1 files changed, 141 insertions, 0 deletions
diff --git a/include/ricochet/net/sys/file_descriptor.hh b/include/ricochet/net/sys/file_descriptor.hh
new file mode 100644
index 0000000..4af56cb
--- /dev/null
+++ b/include/ricochet/net/sys/file_descriptor.hh
@@ -0,0 +1,141 @@
+/**
+ * ---------------------------------------------------------------------------
+ * @notice This file was adapted from the Minnow networking framework,
+ * originally developed for Stanford University's CS144 course.
+ * It has been incorporated into the Ricochet project as foundational
+ * system utility code.
+ * ---------------------------------------------------------------------------
+ */
+
+#pragma once
+
+#include "string_view_range.hh"
+
+#include <bits/types/struct_iovec.h>
+#include <cstddef>
+#include <memory>
+#include <vector>
+
+// A reference-counted handle to a file descriptor
+class FileDescriptor
+{
+public:
+  // Construct from a file descriptor number returned by the kernel
+  explicit FileDescriptor( int fd );
+
+  // Read from the file descriptor into `buffer` (a single string) or `buffers` (a vector of strings)
+  void read( std::string& buffer );
+  void read( std::vector<std::string>& buffers );
+
+  // `write_all` writes a buffer completely.
+  void write_all( std::string_view buffer );
+
+  // `write` writes *from* a buffer or range of buffers and returns the number of bytes it actually wrote.
+  size_t write( std::string_view buffer );
+  size_t write( const StringViewRange auto&& buffers )
+  {
+    static thread_local std::vector<iovec> iovecs;
+    const size_t total_size = to_iovecs( buffers, iovecs );
+    return write( iovecs, total_size );
+  }
+
+  // Close the underlying file descriptor
+  void close() { internal_fd_->close(); }
+
+  // Set blocking(true) or non-blocking(false) status on the file descriptor
+  void set_blocking( bool blocking );
+
+  // Copy a FileDescriptor explicitly, increasing the internal reference count
+  FileDescriptor duplicate() const;
+
+  // The destructor calls close() when no more references remain.
+  ~FileDescriptor() = default;
+
+  // Accessors
+  int fd_num() const { return internal_fd_->fd_; }                        // underlying descriptor number
+  bool eof() const { return internal_fd_->eof_; }                         // EOF flag state
+  bool closed() const { return internal_fd_->closed_; }                   // closed flag state
+  bool blocking() const { return not internal_fd_->non_blocking_; }       // blocking state
+  unsigned int read_count() const { return internal_fd_->read_count_; }   // number of reads
+  unsigned int write_count() const { return internal_fd_->write_count_; } // number of writes
+
+  // Copy/move constructor/assignment operators
+  // FileDescriptor can be moved, but cannot be copied implicitly (see duplicate())
+  FileDescriptor( const FileDescriptor& other ) = delete;            // copy construction is forbidden
+  FileDescriptor& operator=( const FileDescriptor& other ) = delete; // copy assignment is forbidden
+  FileDescriptor( FileDescriptor&& other ) = default;                // move construction is allowed
+  FileDescriptor& operator=( FileDescriptor&& other ) = default;     // move assignment is allowed
+
+private:
+  // FDWrapper: A handle on a kernel file descriptor.
+  // FileDescriptor objects contain a std::shared_ptr to a FDWrapper.
+  class FDWrapper
+  {
+  public:
+    int fd_;                    // The file descriptor number returned by the kernel
+    bool eof_ = false;          // Flag indicating whether FDWrapper::fd_ is at EOF
+    bool closed_ = false;       // Flag indicating whether FDWrapper::fd_ has been closed
+    bool non_blocking_ = false; // Flag indicating whether FDWrapper::fd_ is non-blocking
+    unsigned read_count_ = 0;   // The number of times FDWrapper::fd_ has been read
+    unsigned write_count_ = 0;  // The numberof times FDWrapper::fd_ has been written
+
+    // Construct from a file descriptor number returned by the kernel
+    explicit FDWrapper( int fd );
+    // Closes the file descriptor upon destruction
+    ~FDWrapper();
+    // Calls [close(2)](\ref man2::close) on FDWrapper::fd_
+    void close();
+
+    size_t CheckFDSystemCall( std::string_view what, ssize_t return_value ) const;
+    size_t CheckRead( std::string_view what, ssize_t return_value );
+
+    // An FDWrapper cannot be copied or moved
+    FDWrapper( const FDWrapper& other ) = delete;
+    FDWrapper& operator=( const FDWrapper& other ) = delete;
+    FDWrapper( FDWrapper&& other ) = delete;
+    FDWrapper& operator=( FDWrapper&& other ) = delete;
+  };
+
+  // A reference-counted handle to a shared FDWrapper
+  std::shared_ptr<FDWrapper> internal_fd_;
+
+  // Private constructor used to duplicate the FileDescriptor (increase the reference count)
+  explicit FileDescriptor( std::shared_ptr<FDWrapper> other_shared_ptr );
+
+  // Private write method that takes a vector of iovecs (an internal OS structure)
+  size_t write( const std::vector<iovec>& iovecs, size_t total_size );
+
+protected:
+  // size of buffer to allocate by read(), recv(), etc., when passed-in buffer is empty
+  static constexpr size_t kReadBufferSize = 16384;
+
+  void set_eof() { internal_fd_->eof_ = true; }
+  void register_read() { ++internal_fd_->read_count_; }   // increment read count
+  void register_write() { ++internal_fd_->write_count_; } // increment write count
+
+  size_t CheckFDSystemCall( std::string_view what, ssize_t return_value ) const;
+  size_t CheckRead( std::string_view what, ssize_t return_value );
+
+  // Convert a range of string_view-convertible objects to a vector of iovecs
+  static size_t to_iovecs( const StringViewRange auto& buffers, std::vector<iovec>& iovecs )
+  {
+    if ( buffers.empty() ) {
+      throw std::runtime_error( "to_iovecs called with empty buffer list" );
+    }
+    iovecs.clear();
+    iovecs.reserve( buffers.size() );
+    size_t total_size = 0;
+    for ( const auto& buf : buffers ) {
+      const std::string_view x { buf };
+      if ( x.empty() ) {
+        throw std::runtime_error( "to_iovecs called with empty buffer in buffer list" );
+      }
+      iovecs.push_back( { const_cast<char*>( x.data() ), x.size() } ); // NOLINT(*-const-cast)
+      total_size += x.size();
+    }
+    if ( total_size == 0 ) {
+      throw std::runtime_error( "to_iovecs called with zero-size buffer list" );
+    }
+    return total_size;
+  }
+};