Reactive Publisher to Monix extensions for typed Mongo

mongo/jvm/src/main/scala/com/avsystem/commons/mongo/reactive/ReactiveMongoExtensions.scala

@@ -0,0 +1,31 @@
+package com.avsystem.commons
+package mongo.reactive
+
+import monix.eval.Task
+import monix.reactive.Observable
+import org.reactivestreams.Publisher
+
+trait ReactiveMongoExtensions {
+  import ReactiveMongoExtensions._
+
+  implicit final def publisherOps[T](publisher: Publisher[T]): PublisherOps[T] = new PublisherOps(publisher)
+}
+object ReactiveMongoExtensions extends ReactiveMongoExtensions {
+  /**
+    * Extensions for converting [[Publisher]] to [[Task]]/[[Observable]] Monix types
+    */
+  final class PublisherOps[T](private val publisher: Publisher[T]) extends AnyVal {
+    def asMonix: Observable[T] = Observable.fromReactivePublisher(publisher)
+
+    // prefer using the family of methods below for observables which are intended to only return a single document,
+    // mongo observable implementation sometimes logs an error on server-closed cursors
+    private def singleObservable: Task[Option[T]] = Task.fromReactivePublisher(publisher)
+
+    // handles both an empty Publisher and and a single null item
+    def headOptionL: Task[Option[T]] = singleObservable.map(_.filterNot(_ == null))
+    def headOptL: Task[Opt[T]] = headOptionL.map(_.toOpt)
+    // can return null if Mongo driver for some reason returns null, intentionally don't want to report failure
+    def headL: Task[T] = singleObservable.map(_.get)
+    def completedL: Task[Unit] = headOptionL.void
+  }
+}

mongo/jvm/src/main/scala/com/avsystem/commons/mongo/typed/TypedMongoCollection.scala

@@ -91,7 +91,7 @@ class TypedMongoCollection[E <: BaseMongoEntity] private(
     * to be used for database operations not covered directly by [[TypedMongoCollection]].
     */
   def multiResultNativeOp[T](operation: MongoCollection[E] => Publisher[T]): Observable[T] =
-    Observable.fromReactivePublisher(operation(nativeCollection))
+    multi(operation(nativeCollection))
 
   def drop(): Task[Unit] =
     empty(optionalizeFirstArg(nativeCollection.drop(sessionOrNull)))
@@ -155,7 +155,7 @@ class TypedMongoCollection[E <: BaseMongoEntity] private(
     }
 
     def toObservable[X](publisher: FindPublisher[X]): Observable[X] =
-      Observable.fromReactivePublisher(setupPublisher(publisher))
+      multi(setupPublisher(publisher))
 
     projection match {
       case SelfRef =>
@@ -242,15 +242,14 @@ class TypedMongoCollection[E <: BaseMongoEntity] private(
     filter: MongoDocumentFilter[E] = MongoFilter.empty,
     setupOptions: DistinctPublisher[Any] => DistinctPublisher[Any] = identity,
   ): Observable[T] = {
-
     val publisher =
       optionalizeFirstArg(nativeCollection.distinct(sessionOrNull, property.rawPath, classOf[BsonValue]))
         .filter(filter.toFilterBson(Opt.Empty, property.projectionRefs))
 
     val publisherWithOptions =
       setupOptions(publisher.asInstanceOf[DistinctPublisher[Any]]).asInstanceOf[DistinctPublisher[BsonValue]]
 
-    Observable.fromReactivePublisher(publisherWithOptions).map(property.format.readBson)
+    multi(publisherWithOptions).map(property.format.readBson)
   }
 
   def insertOne(

mongo/jvm/src/main/scala/com/avsystem/commons/mongo/typed/TypedMongoUtils.scala

@@ -7,18 +7,13 @@ import monix.reactive.Observable
 import org.reactivestreams.Publisher
 
 trait TypedMongoUtils {
-  protected final def empty(publisher: Publisher[Void]): Task[Unit] =
-    Observable.fromReactivePublisher(publisher, 1).completedL
-
-  protected final def single[T](publisher: Publisher[T]): Task[T] =
-    Observable.fromReactivePublisher(publisher, 1).firstL
+  import com.avsystem.commons.mongo.reactive.ReactiveMongoExtensions._
 
+  protected final def empty(publisher: Publisher[Void]): Task[Unit] = publisher.completedL
+  protected final def single[T](publisher: Publisher[T]): Task[T] = publisher.headL
   // handles both an empty Publisher and and a single null item
-  protected final def singleOpt[T](publisher: Publisher[T]): Task[Option[T]] =
-    Observable.fromReactivePublisher(publisher, 1).filter(_ != null).firstOptionL
-
-  protected final def multi[T](publisher: Publisher[T]): Observable[T] =
-    Observable.fromReactivePublisher(publisher)
+  protected final def singleOpt[T](publisher: Publisher[T]): Task[Option[T]] = publisher.headOptionL
+  protected final def multi[T](publisher: Publisher[T]): Observable[T] = publisher.asMonix
 
   /**
     * Transforms an expression `method(nullableArg, moreArgs)` into