Ktor as HTTP client for Android

 3r33548. 3r3-31. Retrofit? as an Android developer, I like it, but what about trying to use Ktor as an HTTP client? In my opinion, for Android development, it is no worse and no better, just one of the options, although if you wrap everything up a bit, it can turn out very well. I will consider the basic features with which you can start using Ktor as an HTTP client - creating requests of various kinds, receiving raw answers and answers in the form of text, deserializing json into classes through converters, logging. 3r???.  3r33548. 3r???.  3r33548. Ktor as HTTP client for Android
3r???.  3r33548. 3r???.  3r33548. If in general, Ktor is a framework that can act as an HTTP client. I will consider it from the development side for Android. It is unlikely that you will see very complex use cases below, but the basic features are accurate. The code from the examples below can be viewed at 3r315. GitHub
. 3r???.  3r33548. Ktor uses korutin from Kotlin 1.? a list of available artifacts can be found here is The current version is ??? 3r3485. . 3r???.  3r33548. For requests I will use HttpBin . 3r???.  3r33548. 3r???.  3r33548. 3r3444. Simple use 3r???.  3r33548. To get started, you will need basic dependencies for the Android client: 3r33514.  3r33548. 3r33477. 3r33471. implementation "io.ktor: ktor-client-core: ???"
implementation "io.ktor: ktor-client-android: ???"
3r???.  3r33548. Do not forget to add information in Manifest that you are using the Internet. 3r???.  3r33548. 3r33477. 3r33548. 3r???.  3r33548. Let's try to get the server response as a string, what could be simpler? 3r???.  3r33548. 3r33477. 3r33478. private const val BASE_URL = "https://httpbin.org"
private const val GET_UUID = "$ BASE_URL /uuid"
3r33548. fun simpleCase () {
val client = HttpClient () 3r3353548. 3r33548. GlobalScope.launch (Dispatchers.IO) {3r33548. val data = client.get (GET_UUID) 3r33548. Log.i ("$ BASE_TAG Simple case", data) 3r33535.} 3r33548.} 3r33548. 3r???.  3r33548. You can create a client without parameters, just create an instance of HttpClient () . In this case, Ktor will select the required engine himself and use it with the default settings (we have one connected engine - Android, but there are others, for example, OkHttp). 3r???.  3r33548. Why korutiny? Because get () - this is suspend function. 3r???.  3r33548. What can be done next? You already have data from the server as a string, you just have to parse it and get classes that you can work with. It seems to be easy and fast in this case of use. 3r???.  3r33548. 3r???.  3r33548. 3r3444. We get the raw answer 3r???.  3r33548. Sometimes it is necessary to get a set of bytes instead of a string. Experiment with asynchrony at the same time. 3r???.  3r33548. 3r33477. 3r33478. fun performAllCases () {3r3353548. GlobalScope.launch (Dispatchers.IO) {3r33548. simpleCase ()
bytesCase ()
} 3r33548.} 3r33548. 3r33548. suspend fun simpleCase () {3r3353548. val client = HttpClient () 3r3353548. val data = client.get (GET_UUID) 3r33548. Log.i ("$ BASE_TAG Simple case", data) 3r33535.} 3r33548. 3r33548. suspend fun bytesCase () {3r3353548. val client = HttpClient () 3r3353548. val data = client.call (GET_UUID) .response.readBytes ()
Log.i ("$ BASE_TAG Bytes case", data.joinToString ("", "[", "]") {It.toString (16) .toUpperCase ()}) 3r3548.} 3r33548. 3r???.  3r33548. In places of a call of methods 3r3452. HttpClient such as 3r3452. call () 3r3485. and get () , under the hood will be called await () . So in this case, calls simpleCase () and bytesCase () will always be consistent. It is necessary in parallel - just wrap each call into a separate coruntine. In this example, new methods have appeared. Call call (GET_UUID) returns us an object from which we can get information about the request, its configuration, response and customer. The object contains a lot of useful information - from the response code and the protocol version to the channel with the same bytes. 3r???.  3r33548. 3r???.  3r33548. 3r3444. Do you need to close it somehow? 3r33434. 3r???.  3r33548. The developers indicate that for the correct completion of the HTTP engine, you need to call the client method. close () . If you need to make one call and immediately close the client, then you can use the method. use {} 3r3485. since HttpClient implements interface 3r3452. Closable . 3r???.  3r33548. 3r33477. 3r33478. suspend fun closableSimpleCase () {3r3353548. HttpClient (). Use {3r33548. val dаta: String = it.get (GET_UUID)
Log.i ("$ BASE_TAG Closable case", data) 3r-3548.} 3r33548.} 3r33548. 3r???.  3r33548. 3r3444. Examples besides GET 3r???.  3r33548. In my work, the second most popular method is POST . Consider the example of setting parameters, headers and the request body. 3r???.  3r33548. 3r33477. 3r33478. suspend fun postHeadersCase (client: HttpClient) {3r3353548. val dаta: String = client.post (POST_TEST) {
fillHeadersCaseParameters () 3r3353548.} 3r33548. Log.i ("$ BASE_TAG Post case", data) 3r33548.} 3r33548. 3r33548. private fun HttpRequestBuilder.fillHeadersCaseParameters () {
Parameter ("name", "Andrei") //+ parameter to the query string
url.parameters.appendAll (3r33548. parametersOf (3r33535. "ducks" to listOf ("White duck", "Gray duck"), //+ parameter list in the query string 3r33548. "fish" to listOf ("Goldfish") //+ parameter to the query string 3r33548.) 3r33548.) 3r33548. 3r33548. header ("Ktor", "https://ktor.io") //+ header 3r3548. headers /* get access to the header list builder * /{3r33548. append ("Kotlin", "https://kotl.in")
} 3r33548. headers.append ("Planet", "Mars") //+ header 3r3548. headers.appendMissing ("Planet", listOf ("Mars", "Earth")) //+ only new headers, "Mars" will be missed
headers.appendAll ("Pilot", listOf ("Starman")) //another option for adding the 3r3r4848 header. 3r33548. body = FormDataContent (//create parameters that will be passed to form
Parameters.build {
append ("Low-level", "C")
append ("High-level", "Java") 3r33548.} 3r3-3548.) 3r33548.} 3r33548. 3r???.  3r33548. In fact, in the last parameter of the function post () You have access to HttpRequestBuilder with which you can create any request. 3r???.  3r33548. Method post () just parses the string, converts it to the URL, explicitly specifies the type of the method, and makes the request. 3r???.  3r33548. 3r33477. 3r33478. suspend fun rawPostHeadersCase (client: HttpClient) {3r3353548. val dаta: String = client.call {3r33548. url.takeFrom (POST_TEST)
method = HttpMethod.Post
fillHeadersCaseParameters () 3r3353548.} 3r33548. .response
.readText ()
3r33548. Log.i ("$ BASE_TAG Raw post case", data) 3r33535.} 3r33548. 3r???.  3r33548. If you run the code from the last two methods, the result will be the same. The difference is not great, but it is more convenient to use wrappers. The situation is similar for put () , delete () , patch () , head () and options () therefore we will not consider them. 3r???.  3r33548. However, if you look closely, you can see that there is a difference in typing. When you call 3r3452. call () 3r3485. you get a low-level response and you have to read the data yourself, but what about automatic typing? After all, we all used to connect a converter in Retrofit2 (such as Gson ) And specify the return type as a specific class. We'll talk about converting to classes later, but the method will help to typify the result without being tied to a specific HTTP method. request . 3r???.  3r33548. 3r33477. 3r33478. suspend fun typedRawPostHeadersCase (client: HttpClient) {
val data = client.request () {3r33548. url.takeFrom (POST_TEST)
method = HttpMethod.Post
fillHeadersCaseParameters () 3r3353548.} 3r33548. Log.i ("$ BASE_TAG Typed raw post", data)
} 3r33548. 3r???.  3r33548. 3r3444. Submitting the form data 3r???.  3r33548. Usually, you need to pass parameters either in the query string or in the body. In the example above, we have already considered how to do this using HttpRequestBuilder . But it can be easier. 3r???.  3r33548. Function submitForm accepts a url as a string, parameters for the request, and a boolean flag that tells how to pass parameters — in the query string or as pairs in a form 3r???.  3r33548. 3r33477. 3r33478. suspend fun submitFormCase (client: HttpClient) {
3r33548. val params = Parameters.build {
append ("Star", "Sun") 3r33535. append ("Planet", "Mercury")
} 3r33548. 3r33548. val getdаta: String = client.submitForm (GET_TEST, params, encodeInQuery = true) //parameters in the query string
val postdаta: String = client.submitForm (POST_TEST, params, encodeInQuery = false) //parameters in form
3r33548. Log.i ("$ BASE_TAG Submit form get", getData)
Log.i ("$ BASE_TAG Submit form post", postData)
} 3r33548. 3r???.  3r33548. 3r3444. And what about multipart /form-data? 3r33434. 3r???.  3r33548. In addition to string pairs, you can pass as POST parameters for requesting numbers, byte arrays, and various Input streams. Differences in the function and the formation of parameters. Looks like:
 3r33548. 3r33477. 3r33478. suspend fun submitFormBinaryCase (client: HttpClient) {
3r33548. val inputStream = ByteArrayInputStream (byteArrayOf (7? 7? 79)) 3r3548. 3r33548. val formData = formData {
append ("String value", "My name is") //string parameter
append ("Number value", 179) //numeric 3r33548. append ("Bytes value", byteArrayOf (1? 7? 98)) //set of bytes
append ("Input value", inputStream.asInput (), headersOf ("Stream header", "Stream header value")) //stream and headers 3r3548.} 3r33548. 3r33548. val dаta: String = client.submitFormWithBinaryData (POST_TEST, formData)
Log.i ("$ BASE_TAG Submit binary case", data) 3r-3548.} 3r33548. 3r???.  3r33548. As you can see, you can attach a set of headers to each parameter. 3r???.  3r33548. 3r???.  3r33548. 3r3444. We deserialize the answer to the class 3r???.  3r33548. It is necessary to get some data from the query not in the form of a string or byte, but immediately converted into a class. For a start, we are recommended in the documentation to connect the feature of working with json, but I want to make a reservation that jvm needs a specific dependency and without kotlinx-serialization, all this does not take off. I suggest using Gson as a converter (links to other supported libraries are in the documentation, links to the documentation will be at the end of the article). 3r???.  3r33548. 3r???.  3r33548. build.gradle project level:
 3r33548. 3r33477. 3r33471. buildscript {
dependencies {
classpath "org.jetbrains.kotlin: kotlin-serialization: $ kotlin_version"
} 3r33548.} 3r33548. 3r33548. allprojects {
repositories {
maven {url "https://kotlin.bintray.com/kotlinx"}
} 3r33548.} 3r33548. 3r???.  3r33548. build.gradle application level:
 3r33548. 3r33477. 3r33471. apply plugin: 'kotlinx-serialization'
3r33548. dependencies {
implementation "io.ktor: ktor-client-json-jvm: ???"
implementation "io.ktor: ktor-client-gson: ???"
} 3r33548. 3r???.  3r33548. Now let's execute the query. From the new one there will only be a connection feature of working with Json when creating a client. I will use open weather API. For completeness show the data model. 3r???.  3r33548. 3r33477. 3r33478. data class Weather (3r33535. val consolidated_weather: List , 3r33535. val time: String, 3r3-33548. val sun_rise: String,
val sun_set: String, 3r3353548. val timezone_name: String, 3r3353548 val sources: List , 3r33535. val title: String, 3r33548. val location_type: String,
val woeid: Int,
val latt_long: String, 3r3353548. val timezone: String 3r3353548. 3r33548. data class Source (
val title: String,
val slug: String,
val url: String,
val crawl_rate: Int 3r33535.) 3r33535. 3r33548. data class ConsolidatedWeather (
val id: Long,
val weather_state_name: String,
val weather_state_abbr: String,
val wind_direction_compass: String,
val created: String, 3r3rstrnrnrrrrrrstrm_rc_compass: String,
: Double,
Val max_temp: Double,
Val the_temp: Double,
Val wind_speed: Double,
Val wind_direction: Double,
Val air_pressure: Double,
Double, 3r33548. Val predictability: Int 3r33548.) 3r33548. 3r33548. data class Parent (
val title: String,
val location_type: String,
val woeid: Int,
val latt_long: String
) 3r33535. 3r33548. private const val SF_WEATHER_URL = "https://www.metaweather.com/api/location/2487956/"
3r33548. suspend fun getAndPrintWeather () {
3r33548. val client = HttpClient (Android) {
install (JsonFeature) {3r3353548. serializer = GsonSerializer () 3r3353548.} 3r33548.} 3r33548. 3r33548. val weather: Weather = client.get (SF_WEATHER_URL)
3r33548. Log.i ("$ BASE_TAG Serialization", weather.toString ())
} 3r33548. 3r???.  3r33548. 3r3444. And what else can 3r???.  3r33548. For example, the server returns an error, and you have the code as in the previous example. In this case, you will get a serialization error, but you can configure the client so that with the response code <300 бросалась ошибка BadResponseStatus . It is enough to install when building the client expectSuccess at true . 3r???.  3r33548. 3r33477. 3r33478. val client = HttpClient (Android) {
install (JsonFeature) {3r3353548. serializer = GsonSerializer () 3r3353548.} 3r33548. expectSuccess = true
} 3r33548. 3r???.  3r33548. When debugging, logging may be useful. It is enough to add one dependency and tune the client. 3r???.  3r33548. 3r33477. 3r33471. implementation "io.ktor: ktor-client-logging-jvm: ???"
3r???.  3r33548. 3r33477. 3r33478. val client = HttpClient (Android) {
install (Logging) {
logger = Logger.DEFAULT
level = LogLevel.ALL
} 3r33548.} 3r33548.
3r???.  3r33548. We specify the DEFAULT logger and everything will fall into the LogCat, but you can redefine the interface and make your logger if you wish (although I didn’t see any great opportunities there, there is only a message at the entrance, but there is no log level). We also indicate the level of logs to be reflected. 3r???.  3r33548. 3r???.  3r33548. References: 3r???.  3r33548. 3r???.  3r33548. 3r? 3516.  3r33548. 3r? 3533. 3r?500. Documentation 3r3506. 3r? 3534.  3r33548. 3r? 3533.
Documentation on the implementation of the client 3r3506. 3r? 3534.  3r33548. 3r33636. 3r???.  3r33548. What is not considered:
 3r33548. 3r???.  3r33548. 3r? 3516.  3r33548. 3r? 3533. Work with OkHttp engine 3r33535.  3r33548. 3r? 3533. Engine settings
 3r33548. 3r? 3533. Mock engine and testing
 3r33548. 3r? 3533. The authorization module
 3r33548. 3r? 3533. Separate features of the storage of cookies between requests and others. 3r33434.  3r33548. 3r? 3533. All that does not apply to the HTTP client for Android (other platforms, working through sockets, server implementation, etc. 3r33534.  3r33548. 3r33636. 3r33544. 3r33548. 3r33548. 3r33548. 3r33535. ! function (e) {function t (t, n) {if (! (n in e)) {for (var r, a = e.document, i = a.scripts, o = i.length; o-- ;) if (-1! == i[o].src.indexOf (t)) {r = i[o]; break} if (! r) {r = a.createElement ("script"), r.type = "text /jаvascript", r.async =! ? r.defer =! ? r.src = t, r.charset = "UTF-8"; var d = function () {var e = a.getElementsByTagName ("script")[0]; e.parentNode.insertBefore (r, e)}; "[object Opera]" == e.opera? a.addEventListener? a.addEventListener ("DOMContentLoaded", d,! 1): e.attachEvent ("onload", d ): d ()}}} t ("//mediator.mail.ru/script/2820404/"""_mediator") () (); 3r33542. 3r33548. 3r33544. 3r33548. 3r33548. 3r33548. 3r33548.
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