if generated, ETags now use a random value to keep clean cache states

Author: jkyberneees

README.md

@@ -84,7 +84,7 @@ When using the Cache-Control header, you can omit the custom `x-cache-timeout` h
 #### Direct usage: 
 ```js 
 res.setHeader('cache-control', 'private, no-cache, max-age=300')
-res.setHeader('etag', '1')
+res.setHeader('etag', 'cvbonrw6g00')
 
 res.end('5 minutes cacheable content here....')
 ```
@@ -97,7 +97,7 @@ res.setHeader('x-cache-timeout', '5 minutes')
 The middleware will now transparently generate default `Cache-Control` and `ETag` headers as described below:
 ```js 
 res.setHeader('cache-control', 'private, no-cache, max-age=300')
-res.setHeader('etag', '1')
+res.setHeader('etag', 'ao8onrw6gbt') // random ETag value 
 ```
 This will enable browser clients to keep a copy of the cache on their side, but still being forced to validate 
 the cache state on the server before using the cached response, therefore supporting gateway based cache invalidation. 

index.js

@@ -84,7 +84,7 @@ const middleware = (opts) => async (req, res, next) => {
       }
       // setting ETag if absent
       if (!payload.headers[CACHE_ETAG]) {
-        payload.headers[CACHE_ETAG] = '1'
+        payload.headers[CACHE_ETAG] = Math.random().toString(36).substring(2, 16)
       }
 
       // cache response