Add default global HTTP headers (#85)

This commit adds the ability to add global HTTP headers
to the TransportBuilder, to set HTTP headers for all
API calls made by the client.

HTTP headers can be overridden on
a per API call basis by using the header
function exposed on each builder struct.

Closes #83

(cherry picked from commit 1e619d8)

Author: russcam

elasticsearch/src/http/transport.rs

@@ -6,7 +6,7 @@ use crate::{
     error::Error,
     http::{
         headers::{
-            HeaderMap, HeaderValue, ACCEPT, AUTHORIZATION, CONTENT_TYPE, DEFAULT_ACCEPT,
+            HeaderMap, HeaderName, HeaderValue, ACCEPT, AUTHORIZATION, CONTENT_TYPE, DEFAULT_ACCEPT,
             DEFAULT_CONTENT_TYPE, DEFAULT_USER_AGENT, USER_AGENT,
         },
         request::Body,
@@ -86,6 +86,7 @@ pub struct TransportBuilder {
     proxy: Option<Url>,
     proxy_credentials: Option<Credentials>,
     disable_proxy: bool,
+    headers: HeaderMap
 }
 
 impl TransportBuilder {
@@ -103,6 +104,7 @@ impl TransportBuilder {
             proxy: None,
             proxy_credentials: None,
             disable_proxy: false,
+            headers: HeaderMap::new()
         }
     }
 
@@ -142,10 +144,32 @@ impl TransportBuilder {
         self
     }
 
+    /// Adds a HTTP header that will be added to all client API calls.
+    ///
+    /// A default HTTP header can be overridden on a per API call basis.
+    pub fn header(mut self, key: HeaderName, value: HeaderValue) -> Self {
+        self.headers.insert(key, value);
+        self
+    }
+
+    /// Adds HTTP headers that will be added to all client API calls.
+    ///
+    /// Default HTTP headers can be overridden on a per API call basis.
+    pub fn headers(mut self, headers: HeaderMap) -> Self {
+        for (key, value) in headers.iter() {
+            self.headers.insert(key, value.clone());
+        }
+        self
+    }
+
     /// Builds a [Transport] to use to send API calls to Elasticsearch.
     pub fn build(self) -> Result<Transport, BuildError> {
         let mut client_builder = self.client_builder;
 
+        if self.headers.len() > 0 {
+            client_builder = client_builder.default_headers(self.headers);
+        }
+
         #[cfg(any(feature = "native-tls", feature = "rustls-tls"))]
         {
             if let Some(creds) = &self.credentials {

elasticsearch/tests/client.rs

@@ -30,6 +30,43 @@ async fn default_user_agent_content_type_accept_headers() -> Result<(), failure:
     Ok(())
 }
 
+#[tokio::test]
+async fn default_header() -> Result<(), failure::Error> {
+    let server = server::http(move |req| async move {
+        assert_eq!(req.headers()["x-opaque-id"], "foo");
+        http::Response::default()
+    });
+
+    let builder = client::create_builder(format!("http://{}", server.addr()).as_ref())
+        .header(HeaderName::from_static(X_OPAQUE_ID),
+                HeaderValue::from_static("foo"));
+
+    let client = client::create(builder);
+    let _response = client.ping().send().await?;
+
+    Ok(())
+}
+
+#[tokio::test]
+async fn override_default_header() -> Result<(), failure::Error> {
+    let server = server::http(move |req| async move {
+        assert_eq!(req.headers()["x-opaque-id"], "bar");
+        http::Response::default()
+    });
+
+    let builder = client::create_builder(format!("http://{}", server.addr()).as_ref())
+        .header(HeaderName::from_static(X_OPAQUE_ID),
+                HeaderValue::from_static("foo"));
+
+    let client = client::create(builder);
+    let _response = client.ping()
+        .header(HeaderName::from_static(X_OPAQUE_ID),
+                HeaderValue::from_static("bar"))
+        .send().await?;
+
+    Ok(())
+}
+
 #[tokio::test]
 async fn x_opaque_id_header() -> Result<(), failure::Error> {
     let server = server::http(move |req| async move {