libdpkg: Add pager spawning and reaping support

This will make using a pager way easier, and make it possible to remove
some redundant and unsafe system() usage.

3 files changed, 72 insertions, 0 deletions

diff --git a/lib/dpkg/libdpkg.map b/lib/dpkg/libdpkg.map
index b562d7aad..cb3062845 100644
--- a/lib/dpkg/libdpkg.map
+++ b/lib/dpkg/libdpkg.map
@@ -185,6 +185,8 @@ LIBDPKG_PRIVATE {
 	command_destroy;
 
 	pager_get_exec;
+	pager_spawn;
+	pager_reap;
 
 	setcloexec;
 
diff --git a/lib/dpkg/pager.c b/lib/dpkg/pager.c
index 4922b537a..c9adf5bce 100644
--- a/lib/dpkg/pager.c
+++ b/lib/dpkg/pager.c
@@ -21,12 +21,17 @@
 #include <config.h>
 #include <compat.h>
 
+#include <sys/types.h>
+
+#include <stdbool.h>
 #include <stdlib.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>
 
 /**
@@ -48,3 +53,62 @@ pager_get_exec(void)
 
 	return pager;
 }
+
+struct pager {
+	bool used;
+	const char *desc;
+	pid_t pid;
+	int stdout_old;
+	int pipe[2];
+};
+
+struct pager *
+pager_spawn(const char *desc, const char *filename)
+{
+	struct pager *pager;
+
+	pager = m_calloc(1, sizeof(*pager));
+	pager->used = filename || (isatty(0) && isatty(1));
+	pager->desc = desc;
+
+	if (!pager->used)
+		return pager;
+
+	m_pipe(pager->pipe);
+
+	pager->pid = subproc_fork();
+	if (pager->pid == 0) {
+		struct command cmd;
+		const char *exec;
+
+		exec = pager_get_exec();
+
+		m_dup2(pager->pipe[0], 0);
+		close(pager->pipe[0]);
+		close(pager->pipe[1]);
+
+		command_init(&cmd, exec, desc);
+		command_add_arg(&cmd, exec);
+		command_add_arg(&cmd, filename);
+		command_exec(&cmd);
+	}
+
+	pager->stdout_old = m_dup(1);
+	m_dup2(pager->pipe[1], 1);
+	close(pager->pipe[0]);
+	close(pager->pipe[1]);
+
+	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);
+
+	free(pager);
+}
diff --git a/lib/dpkg/pager.h b/lib/dpkg/pager.h
index 8ecc93b97..7d7ea0dff 100644
--- a/lib/dpkg/pager.h
+++ b/lib/dpkg/pager.h
@@ -36,6 +36,12 @@ struct pager;
 const char *
 pager_get_exec(void);
 
+struct pager *
+pager_spawn(const char *desc, const char *filename);
+
+void
+pager_reap(struct pager *pager);
+
 /** @} */
 
 DPKG_END_DECLS