diff --git a/build.gradle.kts b/build.gradle.kts
index 9600a71..8de9756 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -4,6 +4,7 @@ val kotlin_version: String by project
 plugins {
     kotlin("multiplatform") version "1.7.10"
     kotlin("plugin.serialization") version "1.7.10"
+    id("org.jetbrains.dokka") version "1.7.10"
     `maven-publish`
 }
 
diff --git a/src/commonMain/kotlin/net.sergeych.parsec3/Adapter.kt b/src/commonMain/kotlin/net.sergeych.parsec3/Adapter.kt
index 4b3cefc..e923415 100644
--- a/src/commonMain/kotlin/net.sergeych.parsec3/Adapter.kt
+++ b/src/commonMain/kotlin/net.sergeych.parsec3/Adapter.kt
@@ -1,4 +1,4 @@
-package channel
+package net.sergeych.parsec3
 
 import kotlinx.coroutines.CompletableDeferred
 import kotlinx.coroutines.sync.Mutex
@@ -7,15 +7,11 @@ import kotlinx.serialization.json.Json
 import net.sergeych.boss_serialization.BossDecoder
 import net.sergeych.boss_serialization_mp.BossEncoder
 import net.sergeych.boss_serialization_mp.decodeBoss
-import net.sergeych.cloudoc.api.Package
 import net.sergeych.mp_logger.LogTag
 import net.sergeych.mp_logger.debug
 import net.sergeych.mp_logger.exception
 import net.sergeych.mp_logger.warning
 import net.sergeych.mptools.toDump
-import net.sergeych.parsec3.ExceptionsRegistry
-import net.sergeych.parsec3.InvalidFrameException
-import net.sergeych.parsec3.ParsecException
 
 /**
  * Create adapter, an interface to provide local API commands and invoke remote API commands
@@ -82,7 +78,6 @@ open class Adapter<T>(
     private var lastId = 1
     private val access = Mutex()
 
-
     /**
      * Call the remote party for a type command. See [CommandHost] on how to declare and implement
      * such commands in parsec3. Suspends until receiving answer from a remote party.
@@ -93,7 +88,7 @@ open class Adapter<T>(
      * @return value from remote partm any serializable type.
      */
     @Suppress("UNCHECKED_CAST")
-    suspend fun <A, R> invokeCommand(ca: CommandDescriptor<T, A, R>, args: A = Unit as A): R {
+    suspend fun <A, R> invokeCommand(ca: CommandDescriptor<A, R>, args: A = Unit as A): R {
         var myId = -1
         return CompletableDeferred<ByteArray>().also { dr ->
             sendPackage(
diff --git a/src/commonMain/kotlin/net.sergeych.parsec3/AdapterBuilder.kt b/src/commonMain/kotlin/net.sergeych.parsec3/AdapterBuilder.kt
new file mode 100644
index 0000000..8f13869
--- /dev/null
+++ b/src/commonMain/kotlin/net.sergeych.parsec3/AdapterBuilder.kt
@@ -0,0 +1,40 @@
+package net.sergeych.parsec3
+
+import kotlinx.coroutines.flow.Flow
+import net.sergeych.mp_tools.globalLaunch
+
+class AdapterBuilder<S, H : CommandHost<S>>(
+    val api: H,
+    private val exceptionRegistry: ExceptionsRegistry = ExceptionsRegistry(),
+    f: AdapterBuilder<S, H>.() -> Unit,
+) {
+
+    internal var sessionProducer: (suspend () -> S)? = null
+        private set
+
+
+    fun newSession(f: suspend () -> S) {
+        sessionProducer = f
+    }
+
+    /**
+     * Register command implementation
+     */
+    fun <A, R> on(ca: CommandDescriptor<A, R>, block: suspend S.(A) -> R) {
+        api.on(ca, block)
+    }
+
+    fun <T : Throwable> addError(code: String, handler: (String?) -> T) {
+        exceptionRegistry.register(code, handler)
+    }
+
+    suspend fun createWith(input: Flow<ByteArray>, f: suspend (ByteArray)->Unit ): Adapter<S> {
+        return Adapter<S>(sessionProducer!!(), api, exceptionRegistry) { f(it) }
+            .also { a-> globalLaunch { input.collect { a.receiveFrame(it)} } }
+    }
+
+    init {
+        f(this)
+    }
+
+}
\ No newline at end of file
diff --git a/src/commonMain/kotlin/net.sergeych.parsec3/AdapterDelegate.kt b/src/commonMain/kotlin/net.sergeych.parsec3/AdapterDelegate.kt
index b5e72ed..cbde351 100644
--- a/src/commonMain/kotlin/net.sergeych.parsec3/AdapterDelegate.kt
+++ b/src/commonMain/kotlin/net.sergeych.parsec3/AdapterDelegate.kt
@@ -1,6 +1,5 @@
 package net.sergeych.parsec3
 
-import channel.CommandDescriptor
 import kotlin.reflect.KProperty
 import kotlin.reflect.KType
 
@@ -13,7 +12,7 @@ class AdapterDelegate<I, A, R>(
     val ass: KType,
     val rss: KType,
 ) {
-    operator fun getValue(thisRef: Any?, property: KProperty<*>): CommandDescriptor<I, A, R> {
+    operator fun getValue(thisRef: Any?, property: KProperty<*>): CommandDescriptor<A, R> {
         return CommandDescriptor(
             overrideName ?: property.name,
             ass, rss
diff --git a/src/commonMain/kotlin/net.sergeych.parsec3/CommandDescriptor.kt b/src/commonMain/kotlin/net.sergeych.parsec3/CommandDescriptor.kt
index 59d4570..7dc0599 100644
--- a/src/commonMain/kotlin/net.sergeych.parsec3/CommandDescriptor.kt
+++ b/src/commonMain/kotlin/net.sergeych.parsec3/CommandDescriptor.kt
@@ -1,19 +1,19 @@
-package channel
+package net.sergeych.parsec3
 
 import kotlin.reflect.KType
 
-class CommandDescriptor<I, A, R>(
+class CommandDescriptor<A, R>(
     val name: String,
     val ass: KType,
     val rss: KType,
 ) {
-    suspend operator fun invoke(adapter: Adapter<I>, args: A): R =
+    suspend operator fun invoke(adapter: Adapter<*>, args: A): R =
         adapter.invokeCommand(this, args)
 
     @Suppress("UNCHECKED_CAST")
-    suspend operator fun invoke(adapter: Adapter<I>): R = adapter.invokeCommand(this,Unit as A)
+    suspend operator fun invoke(adapter: Adapter<*>): R = adapter.invokeCommand(this,Unit as A)
 
-    operator fun invoke(commandHost: CommandHost<I>, block: suspend I.(A)->R) {
+    operator fun <I>invoke(commandHost: CommandHost<I>, block: suspend I.(A)->R) {
         commandHost.on(this, block)
     }
 }
diff --git a/src/commonMain/kotlin/net.sergeych.parsec3/CommandHost.kt b/src/commonMain/kotlin/net.sergeych.parsec3/CommandHost.kt
index 04b637b..5e85c1c 100644
--- a/src/commonMain/kotlin/net.sergeych.parsec3/CommandHost.kt
+++ b/src/commonMain/kotlin/net.sergeych.parsec3/CommandHost.kt
@@ -1,9 +1,7 @@
-package channel
+package net.sergeych.parsec3
 
 import net.sergeych.boss_serialization.BossDecoder
 import net.sergeych.boss_serialization_mp.BossEncoder
-import net.sergeych.parsec3.AdapterDelegate
-import net.sergeych.parsec3.CommandNotFoundException
 import kotlin.reflect.typeOf
 
 /**
@@ -39,7 +37,7 @@ open class CommandHost<T> {
      * Provide implementation for a specific command in type-safe compile-time checked manner. the command
      * should be declared with [command] invocation.
      */
-    fun <A, R> on(ca: CommandDescriptor<T, A, R>, block: suspend T.(A) -> R) {
+    fun <A, R> on(ca: CommandDescriptor<A, R>, block: suspend T.(A) -> R) {
         handlers[ca.name] = {args ->
             val decodedArgs = BossDecoder.decodeFrom<A>(ca.ass, args)
             BossEncoder.encode(ca.rss, block(decodedArgs))
diff --git a/src/commonMain/kotlin/net.sergeych.parsec3/Package.kt b/src/commonMain/kotlin/net.sergeych.parsec3/Package.kt
index c8f20a8..656256d 100644
--- a/src/commonMain/kotlin/net.sergeych.parsec3/Package.kt
+++ b/src/commonMain/kotlin/net.sergeych.parsec3/Package.kt
@@ -1,13 +1,32 @@
-package net.sergeych.cloudoc.api
+package net.sergeych.parsec3
 
 import kotlinx.serialization.Serializable
 
+/**
+ * The parsec3 package transmit requests and responses over the parsec3 channel.
+ */
 @Serializable
 sealed class Package {
-
+    /**
+     * Invoke a remote command.
+     * @param id command is a monotonously growing number, that could reset to 0 after getting close
+     *           to `Int.MAX_VALUE`, for example. It uniquely identifies a command that is waiting for an answer.
+     * @param name command's name
+     * @param args whatever arguments the command accepts serialized with BOSS.
+     */
     @Serializable
     data class Command(val id: Int, val name: String, val args: ByteArray) : Package()
 
+
+    /**
+     * Response to a previously issued command. See [ExceptionsRegistry] and [ParsecException] for more information
+     * on passing errors.
+     *
+     * @param tiId if of the command this response is for
+     * @param result packed result. If null, it means the command has thrown an exception and [errorCode] must
+     *               not be null
+     * @param errorCode exception code, if not null then result must be ignored (and assumed to be null).
+     */
     @Serializable
     data class Response(
         val toId: Int,
diff --git a/src/commonTest/kotlin/parsec3/AdapterTest.kt b/src/commonTest/kotlin/parsec3/AdapterTest.kt
index 072e3e5..c11efa9 100644
--- a/src/commonTest/kotlin/parsec3/AdapterTest.kt
+++ b/src/commonTest/kotlin/parsec3/AdapterTest.kt
@@ -1,32 +1,34 @@
 package parsec3
 
-import channel.Adapter
-import channel.CommandHost
+import assertThrows
 import kotlinx.coroutines.channels.Channel
+import kotlinx.coroutines.flow.receiveAsFlow
 import kotlinx.coroutines.launch
 import kotlinx.coroutines.test.runTest
+import net.sergeych.parsec3.*
 import kotlin.test.Test
 import kotlin.test.assertEquals
 
 internal class AdapterTest {
 
-    class Api1: CommandHost<Unit>() {
+    object Api1 : CommandHost<Unit>() {
         // create command `foo` that takes a string argument and
         // returns a string:
-        val foo by command<String,String>()
+        val foo by command<String, String>()
     }
 
-    class Api2: CommandHost<Unit>() {
 
-        val bar by command<String,String>()
+    object Api2 : CommandHost<Unit>() {
+
+        val bar by command<String, String>()
     }
 
     @Test
     fun interconnect() = runTest {
         val ch12 = Channel<ByteArray>()
         val ch21 = Channel<ByteArray>()
-        val api1 = Api1()
-        val api2 = Api2()
+        val api1 = Api1
+        val api2 = Api2
         api1.on(api1.foo) {
             it + "foo"
         }
@@ -34,10 +36,10 @@ internal class AdapterTest {
             it + "bar"
         }
 
-        val a1 = Adapter(Unit,api1) { ch12.send(it) }
-        val a2 = Adapter(Unit,api2) { ch21.send(it) }
-        launch { for( b in ch12) a2.receiveFrame(b) }
-        launch { for( b in ch21) a1.receiveFrame(b) }
+        val a1 = Adapter(Unit, api1) { ch12.send(it) }
+        val a2 = Adapter(Unit, api2) { ch21.send(it) }
+        launch { for (b in ch12) a2.receiveFrame(b) }
+        launch { for (b in ch21) a1.receiveFrame(b) }
 
         assertEquals("123bar", a1.invokeCommand(api2.bar, "123"))
         assertEquals("321foo", a2.invokeCommand(api1.foo, "321"))
@@ -46,4 +48,58 @@ internal class AdapterTest {
         ch21.cancel()
 
     }
+
+    data class TestSession(var buzz: String)
+
+    object ApiS1 : CommandHost<TestSession>() {
+        // create command `foo` that takes a string argument and
+        // returns a string:
+        val foo by command<String, String>()
+        val ex by command<String,Unit>()
+    }
+    class ApiS2<T> : CommandHost<T>() {
+        // create command `foo` that takes a string argument and
+        // returns a string:
+        val bar by command<String, String>()
+    }
+
+    @Test
+    fun builderTest() = runTest {
+        val ch12 = Channel<ByteArray>()
+        val ch21 = Channel<ByteArray>()
+
+        val er = ExceptionsRegistry().also {
+            it.register("foo_x") { IllegalArgumentException("foo_x") }
+        }
+
+        val b1 = AdapterBuilder(ApiS1, er) {
+            newSession { TestSession("42") }
+            on(api.foo) {
+                it + buzz + "foo"
+            }
+            on(ApiS1.ex) {
+                throw ParsecException("foo_x")
+            }
+        }
+        val b2 = AdapterBuilder(ApiS2<Unit>(), er) {
+            newSession { }
+            on(api.bar) {
+                it + "bar"
+            }
+        }
+
+        val a1 = b1.createWith(ch21.receiveAsFlow()) { ch12.send(it) }
+        val a2 = b2.createWith(ch12.receiveAsFlow()) { ch21.send(it) }
+
+        assertEquals("123bar", a1.invokeCommand(ApiS2<Unit>().bar, "123"))
+        assertEquals("32142foo", a2.invokeCommand(ApiS1.foo, "321"))
+
+        assertEquals("---42foo", ApiS1.foo.invoke(a2, "---"))
+        assertThrows<IllegalArgumentException> { ApiS1.ex.invoke(a2, "foobar") }
+
+        ch12.cancel()
+        ch21.cancel()
+
+    }
+
 }
\ No newline at end of file
diff --git a/src/commonTest/kotlin/parsec3/assertThrows.kt b/src/commonTest/kotlin/parsec3/assertThrows.kt
new file mode 100644
index 0000000..fa8c679
--- /dev/null
+++ b/src/commonTest/kotlin/parsec3/assertThrows.kt
@@ -0,0 +1,21 @@
+import kotlin.test.fail
+
+inline fun <reified T : Throwable> assertThrows(f: () -> Unit): T {
+    try {
+        f()
+        fail("expected to throw ${T::class.simpleName} but threw nothing")
+    } catch (e: Throwable) {
+        if (e !is T) {
+            println("unexpected error class: ${e::class.simpleName}")
+            e.printStackTrace()
+            fail("expected to throw ${T::class.simpleName} instead ${e::class.simpleName} was thrown: $e")
+        }
+        return e
+    }
+}
+
+//fun assertThrowsCode(code: String, f: () -> Unit): Unit {
+//    val err = assertThrows<ServiceError> {  f() }
+//    if( err.code != code )
+//        Assert.fail("expected error code '$code' got ${err.code}")
+//}