From 1eb25f236f449ada23a868422f44693a6ef84f7f Mon Sep 17 00:00:00 2001
From: Keenan Brock <keenan@thebrocks.net>
Date: Fri, 6 Oct 2023 14:42:32 -0400
Subject: [PATCH] Abort if StartAt or next_state is not valid

I was running a workflow with an invalid StartAt
This caused a strange error

before
------

```
lib/floe/workflow.rb:76:in `step_nonblock': undefined method `run_nonblock!' for nil:NilClass (NoMethodError)

      current_state.run_nonblock!
                   ^^^^^^^^^^^^^^
	from lib/floe/workflow.rb:63:in `step'
	from lib/floe/workflow.rb:58:in `run!'
	from exe/floe:37:in `<top (required)>'
```

after
-----

```
{"Error"=>"States.Runtime", "Cause"=>"State \"FirstState\" does not exist"}
```
---
 lib/floe/workflow.rb  | 18 ++++++++++++++++--
 spec/workflow_spec.rb | 20 ++++++++++++++++++++
 2 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/lib/floe/workflow.rb b/lib/floe/workflow.rb
index 5f288f31..9fa6c791 100644
--- a/lib/floe/workflow.rb
+++ b/lib/floe/workflow.rb
@@ -71,8 +71,8 @@ def run_nonblock
 
     def step_nonblock
       return Errno::EPERM if end?
+      return 0 unless step_next
 
-      step_next
       current_state.run_nonblock!
     end
 
@@ -103,7 +103,21 @@ def current_state
     private
 
     def step_next
-      context.state = {"Name" => context.next_state, "Input" => context.output} if context.next_state
+      desired_state = context.next_state || context.state_name
+      if !@states_by_name.key?(desired_state)
+        context.state["Error"] = "States.Runtime"
+        context.state["Cause"] = "State \"#{desired_state}\" does not exist"
+        context.output = {"Error" => context.state["Error"], "Cause" => context.state["Cause"]}
+        context.execution["StartTime"] ||= Time.now.utc
+        context.execution["EndTime"] = Time.now.utc.iso8601
+        return false
+      end
+
+      if context.next_state
+        context.state = {"Name" => context.next_state, "Input" => context.output}
+      end
+
+      true
     end
   end
 end
diff --git a/spec/workflow_spec.rb b/spec/workflow_spec.rb
index 8eb854c7..2f6fa7d2 100644
--- a/spec/workflow_spec.rb
+++ b/spec/workflow_spec.rb
@@ -93,6 +93,26 @@
       expect(ctx.running?).to eq(true)
       expect(ctx.ended?).to   eq(false)
     end
+
+    it "detects invalid StartAt" do
+      workflow = Floe::Workflow.new({"StartAt" => "Bogus", "States" => {"FirstState" => {"Type" => "Succeed"}}}, ctx, {})
+
+      workflow.run_nonblock
+
+      expect(ctx.running?).to eq(false)
+      expect(ctx.ended?).to   eq(true)
+      expect(ctx.status).to eq("failure")
+    end
+
+    it "detects invalid Next" do
+      workflow = Floe::Workflow.new({"StartAt" => "FirstState", "States" => {"FirstState" => {"Type" => "Pass", "Next" => "Bogus"}}}, ctx, {})
+
+      workflow.run_nonblock
+
+      expect(ctx.running?).to eq(false)
+      expect(ctx.ended?).to   eq(true)
+      expect(ctx.status).to eq("failure")
+    end
   end
 
   describe "#step" do