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  • How to Check Authenticity of an AJAX Request

    - by Alex Reisner
    I am designing a web site in which users solve puzzles as quickly as they can. JavaScript is used to time each puzzle, and the number of milliseconds is sent to the server via AJAX when the puzzle is completed. How can I ensure that the time received by the server was not forged by the user? I don't think a session-based authenticity token (the kind used for forms in Rails) is sufficient because I need to authenticate the source of a value, not just the legitimacy of the request. Is there a way to cryptographically sign the request? I can't think of anything that couldn't be duplicated by a hacker. Is any JavaScript, by its exposed, client-side nature, subject to tampering? Am I going to have to use something that gets compiled, like Flash? (Yikes.) Or is there some way to hide a secret key? Or something else I haven't thought of? Update: To clarify, I don't want to penalize people with slow network connections (and network speed should be considered inconsistent), so the timing needs to be 100% client-side (the timer starts only when we know the user can see the puzzle). Also, there is money involved so no amount of "trusting the user" is acceptable.

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  • NHibernate with string primary key and relationships

    - by John_
    I've have just been stumped with this problem for an hour and I annoyingly found the problem eventually. THE CIRCUMSTANCES I have a table which users a string as a primary key, this table has various many to one and many to many relationships all off this primary key. When searching for multiple items from the table all relationships were brought back. However whenever I tried to get the object by the primary key (string) it was not bringing back any relationships, they were always set to 0. THE PARTIAL SOLUTION So I looked into my logs to see what the SQL was doing and that was returning the correct results. So I tried various things in all sorts of random ways and eventually worked out it was. The case of the string being passed into the get method was not EXACTLY the same case as it was in the database, so when it tried to match up the relationship items with the main entity it was finding nothing (Or at least NHIbernate wasn't because as I stated above the SQL was actually returning the correct results) THE REAL SOLUTION Has anyone else come across this? If so how do you tell NHibernate to ignore case when matching SQL results to the entity? It is silly because it worked perfectly well before now all of a sudden it has started to pay attention to the case of the string.

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  • Cryptography for P2P card game

    - by zephyr
    I'm considering writing a computer adaptation of a semi-popular card game. I'd like to make it function without a central server, and I'm trying to come up with a scheme that will make cheating impossible without having to trust the client. The basic problem as I see it is that each player has a several piles of cards (draw deck, current hand and discard deck). It must be impossible for either player to alter the composition of these piles except when allowed by the game rules (ie drawing or discarding cards), nor should players be able to know what is in their or their oppponent's piles. I feel like there should be some way to use something like public-key cryptography to accomplish this, but I keep finding holes in my schemes. Can anyone suggest a protocol or point me to some resources on this topic? [Edit] Ok, so I've been thinking about this a bit more, and here's an idea I've come up with. If you can poke any holes in it please let me know. At shuffle time, a player has a stack of cards whose value is known to them. They take these values, concatenate a random salt to each, then hash them. They record the salts, and pass the hashes to their opponent. The opponent concatenates a salt of their own, hashes again, then shuffles the hashes and passes the deck back to the original player. I believe at this point, the deck has been randomized and neither player can have any knowledge of the values. However, when a card is drawn, the opponent can reveal their salt, allowing the first player to determine what the original value is, and when the card is played the player reveals their own salt, allowing the opponent to verify the card value.

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  • MYSQL how to sum rows with same key, then delete the duplicate rows

    - by Bhante-S
    What I have: key data 1      22 1       5 2       6 3       1 3      -3 What I want: key data 1      27 2       6 3      -2 I don’t mind doing this with two or more queries, esp. if they are simple--makes for easier maintenance. Also the tables are fairly small (<2,000 records). The ‘key’ field is indexed and allows duplicates. Muchas Gracias

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  • Apache to read from /home/user/public_html on CentOS 5.7

    - by C.S.Putra
    this is my first experience using CentOS 5.7 / Linux as my web server OS and I have just finished installing Apache. Then I created a new account using WHM. The account is now created and the domain name can be accessed. I have put the web files under /home/user/public_html/ but when I access the domain assigned for that user which I assigned when creating new account in WHM, it doesn't read the files. In /usr/local/apache/conf/httpd.conf : <VirtualHost 175.103.48.66:80> ServerName domain.com ServerAlias www.domain.com DocumentRoot /home/user/public_html ServerAdmin [email protected] User veevou # Needed for Cpanel::ApacheConf <IfModule mod_suphp.c> suPHP_UserGroup group1 group1 </IfModule> <IfModule !mod_disable_suexec.c> SuexecUserGroup group1 group1 </IfModule> CustomLog /usr/local/apache/domlogs/domain.com-bytes_log "%{%s}t %I .\n%{%s}t %O ." CustomLog /usr/local/apache/domlogs/domain.com combined ScriptAlias /cgi-bin/ /home/user/public_html/cgi-bin/ </VirtualHost> Instead of reading from /home/user/public_html/ apache will read the /var/ww/html/ folder. How to set the apache so that when user access www.domain.com, they will access the files under /home/user/public_html/ ? Please advice. Thanks

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  • rsync to EC2 using ssh -i

    - by isomorphismes
    I'm able to ssh -i mykey.pem to EC2. I'm able to scp -i mykey.pem to EC2. But when I try to rsync -avz -e "ssh -i mykey.pem" I get this error: Warning: Identity file mykey.pem not accessible: No such file or directory. Permission denied (publickey). rsync: connection unexpectedly closed (0 bytes received so far) [sender] rsync error: unexplained error (code 255) at io.c(605) [sender=3.0.9] Any suggestions what I've done wrong?

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  • How to find out what is installed on a server

    - by masfenix
    Hi, im an undergrad student and we have special access to a server. The server is a unix server (dont know the OS or anything.. is there a way to find out? ). we also get a website associated with the server. There is a public_html folder. I uploaded with a test file with phpinfo() but the server didnt parse it (yes i had the right extension) . So im guessing PHP isnt installed. is there a way to see what "common" languages ARE installed?

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  • really weird DNS problem in Ubuntu {after one month, seems like ISP problem}

    - by OmniWired
    Hello everyone. I been having this random dns problem, in Ubuntu 10.04 and in 10.10 it started about 2 weeks ago after (I believe) an update. Basically when I go to a website randomly I get that the website I'm visiting is not available ("Oops! Google Chrome could not connect to ..." & "This webpage is not available."). I tested with Chromium "7.0.515.0 (58587)" and Firefox minefield (4.0ish) and 3.6.9. I did these 4 things already: /etc/default/grub GRUB_CMDLINE_LINUX="ipv6.disable=1" and this: /etc/sysctl.conf net.ipv6.conf.all.disable_ipv6 = 1 net.ipv6.conf.default.disable_ipv6 = 1 net.ipv6.conf.lo.disable_ipv6 = 1 *disabling Chromium DNS pre-fetching *using Google and OpenDNS servers as well as ISP DNS servers. But didn't improve, also no other computers in my network have the same problem. All computer wired to the same router. I'm a software engineer that run out of ideas, please help me. Thanks in advance. UPDATE: some programs (synaptic / firefox update/ vuze(azureus)) say connection refused for the error. Most of the time a second try will fix the "refusal". UPDATE2: I found out with Wireshark, that everytime I have this problem i've got this 192.168.0.10 8.8.8.8 ICMP Destination unreachable (Port unreachable) Confirmed an ISP error. ISP;Speedy Location: Argentina, Buenos Aires (capital Federal) Area.

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  • Xen private networking between multiple hosts

    - by Joe
    I have two physical hosts running Xen 3.2, sharing storage via iSCSI. On these two hosts are a number of domUs and I'd like to network them in multiple private networks so they can only contact other domUs on their private network. My understanding of the xen documentation suggests it's possible to do this within one dom0 (ie create virtual networks between domUs), but I've found nothing explaining how this can be implemented across multiple dom0s on different hosts. The only thing that jumps to mind is manually creating iptable rules to route data to the other host, but this seems to lack elegance and could quickly grow cumbersome. Any suggestions? All advice is much appreciated!

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  • How can I open a shared sub calendar in Outlook 2010?

    - by Matt Love
    There is a team in my office that has a shared calendar (the team calendar is set up as a user in Active Directory/Exchange, so treat the team as a user). The team also has 3 sub-calendars for the different team members. Other people in the office need to be able to access this team's calendar. They can go to Open Calendar in Outlook and see the main calendar, but they cannot see the sub-calendars. The sub-calendars all have the Default user permissions set to Reviewer. If you go to File → Account Settings → Change [logged in Exchange account] → More Settings → Advanced and add the team's mailbox, it does show the calendars in Outlook, but it comes up under My Calendars instead of Shared Calendars. We need to be able to go to Open Calendar and open the calendar and open all the sub-calendars this way. How is this possible?

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  • LWJGL SlickUtil Texture Binding

    - by Matthew Dockerty
    I am making a 3D game using LWJGL and I have a texture class with static variables so that I only need to load textures once, even if I need to use them more than once. I am using Slick Util for this. When I bind a texture it works fine, but then when I try to render something else after I have rendered the model with the texture, the texture is still being bound. How do I unbind the texture and set the rendermode to the one that was in use before any textures were bound? Some of my code is below. The problem I am having is the player texture is being used in the box drawn around the player after it the model has been rendered. Model.java public class Model { public List<Vector3f> vertices = new ArrayList<Vector3f>(); public List<Vector3f> normals = new ArrayList<Vector3f>(); public ArrayList<Vector2f> textureCoords = new ArrayList<Vector2f>(); public List<Face> faces = new ArrayList<Face>(); public static Model TREE; public static Model PLAYER; public static void loadModels() { try { TREE = OBJLoader.loadModel(new File("assets/model/tree_pine_0.obj")); PLAYER = OBJLoader.loadModel(new File("assets/model/player.obj")); } catch (Exception e) { e.printStackTrace(); } } public void render(Vector3f position, Vector3f scale, Vector3f rotation, Texture texture, float shinyness) { glPushMatrix(); { texture.bind(); glColor3f(1, 1, 1); glTranslatef(position.x, position.y, position.z); glScalef(scale.x, scale.y, scale.z); glRotatef(rotation.x, 1, 0, 0); glRotatef(rotation.y, 0, 1, 0); glRotatef(rotation.z, 0, 0, 1); glMaterialf(GL_FRONT, GL_SHININESS, shinyness); glBegin(GL_TRIANGLES); { for (Face face : faces) { Vector2f t1 = textureCoords.get((int) face.textureCoords.x - 1); glTexCoord2f(t1.x, t1.y); Vector3f n1 = normals.get((int) face.normal.x - 1); glNormal3f(n1.x, n1.y, n1.z); Vector3f v1 = vertices.get((int) face.vertex.x - 1); glVertex3f(v1.x, v1.y, v1.z); Vector2f t2 = textureCoords.get((int) face.textureCoords.y - 1); glTexCoord2f(t2.x, t2.y); Vector3f n2 = normals.get((int) face.normal.y - 1); glNormal3f(n2.x, n2.y, n2.z); Vector3f v2 = vertices.get((int) face.vertex.y - 1); glVertex3f(v2.x, v2.y, v2.z); Vector2f t3 = textureCoords.get((int) face.textureCoords.z - 1); glTexCoord2f(t3.x, t3.y); Vector3f n3 = normals.get((int) face.normal.z - 1); glNormal3f(n3.x, n3.y, n3.z); Vector3f v3 = vertices.get((int) face.vertex.z - 1); glVertex3f(v3.x, v3.y, v3.z); } texture.release(); } glEnd(); } glPopMatrix(); } } Textures.java public class Textures { public static Texture FLOOR; public static Texture PLAYER; public static Texture SKYBOX_TOP; public static Texture SKYBOX_BOTTOM; public static Texture SKYBOX_FRONT; public static Texture SKYBOX_BACK; public static Texture SKYBOX_LEFT; public static Texture SKYBOX_RIGHT; public static void loadTextures() { try { FLOOR = TextureLoader.getTexture("PNG", new FileInputStream(new File("assets/model/floor.png"))); FLOOR.setTextureFilter(GL11.GL_NEAREST); PLAYER = TextureLoader.getTexture("PNG", new FileInputStream(new File("assets/model/tree_pine_0.png"))); PLAYER.setTextureFilter(GL11.GL_NEAREST); SKYBOX_TOP = TextureLoader.getTexture("PNG", new FileInputStream(new File("assets/textures/skybox_top.png"))); SKYBOX_TOP.setTextureFilter(GL11.GL_NEAREST); SKYBOX_BOTTOM = TextureLoader.getTexture("PNG", new FileInputStream(new File("assets/textures/skybox_bottom.png"))); SKYBOX_BOTTOM.setTextureFilter(GL11.GL_NEAREST); SKYBOX_FRONT = TextureLoader.getTexture("PNG", new FileInputStream(new File("assets/textures/skybox_front.png"))); SKYBOX_FRONT.setTextureFilter(GL11.GL_NEAREST); SKYBOX_BACK = TextureLoader.getTexture("PNG", new FileInputStream(new File("assets/textures/skybox_back.png"))); SKYBOX_BACK.setTextureFilter(GL11.GL_NEAREST); SKYBOX_LEFT = TextureLoader.getTexture("PNG", new FileInputStream(new File("assets/textures/skybox_left.png"))); SKYBOX_LEFT.setTextureFilter(GL11.GL_NEAREST); SKYBOX_RIGHT = TextureLoader.getTexture("PNG", new FileInputStream(new File("assets/textures/skybox_right.png"))); SKYBOX_RIGHT.setTextureFilter(GL11.GL_NEAREST); } catch (Exception e) { e.printStackTrace(); } } } Player.java public class Player { private Vector3f position; private float yaw; private float moveSpeed; public Player(float x, float y, float z, float yaw, float moveSpeed) { this.position = new Vector3f(x, y, z); this.yaw = yaw; this.moveSpeed = moveSpeed; } public void update() { if (Keyboard.isKeyDown(Keyboard.KEY_W)) walkForward(moveSpeed); if (Keyboard.isKeyDown(Keyboard.KEY_S)) walkBackwards(moveSpeed); if (Keyboard.isKeyDown(Keyboard.KEY_A)) strafeLeft(moveSpeed); if (Keyboard.isKeyDown(Keyboard.KEY_D)) strafeRight(moveSpeed); if (Mouse.isButtonDown(0)) yaw += Mouse.getDX(); LowPolyRPG.getInstance().getCamera().setPosition(-position.x, -position.y, -position.z); LowPolyRPG.getInstance().getCamera().setYaw(yaw); } public void walkForward(float distance) { position.setX(position.getX() + distance * (float) Math.sin(Math.toRadians(yaw))); position.setZ(position.getZ() - distance * (float) Math.cos(Math.toRadians(yaw))); } public void walkBackwards(float distance) { position.setX(position.getX() - distance * (float) Math.sin(Math.toRadians(yaw))); position.setZ(position.getZ() + distance * (float) Math.cos(Math.toRadians(yaw))); } public void strafeLeft(float distance) { position.setX(position.getX() + distance * (float) Math.sin(Math.toRadians(yaw - 90))); position.setZ(position.getZ() - distance * (float) Math.cos(Math.toRadians(yaw - 90))); } public void strafeRight(float distance) { position.setX(position.getX() + distance * (float) Math.sin(Math.toRadians(yaw + 90))); position.setZ(position.getZ() - distance * (float) Math.cos(Math.toRadians(yaw + 90))); } public void render() { Model.PLAYER.render(new Vector3f(position.x, position.y + 12, position.z), new Vector3f(3, 3, 3), new Vector3f(0, -yaw + 90, 0), Textures.PLAYER, 128); GL11.glPushMatrix(); GL11.glTranslatef(position.getX(), position.getY(), position.getZ()); GL11.glRotatef(-yaw, 0, 1, 0); GL11.glScalef(5.8f, 21, 2.2f); GL11.glDisable(GL11.GL_LIGHTING); GL11.glLineWidth(3); GL11.glBegin(GL11.GL_LINE_STRIP); GL11.glColor3f(1, 1, 1); glVertex3f(1f, 0f, -1f); glVertex3f(-1f, 0f, -1f); glVertex3f(-1f, 1f, -1f); glVertex3f(1f, 1f, -1f); glVertex3f(-1f, 0f, 1f); glVertex3f(1f, 0f, 1f); glVertex3f(1f, 1f, 1f); glVertex3f(-1f, 1f, 1f); glVertex3f(1f, 1f, -1f); glVertex3f(-1f, 1f, -1f); glVertex3f(-1f, 1f, 1f); glVertex3f(1f, 1f, 1f); glVertex3f(1f, 0f, 1f); glVertex3f(-1f, 0f, 1f); glVertex3f(-1f, 0f, -1f); glVertex3f(1f, 0f, -1f); glVertex3f(1f, 0f, 1f); glVertex3f(1f, 0f, -1f); glVertex3f(1f, 1f, -1f); glVertex3f(1f, 1f, 1f); glVertex3f(-1f, 0f, -1f); glVertex3f(-1f, 0f, 1f); glVertex3f(-1f, 1f, 1f); glVertex3f(-1f, 1f, -1f); GL11.glEnd(); GL11.glEnable(GL11.GL_LIGHTING); GL11.glPopMatrix(); } public Vector3f getPosition() { return new Vector3f(-position.x, -position.y, -position.z); } public float getX() { return position.getX(); } public float getY() { return position.getY(); } public float getZ() { return position.getZ(); } public void setPosition(Vector3f position) { this.position = position; } public void setPosition(float x, float y, float z) { this.position.setX(x); this.position.setY(y); this.position.setZ(z); } } Thanks for the help.

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  • Are XML Comments Necessary Documentation?

    - by Bob Horn
    I used to be a fan of requiring XML comments for documentation. I've since changed my mind for two main reasons: Like good code, methods should be self-explanatory. In practice, most XML comments are useless noise that provide no additional value. Many times we simply use GhostDoc to generate generic comments, and this is what I mean by useless noise: /// <summary> /// Gets or sets the unit of measure. /// </summary> /// <value> /// The unit of measure. /// </value> public string UnitOfMeasure { get; set; } To me, that's obvious. Having said that, if there were special instructions to include, then we should absolutely use XML comments. I like this excerpt from this article: Sometimes, you will need to write comments. But, it should be the exception not the rule. Comments should only be used when they are expressing something that cannot be expressed in code. If you want to write elegant code, strive to eliminate comments and instead write self-documenting code. Am I wrong to think we should only be using XML comments when the code isn't enough to explain itself on its own? I believe this is a good example where XML comments make pretty code look ugly. It takes a class like this... public class RawMaterialLabel : EntityBase { public long Id { get; set; } public string ManufacturerId { get; set; } public string PartNumber { get; set; } public string Quantity { get; set; } public string UnitOfMeasure { get; set; } public string LotNumber { get; set; } public string SublotNumber { get; set; } public int LabelSerialNumber { get; set; } public string PurchaseOrderNumber { get; set; } public string PurchaseOrderLineNumber { get; set; } public DateTime ManufacturingDate { get; set; } public string LastModifiedUser { get; set; } public DateTime LastModifiedTime { get; set; } public Binary VersionNumber { get; set; } public ICollection<LotEquipmentScan> LotEquipmentScans { get; private set; } } ... And turns it into this: /// <summary> /// Container for properties of a raw material label /// </summary> public class RawMaterialLabel : EntityBase { /// <summary> /// Gets or sets the id. /// </summary> /// <value> /// The id. /// </value> public long Id { get; set; } /// <summary> /// Gets or sets the manufacturer id. /// </summary> /// <value> /// The manufacturer id. /// </value> public string ManufacturerId { get; set; } /// <summary> /// Gets or sets the part number. /// </summary> /// <value> /// The part number. /// </value> public string PartNumber { get; set; } /// <summary> /// Gets or sets the quantity. /// </summary> /// <value> /// The quantity. /// </value> public string Quantity { get; set; } /// <summary> /// Gets or sets the unit of measure. /// </summary> /// <value> /// The unit of measure. /// </value> public string UnitOfMeasure { get; set; } /// <summary> /// Gets or sets the lot number. /// </summary> /// <value> /// The lot number. /// </value> public string LotNumber { get; set; } /// <summary> /// Gets or sets the sublot number. /// </summary> /// <value> /// The sublot number. /// </value> public string SublotNumber { get; set; } /// <summary> /// Gets or sets the label serial number. /// </summary> /// <value> /// The label serial number. /// </value> public int LabelSerialNumber { get; set; } /// <summary> /// Gets or sets the purchase order number. /// </summary> /// <value> /// The purchase order number. /// </value> public string PurchaseOrderNumber { get; set; } /// <summary> /// Gets or sets the purchase order line number. /// </summary> /// <value> /// The purchase order line number. /// </value> public string PurchaseOrderLineNumber { get; set; } /// <summary> /// Gets or sets the manufacturing date. /// </summary> /// <value> /// The manufacturing date. /// </value> public DateTime ManufacturingDate { get; set; } /// <summary> /// Gets or sets the last modified user. /// </summary> /// <value> /// The last modified user. /// </value> public string LastModifiedUser { get; set; } /// <summary> /// Gets or sets the last modified time. /// </summary> /// <value> /// The last modified time. /// </value> public DateTime LastModifiedTime { get; set; } /// <summary> /// Gets or sets the version number. /// </summary> /// <value> /// The version number. /// </value> public Binary VersionNumber { get; set; } /// <summary> /// Gets the lot equipment scans. /// </summary> /// <value> /// The lot equipment scans. /// </value> public ICollection<LotEquipmentScan> LotEquipmentScans { get; private set; } }

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  • Soft keyboard "del" key fails in EditText on Gallery widget

    - by droidful
    Hi, I am developing an application in Eclipse build ID 20090920-1017 using android SDK 2.2 and testing on a Google Nexus One. For the purposes of the tests below I am using the IME "Android keyboard" on a non-rooted phone. I have an EditText widget which exhibits some very strange behavior. I can type text, and then press the "del" key to delete that text; but after I enter a 'space' character, the "del" key will no longer remove characters before that space character. An example speaks a thousand words, so consider the following two incredibly simple applications... Example 1: An EditText in a LinearLayout widget: package com.example.linear.edit; import android.app.Activity; import android.os.Bundle; import android.view.ViewGroup.LayoutParams; import android.widget.EditText; import android.widget.Gallery; import android.widget.LinearLayout; public class LinearEdit extends Activity { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); LinearLayout layout = new LinearLayout(getApplicationContext()); layout.setLayoutParams(new Gallery.LayoutParams(Gallery.LayoutParams.MATCH_PARENT, Gallery.LayoutParams.MATCH_PARENT)); EditText edit = new EditText(getApplicationContext()); layout.addView(edit, new LinearLayout.LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT)); setContentView(layout); } } Run the above application, enter text "edit example", then press the "del" key several times until the entire sentence is deleted. Everything Works fine. Now consider example 2: An EditText in a Gallery widget: package com.example.gallery.edit; import android.app.Activity; import android.os.Bundle; import android.view.View; import android.view.ViewGroup; import android.view.ViewGroup.LayoutParams; import android.widget.ArrayAdapter; import android.widget.EditText; import android.widget.Gallery; import android.widget.LinearLayout; public class GalleryEdit extends Activity { private final String[] galleryData = {"string1", "string2", "string3"}; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); Gallery gallery = new Gallery(getApplicationContext()); gallery.setAdapter(new ArrayAdapter(getApplicationContext(), android.R.layout.simple_list_item_1, galleryData) { @Override public View getView(int position, View convertView, ViewGroup parent) { LinearLayout layout = new LinearLayout(getApplicationContext()); layout.setLayoutParams(new Gallery.LayoutParams(Gallery.LayoutParams.MATCH_PARENT, Gallery.LayoutParams.MATCH_PARENT)); EditText edit = new EditText(getApplicationContext()); layout.addView(edit, new LinearLayout.LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT)); return layout; } }); setContentView(gallery); } } Run the above application, enter text "edit example", then press the "del" key several times. If you are getting the same problem as me then you will find that you can't deleted past the 'space' character. All is not well. If anyone could shed some light on this issue I would be most appreciative. Regards

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  • Managing a file-based public maven repository

    - by Roland Ewald
    I am looking for an easy way to manage a public file-based Maven repository. While we are using the open-source version of Artifactory internally, we now want to put a file-based repository of our published artifacts (and their dependencies) on a separate machine that is publicly available. There are several ways how to do this, but none of them seems ideal: Use Maven Dependency plugin: if it is configured correctly and executed with the goal dependency:copy-dependencies for the release-module of our project, it creates a local repository structure that is fine, but this structure does not contain the meta-data.xml files, nor the hash-sums. Use Artifactory to export repo: AFAIK Artifactory only allows to export a repository as a whole. This would include the non-published modules from our project (which would then need to be deleted manually). Also, all dependencies are sitting in another repository, so this needs to be done twice, and many dependencies are not even required by a published artifact (only by artifacts that are still for internal use only). Nevertheless, this method would also include the meta-data.xml files and the hash-sums for all files. To set up an initial version of the repository, I used a mixture of both methods: I first created the Maven repository for all required dependencies via dependency:copy-dependencies and then wrote a script to cherry-pick the meta-data.xml files (etc.) from Artifactory. This is terribly cumbersome, isn't there a better way to solve this? Maybe there is another Maven 3 - plugin that I am unaware of, or some other command-line tool that does the job? I basically just need a simple way to create a Maven repository that contains all artifacts a given artifact depends on (and no more), and also contains all meta-data expected in a remote repository. Any ideas?

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  • C#/.NET Fundamentals: Choosing the Right Collection Class

    - by James Michael Hare
    The .NET Base Class Library (BCL) has a wide array of collection classes at your disposal which make it easy to manage collections of objects. While it's great to have so many classes available, it can be daunting to choose the right collection to use for any given situation. As hard as it may be, choosing the right collection can be absolutely key to the performance and maintainability of your application! This post will look at breaking down any confusion between each collection and the situations in which they excel. We will be spending most of our time looking at the System.Collections.Generic namespace, which is the recommended set of collections. The Generic Collections: System.Collections.Generic namespace The generic collections were introduced in .NET 2.0 in the System.Collections.Generic namespace. This is the main body of collections you should tend to focus on first, as they will tend to suit 99% of your needs right up front. It is important to note that the generic collections are unsynchronized. This decision was made for performance reasons because depending on how you are using the collections its completely possible that synchronization may not be required or may be needed on a higher level than simple method-level synchronization. Furthermore, concurrent read access (all writes done at beginning and never again) is always safe, but for concurrent mixed access you should either synchronize the collection or use one of the concurrent collections. So let's look at each of the collections in turn and its various pros and cons, at the end we'll summarize with a table to help make it easier to compare and contrast the different collections. The Associative Collection Classes Associative collections store a value in the collection by providing a key that is used to add/remove/lookup the item. Hence, the container associates the value with the key. These collections are most useful when you need to lookup/manipulate a collection using a key value. For example, if you wanted to look up an order in a collection of orders by an order id, you might have an associative collection where they key is the order id and the value is the order. The Dictionary<TKey,TVale> is probably the most used associative container class. The Dictionary<TKey,TValue> is the fastest class for associative lookups/inserts/deletes because it uses a hash table under the covers. Because the keys are hashed, the key type should correctly implement GetHashCode() and Equals() appropriately or you should provide an external IEqualityComparer to the dictionary on construction. The insert/delete/lookup time of items in the dictionary is amortized constant time - O(1) - which means no matter how big the dictionary gets, the time it takes to find something remains relatively constant. This is highly desirable for high-speed lookups. The only downside is that the dictionary, by nature of using a hash table, is unordered, so you cannot easily traverse the items in a Dictionary in order. The SortedDictionary<TKey,TValue> is similar to the Dictionary<TKey,TValue> in usage but very different in implementation. The SortedDictionary<TKey,TValye> uses a binary tree under the covers to maintain the items in order by the key. As a consequence of sorting, the type used for the key must correctly implement IComparable<TKey> so that the keys can be correctly sorted. The sorted dictionary trades a little bit of lookup time for the ability to maintain the items in order, thus insert/delete/lookup times in a sorted dictionary are logarithmic - O(log n). Generally speaking, with logarithmic time, you can double the size of the collection and it only has to perform one extra comparison to find the item. Use the SortedDictionary<TKey,TValue> when you want fast lookups but also want to be able to maintain the collection in order by the key. The SortedList<TKey,TValue> is the other ordered associative container class in the generic containers. Once again SortedList<TKey,TValue>, like SortedDictionary<TKey,TValue>, uses a key to sort key-value pairs. Unlike SortedDictionary, however, items in a SortedList are stored as an ordered array of items. This means that insertions and deletions are linear - O(n) - because deleting or adding an item may involve shifting all items up or down in the list. Lookup time, however is O(log n) because the SortedList can use a binary search to find any item in the list by its key. So why would you ever want to do this? Well, the answer is that if you are going to load the SortedList up-front, the insertions will be slower, but because array indexing is faster than following object links, lookups are marginally faster than a SortedDictionary. Once again I'd use this in situations where you want fast lookups and want to maintain the collection in order by the key, and where insertions and deletions are rare. The Non-Associative Containers The other container classes are non-associative. They don't use keys to manipulate the collection but rely on the object itself being stored or some other means (such as index) to manipulate the collection. The List<T> is a basic contiguous storage container. Some people may call this a vector or dynamic array. Essentially it is an array of items that grow once its current capacity is exceeded. Because the items are stored contiguously as an array, you can access items in the List<T> by index very quickly. However inserting and removing in the beginning or middle of the List<T> are very costly because you must shift all the items up or down as you delete or insert respectively. However, adding and removing at the end of a List<T> is an amortized constant operation - O(1). Typically List<T> is the standard go-to collection when you don't have any other constraints, and typically we favor a List<T> even over arrays unless we are sure the size will remain absolutely fixed. The LinkedList<T> is a basic implementation of a doubly-linked list. This means that you can add or remove items in the middle of a linked list very quickly (because there's no items to move up or down in contiguous memory), but you also lose the ability to index items by position quickly. Most of the time we tend to favor List<T> over LinkedList<T> unless you are doing a lot of adding and removing from the collection, in which case a LinkedList<T> may make more sense. The HashSet<T> is an unordered collection of unique items. This means that the collection cannot have duplicates and no order is maintained. Logically, this is very similar to having a Dictionary<TKey,TValue> where the TKey and TValue both refer to the same object. This collection is very useful for maintaining a collection of items you wish to check membership against. For example, if you receive an order for a given vendor code, you may want to check to make sure the vendor code belongs to the set of vendor codes you handle. In these cases a HashSet<T> is useful for super-quick lookups where order is not important. Once again, like in Dictionary, the type T should have a valid implementation of GetHashCode() and Equals(), or you should provide an appropriate IEqualityComparer<T> to the HashSet<T> on construction. The SortedSet<T> is to HashSet<T> what the SortedDictionary<TKey,TValue> is to Dictionary<TKey,TValue>. That is, the SortedSet<T> is a binary tree where the key and value are the same object. This once again means that adding/removing/lookups are logarithmic - O(log n) - but you gain the ability to iterate over the items in order. For this collection to be effective, type T must implement IComparable<T> or you need to supply an external IComparer<T>. Finally, the Stack<T> and Queue<T> are two very specific collections that allow you to handle a sequential collection of objects in very specific ways. The Stack<T> is a last-in-first-out (LIFO) container where items are added and removed from the top of the stack. Typically this is useful in situations where you want to stack actions and then be able to undo those actions in reverse order as needed. The Queue<T> on the other hand is a first-in-first-out container which adds items at the end of the queue and removes items from the front. This is useful for situations where you need to process items in the order in which they came, such as a print spooler or waiting lines. So that's the basic collections. Let's summarize what we've learned in a quick reference table.  Collection Ordered? Contiguous Storage? Direct Access? Lookup Efficiency Manipulate Efficiency Notes Dictionary No Yes Via Key Key: O(1) O(1) Best for high performance lookups. SortedDictionary Yes No Via Key Key: O(log n) O(log n) Compromise of Dictionary speed and ordering, uses binary search tree. SortedList Yes Yes Via Key Key: O(log n) O(n) Very similar to SortedDictionary, except tree is implemented in an array, so has faster lookup on preloaded data, but slower loads. List No Yes Via Index Index: O(1) Value: O(n) O(n) Best for smaller lists where direct access required and no ordering. LinkedList No No No Value: O(n) O(1) Best for lists where inserting/deleting in middle is common and no direct access required. HashSet No Yes Via Key Key: O(1) O(1) Unique unordered collection, like a Dictionary except key and value are same object. SortedSet Yes No Via Key Key: O(log n) O(log n) Unique ordered collection, like SortedDictionary except key and value are same object. Stack No Yes Only Top Top: O(1) O(1)* Essentially same as List<T> except only process as LIFO Queue No Yes Only Front Front: O(1) O(1) Essentially same as List<T> except only process as FIFO   The Original Collections: System.Collections namespace The original collection classes are largely considered deprecated by developers and by Microsoft itself. In fact they indicate that for the most part you should always favor the generic or concurrent collections, and only use the original collections when you are dealing with legacy .NET code. Because these collections are out of vogue, let's just briefly mention the original collection and their generic equivalents: ArrayList A dynamic, contiguous collection of objects. Favor the generic collection List<T> instead. Hashtable Associative, unordered collection of key-value pairs of objects. Favor the generic collection Dictionary<TKey,TValue> instead. Queue First-in-first-out (FIFO) collection of objects. Favor the generic collection Queue<T> instead. SortedList Associative, ordered collection of key-value pairs of objects. Favor the generic collection SortedList<T> instead. Stack Last-in-first-out (LIFO) collection of objects. Favor the generic collection Stack<T> instead. In general, the older collections are non-type-safe and in some cases less performant than their generic counterparts. Once again, the only reason you should fall back on these older collections is for backward compatibility with legacy code and libraries only. The Concurrent Collections: System.Collections.Concurrent namespace The concurrent collections are new as of .NET 4.0 and are included in the System.Collections.Concurrent namespace. These collections are optimized for use in situations where multi-threaded read and write access of a collection is desired. The concurrent queue, stack, and dictionary work much as you'd expect. The bag and blocking collection are more unique. Below is the summary of each with a link to a blog post I did on each of them. ConcurrentQueue Thread-safe version of a queue (FIFO). For more information see: C#/.NET Little Wonders: The ConcurrentStack and ConcurrentQueue ConcurrentStack Thread-safe version of a stack (LIFO). For more information see: C#/.NET Little Wonders: The ConcurrentStack and ConcurrentQueue ConcurrentBag Thread-safe unordered collection of objects. Optimized for situations where a thread may be bother reader and writer. For more information see: C#/.NET Little Wonders: The ConcurrentBag and BlockingCollection ConcurrentDictionary Thread-safe version of a dictionary. Optimized for multiple readers (allows multiple readers under same lock). For more information see C#/.NET Little Wonders: The ConcurrentDictionary BlockingCollection Wrapper collection that implement producers & consumers paradigm. Readers can block until items are available to read. Writers can block until space is available to write (if bounded). For more information see C#/.NET Little Wonders: The ConcurrentBag and BlockingCollection Summary The .NET BCL has lots of collections built in to help you store and manipulate collections of data. Understanding how these collections work and knowing in which situations each container is best is one of the key skills necessary to build more performant code. Choosing the wrong collection for the job can make your code much slower or even harder to maintain if you choose one that doesn’t perform as well or otherwise doesn’t exactly fit the situation. Remember to avoid the original collections and stick with the generic collections.  If you need concurrent access, you can use the generic collections if the data is read-only, or consider the concurrent collections for mixed-access if you are running on .NET 4.0 or higher.   Tweet Technorati Tags: C#,.NET,Collecitons,Generic,Concurrent,Dictionary,List,Stack,Queue,SortedList,SortedDictionary,HashSet,SortedSet

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  • Best Design Pattern for Coupling User Interface Components and Data Structures

    - by szahn
    I have a windows desktop application with a tree view. Due to lack of a sound data-binding solution for a tree view, I've implemented my own layer of abstraction on it to bind nodes to my own data structure. The requirements are as follows: Populate a tree view with nodes that resemble fields in a data structure. When a node is clicked, display the appropriate control to modify the value of that property in the instance of the data structure. The tree view is populated with instances of custom TreeNode classes that inherit from TreeNode. The responsibility of each custom TreeNode class is to (1) format the node text to represent the name and value of the associated field in my data structure, (2) return the control used to modify the property value, (3) get the value of the field in the control (3) set the field's value from the control. My custom TreeNode implementation has a property called "Control" which retrieves the proper custom control in the form of the base control. The control instance is stored in the custom node and instantiated upon first retrieval. So each, custom node has an associated custom control which extends a base abstract control class. Example TreeNode implementation: //The Tree Node Base Class public abstract class TreeViewNodeBase : TreeNode { public abstract CustomControlBase Control { get; } public TreeViewNodeBase(ExtractionField field) { UpdateControl(field); } public virtual void UpdateControl(ExtractionField field) { Control.UpdateControl(field); UpdateCaption(FormatValueForCaption()); } public virtual void SaveChanges(ExtractionField field) { Control.SaveChanges(field); UpdateCaption(FormatValueForCaption()); } public virtual string FormatValueForCaption() { return Control.FormatValueForCaption(); } public virtual void UpdateCaption(string newValue) { this.Text = Caption; this.LongText = newValue; } } //The tree node implementation class public class ExtractionTypeNode : TreeViewNodeBase { private CustomDropDownControl control; public override CustomControlBase Control { get { if (control == null) { control = new CustomDropDownControl(); control.label1.Text = Caption; control.comboBox1.Items.Clear(); control.comboBox1.Items.AddRange( Enum.GetNames( typeof(ExtractionField.ExtractionType))); } return control; } } public ExtractionTypeNode(ExtractionField field) : base(field) { } } //The custom control base class public abstract class CustomControlBase : UserControl { public abstract void UpdateControl(ExtractionField field); public abstract void SaveChanges(ExtractionField field); public abstract string FormatValueForCaption(); } //The custom control generic implementation (view) public partial class CustomDropDownControl : CustomControlBase { public CustomDropDownControl() { InitializeComponent(); } public override void UpdateControl(ExtractionField field) { //Nothing to do here } public override void SaveChanges(ExtractionField field) { //Nothing to do here } public override string FormatValueForCaption() { //Nothing to do here return string.Empty; } } //The custom control specific implementation public class FieldExtractionTypeControl : CustomDropDownControl { public override void UpdateControl(ExtractionField field) { comboBox1.SelectedIndex = comboBox1.FindStringExact(field.Extraction.ToString()); } public override void SaveChanges(ExtractionField field) { field.Extraction = (ExtractionField.ExtractionType) Enum.Parse(typeof(ExtractionField.ExtractionType), comboBox1.SelectedItem.ToString()); } public override string FormatValueForCaption() { return string.Empty; } The problem is that I have "generic" controls which inherit from CustomControlBase. These are just "views" with no logic. Then I have specific controls that inherit from the generic controls. I don't have any functions or business logic in the generic controls because the specific controls should govern how data is associated with the data structure. What is the best design pattern for this?

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  • Writing a JMS Publisher without "public static void main"

    - by The Elite Gentleman
    Hi guys, Every example I've seen on the web, e.g. http://www.codeproject.com/KB/docview/jms_to_jms_bridge_activem.aspx, creates a publisher and subscriber with a public static void main method. I don't think that'll work for my web application. I'm learning JMS and I've setup Apache ActiveMQ to run on JBoss 5 and Tomcat 6 (with no glitches). I'm writing a messaging JMS service that needs to send email asynchronously. I've already written a JMS subscriber that receives the message (the class inherits MessageListener). My question is simple: How do I write a publisher that will so that my web applications can call it? Does it have to be published somewhere? My thought is to create a publisher with a no-attribute constructor (in there) and get the MessageQueue Factory, etc. from the JNDI pool (in the constructor). Is my idea correct? How do I subscribe my subscriber to the Queue Receiver? (So far, the subscriber has no constructor, and if I write a constructor, do I always subscribe myself to the Queue receiver?) Thanks for your help, sorry if my terminology is not up to scratch, there are too many java terminologies that I get lost sometimes (maybe a java GPS will do! :-) ) PS Is there a tutorial out there that explains how to write a "better" (better can mean anything, but in my case it's all about performance in high demand requests) JMS Publisher and Subscriber that I can run on Application Server such as JBoss or Glassfish? Don't forget that the JMS application will needs a "guarantee" uptime as many applications will use this.

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  • MySQL: updating a row and deleting the original in case it becomes a duplicate

    - by Silvio Donnini
    I have a simple table made up of two columns: col_A and col_B. The primary key is defined over both. I need to update some rows and assign to col_A values that may generate duplicates, for example: UPDATE `table` SET `col_A` = 66 WHERE `col_B` = 70 This statement sometimes yields a duplicate key error. I don't want to simply ignore the error with UPDATE IGNORE, because then the rows that generate the error would remain unchanged. Instead, I want them to be deleted when they would conflict with another row after they have been updated I'd like to write something like: UPDATE `table` SET `col_A` = 66 WHERE `col_B` = 70 ON DUPLICATE KEY REPLACE which unfortunately isn't legal in SQL, so I need help finding another way around. Also, I'm using PHP and could consider a hybrid solution (i.e. part query part php code), but keep in mind that I have to perform this updating operation many millions of times. thanks for your attention, Silvio Reminder: UPDATE's syntax has problems with joins with the same table that is being updated

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  • How do API Keys and Secret Keys work?

    - by viatropos
    I am just starting to think about how api keys and secret keys work. Just 2 days ago I signed up for Amazon S3 and installed the S3Fox Plugin. They asked me for both my Access Key and Secret Access Key, both of which require me to login to access. So I'm wondering, if they're asking me for my secret key, they must be storing it somewhere right? Isn't that basically the same thing as asking me for my credit card numbers or password and storing that in their own database? How are secret keys and api keys supposed to work? How secret do they need to be? Are these applications that use the secret keys storing it somehow? Thanks for the insight.

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  • EPL (Eclipse Public Licence) for commercial usage

    - by code-gijoe
    Hi, I'm developing an application which requires a third party framework which is under an Eclipse Public Licence (EPL). The application is a server-side commercial application which will be running on my servers. The EPL software is distributed as binaries (jar files). I'm only using the packages and am not making any contribution, i.e. not making any changes to the source. Under EPL I believe I'm not a "Contributor" nor am I making a "Contribution". But if I want to make my software available to be installed at some offsite server I'm having trouble with REQUIREMENTS of EPL: b.iv - "states that source code for the Program is available from such Contributor, and informs licensees how to obtain it in a reasonable manner on or through a medium customarily used for software exchange". Does this mean that if I where to modify the source code of the 3rd party framework for my own purposes I would need to distribute all of my source code? EPL is supposed to be commercially friendly but it doesn't seem that way to me. Thank you.

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  • Interesting AS3 hash situation. Is it really using strict equality as the documentation says?

    - by Triynko
    AS3 Code: import flash.utils.Dictionary; var num1:Number = Number.NaN; var num2:Number = Math.sqrt(-1); var dic:Dictionary = new Dictionary( true ); trace(num1); //NaN trace(num2); //NaN dic[num1] = "A"; trace( num1 == num2 ); //false trace( num1 === num2 ); //false trace( dic[num1] ); //A trace( dic[num2] ); //A Concerning the key comparison method... "The Dictionary class lets you create a dynamic collection of properties, which uses strict equality (===) for key comparison. When an object is used as a key, the object's identity is used to look up the object, and not the value returned from calling toString() on it." If Dictionary uses strict equality, as the documentation states, then how is it that num1 === num2 is false, and yet dic[num1] resolves to the same hash slot as dic[num2]?

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  • XML Decryption Bug (referencing issue)

    - by OrangePekoe
    Hi, Needing some explanation of what exactly the decryption is doing, in addition to some help on solving the problem. Currently, when a portion of XML is encrypted, and then decrypted, the DOM appears to work correctly. We can see the element is encrypted and then see it return back once it is decrypted. Our problem lies when a user tries to change data in that same element after decryption has occurred. When a user changes some settings, data in the XML should change. However, if the user attempts to change an XML element that has been decrypted the changes are not reflected in the DOM. We have a reference pointer to the XML element that is used to bind the element to an object. If you encrypt the node and then decrypt it, the reference pointer now points to a valid orphaned XML element that is no longer part of the DOM. After decryption, there will be 2 copies of the XML element. One in the DOM as expected (though will not reflect new changes), and one orphaned element in memory that is still referenced by our pointer. The orphaned element is valid (reflects new changes). We can see that this orphaned element is owned by the DOM, but when we try to return its parent, it returns null. The question is: Where did this orphaned xml element come from? And how can we get it to correctly append (replace old data) to the DOM? The code resembles: public static void Decrypt(XmlDocument Doc, SymmetricAlgorithm Alg) { if (Doc == null) throw new ArgumentNullException("Doc"); if (Alg == null) throw new ArgumentNullException("Alg"); XmlElement encryptedElement = Doc.GetElementsByTagName("EncryptedData")[0] as XmlElement; if (encryptedElement == null) { throw new XmlException("The EncryptedData element was not found."); } EncryptedData edElement = new EncryptedData(); edElement.LoadXml(encryptedElement); EncryptedXml exml = new EncryptedXml(); byte[] rgbOutput = exml.DecryptData(edElement, Alg); exml.ReplaceData(encryptedElement, rgbOutput); }

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  • A public struct inside a class

    - by Koning Baard
    I am new to C++, and let's say I have two classes: Creature and Human: /* creature.h */ class Creature { private: public: struct emotion { /* All emotions are percentages */ char joy; char trust; char fear; char surprise; char sadness; char disgust; char anger; char anticipation; char love; }; }; /* human.h */ class Human : Creature { }; And I have this in my main function in main.cpp: Human foo; My question is: how can I set foo's emotions? I tried this: foo->emotion.fear = 5; But GCC gives me this compile error: error: base operand of '-' has non-pointer type 'Human' This: foo.emotion.fear = 5; Gives: error: 'struct Creature::emotion' is inaccessible error: within this context error: invalid use of 'struct Creature::emotion' Can anyone help me? Thanks P.S. No I did not forget the #includes

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  • Alternative to "assign to a function call" in a python

    - by Pythonista's Apprentice
    I'm trying to solve this newbie puzzle: I've created this function: def bucket_loop(htable, key): bucket = hashtable_get_bucket(htable, key) for entry in bucket: if entry[0] == key: return entry[1] else: return None And I have to call it in two other functions (bellow) in the following way: to change the value of the element entry[1] or to append to this list (entry) a new element. But I can't do that calling the function bucket_loop the way I did because "you can't assign to function call" (assigning to a function call is illegal in Python). What is the alternative (most similar to the code I wrote) to do this (bucket_loop(htable, key) = value and hashtable_get_bucket(htable, key).append([key, value]))? def hashtable_update(htable, key, value): if bucket_loop(htable, key) != None: bucket_loop(htable, key) = value else: hashtable_get_bucket(htable, key).append([key, value]) def hashtable_lookup(htable, key): return bucket_loop(htable, key) Thanks, in advance, for any help! This is the rest of the code to make this script works: def make_hashtable(size): table = [] for unused in range(0, size): table.append([]) return table def hash_string(s, size): h = 0 for c in s: h = h + ord(c) return h % size def hashtable_get_bucket(htable, key): return htable[hash_string(key, len(htable))] Similar question (but didn't help me): Python: Cannot Assign Function Call

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