Reduce string copying. (#135)

* Reduce string copying.

Optimized a few unnecessary string copies that should have been moves to
begin with. Additionally, I noticed that we're scanning the headers
twice once to test if a given header exists and another to get its
value, that is a perfect use case for std::optional, but since we need
to stay compatible with C++11 and C++14, we can use the 'outcome' class
instead.

* Fixup: Move state boolean in move assignment

Co-authored-by: Marco Magdy <[email protected]>

Author: marcomagdy

include/aws/http/response.h

@@ -14,6 +14,8 @@
  * permissions and limitations under the License.
  */
 
+#include "aws/lambda-runtime/outcome.h"
+
 #include <string>
 #include <vector>
 #include <algorithm>
@@ -31,7 +33,7 @@ class response {
     inline void add_header(std::string name, std::string const& value);
     inline void append_body(const char* p, size_t sz);
     inline bool has_header(char const* header) const;
-    inline std::string const& get_header(char const* header) const;
+    inline lambda_runtime::outcome<std::string, bool> get_header(char const* header) const;
     inline response_code get_response_code() const { return m_response_code; }
     inline void set_response_code(aws::http::response_code c);
     inline void set_content_type(char const* ct);
@@ -140,7 +142,7 @@ inline std::string const& response::get_body() const
 inline void response::add_header(std::string name, std::string const& value)
 {
     std::transform(name.begin(), name.end(), name.begin(), ::tolower);
-    m_headers.emplace_back(name, value);
+    m_headers.emplace_back(std::move(name), value);
 }
 
 inline void response::append_body(const char* p, size_t sz)
@@ -161,12 +163,15 @@ inline bool response::has_header(char const* header) const
     });
 }
 
-inline std::string const& response::get_header(char const* header) const
+inline lambda_runtime::outcome<std::string, bool> response::get_header(char const* header) const
 {
     auto it = std::find_if(m_headers.begin(), m_headers.end(), [header](std::pair<std::string, std::string> const& p) {
         return p.first == header;
     });
-    assert(it != m_headers.end());
+
+    if (it == m_headers.end()) {
+        return false;
+    }
     return it->second;
 }
 

include/aws/lambda-runtime/outcome.h

@@ -49,14 +49,20 @@ class outcome {
         }
     }
 
-    ~outcome()
+    ~outcome() { destroy(); }
+
+    outcome& operator=(outcome&& other) noexcept
     {
-        if (m_success) {
-            m_s.~TResult();
+        assert(this != &other);
+        destroy();
+        if (other.m_success) {
+            new (&m_s) TResult(std::move(other.m_s));
         }
         else {
-            m_f.~TFailure();
+            new (&m_f) TFailure(std::move(other.m_f));
         }
+        m_success = other.m_success;
+        return *this;
     }
 
     TResult const& get_result() const&
@@ -86,6 +92,16 @@ class outcome {
     bool is_success() const { return m_success; }
 
 private:
+    void destroy()
+    {
+        if (m_success) {
+            m_s.~TResult();
+        }
+        else {
+            m_f.~TFailure();
+        }
+    }
+
     union {
         TResult m_s;
         TFailure m_f;

src/runtime.cpp

@@ -116,9 +116,7 @@ static size_t write_header(char* ptr, size_t size, size_t nmemb, void* userdata)
         if (ptr[i] != ':') {
             continue;
         }
-        std::string key{ptr, i};
-        std::string value{ptr + i + 1, nmemb - i - 1};
-        resp->add_header(trim(key), trim(value));
+        resp->add_header(trim({ptr, i}), trim({ptr + i + 1, nmemb - i - 1}));
         break;
     }
     return size * nmemb;
@@ -266,32 +264,38 @@ runtime::next_outcome runtime::get_next()
         return resp.get_response_code();
     }
 
-    if (!resp.has_header(REQUEST_ID_HEADER)) {
+    auto out = resp.get_header(REQUEST_ID_HEADER);
+    if (!out.is_success()) {
         logging::log_error(LOG_TAG, "Failed to find header %s in response", REQUEST_ID_HEADER);
         return aws::http::response_code::REQUEST_NOT_MADE;
     }
     invocation_request req;
     req.payload = resp.get_body();
-    req.request_id = resp.get_header(REQUEST_ID_HEADER);
+    req.request_id = std::move(out).get_result();
 
-    if (resp.has_header(TRACE_ID_HEADER)) {
-        req.xray_trace_id = resp.get_header(TRACE_ID_HEADER);
+    out = resp.get_header(TRACE_ID_HEADER);
+    if (out.is_success()) {
+        req.xray_trace_id = std::move(out).get_result();
     }
 
-    if (resp.has_header(CLIENT_CONTEXT_HEADER)) {
-        req.client_context = resp.get_header(CLIENT_CONTEXT_HEADER);
+    out = resp.get_header(CLIENT_CONTEXT_HEADER);
+    if (out.is_success()) {
+        req.client_context = std::move(out).get_result();
     }
 
-    if (resp.has_header(COGNITO_IDENTITY_HEADER)) {
-        req.cognito_identity = resp.get_header(COGNITO_IDENTITY_HEADER);
+    out = resp.get_header(COGNITO_IDENTITY_HEADER);
+    if (out.is_success()) {
+        req.cognito_identity = std::move(out).get_result();
     }
 
-    if (resp.has_header(FUNCTION_ARN_HEADER)) {
-        req.function_arn = resp.get_header(FUNCTION_ARN_HEADER);
+    out = resp.get_header(FUNCTION_ARN_HEADER);
+    if (out.is_success()) {
+        req.function_arn = std::move(out).get_result();
     }
 
-    if (resp.has_header(DEADLINE_MS_HEADER)) {
-        auto const& deadline_string = resp.get_header(DEADLINE_MS_HEADER);
+    out = resp.get_header(DEADLINE_MS_HEADER);
+    if (out.is_success()) {
+        auto const& deadline_string = std::move(out).get_result();
         constexpr int base = 10;
         unsigned long ms = strtoul(deadline_string.c_str(), nullptr, base);
         assert(ms > 0);
@@ -303,7 +307,7 @@ runtime::next_outcome runtime::get_next()
             req.payload.c_str(),
             static_cast<int64_t>(req.get_time_remaining().count()));
     }
-    return next_outcome(req);
+    return {req};
 }
 
 runtime::post_outcome runtime::post_success(std::string const& request_id, invocation_response const& handler_response)