Patch safekeeper control file on HTTP request (#6455)

Closes #6397

safekeeper/src/patch_control_file.rs

@@ -0,0 +1,85 @@
+use std::sync::Arc;
+
+use serde::{Deserialize, Serialize};
+use serde_json::Value;
+use tracing::info;
+
+use crate::{state::TimelinePersistentState, timeline::Timeline};
+
+#[derive(Deserialize, Debug, Clone)]
+pub struct Request {
+    /// JSON object with fields to update
+    pub updates: serde_json::Value,
+    /// List of fields to apply
+    pub apply_fields: Vec<String>,
+}
+
+#[derive(Serialize)]
+pub struct Response {
+    pub old_control_file: TimelinePersistentState,
+    pub new_control_file: TimelinePersistentState,
+}
+
+/// Patch control file with given request. Will update the persistent state using
+/// fields from the request and persist the new state on disk.
+pub async fn handle_request(tli: Arc<Timeline>, request: Request) -> anyhow::Result<Response> {
+    let response = tli
+        .map_control_file(|state| {
+            let old_control_file = state.clone();
+            let new_control_file = state_apply_diff(&old_control_file, &request)?;
+
+            info!(
+                "patching control file, old: {:?}, new: {:?}, patch: {:?}",
+                old_control_file, new_control_file, request
+            );
+            *state = new_control_file.clone();
+
+            Ok(Response {
+                old_control_file,
+                new_control_file,
+            })
+        })
+        .await?;
+
+    Ok(response)
+}
+
+fn state_apply_diff(
+    state: &TimelinePersistentState,
+    request: &Request,
+) -> anyhow::Result<TimelinePersistentState> {
+    let mut json_value = serde_json::to_value(state)?;
+
+    if let Value::Object(a) = &mut json_value {
+        if let Value::Object(b) = &request.updates {
+            json_apply_diff(a, b, &request.apply_fields)?;
+        } else {
+            anyhow::bail!("request.updates is not a json object")
+        }
+    } else {
+        anyhow::bail!("TimelinePersistentState is not a json object")
+    }
+
+    let new_state: TimelinePersistentState = serde_json::from_value(json_value)?;
+    Ok(new_state)
+}
+
+fn json_apply_diff(
+    object: &mut serde_json::Map<String, Value>,
+    updates: &serde_json::Map<String, Value>,
+    apply_keys: &Vec<String>,
+) -> anyhow::Result<()> {
+    for key in apply_keys {
+        if let Some(new_value) = updates.get(key) {
+            if let Some(existing_value) = object.get_mut(key) {
+                *existing_value = new_value.clone();
+            } else {
+                anyhow::bail!("key not found in original object: {}", key);
+            }
+        } else {
+            anyhow::bail!("key not found in request.updates: {}", key);
+        }
+    }
+
+    Ok(())
+}