Use Either instead of exceptions in frame decoder

Goals:
* Make code cleaner (in a FP way)
* Avoid costly exception throw each time we wait for the rest of the
frame (collecting stack traces is costly and we do not need them
anyway)

Closes ONAP-437
Change-Id: I40341d3c2cb85f3ff581d89167245cb009dbb070
Signed-off-by: Piotr Jaszczyk <piotr.jaszczyk@nokia.com>
Issue-ID: DCAEGEN2-601

3 files changed, 57 insertions, 25 deletions

diff --git a/hv-collector-core/src/main/kotlin/org/onap/dcae/collectors/veshv/impl/wire/WireChunkDecoder.kt b/hv-collector-core/src/main/kotlin/org/onap/dcae/collectors/veshv/impl/wire/WireChunkDecoder.kt
index d1d72592..502505c4 100644
--- a/hv-collector-core/src/main/kotlin/org/onap/dcae/collectors/veshv/impl/wire/WireChunkDecoder.kt
+++ b/hv-collector-core/src/main/kotlin/org/onap/dcae/collectors/veshv/impl/wire/WireChunkDecoder.kt
@@ -19,14 +19,17 @@
  */
 package org.onap.dcae.collectors.veshv.impl.wire
 
+import arrow.effects.IO
 import io.netty.buffer.ByteBuf
 import io.netty.buffer.ByteBufAllocator
+import org.onap.dcae.collectors.veshv.domain.InvalidWireFrame
+import org.onap.dcae.collectors.veshv.domain.MissingWireFrameBytes
 import org.onap.dcae.collectors.veshv.domain.WireFrame
 import org.onap.dcae.collectors.veshv.domain.WireFrameDecoder
-import org.onap.dcae.collectors.veshv.domain.exceptions.MissingWireFrameBytesException
-import org.onap.dcae.collectors.veshv.impl.VesHvCollector
+import org.onap.dcae.collectors.veshv.domain.WireFrameDecodingError
 import org.onap.dcae.collectors.veshv.utils.logging.Logger
 import reactor.core.publisher.Flux
+import reactor.core.publisher.SynchronousSink
 
 /**
  * @author Piotr Jaszczyk <piotr.jaszczyk@nokia.com>
@@ -53,28 +56,29 @@ internal class WireChunkDecoder(
     }
 
     private fun generateFrames(): Flux<WireFrame> = Flux.generate { next ->
-        try {
-            val frame = decodeFirstFrameFromBuffer()
-            if (frame == null) {
+        decoder.decodeFirst(streamBuffer)
+                .fold(onError(next), onSuccess(next))
+                .unsafeRunSync()
+    }
+
+    private fun onError(next: SynchronousSink<WireFrame>): (WireFrameDecodingError) -> IO<Unit> = { err ->
+        when (err) {
+            is InvalidWireFrame -> IO {
+                next.error(WireFrameException(err))
+            }
+            is MissingWireFrameBytes -> IO {
                 logEndOfData()
                 next.complete()
-            } else {
-                logDecodedWireMessage(frame)
-                next.next(frame)
             }
-        } catch (ex: Exception) {
-            next.error(ex)
         }
     }
 
-
-    private fun decodeFirstFrameFromBuffer(): WireFrame? =
-            try {
-                decoder.decodeFirst(streamBuffer)
-            } catch (ex: MissingWireFrameBytesException) {
-                logger.trace { "${ex.message} - waiting for more data" }
-                null
-            }
+    private fun onSuccess(next: SynchronousSink<WireFrame>): (WireFrame) -> IO<Unit> = { frame ->
+        IO {
+            logDecodedWireMessage(frame)
+            next.next(frame)
+        }
+    }
 
 
     private fun logIncomingMessage(wire: ByteBuf) {
@@ -90,6 +94,6 @@ internal class WireChunkDecoder(
     }
 
     companion object {
-        val logger = Logger(VesHvCollector::class)
+        val logger = Logger(WireChunkDecoder::class)
     }
 }
diff --git a/hv-collector-core/src/main/kotlin/org/onap/dcae/collectors/veshv/impl/wire/WireFrameException.kt b/hv-collector-core/src/main/kotlin/org/onap/dcae/collectors/veshv/impl/wire/WireFrameException.kt
new file mode 100644
index 00000000..83a7cd85
--- /dev/null
+++ b/hv-collector-core/src/main/kotlin/org/onap/dcae/collectors/veshv/impl/wire/WireFrameException.kt
@@ -0,0 +1,29 @@
+/*
+ * ============LICENSE_START=======================================================
+ * dcaegen2-collectors-veshv
+ * ================================================================================
+ * Copyright (C) 2018 NOKIA
+ * ================================================================================
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ * ============LICENSE_END=========================================================
+ */
+package org.onap.dcae.collectors.veshv.impl.wire
+
+import org.onap.dcae.collectors.veshv.domain.WireFrameDecodingError
+
+/**
+ * @author Piotr Jaszczyk <piotr.jaszczyk@nokia.com>
+ * @since June 2018
+ */
+class WireFrameException(error: WireFrameDecodingError)
+    : Exception("${error::class.simpleName}: ${error.message}")
diff --git a/hv-collector-core/src/test/kotlin/org/onap/dcae/collectors/veshv/impl/wire/WireChunkDecoderTest.kt b/hv-collector-core/src/test/kotlin/org/onap/dcae/collectors/veshv/impl/wire/WireChunkDecoderTest.kt
index 1ddcc3dc..33f71684 100644
--- a/hv-collector-core/src/test/kotlin/org/onap/dcae/collectors/veshv/impl/wire/WireChunkDecoderTest.kt
+++ b/hv-collector-core/src/test/kotlin/org/onap/dcae/collectors/veshv/impl/wire/WireChunkDecoderTest.kt
@@ -30,7 +30,6 @@ import org.jetbrains.spek.api.dsl.it
 import org.onap.dcae.collectors.veshv.domain.WireFrame
 import org.onap.dcae.collectors.veshv.domain.WireFrameDecoder
 import org.onap.dcae.collectors.veshv.domain.WireFrameEncoder
-import org.onap.dcae.collectors.veshv.domain.exceptions.InvalidWireFrameMarkerException
 import reactor.test.test
 
 /**
@@ -43,11 +42,11 @@ internal object WireChunkDecoderTest : Spek({
     val anotherPayload = "ala ma kota a kot ma ale".toByteArray()
 
     val encoder = WireFrameEncoder(alloc)
-    
+
     fun WireChunkDecoder.decode(frame: WireFrame) = decode(encoder.encode(frame))
 
     fun createInstance() = WireChunkDecoder(WireFrameDecoder(), alloc)
-    
+
     fun verifyMemoryReleased(vararg byteBuffers: ByteBuf) {
         for (bb in byteBuffers) {
             assertThat(bb.refCnt())
@@ -90,7 +89,7 @@ internal object WireChunkDecoderTest : Spek({
 
             it("should yield error") {
                 createInstance().decode(input).test()
-                        .verifyError(InvalidWireFrameMarkerException::class.java)
+                        .verifyError(WireFrameException::class.java)
             }
 
             it("should leave memory unreleased") {
@@ -132,7 +131,7 @@ internal object WireChunkDecoderTest : Spek({
             it("should yield decoded input frame and error") {
                 createInstance().decode(input).test()
                         .expectNextMatches { it.payloadSize == samplePayload.size }
-                        .verifyError(InvalidWireFrameMarkerException::class.java)
+                        .verifyError(WireFrameException::class.java)
             }
 
             it("should leave memory unreleased") {
@@ -170,7 +169,7 @@ internal object WireChunkDecoderTest : Spek({
                         .expectNextMatches { it.payloadSize == samplePayload.size }
                         .verifyComplete()
                 cut.decode(input2).test()
-                        .verifyError(InvalidWireFrameMarkerException::class.java)
+                        .verifyError(WireFrameException::class.java)
             }
 
             it("should release memory for 1st input") {