added support for purging multiple pages with the same cache key

Purging multiple cache entries due to the "Vary" request header
fails if not specifying the exact same headers in the purge request.

This addition supports purging multiple cache entries by adding a "$"
at the end of the cache key specified with the purge request.

Author: virtion

README.md

@@ -114,6 +114,27 @@ The asterisk must be the last character of the key, so you **must** put the $uri
 
 
 
+Purging multiple cache entries with the same cache key
+======================================================
+Caching requests that use the "Vary" header may result in multiple cache
+entries with the same cache key. For example, when using the request header
+"Vary: Accept-Encoding", a separate cache entry (with different file hash)
+will be stored for each content encoding (like compressed or uncompressed),
+but they will all have the exact same cache key.
+
+Trying to purge such cached content will fail unless both the "Vary" header
+is specified in the purge request, plus all headers as listed in the "Vary"
+header, with the exact same values as used when the request was cached.
+
+To be able to purge *all* pages with the same cache key, specify the key with
+a "$" at the end, like this:
+
+    curl -X PURGE /page$
+
+This will purge all content with the exact key "/page" from the cache.
+
+
+
 Sample configuration (same location syntax)
 ===========================================
     http {

ngx_cache_purge_module.c

@@ -1807,8 +1807,16 @@ ngx_http_cache_purge_partial(ngx_http_request_t *r, ngx_http_file_cache_t *cache
     len = key[0].len;
 
     /* Only check the first key */
-    key_partial = ngx_pcalloc(r->pool, sizeof(u_char) * len);
-    ngx_memcpy(key_partial, key[0].data, sizeof(u_char) * (len - 1));
+    if (key[0].data[key[0].len - 1] == '$') {
+        /* Check key for exact match (key terminated by newline) */
+        key_partial = ngx_pcalloc(r->pool, sizeof(u_char) * (len + 1));
+        ngx_memcpy(key_partial, key[0].data, sizeof(u_char) * (len - 1));
+        key_partial[len - 1] = '\n';
+    } else {
+        /* Check key for prefix match */
+        key_partial = ngx_pcalloc(r->pool, sizeof(u_char) * len);
+        ngx_memcpy(key_partial, key[0].data, sizeof(u_char) * (len - 1));
+    }
 
     /* Walk the tree and remove all the files matching key_partial */
     ngx_tree_ctx_t  tree;
@@ -1833,7 +1841,8 @@ ngx_http_cache_purge_is_partial(ngx_http_request_t *r) {
     key = c->keys.elts;
 
     /* Only check the first key */
-    return key[0].data[key[0].len - 1] == '*';
+    return (key[0].data[key[0].len - 1] == '*' ||
+            key[0].data[key[0].len - 1] == '$');
 }
 
 char *