fix: AWS ApiGW v1 (REST) converter incorrectly parses all query parameters as arrays

.changeset/vast-paws-attack.md

@@ -0,0 +1,5 @@
+---
+"@opennextjs/aws": patch
+---
+
+fix: AWS ApiGW v1 (REST) converter incorrectly parses all query parameters as arrays

packages/open-next/src/overrides/converters/aws-apigw-v1.ts

@@ -53,6 +53,24 @@ function normalizeAPIGatewayProxyEventQueryParams(
   return value ? `?${value}` : "";
 }
 
+function normalizeAPIGatewayProxyEventMultiValueQueryStringParameters(
+  event: APIGatewayProxyEvent,
+): Record<string, string[] | string> {
+  const params: Record<string, string | string[]> = {};
+  for (const [key, value] of Object.entries(
+    event.multiValueQueryStringParameters || {},
+  )) {
+    if (value !== undefined && Array.isArray(value)) {
+      if (value.length === 1) {
+        params[key] = value[0];
+      } else {
+        params[key] = value;
+      }
+    }
+  }
+  return params;
+}
+
 async function convertFromAPIGatewayProxyEvent(
   event: APIGatewayProxyEvent,
 ): Promise<InternalEvent> {
@@ -67,7 +85,7 @@ async function convertFromAPIGatewayProxyEvent(
     headers,
     remoteAddress: requestContext.identity.sourceIp,
     query: removeUndefinedFromQuery(
-      event.multiValueQueryStringParameters ?? {},
+      normalizeAPIGatewayProxyEventMultiValueQueryStringParameters(event),
     ),
     cookies:
       event.multiValueHeaders?.cookie?.reduce(

packages/tests-unit/tests/converters/aws-apigw-v1.test.ts

@@ -137,7 +137,7 @@ describe("convertFrom", () => {
     });
   });
 
-  it("Should handle queryStringParameters and multiValueQueryStringParameters", async () => {
+  it("Should handle queryStringParameters and multiValueQueryStringParameters for single value parameters", async () => {
     const event: APIGatewayProxyEvent = {
       body: JSON.stringify({ message: "Hello, world!" }),
       headers: {},
@@ -172,7 +172,48 @@ describe("convertFrom", () => {
       headers: {},
       remoteAddress: "::1",
       query: {
-        test: ["test"],
+        test: "test",
+      },
+      cookies: {},
+    });
+  });
+
+  it("Should handle queryStringParameters and multiValueQueryStringParameters for multi value parameters", async () => {
+    const event: APIGatewayProxyEvent = {
+      body: JSON.stringify({ message: "Hello, world!" }),
+      headers: {},
+      multiValueHeaders: {},
+      httpMethod: "POST",
+      isBase64Encoded: false,
+      path: "/",
+      pathParameters: null,
+      queryStringParameters: {
+        test: "testB",
+      },
+      multiValueQueryStringParameters: {
+        test: ["testA", "testB"],
+      },
+      stageVariables: null,
+      requestContext: {
+        identity: {
+          sourceIp: "::1",
+        },
+      } as any,
+      resource: "",
+    };
+
+    const response = await converter.convertFrom(event);
+
+    expect(response).toEqual({
+      type: "core",
+      method: "POST",
+      rawPath: "/",
+      url: "https://on/?test=testA&test=testB",
+      body: Buffer.from('{"message":"Hello, world!"}'),
+      headers: {},
+      remoteAddress: "::1",
+      query: {
+        test: ["testA", "testB"],
       },
       cookies: {},
     });