feat(envoy-plugin): Add support to get response backend latency

Signed-off-by: Anurag Singh Rajawat <anuragsinghrajawat22@gmail.com>

Author: anurag-rajawat

filter/envoy/envoy-wasm-filters/src/lib.rs

@@ -55,6 +55,7 @@ struct Reqquest {
 struct Ressponse {
     headers: HashMap<String, String>,
     body: String,
+    backend_latency_in_nanos: u64,
 }
 
 const MAX_BODY_SIZE: usize = 1_000_000; // 1 MB
@@ -213,6 +214,16 @@ impl HttpContext for Plugin {
         if !body.is_empty() && body.len() <= MAX_BODY_SIZE {
             self.api_event.response.body = body;
         }
+
+        if let Some(value) = self.get_property(vec!["response", "backend_latency"]) {
+            // Ensure the byte vector has at least 8 bytes for u64
+            if value.len() >= 8 {
+                // Convert the first 8 bytes to an u64 (nanoseconds)
+                self.api_event.response.backend_latency_in_nanos =
+                    u64::from_ne_bytes(value[..8].try_into().unwrap_or_default());
+            }
+        }
+
         Action::Continue
     }
 }

protobuf/golang/sentryflow.pb.go

@@ -129,7 +129,7 @@ class Request(_message.Message):
     def __init__(self, headers: _Optional[_Mapping[str, str]] = ..., body: _Optional[str] = ...) -> None: ...
 
 class Response(_message.Message):
-    __slots__ = ("headers", "body")
+    __slots__ = ("headers", "body", "backend_latency_in_nanos")
     class HeadersEntry(_message.Message):
         __slots__ = ("key", "value")
         KEY_FIELD_NUMBER: _ClassVar[int]
@@ -139,9 +139,11 @@ class Response(_message.Message):
         def __init__(self, key: _Optional[str] = ..., value: _Optional[str] = ...) -> None: ...
     HEADERS_FIELD_NUMBER: _ClassVar[int]
     BODY_FIELD_NUMBER: _ClassVar[int]
+    BACKEND_LATENCY_IN_NANOS_FIELD_NUMBER: _ClassVar[int]
     headers: _containers.ScalarMap[str, str]
     body: str
-    def __init__(self, headers: _Optional[_Mapping[str, str]] = ..., body: _Optional[str] = ...) -> None: ...
+    backend_latency_in_nanos: int
+    def __init__(self, headers: _Optional[_Mapping[str, str]] = ..., body: _Optional[str] = ..., backend_latency_in_nanos: _Optional[int] = ...) -> None: ...
 
 class APIMetrics(_message.Message):
     __slots__ = ("perAPICounts",)

protobuf/golang/sentryflow_grpc.pb.go

@@ -92,6 +92,7 @@ message Request {
 message Response {
   map<string, string> headers = 1;
   string body = 2;
+  uint64 backend_latency_in_nanos = 3;
 }
 
 message APIMetrics {