http, utility: Allow to optionally decode the parsed param value when parsing query string

source/common/http/utility.cc

@@ -264,15 +264,18 @@ std::string Utility::createSslRedirectPath(const RequestHeaderMap& headers) {
   return fmt::format("https://{}{}", headers.getHostValue(), headers.getPathValue());
 }
 
-Utility::QueryParams Utility::parseQueryString(absl::string_view url) {
+Utility::QueryParams Utility::parseQueryString(absl::string_view url, bool do_percent_decoding) {
   size_t start = url.find('?');
   if (start == std::string::npos) {
     QueryParams params;
     return params;
   }
 
   start++;
-  return parseParameters(url, start);
+  return do_percent_decoding
+             ? parseParameters(PercentEncoding::decode(StringUtil::subspan(url, start, url.size())),
+                               0)
+             : parseParameters(url, start);
 }
 
 Utility::QueryParams Utility::parseFromBody(absl::string_view body) {

source/common/http/utility.h

@@ -189,9 +189,11 @@ std::string createSslRedirectPath(const RequestHeaderMap& headers);
 /**
  * Parse a URL into query parameters.
  * @param url supplies the url to parse.
+ * @param do_percent_decoding supplies the flag to do percent decoding to the query parameters.
+ *        It defaults to false.
  * @return QueryParams the parsed parameters, if any.
  */
-QueryParams parseQueryString(absl::string_view url);
+QueryParams parseQueryString(absl::string_view url, bool do_percent_decoding = false);
 
 /**
  * Parse a a request body into query parameters.

source/server/admin/stats_handler.cc

@@ -140,7 +140,8 @@ Http::Code StatsHandler::handlerStats(absl::string_view url,
 Http::Code StatsHandler::handlerPrometheusStats(absl::string_view path_and_query,
                                                 Http::ResponseHeaderMap&,
                                                 Buffer::Instance& response, AdminStream&) {
-  const Http::Utility::QueryParams params = Http::Utility::parseQueryString(path_and_query);
+  const Http::Utility::QueryParams params =
+      Http::Utility::parseQueryString(path_and_query, /*do_percent_decoding=*/true);
   const bool used_only = params.find("usedonly") != params.end();
   absl::optional<std::regex> regex;
   if (!Utility::filterParam(params, response, regex)) {

test/common/http/utility_test.cc

@@ -38,6 +38,16 @@ TEST(HttpUtility, parseQueryString) {
             Utility::parseQueryString("/hello?hello=&hello2=world2"));
   EXPECT_EQ(Utility::QueryParams({{"name", "admin"}, {"level", "trace"}}),
             Utility::parseQueryString("/logging?name=admin&level=trace"));
+  // A sample of an encoded query string of a request by prometheus:
+  // https://github.com/envoyproxy/envoy/issues/10926#issuecomment-651085261.
+  EXPECT_EQ(
+      Utility::QueryParams(
+          {{"filter", "(cluster.upstream_(rq_total|rq_time_sum|rq_time_count|rq_time_bucket|rq_xx|"
+                      "rq_complete|rq_active|cx_active))|(server.version)"}}),
+      Utility::parseQueryString(
+          "/stats?filter=%28cluster.upstream_%28rq_total%7Crq_time_sum%7Crq_time_count%7Crq_time_"
+          "bucket%7Crq_xx%7Crq_complete%7Crq_active%7Ccx_active%29%29%7C%28server.version%29",
+          /*do_percent_decoding=*/true));
 }
 
 TEST(HttpUtility, getResponseStatus) {
@@ -1188,7 +1198,18 @@ TEST(PercentEncoding, EncodeDecode) {
   validatePercentEncodingEncodeDecode("_-ok-_", "_-ok-_");
 }
 
-TEST(PercentEncoding, Trailing) {
+TEST(PercentEncoding, Decoding) {
+  EXPECT_EQ(Utility::PercentEncoding::decode("hello%20world"), "hello world");
+  EXPECT_EQ(Utility::PercentEncoding::decode("upstream%7Cdownstream"), "upstream|downstream");
+  EXPECT_EQ(
+      Utility::PercentEncoding::decode(
+          "filter=%28cluster.upstream_%28rq_total%7Crq_time_sum%7Crq_time_count%7Crq_time_bucket%"
+          "7Crq_xx%7Crq_complete%7Crq_active%7Ccx_active%29%29%7C%28server.version%29"),
+      "filter=(cluster.upstream_(rq_total|rq_time_sum|rq_time_count|rq_time_bucket|rq_xx|rq_"
+      "complete|rq_active|cx_active))|(server.version)");
+}
+
+TEST(PercentEncoding, DecodingWithTrailingInput) {
   EXPECT_EQ(Utility::PercentEncoding::decode("too%20lar%20"), "too lar ");
   EXPECT_EQ(Utility::PercentEncoding::decode("too%20larg%e"), "too larg%e");
   EXPECT_EQ(Utility::PercentEncoding::decode("too%20large%"), "too large%");