discovery/dns: add DNS service discovery (dns_sd_configs)

Cargo.toml

@@ -15,7 +15,7 @@ exclude = ["tests/otap-compat"]
 [features]
 default = ["arrow", "dto"]
 arrow = ["dep:arrow-array", "dep:arrow-buffer", "dep:arrow-schema"]
-discovery = ["dep:serde", "dep:serde_json"]
+discovery = ["dep:serde", "dep:serde_json", "dep:tokio"]
 dto = ["dep:prost", "dep:prost-types"]
 
 [dependencies]
@@ -27,11 +27,13 @@ prost-types = { version = "0.14", optional = true }
 serde = { version = "1", features = ["derive"], optional = true }
 serde_json = { version = "1", optional = true }
 thiserror = "2"
+tokio = { version = "1", default-features = false, features = ["io-util", "net", "time"], optional = true }
 
 [dev-dependencies]
 benchfmt = { git = "https://github.com/bwplotka/benchfmt.rs" }
 prost-build = "=0.14.4"
 protox = "0.10"
+tokio = { version = "1", default-features = false, features = ["macros", "rt"] }
 
 [[bench]]
 name = "decode"

src/discovery.rs

@@ -11,13 +11,17 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-//! Prometheus-compatible target discovery configuration and target group types.
+//! Prometheus-compatible target discovery (`static_configs` and `dns_sd_configs`).
+
+pub mod dns;
 
 use std::collections::BTreeMap;
 use std::time::Duration;
 
 use serde::{Deserialize, Deserializer, Serialize, Serializer};
 
+pub use dns::{DnsDiscovery, DnsRecord, DnsRecordType, DnsSdConfig, ResolvConf};
+
 /// Reserved Prometheus label holding the `<host>:<port>` scrape target address.
 pub const ADDRESS_LABEL: &str = "__address__";
 
@@ -33,6 +37,9 @@ pub enum DiscoveryError {
     /// I/O or filesystem error.
     #[error("I/O error: {0}")]
     Io(#[from] std::io::Error),
+    /// DNS protocol or lookup error.
+    #[error("DNS error: {0}")]
+    Dns(String),
     /// JSON payload decoding error.
     #[error("JSON decode error: {0}")]
     Json(#[from] serde_json::Error),
@@ -129,11 +136,17 @@ pub struct DiscoveryConfigs {
     /// Static target group configurations (`static_configs`).
     #[serde(default, skip_serializing_if = "Vec::is_empty")]
     pub static_configs: Vec<StaticConfig>,
+    /// DNS service discovery configurations (`dns_sd_configs`).
+    #[serde(default, skip_serializing_if = "Vec::is_empty")]
+    pub dns_sd_configs: Vec<DnsSdConfig>,
 }
 
 impl DiscoveryConfigs {
     /// Validates all configured service discovery sections according to Prometheus rules.
     pub fn validate(&mut self) -> Result<(), DiscoveryError> {
+        for dns_cfg in &mut self.dns_sd_configs {
+            dns_cfg.validate()?;
+        }
         Ok(())
     }
 
@@ -143,6 +156,15 @@ impl DiscoveryConfigs {
     }
 }
 
+/// Joins a host and port into `"host:port"` or `"[ipv6]:port"`, matching Go `net.JoinHostPort`.
+pub(crate) fn join_host_port(host: &str, port: &str) -> String {
+    if host.contains(':') {
+        format!("[{host}]:{port}")
+    } else {
+        format!("{host}:{port}")
+    }
+}
+
 /// Parses a Prometheus duration string (such as `"30s"`, `"1m"`, `"500ms"`, `"1h30m"`, `"7d"`,
 /// `"1w"`, `"1y"`, or `"0"`) into a [`Duration`], matching `prometheus/common/model.ParseDuration`.
 pub fn parse_duration(s: &str) -> Result<Duration, DiscoveryError> {
@@ -248,3 +270,20 @@ pub fn format_duration(d: Duration) -> String {
 
     out
 }
+
+pub(crate) mod serde_duration {
+    use std::time::Duration;
+
+    use serde::{Deserialize, Deserializer, Serializer};
+
+    use super::{format_duration, parse_duration};
+
+    pub fn serialize<S: Serializer>(duration: &Duration, serializer: S) -> Result<S::Ok, S::Error> {
+        serializer.serialize_str(&format_duration(*duration))
+    }
+
+    pub fn deserialize<'de, D: Deserializer<'de>>(deserializer: D) -> Result<Duration, D::Error> {
+        let s = String::deserialize(deserializer)?;
+        parse_duration(&s).map_err(serde::de::Error::custom)
+    }
+}