Startup HttpService implementation

android/app/src/main/java/com/epfl/dedis/hbt/di/HttpModule.kt

@@ -0,0 +1,19 @@
+package com.epfl.dedis.hbt.di
+
+import android.content.Context
+import dagger.Module
+import dagger.Provides
+import dagger.hilt.InstallIn
+import dagger.hilt.android.qualifiers.ApplicationContext
+import dagger.hilt.components.SingletonComponent
+import org.chromium.net.CronetEngine
+import javax.inject.Singleton
+
+@Module
+@InstallIn(SingletonComponent::class)
+class HttpModule {
+    @Provides
+    @Singleton
+    fun provideCronet(@ApplicationContext context: Context): CronetEngine =
+        CronetEngine.Builder(context).build()
+}

android/app/src/main/java/com/epfl/dedis/hbt/service/http/HttpService.kt

@@ -0,0 +1,68 @@
+package com.epfl.dedis.hbt.service.http
+
+import io.reactivex.rxjava3.core.Single
+import io.reactivex.rxjava3.subjects.SingleSubject
+import org.chromium.net.CronetEngine
+import org.chromium.net.CronetException
+import org.chromium.net.UrlRequest
+import org.chromium.net.UrlResponseInfo
+import java.nio.ByteBuffer
+import java.util.concurrent.Executors
+import javax.inject.Inject
+import javax.inject.Singleton
+
+@Singleton
+class HttpService @Inject constructor(private val engine: CronetEngine) {
+
+    private val executor = Executors.newSingleThreadExecutor()
+
+    fun get(url: String): Single<String> {
+        val single = SingleSubject.create<String>()
+
+        engine.newUrlRequestBuilder(url, Callback(single), executor)
+            .setHttpMethod("GET")
+            .build()
+            .start()
+
+        return single
+    }
+
+    private class Callback(private val single: SingleSubject<String>) : UrlRequest.Callback() {
+        override fun onRedirectReceived(
+            request: UrlRequest?,
+            info: UrlResponseInfo?,
+            newLocationUrl: String?
+        ) {
+            request?.followRedirect()
+        }
+
+        override fun onResponseStarted(request: UrlRequest?, info: UrlResponseInfo?) {
+            request?.read(ByteBuffer.allocateDirect(BYTE_BUFFER_CAPACITY_BYTES))
+        }
+
+        override fun onReadCompleted(
+            request: UrlRequest?,
+            info: UrlResponseInfo?,
+            byteBuffer: ByteBuffer?
+        ) {
+            byteBuffer?.clear()
+            request?.read(byteBuffer)
+        }
+
+        override fun onSucceeded(request: UrlRequest?, info: UrlResponseInfo?) {
+            single.onSuccess(info?.httpStatusCode.toString())
+        }
+
+        override fun onFailed(
+            request: UrlRequest?,
+            info: UrlResponseInfo?,
+            error: CronetException?
+        ) {
+            single.onError(error ?: Exception("Unknown error"))
+        }
+
+        companion object {
+            private const val BYTE_BUFFER_CAPACITY_BYTES = 100 * 1024
+        }
+    }
+}