WIP feat: agent-level HTTP client

Cargo.toml

@@ -51,6 +51,7 @@ members = [
   "libdd-tinybytes",
   "libdd-dogstatsd-client",
   "libdd-http-client",
+  "libdd-agent-client",
   "libdd-log",
   "libdd-log-ffi",
 ]

libdd-agent-client/Cargo.toml

@@ -0,0 +1,32 @@
+# Copyright 2026-Present Datadog, Inc. https://www.datadoghq.com/
+# SPDX-License-Identifier: Apache-2.0
+
+[package]
+name = "libdd-agent-client"
+version.workspace = true
+edition.workspace = true
+rust-version.workspace = true
+license.workspace = true
+authors.workspace = true
+description = "Datadog-agent-specialized HTTP client: language metadata injection, per-endpoint send methods, retry, and compression"
+homepage = "https://github.com/DataDog/libdatadog/tree/main/libdd-agent-client"
+repository = "https://github.com/DataDog/libdatadog/tree/main/libdd-agent-client"
+
+[lib]
+bench = false
+
+[dependencies]
+bytes = "1.4"
+flate2 = "1"
+serde = { version = "1.0", features = ["derive"] }
+serde_json = "1.0"
+thiserror = "2"
+tokio = { version = "1.23", features = ["rt"] }
+libdd-http-client = { path = "../libdd-http-client" }
+libdd-common = { version = "3.0.2", path = "../libdd-common", default-features = false }
+
+[dev-dependencies]
+httpmock = "0.8.0-alpha.1"
+rustls = { version = "0.23", default-features = false, features = ["ring"] }
+serial_test = "3.2"
+tokio = { version = "1.23", features = ["rt", "macros"] }

libdd-agent-client/src/agent_info.rs

@@ -0,0 +1,30 @@
+// Copyright 2026-Present Datadog, Inc. https://www.datadoghq.com/
+// SPDX-License-Identifier: Apache-2.0
+
+//! Types for [`crate::AgentClient::agent_info`].
+
+/// Parsed response from a `GET /info` probe.
+///
+/// Returned by [`crate::AgentClient::agent_info`]. Contains agent capabilities and headers.
+#[derive(Debug, Clone)]
+pub struct AgentInfo {
+    /// Available agent endpoints, e.g. `["/v0.4/traces", "/v0.5/traces"]`.
+    pub endpoints: Vec<String>,
+    /// Whether the agent supports client-side P0 dropping.
+    pub client_drop_p0s: bool,
+    /// Raw agent configuration block.
+    pub config: serde_json::Value,
+    /// Agent version string, if reported.
+    pub version: Option<String>,
+    /// Parsed from the `Datadog-Container-Tags-Hash` response header.
+    ///
+    /// Used by dd-trace-py to compute the base tag hash (`agent.py:17-23`).
+    pub container_tags_hash: Option<String>,
+    /// Value of the `Datadog-Agent-State` response header from the last `/info` fetch.
+    ///
+    /// The agent updates this opaque token whenever its internal state changes (e.g. a
+    /// configuration reload). Clients that poll `/info` periodically can skip re-parsing
+    /// the response body by comparing this value to the one returned by the previous call
+    /// and only acting when it differs.
+    pub state_hash: Option<String>,
+}