Generalize client storage from the filesystem (#2194)

* `linera-core`: add `Persistent` trait

* `linera-service`: use new `Persistent` trait

* `linera-service`: don't forget to create the file for `persistent::File::new`

* `linera-service`: refresh PRNG seed more to align with tests

* `linera-service`: rename `Persistent` to `Persist`

This is more in line both with Rust standard library traits, which
tend to be transitive verbs, and also with the Rust trait naming
conventions RFC rust-lang/rfcs#344, which states:

> Prefer (transitive) verbs, nouns, and then adjectives; avoid
> grammatical suffixes (like able).

* `linera-service`: document `Persist` trait

* `linera-service::persistent::File`: when an error occurs during error handling, do not hide the outer error

* `linera_service::persistent`: single-space documentation

Co-authored-by: Andreas Fackler <[email protected]>
Signed-off-by: James Kay <[email protected]>

* `linera-service`: mention bug #2053

* `linera_service::proxy`: replace `expect` with `?`

* `linera_service::persistent`: use the indicative mood for function documentation

---------

Signed-off-by: James Kay <[email protected]>
Co-authored-by: Andreas Fackler <[email protected]>

linera-service/src/cli_wrappers/remote_net.rs

@@ -14,7 +14,7 @@ use crate::{
         local_net::PathProvider, ClientWrapper, Faucet, FaucetOption, LineraNet, LineraNetConfig,
         Network,
     },
-    config::Export,
+    persistent::{self, Persist},
 };
 
 pub struct RemoteNetTestingConfig {
@@ -116,9 +116,11 @@ impl LineraNet for RemoteNet {
 impl RemoteNet {
     async fn new(testing_prng_seed: Option<u64>, faucet: &Faucet) -> Result<Self> {
         let tmp_dir = Arc::new(tempdir()?);
-        let genesis_config = faucet.genesis_config().await?;
         // Write json config to disk
-        genesis_config.write(tmp_dir.path().join("genesis.json").as_path())?;
+        Persist::persist(&mut persistent::File::new(
+            tmp_dir.path().join("genesis.json").as_path(),
+            faucet.genesis_config().await?,
+        )?)?;
         Ok(Self {
             network: Network::Grpc,
             testing_prng_seed,

linera-service/src/cli_wrappers/wallet.rs

@@ -688,7 +688,7 @@ impl ClientWrapper {
     }
 
     pub fn load_wallet(&self) -> Result<Wallet> {
-        Ok(WalletState::from_file(self.wallet_path().as_path())?.into_inner())
+        Ok(WalletState::from_file(self.wallet_path().as_path())?.into_value())
     }
 
     pub fn wallet_path(&self) -> PathBuf {

linera-service/src/config.rs

@@ -2,15 +2,8 @@
 // Copyright (c) Zefchain Labs, Inc.
 // SPDX-License-Identifier: Apache-2.0
 
-use std::{
-    io::{BufRead, BufReader, BufWriter, Write},
-    iter::IntoIterator,
-    path::{Path, PathBuf},
-};
+use std::{iter::IntoIterator, path::Path};
 
-use anyhow::{bail, Context as _};
-use fs4::FileExt as _;
-use fs_err::{self, File, OpenOptions};
 use linera_base::{
     crypto::{BcsSignable, CryptoRng, KeyPair, PublicKey},
     data_types::{Amount, Timestamp},
@@ -23,27 +16,12 @@ use linera_execution::{
 use linera_rpc::config::{ValidatorInternalNetworkConfig, ValidatorPublicNetworkConfig};
 use linera_storage::Storage;
 use linera_views::views::ViewError;
-use serde::{de::DeserializeOwned, Deserialize, Serialize};
-
-use crate::wallet::{UserChain, Wallet};
-
-pub trait Import: DeserializeOwned {
-    fn read(path: &Path) -> Result<Self, std::io::Error> {
-        let data = fs_err::read(path)?;
-        Ok(serde_json::from_slice(data.as_slice())?)
-    }
-}
+use serde::{Deserialize, Serialize};
 
-pub trait Export: Serialize {
-    fn write(&self, path: &Path) -> Result<(), std::io::Error> {
-        let file = OpenOptions::new().create(true).write(true).open(path)?;
-        let mut writer = BufWriter::new(file);
-        let data = serde_json::to_string_pretty(self).unwrap();
-        writer.write_all(data.as_ref())?;
-        writer.write_all(b"\n")?;
-        Ok(())
-    }
-}
+use crate::{
+    persistent::{self, Persist},
+    wallet::{UserChain, Wallet},
+};
 
 /// The public configuration of a validator.
 #[derive(Clone, Debug, Serialize, Deserialize)]
@@ -62,18 +40,12 @@ pub struct ValidatorServerConfig {
     pub internal_network: ValidatorInternalNetworkConfig,
 }
 
-impl Import for ValidatorServerConfig {}
-impl Export for ValidatorServerConfig {}
-
 /// The (public) configuration for all validators.
 #[derive(Debug, Default, Clone, Deserialize, Serialize)]
 pub struct CommitteeConfig {
     pub validators: Vec<ValidatorConfig>,
 }
 
-impl Import for CommitteeConfig {}
-impl Export for CommitteeConfig {}
-
 impl CommitteeConfig {
     pub fn into_committee(self, policy: ResourceControlPolicy) -> Committee {
         let validators = self
@@ -93,147 +65,67 @@ impl CommitteeConfig {
     }
 }
 
-/// A guard that keeps an exclusive lock on a file.
-pub struct FileLock {
-    file: File,
+/// The runtime state of the wallet, persisted atomically on change via an instance of
+/// [`Persist`].
+pub struct WalletState {
+    wallet: persistent::File<Wallet>,
+    prng: Box<dyn CryptoRng>,
 }
 
-impl FileLock {
-    /// Acquires an exclusive lock on a provided `file`, returning a [`FileLock`] which will
-    /// release the lock when dropped.
-    pub fn new(file: File, path: &Path) -> Result<Self, anyhow::Error> {
-        file.file().try_lock_exclusive().with_context(|| {
-            format!(
-                "Error getting write lock to wallet \"{}\". Please make sure the file exists \
-                 and that it is not in use by another process already.",
-                path.display()
-            )
-        })?;
+impl std::ops::Deref for WalletState {
+    type Target = Wallet;
 
-        Ok(FileLock { file })
+    fn deref(&self) -> &Wallet {
+        &self.wallet
     }
 }
 
-impl Drop for FileLock {
-    fn drop(&mut self) {
-        if let Err(error) = self.file.file().unlock() {
-            tracing::warn!("Failed to unlock wallet file: {error}");
-        }
+impl Persist for WalletState {
+    type Error = anyhow::Error;
+
+    fn persist(this: &mut Self) -> anyhow::Result<()> {
+        Persist::mutate(&mut this.wallet).refresh_prng_seed(&mut this.prng);
+        tracing::debug!("Persisted user chains");
+        Ok(())
     }
-}
 
-/// A wrapper around `Wallet` which owns a [`FileLock`] to prevent
-/// two processes accessing it at the same time.
-pub struct WalletState {
-    inner: Wallet,
-    prng: Box<dyn CryptoRng>,
-    wallet_path: PathBuf,
-    _lock: FileLock,
+    fn as_mut(this: &mut Self) -> &mut Wallet {
+        Persist::as_mut(&mut this.wallet)
+    }
 }
 
 impl Extend<UserChain> for WalletState {
     fn extend<Chains: IntoIterator<Item = UserChain>>(&mut self, chains: Chains) {
-        self.inner.extend(chains);
+        Persist::mutate(self).extend(chains);
     }
 }
 
 impl WalletState {
-    pub fn inner(&self) -> &Wallet {
-        &self.inner
-    }
-
-    pub fn inner_mut(&mut self) -> &mut Wallet {
-        &mut self.inner
-    }
-
-    pub fn into_inner(self) -> Wallet {
-        self.inner
+    fn new(wallet: persistent::File<Wallet>) -> Self {
+        Self {
+            prng: wallet.make_prng(),
+            wallet,
+        }
     }
 
     pub fn from_file(path: &Path) -> Result<Self, anyhow::Error> {
-        let file = OpenOptions::new().read(true).write(true).open(path)?;
-        let file_lock = FileLock::new(file, path)?;
-        let inner: Wallet = serde_json::from_reader(BufReader::new(&file_lock.file))?;
-        Ok(Self {
-            prng: inner.make_prng(),
-            inner,
-            wallet_path: path.into(),
-            _lock: file_lock,
-        })
-    }
-
-    pub fn create(
-        path: &Path,
-        genesis_config: GenesisConfig,
-        testing_prng_seed: Option<u64>,
-    ) -> Result<Self, anyhow::Error> {
-        let file = Self::open_options().read(true).open(path)?;
-        let file_lock = FileLock::new(file, path)?;
-        let mut reader = BufReader::new(&file_lock.file);
-        let inner = if reader.fill_buf()?.is_empty() {
-            Wallet::new(genesis_config, testing_prng_seed)
-        } else {
-            serde_json::from_reader(reader)?
-        };
-
-        Ok(Self {
-            prng: inner.make_prng(),
-            inner,
-            wallet_path: path.into(),
-            _lock: file_lock,
-        })
+        Ok(Self::new(persistent::File::read_or_create(path, || {
+            anyhow::bail!("wallet file not found: {}", path.display())
+        })?))
     }
 
-    /// Writes the wallet to disk.
-    ///
-    /// The contents of the wallet need to be over-written completely, so
-    /// a temporary file is created as a backup in case a crash occurs while
-    /// writing to disk.
-    ///
-    /// The temporary file is then renamed to the original wallet name. If
-    /// serialization or writing to disk fails, the temporary filed is
-    /// deleted.
-    pub fn write(&mut self) -> Result<(), anyhow::Error> {
-        let mut temp_file_path = self.wallet_path.clone();
-        temp_file_path.set_extension("json.bak");
-        let backup_file = Self::open_options().open(&temp_file_path)?;
-        let mut temp_file_writer = BufWriter::new(backup_file);
-        if let Err(e) = serde_json::to_writer_pretty(&mut temp_file_writer, &self.inner) {
-            fs_err::remove_file(&temp_file_path)?;
-            bail!("failed to serialize the wallet state: {}", e)
-        }
-        if let Err(e) = temp_file_writer.flush() {
-            fs_err::remove_file(&temp_file_path)?;
-            bail!("failed to write the wallet state: {}", e);
-        }
-        fs_err::rename(&temp_file_path, &self.wallet_path)?;
-        Ok(())
+    pub fn create(path: &Path, wallet: Wallet) -> Result<Self, anyhow::Error> {
+        Ok(Self::new(persistent::File::read_or_create(path, || {
+            Ok(wallet)
+        })?))
     }
 
     pub fn generate_key_pair(&mut self) -> KeyPair {
         KeyPair::generate_from(&mut self.prng)
     }
 
-    pub fn save(&mut self) -> anyhow::Result<()> {
-        self.inner.refresh_prng_seed(&mut self.prng);
-        self.write()?;
-        tracing::info!("Saved user chain states");
-        Ok(())
-    }
-
-    pub fn refresh_prng_seed(&mut self) {
-        self.inner.refresh_prng_seed(&mut self.prng)
-    }
-
-    /// Returns options for opening and writing to the wallet file, creating it if it doesn't
-    /// exist. On Unix, this restricts read and write permissions to the current user.
-    // TODO(#1924): Implement better key management.
-    fn open_options() -> OpenOptions {
-        let mut options = OpenOptions::new();
-        #[cfg(target_family = "unix")]
-        fs_err::os::unix::fs::OpenOptionsExt::mode(&mut options, 0o600);
-        options.create(true).write(true);
-        options
+    pub fn into_value(self) -> Wallet {
+        self.wallet.into_value()
     }
 }
 
@@ -247,8 +139,6 @@ pub struct GenesisConfig {
     pub network_name: String,
 }
 
-impl Import for GenesisConfig {}
-impl Export for GenesisConfig {}
 impl BcsSignable for GenesisConfig {}
 
 impl GenesisConfig {

linera-service/src/lib.rs

@@ -12,6 +12,7 @@ pub mod config;
 pub mod faucet;
 pub mod grpc_proxy;
 pub mod node_service;
+pub mod persistent;
 pub mod project;
 #[cfg(with_metrics)]
 pub mod prometheus_server;