Ktor for Mobile Developers: Fear the server no more!

Building mobile apps is what we love to do, but there’s always one nagging problem — writing server side components to support our apps can be surprisingly complex and difficult. There’s a lot of overhead and a bunch of unfamiliar languages, frameworks, and styles of programming that we're not used to.

But fear the server no more, here comes Ktor!

In this talk we'll walk through a real world example of how Ktor (and your existing knowledge of Kotlin) makes building server side components for your app a breeze. We'll start with a basic introduction of Ktor and its components, but we’ll quickly get to building something real. Using a well known service/API, we’ll walk through everything you normally need to get up and running: authentication, getting data, posting data, and deployment.

By the end of the talk you'll have a good idea of how to hook up your own server side components to pretty much any API out there. Let’s conquer the server with Ktor!

Transcript

1. KTOR FOR MOBILE DEVELOPERS DAN KIM @dankim
2. Server side code? Me?
4. It's been...a while
5. The paradox of choice
6. "I wish there was a way to do simple server stuff with what I already know..."
7. Something familiar
8. Something that maintains my focus
9. Something lightweight and simple
10. Enter Ktor!
11. So here's what we're gonna do...
12. A Google "Dashboard"
13. RESTful API
14. Bonus: WebApp!
15. Let's build the RESTful API!
16. Things we'll be using
17. Ktor OAuth2 Retrofit Moshi Google APIs Google Cloud
18. Things we're not going to get into
19. Quickstart Database Sessions Testing
20. Assumptions
21. You've setup an application on Google Cloud
22. You've authenticated to Google's OAuth2
23. Ktor's basic structure
24. ApplicationEngine
25. CIO Jetty Netty Tomcat
26. Netty CIO Jetty Tomcat
27. fun main(args: Array<String>) { io.ktor.server.netty.EngineMain.main(args) }
28. ApplicationEnvironment
29. application.conf
30. ktor { deployment { port = 8080 watch = [Dev/kotlin/ktor/src] }1 application { modules = [com.dankim.ApplicationKt.module] }1 }1
31. ktor { deployment { port = 8080 watch = [Dev/kotlin/ktor/src] }1 application { modules = [com.dankim.ApplicationKt.module] }1 }1
32. fun main(args: Array<String>) { io.ktor.server.netty.EngineMain.main(args) } fun Application.module() { }
33. Application
34. class Application(val environment: ApplicationEnvironment) : ApplicationCallPipeline(), CoroutineScope { ... }1
35. class Application(val environment: ApplicationEnvironment) : ApplicationCallPipeline(), CoroutineScope { ... }1
36. ApplicationCallPipeline
37. ApplicationCallPipeline
38. Phase 1 Phase 2 Phase 3 Phase 5 Phase 4
39. Interceptor Interceptor Interceptor Interceptor Interceptor Interceptor Interceptor Interceptor
40. 1. Setup 2. Monitoring 3. Features 4. Call 5. Fallback
41. Features Call
42. Features
44. DefaultHeaders Feature
45. fun Application.module() { }1
46. curl -v http://0.0.0.0:8080/ > < HTTP/1.1 404 Not Found < Content-Length: 0
47. fun Application.module() { }1
48. fun Application.module() { install(DefaultHeaders) }1
49. override fun install(...): DefaultHeaders { ... val feature = DefaultHeaders(config) pipeline.intercept(ApplicationCallPipeline.Features) { feature.intercept(call) } ... }
50. curl -v http://0.0.0.0:8080/ < HTTP/1.1 404 Not Found < Date: Wed, 13 Nov 2019 02:08:13 GMT < Server: ktor-server-core/1.2.4 ktor-server-core/ 1.2.4 < Content-Length: 0
51. Routes
52. fun Application.module() { install(DefaultHeaders) }1
53. fun Application.module() { install(DefaultHeaders) install(Routing) }1
54. override fun install(...): Routing { ... val routing = Routing(pipeline).apply(configure) pipeline.intercept(ApplicationCallPipeline.Call) { routing.interceptor(this) } ... }
55. Features Call
56. fun Application.module() { install(DefaultHeaders) install(Routing) }
57. curl -v http://0.0.0.0:8080/ < HTTP/1.1 404 Not Found < Date: Wed, 13 Nov 2019 02:08:13 GMT < Server: ktor-server-core/1.2.4 ktor-server-core/ 1.2.4 < Content-Length: 0
58. fun Application.module() { install(DefaultHeaders) install(Routing) }11
59. fun Application.module() { install(DefaultHeaders) install(Routing) { get("/dashboard.json") { call.respondText { "Hello KotlinConf!" }11 }11 }11 }11
60. curl -v http://0.0.0.0:8080/ < HTTP/1.1 200 OK < Date: Tue, 03 Dec 2019 15:33:23 GMT < Server: ktor-server-core/1.2.4 ktor-server-core/ 1.2.4 ... Hello KotlinConf!
61. Let's get some data
62. GET Gmail Data
63. @JsonClass(generateAdapter = true)11 data class GmailThreads( @Json(name = "threads") val threads: List<GmailThread> )111
64. @JsonClass(generateAdapter = true)11 data class GmailThreads( @Json(name = "threads") val threads: List<GmailThread> )111 @JsonClass(generateAdapter = true) data class GmailThread( @Json(name = "id") val id: String, @Json(name = "snippet") val snippet: String )1
65. @GET("gmail/v1/users/{user}/threads") fun getGmailThreads(@Path("user") user: String): Call<GmailThreads>
66. private fun getGmailData(): GmailThreads? { val response = getGoogleServicesInstance() .getGmailThreads("dan@basecamp.com") .execute() return when { response.isSuccessful -> response.body() else -> { handleError(response.errorBody().toString()) null }1 }1 }1
67. private fun getGmailData(): GmailThreads? { val response = getGoogleServicesInstance() .getGmailThreads("dan@basecamp.com") .execute() return when { response.isSuccessful -> response.body() else -> { handleError(response.errorBody().toString()) null }1 }1 }1
68. private fun getGmailData(): GmailThreads? { val response = getGoogleServicesInstance() .getGmailThreads("dan@basecamp.com") .execute() return when { response.isSuccessful -> response.body() else -> { handleError(response.errorBody().toString()) null }1 }1 }1
69. fun Application.module() { install(DefaultHeaders) install(Routing) { }11 }1
70. fun Application.module() { install(DefaultHeaders) install(Routing) { get("/dashboard.json") { val gmailData = getGmailData() call.respondText { gmailData.toJson() }1111 }111 }11 }1
71. fun Application.module() { install(DefaultHeaders) install(Routing) { get("/dashboard.json") { val gmailData = getGmailData() call.respondText { gmailData.toJson() }1 }1 }1 }1
72. fun Application.module() { install(DefaultHeaders) install(Routing) { get("/dashboard.json") { val gmailData = getGmailData() call.respondText { gmailData.toJson() }1 }1 }1 }1
73. curl -H "Authorization: Bearer <bearer_token>" http://0.0.0.0:8080/dashboard.json
74. curl -H "Authorization: Bearer <bearer_token>" http://0.0.0.0:8080/dashboard.json
75. GET Gtasks Data
76. @JsonClass(generateAdapter = true)111 data class GoogleTasks( @Json(name = "items") val tasks: List<GoogleTask>? = null )111
77. @JsonClass(generateAdapter = true)111 data class GoogleTasks( @Json(name = "items") val tasks: List<GoogleTask>? = null )111 @JsonClass(generateAdapter = true)11 data class GoogleTask( @Json(name = "id") val id: String? = null, @Json(name = "title") val title: String? = null, @Json(name = "status") val status: String? = null )11
78. @JsonClass(generateAdapter = true)111 data class GoogleTasks( @Json(name = "items") val tasks: List<GoogleTask>? = null )111 @JsonClass(generateAdapter = true)11 data class GoogleTask( @Json(name = "id") val id: String? = null, @Json(name = "title") val title: String? = null, @Json(name = "status") val status: String? = null )11 @JsonClass(generateAdapter = true)1 data class MyGoogleDashboard( @Json(name = "tasks") val tasks: List<GoogleTask>, @Json(name = "emails") val emails: List<GmailThread> )1
79. @GET("tasks/v1/lists/{listId}/tasks") fun getTasks(@Path("listId") listId: String): Call<GoogleTasks>
80. private fun getTaskList(listId: String): GoogleTasks? { val response = getGoogleServicesInstance().getTasks(listId).execute() return if (response.isSuccessful) { response.body() } else { handleError(response.errorBody().toString()) null }1 }1
81. private fun getTaskList(listId: String): GoogleTasks? { val response = getGoogleServicesInstance().getTasks(listId).execute() return if (response.isSuccessful) { response.body() } else { handleError(response.errorBody().toString()) null }1 }1
82. private fun getTaskList(listId: String): GoogleTasks? { val response = getGoogleServicesInstance().getTasks(listId).execute() return if (response.isSuccessful) { response.body() } else { handleError(response.errorBody().toString()) null }1 }1
83. get("/dashboard.json") { val gmailData = getGmailData() val taskList = getTaskList("<listId>") val myGoogleDashboard = MyGoogleDashboard( tasks = taskList?.tasks, emails = gmailData?.threads ) call.respondText { myGoogleDashboard.toJson() }1 }1
84. get("/dashboard.json") { val gmailData = getGmailData() val taskList = getTaskList("<listId>") val myGoogleDashboard = MyGoogleDashboard( tasks = taskList?.tasks, emails = gmailData?.threads ) call.respondText { myGoogleDashboard.toJson() }1 }1
85. get("/dashboard.json") { val gmailData = getGmailData() val taskList = getTaskList("<listId>") val myGoogleDashboard = MyGoogleDashboard( tasks = taskList?.tasks, emails = gmailData?.threads ) call.respondText { myGoogleDashboard.toJson() }1 }1
86. get("/dashboard.json") { val gmailData = getGmailData() val taskList = getTaskList("<listId>") val myGoogleDashboard = MyGoogleDashboard( tasks = taskList?.tasks, emails = gmailData?.threads ) call.respondText { myGoogleDashboard.toJson() }1 }1
87. curl -H "Authorization: Bearer <bearer_token>" http://0.0.0.0:8080/dashboard.json
88. curl -H "Authorization: Bearer <bearer_token>" http://0.0.0.0:8080/dashboard.json
89. Gtasks POST
90. @POST("tasks/v1/lists/{listId}/tasks") fun createTask(@Path("listId") listId: String, @Body task: GoogleTask): Call<ResponseBody>
91. post("/tasks/new") { val postParams = call.receiveParameters() val taskName = postParams.entries() .find { it.key == "taskName" }?.value?.first() val task = GoogleTask(title = taskName) val response = getGoogleServicesInstance().createTask("<id>",task).execute() return if (response.isSuccessful) { call.respond(HttpStatusCode.OK) } else { handleError(response.errorBody().toString()) null }1 }1
92. post("/tasks/new") { val postParams = call.receiveParameters() val taskName = postParams.entries() .find { it.key == "taskName" }?.value?.first() val task = GoogleTask(title = taskName) val response = getGoogleServicesInstance().createTask("<id>",task).execute() return if (response.isSuccessful) { call.respond(HttpStatusCode.OK) } else { handleError(response.errorBody().toString()) null }1 }1
93. post("/tasks/new") { val postParams = call.receiveParameters() val taskName = postParams.entries() .find { it.key == "taskName" }?.value?.first() val task = GoogleTask(title = taskName) val response = getGoogleServicesInstance().createTask("<id>",task).execute() return if (response.isSuccessful) { call.respond(HttpStatusCode.OK) } else { handleError(response.errorBody().toString()) null }1 }1
94. post("/tasks/new") { val postParams = call.receiveParameters() val taskName = postParams.entries() .find { it.key == "taskName" }?.value?.first() val task = GoogleTask(title = taskName) val response = getGoogleServicesInstance().createTask("<listId>",task).execute() return if (response.isSuccessful) { call.respond(HttpStatusCode.OK) } else { handleError(response.errorBody().toString()) null }1 }1
95. post("/tasks/new") { val postParams = call.receiveParameters() val taskName = postParams.entries() .find { it.key == "taskName" }?.value?.first() val task = GoogleTask(title = taskName) val response = getGoogleServicesInstance().createTask("<listId>",task).execute() return if (response.isSuccessful) { call.respond(HttpStatusCode.OK) } else { handleError(response.errorBody().toString()) null }1 }1
96. curl -v -F 'taskName=This is super cool!' -H "Accept: application/json" http://0.0.0.0:8080/tasks/new < HTTP/1.1 200 OK < Date: Tue, 19 Nov 2019 02:58:41 GMT < Server: ktor-server-core/1.2.4 ktor-server-core/1.2.4 < Content-Length: 0
98. Webapp
99. Authentication
100. OAuth 2
102. val googleOauthProvider = OAuthServerSettings.OAuth2ServerSettings( name = "google", authorizeUrl = "https://accounts.google.com/o/oauth2/auth", accessTokenUrl = "https://www.googleapis.com/oauth2/v3/token", requestMethod = HttpMethod.Post, clientId = "<yourClientId>", clientSecret = "<yourClientSecret>", defaultScopes = listOf( "profile", "email", "https://www.googleapis.com/auth/gmail.readonly", "https://www.googleapis.com/auth/tasks" ) )
103. fun Application.module() { // ... install(Authentication) { oauth("google-oauth") { client = HttpClient(Apache) providerLookup = { googleOauthProvider } urlProvider = { redirectUrl("/login") } } } }
104. fun Application.module() { ... install(Routing) { authenticate("google-oauth") { route("/login") { handle { val principal = call.authentication.principal<OAuthAccessTokenResponse.OAuth2>() ?: error("No principal") saveOAuthToken(principal.accessToken) call.respondRedirect("/") }11111 }1111 }1111 }11 }11
105. fun Application.module() { ... install(Routing) { authenticate("google-oauth") { route("/login") { handle { val principal = call.authentication.principal<OAuthAccessTokenResponse.OAuth2>() ?: error("No principal") saveOAuthToken(principal.accessToken) call.respondRedirect("/") }11111 }1111 }111 }11 }11
106. fun Application.module() { ... install(Routing) { authenticate("google-oauth") { route("/login") { handle { val principal = call.authentication.principal<OAuthAccessTokenResponse.OAuth2>() ?: error("No principal") saveOAuthToken(principal.accessToken) call.respondRedirect("/") }1 }1 }1 }1 }1
107. Web: showing the data
108. get("/dashboard") { val gmailData = getGmailData() val taskList = getTaskList("<listId>") ... }
109. call.respondHtml { body { p { h1 { +"Dashboard" } h2 { +"Tasks:" } ul { taskList?.tasks?.forEach { li { +it.title!! } }1 }1 h2 { +"Emails:" } ul { gmailData?.threads?.forEach { li { +StringEscapeUtils.unescapeHtml4(it.snippet) } }1 }1 }1 }1 }1
110. body { p { h1 { +"Dashboard" } h2 { +"Tasks:" } ul { taskList?.tasks?.forEach { li { +it.title } }11 }11 h2 { +"Emails:" } ul { gmailData?.threads?.forEach { li { +StringEscapeUtils.unescapeHtml4(it.snippet) } }1 }1 }1 }1
111. body { p { h1 { +"Dashboard" } h2 { +"Tasks:" } ul {11 taskList?.tasks?.forEach { li { +it.title } }11 }11 h2 { +"Emails:" } ul {1 gmailData?.threads?.forEach { li { +StringEscapeUtils.unescapeHtml4(it.snippet) } }1 }1 }1 }1
112. body { p { h1 { +"Dashboard" } h2 { +"Tasks:" } ul {11 taskList?.tasks?.forEach { li { +it.title } }11 }11 h2 { +"Emails:" } ul {1 gmailData?.threads?.forEach { li { +StringEscapeUtils.unescapeHtml4(it.snippet) } }1 }1 }1 }1
114. Web: posting data
115. get("/tasks/new") { call.respondHtml { body { form("/tasks/new", encType = FormEncType.applicationXWwwFormUrlEncoded, method = FormMethod.post ) { acceptCharset = "utf-8" p { label { +"Task: " } textInput { name = "taskName" } }1 p { submitInput { value = "send" } }1 }1 }1 }1 }1
116. get("/tasks/new") { call.respondHtml { body { form("/tasks/new", encType = FormEncType.applicationXWwwFormUrlEncoded, method = FormMethod.post ) { acceptCharset = "utf-8" p { label { +"Task: " } textInput { name = "taskName" } }111111 p { submitInput { value = "send" } }11111 }1111 }111 }111 }1
117. get("/tasks/new") { call.respondHtml { body { form("/tasks/new", encType = FormEncType.applicationXWwwFormUrlEncoded, method = FormMethod.post ) { acceptCharset = "utf-8" p { label { +"Task: " } textInput { name = "taskName" } }111111 p { submitInput { value = "send" } }11111 }1111 }111 }11 }1
119. post("/tasks/new") { val postParams = call.receiveParameters() val taskName = postParams.entries() .find { it.key == "taskName" }?.value?.first() val acceptHeader = call.request.headers.get("Accept") val task = GoogleTask(title = taskName) val response = getGoogleServicesInstance().createTask( "<listId>", task).execute() when (acceptHeader) { "application/json" -> call.respond(HttpStatusCode.OK) else -> call.respondRedirect("/dashboard") }1 }1
120. post("/tasks/new") { val postParams = call.receiveParameters() val taskName = postParams.entries() .find { it.key == "taskName" }?.value?.first() val acceptHeader = call.request.headers.get("Accept") val task = GoogleTask(title = taskName) val response = getGoogleServicesInstance().createTask( "<listId>", task).execute() when (acceptHeader) { "application/json" -> call.respond(HttpStatusCode.OK) else -> call.respondRedirect("/dashboard") }1 }1
121. post("/tasks/new") { val postParams = call.receiveParameters() val taskName = postParams.entries() .find { it.key == "taskName" }?.value?.first() val acceptHeader = call.request.headers.get("Accept") val task = GoogleTask(title = taskName) val response = getGoogleServicesInstance().createTask( "<listId>", task).execute() when (acceptHeader) { "application/json" -> call.respond(HttpStatusCode.OK) else -> call.respondRedirect("/dashboard") }1 }1
123. Deployment
124. Google Cloud
125. https://cloud.google.com/ community/tutorials/kotlin-ktor-app- engine-java8
126. XML config files
127. ../src/main/webapp/WEB-INF/appengine-web.xml
128. ../src/main/webapp/WEB-INF/appengine-web.xml ../src/main/webapp/WEB-INF/web.xml
129. Cloud projects cost money!
131. gcloud projects delete [PROJECT_ID]
132. Wrap it up!
133. THANK YOU AND REMEMBER TO VOTE Dan Kim @dankim