From 8bb7792ee380c14c076f77d7d57d68fb9c863c61 Mon Sep 17 00:00:00 2001
From: n8fr8 <nathan@freitas.net>
Date: Wed, 1 Jul 2026 13:31:24 -0400
Subject: [PATCH] add logic for dynamic IP lookup for deltachat links and
 install #31

---
 app/routes.py      | 36 +++++++++++++++++++++++++++++++++++-
 install_madmail.py | 30 +++++++++++++++++++++++++++++-
 2 files changed, 64 insertions(+), 2 deletions(-)

diff --git a/app/routes.py b/app/routes.py
index 196e9de..e2bed77 100644
--- a/app/routes.py
+++ b/app/routes.py
@@ -1,5 +1,6 @@
 import io
 import re
+import socket
 import subprocess
 
 from app import app
@@ -26,6 +27,39 @@ from install_madmail import run_madmail_installer
 CHANGES_REQUIRING_RESTART = ['wifi_password', 'ssid', 'enable_access_point', 'enable_chat', 'enable_delta_chat', 'butterbox_hostname', 'ssh_access_settings', 'root_account_settings', 'root_password']
 RASPAP_INSTALLED = os.path.exists("/var/www/html/raspap")
 
+def resolve_butterbox_ip() -> str:
+    """Best-effort lookup of the address clients should use to reach this box.
+
+    ``BUTTERBOX_DEFAULT_IP`` is only correct while the box serves its own
+    access point. When it's joined to another network its address differs, so
+    try to discover the real one and only fall back to the configured default.
+    """
+    hostname = get_setting('butterbox_hostname') or app.config['BUTTERBOX_HOSTNAME']
+
+    # 1. Resolve the box's own mDNS/.local name. This is the same name the
+    #    DeltaChat link uses for the mail host, so avahi/nss-mdns is present.
+    try:
+        ip = socket.gethostbyname(f"{hostname}.local")
+        if ip and not ip.startswith("127."):
+            return ip
+    except OSError:
+        pass
+
+    # 2. Fall back to the address of the primary outbound interface. The
+    #    connect() picks a route without sending any packets.
+    try:
+        with socket.socket(socket.AF_INET, socket.SOCK_DGRAM) as s:
+            s.connect(("8.8.8.8", 80))
+            ip = s.getsockname()[0]
+            if ip and not ip.startswith("127."):
+                return ip
+    except OSError:
+        pass
+
+    # 3. Give up and use the configured access-point default.
+    return app.config['BUTTERBOX_DEFAULT_IP']
+
+
 def gen_username() -> str:
     words = top_n_list("en", 5000)
     prefix = random.randint(1000, 9999)
@@ -370,7 +404,7 @@ def messaging():
 
 @app.route("/deltachat_credentials", methods=["POST"])
 def deltachat_credentials():
-    ip = app.config['BUTTERBOX_DEFAULT_IP']
+    ip = resolve_butterbox_ip()
     username = gen_username()
     password = gen_password()
     hostname = f"{get_setting('butterbox_hostname')}.local"
diff --git a/install_madmail.py b/install_madmail.py
index c71ea50..9deb016 100644
--- a/install_madmail.py
+++ b/install_madmail.py
@@ -1,8 +1,36 @@
 import pexpect
 import json
+import socket
 from app import app
 from subprocess import run
 
+def resolve_butterbox_ip(hostname):
+    """Best-effort lookup of the box's current address, falling back to the
+    configured default. Mirrors app.routes.resolve_butterbox_ip but avoids a
+    circular import (routes imports this module) and reuses the hostname that
+    was already loaded from settings.txt."""
+    # 1. Resolve the box's own mDNS/.local name.
+    try:
+        ip = socket.gethostbyname(f"{hostname}.local")
+        if ip and not ip.startswith("127."):
+            return ip
+    except OSError:
+        pass
+
+    # 2. Fall back to the address of the primary outbound interface. The
+    #    connect() picks a route without sending any packets.
+    try:
+        with socket.socket(socket.AF_INET, socket.SOCK_DGRAM) as s:
+            s.connect(("8.8.8.8", 80))
+            ip = s.getsockname()[0]
+            if ip and not ip.startswith("127."):
+                return ip
+    except OSError:
+        pass
+
+    # 3. Give up and use the configured access-point default.
+    return app.config['BUTTERBOX_DEFAULT_IP']
+
 def run_madmail_installer():
     with open("./settings.txt", "r") as f:
         settings = json.load(f)
@@ -18,7 +46,7 @@ def run_madmail_installer():
     child.expect("MX record")
     child.sendline(f"{butterbox_hostname}.local")
     child.expect("Public IP address")
-    child.sendline(app.config['BUTTERBOX_DEFAULT_IP'])
+    child.sendline(resolve_butterbox_ip(butterbox_hostname))
     child.expect("Additional domains")
     child.sendline("")
     child.expect("State directory")