blackjack

A simple blackjack server with client.

npm install blackjack
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Blackjack

Running

First start the server:

  • cd to the root of this project where the package.json is
  • Run: ./bin/server.sh

Then, start a client:

  • cd to the root of this project where the package.json is
  • Run: ./bin/client.sh

Requirements

  • Server must have an REST API for playing Blackjack (done)
  • Must support: way to receive 2 starting cards & dealer's initial card (done)
  • Must support player actions:
    • login (done)
    • logout (done)
    • view the tables (done)
    • join a table (done)
    • leave a table (done)
    • bet (done)
    • hit (done)
    • stand (done)
    • double down (not implemented)
    • surrender (not implemented)
    • split (not implemented)
  • After a player's final action in a hand, they should learn the outcome (done)
  • Use a typical dealer strategy of standing on 17 or greater (done)
    • Dealer will draw on soft 17 (done)
    • Dealer will draw if under hard 17 and player has a better hand (done)
  • Support multiple players (done)
    • Works, but multiple players at the same table is not tested
    • The client needs to poll to detect when hand is over (not implemented)
  • Support multiple concurrent blackjack games (done)
    • Works, limit 1 player per table
  • Use an 8-deck shoe with a cut-point 75% into the shoe (done)
    • After each hand, if the deck is past the cut point, the old shoe is discarded and a new shoe is created (done)
  • If a player is not at a table, they are in the "lobby" (done)
    • From the lobby, players can join tables, view tables and quit (done)
  • When players leave a table or quit and have a bet on a hand in-progress, they should lose the bet (done)

Stretch goals

  • Character-based Node.js client (done)
  • Test framework with multiple concurrent clients that do set actions and random actions (done)
  • Discovery between client and server using UDP broadcast (not implemented)
  • Chat functionality for players (not implemented)
  • Player persistance for score (winnings) (not implemented)

Comments

I was able to complete this amount of work by leveraging existing modules. Mocha, async, prompt and request all saved an immense amount of time.

Additionally, many of the modules were written previously by myself:

  • config-js - config module. Support for regions and auto-load when file changes
  • fuzelog - logger fusing log.js with log4js's layouts and colors, supporting console and file logging
  • is2 - type checking library where each function returns either true or false
  • json-rest-api - lightweight REST API that receives and responds to JSON HTTP requests, supports all verbs
  • sprintf.js - almost complete implementation of the printf and sprintf
  • tcp-port-used - check if a TCP port is already bound

Reflections

I'm happy with how it came out. The try/catch on the end-points enabled liberal use of "assert" and "have" worry-free since everything happens as a result of a REST call and there is no asynchronous code outside of the networking, due to no persistence (so domains were not needed).

There are things I would change, though:

  • More unit tests.
  • More behaviors for the user tests.
  • The mersenne-twister module is entirely JavaScript and is too slow.
    • You can see how the creation of the 8-deck shoe takes over 100ms (too long) by running the unit tests
  • The representation of the cards as self-describing objects in the decks made the client simplier, but for a production system, I would use indicies referring to the ordered deck to reduce the memory footprint.
  • json-rest-api, while faster than express.js (due to simplicity), needs a concept of middleware and I was surprised I did not add support for query strings. If I was serious about this, I'd either switch to express or put work into json-rest-api.
  • In a production system there would be async calls for persistance, and with that, I would need to add support for domains.
  • config-js really needs to use NODE_ENV to have support for development, staging and production configuration files.

REST API

All responses have:

  • a JSON body
  • a "cmd" property with the name of the command
  • a "success" boolean property that is either "true" or "false"
  • if "success" if false, there is an "error" property with a string message

If the request is a POST, then the request body is JSON.

The REST API commands follow.

login

Allows players to login to the game, where they can view tables and join a game.

Request Format

  • Method: POST
  • URI path: /login

JSON Request Body

{ "playername": "Edmond" }
  • name - the name you want to play as.

JSON Response

{
  "success": true,
  "cmd": "login",
  "playerId": 1,
  "tables": {
    "1": {
      "id": 1,
      "players": { },
      "numPlayers": 0,
      "state": "waiting for players"
    }
  }
}
  • id - player id, a positive integer, to be re-used for all subsequent requests

viewTables

Allows players to see the tables and who is at each table.

Request Format

  • Method: GET
  • URI path: /viewTables

JSON Response

{
  "success": true,
  "cmd": "viewTables",
  "tables": {
    "1": {
      "id": 1,
      "players": { },
      "numPlayers": 0,
      "state": "waiting for players"
    }
  }
}
  • tables - an arary of all the tables where the key is the table id and the data describes the table
    • players - array of the players at the table
    • state - game state for the table

joinTable

Allows players to join a table and play the next hand dealt. Because a hand may be progress at the time, clients have to check back on an interval to get their hand. This means a keep-alive connection should be used, however at scale, this would not be ideal, as you'd want to keep the connections to a minimum to scale.

Request Format

  • Method: POST
  • URI path: /joinTable

JSON Request Body

{ "playerid": 3 }
  • id - the player id received on login

JSON Response

{
  "success": true,
  "cmd": "joinTable",
  "table": {
    "id": 1,
    "players": {
      "1": {
        "name": "Edmond",
        "bet": -1,
        "hand": [ ],
        "done": false,
        "busted": false
      }
    },
    "numPlayers": 1,
    "state": "betting"
  }
}
  • interval - time to check for next hand of dealt cards in milliseconds
  • balance - player's winnings (or losses)

leaveTable

Allows the player to leave the table. If a hand is in play, the player will lose the bet to the house. The player returns to the lobby and then receices information describing all the tables.

Request Format

  • Method: POST
  • URI path: /leaveTable

JSON Request Body

{ "playerid": 3 }
  • id - the player id received on login

JSON Response

{
  "success": true,
  "cmd": "leaveTable",
  "tables": {
    "1": {
      "id": 1,
      "players": { },
      "numPlayers": 0,
      "state": "waiting for players"
    }
  }
}
  • interval - time to check for next hand of dealt cards in milliseconds
  • balance - player's winnings (or losses)

logout

Allows players to drop out of the game.

Request Format

  • Method: POST
  • URI path: /logout

JSON Request Body

{ "playerId": 3 }
  • id - player id, a positive integer, to be re-used for all subsequent requests

JSON Response

{ "success": true, "cmd": "logout", "credits": 1023 }

bet

Indicates players are in on the next hand and the amount they are betting.

Request Format

  • Method: POST
  • URI path: /bet

JSON Request Body

{ "playerId": 3, "bet": 10 }
  • id - player id received when joining the game
  • bet - amount of currency to bet on the next hand

JSON Response

{
  "success": true,
  "cmd": "bet",
  "bet": 10,
  "hand": [
    { "suit": "spades", "rank": "Queen", "value": 10 },
    { "suit": "spades", "rank": "2", "value": 2 }
  ],
  "table": {
    "id": 1,
    "players": {
      "1": {
        "name": "Edmond",
        "bet": 10,
        "hand": [
          { "suit": "spades", "rank": "Queen", "value": 10 },
          { "suit": "spades", "rank": "2", "value": 2 }
        ],
        "done": false,
        "busted": false
      }
    },
    "dealer": {
      "name": "Dealer",
      "hand": [
        { "suit": "hearts", "rank": "4", "value": 4 },
        "face down card"
      ]
    },
    "numPlayers": 1,
    "state": "dealing"
  }
}
  • balance - player's currency balance minus the bet they just placed
  • hand - cards in the player&#39s hand. By index position in a deck. If player has split, there will also be a "hand2"
  • total - total value of the hand. If there is an ace present the value will an array containing all possible values
  • h1Over21 - True, if the player value is over 21 on hand1. If there is a hand2, from a split, there will also be a h2Over21
  • done - True if the player's interest in the hand is concluded

hit

Informs the dealer to add another card to the player's hand. If the player exceeds 21, the player loses the hand.

Request Format

  • Method: POST
  • URI path: /hit

JSON Request Body

{ "playerId": 3, hand: 3 }
  • id - player id given when the player joins the game
  • hand - hand, upon which, to hit:
    • 1 - for default, if not specified, 1 is assumed
    • 2 - stand on the second hand only
    • 3 - stand on both hands

JSON Reponse

{
  "success": true,
  "cmd": "hit",
  "hand": [
    { "suit": "spades", "rank": "Queen", "value": 10 },
    { "suit": "spades", "rank": "2", "value": 2 },
    { "suit": "clubs", "rank": "2", "value": 2 }
  ],
  "table": {
    "id": 1,
    "players": {
      "1": {
        "name": "Edmond",
        "bet": 10,
        "hand": [
          { "suit": "spades", "rank": "Queen", "value": 10 },
          { "suit": "spades", "rank": "2", "value": 2 },
          { "suit": "clubs", "rank": "2", "value": 2 }
        ],
        "done": false,
        "busted": false
      }
    },
    "dealer": {
      "name": "Dealer",
      "hand": [
        { "suit": "hearts", "rank": "4", "value": 4 },
        "face down card"
      ]
    },
    "numPlayers": 1,
    "state": "dealing"
  }
}
  • balance - player's currency balance minus the bet they just placed.
  • hand - cards in the player&#39s hand. By index position in a deck. If player has split, there will also be a "hand2"
  • total - total value of the hand. If there is an ace present the value will an array containing all possible values
  • h1Over21 - True, if the player value is over 21 on hand1. If there is a hand2, there will also be a h2_over21
  • done - True if the player's interest in the hand is concluded

stand

Informs the dealer, you want to stand on your hand, no more cards are to be dealt. Once all players are concluded, the dealer will handle their hand and the results are known.

Request Format

  • Method: POST
  • URI path: /stand

JSON Request Body

{ "playerId": 3, "hand": 1 }
  • id - The player id given when the player joins the game
  • hand - Optional. If not present, 1 is the default. The hand upon which, to stand:
    • 1 - for default, if not specified, 1 is assumed
    • 2 - stand on the second hand only
    • 3 - stand on both hands

JSON Reponse:

{
   "success": true,
   "cmd": "stand",
   "hand": [

   ],
   "table": {
      "id": 1,
      "players": {
         "1": {
            "name": "Edmond",
            "bet": -1,
            "hand": [
            ],
            "done": true,
            "busted": false
         }
      },
      "dealer": {
         "name": "Dealer",
         "hand": [ { "suit": "hearts", "rank": "4", "value": 4 },
            { "suit": "clubs", "rank": "4", "value": 4 },
            { "suit": "clubs", "rank": "Jack", "value": 10 }
         ]
      },
      "numPlayers": 1,
      "state": "betting"
   }
}
  • balance - the player's currency balance minus the bet they just placed
  • hand - cards in the player&#39s hand. By index position in a deck. If player has split, there will also be a "hand2"
  • total - total value of the hand. If there is an ace present the value t will be an array containing all possible values
  • h1Over21 - True, if the player value is over 21 on hand1. If there is a hand2, there will also be a h2_over21
  • done - True if the player's interest in the hand is concluded

doubledown

The player may increase the initial bet by up to 100% in exchange for committing to stand after receiving exactly one more card. The additional bet is placed in the betting box next to the original bet. Some games do not permit the player to increase the bet by amounts other than 100%. Non-controlling players may double their wager or decline to do so, but they are bound by the controlling player's decision to take only one card.

Signal: Place additional chips beside the original bet outside the betting box, and point with one finger.

Request Format

  • Method: POST
  • URI path: /doubledown

JSON Request Body

{ "playerId": 3 }

JSON Reponse

  • balance - player's currency balance minus the bet they just placed
  • bet - player&#39s current bet
  • hand - cards in the player&#39s hand. By index position in a deck. If player has split, there will also be a "hand2"
  • total - The total value of the hand. If there is an ace present the value will an array containing all possible values
  • h1Over21 - True, if the player value is over 21 on hand1. If there is a hand2, there will also be a h2_over21
  • done - True if the player's interest in the hand is concluded

surrender

Only available as first decision of a hand: Some games offer the option to "surrender", usually in hole-card games and directly after the dealer has checked for blackjack When the player surrenders, the house takes half the player's bet and returns the other half to the player; this terminates the player's interest in the hand. The request to surrender is made verbally, there being no standard hand signal.

Request Format

  • Method: POST
  • URI path: /surrender

JSON Request Body

{ "playerId": 3 }

JSON Reponse

  • balance - the player's currency balance minus the bet they just placed
  • bet - the player&#39s current bet
  • hand - The cards in the player&#39s hand. By index position in a deck. If player has split, there will also be a "hand2"
  • total - The total value of the hand. If there is an ace present the value will an array containing all possible values
  • h1Over21 - True, if the player value is over 21 on hand1. If there is a hand2, there will also be a h2_over21
  • done - True if the player's interest in the hand is concluded

split

Only available as the first decision of a hand: If the first two cards have the same value, the player can split them into two hands, by moving a second bet equal to the first into an area outside the betting box. The dealer separates the two cards and draws an additional card on each, placing one bet with each hand. The player then plays out the two separate hands in turn, with some restrictions. Occasionally, in the case of ten-valued cards, some casinos allow splitting only when the cards have the identical ranks; for instance, a hand of 10-10 may be split, but not one of 10-king. However, usually all 10-value cards are treated the same. Doubling and further splitting of post-split hands may be restricted, and blackjacks after a split are counted as non-blackjack 21 when comparing against the dealer's hand. Hitting split aces is usually not allowed. Non-controlling players may follow the controlling player by putting down an additional bet or decline to do so, instead associating their existing wager with one of the two post-split hands. In that case they must choose which hand to play behind before the second cards are drawn. Some casinos do not give non-controlling players this option, and require that the wager of a player not electing to split remains with the first of the two post-split hands.

Signal: Place additional chips next to the original bet outside the betting box; point with two fingers spread into a V formation.

Request Format

  • Method: POST
  • URI path: /split

Request Body

{ "playerId": 3 }

JSON Reponse

  • balance - player's currency balance minus the bet they just placed
  • bet - player&#39s current bet which is now an array, 1 bet for each hand
  • hand - cards in the player&#39s hand. By index position in a deck. If player has split, there will also be a "hand2"
  • total - total value of the hand. If there is an ace present the value will an array containing all possible values
  • h1Over21 - True, if the player value is over 21 on hand1. If there is a hand2, there will also be a h2_over21
  • done - True if the player's interest in the hand is concluded

debugCredits

Allows developers to set the amount of credits a player has to any value.

Request Format

  • Method: POST`
  • URI path: /debugCredits

Request Body

{ "playerId": 3, "credits": 999 }

debugGetPlayer

Allows developers to get the player information. It uses a POST because I was too pressed for time to expand json-rest-api to handle query strings.

Request Format

  • Method: POST`
  • URI path: /debugGetPlayer

Request Body

{ "playerId": 3 }
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