FileResourceHandler: Open file once on init, more error handling

Keeping the file open allows better prefetching/caching on both
the application layer (ifstream) and OS level (vfs layer) as
the access pattern is sequential and predictable. We also save
three syscalls (open, seek, close) for every chunk we send to
the client (256kb).

src/libs/core/impl/FileResourceHandler.cpp

@@ -19,8 +19,6 @@
 
 #include "FileResourceHandler.hpp"
 
-#include <fstream>
-
 #include "core/ILogger.hpp"
 #include "core/MimeTypes.hpp"
 
@@ -32,38 +30,37 @@ namespace lms::core
     }
 
     FileResourceHandler::FileResourceHandler(const std::filesystem::path& path, std::string_view mimeType)
-        : _path{ path }
-        , _mimeType{ mimeType }
+        : _mimeType{ mimeType }
+        , _ifs{ path, std::ios::in | std::ios::binary }
     {
+        if (!_ifs)
+            LMS_LOG(UTILS, ERROR, "Cannot open file stream for " << path);
+        else
+        {
+            _ifs.seekg(0, std::ios::end);
+            if (!_ifs.fail())
+                _fileSize = static_cast<::uint64_t>(_ifs.tellg());
+            LMS_LOG(UTILS, DEBUG, "File " << path << ", fileSize = " << _fileSize);
+        }
     }
 
     Wt::Http::ResponseContinuation* FileResourceHandler::processRequest(const Wt::Http::Request& request, Wt::Http::Response& response)
     {
-        ::uint64_t startByte{ _offset };
-        std::ifstream ifs{ _path, std::ios::in | std::ios::binary };
-
-        if (startByte == 0)
+        if (_offset == 0)
         {
-            if (!ifs)
+            if (!_ifs)
             {
-                LMS_LOG(UTILS, ERROR, "Cannot open file stream for " << _path);
                 response.setStatus(404);
                 return {};
             }
 
-            ifs.seekg(0, std::ios::end);
-            const ::uint64_t fileSize{ static_cast<::uint64_t>(ifs.tellg()) };
-            ifs.seekg(0, std::ios::beg);
-
-            LMS_LOG(UTILS, DEBUG, "File " << _path << ", fileSize = " << fileSize);
-
             response.addHeader("Accept-Ranges", "bytes");
 
-            const Wt::Http::Request::ByteRangeSpecifier ranges{ request.getRanges(fileSize) };
+            const Wt::Http::Request::ByteRangeSpecifier ranges{ request.getRanges(_fileSize) };
             if (!ranges.isSatisfiable())
             {
                 std::ostringstream contentRange;
-                contentRange << "bytes */" << fileSize;
+                contentRange << "bytes */" << _fileSize;
                 response.setStatus(416); // Requested range not satisfiable
                 response.addHeader("Content-Range", contentRange.str());
 
@@ -76,57 +73,51 @@ namespace lms::core
                 LMS_LOG(UTILS, DEBUG, "Range requested = " << ranges[0].firstByte() << "-" << ranges[0].lastByte());
 
                 response.setStatus(206);
-                startByte = ranges[0].firstByte();
+                _offset = ranges[0].firstByte();
                 _beyondLastByte = ranges[0].lastByte() + 1;
 
                 std::ostringstream contentRange;
-                contentRange << "bytes " << startByte << "-"
-                             << _beyondLastByte - 1 << "/" << fileSize;
+                contentRange << "bytes " << _offset << "-"
+                             << _beyondLastByte - 1 << "/" << _fileSize;
 
                 response.addHeader("Content-Range", contentRange.str());
-                response.setContentLength(_beyondLastByte - startByte);
+                response.setContentLength(_beyondLastByte - _offset);
             }
             else
             {
                 LMS_LOG(UTILS, DEBUG, "No range requested");
 
                 response.setStatus(200);
-                _beyondLastByte = fileSize;
+                _beyondLastByte = _fileSize;
                 response.setContentLength(_beyondLastByte);
             }
 
             LMS_LOG(UTILS, DEBUG, "Mimetype set to '" << _mimeType << "'");
             response.setMimeType(_mimeType);
-        }
-        else if (!ifs)
-        {
-            LMS_LOG(UTILS, ERROR, "Cannot reopen file stream for " << _path);
-            return {};
-        }
 
-        ifs.seekg(static_cast<std::istream::pos_type>(startByte));
+            _ifs.seekg(static_cast<std::istream::pos_type>(_offset));
+        } // end initial response setup
 
-        std::vector<char> buf;
-        buf.resize(_chunkSize);
+        ::uint64_t restSize = _beyondLastByte - _offset;
+        ::uint64_t pieceSize = std::min(restSize, _chunkSize);
 
-        ::uint64_t restSize = _beyondLastByte - startByte;
-        ::uint64_t pieceSize = buf.size() > restSize ? restSize : buf.size();
+        std::vector<char> buf(pieceSize);
 
-        ifs.read(&buf[0], pieceSize);
-        const ::uint64_t actualPieceSize{ static_cast<::uint64_t>(ifs.gcount()) };
+        _ifs.read(buf.data(), buf.size());
+        const ::uint64_t actualPieceSize{ static_cast<::uint64_t>(_ifs.gcount()) };
         if (actualPieceSize > 0)
         {
-            response.out().write(&buf[0], actualPieceSize);
-            LMS_LOG(UTILS, DEBUG, "Written " << actualPieceSize << " bytes, range = " << startByte << "-" << startByte + actualPieceSize - 1 << "");
+            response.out().write(buf.data(), actualPieceSize);
+            LMS_LOG(UTILS, DEBUG, "Written " << actualPieceSize << " bytes, range = " << _offset << "-" << _offset + actualPieceSize - 1 << "");
         }
         else
-        {
             LMS_LOG(UTILS, DEBUG, "Written 0 byte");
-        }
 
-        if (ifs.good() && actualPieceSize < restSize)
+        if (!_ifs.good())
+            LMS_LOG(UTILS, WARNING, "Error reading from file!");
+        else if (actualPieceSize < restSize)
         {
-            _offset = startByte + actualPieceSize;
+            _offset += actualPieceSize;
             LMS_LOG(UTILS, DEBUG, "Job not complete! Remaining range: " << _offset << "-" << _beyondLastByte - 1);
 
             return response.createContinuation();

src/libs/core/impl/FileResourceHandler.hpp

@@ -22,6 +22,7 @@
 #include <filesystem>
 #include <string>
 #include <string_view>
+#include <fstream>
 
 #include "core/IResourceHandler.hpp"
 
@@ -38,9 +39,10 @@ namespace lms::core
 
         static constexpr std::size_t _chunkSize{ 262'144 };
 
-        std::filesystem::path _path;
         std::string _mimeType;
         ::uint64_t _beyondLastByte{};
         ::uint64_t _offset{};
+        ::uint64_t _fileSize{};
+        std::ifstream _ifs;
     };
 } // namespace lms::core