feat(api): Add Get Signed Tree Head endpoint

src/api/endpoints.rs

@@ -43,7 +43,7 @@ type Endpoint<'a> = (reqwest::Method, &'a str);
 /// we could completely change it without requiring an upgrade to v1
 /// clients.)
 /// ```
-pub const ADD_CHAIN_ENDPOINT: Endpoint = (reqwest::Method::POST, "/ct/v1/add-chain");
+pub const ADD_CHAIN: Endpoint = (reqwest::Method::POST, "/ct/v1/add-chain");
 
 /// Reference: https://datatracker.ietf.org/doc/html/rfc6962#section-4.2
 /// ```txt
@@ -59,4 +59,22 @@ pub const ADD_CHAIN_ENDPOINT: Endpoint = (reqwest::Method::POST, "/ct/v1/add-cha
 ///
 /// Outputs are the same as in Section 4.1.
 /// ```
-pub const ADD_PRE_CHAIN_ENDPOINT: Endpoint = (reqwest::Method::POST, "/ct/v1/add-pre-chain");
+pub const ADD_PRE_CHAIN: Endpoint = (reqwest::Method::POST, "/ct/v1/add-pre-chain");
+
+/// Reference: https://datatracker.ietf.org/doc/html/rfc6962#section-4.3
+/// ```txt
+/// GET https://<log server>/ct/v1/get-sth
+///
+/// No inputs.
+///
+/// Outputs:
+///
+///    tree_size:  The size of the tree, in entries, in decimal.
+///
+///    timestamp:  The timestamp, in decimal.
+///
+///    sha256_root_hash:  The Merkle Tree Hash of the tree, in base64.
+///
+///    tree_head_signature:  A TreeHeadSignature for the above data.
+/// ```
+pub const GET_STH: Endpoint = (reqwest::Method::GET, "/ct/v1/get-sth");

src/api/mod.rs

@@ -1,5 +1,5 @@
 use reqwest::Url;
-use responses::{AddChainRequest, AddChainResponse};
+use responses::{AddChainRequest, AddChainResponse, GetSthResponse};
 
 pub mod endpoints;
 pub mod responses;
@@ -34,8 +34,8 @@ impl CtApiClient {
 	) -> reqwest::Result<AddChainResponse> {
 		self.inner_client
 			.request(
-				endpoints::ADD_CHAIN_ENDPOINT.0,
-				self.log_url.to_string() + endpoints::ADD_CHAIN_ENDPOINT.1
+				endpoints::ADD_CHAIN.0,
+				self.log_url.to_string() + endpoints::ADD_CHAIN.1
 			)
 			.json(&AddChainRequest { chain })
 			.send()
@@ -67,8 +67,8 @@ impl CtApiClient {
 	) -> reqwest::Result<AddChainResponse> {
 		self.inner_client
 			.request(
-				endpoints::ADD_PRE_CHAIN_ENDPOINT.0,
-				self.log_url.to_string() + endpoints::ADD_PRE_CHAIN_ENDPOINT.1
+				endpoints::ADD_PRE_CHAIN.0,
+				self.log_url.to_string() + endpoints::ADD_PRE_CHAIN.1
 			)
 			.json(&AddChainRequest { chain })
 			.send()
@@ -77,4 +77,19 @@ impl CtApiClient {
 			.json()
 			.await
 	}
+
+	pub async fn get_signed_tree_head(
+		&self
+	) -> reqwest::Result<GetSthResponse> {
+		self.inner_client
+			.request(
+				endpoints::GET_STH.0,
+				self.log_url.to_string() + endpoints::GET_STH.1
+			)
+			.send()
+			.await?
+			.error_for_status()?
+			.json()
+			.await
+	}
 }

src/api/responses.rs

@@ -2,15 +2,17 @@ use serde::{Deserialize, Serialize};
 
 /// A request payload for adding a chain to a CT log
 ///
-/// See: [`super::endpoints::ADD_CHAIN_ENDPOINT`] or [`super::endpoints::ADD_PRE_CHAIN_ENDPOINT`]
+/// See: [`super::endpoints::ADD_CHAIN`] or
+/// [`super::endpoints::ADD_PRE_CHAIN`]
 #[derive(Debug, Serialize)]
 pub struct AddChainRequest {
-    pub chain: Vec<String>
+	pub chain: Vec<String>
 }
 
 /// A response given when adding a chain to a CT log
 ///
-/// See: [`super::endpoints::ADD_CHAIN_ENDPOINT`] or [`super::endpoints::ADD_PRE_CHAIN_ENDPOINT`]
+/// See: [`super::endpoints::ADD_CHAIN`] or
+/// [`super::endpoints::ADD_PRE_CHAIN`]
 #[derive(Debug, Deserialize)]
 pub struct AddChainResponse {
 	pub sct_version: u8,
@@ -19,3 +21,14 @@ pub struct AddChainResponse {
 	pub extensions: String,
 	pub signature: String
 }
+
+/// A response given when fetching the Signed Tree Head of a CT log
+/// 
+/// See: [`super::endpoints::GET_STH`]
+#[derive(Debug, Deserialize)]
+pub struct GetSthResponse {
+	pub tree_size: u64,
+	pub timestamp: u64,
+	pub sha256_root_hash: String,
+	pub tree_head_signature: String
+}