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  • Tinkerforge Rotation/LCD & JavaFX Plans

    - by Geertjan
    The first time I integrated two Tinkerforge bricklets, the day before yesterday, was pretty cool: import com.tinkerforge.BrickMaster; import com.tinkerforge.BrickletLCD20x4; import com.tinkerforge.BrickletRotaryPoti; import com.tinkerforge.IPConnection; import java.util.Calendar; public class TFConnectionDemo { private static final String HOST = "localhost"; private static final int PORT = 4223; private static final String MASTERBRICKUID = "somethingabc"; private static final String LCDUID = "somethingabc"; private static final String ROTIUID = "somethingabc"; private static IPConnection ipc; private static BrickMaster master = new BrickMaster(MASTERBRICKUID); private static BrickletLCD20x4 lcd = new BrickletLCD20x4(LCDUID); private static BrickletRotaryPoti poti = new BrickletRotaryPoti(ROTIUID); public static void main(String[] args) { try { ipc = new IPConnection(HOST, PORT); ipc.addDevice(master); ipc.addDevice(lcd); ipc.addDevice(poti); poti.setPositionCallbackPeriod(50); poti.addListener(new BrickletRotaryPoti.PositionListener() { @Override public void position(short position) { lcd.clearDisplay(); Calendar cal = Calendar.getInstance(); lcd.writeLine((short) 0, (short) 0, cal.getTime().toString()); lcd.writeLine((short) 1, (short) 0, "Rotation: " + position); } }); } catch (Exception e) { } } } The result is that the display text in the LCD bricklet changes while I turn the rotation bricklet: Now imagine that you have some JavaFX charts and, while you turn the rotation bricklet (i.e., the dial thing that I'm turning above), the values of the charts change. That would be pretty cool because you'd be able to animate the JavaFX charts by rotating an object externally, i.e., without even touching the keyboard. That would be pretty cool to see and shouldn't be hard to implement.

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  • ORA-600 Troubleshooting

    - by [email protected]
    Have you observed an ORA-0600 or ORA-07445 reported in your alert log? The ORA-600 error is the generic internal error number for Oracle program exceptions. It indicates that a process has encountered a low-level, unexpected condition. The ORA-600 error statement includes a list of arguments in square brackets: ORA 600 "internal error code, arguments: [%s], [%s],[%s], [%s], [%s]" The first argument is the internal message number or character string. This argument and the database version number are critical in identifying the root cause and the potential impact to your system.  The remaining arguments in the ORA-600 error text are used to supply further information (e.g. values of internal variables etc).   Looking for the best way to diagnose? There is an ORA-600 Troubleshooter Tool available in My Oracle Support.  This tool will lead you to applicable content in My Oracle Support on the problem and can be used to investigate the problem with argument data from the error message or you can pull out the first 10 or 15 stack pointers from the associated trace file to match up against known bugs. Note 153788.1 ORA-600/ORA-7445 TroubleshooterNote 1082674.1 A Video To Demonstrate The Usage Of The ORA-600/ORA-7445 Lookup Tool [Video] Also, take a quick look at the Master Note for Diagnosing ORA-600 ( MasterNoteORA600.docx) for some tips on diagnosing.

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  • Simplify Your Code with LINQ

    - by dwahlin
    I’m a big fan of LINQ and use it wherever I can to minimize code and make applications easier to maintain overall. I was going through a code file today refactoring it based on suggestions provided by Resharper and came across the following method: private List<string> FilterTokens(List<string> tokens) { var cleanedTokens = new List<string>(); for (int i = 0; i < tokens.Count; i++) { string token = tokens[i]; if (token != null) { cleanedTokens.Add(token); } } return cleanedTokens; }   In looking through the code I didn’t see anything wrong but Resharper was suggesting that I convert it to a LINQ expression: In thinking about it more the suggestion made complete sense because I simply wanted to add all non-null token values into a List<string> anyway. After following through with the Resharper suggestion the code changed to the following. Much, much cleaner and yet another example of why LINQ (and Resharper) rules: private List<string> FilterTokens(IEnumerable<string> tokens) { return tokens.Where(token => token != null).ToList(); }

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  • Tomcat memory usage grows until crash with no GC run

    - by Phil
    I'm administrating a server running Tomcat that is getting a lot of traffic lately. If I monitor memory usage in Task Manager I can see the memory usage growing and eventually tomcat crashes around the 1GB mark. Here's the memory relevent bits I've set in Tomcat Properties (this is a Windows Server): Intial memory pool: 1024 MB Maximum memory pool: 1024 MB -XX:MaxPermSize=256M The weird thing is since these problems arose I've deployed Lambda Probe to the Tomcat instance and the memory usage values I see there are much lower, for example Task Manager might show 467MB used while the "Total" used in Probe is 212 MB. Also, the Maximum Total listed in Probe is 1.29GB, when I would have expected 1GB, the maximum memory set above. If I force the garbage collector to run using Probe, I can keep Tomcat from crashing for a while (indefinitely, AFAIK). So why doesn't the GC run automatically and stop Tomcat from crashing? Thanks.

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  • Difference between multiple NS and NS having multiple A

    - by Jake
    I found this Can an NS Record Point To Multiple A Records?, but wonders what is the difference, if any. For example: mydomain.com. IN NS ns1.myhost.com. mydomain.com. IN NS ns2.myhost.com. ns1.myhost.com. IN A 111.222.333.1 ns2.myhost.com. IN A 111.222.333.2 versus mydomain.com. IN NS ns.myhost.com. ns.myhost.com. IN A 111.222.333.1 ns.myhost.com. IN A 111.222.333.2 EDIT: actually, come to think of it, it could be said the same for MX records. Any breaking differences? EDIT 2: then again, MX allow use of priority values so its a different case, in that one-ip-per-domain is more useful sometimes.

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  • Using orientation to calculate position on Windows Phone 7

    - by Lavinski
    I'm using the motion API and I'm trying to figure out a control scheme for the game I'm currently developing. What I'm trying to achive is for a orienation of the device to correlate directly to a position. Such that tilting the phone forward and to the left represents the top left position and back to the right would be the bottom right position. Photos to make it clearer (the red dot would be the calculated position). Forward and Left Back and Right Now for the tricky bit. I also have to make sure that the values take into account left landscape and right landscape device orientations (portrait is the default so no calculations would be needed for it). Has anyone done anything like this? Notes: I've tried using the yaw, pitch, roll and Quaternion readings. Sample: // Get device facing vector public static Vector3 GetState() { lock (lockable) { var down = Vector3.Forward; var direction = Vector3.Transform(down, state); switch (Orientation) { case Orientation.LandscapeLeft: return Vector3.TransformNormal(direction, Matrix.CreateRotationZ(-rightAngle)); case Orientation.LandscapeRight: return Vector3.TransformNormal(direction, Matrix.CreateRotationZ(rightAngle)); } return direction; } }

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  • What's the best algorithm for... [closed]

    - by Paska
    Hi programmers! Today come out a little problem. I have an array of coordinates (latitude and longitude) maded in this way: [0] = "45.01234,9.12345" [1] = "46.11111,9.12345" [2] = "47.22222,9.98765" [...] etc In a loop, convert these coordinates in meters (UTM northing / UTM easting) and after that i convert these coords in pixel (X / Y) on screen (the output device is an iphone) to draw a route line on a custom map. [0] = "512335.00000,502333.666666" [...] etc The returning pixel are passed to a method that draw a line on screen (simulating a route calculation). [0] = "20,30" [1] = "21,31" [2] = "25,40" [...] etc As coordinate (lat/lon) are too many, i need to truncate lat/lon array eliminating the values that doesn't fill in the map bound (the visible part of map on screen). Map bounds are 2 couple of coords lat/lon, upper left and lower right. Now, what is the best way to loop on this array (NOT SORTED) and check if a value is or not in bound and after remove the value that is outside? To return a clean array that contains only the coords visible on screen? Note: the coords array is a very big array. 4000/5000 couple of items. This is a method that should be looped every drag or zoom. Anyone have an idea to optimize search and controls in this array? many thanks, A

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  • OOP concept: is it possible to update the class of an instantiated object?

    - by Federico
    I am trying to write a simple program that should allow a user to save and display sets of heterogeneous, but somehow related data. For clarity sake, I will use a representative example of vehicles. The program flow is like this: The program creates a Garage object, which is basically a class that can contain a list of vehicles objects Then the users creates Vehicles objects, these Vehicles each have a property, lets say License Plate Nr. Once created, the Vehicle object get added to a list within the Garage object --Later on--, the user can specify that a given Vehicle object is in fact a Car object or a Truck object (thus giving access to some specific attributes such as Number of seats for the Car, or Cargo weight for the truck) At first sight, this might look like an OOP textbook question involving a base class and inheritance, but the problem is more subtle because at the object creation time (and until the user decides to give more info), the computer doesn't know the exact Vehicle type. Hence my question: how would you proceed to implement this program flow? Is OOP the way to go? Just to give an initial answer, here is what I've came up until now. There is only one Vehicle class and the various properties/values are handled by the main program (not the class) through a dictionary. However, I'm pretty sure that there must be a more elegant solution (I'm developing using VB.net): Public Class Garage Public GarageAdress As String Private _ListGarageVehicles As New List(Of Vehicles) Public Sub AddVehicle(Vehicle As Vehicles) _ListGarageVehicles.Add(Vehicle) End Sub End Class Public Class Vehicles Public LicensePlateNumber As String Public Enum VehicleTypes Generic = 0 Car = 1 Truck = 2 End Enum Public VehicleType As VehicleTypes Public DictVehicleProperties As New Dictionary(Of String, String) End Class NOTE that in the example above the public/private modifiers do not necessarily reflect the original code

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  • The internal storage of a DATETIMEOFFSET value

    - by Peter Larsson
    Today I went for investigating the internal storage of DATETIME2 datatype. What I found out was that for a datetime2 value with precision 0 (seconds only), SQL Server need 6 bytes to represent the value, but stores 7 bytes. This is because SQL Server add one byte that holds the precision for the datetime2 value. Start with this very simple repro declare    @now datetimeoffset(7) = '2010-12-15 21:04:03.6934231 +03:30'   select     cast(cast(@now as datetimeoffset(0)) as binary(9)),            cast(cast(@now as datetimeoffset(1)) as binary(9)),            cast(cast(@now as datetimeoffset(2)) as binary(9)),            cast(cast(@now as datetimeoffset(3)) as binary(10)),            cast(cast(@now as datetimeoffset(4)) as binary(10)),            cast(cast(@now as datetimeoffset(5)) as binary(11)),            cast(cast(@now as datetimeoffset(6)) as binary(11)),            cast(cast(@now as datetimeoffset(7)) as binary(11)) Now we are going to copy and paste these binary values and investigate which value is representing what time part. Prefix  Ticks       Ticks         Days    Days    Suffix  Suffix  Original value ------  ----------  ------------  ------  ------  ------  ------  ------------------------ 0x  00  0CF700             63244  A8330B  734120  D200       210  0x000CF700A8330BD200 0x  01  75A609            632437  A8330B  734120  D200       210 0x0175A609A8330BD200 0x  02  918060           6324369  A8330B  734120  D200       210  0x02918060A8330BD200 0x  03  AD05C503        63243693  A8330B  734120  D200       210  0x03AD05C503A8330BD200 0x  04  C638B225       632502470  A8330B  734120  D200       210  0x04C638B225A8330BD200 0x  05  BE37F67801    6324369342  A8330B  734120  D200       210  0x05BE37F67801A8330BD200 0x  06  6F2D9EB90E   63243693423  A8330B  734120  D200       210  0x066F2D9EB90EA8330BD200 0x  07  57C62D4093  632436934231  A8330B  734120  D200       210  0x0757C62D4093A8330BD200 Let us use the following color schema Red - Prefix Green - Time part Blue - Day part Purple - UTC offset What you can see is that the date part is equal in all cases, which makes sense since the precision doesn't affect the datepart. If you add 63244 seconds to midnight, you get 17:34:04, which is the correct UTC time. So what is stored is the UTC time and the local time can be found by adding "utc offset" minutes. And if you look at it, it makes perfect sense that each following value is 10 times greater when the precision is increased one step too. //Peter

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  • new vhost - main host AWstats

    - by vn
    Hi, I just began working at this new job and I have to config a new host for stats with awstats. I once used awstats on my own server, no biggie. Now, I'm on a multi-sites server with the acces_log files nicely splitted. I copied a awstats.conf file from one of the sites that already has (working) stats. I changed the LogFile and SiteDomain values as mentioned from http://awstats.sourceforge.net/docs/awstats_setup.html#BUILD_UPDATE, saved the conf and ran the commands perl awstats.pl -config=mysite -update and perl awstats.pl -config=mysite -output -staticlinks awstats.mysite.html (yes I changed it with my infos...) PROBLEM IS : whenever I try to access the html file or the dynamic page (with the config option on awstats.pl like my working site does), I get the stats of the MAIN site from access.log itself (and not access_log-mysite) from what it says at the top of the page and from the hostname on the left tab (stats for mysite.com)... what did I do wrong? There's no errors from what I see... Thanks a lot for any help

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  • Illumination and Shading for computer graphics class

    - by Sam I Am
    I am preparing for my test tomorrow and this is one of the practice questions. I solved it partially but I am confused with the rest. Here is the problem: Consider a gray world with no ambient and specular lighting ( only diffuse lighting). The screen coordinates of a triangle P1,P2,P3, are P1=(100,100), P2= (300,150), P3 = (200, 200). The gray values at P!,P2,P3 are 1/2, 3/4, and 1/4 respectively. The light is at infinity and its direction and gray color are (1,1,1) and 1.0 respectively. The coefficients of diffused reflection is 1/2. The normals of P1,P2,P3 are N1= (0,0,1), N2 = (1,0,0), and N3 = (0,1,0) respectively. Consider the coordinates of three points P1,P2,P3 to be 0. Do not normalize the normals. I have computed that the illumination at the 3 vertices P1,P2,P3 is (1/4,3/8,1/8). Also I computed that interpolation coefficients of a point P inside the triangle whose coordinates are (220, 160) are given by (1/5,2/5,2/5). Now I have 4 more questions regarding this problem. 1) The illumination at P using Gouraud Shading is: i) 1/2 The answer is 1/2, but I have no idea how to compute it.. 2) The interpolated normal at P is given by i) (2/5, 2/5,1/5) ii) (1/2, 1/4, 1/4) iii) (3/5, 1/5, 1/5) 3) The interpolated color at P is given by: i) 1/2 Again, I know the correct answer but no idea how to solve it 4) The illumination at P using Phong Shading is i) 1/4 ii) 9/40 iii) 1/2

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  • Share on: FB, Tweet, Digg, Linkedin, Delicious, My mother, ... it's just on fashion, or some real value?

    - by Marco Demaio
    Nowadays your site is not in fashion if you don't show at least a couple of share buttons like these: Is this just fashion, or do people actually get something good out of it? When I say "something good" I mostly mean something that you could measure, and not just the feeling that was good. Maybe I can better explain with an example: did you notice (in some way) that many people clicked on those links to share your page/s on those web 2.0 social sites? And in such a case on which social networks did you see they mostly share your pages? BTW I'm not talking about Google PR, i know all web 2.0 social sites use nofollow everywhere and even hidden links, so they are useless by themselves for PR. UPDATE: According to this video, Google's Alter Ego says that they now use in some way data from social sites in ranking. If this is true, it's obvious that the Share on button for FB, Tweet, etc are definitely of some values. But again my question is more about what you noticed in your real experience to be a direct benefit of adding those type of "Share On" links on your webisite? I.e. did you see more traffic coming in form FB, or some users who bought your products because of FB or Twitter? Or any other benefits? Thanks

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  • Tie stock quote value to cell in Excel 2011 Mac

    - by vedantchandra
    I've been working on a mock stock portfolio in Excel, and I've been looking for ways to automatically update the data, eg. stock price and P/E ratio. I have tried using a web query to MSN Money, but that just brings up the whole stock quote across multiple cells, I want data to be updated in individual cells only. The only web query solution I can think of is if someone hosted a website where each value in the stock quote was saved on a different HTML file. I could then WebQuery to that file for each cell requiring that value. However, no website offers this. So in essence, is there any tool on Excel 2011 Mac that will let me pull individual values from a stock quote and assign them to a single cell?

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  • Group Policy for IE Security Zones

    - by Doug Luxem
    We are currently using the following Group Policy to control the Internet Explorer security zones: User Configuration\Administrative Templates\Windows Components\Internet Explorer\Internet Control Panel\Security Page Then setting the Site to Zone Assignment List with the various values using the following chart: Value Setting ------------------------------ 0 My Computer 1 Local Intranet Zone 2 Trusted sites Zone 3 Internet Zone 4 Restricted Sites Zone This works well; however, users are then unable to edit (or especially add) to their zone settings. Is there a way to lock in our custom zone settings while still giving users the ability to add their own sites to the security zones? Yes, I do realize the slight security risk in opening this up.

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  • Can anyone explain step-by-step how the as3isolib depth-sorts isometric objects?

    - by Rob Evans
    The library manages to depth-sort correctly, even when using items of non-1x1 sizes. I took a look through the code but it's a big project to go through line by line! There are some questions about the process such as: How are the x, y, z values of each object defined? Are they the center points of the objects or something else? I noticed that the IBounds defines the bounds of the object. If you were to visualise a cuboid of 40, 40, 90 in size, where would each of the IBounds metrics be? I would like to know how as3isolib achieves this although I would also be happy with a generalised pseudo-code version. At present I have a system that works 90% of the time but in cases of objects that are along the same horizontal line, the depth is calculated as the same value. The depth calculation currently works like this: x = object horizontal center point y = object vertical center point originX and Y = the origin point relative to the object so if you want the origin to be the center, the value would be originX = 0.5, originY = 0.5. If you wanted the origin to be vertical center, horizontal far right of the object it would be originX = 1.0, originY = 0.5. The origin adjusts the position that the object is transformed from. AABB_width = The bounding box width. AABB_height = The bounding box height. depth = x + (AABB_width * originX) + y + (AABB_height * originY) - z; This generates the same depth for all objects along the same horizontal x.

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  • EJB Persist On Master Child Relationship

    - by deepak.siddappa(at)oracle.com
    Let us take scenario where in users wants to persist master child relationship. Here will have two tables dept, emp (using Scott Schema) which are having master child relation.Model Diagram: Here in the above model diagram, Dept is the Master table and Emp is child table and Dept is related to emp by one to n relationship. Lets assume we need to make new entries in emp table using EJB persist method. Create a Emp form manually dropping the fields, where deptno will be dropped as Single Selection -> ADF Select One Choice (which is a foreign key in emp table) from deptFindAll DC. Make sure to bind all field variables in backing bean.Employee Form:Once the Emp form created, If the persistEmp() method is used to commit the record this will persist all the Emp fields into emp table except deptno, because the deptno will be passed as a Object reference in persistEmp method  (Its foreign key reference). So directly deptno can't be passed to the persistEmp method instead deptno should be explicitly set to the emp object, then the persist will save the deptno to the emp table.Below solution is one way of work around to achieve this scenario -Create a method in sessionBean for adding emp records and expose this method in DataControl.     For Ex: Here in the below code 'em" is a EntityManager.            private EntityManager em - will be member variable in sessionEJBBeanpublic void addEmpRecord(String ename, String job, BigDecimal deptno) { Emp emp = new Emp(); emp.setEname(ename); emp.setJob(job); //setting the deptno explicitly Dept dept = new Dept(); dept.setDeptno(deptno); //passing the dept object emp.setDept(dept); //persist the emp object data to Emp table em.persist(emp); }From DataControl palette Drop addEmpRecord as Method ADF button, In Edit action binding window enter the parameter values which are binded in backing bean.     For Ex:     If the name deptno textfield is binded with "deptno" variable in backing bean, then El Expression Builder pass value as "#{backingbean.deptno.value}"Binding:

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  • App Pool doesn't respect memory limits

    - by lucuma
    I am dealing with a legacy .NET app that has a memory leak. In order to try and mitigate a run away memory situation, I've set the app pool memory limits from anywhere between 500KB to 500000KB (500MB) however the app pool doesn't seem to respect the settings as I can login and view the physical memory for it (5GB and above no matter what values). This app is killing the server and I can't seem to determine how to adjust the app pool. What settings do you recommend in order to ensure this app pool doesn't exceed around 500mb of memory. Here is an example, the app pool is using 3.5GB of

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  • Does the advanced format tool bundled by manufacturers actually do anything which mkntfs doesn't?

    - by neurolysis
    I recently bought a new drive (specifically, a 2TB Samsung Spinpoint) that says on the label that it supports advanced format, and that I should download the tool from their site. Unless I'm missing something, mkntfs has always had its maximum sector size at 4096b: -s, --sector-size BYTES Specify the size of sectors in bytes. Valid sector size values are 256, 512, 1024, 2048 and 4096 bytes per sector. If omitted, mkntfs attempts to determine the sector-size automatically and if that fails a default of 512 bytes per sector is used. Will this tool on Samsung's site do anything other than format the drive in the same way doing mkntfs -s 4K /dev/sdb1 would do? To be specific, I'm intending to use this drive on a machine that will primarily run Windows XP, but I'd rather boot into Linux/BSD and format the disk manually than have bloated software. I do want to have the new AF style sectors though -- that's essential. So if I did the command above, would it have exactly the same effect as using the advanced format tool?

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  • Sending an email with attachment from server side

    - by SaravananArumugam
    I have to create a word document in a specific format and send it as attachment to some email addresses. I have a preview screen for the report which on approval has to be send in email. This is an ASP.NET MVC 3 application. I am left with a few options here. I am creating the preview using html. I can convert this html into doc and send it, which would be a straight solution. But capturing the Response object's output is being a tough job. I thought of using Mail merge functionality of MS word, where I'll be filling the placeholders of the doc template. But the problem is conceptually, it doesn't appear to be mail merge. I have found someone suggesting to use RTF format and replace the placeholders with database values. Which is the right thing to do? What's the best solution here? Is there any other option than the three listed above?

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  • Netcat I/O enhancements

    - by user13277689
    When Netcat integrated into OpenSolaris it was already clear that there will be couple of enhancements needed. The biggest set of the changes made after Solaris 11 Express was released brings various I/O enhancements to netcat shipped with Solaris 11. Also, since Solaris 11, the netcat package is installed by default in all distribution forms (live CD, text install, ...). Now, let's take a look at the new functionality: /usr/bin/netcat alternative program name (symlink) -b bufsize I/O buffer size -E use exclusive bind for the listening socket -e program program to execute -F no network close upon EOF on stdin -i timeout extension of timeout specification -L timeout linger on close timeout -l -p port addr previously not allowed usage -m byte_count Quit after receiving byte_count bytes -N file pattern for UDP scanning -I bufsize size of input socket buffer -O bufsize size of output socket buffer -R redir_spec port redirection addr/port[/{tcp,udp}] syntax of redir_spec -Z bypass zone boundaries -q timeout timeout after EOF on stdin Obviously, the Swiss army knife of networking tools just got a bit thicker. While by themselves the options are pretty self explanatory, their combination together with other options, context of use or boundary values of option arguments make it possible to construct small but powerful tools. For example: the port redirector allows to convert TCP stream to UDP datagrams. the buffer size specification makes it possible to send one byte TCP segments or to produce IP fragments easily. the socket linger option can be used to produce TCP RST segments by setting the timeout to 0 execute option makes it possible to simulate TCP/UDP servers or clients with shell/python/Perl/whatever script etc. If you find some other helpful ways use please share via comments. Manual page nc(1) contains more details, along with examples on how to use some of these new options.

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  • Why unhandled exceptions are useful

    - by Simon Cooper
    It’s the bane of most programmers’ lives – an unhandled exception causes your application or webapp to crash, an ugly dialog gets displayed to the user, and they come complaining to you. Then, somehow, you need to figure out what went wrong. Hopefully, you’ve got a log file, or some other way of reporting unhandled exceptions (obligatory employer plug: SmartAssembly reports an application’s unhandled exceptions straight to you, along with the entire state of the stack and variables at that point). If not, you have to try and replicate it yourself, or do some psychic debugging to try and figure out what’s wrong. However, it’s good that the program crashed. Or, more precisely, it is correct behaviour. An unhandled exception in your application means that, somewhere in your code, there is an assumption that you made that is actually invalid. Coding assumptions Let me explain a bit more. Every method, every line of code you write, depends on implicit assumptions that you have made. Take this following simple method, that copies a collection to an array and includes an item if it isn’t in the collection already, using a supplied IEqualityComparer: public static T[] ToArrayWithItem( ICollection<T> coll, T obj, IEqualityComparer<T> comparer) { // check if the object is in collection already // using the supplied comparer foreach (var item in coll) { if (comparer.Equals(item, obj)) { // it's in the collection already // simply copy the collection to an array // and return it T[] array = new T[coll.Count]; coll.CopyTo(array, 0); return array; } } // not in the collection // copy coll to an array, and add obj to it // then return it T[] array = new T[coll.Count+1]; coll.CopyTo(array, 0); array[array.Length-1] = obj; return array; } What’s all the assumptions made by this fairly simple bit of code? coll is never null comparer is never null coll.CopyTo(array, 0) will copy all the items in the collection into the array, in the order defined for the collection, starting at the first item in the array. The enumerator for coll returns all the items in the collection, in the order defined for the collection comparer.Equals returns true if the items are equal (for whatever definition of ‘equal’ the comparer uses), false otherwise comparer.Equals, coll.CopyTo, and the coll enumerator will never throw an exception or hang for any possible input and any possible values of T coll will have less than 4 billion items in it (this is a built-in limit of the CLR) array won’t be more than 2GB, both on 32 and 64-bit systems, for any possible values of T (again, a limit of the CLR) There are no threads that will modify coll while this method is running and, more esoterically: The C# compiler will compile this code to IL according to the C# specification The CLR and JIT compiler will produce machine code to execute the IL on the user’s computer The computer will execute the machine code correctly That’s a lot of assumptions. Now, it could be that all these assumptions are valid for the situations this method is called. But if this does crash out with an exception, or crash later on, then that shows one of the assumptions has been invalidated somehow. An unhandled exception shows that your code is running in a situation which you did not anticipate, and there is something about how your code runs that you do not understand. Debugging the problem is the process of learning more about the new situation and how your code interacts with it. When you understand the problem, the solution is (usually) obvious. The solution may be a one-line fix, the rewrite of a method or class, or a large-scale refactoring of the codebase, but whatever it is, the fix for the crash will incorporate the new information you’ve gained about your own code, along with the modified assumptions. When code is running with an assumption or invariant it depended on broken, then the result is ‘undefined behaviour’. Anything can happen, up to and including formatting the entire disk or making the user’s computer sentient and start doing a good impression of Skynet. You might think that those can’t happen, but at Halting problem levels of generality, as soon as an assumption the code depended on is broken, the program can do anything. That is why it’s important to fail-fast and stop the program as soon as an invariant is broken, to minimise the damage that is done. What does this mean in practice? To start with, document and check your assumptions. As with most things, there is a level of judgement required. How you check and document your assumptions depends on how the code is used (that’s some more assumptions you’ve made), how likely it is a method will be passed invalid arguments or called in an invalid state, how likely it is the assumptions will be broken, how expensive it is to check the assumptions, and how bad things are likely to get if the assumptions are broken. Now, some assumptions you can assume unless proven otherwise. You can safely assume the C# compiler, CLR, and computer all run the method correctly, unless you have evidence of a compiler, CLR or processor bug. You can also assume that interface implementations work the way you expect them to; implementing an interface is more than simply declaring methods with certain signatures in your type. The behaviour of those methods, and how they work, is part of the interface contract as well. For example, for members of a public API, it is very important to document your assumptions and check your state before running the bulk of the method, throwing ArgumentException, ArgumentNullException, InvalidOperationException, or another exception type as appropriate if the input or state is wrong. For internal and private methods, it is less important. If a private method expects collection items in a certain order, then you don’t necessarily need to explicitly check it in code, but you can add comments or documentation specifying what state you expect the collection to be in at a certain point. That way, anyone debugging your code can immediately see what’s wrong if this does ever become an issue. You can also use DEBUG preprocessor blocks and Debug.Assert to document and check your assumptions without incurring a performance hit in release builds. On my coding soapbox… A few pet peeves of mine around assumptions. Firstly, catch-all try blocks: try { ... } catch { } A catch-all hides exceptions generated by broken assumptions, and lets the program carry on in an unknown state. Later, an exception is likely to be generated due to further broken assumptions due to the unknown state, causing difficulties when debugging as the catch-all has hidden the original problem. It’s much better to let the program crash straight away, so you know where the problem is. You should only use a catch-all if you are sure that any exception generated in the try block is safe to ignore. That’s a pretty big ask! Secondly, using as when you should be casting. Doing this: (obj as IFoo).Method(); or this: IFoo foo = obj as IFoo; ... foo.Method(); when you should be doing this: ((IFoo)obj).Method(); or this: IFoo foo = (IFoo)obj; ... foo.Method(); There’s an assumption here that obj will always implement IFoo. If it doesn’t, then by using as instead of a cast you’ve turned an obvious InvalidCastException at the point of the cast that will probably tell you what type obj actually is, into a non-obvious NullReferenceException at some later point that gives you no information at all. If you believe obj is always an IFoo, then say so in code! Let it fail-fast if not, then it’s far easier to figure out what’s wrong. Thirdly, document your assumptions. If an algorithm depends on a non-trivial relationship between several objects or variables, then say so. A single-line comment will do. Don’t leave it up to whoever’s debugging your code after you to figure it out. Conclusion It’s better to crash out and fail-fast when an assumption is broken. If it doesn’t, then there’s likely to be further crashes along the way that hide the original problem. Or, even worse, your program will be running in an undefined state, where anything can happen. Unhandled exceptions aren’t good per-se, but they give you some very useful information about your code that you didn’t know before. And that can only be a good thing.

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  • Fuzzing for Security

    - by Sylvain Duloutre
    Yesterday, I attended an internal workshop about ethical hacking. Hacking skills like fuzzing can be used to quantitatively assess and measure security threats in software.  Fuzzing is a software testing technique used to discover coding errors and security loopholes in software, operating systems or networks by injecting massive amounts of random data, called fuzz, to the system in an attempt to make it crash. If the program contains a vulnerability that can leads to an exception, crash or server error (in the case of web apps), it can be determined that a vulnerability has been discovered.A fuzzer is a program that generates and injects random (and in general faulty) input to an application. Its main purpose is to make things easier and automated.There are typically two methods for producing fuzz data that is sent to a target, Generation or Mutation. Generational fuzzers are capable of building the data being sent based on a data model provided by the fuzzer creator. Sometimes this is simple and dumb as sending random bytes, swapping bytes or much smarter by knowing good values and combining them in interesting ways.Mutation on the other hand starts out with a known good "template" which is then modified. However, nothing that is not present in the "template" or "seed" will be produced.Generally fuzzers are good at finding buffer overflow, DoS, SQL Injection, Format String bugs etc. They do a poor job at finding vulnerabilites related to information disclosure, encryption flaws and any other vulnerability that does not cause the program to crash.  Fuzzing is simple and offers a high benefit-to-cost ratio but does not replace other proven testing techniques.What is your computer doing over the week-end ?

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  • Efficient Trie implementation for unicode strings

    - by U Mad
    I have been looking for an efficient String trie implementation. Mostly I have found code like this: Referential implementation in Java (per wikipedia) I dislike these implementations for mostly two reasons: They support only 256 ASCII characters. I need to cover things like cyrillic. They are extremely memory inefficient. Each node contains an array of 256 references, which is 4096 bytes on a 64 bit machine in Java. Each of these nodes can have up to 256 subnodes with 4096 bytes of references each. So a full Trie for every ASCII 2 character string would require a bit over 1MB. Three character strings? 256MB just for arrays in nodes. And so on. Of course I don't intend to have all of 16 million three character strings in my Trie, so a lot of space is just wasted. Most of these arrays are just null references as their capacity far exceeds the actual number of inserted keys. And if I add unicode, the arrays get even larger (char has 64k values instead of 256 in Java). Is there any hope of making an efficient trie for strings? I have considered a couple of improvements over these types of implementations: Instead of using array of references, I could use an array of primitive integer type, which indexes into an array of references to nodes whose size is close to the number of actual nodes. I could break strings into 4 bit parts which would allow for node arrays of size 16 at the cost of a deeper tree.

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  • MySQL on Windows - how do I set the wait_timeout for connections using named pipes?

    - by gustafc
    I use a MySQL database running on a Windows box, and for performance reasons I'm connecting to it using named pipes. The (Java) application using the database (through Hibernate) can let the connection lie idle for quite a long time, which causes the connection to fail with the following message: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: The last packet successfully received from the server was 33 558 297 milliseconds ago. The last packet sent successfully to the server was 33 558 297 milliseconds ago. is longer than the server configured value of 'wait_timeout'. You should consider either expiring and/or testing connection validity before use in your application, increasing the server configured values for client timeouts, or using the Connector/J connection property 'autoReconnect=true' to avoid this problem. autoReconnect unfortunately has no effect (and neither does autoReconnectForPools), but the wait_timeout docs state that wait_timeout only applies "to TCP/IP and Unix socket file connections, not to connections made via named pipes, or shared memory". How can I change the wait_timeout for named pipes?

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  • What is the difference between sar -B verses sar -W

    - by Mark
    I am trying to understand why my system is running slowly. I found the sar command, but wanted to know the difference between sar -B and sar -W I read the man page, and I understand that -B gives me the paging statistics and -W gives me the swapping statistics. What I would like to understand is the following: What is the correlation between the two sets of statistics. When should I be concerned about -B and when about -W? ie, what values from each command should I be concerned with? Which statistic is more closely related to system performance Thanks

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