[PATCH v2 3/5] pager: introduce wait_for_pager

["Rubén Justo" <rjusto@gmail.com>]

Since f67b45f862 (Introduce trivial new pager.c helper infrastructure,
2006-02-28) we have the machinery to send our output to a pager.

That machinery, once set up, does not allow us to regain the original
stdio streams.

In the interactive commands (i.e.: add -p) we want to use the pager for
some output, while maintaining the interaction with the user.

Modify the pager machinery so that we can use setup_pager and, once
we've finished sending the desired output for the pager, wait for the
pager termination using a new function wait_for_pager.   Make this
function reset the pager machinery before returning.

Signed-off-by: Rubén Justo <rjusto@gmail.com>
---
 pager.c | 37 +++++++++++++++++++++++++++++++------
 pager.h |  1 +
 2 files changed, 32 insertions(+), 6 deletions(-)

diff --git a/pager.c b/pager.c
index 3ef6798f7e..2fa06c43c4 100644
--- a/pager.c
+++ b/pager.c
@@ -14,12 +14,11 @@ int pager_use_color = 1;
 
 static struct child_process pager_process;
 static const char *pager_program;
-static int old_fd2 = -1;
+static int old_fd1 = -1, old_fd2 = -1;
 
 /* Is the value coming back from term_columns() just a guess? */
 static int term_columns_guessed;
 
-
 static void close_pager_fds(void)
 {
 	/* signal EOF to pager */
@@ -30,14 +29,35 @@ static void close_pager_fds(void)
 
 static void wait_for_pager_atexit(void)
 {
+	if (old_fd1 == -1)
+		return;
+
 	fflush(stdout);
 	fflush(stderr);
 	close_pager_fds();
 	finish_command(&pager_process);
 }
 
+void wait_for_pager(void)
+{
+	if (old_fd1 == -1)
+		return;
+
+	wait_for_pager_atexit();
+	unsetenv("GIT_PAGER_IN_USE");
+	dup2(old_fd1, 1);
+	old_fd1 = -1;
+	if (old_fd2 != -1) {
+		dup2(old_fd2, 2);
+		old_fd2 = -1;
+	}
+}
+
 static void wait_for_pager_signal(int signo)
 {
+	if (old_fd1 == -1)
+		return;
+
 	close_pager_fds();
 	finish_command_in_signal(&pager_process);
 	sigchain_pop(signo);
@@ -113,11 +133,14 @@ void prepare_pager_args(struct child_process *pager_process, const char *pager)
 
 void setup_pager(void)
 {
+	static int once = 0;
 	const char *pager = git_pager(isatty(1));
 
 	if (!pager)
 		return;
 
+	assert(old_fd1 == -1);
+
 	/*
 	 * After we redirect standard output, we won't be able to use an ioctl
 	 * to get the terminal size. Let's grab it now, and then set $COLUMNS
@@ -142,16 +165,18 @@ void setup_pager(void)
 		return;
 
 	/* original process continues, but writes to the pipe */
+	old_fd1 = dup(1);
 	dup2(pager_process.in, 1);
 	if (isatty(2)) {
-		old_fd2 = 1;
+		old_fd2 = dup(2);
 		dup2(pager_process.in, 2);
 	}
 	close(pager_process.in);
 
-	/* this makes sure that the parent terminates after the pager */
-	sigchain_push_common(wait_for_pager_signal);
-	atexit(wait_for_pager_atexit);
+	if (!once++) {
+		sigchain_push_common(wait_for_pager_signal);
+		atexit(wait_for_pager_atexit);
+	}
 }
 
 int pager_in_use(void)
diff --git a/pager.h b/pager.h
index b77433026d..103ecac476 100644
--- a/pager.h
+++ b/pager.h
@@ -5,6 +5,7 @@ struct child_process;
 
 const char *git_pager(int stdout_is_tty);
 void setup_pager(void);
+void wait_for_pager(void);
 int pager_in_use(void);
 int term_columns(void);
 void term_clear_line(void);
-- 
2.45.1.221.gd3c11dbb1d