Modify response headers

Signed-off-by: Sanskar Jaiswal <jaiswalsanskar078@gmail.com>

Author: aryan9600

linkerd/app/core/src/errors.rs

@@ -1,4 +1,4 @@
-use http::{header::HeaderValue, StatusCode};
+use http::{header::HeaderValue, StatusCode, version::Version};
 use linkerd_errno::Errno;
 use linkerd_error::Error;
 use linkerd_error_metrics as metrics;
@@ -174,13 +174,29 @@ impl<RspB: Default + hyper::body::HttpBody> respond::Respond<http::Response<RspB
 
     fn respond(&self, res: Result<http::Response<RspB>, Error>) -> Result<Self::Response, Error> {
         match res {
-            Ok(response) => Ok(response.map(|b| match *self {
-                Respond { is_grpc: true, .. } => ResponseBody::Grpc {
-                    inner: b,
-                    trailers: None,
-                },
-                _ => ResponseBody::NonGrpc(b),
-            })),
+            Ok(mut response) => {
+                let pseudonym = "linkerd-proxy";
+                let version = match self.version {
+                    Version::HTTP_10 => "HTTP/1.0",
+                    Version::HTTP_11 => "HTTP/1.1",
+                    Version::HTTP_2 => "HTTP/2",
+                    _ => ""
+                };
+                let via_header = HeaderValue::from_str(format!("{} {}", version, pseudonym).as_str());
+                if let Ok(val) = via_header {
+                    debug!(?val, "via");
+                    response.headers_mut().insert(http::header::VIA, val);
+                    let headers = response.headers();
+                    debug!(?headers, "response_headers");
+                }
+                Ok(response.map(|b| match *self {
+                    Respond { is_grpc: true, .. } => ResponseBody::Grpc {
+                        inner: b,
+                        trailers: None,
+                    },
+                    _ => ResponseBody::NonGrpc(b),
+                }))
+            }
             Err(error) => {
                 let addr = self
                     .client
@@ -218,11 +234,13 @@ impl<RspB: Default + hyper::body::HttpBody> respond::Respond<http::Response<RspB
                 }
 
                 let status = http_status(&*error);
+                const SERVER_HEADER: &'static str = concat!("linkerd-proxy/", env!("CARGO_PKG_VERSION"));
                 debug!(%status, version = ?self.version, "Handling error with HTTP response");
                 Ok(http::Response::builder()
                     .version(self.version)
                     .status(status)
                     .header(http::header::CONTENT_LENGTH, "0")
+                    .header(http::header::SERVER, SERVER_HEADER)
                     .body(ResponseBody::default())
                     .expect("error response must be valid"))
             }