Encapsulate the STDOUT/STDERR capturing

meson.build

@@ -94,7 +94,10 @@ host_sources = [
 ]
 
 individual_host_sources = host_sources + ['src/wine-host/individual-host.cpp']
-group_host_sources = host_sources + ['src/wine-host/group-host.cpp']
+group_host_sources = host_sources + [
+  'src/wine-host/bridges/group.cpp',
+  'src/wine-host/group-host.cpp',
+]
 
 executable(
   individual_host_name_64bit,

src/wine-host/bridges/group.cpp

@@ -0,0 +1,44 @@
+// 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/>.
+
+#include "group.h"
+
+#include <unistd.h>
+
+StdIoCapture::StdIoCapture(boost::asio::io_context& io_context,
+                           int file_descriptor)
+    : pipe(io_context),
+      target_fd(file_descriptor),
+      original_fd_copy(dup(file_descriptor)) {
+    // We'll use the second element of these two file descriptors to reopen
+    // `file_descriptor`, and the first one to read the captured contents from
+    ::pipe(pipe_fd);
+
+    // We've already created a copy of the original file descriptor, so we can
+    // reopen it using the newly created pipe
+    dup2(pipe_fd[1], target_fd);
+    close(pipe_fd[1]);
+
+    pipe.assign(pipe_fd[0]);
+}
+
+StdIoCapture::~StdIoCapture() {
+    // Restore the original file descriptor and close the pipe. The other wend
+    // was already closed in the constructor.
+    dup2(original_fd_copy, target_fd);
+    close(original_fd_copy);
+    close(pipe_fd[0]);
+}

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];
+};

src/wine-host/group-host.cpp

@@ -16,8 +16,6 @@
 
 #include "boost-fix.h"
 
-#include <unistd.h>
-#include <boost/asio/posix/stream_descriptor.hpp>
 #include <boost/asio/read_until.hpp>
 #include <boost/asio/streambuf.hpp>
 #include <boost/filesystem.hpp>
@@ -29,6 +27,7 @@
 #include <src/common/config/config.h>
 #include <src/common/config/version.h>
 
+#include "bridges/group.h"
 #include "bridges/vst2.h"
 
 // FIXME: `std::filesystem` is broken in wineg++, at least under Wine 5.8. Any
@@ -97,25 +96,14 @@ int __cdecl main(int argc, char* argv[]) {
     // process the output and redirect it to a logger. Needed to capture Wine
     // debug output, since this process will likely outlive the yabridge
     // instance that originally spawned it.
-    int stdout_pipe[2];
-    pipe(stdout_pipe);
-    dup2(stdout_pipe[1], STDOUT_FILENO);
-    close(stdout_pipe[1]);
-
-    int stderr_pipe[2];
-    pipe(stderr_pipe);
-    dup2(stderr_pipe[1], STDERR_FILENO);
-    close(stderr_pipe[1]);
-
     boost::asio::io_context io_context;
     boost::asio::streambuf stdout_buffer;
     boost::asio::streambuf stderr_buffer;
-    boost::asio::posix::stream_descriptor stdout_redirect(io_context,
-                                                          stdout_pipe[0]);
-    boost::asio::posix::stream_descriptor stderr_redirect(io_context,
-                                                          stderr_pipe[0]);
-    log_lines(logger, stdout_redirect, stdout_buffer, "[STDOUT] ");
-    log_lines(logger, stderr_redirect, stderr_buffer, "[STDERR] ");
+    StdIoCapture stdout_redirect(io_context, STDOUT_FILENO);
+    StdIoCapture stderr_redirect(io_context, STDERR_FILENO);
+    log_lines(logger, stdout_redirect.pipe, stdout_buffer, "[STDOUT] ");
+    log_lines(logger, stderr_redirect.pipe, stderr_buffer, "[STDERR] ");
+
     std::thread io_handler([&]() { io_context.run(); });
 
     logger.log("Initializing yabridge group host version " +