net.device-validate
Validate one network inventory entry: name, host, ports, optional MAC and subnet, with every problem listed.
1.0.0 · published 2026-10-03 by charlie · Anterra
Pinned by 17 tests, run in TypeScript, Python and Rust.
What it does
Checks one entry of a network inventory file (the list of devices a monitor probes) and reports every problem with it at once, instead of the first one. An entry looks like this:
{ "name": "core-switch", "host": "10.0.0.2", "ports": [22, 443], "mac": "AA-BB-CC-DD-EE-FF", "subnet": "10.0.0.0/24" }
For example
validate_device(name router, host 192.168.1.1, ports 22, 80)→ valid true, errors , name router, host 192.168.1.1, host kind ipv4, ports 22, 80, mac —, subnet — a minimal IPv4 entry is valid and passed throughvalidate_device(name core switch , host 10.0.0.2, ports 22, mac AA-BB-CC-DD-EE-FF, subnet 10.0.0.77/24)→ valid true, errors , name core switch, host 10.0.0.2, host kind ipv4, ports 22, mac aa:bb:cc:dd:ee:ff, subnet 10.0.0.0/24 name is trimmed, MAC made canonical, subnet host bits clearedvalidate_device(name v6, host 2001:DB8:0:0:0:0:0:1, ports 443, subnet 2001:db8::ffff/32)→ valid true, errors , name v6, host 2001:db8::1, host kind ipv6, ports 443, mac —, subnet 2001:db8::/32 an IPv6 host and subnet are written in RFC 5952 form
The function
The same function in TypeScript, Python and Rust, pinned by the same tests. Pick your language; the choice follows you around the registry.
def validate_device(entry: Mapping[str, Any]) -> DeviceValidation
| entry | record | {name, host, ports, mac?, subnet?} as read from an inventory file |
| returns | DeviceValidation |
The type it declares, generated into your project
@dataclass(frozen=True)
class DeviceValidation:
"""An inventory entry checked field by field, normalised where valid."""
valid: bool
#: every problem, in field order; empty when valid
errors: List[str]
name: Optional[str]
#: IPv4 as given, IPv6 canonical, host name lower-case
host: Optional[str]
#: ipv4, ipv6 or hostname
host_kind: Optional[str]
#: the valid ports, in order
ports: List[int]
#: canonical
mac: Optional[str]
#: canonical block
subnet: Optional[str]
Your code names it in one line, in the file that uses it
from fune.net.device_validate import validate_device # net.device-validate@^1
Imports name this capability’s declared dependencies, which fune builds next to it in your project; each one links to its page.
from typing import Any, List, Mapping, Optional
from .net_cidr import cidr_info, is_cidr ← from net.cidr ^1.0.0 · built alongside by fune
from .net_device_validate_types import DeviceValidation
from .net_hostname_validate import validate_hostname ← from net.hostname-validate ^1.0.0 · built alongside by fune
from .net_ipv4 import is_ipv4 ← from net.ipv4 ^1.0.0 · built alongside by fune
from .net_ipv6 import format_ipv6, is_ipv6, parse_ipv6 ← from net.ipv6 ^1.0.0 · built alongside by fune
from .net_mac_address import validate_mac_address ← from net.mac-address ^1.0.0 · built alongside by fune
from .net_port import is_port ← from net.port ^1.0.0 · built alongside by fune
KNOWN = ("name", "host", "ports", "mac", "subnet")
def _present(entry: Mapping[str, Any], key: str) -> bool:
return key in entry and entry[key] is not None
def _whole_number(value: Any) -> Optional[int]:
"""A whole number, whichever way the JSON reader stored it (22 and 22.0 are the same port)."""
if isinstance(value, bool):
return None
if isinstance(value, int):
return value
if isinstance(value, float) and value == value and value not in (float("inf"), float("-inf")) and value.is_integer():
return int(value)
return None
def _canonical_ipv6_block(text: str) -> str:
"""An IPv6 block with its host bits cleared and its address in RFC 5952 form."""
address, _, prefix_text = text.partition("/")
prefix = int(prefix_text)
groups = []
for i, g in enumerate(parse_ipv6(address)):
bits = min(16, max(0, prefix - 16 * i))
groups.append(0 if bits == 0 else g & ((0xFFFF << (16 - bits)) & 0xFFFF))
return "%s/%d" % (format_ipv6(groups), prefix)
def validate_device(entry: Mapping[str, Any]) -> DeviceValidation:
"""Check one inventory entry and say everything that is wrong with it at once,
so a person fixing a file does not play whack-a-mole one error per run.
Never raises: a bad entry is a result, not a crash.
"""
errors: List[str] = []
name: Optional[str] = None
if not _present(entry, "name"):
errors.append("name is required")
elif not isinstance(entry["name"], str):
errors.append("name must be text")
elif entry["name"].strip(" \t\n\r\f\v") == "":
errors.append("name must not be empty")
else:
name = entry["name"].strip(" \t\n\r\f\v")
host: Optional[str] = None
host_kind: Optional[str] = None
if not _present(entry, "host"):
errors.append("host is required")
elif not isinstance(entry["host"], str):
errors.append("host must be text")
elif is_ipv4(entry["host"]):
host = entry["host"]
host_kind = "ipv4"
elif is_ipv6(entry["host"]):
host = format_ipv6(parse_ipv6(entry["host"]))
host_kind = "ipv6"
else:
check = validate_hostname(entry["host"])
if check.valid:
host = check.hostname
host_kind = "hostname"
else:
errors.append('host "%s" is not an IPv4 address, IPv6 address or host name: %s' % (entry["host"], check.reason))
ports: List[int] = []
if not _present(entry, "ports"):
errors.append("ports is required")
elif not isinstance(entry["ports"], (list, tuple)):
errors.append("ports must be a list")
elif len(entry["ports"]) == 0:
errors.append("ports must not be empty")
else:
for i, item in enumerate(entry["ports"]):
port = _whole_number(item)
if port is None:
errors.append("ports[%d] must be a whole number" % i)
elif not is_port(port):
errors.append("ports[%d] %d is not a port (1-65535)" % (i, port))
elif port in ports:
errors.append("ports[%d] %d is listed twice" % (i, port))
else:
ports.append(port)
mac: Optional[str] = None
if _present(entry, "mac"):
if not isinstance(entry["mac"], str):
errors.append("mac must be text")
else:
check = validate_mac_address(entry["mac"])
if check.valid:
mac = check.canonical
else:
errors.append('mac "%s" is not valid: %s' % (entry["mac"], check.reason))
subnet: Optional[str] = None
if _present(entry, "subnet"):
if not isinstance(entry["subnet"], str):
errors.append("subnet must be text")
elif not is_cidr(entry["subnet"]):
errors.append('subnet "%s" is not a CIDR block' % entry["subnet"])
elif ":" in entry["subnet"]:
subnet = _canonical_ipv6_block(entry["subnet"])
else:
subnet = cidr_info(entry["subnet"]).cidr
# Sorted, not in file order: JavaScript lists integer-like keys first, so
# "file order" would differ between languages.
for key in sorted(k for k in entry.keys() if k not in KNOWN):
errors.append('unknown field "%s"' % key)
return DeviceValidation(
valid=len(errors) == 0,
errors=errors,
name=name,
host=host,
host_kind=host_kind,
ports=ports,
mac=mac,
subnet=subnet,
)Install
fune build
With that line in your source, in a Python project (language python in fune.project), fune build resolves it and its 6 dependencies, pins them in fune.lock, downloads only the Python package of each, and builds the code above into your project’s .fune/build, one readable file per capability with a header linking back here. Or pin a range in fune.project and build in one step:
fune add net.device-validate
The manifest, vectors and README with only the Python implementation. Install it without the registry with fune add ./net.device-validate-1.0.0-python.fune, or fetch it from a terminal with fune pull net.device-validate@1.0.0:python.
The whole function, every language, is one file too: net.device-validate-1.0.0.fune, 29,150 bytes, sha256 f74a06dc52d0c5f4093e13b770f7f2c0508d155be2bfb2ef9ebed0ff496ad420. It installs into a project of any language.
Customise it in your app
The seams this capability offers. Put a marker directly above a function of your own and fune build wires it into the built code; the package on the registry is not changed, the built file’s header lists it under CUSTOMISED, and fune hooks lists every hook in the project. How hooks work.
before — your function gets the arguments and returns them, changed or not, or throws to refuse the call.
# fune: before net.device-validate
after — your function gets the result and the arguments, and returns the final result.
# fune: after net.device-validate
replace — inside this capability’s code only, calls to a dependency go to your function, with the same signature. Other capabilities that use it are unaffected; write in * to replace it everywhere.
# fune: replace net.cidr in net.device-validate
# fune: replace net.hostname-validate in net.device-validate
# fune: replace net.ipv4 in net.device-validate
# fune: replace net.ipv6 in net.device-validate
# fune: replace net.mac-address in net.device-validate
# fune: replace net.port in net.device-validate
step — your function runs at a numbered point inside the function’s body, receives the in-scope values it names as parameters, and may return replacements. List the points with fune show net.device-validate --steps.
# fune: step net.device-validate after <n|label>
Tests
A version published now needs at least 8 tests for every function, and one that expects the error for each function that throws; the registry refuses it otherwise. fune verify --all runs each case in TypeScript, Python and Rust, and a project runs them again with fune verify. This page lists the cases; it does not run them. The exact JSON is vectors.json.
| Case | Arguments | Expected | |
|---|---|---|---|
| a minimal IPv4 entry is valid and passed through | name router, host 192.168.1.1, ports 22, 80 | → | valid true, errors , name router, host 192.168.1.1, host kind ipv4, ports 22, 80, mac —, subnet — |
| name is trimmed, MAC made canonical, subnet host bits cleared | name core switch , host 10.0.0.2, ports 22, mac AA-BB-CC-DD-EE-FF, subnet 10.0.0.77/24 | → | valid true, errors , name core switch, host 10.0.0.2, host kind ipv4, ports 22, mac aa:bb:cc:dd:ee:ff, subnet 10.0.0.0/24 |
| an IPv6 host and subnet are written in RFC 5952 form | name v6, host 2001:DB8:0:0:0:0:0:1, ports 443, subnet 2001:db8::ffff/32 | → | valid true, errors , name v6, host 2001:db8::1, host kind ipv6, ports 443, mac —, subnet 2001:db8::/32 |
| a host name is lower-cased and loses its trailing dot | name nas, host NAS.Example.COM., ports 445, mac aabb.ccdd.eeff | → | valid true, errors , name nas, host nas.example.com, host kind hostname, ports 445, mac aa:bb:cc:dd:ee:ff, subnet — |
| null optional fields are the same as leaving them out | name x, host x, ports 1, mac —, subnet — | → | valid true, errors , name x, host x, host kind hostname, ports 1, mac —, subnet — |
| an empty entry lists every required field | → | valid false, errors name is required, host is required, ports is required, name —, host —, host kind —, ports , mac —, subnet — | |
| wrong types are named field by field | name 5, host x, ports 22, mac 1, subnet true | → | valid false, errors name must be text, host must be text, ports must be a list, mac must be text, subnet must be text, name —, host —, host kind —, ports , mac —, subnet — |
| every bad port is reported with its index; 8080.0 is port 8080 | name a, host a.example, ports 0, 22.5, 80, 443, 443, 65,536, 8,080, true | → | valid false, errors ports[0] 0 is not a port (1-65535), ports[1] must be a whole number, ports[2] must be a whole number, ports[4] 443 is listed twice, ports[5] 65536 is not a por… |
| an empty port list is refused | name a, host 10.0.0.1, ports | → | valid false, errors ports must not be empty, name a, host 10.0.0.1, host kind ipv4, ports , mac —, subnet — |
| 192.168.1.256 is neither an address nor a host name (numeric top-level label) | name bad, host 192.168.1.256, ports 80 | → | valid false, errors host "192.168.1.256" is not an IPv4 address, IPv6 address or host name: top-level label is all numeric, name bad, host —, host kind —, ports 80, mac —, subnet — |
Show the other 7 tests
| Case | Arguments | Expected | |
|---|---|---|---|
| a leading-zero quad is refused rather than read as octal or as a name | name octal, host 010.0.0.1, ports 80 | → | valid false, errors host "010.0.0.1" is not an IPv4 address, IPv6 address or host name: top-level label is all numeric, name octal, host —, host kind —, ports 80, mac —, subnet — |
| a doubled dot is an empty label | name p, host printer..office, ports 631 | → | valid false, errors host "printer..office" is not an IPv4 address, IPv6 address or host name: empty label, name p, host —, host kind —, ports 631, mac —, subnet — |
| a blank name and an empty host | name , host , ports 22 | → | valid false, errors name must not be empty, host "" is not an IPv4 address, IPv6 address or host name: empty, name —, host —, host kind —, ports 22, mac —, subnet — |
| a trailing newline makes the host invalid | name nl, host 10.0.0.1 , ports 22 | → | valid false, errors host "10.0.0.1 " is not an IPv4 address, IPv6 address or host name: character other than a letter, digit, hyphen or dot, name nl, host —, host kind —, ports 22… |
| a bad MAC and a bad subnet are both reported | name m, host 10.1.1.1, ports 22, mac aa:bb:cc:dd:ee:gg, subnet 10.0.0.0/33 | → | valid false, errors mac "aa:bb:cc:dd:ee:gg" is not valid: not a hex digit, subnet "10.0.0.0/33" is not a CIDR block, name m, host 10.1.1.1, host kind ipv4, ports 22, mac —, subnet… |
| a subnet without a prefix is not a CIDR block | name s, host 10.1.1.1, ports 22, subnet 10.0.0.0 | → | valid false, errors subnet "10.0.0.0" is not a CIDR block, name s, host 10.1.1.1, host kind ipv4, ports 22, mac —, subnet — |
| unknown fields are reported in sorted order after everything else | zone a, name x, host x, ports 1, colour b | → | valid false, errors unknown field "colour", unknown field "zone", name x, host x, host kind hostname, ports 1, mac —, subnet — |
More from the author
`name`, `host` and `ports` are required; `mac` and `subnet` are optional (null is the same as leaving them out). The function never throws: a bad entry is a result with `valid: false` and a list of `errors`, so a monitor can report it and carry on with the rest of the file.
## What each field must be
| field | rule | built on | |-------|------|----------| | `name` | text, not blank; ASCII whitespace around it is trimmed | | | `host` | an IPv4 address, an IPv6 address or an RFC 1123 host name, tried in that order | `net.ipv4`, `net.ipv6`, `net.hostname-validate` | | `ports` | a non-empty list of whole numbers 1-65535, each once | `net.port` | | `mac` | an EUI-48 MAC in any of the forms `net.mac-address` accepts | `net.mac-address` | | `subnet` | an IPv4 or IPv6 CIDR block | `net.cidr` |
Anything else in the entry is reported as `unknown field "x"`, which catches typos such as `"port"` for `"ports"`. Unknown fields are listed in sorted order after the field errors, because JavaScript orders integer-like keys first and "file order" would differ between languages.
## The normal forms returned
- `host`: an IPv4 address as given (it can only be valid in one spelling), IPv6 in RFC 5952 canonical form, a host name lower-cased without its trailing dot. `hostKind` says which of `ipv4`, `ipv6` or `hostname` it is. - `ports`: the valid ports in order, a repeated one only once. `22.0` is port 22, since a JSON reader may store it as a float. - `mac`: lower-case, colon-separated. - `subnet`: host bits cleared (`10.0.0.77/24` is `10.0.0.0/24`), the address of an IPv6 block in RFC 5952 form.
Fields that fail are null (or left out of `ports`) in the result, while the rest are still normalised, so a report can name the device whose MAC is bad.
## Edge cases
- `192.168.1.256` and `010.0.0.1` are not IPv4 addresses (out of range, and a leading zero that some parsers read as octal), and they are not host names either: a top-level label may not be all digits (RFC 3696 section 2). A naive check lets them through as names. - A trailing newline is not trimmed from `host`; it makes the entry invalid. - Subnet membership is not checked here: a host name has no address until it is resolved, which is I/O. Check it afterwards with `net.cidr`'s `cidrContains` on the resolved address.
Files
| Path | Bytes |
|---|---|
| README.md | 2,654 |
| impl/python.py | 4,887 |
| impl/rust.rs | 6,750 |
| impl/typescript.ts | 4,582 |
| vectors.json | 5,958 |