Fix hashing step ids in loops (#72)

Per https://github.com/inngest/inngest/blob/main/docs/SDK_SPEC.md#512-ids-and-hashing,
add `:n` starting with `:1` for repeated instances of a step id

Refactored to be a combination of golang and inngest-js implementation to handle edge case of user defined stepId colliding
- https://github.com/inngest/inngestgo/blob/0a00daba0b2db68ff0f080f787cf63f0a63b44d8/internal/sdkrequest/manager.go#L123-L131
- https://github.com/inngest/inngest-js/blob/79069e1a3d700624ce49b323922c113fc952bcc6/packages/inngest/src/components/execution/v1.ts#L819-L831

* Use combination of hash and loop to find next unused stepId

The hash means we don't have to loop from 0 every time and for most
cases will just correctly return us the next unused stepId, but looping
afterwards guarantees we don't collide with a user defined stepId.

So this will be O(1) in most cases and potentially O(n) for pathological
functions that have many steps manually named with the `:n` suffix

* The inngest-js SDK currently optionally warns of parallel indexing, but
this isn't in scope for beta so I left it out.

inngest-spring-boot-demo/src/main/java/com/inngest/springbootdemo/testfunctions/LoopFunction.java

@@ -0,0 +1,45 @@
+package com.inngest.springbootdemo.testfunctions;
+
+import com.inngest.FunctionContext;
+import com.inngest.InngestFunction;
+import com.inngest.InngestFunctionConfigBuilder;
+import com.inngest.Step;
+import org.jetbrains.annotations.NotNull;
+
+public class LoopFunction extends InngestFunction {
+
+    @NotNull
+    @Override
+    public InngestFunctionConfigBuilder config(InngestFunctionConfigBuilder builder) {
+        return builder
+            .id("loop-fn")
+            .name("Loop Function")
+            .triggerEvent("test/loop");
+    }
+
+
+    @Override
+    public Integer execute(FunctionContext ctx, Step step) {
+        int runningCount = 10;
+
+        // explicitly naming a step that the SDK will try to use in the loop shouldn't break the loop
+        int effectivelyFinalVariableForLambda1 = runningCount;
+        runningCount = step.run("add-num:3", () -> effectivelyFinalVariableForLambda1 + 50, Integer.class);
+
+        for (int i = 0; i < 5; i++) {
+            int effectivelyFinalVariableForLambda2 = runningCount;
+            // The actual stepIds used will be add-num, add-num:1, add-num:2, add-num:4, add-num:5
+            runningCount = step.run("add-num", () -> effectivelyFinalVariableForLambda2 + 10, Integer.class);
+        }
+
+        // explicitly reusing step names that the SDK used during the loop should both execute
+        // These will be modified to add-num:4:1 and add-num:4:2 respectively
+        int effectivelyFinalVariableForLambda3 = runningCount;
+        runningCount = step.run("add-num:4", () -> effectivelyFinalVariableForLambda3 + 30, Integer.class);
+        int effectivelyFinalVariableForLambda4 = runningCount;
+        runningCount = step.run("add-num:4", () -> effectivelyFinalVariableForLambda4 + 30, Integer.class);
+
+        return runningCount;
+    }
+}
+

inngest-spring-boot-demo/src/test/java/com/inngest/springbootdemo/DemoTestConfiguration.java

@@ -31,6 +31,7 @@ protected HashMap<String, InngestFunction> functions() {
         addInngestFunction(functions, new Scale2DObjectFunction());
         addInngestFunction(functions, new MultiplyMatrixFunction());
         addInngestFunction(functions, new WithOnFailureFunction());
+        addInngestFunction(functions, new LoopFunction());
 
         return functions;
     }

inngest-spring-boot-demo/src/test/java/com/inngest/springbootdemo/LoopFunctionIntegrationTest.java

@@ -0,0 +1,30 @@
+package com.inngest.springbootdemo;
+
+import com.inngest.Inngest;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.parallel.Execution;
+import org.junit.jupiter.api.parallel.ExecutionMode;
+import org.springframework.beans.factory.annotation.Autowired;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+@IntegrationTest
+@Execution(ExecutionMode.CONCURRENT)
+class LoopFunctionIntegrationTest {
+    @Autowired
+    private DevServerComponent devServer;
+
+    @Autowired
+    private Inngest client;
+
+    @Test
+    void testStepsInLoopExecuteCorrectly() throws Exception {
+        String loopEvent = InngestFunctionTestHelpers.sendEvent(client, "test/loop").getIds()[0];
+        Thread.sleep(2000);
+
+        RunEntry<Object> loopRun = devServer.runsByEvent(loopEvent).first();
+        assertEquals("Completed", loopRun.getStatus());
+
+        assertEquals(170, loopRun.getOutput());
+    }
+}

inngest/src/main/kotlin/com/inngest/State.kt

@@ -9,8 +9,14 @@ class StateNotFound : Throwable("State not found for id")
 class State(
     private val payloadJson: String,
 ) {
+    private val stepIdsToNextStepNumber = mutableMapOf<String, Int>()
+    private val stepIds = mutableSetOf<String>()
+
     fun getHashFromId(id: String): String {
-        val bytes = id.toByteArray(Charsets.UTF_8)
+        val idToHash: String = findNextAvailableStepId(id)
+        stepIds.add(idToHash)
+
+        val bytes = idToHash.toByteArray(Charsets.UTF_8)
         val digest = MessageDigest.getInstance("SHA-1")
         val hashedBytes = digest.digest(bytes)
         val sb = StringBuilder()
@@ -20,6 +26,25 @@ class State(
         return sb.toString()
     }
 
+    private fun findNextAvailableStepId(id: String): String {
+        if (id !in stepIds) {
+            return id
+        }
+
+        // start with the seen count so far for current stepId
+        // but loop over all seen stepIds to make sure a user didn't explicitly define
+        // a step using the same step number
+        var stepNumber = stepIdsToNextStepNumber.getOrDefault(id, 1)
+        while ("$id:$stepNumber" in stepIds) {
+            stepNumber = stepNumber + 1
+        }
+        // now we know stepNumber is unused and can be used for the current stepId
+        // save stepNumber + 1 to the hash for next time
+        stepIdsToNextStepNumber[id] = stepNumber + 1
+
+        return "$id:$stepNumber"
+    }
+
     inline fun <reified T> getState(
         hashedId: String,
         fieldName: String = "data",