LibHTTP: Don't copy payload slices in flush_received_buffers()

Instead of using ByteBuffer::slice() to carve off the remaining part of
the payload every time we flush a part of it, we now keep a sliding
span (ReadonlyBytes) over it.

Author: awesomekling

Userland/Libraries/LibHTTP/Job.cpp

@@ -110,7 +110,7 @@ void Job::flush_received_buffers()
         return;
     dbgln_if(JOB_DEBUG, "Job: Flushing received buffers: have {} bytes in {} buffers for {}", m_buffered_size, m_received_buffers.size(), m_request.url());
     for (size_t i = 0; i < m_received_buffers.size(); ++i) {
-        auto& payload = m_received_buffers[i];
+        auto& payload = m_received_buffers[i].pending_flush;
         auto result = do_write(payload);
         if (result.is_error()) {
             if (!result.error().is_errno()) {
@@ -127,7 +127,7 @@ void Job::flush_received_buffers()
         m_buffered_size -= written;
         if (written == payload.size()) {
             // FIXME: Make this a take-first-friendly object?
-            m_received_buffers.take_first();
+            (void)m_received_buffers.take_first();
             --i;
             continue;
         }
@@ -506,7 +506,7 @@ void Job::on_socket_connected()
                 }
             }
 
-            m_received_buffers.append(payload);
+            m_received_buffers.append(make<ReceivedBuffer>(payload));
             m_buffered_size += payload.size();
             m_received_size += payload.size();
             flush_received_buffers();
@@ -579,8 +579,8 @@ void Job::finish_up()
 
         u8* flat_ptr = flattened_buffer.data();
         for (auto& received_buffer : m_received_buffers) {
-            memcpy(flat_ptr, received_buffer.data(), received_buffer.size());
-            flat_ptr += received_buffer.size();
+            memcpy(flat_ptr, received_buffer.pending_flush.data(), received_buffer.pending_flush.size());
+            flat_ptr += received_buffer.pending_flush.size();
         }
         m_received_buffers.clear();
 
@@ -595,7 +595,7 @@ void Job::finish_up()
         }
 
         m_buffered_size = flattened_buffer.size();
-        m_received_buffers.append(move(flattened_buffer));
+        m_received_buffers.append(make<ReceivedBuffer>(move(flattened_buffer)));
         m_can_stream_response = true;
     }
 

Userland/Libraries/LibHTTP/Job.h

@@ -8,6 +8,7 @@
 
 #include <AK/FileStream.h>
 #include <AK/HashMap.h>
+#include <AK/NonnullOwnPtrVector.h>
 #include <AK/Optional.h>
 #include <LibCore/NetworkJob.h>
 #include <LibHTTP/HttpRequest.h>
@@ -54,7 +55,23 @@ class Job : public Core::NetworkJob {
     int m_code { -1 };
     HashMap<String, String, CaseInsensitiveStringTraits> m_headers;
     Vector<String> m_set_cookie_headers;
-    Vector<ByteBuffer, 2> m_received_buffers;
+
+    struct ReceivedBuffer {
+        ReceivedBuffer(ByteBuffer d)
+            : data(move(d))
+            , pending_flush(data.bytes())
+        {
+        }
+
+        // The entire received buffer.
+        ByteBuffer data;
+
+        // The bytes we have yet to flush. (This is a slice of `data`)
+        ReadonlyBytes pending_flush;
+    };
+
+    NonnullOwnPtrVector<ReceivedBuffer> m_received_buffers;
+
     size_t m_buffered_size { 0 };
     size_t m_received_size { 0 };
     Optional<u32> m_content_length;