nuageinit: add hostname validation (RFC 952/1123) to sethostname()

Validate hostnames before writing them:
- Reject empty hostnames
- Reject hostnames longer than 253 characters
- Reject hostnames with invalid characters
- Reject hostnames starting or ending with dot/hyphen
- Reject labels longer than 63 characters
- Reject labels starting or ending with hyphen

Expand the sethostname test to cover all rejection cases.
Update nuage.sh sethostname_body to ignore stderr (warnings).

2 files changed, 69 insertions, 1 deletions

diff --git a/libexec/nuageinit/tests/nuage.sh b/libexec/nuageinit/tests/nuage.sh
index 348a8d93ba09..97c5224c7813 100644
--- a/libexec/nuageinit/tests/nuage.sh
+++ b/libexec/nuageinit/tests/nuage.sh
@@ -29,7 +29,7 @@ settimezone_body()
 
 sethostname_body()
 {
-	atf_check /usr/libexec/flua $(atf_get_srcdir)/sethostname.lua
+	atf_check -e ignore /usr/libexec/flua $(atf_get_srcdir)/sethostname.lua
 	if [ ! -f etc/rc.conf.d/hostname ]; then
 		atf_fail "hostname not written"
 	fi
diff --git a/libexec/nuageinit/tests/sethostname.lua b/libexec/nuageinit/tests/sethostname.lua
index 47632497b545..0bc7eb2c4475 100644
--- a/libexec/nuageinit/tests/sethostname.lua
+++ b/libexec/nuageinit/tests/sethostname.lua
@@ -1,5 +1,73 @@
 #!/usr/libexec/flua
+---
+-- SPDX-License-Identifier: BSD-2-Clause
+--
+-- Copyright (c) 2026 Baptiste Daroussin <bapt@FreeBSD.org>
 
 local n = require("nuage")
 
+local root = os.getenv("NUAGE_FAKE_ROOTDIR")
+if not root then
+	root = ""
+end
+
+local hostnamepath = root .. "/etc/rc.conf.d/hostname"
+
+local function check_hostname(expected)
+	local f = io.open(hostnamepath, "r")
+	if not f then
+		n.err("hostname file not found, expected: " .. expected)
+	end
+	local content = f:read("*a")
+	f:close()
+	local expected_content = 'hostname="' .. expected:gsub('"', '\\"') .. '"\n'
+	if content ~= expected_content then
+		n.err("hostname mismatch: got '" .. content ..
+		    "', expected '" .. expected_content .. "'")
+	end
+end
+
+local function check_no_hostname()
+	if io.open(hostnamepath, "r") then
+		n.err("hostname file should not exist")
+	end
+end
+
+-- nil hostname: no-op
+n.sethostname(nil)
+check_no_hostname()
+
+-- Empty hostname: invalid
+n.sethostname("")
+check_no_hostname()
+
+-- Hostname too long (>253 chars): invalid
+n.sethostname(string.rep("a", 254))
+check_no_hostname()
+
+-- Invalid characters: invalid
+n.sethostname("host;name")
+check_no_hostname()
+
+-- Starts with dot: invalid
+n.sethostname(".hostname")
+check_no_hostname()
+
+-- Ends with hyphen: invalid
+n.sethostname("hostname-")
+check_no_hostname()
+
+-- Label too long (>63 chars): invalid
+n.sethostname(string.rep("a", 64) .. ".example.com")
+check_no_hostname()
+
+-- Label starts with hyphen: invalid
+n.sethostname("myhost.-label.com")
+check_no_hostname()
+
+-- Valid simple hostname
+n.sethostname("myhostname")
+check_hostname("myhostname")
+
+-- Final: set a valid hostname for the shell test
 n.sethostname("myhostname")