mikolak-net / Travesty
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= Travesty :repoBaseUrl: https://github.com/mikolak-net/travesty :fileBrowseBaseUrl: {repoBaseUrl}/blob/master/ :issueBaseUrl: {repoBaseUrl}/issues/ :toc: :icons: font
image:https://travis-ci.org/mikolak-net/travesty.svg?branch=master["Build Status", link="https://travis-ci.org/mikolak-net/travesty"] image:https://maven-badges.herokuapp.com/maven-central/net.mikolak/travesty_2.12/badge.svg["Latest 2.12 version", link="https://maven-badges.herokuapp.com/maven-central/net.mikolak/travesty_2.12"]
== What is it?
Travesty is a utility library for Akka Streams. It has two uses:
- generating structural diagrams of your Akka Streams, both as graphics and text (the latter useful for logging). Example:
image::doc/example_graph.svg[]
- generating https://tinkerpop.apache.org/[Tinkerpop 3 / Gremlin^] graph data structures - usable for e.g. writing tests that check stage sequencing in dynamically constructed Streams.
== What's new?
=== 0.9.1
- Fixed issue with graph not generating when some of the stages have no names (thanks to @FXHibon for the fix).
=== 0.9
- Added support for partial graphs (see below for example),
- Added support for Akka 2.5.10-11.
=== 0.8
- Added "manual support" for typed diagrams/graphs (see link:#typed-diagrams[Typed diagrams]),
- made Graphviz engine selection configurable for better speed/compatibility ({issueBaseUrl}3[#3^]),
- fixed {issueBaseUrl}4[#4^],
- extended Akka version support up to 2.5.9 .
== How to use it
=== Include in your project
Add to your build.sbt
[source,scala]
//repo of dependency used for text rendering resolvers += "indvd00m-github-repo" at "https://raw.githubusercontent.com/indvd00m/maven-repo/master/repository"
"net.mikolak" %% "travesty" % "0.9_AKKAVERSION" //for example "net.mikolak" %% "travesty" % "0.9_2.5.11"
Where AKKAVERSION is the version of Akka (Streams) you're using in your project. Currently supported
are versions 2.5.[4-11], and Scala 2.12.
You can review all available versions on link:http://search.maven.org/#search%7Cgav%7C1%7Cg%3A%22net.mikolak%22%20AND%20a%3A%22travesty_2.12%22[Maven Central^].
=== Diagram generation
[source,scala]
import net.mikolak.travesty import net.mikolak.travesty.OutputFormat
val graph = ??? //your graph here
//render as image to file, PNG is supported as well travesty.toFile(graph, OutputFormat.SVG)("/tmp/stream.svg")
//render as text "image" log.info(travesty.toString(graph)) //take care NOT to wrap the text
==== Example text output
Here's how a typical travesty.toString(graph) may look like:
[source]
********* *******
**** **** ** **
* *
*INLET* * seqSink *
* *
**** **** ●●● ** **
********* ●●● ●● ●● *******
●●●●● ●● ●●
●●●●●● ● ●●●●● ●
●●●●● ********* ********* ●●●●●
●●●● **** **** *** *** ●●●
* * ●● * *
ZipWith2 ●●●●●●●●● ●● * broadcast *
* * ●● * *
**** **** ● *** ***
●●●● ********* ********* ●●
●●●●●●●●●● ●●●● ●
●●●● ● ●●●●● ●●
************* ●● ●●●●●● *************
******************* ●● ******* *******
** ** * *
singleSource * *OUTLET* *
** ** * *
******************* ******* *******
************* *************
Flow[String,String,akka.NotUsed]
And here's the same example in a vertical orientation, i.e. travesty.toString(graph, direction = BottomToTop):
[source]
************* *********
******************* **** ****
** ** * *
singleSource *INLET*
** ** * *
******************* **** ****
************* *********
● ●
● ●
● ●
● ●
● ●
● ●
● ●
● ●
● ●
● ● ● ●
●● ● ●
● ● ● ●●
●●● ●●●
● ●
*********
**** ****
* *
ZipWith2
* *
**** ****
*********
●
●
●
●
●
●
●
●
●
●● ●
● ●
●●
●
*********
*** ***
* *
* broadcast *
* *
*** ***
*********
● ●
● ●
● ●
● ●
● ●
● ●
● ●
● ●
● ●
●● ●●
● ● ● ●
●●● ●●●
● ●
************* *******
******* ******* ** **
* *OUTLET* * seqSink
* * * *
* *
******* ******* ** **
************* *******
Flow[String,String,akka.NotUsed]
=== Naming stages
Travesty uses the name attribute, which all graph stages have, to label the nodes of the graphs. This means you can
easily override the naming by invoking .named on the relevant stage.
This example:
[source,scala]
Source.single("t").named("beginning") <1> .map(_ + "a") .to(Sink.ignore.named("end")) <2>
<1> custom name <2> another custom name
will render as:
image::doc/example_named.svg[]
Alternatively, if you're making a one-shot sketch, you can render the image as an SVG, and edit the names as text in any SVG editor such as Inkscape.
=== Partial graphs
Travesty now supports Akka Stream graphs with any shape.
For example, this:
[source,scala]
Flow[String].map(_ + "a").to(Sink.ignore)
will render as:
image::doc/example_partial_graph.svg[]
The labels for open inlets and outlets are configurable via the partial-names section of the config:
[source,hocon]
travesty.partial-names { inlet = "INLET" outlet = "OUTLET" }
=== Typed diagrams
Currently, it works like this:
[source,scala]
import net.mikolak.travesty import net.mikolak.travesty.OutputFormat import registry._ //adds special .↓ and .register methods to stages
val graph = Source.single("1").↓.via(Flow[String].map(_.toInt).↓).to(Sink.seq)
//render as image to file, PNG is supported as well travesty.toFile(graph, OutputFormat.SVG)("/tmp/stream.svg")
image::doc/example_typed_graph.svg[]
register, aliased to ↓, is a special pass-through extension method that allows Travesty to recognize the types going through your stream. Append .register/.↓ to every stage you need type labels for.
Automatic support is coming, but unfortunately is a non-trivial problem to solve. For more details, see issue {issueBaseUrl}1[#1^].
=== Graph testing
[source,scala]
import net.mikolak.travesty import gremlin.scala._ //traversal operations
val graph = ??? //your graph here
val tested = travesty.toAbstractGraph(graph)
//checks whether the only path through the stream has length two tested.E().simplePath().toList() must have size 2
For more examples, see e.g. link:blob/master/src/test/scala/net/mikolak/travesty/TravestyToGraphSpec.scala[TravestyToGraphSpec^].
For general examples of what you can do with Gremlin in Scala, see the appropriately named https://github.com/mpollmeier/gremlin-scala[gremlin-scala project^].
=== Advanced usage
For further tweaking the rendering, you can use LowLevelApi:
[source,scala]
val vizGraph = LowLevelApi.toVizGraph(travesty.toAbstractGraph(graph))
//use the instance to change splines, node shapes, etc. etc.
//and finally, use the Java API to render vizGraph.render(Format.PNG)
== How does it work?
Generally, creating a graph of an Akka Stream is hard. This is because it's difficult to "get to" the internals of a Stream and infer its structure. There definitely is no easy solution.
Travesty "cheats" by using https://github.com/akka/akka/blob/master/akka-stream/src/main/scala/akka/stream/impl/TraversalBuilder.scala[the internal Traversal API^]. The Traversal is a stack-like structure containing instructions on how to construct a running Stream.
This stack is parsed and converted into a Gremlin graph, convenient for annotating, pre-processing (e.g. additional decoration of Sources and Sinks), and testing.
The Gremlin graph is converted into a https://graphviz.gitlab.io/[Graphviz^] graph, using https://github.com/nidi3/graphviz-java[graphviz-java^].
Finally, the Graphviz graph is rendered into the required output format.
== Caveats
=== No materialization annotations (for now)
Completely doable, but not present in the current version. Track {issueBaseUrl}2[#2^] to be notified when this gets added.
=== Represents the graph "blueprint", not running stream
The graph/diagram generated from the Traversal object does not correspond 1:1 to what will be present in the running Stream. There are at least two reasons for this:
- the default materializer uses https://doc.akka.io/docs/akka/current/stream/stream-flows-and-basics.html?language=scala#operator-fusion[fusing^] to join stages that can be processed synchronously;
- there can be other optimizations used by the materializer, such as ignoring stages, adding new stages, etc. Currently, the most prominent are the "virtual"
Sinkstages that can appear in some scenarios.
=== Slooooow
graphviz-java provides several implementations of Graphviz to use. However, the one selected as default
by travesty, for maximum portability, is also the slowest one. While generating the graph is always fast,
rendering the diagram may take up to ~10 seconds.
If you would like to try switching to a faster engine, see {fileBrowseBaseUrl}src/main/resources/reference.conf[reference.conf] for more info.
=== Tight coupling with Akka Stream's internals
As mentioned before, travesty uses the internal API for graph/diagram generation. This is why the
version number follows Akka's versioning scheme.