udp: Extend hash policies with key based hashing

Co-authored-by: DongRyeol Cha <[email protected]>
Signed-off-by: Kornel David <[email protected]>

api/envoy/extensions/filters/udp/udp_proxy/v3/udp_proxy.proto

@@ -33,6 +33,9 @@ message UdpProxyConfig {
 
       // The source IP will be used to compute the hash used by hash-based load balancing algorithms.
       bool source_ip = 1 [(validate.rules).bool = {const: true}];
+
+      // A given key will be used to compute the hash used by hash-based load balancing algorithms.
+      string key = 2 [(validate.rules).string = {min_len: 1}];
     }
   }
 

source/extensions/filters/udp/udp_proxy/hash_policy_impl.cc

@@ -20,13 +20,34 @@ class SourceIpHashMethod : public HashPolicyImpl::HashMethod {
   }
 };
 
+class KeyHashMethod : public HashPolicyImpl::HashMethod {
+public:
+  KeyHashMethod(const std::string& key) : Key(key) {}
+  const std::string& Key;
+
+  absl::optional<uint64_t>
+  evaluate(const Network::Address::Instance& downstream_addr) const override {
+    (void)downstream_addr;
+    // ASSERT(!Key.empty());
+    if (!Key.empty()) {
+      uint64_t hash = HashUtil::xxHash64(Key);
+      return hash;
+    }
+
+    return absl::nullopt;
+  }
+};
+
 HashPolicyImpl::HashPolicyImpl(
     const absl::Span<const UdpProxyConfig::HashPolicy* const>& hash_policies) {
   ASSERT(hash_policies.size() == 1);
   switch (hash_policies[0]->policy_specifier_case()) {
   case UdpProxyConfig::HashPolicy::PolicySpecifierCase::kSourceIp:
     hash_impl_ = std::make_unique<SourceIpHashMethod>();
     break;
+  case UdpProxyConfig::HashPolicy::PolicySpecifierCase::kKey:
+    hash_impl_ = std::make_unique<KeyHashMethod>(hash_policies[0]->key());
+    break;
   default:
     NOT_REACHED_GCOVR_EXCL_LINE;
   }