1 files changed, 184 insertions, 0 deletions
diff --git a/pager.c b/pager.c
new file mode 100644
index 0000000000..0cc75a8eee
--- /dev/null
+++ b/pager.c
@@ -0,0 +1,184 @@
+#include "cache.h"
+#include "run-command.h"
+#include "sigchain.h"
+
+#ifndef DEFAULT_PAGER
+#define DEFAULT_PAGER "less"
+#endif
+
+struct pager_config {
+	const char *cmd;
+	int want;
+	char *value;
+};
+
+/*
+ * This is split up from the rest of git so that we can do
+ * something different on Windows.
+ */
+
+static const char *pager_argv[] = { NULL, NULL };
+static struct child_process pager_process;
+
+static void wait_for_pager(void)
+{
+	fflush(stdout);
+	fflush(stderr);
+	/* signal EOF to pager */
+	close(1);
+	close(2);
+	finish_command(&pager_process);
+}
+
+static void wait_for_pager_signal(int signo)
+{
+	wait_for_pager();
+	sigchain_pop(signo);
+	raise(signo);
+}
+
+const char *git_pager(int stdout_is_tty)
+{
+	const char *pager;
+
+	if (!stdout_is_tty)
+		return NULL;
+
+	pager = getenv("GIT_PAGER");
+	if (!pager) {
+		if (!pager_program)
+			git_config(git_default_config, NULL);
+		pager = pager_program;
+	}
+	if (!pager)
+		pager = getenv("PAGER");
+	if (!pager)
+		pager = DEFAULT_PAGER;
+	if (!*pager || !strcmp(pager, "cat"))
+		pager = NULL;
+
+	return pager;
+}
+
+void setup_pager(void)
+{
+	const char *pager = git_pager(isatty(1));
+
+	if (!pager || pager_in_use())
+		return;
+
+	/*
+	 * force computing the width of the terminal before we redirect
+	 * the standard output to the pager.
+	 */
+	(void) term_columns();
+
+	setenv("GIT_PAGER_IN_USE", "true", 1);
+
+	/* spawn the pager */
+	pager_argv[0] = pager;
+	pager_process.use_shell = 1;
+	pager_process.argv = pager_argv;
+	pager_process.in = -1;
+	if (!getenv("LESS") || !getenv("LV")) {
+		static const char *env[3];
+		int i = 0;
+
+		if (!getenv("LESS"))
+			env[i++] = "LESS=FRSX";
+		if (!getenv("LV"))
+			env[i++] = "LV=-c";
+		env[i] = NULL;
+		pager_process.env = env;
+	}
+	if (start_command(&pager_process))
+		return;
+
+	/* original process continues, but writes to the pipe */
+	dup2(pager_process.in, 1);
+	if (isatty(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);
+}
+
+int pager_in_use(void)
+{
+	const char *env;
+	env = getenv("GIT_PAGER_IN_USE");
+	return env ? git_config_bool("GIT_PAGER_IN_USE", env) : 0;
+}
+
+/*
+ * Return cached value (if set) or $COLUMNS environment variable (if
+ * set and positive) or ioctl(1, TIOCGWINSZ).ws_col (if positive),
+ * and default to 80 if all else fails.
+ */
+int term_columns(void)
+{
+	static int term_columns_at_startup;
+
+	char *col_string;
+	int n_cols;
+
+	if (term_columns_at_startup)
+		return term_columns_at_startup;
+
+	term_columns_at_startup = 80;
+
+	col_string = getenv("COLUMNS");
+	if (col_string && (n_cols = atoi(col_string)) > 0)
+		term_columns_at_startup = n_cols;
+#ifdef TIOCGWINSZ
+	else {
+		struct winsize ws;
+		if (!ioctl(1, TIOCGWINSZ, &ws) && ws.ws_col)
+			term_columns_at_startup = ws.ws_col;
+	}
+#endif
+
+	return term_columns_at_startup;
+}
+
+/*
+ * How many columns do we need to show this number in decimal?
+ */
+int decimal_width(int number)
+{
+	int i, width;
+
+	for (width = 1, i = 10; i <= number; width++)
+		i *= 10;
+	return width;
+}
+
+static int pager_command_config(const char *var, const char *value, void *data)
+{
+	struct pager_config *c = data;
+	if (starts_with(var, "pager.") && !strcmp(var + 6, c->cmd)) {
+		int b = git_config_maybe_bool(var, value);
+		if (b >= 0)
+			c->want = b;
+		else {
+			c->want = 1;
+			c->value = xstrdup(value);
+		}
+	}
+	return 0;
+}
+
+/* returns 0 for "no pager", 1 for "use pager", and -1 for "not specified" */
+int check_pager_config(const char *cmd)
+{
+	struct pager_config c;
+	c.cmd = cmd;
+	c.want = -1;
+	c.value = NULL;
+	git_config(pager_command_config, &c);
+	if (c.value)
+		pager_program = c.value;
+	return c.want;
+}