1 files changed, 145 insertions, 0 deletions
diff --git a/lib/dpkg/pager.c b/lib/dpkg/pager.c
new file mode 100644
index 0000000..4eab2f0
--- /dev/null
+++ b/lib/dpkg/pager.c
@@ -0,0 +1,145 @@
+/*
+ * libdpkg - Debian packaging suite library routines
+ * pager.c - pager execution support
+ *
+ * Copyright © 2018 Guillem Jover <guillem@debian.org>
+ *
+ * This 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 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This 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 <config.h>
+#include <compat.h>
+
+#include <sys/types.h>
+
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+#include <signal.h>
+#include <unistd.h>
+
+#include <dpkg/dpkg.h>
+#include <dpkg/i18n.h>
+#include <dpkg/string.h>
+#include <dpkg/subproc.h>
+#include <dpkg/command.h>
+#include <dpkg/pager.h>
+
+static bool pager_enabled = true;
+
+void
+pager_enable(bool enable)
+{
+	pager_enabled = enable;
+}
+
+/**
+ * Get a suitable pager.
+ *
+ * @return A string representing a pager.
+ */
+const char *
+pager_get_exec(void)
+{
+	const char *pager;
+
+	if (!isatty(0) || !isatty(1))
+		return CAT;
+
+	pager = getenv("DPKG_PAGER");
+	if (str_is_unset(pager))
+		pager = getenv("PAGER");
+	if (str_is_unset(pager))
+		pager = DEFAULTPAGER;
+
+	return pager;
+}
+
+struct pager {
+	bool used;
+	const char *desc;
+	pid_t pid;
+	struct sigaction sigpipe;
+	int stdout_old;
+	int pipe[2];
+};
+
+struct pager *
+pager_spawn(const char *desc)
+{
+	struct sigaction sa;
+	struct pager *pager;
+	const char *exec;
+
+	pager = m_calloc(1, sizeof(*pager));
+	pager->used = isatty(0) && isatty(1);
+	pager->desc = desc;
+
+	exec = pager_get_exec();
+	if (strcmp(exec, CAT) == 0)
+		pager->used = false;
+
+	if (!pager_enabled)
+		pager->used = false;
+
+	if (!pager->used)
+		return pager;
+
+	m_pipe(pager->pipe);
+
+	memset(&sa, 0, sizeof(sa));
+	sigemptyset(&sa.sa_mask);
+	sa.sa_handler = SIG_IGN;
+	sa.sa_flags = 0;
+
+	sigaction(SIGPIPE, &sa, &pager->sigpipe);
+
+	pager->pid = subproc_fork();
+	if (pager->pid == 0) {
+		/* Set better defaults for less if not already set. */
+		setenv("LESS", "-FRSXMQ", 0);
+
+		m_dup2(pager->pipe[0], 0);
+		close(pager->pipe[0]);
+		close(pager->pipe[1]);
+
+		command_shell(exec, desc);
+	}
+
+	pager->stdout_old = m_dup(1);
+	m_dup2(pager->pipe[1], 1);
+	close(pager->pipe[0]);
+	close(pager->pipe[1]);
+
+	/* Force the output to fully buffered, because originally stdout was
+	 * a tty, so it was set as line buffered. This way we send as much as
+	 * possible to the pager, which will handle the output by itself. */
+	setvbuf(stdout, NULL, _IOFBF, 0);
+
+	return pager;
+}
+
+void
+pager_reap(struct pager *pager)
+{
+	if (!pager->used)
+		return;
+
+	m_dup2(pager->stdout_old, 1);
+	subproc_reap(pager->pid, pager->desc, SUBPROC_NOPIPE);
+
+	sigaction(SIGPIPE, &pager->sigpipe, NULL);
+
+	free(pager);
+}