fix: ensure response header value is string type (#474)

Author: etamity

__tests__/integration.js

@@ -168,7 +168,7 @@ describe.each(EACH_MATRIX)('%s:%s: integration tests', (eventSourceName, framewo
     const expectedResponse = makeResponse({
       eventSourceName,
       multiValueHeaders: {
-        'content-length': [151],
+        'content-length': ['151'],
         'content-security-policy': ["default-src 'none'"],
         'content-type': ['text/html; charset=utf-8'],
         'x-content-type-options': ['nosniff']
@@ -223,7 +223,7 @@ describe.each(EACH_MATRIX)('%s:%s: integration tests', (eventSourceName, framewo
       multiValueHeaders: {
         'accept-ranges': ['bytes'],
         'cache-control': ['public, max-age=0'],
-        'content-length': [15933],
+        'content-length': ['15933'],
         'content-type': ['image/png']
       },
       isBase64Encoded: true

src/event-sources/utils.js

@@ -59,7 +59,7 @@ function getMultiValueHeaders ({ headers }) {
   const multiValueHeaders = {}
 
   Object.entries(headers).forEach(([headerKey, headerValue]) => {
-    const headerArray = Array.isArray(headerValue) ? headerValue : [headerValue]
+    const headerArray = Array.isArray(headerValue) ? headerValue.map(String) : [String(headerValue)]
 
     multiValueHeaders[headerKey.toLowerCase()] = headerArray
   })