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  • How to keep Varnish cached populate after backend down for an extended period?

    - by Nicholas Tolley Cottrell
    We have Varnish 3.0.2 running on Amazon's Linux and it works great. We have a ttl of 48 hours for most content pages and much longer for images, PDFs etc. This weekend we've taken the backend down for some maintenance, so I upped the ttl to 5 days earlier in the week. I had assumed that anything in cache would continue to be served for up to 5 days, but much to our disappointment we checked varnishstat this morning and the cache was almost completely empty and varnish was serving "page not found" messages. I know that this is not what Varnish is designed to do, but why would it reset its cache when the backend is down? And how can I prevent it for next time?

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  • Cron Script to Delete Folder Contents Every 5 Minutes on Media Temple

    - by Brian Iannone
    I'm not familiar with server-side scripting, but I'm currently using a PHP application on Media Temple to cache JPEGs from four webcams hosted on a server located in the middle of the Indian Ocean. (Hence my reason for caching them in the US.) The webcams are updated every five minutes. The PHP application stores the cached images in http://static.rigic.co/cache/. I would like to create a cron script to automatically delete the contents of "cache" (not the folder itself; just the files inside) at a regular interval.

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  • CSC folder data access AND roaming profiles issues (Vista with Server 2003, then 2008)

    - by Alex Jones
    I'm a junior sysadmin for an IT contractor that helps small, local government agencies, like little towns and the like. One of our clients, a public library with ~ 50 staff users, was recently migrated from Server 2003 Standard to Server 2008 R2 Standard in a very short timeframe; our senior employee, the only network engineer, had suddenly put in his two weeks notice, so management pushed him to do this project before quitting. A bit hasty on management's part? Perhaps. Could we do anything about that? Nope. Do I have to fix this all by myself? Pretty much. The network is set up like this: a) 50ish staff workstations, all running Vista Business SP2. All staff use MS Outlook, which uses RPC-over-HTTPS ("Outlook Anywhere") for cached Exchange access to an offsite location. b) One new (virtualized) Server 2008 R2 Standard instance, running atop a Server 2008 R2 host via Hyper-V. The VM is the domain's DC, and also the site's one and only file server. Let's call that VM "NEWBOX". c) One old physical Server 2003 Standard server, running the same roles. Let's call it "OLDBOX". It's still on the network and accessible, but it's been demoted, and its shares have been disabled. No data has been deleted. c) Gigabit Ethernet everywhere. The organization's only has one domain, and it did not change during the migration. d) Most users were set up for a combo of redirected folders + offline files, but some older employees who had been with the organization a long time are still on roaming profiles. To sum up: the servers in question handle user accounts and files, nothing else (eg, no TS, no mail, no IIS, etc.) I have two major problems I'm hoping you can help me with: 1) Even though all domain users have had their redirected folders moved to the new server, and loggin in to their workstations and testing confirms that the Documents/Music/Whatever folders point to the new paths, it appears some users (not laptops or anything either!) had been working offline from OLDBOX for a long time, and nobody realized it. Here's the ugly implication: a bunch of their data now lives only in their CSC folders, because they can't access the share on OLDBOX and sync with it finally. How do I get this data out of those CSC folders, and onto NEWBOX? 2) What's the best way to migrate roaming profile users to non-roaming ones, without losing vital data like documents, any lingering PSTs, etc? Things I've thought about trying: For problem 1: a) Reenable the documents share on OLDBOX, force an Offline Files sync for ALL domain users, then copy OLDBOX's share's data to the equivalent share on NEWBOX. Reinitialize the Offline Files cache for every user. With this: How do I safely force a domain-wide Offline Files sync? Could I lose data by reenabling the share on OLDBOX and forcing the sync? Afterwards, how can I reinitialize the Offline Files cache for every user, without doing it manually, workstation by workstation? b) Determine which users have unsynced changes to OLDBOX (again, how?), search each user's CSC folder domain-wide via workstation admin shares, and grab the unsynched data. Reinitialize the Offline Files cache for every user. With this: How can I detect which users have unsynched changes with a script? How can I search each user's CSC folder, when the ownership and permissions set for CSC folders are so restrictive? Again, afterwards, how can I reinitialize the Offline Files cache for every user, without doing it manually, workstation by workstation? c) Manually visit each workstation, copy the contents of the CSC folder, and manually copy that data onto NEWBOX. Reinitialize the Offline Files cache for every user. With this: Again, how do I 'break into' the CSC folder and get to its data? As an experiment, I took one workstation's HD offsite, imaged it for safety, and then tried the following with one of our shop PCs, after attaching the drive: grant myself full control of the folder (failed), grant myself ownership of the folder (failed), run chkdsk on the whole drive to make sure nothing's messed up (all OK), try to take full control of the entire drive (failed), try to take ownership of the entire drive (failed) MS KB articles and Googling around suggests there's a utility called CSCCMD that's meant for this exact scenario...but it looks like it's available for XP, not Vista, no? Again, afterwards, how can I reinitialize the Offline Files cache for every user, without doing it manually, workstation by workstation? For problem 2: a) Figure out which users are on roaming profiles, and where their profiles 'live' on the server. Create new folders for them in the redirected folders repository, migrate existing data, and disable the roaming. With this: Finding out who's roaming isn't hard. But what's the best way to disable the roaming itself? In AD Users and Computers, or on each user's workstation? Doing it centrally on the server seems more efficient; that said, all of the KB research I've done turns up articles on how to go from local to roaming, not the other way around, so I don't have good documentation on this. In closing: we have good backups of NEWBOX and OLDBOX, but not of the workstations themselves, so anything drastic on the client side would need imaging and testing for safety. Thanks for reading along this far! Hopefully you can help me dig us out of this mess.

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  • Translating C++'s sprintf format string to C#'s string.Format

    - by thebackup
    I found the following C++ code (comments added myself): // frame_name is a char array // prefix is std::string // k is a for loop counter // frames is a std::vector string sprintf(frameName, "%s_%0*s.bmp", prefix.c_str(), k, frames[k].c_str()); I then try to translate it to C# // prefix is string // k is a for loop counter // frames is List<string> string frameName = string.Format("{0}_(what goes in here?).bmp", prefix, k, frames[k]); Basically, what would be the C# equivalent of the C++ format string "%s_%0*s.bmp"?

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  • using markers instead of if and else statement in php

    - by Mac Taylor
    hey guys i need to shorten or better to say ., harden my codes this is my original code : if ($type = "recent") { $OrderType = "sid DESC"; }elseif ($type = "pop"){ $OrderType = "counter DESC"; }else { $OrderType = "RAND()"; } now how can i use markers like this : $OrderType = ($type = "recent") ? "sid DESC" : "counter DESC" ; i tried but i didnt know how to write elseif in marker way

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  • The simplest concurrency pattern

    - by Ilya Kogan
    Please, would you help me in reminding me of one of the simplest parallel programming techniques. How do I do the following in C#: Initial state: semaphore counter = 0 Thread 1: // Block until semaphore is signalled semaphore.Wait(); // wait until semaphore counter is 1 Thread 2: // Allow thread 1 to run: semaphore.Signal(); // increments from 0 to 1 It's not a mutex because there is no critical section, or rather you can say there is an infinite critical section. So what is it?

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  • how to obtain the relative path of a resource in a j2ee project

    - by Neeraj
    I have a Dynamic Web Project having a flat file (or say text file). I have created a servlet in which I need to use this file. My code is as following: protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // String resource = request.getParameter ("json") ; if ( resource != null && !resource.equals ( "" ) ) { //use getResourceAsStream ( ) to properly get the file. InputStream is = getServletContext ().getResourceAsStream ("rateJSON") ; if ( is != null ) { // the resource exists response.setContentType("application/json"); response.setHeader("Pragma", "No-cache"); response.setDateHeader("Expires", 0); response.setHeader("Cache-Control", "no-cache"); StringWriter sw = new StringWriter ( ) ; for ( int c = is.read ( ) ; c != -1; c = is.read ( ) ) { sw.write ( c ) ; } PrintWriter out = response.getWriter(); out.print (sw.toString ()) ; out.flush(); } } } The problem is that the InputStream is has null value. I'm not sure how to get the correct relative path. I'm using JBOSS as the app server. I have added the resource file in the WebContent directory of a Dynamic Web Project. As a different approch, I tried this: protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub ServletConfig config = getServletConfig(); String contextName = config.getInitParameter("ApplicationName"); System.out.println("context name"+ contextName); String contextPath = config.getServletContext().getRealPath(contextName); System.out.println("context Path"+contextPath); //contextPath = contextPath.substring(0, contextPath.indexOf(contextName)); contextPath += "\\rateJSON.txt"; System.out.println(contextPath); String resource = request.getParameter ("json") ; System.out.println("Hi there1"+resource); if ( resource != null && !resource.equals ( "" ) ) { System.out.println("Hi there"); //use getResourceAsStream ( ) to properly get the file. //InputStream is = getServletContext ().getResourceAsStream (resource) ; InputStream is = getServletConfig().getServletContext().getResourceAsStream(contextPath); if ( is != null ) { // the resource exists System.out.println("Hi there2"); response.setContentType("application/json"); response.setHeader("Pragma", "No-cache"); response.setDateHeader("Expires", 0); response.setHeader("Cache-Control", "no-cache"); StringWriter sw = new StringWriter ( ); for ( int c = is.read ( ) ; c != -1; c = is.read ( ) ) { sw.write ( c ) ; System.out.println(c); } PrintWriter out = response.getWriter(); out.print (sw.toString ()) ; System.out.println(sw.toString()); out.flush(); } } } The value of contextPath is now: C:\JBOSS\jboss-5.0.1.GA\server\default\tmp\4p72206b-uo5r7k-g0vn9pof-1-g0vsh0o9-b7\Nationwide.war\WEB-INF\rateJSON But at this location the rateJSON file is not there? It seems JBOSS is not putting this file in the App.war or doesn't deploy it??? Could someone please help me?

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  • Websocket handshake response not forwarded from TCP to client

    - by Saharsh
    I am trying to create a websocket server. I can see the websocket client's opening handhshake. My response to it is received by the client laptop (I can see this on wireshark). So the TCP connection has been established. But the client (a chrome websocket client extension) does not receive the handshake packet. What could be a possible reason for TCP to not forward the handshake to the client or for the client to not be able to read the TCP message? Client handshake: GET HTTP/1.1 Upgrade: websocket Connection:Upgrade Cache-Control:no-cache Host:192.168.0.101 Origin:http://www.websocket.org Pragma:no-cache Sec-WebSocket-Extensions:permessage-deflate; client_max_window_bits, x-webkit-deflate-frame Sec-WebSocket-Key: qrmw/m+BoZije6h9HYKmVw== Sec-WebSocket-Version:13 Upgrade:websocket Server Response: HTTP/1.1 101 Switching Protocols Upgrade: websocket Connection: Upgrade Sec-WebSocket-Accept: jj1g5Io57m9ks8cme3jkbyo2asc= Access-Control-Allow-Origin: http://www.websocket.org Server: xyz Sec-WebSocket-Extensions: Thanks!

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  • Configuring memcached for a particular scenario

    - by pradeepchhetri
    I have a web application which queries opentsdb server(which in backend using Hbase cluster) for the datapoints of different metrics and using dygraph javascript graphing library, I am plotting those metrics. Since getting all the datapoints of past one day from opentsdb for a particular metric is itself taking nearly 2 seconds, my application which is plotting nearly 25 metrics is becoming very slow. In order to reduce this latency, I am thinking of using memcached module of php5 for caching all the queries. But I have few questions regarding memcached. Is there any way I can configure memcache to keep on updating its cache in the background by running some command line queries after particular interval of time. Is there any way I can configure memcache to always reply for a query using cache instead of first updating its cache because my application just plots datapoints for past one day. Missing out some datapoints is not that critical.

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  • High-End Gaming Desktop PC in France [closed]

    - by Lerikunus
    Hello, I was looking to buy an ALIENWARE AREA 51, as my Desktop crashed some days ago. But the Preliminary Ship date is 03.01.11 and I need the new PC until Friday next week =( Does someone know a(n) (online)-store where Build&Shipping time is quite low so I can get it until next Friday? I am living in France (Nice). Or any place I can ask fot his kind of advice? This is my desired configuration: Overclocked Intel® Core™ i7 980x Extreme Six Core Processor (4.0GHz, 12MB Cache) 12GB Triple Channel 1600MHz DDR3 Dual 2GB ATI Radeon™ HD 6950 2TB RAID 1+0 (4x 1TB SATA-II, 7,200 RPM, 32MB Cache HDDs) 2TB RAID 1 (2x2TB SATA-II, 7,200 RPM, 32MB Cache HDDs) Thank you very much!

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  • How to combine wildcards and spaces (quotes) in an Windows command?

    - by Jan Fabry
    I want to remove directories of the following format: C:\Program Files\FogBugz\Plugins\cache\[email protected]_NN NN is a number, so I want to use a wildcard (this is part of a post-build step in Visual Studio). The problem is that I need to combine quotes around the path name (for the space in Program Files) with a wildcard to match the end of the path. I already found out that rd is the remove command that accepts wildcards, but where do I put the quotes? I have tried no ending quote (works for dir), ...example.com*", ...example.com"*, ...example.com_??", ...cache\"[email protected]*, ...cache"\[email protected]*, but none of them work. (How many commands to remove a file/directory are there in Windows anyway? And why do they all differ in capabilities?)

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  • In python, what does len(list) do?

    - by nsharish
    My doubt is that if the len(list) calculates the length of the list everytime it is called or it returns the value of the builtin counter.I have a context where i need to check the length of list everytime in a loop, likelistData = [] for value in ioread(): if len(listData)=25: processlistdata() clearlistdata() listData.append(value) Should I check len(listData) every iteration, or can I have a counter for the length of the list.

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  • What is excessive swapping.

    - by amateur barista
    This post led me to ask that question. Cache contention On a large site, if you are using MyISAM, contention occurs in the database tables when the cache is forced to clear after a node or a comment is added. With tens of thousands of filter text snippets needing to be deleted, the table will be locked for a long period, and any accesses to it will be queued pending the purge of the data in it. The same is true for the page cache as well. This often causes a "site hang" for a minute or two. During that time new requests keep piling up, and if you do not have the MaxClients parameter in Apache setup correctly, the system can go into thrashing because of excessive swapping.

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  • Add effects to datagrid invalidate

    - by MooCow
    Is it possible to add an effect to a datagrid when I call invalidatelist to update the data? If it can be done, can the effects be selectively applied to only certain cells in the grid? The grid is showing an array with some nested array in it. I'm using an int counter to keep track of the nested array element position. When the counter is advanced, I tell the grid to update using invalidatelist.

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  • Run script when Varnish starts

    - by kipusoep
    I'd like to run a script when Varnish starts. This script should execute a webrequest to a webserver (its backend), which then makes sure Varnish's cache gets filled with all pages residing on this webserver. So this script makes sure everyting is in Varnish's cache when Varnish (re)starts, because we're using Varnish as cache and fail-over (the webserver should be able to be down for let's say a week for example, without any consequences). What are the possibilities to do this? We can't just edit /etc/init.d/varnish and /usr/sbin/varnishd because they can het overwritten when updating varnish? Thanks!

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  • Override `drop` for a custom sequence

    - by Bruno Reis
    In short: in Clojure, is there a way to redefine a function from the standard sequence API (which is not defined on any interface like ISeq, IndexedSeq, etc) on a custom sequence type I wrote? 1. Huge data files I have big files in the following format: A long (8 bytes) containing the number n of entries n entries, each one being composed of 3 longs (ie, 24 bytes) 2. Custom sequence I want to have a sequence on these entries. Since I cannot usually hold all the data in memory at once, and I want fast sequential access on it, I wrote a class similar to the following: (deftype DataSeq [id ^long cnt ^long i cached-seq] clojure.lang.IndexedSeq (index [_] i) (count [_] (- cnt i)) (seq [this] this) (first [_] (first cached-seq)) (more [this] (if-let [s (next this)] s '())) (next [_] (if (not= (inc i) cnt) (if (next cached-seq) (DataSeq. id cnt (inc i) (next cached-seq)) (DataSeq. id cnt (inc i) (with-open [f (open-data-file id)] ; open a memory mapped byte array on the file ; seek to the exact position to begin reading ; decide on an optimal amount of data to read ; eagerly read and return that amount of data )))))) The main idea is to read ahead a bunch of entries in a list and then consume from that list. Whenever the cache is completely consumed, if there are remaining entries, they are read from the file in a new cache list. Simple as that. To create an instance of such a sequence, I use a very simple function like: (defn ^DataSeq load-data [id] (next (DataSeq. id (count-entries id) -1 []))) ; count-entries is a trivial "open file and read a long" memoized As you can see, the format of the data allowed me to implement count in very simply and efficiently. 3. drop could be O(1) In the same spirit, I'd like to reimplement drop. The format of these data files allows me to reimplement drop in O(1) (instead of the standard O(n)), as follows: if dropping less then the remaining cached items, just drop the same amount from the cache and done; if dropping more than cnt, then just return the empty list. otherwise, just figure out the position in the data file, jump right into that position, and read data from there. My difficulty is that drop is not implemented in the same way as count, first, seq, etc. The latter functions call a similarly named static method in RT which, in turn, calls my implementation above, while the former, drop, does not check if the instance of the sequence it is being called on provides a custom implementation. Obviously, I could provide a function named anything but drop that does exactly what I want, but that would force other people (including my future self) to remember to use it instead of drop every single time, which sucks. So, the question is: is it possible to override the default behaviour of drop? 4. A workaround (I dislike) While writing this question, I've just figured out a possible workaround: make the reading even lazier. The custom sequence would just keep an index and postpone the reading operation, that would happen only when first was called. The problem is that I'd need some mutable state: the first call to first would cause some data to be read into a cache, all the subsequent calls would return data from this cache. There would be a similar logic on next: if there's a cache, just next it; otherwise, don't bother populating it -- it will be done when first is called again. This would avoid unnecessary disk reads. However, this is still less than optimal -- it is still O(n), and it could easily be O(1). Anyways, I don't like this workaround, and my question is still open. Any thoughts? Thanks.

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  • PHP Array Not Working in Function

    - by lemonpole
    Hello all. I'm currently experimenting with arrays in PHP, and I created a fake environment where a team's information will be displayed. $t1 = array ( "basicInfo" => array ( "The Sineps", "December 25, 2010", "lemonpole" ), "overallRecord" => array (0, 0, 0, 0), "overallSeasons" => array ( 1 => array (14, 0, 0), 2 => array (9, 5, 2), 3 => array (12, 4, 0), 4 => array (3, 11, 2) ), "games" => array ( "<img src=\"images/cs.gif\" alt=\"Counter-Strike\" />", "<img src=\"images/cs.gif\" alt=\"Counter-Strike\" />", "<img src=\"images/cs.gif\" alt=\"Counter-Strike\" />", "<img src=\"images/cs.gif\" alt=\"Counter-Strike\" />" ), "seasonHistory" => array ( "Season I", "Season II", "Season III", "Season IV" ), "divisions" => array ( "Open", "Main", "Main", "Invite" ) ); // Displays the seasons the team has been in along // with the record of each season. function seasonHistory() { // Make array variable local-scope. global $t1; // Count the number of seasons. $numrows = count($t1["seasonHistory"]); // Loop through all the variables until // it reaches the last entry made and display // each item seperately. for($v = 0; $v <= $numrows; $v++) { // Echo each season. echo "<tr><td>{$t1["games"][$v]}</td>"; echo "<td>{$t1["seasonHistory"][$v]}</td>"; echo "<td>{$t1["divisions"][$v]}</td></tr>"; } } I have tested several possible problems out and after narrowing them down I have come down to one conclusion and that is my function is not connecting to the array for some reason. I don't know what else to do because I thought making the array global would fix that problem. What works: I can echo $t1["games"][0] on the page I need it to display and it gives me the content. I tried echo $t1["games"][0] INSIDE the function and then calling the function and it doesn't display anything.

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  • Varnishhist x- and y-axis

    - by pst
    In varnishhist the x-axis shows the time varnish took between getting the request from the kernel and sending it back to kernel. The y-axis shows the number of requests. | => cache hit # => cache miss That is what I understood from the manpage. Correct me if I'm wrong. Yet there is one thing I'm unsure about. The pipes (|) on the far left side, do they also stand for cache hits or are they just there to print the y-axis? I'm voting for the latter, but would like to be sure.

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  • Implementing a 30 day time trial

    - by svintus
    Question for indie Mac developers out there: How do I implement a 30-day time trial in a non-evil fashion? Putting a counter in the prefs is not an option, since wiping prefs once a month is not a problem for an average user. Putting the counter in a hidden file somewhere sounds a bit dodgy - as a user I hate when apps sprinkle my hard drive with random files. Any ideas?

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  • ASP.NET GZip Encoding Caveats

    - by Rick Strahl
    GZip encoding in ASP.NET is pretty easy to accomplish using the built-in GZipStream and DeflateStream classes and applying them to the Response.Filter property.  While applying GZip and Deflate behavior is pretty easy there are a few caveats that you have watch out for as I found out today for myself with an application that was throwing up some garbage data. But before looking at caveats let’s review GZip implementation for ASP.NET. ASP.NET GZip/Deflate Basics Response filters basically are applied to the Response.OutputStream and transform it as data is written to it through the ASP.NET Response object. So a Response.Write eventually gets written into the output stream which if a filter is also written through the filter stream’s interface. To perform the actual GZip (and Deflate) encoding typically used by Web pages .NET includes the GZipStream and DeflateStream stream classes which can be readily assigned to the Repsonse.OutputStream. With these two stream classes in place it’s almost trivially easy to create a couple of reusable methods that allow you to compress your HTTP output. In my standard WebUtils utility class (from the West Wind West Wind Web Toolkit) created two static utility methods – IsGZipSupported and GZipEncodePage – that check whether the client supports GZip encoding and then actually encodes the current output (note that although the method includes ‘Page’ in its name this code will work with any ASP.NET output). /// <summary> /// Determines if GZip is supported /// </summary> /// <returns></returns> public static bool IsGZipSupported() { string AcceptEncoding = HttpContext.Current.Request.Headers["Accept-Encoding"]; if (!string.IsNullOrEmpty(AcceptEncoding) && (AcceptEncoding.Contains("gzip") || AcceptEncoding.Contains("deflate"))) return true; return false; } /// <summary> /// Sets up the current page or handler to use GZip through a Response.Filter /// IMPORTANT: /// You have to call this method before any output is generated! /// </summary> public static void GZipEncodePage() { HttpResponse Response = HttpContext.Current.Response; if (IsGZipSupported()) { string AcceptEncoding = HttpContext.Current.Request.Headers["Accept-Encoding"]; if (AcceptEncoding.Contains("deflate")) { Response.Filter = new System.IO.Compression.DeflateStream(Response.Filter, System.IO.Compression.CompressionMode.Compress); Response.Headers.Remove("Content-Encoding"); Response.AppendHeader("Content-Encoding", "deflate"); } else { Response.Filter = new System.IO.Compression.GZipStream(Response.Filter, System.IO.Compression.CompressionMode.Compress); Response.Headers.Remove("Content-Encoding"); Response.AppendHeader("Content-Encoding", "gzip"); } } } As you can see the actual assignment of the Filter is as simple as: Response.Filter = new DeflateStream(Response.Filter, System.IO.Compression.CompressionMode.Compress); which applies the filter to the OutputStream. You also need to ensure that your response reflects the new GZip or Deflate encoding and ensure that any pages that are cached in Proxy servers can differentiate between pages that were encoded with the various different encodings (or no encoding). To use this utility function now is trivially easy: In any ASP.NET code that wants to compress its Response output you simply use: protected void Page_Load(object sender, EventArgs e) { WebUtils.GZipEncodePage(); Entry = WebLogFactory.GetEntry(); var entries = Entry.GetLastEntries(App.Configuration.ShowEntryCount, "pk,Title,SafeTitle,Body,Entered,Feedback,Location,ShowTopAd", "TEntries"); if (entries == null) throw new ApplicationException("Couldn't load WebLog Entries: " + Entry.ErrorMessage); this.repEntries.DataSource = entries; this.repEntries.DataBind(); } Here I use an ASP.NET page, but the above WebUtils.GZipEncode() method call will work in any ASP.NET application type including HTTP Handlers. The only requirement is that the filter needs to be applied before any other output is sent to the OutputStream. For example, in my CallbackHandler service implementation by default output over a certain size is GZip encoded. The output that is generated is JSON or XML and if the output is over 5k in size I apply WebUtils.GZipEncode(): if (sbOutput.Length > GZIP_ENCODE_TRESHOLD) WebUtils.GZipEncodePage(); Response.ContentType = ControlResources.STR_JsonContentType; HttpContext.Current.Response.Write(sbOutput.ToString()); Ok, so you probably get the idea: Encoding GZip/Deflate content is pretty easy. Hold on there Hoss –Watch your Caching Or is it? There are a few caveats that you need to watch out for when dealing with GZip content. The fist issue is that you need to deal with the fact that some clients don’t support GZip or Deflate content. Most modern browsers support it, but if you have a programmatic Http client accessing your content GZip/Deflate support is by no means guaranteed. For example, WinInet Http clients don’t support GZip out of the box – it has to be explicitly implemented. Other low level HTTP clients on other platforms too don’t support GZip out of the box. The problem is that your application, your Web Server and Proxy Servers on the Internet might be caching your generated content. If you return content with GZip once and then again without, either caching is not applied or worse the wrong type of content is returned back to the client from a cache or proxy. The result is an unreadable response for *some clients* which is also very hard to debug and fix once in production. You already saw the issue of Proxy servers addressed in the GZipEncodePage() function: // Allow proxy servers to cache encoded and unencoded versions separately Response.AppendHeader("Vary", "Content-Encoding"); This ensures that any Proxy servers also check for the Content-Encoding HTTP Header to cache their content – not just the URL. The same thing applies if you do OutputCaching in your own ASP.NET code. If you generate output for GZip on an OutputCached page the GZipped content will be cached (either by ASP.NET’s cache or in some cases by the IIS Kernel Cache). But what if the next client doesn’t support GZip? She’ll get served a cached GZip page that won’t decode and she’ll get a page full of garbage. Wholly undesirable. To fix this you need to add some custom OutputCache rules by way of the GetVaryByCustom() HttpApplication method in your global_ASAX file: public override string GetVaryByCustomString(HttpContext context, string custom) { // Override Caching for compression if (custom == "GZIP") { string acceptEncoding = HttpContext.Current.Response.Headers["Content-Encoding"]; if (string.IsNullOrEmpty(acceptEncoding)) return ""; else if (acceptEncoding.Contains("gzip")) return "GZIP"; else if (acceptEncoding.Contains("deflate")) return "DEFLATE"; return ""; } return base.GetVaryByCustomString(context, custom); } In a page that use Output caching you then specify: <%@ OutputCache Duration="180" VaryByParam="none" VaryByCustom="GZIP" %> To use that custom rule. It’s all Fun and Games until ASP.NET throws an Error Ok, so you’re up and running with GZip, you have your caching squared away and your pages that you are applying it to are jamming along. Then BOOM, something strange happens and you get a lovely garbled page that look like this: Lovely isn’t it? What’s happened here is that I have WebUtils.GZipEncode() applied to my page, but there’s an error in the page. The error falls back to the ASP.NET error handler and the error handler removes all existing output (good) and removes all the custom HTTP headers I’ve set manually (usually good, but very bad here). Since I applied the Response.Filter (via GZipEncode) the output is now GZip encoded, but ASP.NET has removed my Content-Encoding header, so the browser receives the GZip encoded content without a notification that it is encoded as GZip. The result is binary output. Here’s what Fiddler says about the raw HTTP header output when an error occurs when GZip encoding was applied: HTTP/1.1 500 Internal Server Error Cache-Control: private Content-Type: text/html; charset=utf-8 Date: Sat, 30 Apr 2011 22:21:08 GMT Content-Length: 2138 Connection: close ?`I?%&/m?{J?J??t??` … binary output striped here Notice: no Content-Encoding header and that’s why we’re seeing this garbage. ASP.NET has stripped the Content-Encoding header but left our filter intact. So how do we fix this? In my applications I typically have a global Application_Error handler set up and in this case I’ve been using that. One thing that you can do in the Application_Error handler is explicitly clear out the Response.Filter and set it to null at the top: protected void Application_Error(object sender, EventArgs e) { // Remove any special filtering especially GZip filtering Response.Filter = null; … } And voila I get my Yellow Screen of Death or my custom generated error output back via uncompressed content. BTW, the same is true for Page level errors handled in Page_Error or ASP.NET MVC Error handling methods in a controller. Another and possibly even better solution is to check whether a filter is attached just before the headers are sent to the client as pointed out by Adam Schroeder in the comments: protected void Application_PreSendRequestHeaders() { // ensure that if GZip/Deflate Encoding is applied that headers are set // also works when error occurs if filters are still active HttpResponse response = HttpContext.Current.Response; if (response.Filter is GZipStream && response.Headers["Content-encoding"] != "gzip") response.AppendHeader("Content-encoding", "gzip"); else if (response.Filter is DeflateStream && response.Headers["Content-encoding"] != "deflate") response.AppendHeader("Content-encoding", "deflate"); } This uses the Application_PreSendRequestHeaders() pipeline event to check for compression encoding in a filter and adjusts the content accordingly. This is actually a better solution since this is generic – it’ll work regardless of how the content is cleaned up. For example, an error Response.Redirect() or short error display might get changed and the filter not cleared and this code actually handles that. Sweet, thanks Adam. It’s unfortunate that ASP.NET doesn’t natively clear out Response.Filters when an error occurs just as it clears the Response and Headers. I can’t see where leaving a Filter in place in an error situation would make any sense, but hey - this is what it is and it’s easy enough to fix as long as you know where to look. Riiiight! IIS and GZip I should also mention that IIS 7 includes good support for compression natively. If you can defer encoding to let IIS perform it for you rather than doing it in your code by all means you should do it! Especially any static or semi-dynamic content that can be made static should be using IIS built-in compression. Dynamic caching is also supported but is a bit more tricky to judge in terms of performance and footprint. John Forsyth has a great article on the benefits and drawbacks of IIS 7 compression which gives some detailed performance comparisons and impact reviews. I’ll post another entry next with some more info on IIS compression since information on it seems to be a bit hard to come by. Related Content Built-in GZip/Deflate Compression in IIS 7.x HttpWebRequest and GZip Responses © Rick Strahl, West Wind Technologies, 2005-2011Posted in ASP.NET   IIS7  

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