0
# Server Engine Abstraction
1

2
Engine abstraction layer for different server implementations providing a unified interface for HTTP server management, environment configuration, and connector setup for various server backends like Netty, Jetty, and CIO.
3

4
## Capabilities
5

6
### Application Engine Interface
7

8
Core interface for server engine implementations providing lifecycle management and environment access.
9

10
```kotlin { .api }
11
/**
12
 * Interface for server engine implementations
13
 */
14
interface ApplicationEngine {
15
    /** Application engine environment */
16
    val environment: ApplicationEngineEnvironment
17
    
18
    /** Start the server engine */
19
    fun start(wait: Boolean = true): ApplicationEngine
20
    /** Stop the server engine */
21
    fun stop(gracePeriodMillis: Long, timeoutMillis: Long)
22
    /** Add shutdown hook */
23
    fun addShutdownHook(hook: () -> Unit)
24
}
25

26
/**
27
 * Base implementation for application engines
28
 */
29
abstract class BaseApplicationEngine(
30
    final override val environment: ApplicationEngineEnvironment,
31
    val pipeline: EnginePipeline = defaultEnginePipeline(environment)
32
) : ApplicationEngine {
33
    /** Engine is running */
34
    val isRunning: Boolean
35
    /** Engine monitor for lifecycle events */
36
    val monitor: Events
37
    
38
    /** Execute engine pipeline */
39
    protected suspend fun executeEngine(call: ApplicationCall)
40
    /** Start engine implementation */
41
    protected abstract fun start(wait: Boolean): ApplicationEngine
42
    /** Stop engine implementation */
43
    protected abstract fun stop(gracePeriodMillis: Long, timeoutMillis: Long)
44
}
45
```
46

47
### Application Engine Environment
48

49
Environment configuration for application engines including connectors, modules, and application lifecycle.
50

51
```kotlin { .api }
52
/**
53
 * Environment for application engines
54
 */
55
interface ApplicationEngineEnvironment {
56
    /** Application instance */
57
    val application: Application
58
    /** Environment logger */
59
    val log: Logger
60
    /** Environment configuration */
61
    val config: ApplicationConfig
62
    /** Event monitor */
63
    val monitor: Events
64
    /** Development mode flag */
65
    val developmentMode: Boolean
66
    /** Server connectors configuration */
67
    val connectors: List<EngineConnectorConfig>
68
    /** Application modules to load */
69
    val modules: List<Application.() -> Unit>
70
    /** Parent coroutine context */
71
    val parentCoroutineContext: CoroutineContext
72
    /** Watch paths for development mode */
73
    val watchPatterns: List<String>
74
    /** Root path for the application */
75
    val rootPath: String
76
}
77

78
/**
79
 * Builder for creating engine environments
80
 */
81
class ApplicationEngineEnvironmentBuilder {
82
    /** Set parent coroutine context */
83
    var parentCoroutineContext: CoroutineContext = EmptyCoroutineContext
84
    /** Set development mode */
85
    var developmentMode: Boolean = false
86
    /** Set root path */
87
    var rootPath: String = "/"
88
    /** Watch patterns for auto-reload */
89
    val watchPatterns: MutableList<String> = mutableListOf()
90
    /** Connector configurations */
91
    val connectors: MutableList<EngineConnectorConfig> = mutableListOf()
92
    /** Application modules */
93
    val modules: MutableList<Application.() -> Unit> = mutableListOf()
94
    
95
    /** Add HTTP connector */
96
    fun connector(block: EngineConnectorConfigBuilder.() -> Unit)
97
    /** Add application module */  
98
    fun module(body: Application.() -> Unit)
99
    /** Build environment */
100
    fun build(): ApplicationEngineEnvironment
101
}
102
```
103

104
### Engine Connectors
105

106
Configuration for HTTP/HTTPS connectors with customizable host, port, and protocol settings.
107

108
```kotlin { .api }
109
/**
110
 * Engine connector configuration
111
 */
112
interface EngineConnectorConfig {
113
    /** Connector type (HTTP, HTTPS) */
114
    val type: ConnectorType
115
    /** Server host */
116
    val host: String
117
    /** Server port */
118
    val port: Int
119
}
120

121
/**
122
 * Builder for engine connector configuration
123
 */
124
class EngineConnectorConfigBuilder {
125
    /** Connector host (default: 0.0.0.0) */
126
    var host: String = "0.0.0.0"
127
    /** Connector port (default: 80) */
128
    var port: Int = 80
129
    
130
    /** Build connector configuration */
131
    fun build(): EngineConnectorConfig
132
}
133

134
/**
135
 * Connector types
136
 */
137
enum class ConnectorType {
138
    HTTP,
139
    HTTPS
140
}
141

142
/**
143
 * HTTP connector configuration
144
 */
145
class HttpConnectorConfig(
146
    override val host: String = "0.0.0.0",
147
    override val port: Int = 80
148
) : EngineConnectorConfig {
149
    override val type: ConnectorType = ConnectorType.HTTP
150
}
151

152
/**
153
 * HTTPS connector configuration  
154
 */
155
class HttpsConnectorConfig(
156
    override val host: String = "0.0.0.0",
157
    override val port: Int = 443,
158
    val keyStorePath: String,
159
    val keyStorePassword: String,
160
    val privateKeyPassword: String? = null
161
) : EngineConnectorConfig {
162
    override val type: ConnectorType = ConnectorType.HTTPS
163
}
164
```
165

166
### Engine Pipeline
167

168
Pipeline system for processing HTTP requests at the engine level before application processing.
169

170
```kotlin { .api }
171
/**
172
 * Engine pipeline for request processing
173
 */
174
class EnginePipeline : Pipeline<Unit, ApplicationCall> {
175
    companion object {
176
        /** Before phase for engine pre-processing */
177
        val Before: PipelinePhase = PipelinePhase("Before")
178
        /** Call phase for application call processing */  
179
        val Call: PipelinePhase = PipelinePhase("Call")
180
        /** After phase for engine post-processing */
181
        val After: PipelinePhase = PipelinePhase("After")
182
    }
183
}
184

185
/**
186
 * Create default engine pipeline
187
 * @param environment - Engine environment
188
 * @return Configured engine pipeline
189
 */
190
fun defaultEnginePipeline(environment: ApplicationEngineEnvironment): EnginePipeline
191
```
192

193
### Command Line Configuration
194

195
Utilities for parsing command line arguments and configuring engines from command line options.
196

197
```kotlin { .api }
198
/**
199
 * Command line configuration parser
200
 */
201
class CommandLineConfig(args: Array<String>) {
202
    /** Parsed configuration */
203
    val config: ApplicationConfig
204
    /** Server host from command line */
205
    val host: String?
206
    /** Server port from command line */
207
    val port: Int?
208
    /** Development mode flag */
209
    val developmentMode: Boolean
210
    /** Watch patterns from command line */
211
    val watchPatterns: List<String>
212
    
213
    /** Create engine environment from command line */
214
    fun createEnvironment(): ApplicationEngineEnvironment
215
}
216

217
/**
218
 * Parse command line arguments
219
 * @param args - Command line arguments array
220
 * @return Parsed command line configuration
221
 */
222
fun parseCommandLineArgs(args: Array<String>): CommandLineConfig
223
```
224

225
### Environment Utilities
226

227
Utility functions for creating and configuring application engine environments.
228

229
```kotlin { .api }
230
/**
231
 * Create application engine environment
232
 * @param configure - Environment configuration block
233
 * @return Configured environment
234
 */
235
fun applicationEngineEnvironment(configure: ApplicationEngineEnvironmentBuilder.() -> Unit): ApplicationEngineEnvironment
236

237
/**
238
 * Create development environment with auto-reload
239
 * @param configure - Environment configuration block
240
 * @return Development environment
241
 */
242
fun developmentEnvironment(configure: ApplicationEngineEnvironmentBuilder.() -> Unit): ApplicationEngineEnvironment
243

244
/**
245
 * Create production environment  
246
 * @param configure - Environment configuration block
247
 * @return Production environment
248
 */
249
fun productionEnvironment(configure: ApplicationEngineEnvironmentBuilder.() -> Unit): ApplicationEngineEnvironment
250
```
251

252
### Engine Events
253

254
Event system for engine lifecycle monitoring and health checking.
255

256
```kotlin { .api }
257
/**
258
 * Engine lifecycle events
259
 */
260
object EngineEvents {
261
    /** Engine starting event */
262
    val EngineStarting: EventDefinition<ApplicationEngine>
263
    /** Engine started event */
264
    val EngineStarted: EventDefinition<ApplicationEngine>
265
    /** Engine stopping event */
266
    val EngineStopping: EventDefinition<ApplicationEngine>
267
    /** Engine stopped event */
268
    val EngineStopped: EventDefinition<ApplicationEngine>
269
}
270

271
/**
272
 * Event monitoring for engines
273
 */
274
interface Events {
275
    /** Subscribe to event */
276
    fun <T> subscribe(definition: EventDefinition<T>, handler: (T) -> Unit)
277
    /** Unsubscribe from event */
278
    fun <T> unsubscribe(definition: EventDefinition<T>, handler: (T) -> Unit)
279
    /** Raise event */
280
    fun <T> raise(definition: EventDefinition<T>, value: T)
281
}
282

283
/**
284
 * Event definition
285
 */
286
data class EventDefinition<T>(val name: String)
287
```
288

289
**Usage Examples:**
290

291
```kotlin
292
import io.ktor.server.application.*
293
import io.ktor.server.engine.*
294
import io.ktor.server.response.*
295
import io.ktor.server.routing.*
296

297
// Basic engine environment setup
298
fun createBasicEnvironment(): ApplicationEngineEnvironment {
299
    return applicationEngineEnvironment {
300
        // Add HTTP connector
301
        connector {
302
            host = "0.0.0.0"
303
            port = 8080
304
        }
305
        
306
        // Add application module
307
        module {
308
            routing {
309
                get("/") {
310
                    call.respondText("Hello from Ktor!")
311
                }
312
            }
313
        }
314
    }
315
}
316

317
// Development environment with auto-reload
318
fun createDevelopmentEnvironment(): ApplicationEngineEnvironment {
319
    return developmentEnvironment {
320
        developmentMode = true
321
        
322
        // Watch for changes
323
        watchPatterns += "src/main/kotlin/**/*.kt"
324
        watchPatterns += "src/main/resources/**/*"
325
        
326
        connector {
327
            host = "localhost"
328
            port = 8080
329
        }
330
        
331
        module(Application::developmentModule)
332
    }
333
}
334

335
// Production environment with HTTPS
336
fun createProductionEnvironment(): ApplicationEngineEnvironment {
337
    return productionEnvironment {
338
        developmentMode = false
339
        
340
        // HTTP connector (for redirects)
341
        connector {
342
            host = "0.0.0.0"
343
            port = 80
344
        }
345
        
346
        // HTTPS connector
347
        connector {
348
            host = "0.0.0.0"
349
            port = 443
350
            // Note: HTTPS configuration would be engine-specific
351
        }
352
        
353
        module(Application::productionModule)
354
    }
355
}
356

357
// Multiple connectors setup
358
fun createMultiConnectorEnvironment(): ApplicationEngineEnvironment {
359
    return applicationEngineEnvironment {
360
        // Public HTTP connector
361
        connector {
362
            host = "0.0.0.0"
363
            port = 8080
364
        }
365
        
366
        // Admin connector on different port
367
        connector {
368
            host = "127.0.0.1"
369
            port = 8081
370
        }
371
        
372
        module {
373
            routing {
374
                get("/") {
375
                    call.respondText("Public API")
376
                }
377
                
378
                get("/admin") {
379
                    // Check if request came from admin connector
380
                    val localPort = call.request.local.port
381
                    if (localPort == 8081) {
382
                        call.respondText("Admin Interface")
383
                    } else {
384
                        call.respond(HttpStatusCode.NotFound)
385
                    }
386
                }
387
            }
388
        }
389
    }
390
}
391

392
// Command line configuration
393
fun main(args: Array<String>) {
394
    val commandLineConfig = parseCommandLineArgs(args)
395
    val environment = commandLineConfig.createEnvironment()
396
    
397
    // Engine would be started here with the environment
398
    // Example: embeddedServer(Netty, environment).start(wait = true)
399
}
400

401
// Custom engine implementation example
402
abstract class CustomApplicationEngine(
403
    environment: ApplicationEngineEnvironment
404
) : BaseApplicationEngine(environment) {
405
    
406
    override fun start(wait: Boolean): ApplicationEngine {
407
        // Subscribe to engine events
408
        environment.monitor.subscribe(EngineEvents.EngineStarting) { engine ->
409
            environment.log.info("Starting custom engine...")
410
        }
411
        
412
        environment.monitor.subscribe(EngineEvents.EngineStarted) { engine ->
413
            environment.log.info("Custom engine started on ${environment.connectors.joinToString { "${it.host}:${it.port}" }}")
414
        }
415
        
416
        // Start server implementation
417
        startServer()
418
        
419
        if (wait) {
420
            // Wait for shutdown
421
            Runtime.getRuntime().addShutdownHook(Thread {
422
                stop(1000, 5000)
423
            })
424
        }
425
        
426
        return this
427
    }
428
    
429
    override fun stop(gracePeriodMillis: Long, timeoutMillis: Long) {
430
        environment.monitor.raise(EngineEvents.EngineStopping, this)
431
        
432
        // Stop server implementation
433
        stopServer(gracePeriodMillis, timeoutMillis)
434
        
435
        environment.monitor.raise(EngineEvents.EngineStopped, this)
436
    }
437
    
438
    protected abstract fun startServer()
439
    protected abstract fun stopServer(gracePeriodMillis: Long, timeoutMillis: Long)
440
}
441

442
// Environment with custom configuration
443
fun createConfigurableEnvironment(config: ApplicationConfig): ApplicationEngineEnvironment {
444
    return applicationEngineEnvironment {
445
        // Load configuration
446
        val serverConfig = config.config("server")
447
        val host = serverConfig.property("host").getString()
448
        val port = serverConfig.property("port").getInt()
449
        
450
        connector {
451
            this.host = host
452
            this.port = port
453
        }
454
        
455
        // Set development mode from config
456
        developmentMode = config.propertyOrNull("app.development")?.getBoolean() ?: false
457
        
458
        // Set root path from config
459
        rootPath = config.propertyOrNull("app.rootPath")?.getString() ?: "/"
460
        
461
        // Load modules based on configuration
462
        val enabledModules = config.propertyOrNull("app.modules")?.getList() ?: emptyList()
463
        
464
        if ("routing" in enabledModules) {
465
            module(Application::routingModule)
466
        }
467
        
468
        if ("authentication" in enabledModules) {
469
            module(Application::authenticationModule)  
470
        }
471
        
472
        if ("monitoring" in enabledModules) {
473
            module(Application::monitoringModule)
474
        }
475
    }
476
}
477

478
// Extension modules
479
fun Application.developmentModule() {
480
    routing {
481
        get("/") {
482
            call.respondText("Development Server")
483
        }
484
        
485
        get("/reload") {
486
            call.respondText("Auto-reload enabled")
487
        }
488
    }
489
}
490

491
fun Application.productionModule() {
492
    routing {
493
        get("/") {
494
            call.respondText("Production Server")
495
        }
496
        
497
        get("/health") {
498
            call.respond(HttpStatusCode.OK, mapOf("status" to "healthy"))
499
        }
500
    }
501
}
502

503
fun Application.routingModule() {
504
    routing {
505
        get("/api/status") {
506
            call.respond(mapOf("service" to "running"))
507
        }
508
    }
509
}
510

511
fun Application.authenticationModule() {
512
    // Authentication setup would go here
513
}
514

515
fun Application.monitoringModule() {
516
    // Monitoring and metrics setup would go here
517
}
518
```