Encapsulate the STDOUT/STDERR capturing

src/wine-host/bridges/group.h

@@ -0,0 +1,78 @@
+// yabridge: a Wine VST bridge
+// Copyright (C) 2020  Robbert van der Helm
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+#pragma once
+
+#include "../boost-fix.h"
+
+#include <boost/asio/posix/stream_descriptor.hpp>
+
+/**
+ * Encapsulate capturing the STDOUT or STDERR stream by opening a pipe and
+ * reopening the passed file descriptor as one of the ends of the newly opened
+ * pipe. This allows all output sent to be read from that pipe. This is needed
+ * to capture all (debug) output from Wine and the hosted plugins so we can
+ * prefix it with a timestamp and a group identifier and potentially write it to
+ * a log file. Since the host application is run independently of the yabridge
+ * instance that spawned it, this can't simply be done by the caller like we're
+ * doing for Wine output in individually hosted plugins.
+ */
+class StdIoCapture {
+   public:
+    /**
+     * Redirect all output sent to a file descriptor (e.g. `STDOUT_FILENO` or
+     * `STDERR_FILENO`) to a pipe. `StdIoCapture::pipe` can be used to read from
+     * this pipe.
+     *
+     * @param io_context The IO context to create the captured pipe stream on.
+     * @param file_descriptor The file descriptor to remap.
+     */
+    StdIoCapture(boost::asio::io_context& io_context, int file_descriptor);
+
+    StdIoCapture(const StdIoCapture&) = delete;
+    StdIoCapture& operator=(const StdIoCapture&) = delete;
+
+    /**
+     * On cleanup, close the outgoing file descriptor from the pipe and restore
+     * the original file descriptor for the captured stream.
+     */
+    ~StdIoCapture();
+
+    /**
+     * The pipe endpoint where all output from the original file descriptor gets
+     * redirected to. This can be read from like any other `Boost.Asio` stream.
+     */
+    boost::asio::posix::stream_descriptor pipe;
+
+   private:
+    /**
+     * The file descriptor of the stream we're capturing.
+     */
+    const int target_fd;
+
+    /**
+     * A copy of the original file descriptor. Will be used to undo
+     * the capture when this object gets destroyed.
+     */
+    const int original_fd_copy;
+
+    /**
+     * The two file descriptors generated by the `pipe()` function call.
+     * `pipe_fd[1]` is used to reopen/capture the passed file descriptor, and
+     * `pipe_fd[0]` can be used to read the captured output from.
+     */
+    int pipe_fd[2];
+};