From 15f0c7040bb451973e344199ad72a98908513977 Mon Sep 17 00:00:00 2001
From: Mike Fortman <michael.fortman@datastax.com>
Date: Fri, 13 Jun 2025 11:19:34 -0500
Subject: [PATCH] refactor: Update access link for langflow run (#8492)

* Update host selection

* cleanup

* [autofix.ci] apply automated fixes

* ruff check fix2

* Merge branch 'main' of github.com:langflow-ai/langflow into lfoss-1357

---------

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
---
 src/backend/base/langflow/__main__.py | 80 ++++++++++++++++++++++++++-
 1 file changed, 78 insertions(+), 2 deletions(-)

diff --git a/src/backend/base/langflow/__main__.py b/src/backend/base/langflow/__main__.py
index 30da0aa65..e7f997725 100644
--- a/src/backend/base/langflow/__main__.py
+++ b/src/backend/base/langflow/__main__.py
@@ -8,6 +8,7 @@ import sys
 import time
 import warnings
 from contextlib import suppress
+from ipaddress import ip_address
 from pathlib import Path
 
 import click
@@ -239,7 +240,8 @@ def run(
             # Run using gunicorn on Linux
             process = run_on_mac_or_linux(host, port, log_level, options, app, protocol)
         if open_browser and not backend_only:
-            click.launch(f"http://{host}:{port}")
+            browser_host = get_best_access_host(host, port)
+            click.launch(f"{protocol}://{browser_host}:{port}")
         if process:
             process.join()
     except (KeyboardInterrupt, SystemExit) as e:
@@ -316,6 +318,80 @@ def get_free_port(port):
     return port
 
 
+def is_loopback_address(host: str) -> bool:
+    """Check if a host is a loopback address (localhost, 127.0.0.1, ::1, etc.).
+
+    Args:
+        host: The host address to check
+
+    Returns:
+        bool: True if the host is a loopback address, False otherwise
+    """
+    # Check if it's exactly "localhost"
+    if host == "localhost":
+        return True
+
+    # Check if it's exactly "0.0.0.0" (which binds to all interfaces)
+    if host == "0.0.0.0":  # noqa: S104
+        return True
+
+    try:
+        # Convert string to IP address object
+        ip = ip_address(host)
+        # Check if it's a loopback address (127.0.0.0/8 for IPv4, ::1 for IPv6)
+        return bool(ip.is_loopback)
+    except ValueError:
+        # If the IP address is invalid, default to False
+        return False
+
+
+def get_best_access_host(host: str, port: int) -> str:
+    """Get the best host to use for accessing the server.
+
+    For loopback addresses, we prefer 'localhost' over IP addresses like '127.0.0.1'
+    because 'localhost' is more universally supported across different operating systems
+    and network configurations.
+
+    Args:
+        host: The original host address
+        port: The port number
+        protocol: The protocol (http or https)
+
+    Returns:
+        str: The best host address to use for access
+    """
+    if not is_loopback_address(host):
+        return host
+
+    # For loopback addresses, prefer localhost
+    preferred_host = "localhost"
+
+    # Test connectivity to both localhost and the original host if it's different
+    if host != preferred_host:
+        # Test if localhost works
+        try:
+            with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
+                s.settimeout(1)  # 1 second timeout
+                result = s.connect_ex((preferred_host, port))
+                if result == 0:
+                    return preferred_host
+        except Exception as exc:  # noqa: BLE001
+            logger.debug(f"Failed to connect to {preferred_host}:{port}: {exc}")
+
+        # If localhost doesn't work, test the original host
+        try:
+            with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
+                s.settimeout(1)  # 1 second timeout
+                result = s.connect_ex((host, port))
+                if result == 0:
+                    return host
+        except Exception as exc:  # noqa: BLE001
+            logger.debug(f"Failed to connect to {host}:{port}: {exc}")
+
+    # Default to localhost for loopback addresses
+    return preferred_host
+
+
 def get_letter_from_version(version: str) -> str | None:
     """Get the letter from a pre-release version."""
     if "a" in version:
@@ -415,7 +491,7 @@ def print_banner(host: str, port: int, protocol: str) -> None:
             "To contribute, set: [bold]DO_NOT_TRACK=false[/bold] in your environment."
         )
     )
-    access_host = host if host != "0.0.0.0" else "localhost"  # noqa: S104
+    access_host = get_best_access_host(host, port)
     access_link = f"[bold]🟢 Open Langflow →[/bold] [link={protocol}://{access_host}:{port}]{protocol}://{access_host}:{port}[/link]"
 
     message = f"{title}\n{info_text}\n\n{telemetry_text}\n\n{access_link}"