aws-lambda-cpp-add-xray-response.patch

diff --git a/include/aws/lambda-runtime/runtime.h b/include/aws/lambda-runtime/runtime.h
index 94e1e22..ee356ff 100644
--- a/include/aws/lambda-runtime/runtime.h
+++ b/include/aws/lambda-runtime/runtime.h
@@ -85,6 +85,11 @@ private:
      */
     bool m_success;
 
+    /**
+     * The serialized XRay response header.
+     */
+    std::string m_xray_response;
+
     /**
      * Instantiate an empty response. Used by the static functions 'success' and 'failure' to create a populated
      * invocation_response
@@ -97,10 +102,12 @@ public:
     // To support clients that need to control the entire error response body (e.g. adding a stack trace), this
     // constructor should be used instead.
     // Note: adding an overload to invocation_response::failure is not feasible since the parameter types are the same.
-    invocation_response(std::string const& payload, std::string const& content_type, bool success)
-        : m_payload(payload), m_content_type(content_type), m_success(success)
-    {
-    }
+    invocation_response(std::string const& payload, std::string const& content_type, bool success, std::string const& xray_response):
+        m_payload(payload),
+        m_content_type(content_type),
+        m_success(success),
+        m_xray_response(xray_response)
+        {}
 
     /**
      * Create a successful invocation response with the given payload and content-type.
@@ -111,7 +118,7 @@ public:
      * Create a failure response with the given error message and error type.
      * The content-type is always set to application/json in this case.
      */
-    static invocation_response failure(std::string const& error_message, std::string const& error_type);
+    static invocation_response failure(std::string const& error_message, std::string const& error_type, std::string const& xray_response);
 
     /**
      * Get the MIME type of the payload.
@@ -127,6 +134,11 @@ public:
      * Returns true if the payload and content-type are set. Returns false if the error message and error types are set.
      */
     bool is_success() const { return m_success; }
+
+    /**
+    * Get the XRay response string. The string isassumed to be UTF-8 encoded.
+    */
+    std::string const& get_xray_response() const { return m_xray_response; }
 };
 
 struct no_result {
diff --git a/src/runtime.cpp b/src/runtime.cpp
index 9175084..230ce6f 100644
--- a/src/runtime.cpp
+++ b/src/runtime.cpp
@@ -333,6 +333,7 @@ runtime::post_outcome runtime::do_post(
         headers = curl_slist_append(headers, ("content-type: " + handler_response.get_content_type()).c_str());
     }
 
+    headers = curl_slist_append(headers, ("lambda-runtime-function-xray-error-cause: " + handler_response.get_xray_response()).c_str());
     headers = curl_slist_append(headers, "Expect:");
     headers = curl_slist_append(headers, "transfer-encoding:");
     headers = curl_slist_append(headers, m_user_agent_header.c_str());
@@ -507,13 +508,15 @@ invocation_response invocation_response::success(std::string const& payload, std
 }
 
 AWS_LAMBDA_RUNTIME_API
-invocation_response invocation_response::failure(std::string const& error_message, std::string const& error_type)
+invocation_response invocation_response::failure(std::string const& error_message, std::string const& error_type, std::string const& xray_response)
 {
     invocation_response r;
     r.m_success = false;
     r.m_content_type = "application/json";
     r.m_payload = R"({"errorMessage":")" + json_escape(error_message) + R"(","errorType":")" + json_escape(error_type) +
                   R"(", "stackTrace":[]})";
+    r.m_xray_response = xray_response;
+
     return r;
 }