	Step 4: Highlight "Choose Another Network Location" (if it is not already) and click "Next."
	Step 5: Copy the WebDAV URL listed in the file storage folder you want to access and paste it in as the "Internet or Network Address" for your connection.
	Step 6: Select "Yes" when you are prompted with the Security Alert dialog.
	Step 7: Enter the email address you use to log into the site (or username if your site uses usernames) and password in the "Connect to:" dialog box. This establishes your connection to the Network Place.
	Step 8: Create a name for the new Network Place or accept the default and then click "Next."
	Step 9: Leave "Open this network place when I click Finish" checked. Click "Finish" to complete the Wizard.
	Step 10: The first time you do this, you may be prompted again with the Security alert and a login screen. Please say "Yes" to the alert.
	Step 11: You may also need to login again using your site email address and password. (This is a Microsoft thing, not a bug and we can't do anything about it.)
	Voila! Your new Network Place will open and you will see the folders as they appear in file-storage on your site. You can now open Explorer and select, drag and drop multiple files or folders from your machine into SloanSpace. After you do this, refresh your browser to see the files/folders. The Network Place is permanent, so you only need to set it up once and reconnect to it when you need to (through My Network Places.

Running OpenACS behind a proxy

Created by Gustaf Neumann, last modified by Michael Aram 18 Mar 2019, at 10:14 AM

If one is running OpenACS behind a reverse proxy such as NGINX or pound, one should use the following configuration options.

1. Make sure, the proxy server adds the following request header fields:
   • X-Forwarded-For: containing the IP address if the client making the actual request
   • X-SSL-Request: this parameter should be set, when the incoming requests of the proxy was an HTTPS request. This way, OpenACS can treat connections as secure, even when the the connection between the reverse proxy and NaviServer is a plain HTTP connection.
      
2. In the configuration file of NaviServer (or AOLserver), make sure, the following parameter are set:
   • Parameter ReverseProxyMode in the global parameters (under ns/parameters). This parameter is used by the Tcl code to obtain the right value via [ad_conn peeraddr] or [ad_conn behind_proxy_p]. When the reverse proxy sets the X-SSL-Request header field, also [ad_conn behind_secure_proxy_p] will be true.
   • Parameter checkforproxy in the nslog section. By activating it, the entries in the access log will have the value provided from the proxy via the X-Forwarded-For header. If this is not set, the access log will show always the IP address of the proxy server (last mile connection).

In order to check, whether the settings are correct, check the results of the following command calls in ds/shell (when acs-developer-support is installed)

• ad_conn behind_proxy_p
• ad_conn behind_secure_proxy_p

Note that when a server is running behind a secure proxy, but ad_conn behind_secure_proxy_p returns 0, the security ratings of the server will be downgraded, since no secure cookies will be used, etc. To check the settings, run the following command in ds/shell, which should return a non-empty result.

• ad_get_cookie ad_user_login_secure ""

F. A. Q.

Created by Robert Taylor, last modified by Gustaf Neumann 17 Oct 2017, at 08:40 AM

• What is OpenACS? See en:docs-end-user
• What features does OpenACS have? See en:docs-eng
• How to get admin-level help en:docs-admin-help
• How to get help with OpenACS en:community-culture
• How do I format X in XoWiki? See the documentation: http://alice.wu-wien.ac.at:8000/xowiki-doc/
• How to create a patch to submit via bugtracker? //bugtracker/openacs/patch-submission-instructions

Previous version of FAQ (with many more Q and A):  /faq 

A cookbook of procedures is available at: OpenACS Cookbook 

Refactoring Recipes

Created by Michael Aram, last modified by Michael Aram 04 Jul 2017, at 05:31 PM

The intention of this page is to collect small refactoring snippets that one can/should apply to an existing OpenACS installation in order to improve and modernize its code base. Most of the recipes have already been applied to the official core packages.

Modernize Tcl

1. Refactor foreach {var1.. varN} $list {break} to lassign

   See http://wiki.tcl.tk/1530

   Deprecated code example

   foreach {dog cat} $animalslist break

   Recommended code example

   lassign $animalslist dog cat

   Command line for finding/replacing code

   todo

2. Refactor multiple lindex operations to lassign

   Deprecated code example

   set dog [lindex $animalslist 0]
set cat [lindex $animalslist 1]

   Recommended code example

   lassign $animalslist dog cat

   Command line for finding/replacing code

   todo

3. Brace expr expressions

   Deprecated code example

   [expr $money - 1]

   Recommended code example

   [expr {$money - 1}]

   Command line for finding/replacing code

   todo

4. Replace string equal with eq in expressions

   Deprecated code example

   if {[string equal "" $dog]} {error "I want a dog!"}

   Recommended code example

   if {$dog eq ""} {error "I want a dog!"}

   Command line for finding/replacing code

   todo

5. Replace lsearch with in or ni in expressions

   Deprecated code example

   if {[lsearch -exact $animalslist $dog] != -1 } {error "I dont want a dog!"}

   Recommended code example

   if {$dog in $animalslist} {error "I dont want a dog!"}

   Command line for finding/replacing code

   todo

6. Replace eval with {*} if possible

   Deprecated code example

   eval mycommand $args

   Recommended code example

   mycommand {*}$args

   Command line for finding/replacing code

   todo

Best Practices

1. Use bind variables in SQL statements

   Deprecated code example

   db_string check "SELECT * FROM animals WHERE color = $color;"

   Recommended code example

   db_string check "SELECT * FROM animals WHERE color = :color;"

   Command line for finding/replacing code

   todo

2. Use util::http instead of util_http*, ns_httpget, ::http, ::xo::HttpRequest

Substitute Deprecated Procedures

1. Replace empty_string_p with eq ""

   Deprecated code example

   if {[empty_string_p $dog]} {error "I want a dog!"}
if {![empty_string_p $cat]} {error "I dont want a cat!"}

   Recommended code example

   if {$dog eq ""} {error "I want a dog!"}
if {$cat ne ""} {error "I dont want a cat!"}

   Command line for finding/replacing code

   todo

   Rationale

   Byte-compiled comparisons are faster.

2. Replace exists_and_not_null with info exists and ne

   Deprecated code example

   if {[exists_and_not_null cat]} {error "I dont want a cat!"}

   Recommended code example

   if {[info exists cat] && $cat ne "" } {error "I dont want a cat!"}

   Command line for finding/replacing code

   todo

   Rationale

   Byte-compiled comparisons are faster.

3. Replace ad_parameter with parameter::get

   Deprecated code example

   ad_parameter -package_id 123 SystemURL ""

   Recommended code example

   parameter::get -package_id 123 SystemURL -default ""

   Command line for finding/replacing code

   todo

4. Replace ad_require_permission with permission::require_permission

   Deprecated code example

   ad_require_permission $oid "read"

   Recommended code example

   permission::require_permission -object_id $oid -privilege "read"

   Command line for finding/replacing code

   fgrep -rl "ad_require_permission" packages/ | xargs sed -i.sedbak -r 's/ad_require_permission\s+([^\s]*)\s+([^\s]*)/permission::require_permission -object_id \1 -privilege \2/g'

5. Replace util_unlist with lassign

   Deprecated code example

   util_unlist $animalslist dog cat

   Recommended code example

   lassign $animalslist dog cat

   Command line for finding/replacing code

   todo

Modifying the look of an installation

Created by Ryan Gallimore, last modified by Benjamin Brink 30 Jun 2017, at 05:23 PM

Please refer to OACS Theming for newer templating information & tutorial.

Template Files 

Almost all pages on an OpenACS site use ACS Templating, and so their appearance is driven by a layer of different files. Let's examine how this works:

• A templated page uses an ADP/Tcl pair. The first line in the ADP file is usually:

  <master>

  If it appears exactly like this, without any arguments, the template processor uses default-master for that subsite. For pages in /var/lib/aolserver/$OPENACS_SERVICE_NAME/www, this is /var/lib/aolserver/$OPENACS_SERVICE_NAME/www/default-master.adp and the associated .tcl file.

• The default-master is itself a normal ADP page. It draws the subsite navigation elements and invokes site-master (/var/lib/aolserver/$OPENACS_SERVICE_NAME/www/site-master.adp and .tcl)

• The site-master draws site-wide navigation elements and invokes blank-master (/var/lib/aolserver/$OPENACS_SERVICE_NAME/www/blank-master.adp and .tcl).

• Blank-master does HTML housekeeping and provides a framework for special sitewide navigation "meta" elements such as Translator widgets and Admin widgets.

Figure 1. Site Templates

CSS Files

 /packages/acs-subsite/www/resources/site-master.css contains styles for the following elements:

• Header
• User Bar
• Footer
• Navigation
• Widgets (Buttons)
• Text Styles
• Portlets
• acs-developer-support (along with /packages/acs-developer-support/www/resources/acs-developer-support.css)

 /packages/acs-subsite/www/resources/default-master.css defines styles for the following elements:

• Table, TR, TD
• Calendar package
• combo boxes (for date dropdowns)

/packages/acs-templating/www/resources contains many other css stylesheets that are appropriately named. Each package may also often have its own stylesheet.

Selva Theme 

Selva simplifies the work of customizing the look and feel of your OpenACS/dotLRN website. You will find Selva's documentation on each installation of openacs, once the package is installed, you will find its documentation as follows: http://yoursite/doc/theme-selva.

Since Selva is based purely on css you can have a better accessibility on designing your site.

Steps in placing logo using Selva 

• Go to http://yoursite/admin/site-map/
• Search on theme-selva package and Click on its parameter link
• Look for the parameter named " logoUrl" and place the the filename or URL of the Logo that you want to put in.
• Go to http://yoursite/admin/site-map/, look for "Main Site" and click on parameters, then set the DefaultMaster parameter to  /packages/theme-selva/www/selva-master

Note: This instruction assumed that you have already installed the package theme-selva in your openacs installation.

XoWiki: List of the available includelets

Created by Gustaf Neumann, last modified by Benjamin Brink 30 Jun 2017, at 07:11 AM

This is a list of the includelets, which can be included in a xowiki page: 

XoWiki: How to save files directly in the wiki

Created by Gustaf Neumann, last modified by Benjamin Brink 30 Jun 2017, at 07:08 AM

In order to save files directly in the wiki, just add a link with the content file:yourfile to a page (as for other links, between curly double brackets).

[[file:oacs-dotlrn-vienna-xowiki.pdf|XoWiki Slides from the Vienna OpenACS conference]]

When the file link is added, and the file does not exist, the wiki marks the link with a handle to upload the file. According to the current policies, everybody who is logged-in has sufficient permissions is allowed to edit pages.. 

Here is an example of a file-link, pointing to the xowiki slides from the the Vienna oacs-dotlrn conference XoWiki Slides from the Vienna OpenACS conference

OpenACS Performance Tuning

Created by OpenACS community, last modified by Benjamin Brink 30 Jun 2017, at 06:56 AM

OpenACS Performance Tuning

Here is some documentation on general OpenACS performance tuning:

• Boost_your_application_performance_to_serve_large_files
• Diagnosing Performance Problems

Much performance tuning is targeted at the subsystems level, and so you will find some specific tuning information in these pages:

• en:aolserver-admin
• en:postgresql-admin

A broad scope of causes can be attributed to OpenACS performance issues. These forum threads help identify useful diagnostic techniques and accurate testing to help narrow the scope of problem areas etc.

• AOLserver and OpenACS Benchmarks (Why is my OpenACS so slow?)
• Server Performance Benchmarks with Apache Benchmark and Traffic Jamme
• How would one handle 12,000 db backed requests per second?
• Network performance monitoring tools
• Help Needed in Setting up .LRN to Scale
• Why is [my] OpenACS becoming so slow?
• Performance Problems - what is the bottleneck?
• Postgres connections [maxed out] and OpenACS
• Performance boost for older installations