From de8938eb8b17912ac03836b86fbab652d2f17a57 Mon Sep 17 00:00:00 2001
From: Lew Gordon <legordon@twilio.com>
Date: Mon, 11 Jul 2022 10:17:22 -0400
Subject: [PATCH] fix(getCanonicalHeaders): ignores undefined header values

It seems like there are certain edge cases that cause header values
to become undefined. In these scenarios we'll hit an exception.
---
 .../src/getCanonicalHeaders.spec.ts           | 19 +++++++++++++++++++
 .../signature-v4/src/getCanonicalHeaders.ts   |  4 ++++
 2 files changed, 23 insertions(+)

diff --git a/packages/signature-v4/src/getCanonicalHeaders.spec.ts b/packages/signature-v4/src/getCanonicalHeaders.spec.ts
index 7eaf540518ad..360950b3085d 100644
--- a/packages/signature-v4/src/getCanonicalHeaders.spec.ts
+++ b/packages/signature-v4/src/getCanonicalHeaders.spec.ts
@@ -1,4 +1,5 @@
 import { HttpRequest } from "@aws-sdk/protocol-http";
+import { HeaderBag } from "@aws-sdk/types";
 
 import { ALWAYS_UNSIGNABLE_HEADERS } from "./constants";
 import { getCanonicalHeaders } from "./getCanonicalHeaders";
@@ -49,6 +50,24 @@ describe("getCanonicalHeaders", () => {
     });
   });
 
+  it("should ignore headers with undefined values", () => {
+    const headers: HeaderBag = {
+      "x-amz-user-agent": "aws-sdk-js-v3",
+      host: "foo.us-east-1.amazonaws.com",
+    };
+
+    (headers.foo as any) = undefined;
+    const request = new HttpRequest({
+      method: "POST",
+      protocol: "https:",
+      path: "/",
+      headers,
+      hostname: "foo.us-east-1.amazonaws.com",
+    });
+
+    expect(getCanonicalHeaders(request)).toEqual(headers);
+  });
+
   it("should allow specifying custom unsignable headers", () => {
     const request = new HttpRequest({
       method: "POST",
diff --git a/packages/signature-v4/src/getCanonicalHeaders.ts b/packages/signature-v4/src/getCanonicalHeaders.ts
index 927d2987c814..66c49fa09366 100644
--- a/packages/signature-v4/src/getCanonicalHeaders.ts
+++ b/packages/signature-v4/src/getCanonicalHeaders.ts
@@ -12,6 +12,10 @@ export const getCanonicalHeaders = (
 ): HeaderBag => {
   const canonical: HeaderBag = {};
   for (const headerName of Object.keys(headers).sort()) {
+    if (!headers[headerName]) {
+      continue;
+    }
+
     const canonicalHeaderName = headerName.toLowerCase();
     if (
       canonicalHeaderName in ALWAYS_UNSIGNABLE_HEADERS ||