From fb20df91ea260cbd03b5a4078b64545e4649dc78 Mon Sep 17 00:00:00 2001
From: Maurus Decimus <11444311+mdecimus@users.noreply.github.com>
Date: Thu, 7 May 2026 15:30:11 +0200
Subject: [PATCH] Fix Network: Attempt binding to IPv4 when binding to IPv6
 fails with `EAFNOSUPPORT` error

---
 CHANGELOG.md                                |  1 +
 crates/common/src/config/server/listener.rs | 50 ++++++++++++++++++++-
 2 files changed, 49 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0a1e9775..2751e078 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,6 +16,7 @@ If you are upgrading from v0.16.x, replace the binary (or run `docker pull`). If
   - Patching ids containing digits in JSON Pointers failes.
   - Patching nested objects with `null` values fails.
 - SQL directory: Return `Failed` instead of `Error` when the query returns no results.
+- Network: Attempt binding to IPv4 when binding to IPv6 fails with `EAFNOSUPPORT` error.
 
 ## [0.16.4] - 2026-05-05
 
diff --git a/crates/common/src/config/server/listener.rs b/crates/common/src/config/server/listener.rs
index 2970d85a..94504dd6 100644
--- a/crates/common/src/config/server/listener.rs
+++ b/crates/common/src/config/server/listener.rs
@@ -24,7 +24,11 @@ use rustls::{
     ALL_VERSIONS, ServerConfig, SupportedCipherSuite,
     crypto::aws_lc_rs::{ALL_CIPHER_SUITES, cipher_suite::*, default_provider},
 };
-use std::{str::FromStr, sync::Arc};
+use std::{
+    net::{IpAddr, Ipv4Addr, SocketAddr as StdSocketAddr},
+    str::FromStr,
+    sync::Arc,
+};
 use store::registry::{RegistryObject, bootstrap::Bootstrap};
 use tokio::net::TcpSocket;
 use tokio_rustls::TlsAcceptor;
@@ -109,13 +113,39 @@ impl Listeners {
         let mut listeners = Vec::new();
         for addr in listener.bind.iter() {
             // Parse bind address and build socket
-            let addr = addr.0;
+            let mut addr = addr.0;
             let socket = match if addr.is_ipv4() {
                 TcpSocket::new_v4()
             } else {
                 TcpSocket::new_v6()
             } {
                 Ok(socket) => socket,
+                Err(err)
+                    if is_eafnosupport(&err)
+                        && addr.is_ipv6()
+                        && addr.ip().is_unspecified() =>
+                {
+                    let v4_addr =
+                        StdSocketAddr::new(IpAddr::V4(Ipv4Addr::UNSPECIFIED), addr.port());
+                    bp.build_warning(
+                        id,
+                        format!(
+                            "IPv6 unavailable on this host ({err}); \
+                             falling back from {addr} to {v4_addr}"
+                        ),
+                    );
+                    addr = v4_addr;
+                    match TcpSocket::new_v4() {
+                        Ok(socket) => socket,
+                        Err(err) => {
+                            bp.build_error(
+                                id,
+                                format!("Failed to create IPv4 fallback socket: {err}"),
+                            );
+                            return;
+                        }
+                    }
+                }
                 Err(err) => {
                     bp.build_error(id, format!("Failed to create socket: {err}"));
                     return;
@@ -284,3 +314,19 @@ impl Listeners {
         }
     }
 }
+
+fn is_eafnosupport(err: &std::io::Error) -> bool {
+    let code = err.raw_os_error();
+    #[cfg(unix)]
+    {
+        code == Some(libc::EAFNOSUPPORT)
+    }
+    #[cfg(windows)]
+    {
+        code == Some(10047)
+    }
+    #[cfg(not(any(unix, windows)))]
+    {
+        false
+    }
+}