Add circular buffer to coral library

source/coral.cpp

@@ -452,12 +452,34 @@ export namespace coral {
 		unavailable,
 	};
 
+	/**
+	 * Readable resource interface.
+	 */
 	struct reader {
-		virtual expected<usize, io_error> read(slice<u8> const & buffer) = 0;
+		virtual ~reader() {}
+
+		/**
+		 * Attempts to fill `data` with whatever data the reader has to offer, returning the number
+		 * of bytes actually read.
+		 *
+		 * Should the read operation fail for any reason, a [io_error] is returned instead.
+		 */
+		virtual expected<usize, io_error> read(slice<u8> const & data) = 0;
 	};
 
+	/**
+	 * Writable resource interface.
+	 */
 	struct writer {
-		virtual expected<usize, io_error> write(slice<u8 const> const & buffer) = 0;
+		virtual ~writer() {}
+
+		/**
+		 * Attempts to write `data` out to the writer, returning the number of bytes actually
+		 * written.
+		 *
+		 * Should the write operation fail for any reason, a [io_error] is returned instead.
+		 */
+		virtual expected<usize, io_error> write(slice<u8 const> const & data) = 0;
 	};
 }
 
@@ -617,4 +639,93 @@ export namespace coral {
 
 		return a;
 	}
+
+	/**
+	 * Multiplexing byte buffer of `capacity` size that may be used for memory-backed I/O
+	 * operations and lightweight data construction.
+	 */
+	template<usize capacity> struct ring_buffer : public writer, public reader {
+		ring_buffer(coral::u8 fill_value) : data{fill_value} {}
+
+		/**
+		 * Returns the base pointer of the buffer data.
+		 */
+		u8 * begin() {
+			return this->data;
+		}
+
+		/**
+		 * Returns the base pointer of the buffer data.
+		 */
+		u8 const * begin() const {
+			return this->data;
+		}
+
+		/**
+		 * Returns the tail pointer of the buffer data.
+		 */
+		u8 * end() {
+			return this->data + this->cursor;
+		}
+
+		/**
+		 * Returns the tail pointer of the buffer data.
+		 */
+		u8 const * end() const {
+			return this->data + this->cursor;
+		}
+
+		/**
+		 * Returns `true` if the buffer has been completely filled with data.
+		 */
+		bool is_full() const {
+			return this->filled == capacity;
+		}
+
+		/**
+		 * Reads whatever data is in the buffer into `data`, returning the number of bytes read
+		 * from the buffer.
+		 */
+		expected<usize, io_error> read(slice<u8> const & data) override {
+			slice const readable_data{this->data, min(this->filled, data.length)};
+
+			this->filled -= readable_data.length;
+
+			for (usize index = 0; index < readable_data.length; index += 1) {
+				data[index] = this->data[this->read_index];
+				this->read_index = (this->read_index + 1) % capacity;
+			}
+
+			return readable_data.length;
+		}
+
+		/**
+		 * Attempts to write `data` to the buffer, returning the number of bytes written or
+		 * [io_error::unavailable] if it has been completely filled and no more bytes can be
+		 * written.
+		 */
+		expected<usize, io_error> write(slice<u8 const> const & data) override {
+			if (this->is_full()) return io_error::unavailable;
+
+			slice const writable_data{data.sliced(0, min(data.length, this->filled))};
+
+			this->filled += writable_data.length;
+
+			for (usize index = 0; index < writable_data.length; index += 1) {
+				this->data[this->write_index] = data[index];
+				this->write_index = (this->write_index + 1) % capacity;
+			}
+
+			return writable_data.length;
+		}
+
+		private:
+		usize filled = 0;
+
+		usize read_index = 0;
+
+		usize write_index = 0;
+
+		u8 data[capacity];
+	};
 }