Created a new stream.h file for dealing with output streaming.

1 files changed, 142 insertions, 0 deletions

diff --git a/src/stream.cc b/src/stream.cc
new file mode 100644
index 00000000..0394c042
--- /dev/null
+++ b/src/stream.cc
@@ -0,0 +1,142 @@
+/*
+ * Copyright (c) 2003-2009, John Wiegley.  All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ *   notice, this list of conditions and the following disclaimer in the
+ *   documentation and/or other materials provided with the distribution.
+ *
+ * - Neither the name of New Artisans LLC nor the names of its
+ *   contributors may be used to endorse or promote products derived from
+ *   this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "utils.h"
+
+#ifdef HAVE_UNIX_PIPES
+#include <sys/types.h>
+#include <sys/wait.h>
+#include "fdstream.h"
+#endif
+
+namespace ledger {
+
+namespace {
+  /**
+   * @brief Forks a child process so that Ledger may handle running a
+   * pager
+   *
+   * In order for the pager option to work, Ledger has to run the pager
+   * itself, which requires Ledger to fork a new process in order to run
+   * the pager.  This function does the necessary fork.  After the fork,
+   * two processes exist.  One of them is exec'd to create the pager;
+   * the other is still Ledger.
+   *
+   * This function returns only for the process that is still Ledger.
+   *
+   * @param out Pointer to a pointer to the output stream.  This The
+   * pointer to the output stream is changed so that the stream is
+   * connected to the stdin of the pager.  The caller is responsible for
+   * cleaning this up.
+   *
+   * @param pager_path Path to the pager command.
+   *
+   * @return The file descriptor of the pipe to the pager.  The caller
+   * is responsible for cleaning this up.
+   *
+   * @exception std::logic_error Some problem was encountered, such as
+   * failure to create a pipe or failure to fork a child process.
+   */
+  int do_fork(std::ostream ** os, const path& pager_path)
+  {
+    int pfd[2];
+
+    int status = pipe(pfd);
+    if (status == -1)
+      throw std::logic_error("Failed to create pipe");
+
+    status = fork();
+    if (status < 0) {
+      throw std::logic_error("Failed to fork child process");
+    }
+    else if (status == 0) {	// child
+      const char *arg0;
+
+      // Duplicate pipe's reading end into stdin
+      status = dup2(pfd[0], STDIN_FILENO);
+      if (status == -1)
+	perror("dup2");
+
+      // Close unuseful file descriptors: the pipe's writing and reading
+      // ends (the latter is not needed anymore, after the duplication).
+      close(pfd[1]);
+      close(pfd[0]);
+
+      // Find command name: its the substring starting right of the
+      // rightmost '/' character in the pager pathname.  See manpage for
+      // strrchr.
+      path basename(pager_path.leaf());
+      execlp(pager_path.string().c_str(), basename.string().c_str(),
+	     (char *)0);
+
+      // We should never, ever reach here
+      perror("execl");
+      exit(1);
+    }
+    else {			// parent
+      close(pfd[0]);
+      *os = new boost::fdostream(pfd[1]);
+    }
+    return pfd[1];
+  }
+}
+
+void output_stream_t::initialize(const optional<path>& output_file,
+				 const optional<path>& pager_path)
+{
+  TRACE_CTOR(output_stream_t, "const path&, const path&");
+
+  if (output_file)
+    os = new ofstream(*output_file);
+  else if (pager_path && exists(*pager_path))
+    pipe_to_pager_fd = do_fork(&os, *pager_path);
+  else
+    os = &std::cout;
+}
+
+output_stream_t::~output_stream_t()
+{
+  TRACE_DTOR(output_stream_t);
+
+  if (os && os != &std::cout)
+    checked_delete(os);
+
+  if (pipe_to_pager_fd != -1) {
+    close(pipe_to_pager_fd);
+
+    int status;
+    wait(&status);
+    if (status & 0xffff != 0)
+      throw std::logic_error("Something went wrong in the pager");
+  }
+}
+
+} // namespace ledger