From 50753359eb7a760bcadd54611431c0888867c21c Mon Sep 17 00:00:00 2001
From: Casey Fitzpatrick <kcghost@gmail.com>
Date: Sat, 28 Jan 2023 09:46:53 -0500
Subject: [PATCH] Spawn new tabs in working directory of selected clients child

When used with st or xterm the working directory of the new tab
should be the same as the currently selected tab.
---
 tabbed.c | 57 +++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 56 insertions(+), 1 deletion(-)

diff --git a/tabbed.c b/tabbed.c
index eafe28a..eb046d0 100644
--- a/tabbed.c
+++ b/tabbed.c
@@ -10,6 +10,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
+#include <linux/limits.h>
 #include <X11/Xatom.h>
 #include <X11/Xlib.h>
 #include <X11/Xproto.h>
@@ -84,6 +85,7 @@ typedef struct {
 	int tabx;
 	Bool urgent;
 	Bool closed;
+	pid_t pid;
 } Client;
 
 /* function declarations */
@@ -168,6 +170,7 @@ static int cmd_append_pos;
 static char winid[64];
 static char **cmd;
 static char *wmname = "tabbed";
+static pid_t nextpid;
 static const char *geometry;
 
 char *argv0;
@@ -175,6 +178,49 @@ char *argv0;
 /* configuration, allows nested code to access above variables */
 #include "config.h"
 
+// Given a pid, return its cwd to buf
+int getpidcwd(pid_t pid, char* buf, size_t bufsiz) {
+	static const int proc_max = 20; // '/proc/4194304/cwd'
+	int sn_ret;
+	ssize_t rl_ret;
+	char path[proc_max];
+
+	sn_ret = snprintf(path, proc_max, "/proc/%d/cwd", pid);
+	if(sn_ret < 0 || sn_ret >= proc_max)
+		return -1;
+
+	rl_ret = readlink(path, buf, bufsiz);
+	if(rl_ret < 0 || rl_ret == bufsiz)
+		return -1;
+
+	buf[rl_ret] = 0;
+	return 0;
+}
+
+// Given a pid, return a reasonable guess at its child pid
+pid_t getchildpid(pid_t pid) {
+	// '/proc/4194304/task/4194304/children'
+	static const int proc_max = 40;
+	int sn_ret;
+	char path[proc_max];
+	FILE* f;
+
+	// guessing tid == pid
+	sn_ret = snprintf(path, proc_max, "/proc/%d/task/%d/children", pid, pid);
+	if (sn_ret < 0 || sn_ret >= proc_max)
+		return -1;
+
+	f = fopen(path, "r");
+	if(f == NULL)
+		return -1;
+
+	// guess first child
+	if(fscanf(f, "%d ", &pid) != 1)
+		return -1;
+
+	return pid;
+}
+
 void
 buttonpress(const XEvent *e)
 {
@@ -725,6 +771,7 @@ manage(Window w)
 
 		c = ecalloc(1, sizeof *c);
 		c->win = w;
+		c->pid = nextpid;
 
 		nclients++;
 		clients = erealloc(clients, sizeof(Client *) * nclients);
@@ -1090,11 +1137,17 @@ sigchld(int unused)
 void
 spawn(const Arg *arg)
 {
-	if (fork() == 0) {
+	char sel_cwd[PATH_MAX];
+
+	pid_t pid = fork();
+	if (pid == 0) {
 		if(dpy)
 			close(ConnectionNumber(dpy));
 
 		setsid();
+		if (sel >= 0 && clients[sel] && clients[sel]->pid > 0 && getpidcwd(getchildpid(clients[sel]->pid), sel_cwd, PATH_MAX) == 0) {
+			chdir(sel_cwd);
+		}
 		if (arg && arg->v) {
 			execvp(((char **)arg->v)[0], (char **)arg->v);
 			fprintf(stderr, "%s: execvp %s", argv0,
@@ -1106,6 +1159,8 @@ spawn(const Arg *arg)
 		}
 		perror(" failed");
 		exit(0);
+	} else {
+		nextpid = pid;
 	}
 }
 
-- 
2.25.1