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Hand-crafted captcha

If you are using OkHttp We recommend applying solution with a ready-made Interceptor .

This instruction describes how to manually adjust the display and processing of the captcha if you are not using OkHttp , as well as examples independent implementation of Interceptors .

For manual processing of captcha in VK ID Captcha SDK Android, listener interfaces are used. The processing depends on the type of error that came from the API VKontakte>

•
Error with code 14 . More details in section Error with redirect_uri .
•
Titles X-Challenge ?1? X-Challenge-Url .

Before processing is required connect VK ID Captcha SDK Android.

Error handling with code `14`

1.

Handle it captcha Error from the API VKontakte and get the URL from the field redirect_uri .

Kotlin
val url = "https://api.vk.ru/method/some_method" val request = Request.Builder().url(url).build() val response = OkHttpClient.Builder().build().newCall(request).execute() val responseBody = JSONObject(response.peekBody(Long.MAX_VALUE).string()) val error14ChallengeUrl = if (responseBody.has("error")) { val error = responseBody.getJSONObject("error") val redirectUri = if (error.getInt("error_code") == 14) { error.getString("redirect_uri") } else { null } }
2.

Set up captcha tracking using the interface VKCaptchaResultListener :

Kotlin
val listener = object : VKCaptchaResultListener { override fun onResult(result: VKCaptchaResult) { // результат прохождения капчи } }
3.
To display the captcha, call the method VKCaptcha.openCaptcha() and pass it on:
- •
  URL RECEIVED from the field redirect_uri на шаге 1.
- •
  The domain where the captcha came from.
- •
  Captcha tracking interface VKCaptchaResultListener .
Kotlin
VKCaptcha.openCaptcha(domain, redirectUri, listener)
4.

Get the result of passing the captcha (token success_token ) in the method onResult() inside the transmitted listener interface.
5.

Pass the received token success_token in the query parameter of the query to the API VKontakte for which the captcha had to be passed.

Kotlin
val url = HttpUrl.Builder().addQueryParameter("success_token", token).build() val request = Request.Builder().url(url).build()

Handling Headers `X-Challenge` ?1? `X-Challenge-URL`

1.

Handle Headers X-Challenge ?1? X-Challenge-Url from API VKontakte remember the URL from the header X-Challenge-Url You will need it in the next step.

Kotlin
val url = "https://api.vk.ru/method/some_method" val request = Request.Builder().url(url).build() val response = OkHttpClient.Builder().build().newCall(request).execute() val challengeUrl = domain + response.headers("X-Challenge-Url").firstOrNull()
2.

Set up captcha tracking using the interface VKCaptchaResultListener :

Kotlin
val listener = object : VKCaptchaResultListener { override fun onResult(result: VKCaptchaResult) { // результат прохождения when (result) { is VKCaptchaResult.Success -> // успешное прохождение капчи is VKCaptchaResult.Error -> // ошибка при прохождении капчи } } }
3.
To display the captcha, call the method VKCaptcha.openCaptcha() .
Send it:
- •
  challengeUrl which you received when you joined domain ?1? X-Challenge-Url на шаге 1.
- •
  The domain where the captcha came from.
  Note that the domain must be specified with a protocol, for example: https://api.vk.ru .
- •
  Captcha tracking interface VKCaptchaResultListener .
Kotlin
VKCaptcha.openCaptcha(domain, challengeUrl, listener)
4.

Get the result of passing the captcha (token) in the method onResult() inside the transmitted listener interface.
5.

Pass the token in the header header в параметре X-Challenge-Solution .

Kotlin
val request = Request.Builder().header("X-Challenge-Solution", token).build()

Independent Integration with Interceptors

You can manually configure captcha display and processing as described above to implement its interceptor.

The following are examples of self-implementation of an interseptor for OkHttp which can be used as a basis for their implementation:

•
When handling an error with code 14 . More details in section Error with redirect_uri .
•
When processing headers .

Error with code `14`

An example implementation of an interseptor for OkHttp Error handling with code 14 :

Kotlin

//  Интерсептор, который обрабатывает ошибку с кодом `14`
public class Error14HandlingInterceptor(
    private val domains: Set<String> = emptySet(),
) : Interceptor {
 
    private val cookie = AtomicReference<String?>(null)
 
    private companion object {
        private const val CAPTCHA_ERROR_CODE = 14
        private val executor = Executors.newSingleThreadExecutor()
    }
 
    override fun intercept(chain: Interceptor.Chain): Response {
        val request = chain.request().withCookie()
        val response = chain.proceed(request)
        response.parseCookie()
        if (request.shouldSkipCaptcha()) return response
        val redirectUri = response.getRedirectUri() ?: return response
        val token = passCaptchaAndGetToken(redirectUri)
        return chain.proceed(chain.request().withCookie().withSuccessToken(token))
    }
 
    // Запускает процесс проверки капчи
    private fun passCaptchaAndGetToken(redirectUri: String): String = synchronized(this) {
        val tokenResult = AtomicReference<Result<String>>(Result.failure(Exception("No result")))
        executor.submit {
            VKCaptcha.openCaptcha(
                domain = redirectUri.toHttpUrl().run { "$scheme://$host" },
                redirectUri = redirectUri,
                listener = object : VKCaptchaResultListener {
                    override fun onResult(result: VKCaptchaResult) {
                        synchronized(tokenResult) {
                            tokenResult.set(wrapResult(result))
                            tokenResult.notifyAll()
                        }
                    }
                }
            )
        }
        synchronized(tokenResult) {
            if (tokenResult.get().getOrNull() == null) {
                tokenResult.wait()
            }
            tokenResult.get().getOrThrow()
        }
    }

    // Преобразует результат проверки капчи в результат, который содержит полученный токен
    private fun wrapResult(result: VKCaptchaResult): Result<String> {
        return when (result) {
            is VKCaptchaResult.Error -> Result.failure(Exception(result.error.message, result.error.error))
            is VKCaptchaResult.Success -> Result.success(result.token)
        }
    }
 
     // Добавляет полученный токен в запрос
    private fun Request.withSuccessToken(token: String): Request {
        return newBuilder()
            .url(url.newBuilder().addQueryParameter("success_token", token).build())
            .build()
    }
 
    // Получает redirect_uri из ответа
    private fun Response.getRedirectUri(): String? {
        val responseBody = JSONObject(peekBody(Long.MAX_VALUE).string())
        return if (responseBody.has("error")) {
            val error = responseBody.getJSONObject("error")
            if (error.getInt("error_code") == CAPTCHA_ERROR_CODE) {
                error.getString("redirect_uri")
            } else {
                null
            }
        } else {
            null
        }
    }
 
    // Проверяет, нужно ли запускать капчу для домена, переданного в запросе
    private fun Request.shouldSkipCaptcha(): Boolean {
        return !domains.contains(url.toUrl().host) && domains.isNotEmpty()
    }
 
     // Получает cookie из ответа
    private fun Response.parseCookie() {
        headers("Set-Cookie").firstOrNull { it.contains("remixstlid") }?.let(cookie::set)
    }
 
    // Добавляет cookie в запрос
    private fun Request.withCookie(): Request {
        return newBuilder().apply { cookie.get()?.let { addHeader("Cookie", it) } }.build()
    }
}
 
// Добавляет интерсептор в HTTP-клиент
OkHttpClient.Builder().addInterceptor(Error14HandlingInterceptor())

For headings `X-Challenge` ?1? `X-Challenge-URL`

An example implementation of an interseptor for OkHttp When processing headers X-Challenge-Solution ?1? X-Challenge-Url :

Kotlin

// Интерсептор, который обрабатывает ошибки в заголовках
public class CaptchaHeadersInterceptor(
    private val domains: Set<String> = emptySet(),
) : Interceptor {

    private companion object {
        private const val HEADER_CHALLENGE_SOLUTION = "X-Challenge-Solution"
        private const val HEADER_CHALLENGE_URL = "X-Challenge-Url"
        private const val HEADER_CHALLENGE = "X-Challenge"
        private val executor = Executors.newSingleThreadExecutor()
    }

    override fun intercept(chain: Interceptor.Chain): Response {
        val domain = chain.request().getDomain()
        val request = chain.request().withSavedChallengeSolution()
        val response = chain.proceed(request)
        if (shouldSkipCaptcha(response, domain)) return response
        val challengeUrl = response.headers(HEADER_CHALLENGE_URL).firstOrNull() ?: return response
        val token = passCaptchaAndGetToken(domain, challengeUrl)
        response.close()
        return chain.proceed(chain.request().withChallengeSolution(token))
    }

    // Запускает процесс проверки капчи
    private fun passCaptchaAndGetToken(
        domain: String,
        challengeUrl: String,
    ): String = synchronized(this) {
        val tokenResult = AtomicReference<Result<String>>(Result.failure(Exception("No result")))
        executor.submit {
            VKCaptcha.openCaptcha(
                domain = domain,
                redirectUri = domain + challengeUrl,
                listener = object : VKCaptchaResultListener {
                    override fun onResult(result: VKCaptchaResult) {
                        synchronized(tokenResult) {
                            tokenResult.set(wrapResult(result))
                            tokenResult.notifyAll()
                        }
                    }
                }
            )
        }
        synchronized(tokenResult) {
            if (tokenResult.get().getOrNull() == null) {
                tokenResult.wait()
            }
            tokenResult.get().getOrThrow()
        }
    }

    // Преобразует результат проверки капчи в kotlin Result
    private fun wrapResult(result: VKCaptchaResult): Result<String> {
        return when (result) {
            is VKCaptchaResult.Error -> Result.failure(Exception(result.error.message, result.error.error))
            is VKCaptchaResult.Success -> Result.success(result.token)
        }
    }
   
    // Добавляет токен в заголовок запроса X-Challenge-Solution
    private fun Request.withChallengeSolution(token: String): Request {
        return newBuilder()
            .header(HEADER_CHALLENGE_SOLUTION, token)
            .build()
    }

    // Добавляет сохранённый токен в заголовок запроса X-Challenge-Solution
    private fun Request.withSavedChallengeSolution(): Request {
        val headersToken = VKCaptcha.getToken(getDomain())
        return if (header(HEADER_CHALLENGE_SOLUTION) == null && headersToken != null) {
            newBuilder().addHeader(HEADER_CHALLENGE_SOLUTION, headerToken).build()
        } else {
            this
        }
    }

    // Проверяет, нужно ли передавать капчу в домен ответа
    private fun shouldSkipCaptcha(response: Response, domain: String): Boolean {
        return !domains.contains(domain) && domains.isNotEmpty() || response.headers(HEADER_CHALLENGE).all { it != "required" }
    }

   // Получает домен из запроса
    private fun Request.getDomain(): String {
        val url = url.toUrl()
        return URL(url.protocol, url.host, url.port, "").toString()
    }
}

// Добавляет интерсептор для обработки ошибок капчи в заголовках
OkHttpClient.Builder().addInterceptor(CaptchaHeadersInterceptor())

Hand-crafted captcha

Error handling with code 14

Handling Headers X-Challenge ?1? X-Challenge-URL

Independent Integration with Interceptors

Error with code 14

For headings X-Challenge ?1? X-Challenge-URL

Технические работы

Error handling with code `14`

Handling Headers `X-Challenge` ?1? `X-Challenge-URL`

Error with code `14`

For headings `X-Challenge` ?1? `X-Challenge-URL`