fix(codegen): allow empty string field values for headers

fix(codegen): utilize loose equality for falsy null/undefined

bring isSerializableHeaderValue into smithy-client

Author: siddsriv

.changeset/small-gifts-tease.md

@@ -0,0 +1,5 @@
+---
+"@smithy/smithy-client": patch
+---
+
+serialize empty strings and collections in headers

packages/smithy-client/src/index.ts

@@ -13,6 +13,7 @@ export * from "./exceptions";
 export * from "./extended-encode-uri-component";
 export * from "./get-array-if-single-item";
 export * from "./get-value-from-text-node";
+export * from "./is-serializable-header-value";
 export * from "./lazy-json";
 export * from "./object-mapping";
 export * from "./parse-utils";

packages/smithy-client/src/is-serializable-header-value.spec.ts

@@ -0,0 +1,23 @@
+import { isSerializableHeaderValue } from "./is-serializable-header-value";
+
+describe(isSerializableHeaderValue.name, () => {
+  it("considers empty strings serializable", () => {
+    expect(isSerializableHeaderValue("")).toBe(true);
+  });
+
+  it("considers empty collections serializable", () => {
+    expect(isSerializableHeaderValue(new Set())).toBe(true);
+    expect(isSerializableHeaderValue([])).toBe(true);
+  });
+
+  it("considers most falsy data values to be serializable", () => {
+    expect(isSerializableHeaderValue(false)).toBe(true);
+    expect(isSerializableHeaderValue(0)).toBe(true);
+    expect(isSerializableHeaderValue(new Date(0))).toBe(true);
+  });
+
+  it("considered undefined and null to be unserializable", () => {
+    expect(isSerializableHeaderValue(undefined)).toBe(false);
+    expect(isSerializableHeaderValue(null)).toBe(false);
+  });
+});

packages/smithy-client/src/is-serializable-header-value.ts

@@ -0,0 +1,7 @@
+/**
+ * @internal
+ * @returns whether the header value is serializable.
+ */
+export const isSerializableHeaderValue = (value: any) => {
+  return value != null;
+};