feat(tvix/store): add pathinfoservice

This adds a PathInfoService trait, and an implementation for it using
sled, and one using a HashMap.

Change-Id: I85fe4c9b6105808d7b0c095441326424ffc2d2bb
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8099
Tested-by: BuildkiteCI
Reviewed-by: raitobezarius <tvl@lahfa.xyz>

tvix/store/src/pathinfoservice/memory.rs

@@ -0,0 +1,62 @@
+use std::{
+    collections::HashMap,
+    sync::{Arc, RwLock},
+};
+
+use crate::{proto, Error};
+use nix_compat::store_path::DIGEST_SIZE;
+
+use super::PathInfoService;
+
+pub struct MemoryPathInfoService {
+    db: Arc<RwLock<HashMap<Vec<u8>, proto::PathInfo>>>,
+}
+
+impl MemoryPathInfoService {
+    pub fn new() -> Self {
+        let db = Arc::new(RwLock::new(HashMap::default()));
+
+        Self { db }
+    }
+}
+
+impl PathInfoService for MemoryPathInfoService {
+    fn get(
+        &self,
+        by_what: proto::get_path_info_request::ByWhat,
+    ) -> Result<Option<proto::PathInfo>, Error> {
+        match by_what {
+            proto::get_path_info_request::ByWhat::ByOutputHash(digest) => {
+                if digest.len() != DIGEST_SIZE {
+                    return Err(Error::InvalidRequest("invalid digest length".to_string()));
+                }
+
+                let db = self.db.read().unwrap();
+
+                match db.get(&digest) {
+                    None => Ok(None),
+                    Some(path_info) => Ok(Some(path_info.clone())),
+                }
+            }
+        }
+    }
+
+    fn put(&self, path_info: proto::PathInfo) -> Result<proto::PathInfo, Error> {
+        // Call validate on the received PathInfo message.
+        match path_info.validate() {
+            Err(e) => Err(Error::InvalidRequest(format!(
+                "failed to validate PathInfo: {}",
+                e
+            ))),
+
+            // In case the PathInfo is valid, and we were able to extract a NixPath, store it in the database.
+            // This overwrites existing PathInfo objects.
+            Ok(nix_path) => {
+                let mut db = self.db.write().unwrap();
+                db.insert(nix_path.digest.to_vec(), path_info.clone());
+
+                Ok(path_info)
+            }
+        }
+    }
+}