move pull_timeline to safekeeper_api and add SafekeeperGeneration (#10863)

Preparations for a successor of #10440: 

* move `pull_timeline` to `safekeeper_api` and add it to
`SafekeeperClient`. we want to do `pull_timeline` on any creations that
we couldn't do initially.
* Add a `SafekeeperGeneration` type instead of relying on a type alias.
we want to maintain a safekeeper specific generation number now in the
storcon database. A separate type is important to make it impossible to
mix it up with the tenant's pageserver specific generation number. We
absolutely want to avoid that for correctness reasons. If someone mixes
up a safekeeper and pageserver id (both use the `NodeId` type), that's
bad but there is no wrong generations flying around.

part of #9011

libs/safekeeper_api/src/membership.rs

@@ -9,13 +9,43 @@ use anyhow::bail;
 use serde::{Deserialize, Serialize};
 use utils::id::NodeId;
 
-/// Number uniquely identifying safekeeper configuration.
-/// Note: it is a part of sk control file.
-pub type Generation = u32;
 /// 1 is the first valid generation, 0 is used as
 /// a placeholder before we fully migrate to generations.
-pub const INVALID_GENERATION: Generation = 0;
-pub const INITIAL_GENERATION: Generation = 1;
+pub const INVALID_GENERATION: SafekeeperGeneration = SafekeeperGeneration::new(0);
+pub const INITIAL_GENERATION: SafekeeperGeneration = SafekeeperGeneration::new(1);
+
+/// Number uniquely identifying safekeeper configuration.
+/// Note: it is a part of sk control file.
+///
+/// Like tenant generations, but for safekeepers.
+#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Serialize, Deserialize)]
+pub struct SafekeeperGeneration(u32);
+
+impl SafekeeperGeneration {
+    pub const fn new(v: u32) -> Self {
+        Self(v)
+    }
+
+    #[track_caller]
+    pub fn previous(&self) -> Option<Self> {
+        Some(Self(self.0.checked_sub(1)?))
+    }
+
+    #[track_caller]
+    pub fn next(&self) -> Self {
+        Self(self.0 + 1)
+    }
+
+    pub fn into_inner(self) -> u32 {
+        self.0
+    }
+}
+
+impl Display for SafekeeperGeneration {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}", self.0)
+    }
+}
 
 /// Membership is defined by ids so e.g. walproposer uses them to figure out
 /// quorums, but we also carry host and port to give wp idea where to connect.
@@ -89,7 +119,7 @@ impl Display for MemberSet {
 #[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
 pub struct Configuration {
     /// Unique id.
-    pub generation: Generation,
+    pub generation: SafekeeperGeneration,
     /// Current members of the configuration.
     pub members: MemberSet,
     /// Some means it is a joint conf.

libs/safekeeper_api/src/models.rs

@@ -282,3 +282,18 @@ pub struct TimelineTermBumpResponse {
 pub struct SafekeeperUtilization {
     pub timeline_count: u64,
 }
+
+/// pull_timeline request body.
+#[derive(Debug, Deserialize, Serialize)]
+pub struct PullTimelineRequest {
+    pub tenant_id: TenantId,
+    pub timeline_id: TimelineId,
+    pub http_hosts: Vec<String>,
+}
+
+#[derive(Debug, Serialize, Deserialize)]
+pub struct PullTimelineResponse {
+    // Donor safekeeper host
+    pub safekeeper_host: String,
+    // TODO: add more fields?
+}