mdns_sd/

service_info.rs

//! Define `ServiceInfo` to represent a service and its operations.

#[cfg(feature = "logging")]
use crate::log::error;
use crate::{dns_parser::split_sub_domain, Error, Result};
use if_addrs::{IfAddr, Interface};
use std::{
    collections::{HashMap, HashSet},
    convert::TryInto,
    fmt,
    net::{IpAddr, Ipv4Addr},
    str::FromStr,
};

/// Default TTL values in seconds
const DNS_HOST_TTL: u32 = 120; // 2 minutes for host records (A, SRV etc) per RFC6762
const DNS_OTHER_TTL: u32 = 4500; // 75 minutes for non-host records (PTR, TXT etc) per RFC6762

/// Complete info about a Service Instance.
///
/// We can construct some PTR, one SRV and one TXT record from this info,
/// as well as A (IPv4 Address) and AAAA (IPv6 Address) records.
#[derive(Debug, Clone)]
pub struct ServiceInfo {
    ty_domain: String, // <service>.<domain>

    /// See RFC6763 section 7.1 about "Subtypes":
    /// <https://datatracker.ietf.org/doc/html/rfc6763#section-7.1>
    sub_domain: Option<String>, // <subservice>._sub.<service>.<domain>

    fullname: String, // <instance>.<service>.<domain>
    server: String,   // fully qualified name for service host
    addresses: HashSet<IpAddr>,
    port: u16,
    host_ttl: u32,  // used for SRV and Address records
    other_ttl: u32, // used for PTR and TXT records
    priority: u16,
    weight: u16,
    txt_properties: TxtProperties,
    addr_auto: bool, // Let the system update addresses automatically.
}

impl ServiceInfo {
    /// Creates a new service info.
    ///
    /// `ty_domain` is the service type and the domain label, for example
    /// "_my-service._udp.local.".
    ///
    /// `my_name` is the instance name, without the service type suffix.
    ///
    /// `host_name` is the "host" in the context of DNS. It is used as the "name"
    /// in the address records (i.e. TYPE_A and TYPE_AAAA records). It means that
    /// for the same hostname in the same local network, the service resolves in
    /// the same addresses. Be sure to check it if you see unexpected addresses resolved.
    ///
    /// `properties` can be `None` or key/value string pairs, in a type that
    /// implements [`IntoTxtProperties`] trait. It supports:
    /// - `HashMap<String, String>`
    /// - `Option<HashMap<String, String>>`
    /// - slice of tuple: `&[(K, V)]` where `K` and `V` are [`std::string::ToString`].
    ///
    /// `ip` can be one or more IP addresses, in a type that implements
    /// [`AsIpAddrs`] trait. It supports:
    ///
    /// - Single IPv4: `"192.168.0.1"`
    /// - Single IPv6: `"2001:0db8::7334"`
    /// - Multiple IPv4 separated by comma: `"192.168.0.1,192.168.0.2"`
    /// - Multiple IPv6 separated by comma: `"2001:0db8::7334,2001:0db8::7335"`
    /// - A slice of IPv4: `&["192.168.0.1", "192.168.0.2"]`
    /// - A slice of IPv6: `&["2001:0db8::7334", "2001:0db8::7335"]`
    /// - A mix of IPv4 and IPv6: `"192.168.0.1,2001:0db8::7334"`
    /// - All the above formats with [IpAddr] or `String` instead of `&str`.
    ///
    /// The host TTL and other TTL are set to default values.
    pub fn new<Ip: AsIpAddrs, P: IntoTxtProperties>(
        ty_domain: &str,
        my_name: &str,
        host_name: &str,
        ip: Ip,
        port: u16,
        properties: P,
    ) -> Result<Self> {
        let (ty_domain, sub_domain) = split_sub_domain(ty_domain);

        let fullname = format!("{}.{}", my_name, ty_domain);
        let ty_domain = ty_domain.to_string();
        let sub_domain = sub_domain.map(str::to_string);
        let server = normalize_hostname(host_name.to_string());
        let addresses = ip.as_ip_addrs()?;
        let txt_properties = properties.into_txt_properties();

        // RFC6763 section 6.4: https://www.rfc-editor.org/rfc/rfc6763#section-6.4
        // The characters of a key MUST be printable US-ASCII values (0x20-0x7E)
        // [RFC20], excluding '=' (0x3D).
        for prop in txt_properties.iter() {
            let key = prop.key();
            if !key.is_ascii() {
                return Err(Error::Msg(format!(
                    "TXT property key {} is not ASCII",
                    prop.key()
                )));
            }
            if key.contains('=') {
                return Err(Error::Msg(format!(
                    "TXT property key {} contains '='",
                    prop.key()
                )));
            }
        }

        let this = Self {
            ty_domain,
            sub_domain,
            fullname,
            server,
            addresses,
            port,
            host_ttl: DNS_HOST_TTL,
            other_ttl: DNS_OTHER_TTL,
            priority: 0,
            weight: 0,
            txt_properties,
            addr_auto: false,
        };

        Ok(this)
    }

    /// Indicates that the library should automatically
    /// update the addresses of this service, when IP
    /// address(es) are added or removed on the host.
    pub const fn enable_addr_auto(mut self) -> Self {
        self.addr_auto = true;
        self
    }

    /// Returns if the service's addresses will be updated
    /// automatically when the host IP addrs change.
    pub const fn is_addr_auto(&self) -> bool {
        self.addr_auto
    }

    /// Returns the service type including the domain label.
    ///
    /// For example: "_my-service._udp.local.".
    #[inline]
    pub fn get_type(&self) -> &str {
        &self.ty_domain
    }

    /// Returns the service subtype including the domain label,
    /// if subtype has been defined.
    ///
    /// For example: "_printer._sub._http._tcp.local.".
    #[inline]
    pub const fn get_subtype(&self) -> &Option<String> {
        &self.sub_domain
    }

    /// Returns a reference of the service fullname.
    ///
    /// This is useful, for example, in unregister.
    #[inline]
    pub fn get_fullname(&self) -> &str {
        &self.fullname
    }

    /// Returns the properties from TXT records.
    #[inline]
    pub const fn get_properties(&self) -> &TxtProperties {
        &self.txt_properties
    }

    /// Returns a property for a given `key`, where `key` is
    /// case insensitive.
    ///
    /// Returns `None` if `key` does not exist.
    pub fn get_property(&self, key: &str) -> Option<&TxtProperty> {
        self.txt_properties.get(key)
    }

    /// Returns a property value for a given `key`, where `key` is
    /// case insensitive.
    ///
    /// Returns `None` if `key` does not exist.
    pub fn get_property_val(&self, key: &str) -> Option<Option<&[u8]>> {
        self.txt_properties.get_property_val(key)
    }

    /// Returns a property value string for a given `key`, where `key` is
    /// case insensitive.
    ///
    /// Returns `None` if `key` does not exist.
    pub fn get_property_val_str(&self, key: &str) -> Option<&str> {
        self.txt_properties.get_property_val_str(key)
    }

    /// Returns the service's hostname.
    #[inline]
    pub fn get_hostname(&self) -> &str {
        &self.server
    }

    /// Returns the service's port.
    #[inline]
    pub const fn get_port(&self) -> u16 {
        self.port
    }

    /// Returns the service's addresses
    #[inline]
    pub const fn get_addresses(&self) -> &HashSet<IpAddr> {
        &self.addresses
    }

    /// Returns the service's IPv4 addresses only.
    pub fn get_addresses_v4(&self) -> HashSet<&Ipv4Addr> {
        let mut ipv4_addresses = HashSet::new();

        for ip in &self.addresses {
            if let IpAddr::V4(ipv4) = ip {
                ipv4_addresses.insert(ipv4);
            }
        }

        ipv4_addresses
    }

    /// Returns the service's TTL used for SRV and Address records.
    #[inline]
    pub const fn get_host_ttl(&self) -> u32 {
        self.host_ttl
    }

    /// Returns the service's TTL used for PTR and TXT records.
    #[inline]
    pub const fn get_other_ttl(&self) -> u32 {
        self.other_ttl
    }

    /// Returns the service's priority used in SRV records.
    #[inline]
    pub const fn get_priority(&self) -> u16 {
        self.priority
    }

    /// Returns the service's weight used in SRV records.
    #[inline]
    pub const fn get_weight(&self) -> u16 {
        self.weight
    }

    /// Returns a list of addresses that are in the same LAN as
    /// the interface `intf`.
    pub(crate) fn get_addrs_on_intf(&self, intf: &Interface) -> Vec<IpAddr> {
        self.addresses
            .iter()
            .filter(|a| valid_ip_on_intf(a, intf))
            .copied()
            .collect()
    }

    /// Returns whether the service info is ready to be resolved.
    pub(crate) fn is_ready(&self) -> bool {
        let some_missing = self.ty_domain.is_empty()
            || self.fullname.is_empty()
            || self.server.is_empty()
            || self.addresses.is_empty();
        !some_missing
    }

    /// Insert `addr` into service info addresses.
    pub(crate) fn insert_ipaddr(&mut self, addr: IpAddr) {
        self.addresses.insert(addr);
    }

    pub(crate) fn remove_ipaddr(&mut self, addr: &IpAddr) {
        self.addresses.remove(addr);
    }

    pub(crate) fn generate_txt(&self) -> Vec<u8> {
        encode_txt(self.get_properties().iter())
    }

    pub(crate) fn set_port(&mut self, port: u16) {
        self.port = port;
    }

    pub(crate) fn set_hostname(&mut self, hostname: String) {
        self.server = normalize_hostname(hostname);
    }

    /// Returns true if properties are updated.
    pub(crate) fn set_properties_from_txt(&mut self, txt: &[u8]) -> bool {
        let properties = decode_txt_unique(txt);
        if self.txt_properties.properties != properties {
            self.txt_properties = TxtProperties { properties };
            true
        } else {
            false
        }
    }

    pub(crate) fn set_subtype(&mut self, subtype: String) {
        self.sub_domain = Some(subtype);
    }

    /// host_ttl is for SRV and address records
    /// currently only used for testing.
    pub(crate) fn _set_host_ttl(&mut self, ttl: u32) {
        self.host_ttl = ttl;
    }

    /// other_ttl is for PTR and TXT records.
    pub(crate) fn _set_other_ttl(&mut self, ttl: u32) {
        self.other_ttl = ttl;
    }
}

/// Removes potentially duplicated ".local." at the end of "hostname".
fn normalize_hostname(mut hostname: String) -> String {
    if hostname.ends_with(".local.local.") {
        let new_len = hostname.len() - "local.".len();
        hostname.truncate(new_len);
    }
    hostname
}

/// This trait allows for parsing an input into a set of one or multiple [`Ipv4Addr`].
pub trait AsIpAddrs {
    fn as_ip_addrs(&self) -> Result<HashSet<IpAddr>>;
}

impl<T: AsIpAddrs> AsIpAddrs for &T {
    fn as_ip_addrs(&self) -> Result<HashSet<IpAddr>> {
        (*self).as_ip_addrs()
    }
}

/// Supports one address or multiple addresses separated by `,`.
/// For example: "127.0.0.1,127.0.0.2".
///
/// If the string is empty, will return an empty set.
impl AsIpAddrs for &str {
    fn as_ip_addrs(&self) -> Result<HashSet<IpAddr>> {
        let mut addrs = HashSet::new();

        if !self.is_empty() {
            let iter = self.split(',').map(str::trim).map(IpAddr::from_str);
            for addr in iter {
                let addr = addr.map_err(|err| Error::ParseIpAddr(err.to_string()))?;
                addrs.insert(addr);
            }
        }

        Ok(addrs)
    }
}

impl AsIpAddrs for String {
    fn as_ip_addrs(&self) -> Result<HashSet<IpAddr>> {
        self.as_str().as_ip_addrs()
    }
}

/// Support slice. Example: &["127.0.0.1", "127.0.0.2"]
impl<I: AsIpAddrs> AsIpAddrs for &[I] {
    fn as_ip_addrs(&self) -> Result<HashSet<IpAddr>> {
        let mut addrs = HashSet::new();

        for result in self.iter().map(I::as_ip_addrs) {
            addrs.extend(result?);
        }

        Ok(addrs)
    }
}

/// Optimization for zero sized/empty values, as `()` will never take up any space or evaluate to
/// anything, helpful in contexts where we just want an empty value.
impl AsIpAddrs for () {
    fn as_ip_addrs(&self) -> Result<HashSet<IpAddr>> {
        Ok(HashSet::new())
    }
}

impl AsIpAddrs for std::net::IpAddr {
    fn as_ip_addrs(&self) -> Result<HashSet<IpAddr>> {
        let mut ips = HashSet::new();
        ips.insert(*self);

        Ok(ips)
    }
}

/// Represents properties in a TXT record.
///
/// The key string of a property is case insensitive, and only
/// one [`TxtProperty`] is stored for the same key.
///
/// [RFC 6763](https://www.rfc-editor.org/rfc/rfc6763#section-6.4):
/// "A given key SHOULD NOT appear more than once in a TXT record."
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct TxtProperties {
    // Use `Vec` instead of `HashMap` to keep the order of insertions.
    properties: Vec<TxtProperty>,
}

impl TxtProperties {
    /// Returns an iterator for all properties.
    pub fn iter(&self) -> impl Iterator<Item = &TxtProperty> {
        self.properties.iter()
    }

    /// Returns the number of properties.
    pub fn len(&self) -> usize {
        self.properties.len()
    }

    /// Returns if the properties are empty.
    pub fn is_empty(&self) -> bool {
        self.properties.is_empty()
    }

    /// Returns a property for a given `key`, where `key` is
    /// case insensitive.
    pub fn get(&self, key: &str) -> Option<&TxtProperty> {
        let key = key.to_lowercase();
        self.properties
            .iter()
            .find(|&prop| prop.key.to_lowercase() == key)
    }

    /// Returns a property value for a given `key`, where `key` is
    /// case insensitive.
    ///
    /// Returns `None` if `key` does not exist.
    /// Returns `Some(Option<&u8>)` for its value.
    pub fn get_property_val(&self, key: &str) -> Option<Option<&[u8]>> {
        self.get(key).map(|x| x.val())
    }

    /// Returns a property value string for a given `key`, where `key` is
    /// case insensitive.
    ///
    /// Returns `None` if `key` does not exist.
    /// Returns `Some("")` if its value is `None` or is empty.
    pub fn get_property_val_str(&self, key: &str) -> Option<&str> {
        self.get(key).map(|x| x.val_str())
    }
}

impl fmt::Display for TxtProperties {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let delimiter = ", ";
        let props: Vec<String> = self.properties.iter().map(|p| p.to_string()).collect();
        write!(f, "({})", props.join(delimiter))
    }
}

/// Represents a property in a TXT record.
#[derive(Clone, PartialEq, Eq)]
pub struct TxtProperty {
    /// The name of the property. The original cases are kept.
    key: String,

    /// RFC 6763 says values are bytes, not necessarily UTF-8.
    /// It is also possible that there is no value, in which case
    /// the key is a boolean key.
    val: Option<Vec<u8>>,
}

impl TxtProperty {
    /// Returns the key of a property.
    pub fn key(&self) -> &str {
        &self.key
    }

    /// Returns the value of a property, which could be `None`.
    ///
    /// To obtain a `&str` of the value, use `val_str()` instead.
    pub fn val(&self) -> Option<&[u8]> {
        self.val.as_deref()
    }

    /// Returns the value of a property as str.
    pub fn val_str(&self) -> &str {
        self.val
            .as_ref()
            .map_or("", |v| std::str::from_utf8(&v[..]).unwrap_or_default())
    }
}

/// Supports constructing from a tuple.
impl<K, V> From<&(K, V)> for TxtProperty
where
    K: ToString,
    V: ToString,
{
    fn from(prop: &(K, V)) -> Self {
        Self {
            key: prop.0.to_string(),
            val: Some(prop.1.to_string().into_bytes()),
        }
    }
}

impl<K, V> From<(K, V)> for TxtProperty
where
    K: ToString,
    V: AsRef<[u8]>,
{
    fn from(prop: (K, V)) -> Self {
        Self {
            key: prop.0.to_string(),
            val: Some(prop.1.as_ref().into()),
        }
    }
}

/// Support a property that has no value.
impl From<&str> for TxtProperty {
    fn from(key: &str) -> Self {
        Self {
            key: key.to_string(),
            val: None,
        }
    }
}

impl fmt::Display for TxtProperty {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{}={}", self.key, self.val_str())
    }
}

/// Mimic the default debug output for a struct, with a twist:
/// - If self.var is UTF-8, will output it as a string in double quotes.
/// - If self.var is not UTF-8, will output its bytes as in hex.
impl fmt::Debug for TxtProperty {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let val_string = self.val.as_ref().map_or_else(
            || "None".to_string(),
            |v| {
                std::str::from_utf8(&v[..]).map_or_else(
                    |_| format!("Some({})", u8_slice_to_hex(&v[..])),
                    |s| format!("Some(\"{}\")", s),
                )
            },
        );

        write!(
            f,
            "TxtProperty {{key: \"{}\", val: {}}}",
            &self.key, &val_string,
        )
    }
}

const HEX_TABLE: [u8; 16] = [
    b'0', b'1', b'2', b'3', b'4', b'5', b'6', b'7', b'8', b'9', b'a', b'b', b'c', b'd', b'e', b'f',
];

/// Create a hex string from `slice`, with a "0x" prefix.
///
/// For example, [1u8, 2u8] -> "0x0102"
fn u8_slice_to_hex(slice: &[u8]) -> String {
    let mut hex = Vec::with_capacity(slice.len() * 2 + 2);
    hex.push(b'0');
    hex.push(b'x');
    for b in slice.iter() {
        hex.push(HEX_TABLE[(b >> 4) as usize]);
        hex.push(HEX_TABLE[(b & 0x0F) as usize]);
    }

    String::from_utf8(hex).unwrap()
}

/// This trait allows for converting inputs into [`TxtProperties`].
pub trait IntoTxtProperties {
    fn into_txt_properties(self) -> TxtProperties;
}

impl IntoTxtProperties for HashMap<String, String> {
    fn into_txt_properties(mut self) -> TxtProperties {
        let properties = self
            .drain()
            .map(|(key, val)| TxtProperty {
                key,
                val: Some(val.into_bytes()),
            })
            .collect();
        TxtProperties { properties }
    }
}

/// Mainly for backward compatibility.
impl IntoTxtProperties for Option<HashMap<String, String>> {
    fn into_txt_properties(self) -> TxtProperties {
        self.map_or_else(
            || TxtProperties {
                properties: Vec::new(),
            },
            |h| h.into_txt_properties(),
        )
    }
}

/// Support Vec like `[("k1", "v1"), ("k2", "v2")]`.
impl<'a, T: 'a> IntoTxtProperties for &'a [T]
where
    TxtProperty: From<&'a T>,
{
    fn into_txt_properties(self) -> TxtProperties {
        let mut properties = Vec::new();
        let mut keys = HashSet::new();
        for t in self.iter() {
            let prop = TxtProperty::from(t);
            let key = prop.key.to_lowercase();
            if keys.insert(key) {
                // Only push a new entry if the key did not exist.
                //
                // RFC 6763: https://www.rfc-editor.org/rfc/rfc6763#section-6.4
                //
                // "If a client receives a TXT record containing the same key more than
                //    once, then the client MUST silently ignore all but the first
                //    occurrence of that attribute. "
                properties.push(prop);
            }
        }
        TxtProperties { properties }
    }
}

// Convert from properties key/value pairs to DNS TXT record content
fn encode_txt<'a>(properties: impl Iterator<Item = &'a TxtProperty>) -> Vec<u8> {
    let mut bytes = Vec::new();
    for prop in properties {
        let mut s = prop.key.clone().into_bytes();
        if let Some(v) = &prop.val {
            s.extend(b"=");
            s.extend(v);
        }

        // TXT uses (Length,Value) format for each property,
        // i.e. the first byte is the length.
        bytes.push(s.len().try_into().unwrap());
        bytes.extend(s);
    }
    if bytes.is_empty() {
        bytes.push(0);
    }
    bytes
}

// Convert from DNS TXT record content to key/value pairs
pub(crate) fn decode_txt(txt: &[u8]) -> Vec<TxtProperty> {
    let mut properties = Vec::new();
    let mut offset = 0;
    while offset < txt.len() {
        let length = txt[offset] as usize;
        if length == 0 {
            break; // reached the end
        }
        offset += 1; // move over the length byte

        let offset_end = offset + length;
        if offset_end > txt.len() {
            error!("DNS TXT record contains invalid data: Size given for property would be out of range. (offset={}, length={}, offset_end={}, record length={})", offset, length, offset_end, txt.len());
            break; // Skipping the rest of the record content, as the size for this property would already be out of range.
        }
        let kv_bytes = &txt[offset..offset_end];

        // split key and val using the first `=`
        let (k, v) = kv_bytes.iter().position(|&x| x == b'=').map_or_else(
            || (kv_bytes.to_vec(), None),
            |idx| (kv_bytes[..idx].to_vec(), Some(kv_bytes[idx + 1..].to_vec())),
        );

        // Make sure the key can be stored in UTF-8.
        match String::from_utf8(k) {
            Ok(k_string) => {
                properties.push(TxtProperty {
                    key: k_string,
                    val: v,
                });
            }
            Err(e) => error!("failed to convert to String from key: {}", e),
        }

        offset += length;
    }

    properties
}

fn decode_txt_unique(txt: &[u8]) -> Vec<TxtProperty> {
    let mut properties = decode_txt(txt);

    // Remove duplicated keys and retain only the first appearance
    // of each key.
    let mut keys = HashSet::new();
    properties.retain(|p| {
        let key = p.key().to_lowercase();
        keys.insert(key) // returns True if key is new.
    });
    properties
}

/// Returns true if `addr` is in the same network of `intf`.
pub fn valid_ip_on_intf(addr: &IpAddr, intf: &Interface) -> bool {
    match (addr, &intf.addr) {
        (IpAddr::V4(addr), IfAddr::V4(intf)) => {
            let netmask = u32::from(intf.netmask);
            let intf_net = u32::from(intf.ip) & netmask;
            let addr_net = u32::from(*addr) & netmask;
            addr_net == intf_net
        }
        (IpAddr::V6(addr), IfAddr::V6(intf)) => {
            let netmask = u128::from(intf.netmask);
            let intf_net = u128::from(intf.ip) & netmask;
            let addr_net = u128::from(*addr) & netmask;
            addr_net == intf_net
        }
        _ => false,
    }
}

#[cfg(test)]
mod tests {
    use super::{decode_txt, encode_txt, u8_slice_to_hex, ServiceInfo, TxtProperty};

    #[test]
    fn test_txt_encode_decode() {
        let properties = vec![
            TxtProperty::from(&("key1", "value1")),
            TxtProperty::from(&("key2", "value2")),
        ];

        // test encode
        let property_count = properties.len();
        let encoded = encode_txt(properties.iter());
        assert_eq!(
            encoded.len(),
            "key1=value1".len() + "key2=value2".len() + property_count
        );
        assert_eq!(encoded[0] as usize, "key1=value1".len());

        // test decode
        let decoded = decode_txt(&encoded);
        assert!(properties[..] == decoded[..]);

        // test empty value
        let properties = vec![TxtProperty::from(&("key3", ""))];
        let property_count = properties.len();
        let encoded = encode_txt(properties.iter());
        assert_eq!(encoded.len(), "key3=".len() + property_count);

        let decoded = decode_txt(&encoded);
        assert_eq!(properties, decoded);

        // test non-string value
        let binary_val: Vec<u8> = vec![123, 234, 0];
        let binary_len = binary_val.len();
        let properties = vec![TxtProperty::from(("key4", binary_val))];
        let property_count = properties.len();
        let encoded = encode_txt(properties.iter());
        assert_eq!(encoded.len(), "key4=".len() + binary_len + property_count);

        let decoded = decode_txt(&encoded);
        assert_eq!(properties, decoded);

        // test value that contains '='
        let properties = vec![TxtProperty::from(("key5", "val=5"))];
        let property_count = properties.len();
        let encoded = encode_txt(properties.iter());
        assert_eq!(
            encoded.len(),
            "key5=".len() + "val=5".len() + property_count
        );

        let decoded = decode_txt(&encoded);
        assert_eq!(properties, decoded);

        // test a property that has no value.
        let properties = vec![TxtProperty::from("key6")];
        let property_count = properties.len();
        let encoded = encode_txt(properties.iter());
        assert_eq!(encoded.len(), "key6".len() + property_count);
        let decoded = decode_txt(&encoded);
        assert_eq!(properties, decoded);
    }

    #[test]
    fn test_set_properties_from_txt() {
        // Three duplicated keys.
        let properties = vec![
            TxtProperty::from(&("one", "1")),
            TxtProperty::from(&("ONE", "2")),
            TxtProperty::from(&("One", "3")),
        ];
        let encoded = encode_txt(properties.iter());

        // Simple decode does not remove duplicated keys.
        let decoded = decode_txt(&encoded);
        assert_eq!(decoded.len(), 3);

        // ServiceInfo removes duplicated keys and keeps only the first one.
        let mut service_info =
            ServiceInfo::new("_test._tcp", "prop_test", "localhost", "", 1234, None).unwrap();
        service_info.set_properties_from_txt(&encoded);
        assert_eq!(service_info.get_properties().len(), 1);

        // Verify the only one property.
        let prop = service_info.get_properties().iter().next().unwrap();
        assert_eq!(prop.key, "one");
        assert_eq!(prop.val_str(), "1");
    }

    #[test]
    fn test_u8_slice_to_hex() {
        let bytes = [0x01u8, 0x02u8, 0x03u8];
        let hex = u8_slice_to_hex(&bytes);
        assert_eq!(hex.as_str(), "0x010203");

        let slice = "abcdefghijklmnopqrstuvwxyz";
        let hex = u8_slice_to_hex(slice.as_bytes());
        assert_eq!(hex.len(), slice.len() * 2 + 2);
        assert_eq!(
            hex.as_str(),
            "0x6162636465666768696a6b6c6d6e6f707172737475767778797a"
        );
    }

    #[test]
    fn test_txt_property_debug() {
        // Test UTF-8 property value.
        let prop_1 = TxtProperty {
            key: "key1".to_string(),
            val: Some("val1".to_string().into()),
        };
        let prop_1_debug = format!("{:?}", &prop_1);
        assert_eq!(
            prop_1_debug,
            "TxtProperty {key: \"key1\", val: Some(\"val1\")}"
        );

        // Test non-UTF-8 property value.
        let prop_2 = TxtProperty {
            key: "key2".to_string(),
            val: Some(vec![150u8, 151u8, 152u8]),
        };
        let prop_2_debug = format!("{:?}", &prop_2);
        assert_eq!(
            prop_2_debug,
            "TxtProperty {key: \"key2\", val: Some(0x969798)}"
        );
    }

    #[test]
    fn test_txt_decode_property_size_out_of_bounds() {
        // Construct a TXT record with an invalid property length that would be out of bounds.
        let encoded: Vec<u8> = vec![
            0x0b, // Length 11
            b'k', b'e', b'y', b'1', b'=', b'v', b'a', b'l', b'u', b'e',
            b'1', // key1=value1 (Length 11)
            0x10, // Length 16 (Would be out of bounds)
            b'k', b'e', b'y', b'2', b'=', b'v', b'a', b'l', b'u', b'e',
            b'2', // key2=value2 (Length 11)
        ];
        // Decode the record content
        let decoded = decode_txt(&encoded);
        // We expect the out of bounds length for the second property to have caused the rest of the record content to be skipped.
        // Test that we only parsed the first property.
        assert_eq!(decoded.len(), 1);
        // Test that the key of the property we parsed is "key1"
        assert_eq!(decoded[0].key, "key1");
    }
}