add smithy-go container LRU impl and debounce returns in v2 endpoint …

…resolution (#443)

.changelog/d2db122d1fda4d9e85a8f482949f7e3e.json

@@ -0,0 +1,8 @@
+{
+    "id": "d2db122d-1fda-4d9e-85a8-f482949f7e3e",
+    "type": "bugfix",
+    "description": "Prevent duplicated error returns in EndpointResolverV2 default implementation.",
+    "modules": [
+        "."
+    ]
+}

codegen/smithy-go-codegen/src/main/java/software/amazon/smithy/go/codegen/ServiceGenerator.java

@@ -122,7 +122,11 @@ private void writeConfigFieldResolvers(
                         writer.writeInline(", opID");
                     }
                     if (resolver.isWithClientInput()) {
-                        writer.writeInline(", *c");
+                        if (resolver.getLocation() == ConfigFieldResolver.Location.CLIENT) {
+                            writer.writeInline(", client");
+                        } else {
+                            writer.writeInline(", *c");
+                        }
                     }
                     writer.write(")");
                     writer.write("");
@@ -153,17 +157,17 @@ private void generateConstructor(Symbol serviceSymbol) {
                     writer.openBlock("for _, fn := range optFns {", "}", () -> writer.write("fn(&options)"));
                     writer.write("");
 
+                    writer.openBlock("client := &$T{", "}", serviceSymbol, () -> {
+                        writer.write("options: options,");
+                    }).write("");
+
                     // Run any config finalization functions registered by runtime plugins.
                     for (RuntimeClientPlugin plugin : plugins) {
                         writeConfigFieldResolvers(writer, plugin, resolver ->
                                 resolver.getLocation() == ConfigFieldResolver.Location.CLIENT
                                         && resolver.getTarget() == ConfigFieldResolver.Target.FINALIZATION);
                     }
 
-                    writer.openBlock("client := &$T{", "}", serviceSymbol, () -> {
-                        writer.write("options: options,");
-                    }).write("");
-
                     // Run any client member resolver functions registered by runtime plugins.
                     for (RuntimeClientPlugin plugin : plugins) {
                         writeClientMemberResolvers(writer, plugin, resolver -> true);

codegen/smithy-go-codegen/src/main/java/software/amazon/smithy/go/codegen/endpoints/EndpointResolverGenerator.java

@@ -225,21 +225,17 @@ private GoWriter.Writable generateRulesList(List<Rule> rules, Scope scope) {
             });
 
             if (!rules.isEmpty() && !(rules.get(rules.size() - 1).getConditions().isEmpty())) {
-                // the rules tree can be constructed in a manner that tricks us
-                // into writing this twice consecutively (we write it, return
-                // to the outer generateRulesList call, and write it again
-                // without having closed the outer parentheses
-                //
-                // ensure we write only once to avoid unreachable code, but
-                // this should most likely be handled/fixed elsewhere
+                // FIXME: there's currently a bug in traversal that sometimes causes subsequent returns to be generated
+                // which fails vet. Patch over it via debounce for now
                 ensureFinalTreeRuleError(w);
             }
         };
     }
 
     private void ensureFinalTreeRuleError(GoWriter w) {
-        final String expected = "return endpoint, fmt.Errorf(\"" + ERROR_MESSAGE_ENDOFTREE + "\")";
-        if (!w.toString().trim().endsWith(expected)) {
+        final String[] lines = w.toString().split("\n");
+        final String lastLine = lines[lines.length - 1];
+        if (!lastLine.trim().startsWith("return")) {
             w.writeGoTemplate(
                 "return endpoint, $fmtErrorf:T(\"" + ERROR_MESSAGE_ENDOFTREE + "\")",
                 commonCodegenArgs

codegen/smithy-go-codegen/src/main/java/software/amazon/smithy/go/codegen/integration/ConfigFieldResolver.java

@@ -61,7 +61,7 @@ public boolean isWithOperationName() {
     }
 
     public boolean isWithClientInput() {
-        return withClientInput && location == Location.OPERATION;
+        return withClientInput;
     }
 
     public static Builder builder() {

container/private/cache/cache.go

@@ -0,0 +1,19 @@
+// Package cache defines the interface for a key-based data store.
+//
+// This package is designated as private and is intended for use only by the
+// smithy client runtime. The exported API therein is not considered stable and
+// is subject to breaking changes without notice.
+package cache
+
+// Cache defines the interface for an opaquely-typed, key-based data store.
+//
+// The thread-safety of this interface is undefined and is dictated by
+// implementations.
+type Cache interface {
+	// Retrieve the value associated with the given key. The returned boolean
+	// indicates whether the cache held a value for the given key.
+	Get(k interface{}) (interface{}, bool)
+
+	// Store a value under the given key.
+	Put(k interface{}, v interface{})
+}

container/private/cache/lru/lru.go

@@ -0,0 +1,63 @@
+// Package lru implements [cache.Cache] with an LRU eviction policy.
+//
+// This implementation is NOT thread-safe.
+//
+// This package is designated as private and is intended for use only by the
+// smithy client runtime. The exported API therein is not considered stable and
+// is subject to breaking changes without notice.
+package lru
+
+import (
+	"container/list"
+
+	"github.com/aws/smithy-go/container/private/cache"
+)
+
+// New creates a new LRU cache with the given capacity.
+func New(cap int) cache.Cache {
+	return &lru{
+		entries: make(map[interface{}]*list.Element, cap),
+		cap:     cap,
+		mru:     list.New(),
+	}
+}
+
+type lru struct {
+	entries map[interface{}]*list.Element
+	cap     int
+
+	mru *list.List // least-recently used is at the back
+}
+
+type element struct {
+	key   interface{}
+	value interface{}
+}
+
+func (l *lru) Get(k interface{}) (interface{}, bool) {
+	e, ok := l.entries[k]
+	if !ok {
+		return nil, false
+	}
+
+	l.mru.MoveToFront(e)
+	return e.Value.(*element).value, true
+}
+
+func (l *lru) Put(k interface{}, v interface{}) {
+	if len(l.entries) == l.cap {
+		l.evict()
+	}
+
+	ev := &element{
+		key:   k,
+		value: v,
+	}
+	e := l.mru.PushFront(ev)
+	l.entries[k] = e
+}
+
+func (l *lru) evict() {
+	e := l.mru.Remove(l.mru.Back())
+	delete(l.entries, e.(*element).key)
+}

container/private/cache/lru/lru_test.go

@@ -0,0 +1,69 @@
+package lru
+
+import "testing"
+
+func TestCache(t *testing.T) {
+	cache := New(4).(*lru)
+
+	// fill cache
+	cache.Put(1, 2)
+	cache.Put(2, 3)
+	cache.Put(3, 4)
+	cache.Put(4, 5)
+	assertEntry(t, cache, 1, 2)
+	assertEntry(t, cache, 2, 3)
+	assertEntry(t, cache, 3, 4)
+	assertEntry(t, cache, 4, 5)
+
+	// touch the last entry
+	cache.Get(1)
+	cache.Put(5, 6)
+	assertNoEntry(t, cache, 2)
+	assertEntry(t, cache, 3, 4)
+	assertEntry(t, cache, 4, 5)
+	assertEntry(t, cache, 1, 2)
+	assertEntry(t, cache, 5, 6)
+
+	// put something new, 3 should now be the oldest
+	cache.Put(6, 7)
+	assertNoEntry(t, cache, 3)
+	assertEntry(t, cache, 4, 5)
+	assertEntry(t, cache, 1, 2)
+	assertEntry(t, cache, 5, 6)
+	assertEntry(t, cache, 6, 7)
+
+	// touch something in the middle
+	cache.Get(5)
+	assertEntry(t, cache, 4, 5)
+	assertEntry(t, cache, 1, 2)
+	assertEntry(t, cache, 5, 6)
+	assertEntry(t, cache, 6, 7)
+
+	// put 3 new things, 5 should remain after the touch
+	cache.Put(7, 8)
+	cache.Put(8, 9)
+	cache.Put(9, 0)
+	assertNoEntry(t, cache, 4)
+	assertNoEntry(t, cache, 1)
+	assertNoEntry(t, cache, 6)
+	assertEntry(t, cache, 5, 6)
+	assertEntry(t, cache, 7, 8)
+	assertEntry(t, cache, 8, 9)
+	assertEntry(t, cache, 9, 0)
+}
+
+func assertEntry(t *testing.T, c *lru, k interface{}, v interface{}) {
+	e, ok := c.entries[k]
+	if !ok {
+		t.Errorf("expected entry %v=%v, but no entry found", k, v)
+	}
+	if actual := e.Value.(*element).value; actual != v {
+		t.Errorf("expected entry %v=%v, but got entry value %v", k, v, actual)
+	}
+}
+
+func assertNoEntry(t *testing.T, c *lru, k interface{}) {
+	if _, ok := c.Get(k); ok {
+		t.Errorf("expected no entry for %v, but one was found", k)
+	}
+}