Play: Add option to write NDJSON "replay file".

board/replay.go

@@ -0,0 +1,55 @@
+package board
+
+import (
+	"os"
+	"encoding/json"
+	"fmt"
+	"io"
+
+	log "github.com/spf13/jwalterweatherman"
+)
+
+type ReplayFile struct {
+	handle io.WriteCloser
+}
+
+func NewReplayFile(path string) *ReplayFile {
+	fd, err := os.OpenFile(path, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0644)
+	if err != nil {
+		log.ERROR.Fatalf("Failed to open replay file: %w", err)
+	}
+
+	return &ReplayFile{
+		handle: fd,
+	}
+}
+
+func (replay *ReplayFile) WriteGameInfo(game Game) {
+	// TODO(schoon): Provide a clear delimiter between game info and frames.
+	// Additionally, we probably want to ensure they're ordered. Take in the
+	// `Game` in `NewReplayFile` (much like `NewBoardServer` and write
+	// game info as front matter?
+	jsonStr, err := json.Marshal(struct {
+		Game Game
+	}{game})
+	if err != nil {
+		log.ERROR.Printf("Unable to serialize event for replay file: %v", err)
+	}
+
+	_, err = io.WriteString(replay.handle, fmt.Sprintf("%s\n", jsonStr))
+	if err != nil {
+		log.WARN.Printf("Unable to write to replay file: %v", err)
+	}
+}
+
+func (replay *ReplayFile) WriteEvent(event GameEvent) {
+	jsonStr, err := json.Marshal(event)
+	if err != nil {
+		log.ERROR.Printf("Unable to serialize event for replay file: %v", err)
+	}
+
+	_, err = io.WriteString(replay.handle, fmt.Sprintf("%s\n", jsonStr))
+	if err != nil {
+		log.WARN.Printf("Unable to write to replay file: %v", err)
+	}
+}

cli/commands/play.go

@@ -59,6 +59,7 @@ type GameState struct {
 	Seed                int64
 	TurnDelay           int
 	OutputPath          string
+	ReplayFilePath      string
 	ViewInBrowser       bool
 	BoardURL            string
 	FoodSpawnChance     int
@@ -74,6 +75,7 @@ type GameState struct {
 	ruleset     rules.Ruleset
 	gameMap     maps.GameMap
 	outputFile  io.WriteCloser
+	replayFile  *board.ReplayFile
 	idGenerator func(int) string
 }
 
@@ -108,6 +110,7 @@ func NewPlayCommand() *cobra.Command {
 	playCmd.Flags().IntVarP(&gameState.TurnDelay, "delay", "d", 0, "Turn Delay in Milliseconds")
 	playCmd.Flags().IntVarP(&gameState.TurnDuration, "duration", "D", 0, "Minimum Turn Duration in Milliseconds")
 	playCmd.Flags().StringVarP(&gameState.OutputPath, "output", "o", "", "File path to output game state to. Existing files will be overwritten")
+	playCmd.Flags().StringVar(&gameState.ReplayFilePath, "replay", "", "File path to write game frames to for replaying later. Existing files will be overwritten")
 	playCmd.Flags().BoolVar(&gameState.ViewInBrowser, "browser", false, "View the game in the browser using the Battlesnake game board")
 	playCmd.Flags().StringVar(&gameState.BoardURL, "board-url", "https://board.battlesnake.com", "Base URL for the game board when using --browser")
 
@@ -170,6 +173,10 @@ func (gameState *GameState) Initialize() error {
 		gameState.outputFile = f
 	}
 
+	if gameState.ReplayFilePath != "" {
+		gameState.replayFile = board.NewReplayFile(gameState.ReplayFilePath);
+	}
+
 	return nil
 }
 
@@ -235,6 +242,11 @@ func (gameState *GameState) Run() error {
 		boardServer.SendEvent(gameState.buildFrameEvent(boardState))
 	}
 
+	if gameState.replayFile != nil {
+		gameState.replayFile.WriteGameInfo(boardGame)
+		gameState.replayFile.WriteEvent(gameState.buildFrameEvent(boardState))
+	}
+
 	log.INFO.Printf("Ruleset: %v, Seed: %v", gameState.GameType, gameState.Seed)
 
 	if gameState.ViewMap {
@@ -293,6 +305,10 @@ func (gameState *GameState) Run() error {
 			boardServer.SendEvent(gameState.buildFrameEvent(boardState))
 		}
 
+		if gameState.replayFile != nil {
+			gameState.replayFile.WriteEvent(gameState.buildFrameEvent(boardState))
+		}
+
 		if exportGame {
 			for _, snakeState := range gameState.snakeStates {
 				snakeRequest := gameState.getRequestBodyForSnake(boardState, snakeState)
@@ -334,6 +350,13 @@ func (gameState *GameState) Run() error {
 		})
 	}
 
+	if gameState.replayFile != nil {
+		gameState.replayFile.WriteEvent(board.GameEvent{
+			EventType: board.EVENT_TYPE_GAME_END,
+			Data:      boardGame,
+		})
+	}
+
 	if exportGame {
 		lines, err := gameExporter.FlushToFile(gameState.outputFile)
 		if err != nil {