introduce RwLock to control access to local archive index files

Author: syphar

Cargo.toml

@@ -64,7 +64,7 @@ sysinfo = { version = "0.37.2", default-features = false, features = ["system"]
 derive_builder = "0.20.2"
 
 # Async
-tokio = { version = "1.0", features = ["rt-multi-thread", "signal", "macros", "process"] }
+tokio = { version = "1.0", features = ["rt-multi-thread", "signal", "macros", "process", "sync"] }
 tokio-util = { version = "0.7.15", default-features = false, features = ["io"] }
 tracing-futures= { version = "0.2.5", features = ["std-future", "futures-03"] }
 futures-util = "0.3.5"

src/config.rs

@@ -1,6 +1,6 @@
 use crate::{cdn::CdnKind, storage::StorageKind};
 use anyhow::{Context, Result, anyhow, bail};
-use std::{env::VarError, error::Error, path::PathBuf, str::FromStr, time::Duration};
+use std::{env::VarError, error::Error, io, path, path::PathBuf, str::FromStr, time::Duration};
 use tracing::trace;
 use url::Url;
 
@@ -209,10 +209,10 @@ impl Config {
             .cdn_max_queued_age(Duration::from_secs(env("DOCSRS_CDN_MAX_QUEUED_AGE", 3600)?))
             .cloudfront_distribution_id_web(maybe_env("CLOUDFRONT_DISTRIBUTION_ID_WEB")?)
             .cloudfront_distribution_id_static(maybe_env("CLOUDFRONT_DISTRIBUTION_ID_STATIC")?)
-            .local_archive_cache_path(env(
+            .local_archive_cache_path(ensure_absolute_path(env(
                 "DOCSRS_ARCHIVE_INDEX_CACHE_PATH",
                 prefix.join("archive_cache"),
-            )?)
+            )?)?)
             .compiler_metrics_collection_path(maybe_env("DOCSRS_COMPILER_METRICS_PATH")?)
             .temp_dir(temp_dir)
             .rustwide_workspace(env(
@@ -235,6 +235,14 @@ impl Config {
     }
 }
 
+fn ensure_absolute_path(path: PathBuf) -> io::Result<PathBuf> {
+    if path.is_absolute() {
+        Ok(path)
+    } else {
+        Ok(path::absolute(&path)?)
+    }
+}
+
 fn env<T>(var: &str, default: T) -> Result<T>
 where
     T: FromStr,

src/storage/mod.rs

@@ -22,27 +22,33 @@ use crate::{
 };
 use anyhow::anyhow;
 use chrono::{DateTime, Utc};
+use dashmap::DashMap;
 use fn_error_context::context;
-use futures_util::stream::BoxStream;
+use futures_util::{StreamExt as _, stream::BoxStream};
 use mime::Mime;
 use path_slash::PathExt;
 use std::{
     fmt,
     fs::{self, File},
     io::{self, BufReader},
+    iter,
     num::ParseIntError,
     ops::RangeInclusive,
     path::{Path, PathBuf},
+    str::FromStr,
     sync::Arc,
+    time::{Instant, SystemTime},
 };
-use std::{iter, str::FromStr};
 use tokio::{
     io::{AsyncRead, AsyncWriteExt},
     runtime,
+    sync::RwLock,
 };
-use tracing::{error, info_span, instrument, trace};
+use tracing::{debug, error, info_span, instrument, trace};
 use walkdir::WalkDir;
 
+static ARCHIVE_INDEX_FILE_EXTENSION: &str = "index";
+
 type FileRange = RangeInclusive<u64>;
 
 #[derive(Debug, thiserror::Error)]
@@ -181,6 +187,8 @@ enum StorageBackend {
 pub struct AsyncStorage {
     backend: StorageBackend,
     config: Arc<Config>,
+    /// Locks to synchronize access to the locally cached archive index files.
+    locks: DashMap<PathBuf, Arc<RwLock<()>>>,
 }
 
 impl AsyncStorage {
@@ -199,6 +207,7 @@ impl AsyncStorage {
                 }
             },
             config,
+            locks: DashMap::new(),
         })
     }
 
@@ -313,12 +322,10 @@ impl AsyncStorage {
         path: &str,
     ) -> Result<bool> {
         match self
-            .download_archive_index(archive_path, latest_build_id)
+            .find_in_archive_index(archive_path, latest_build_id, path)
             .await
         {
-            Ok(index_filename) => Ok(archive_index::find_in_file(index_filename, path)
-                .await?
-                .is_some()),
+            Ok(file_info) => Ok(file_info.is_some()),
             Err(err) => {
                 if err.downcast_ref::<PathNotFoundError>().is_some() {
                     Ok(false)
@@ -375,41 +382,67 @@ impl AsyncStorage {
         Ok(blob.decompress())
     }
 
+    fn local_index_cache_lock(&self, local_index_path: impl AsRef<Path>) -> Arc<RwLock<()>> {
+        let local_index_path = local_index_path.as_ref().to_path_buf();
+
+        self.locks
+            .entry(local_index_path)
+            .or_insert_with(|| Arc::new(RwLock::new(())))
+            .downgrade()
+            .clone()
+    }
+
     #[instrument]
-    pub(super) async fn download_archive_index(
+    async fn find_in_archive_index(
         &self,
         archive_path: &str,
         latest_build_id: Option<BuildId>,
-    ) -> Result<PathBuf> {
-        // remote/folder/and/x.zip.index
-        let remote_index_path = format!("{archive_path}.index");
+        path_in_archive: &str,
+    ) -> Result<Option<archive_index::FileInfo>> {
+        // we know that config.local_archive_cache_path is an absolute path, not relative.
+        // So it will be usable as key in the DashMap.
         let local_index_path = self.config.local_archive_cache_path.join(format!(
-            "{archive_path}.{}.index",
+            "{archive_path}.{}.{ARCHIVE_INDEX_FILE_EXTENSION}",
             latest_build_id.map(|id| id.0).unwrap_or(0)
         ));
 
-        if !local_index_path.exists() {
-            let index_content = self.get(&remote_index_path, usize::MAX).await?.content;
+        let rwlock = self.local_index_cache_lock(&local_index_path);
 
-            tokio::fs::create_dir_all(
-                local_index_path
-                    .parent()
-                    .ok_or_else(|| anyhow!("index path without parent"))?,
-            )
-            .await?;
+        // directly acquire the read-lock, so the syscall (`path.exists()`) below is already
+        // protected.
+        let mut _read_guard = rwlock.read().await;
+
+        if !tokio::fs::try_exists(&local_index_path).await? {
+            // upgrade the lock to a write-lock for downloading & storing the index.
+            drop(_read_guard);
+            let _write_guard = rwlock.write().await;
+
+            // check existance again in case of Race Condition (TOCTOU)
+            if !tokio::fs::try_exists(&local_index_path).await? {
+                // remote/folder/and/x.zip.index
+                let remote_index_path = format!("{archive_path}.{ARCHIVE_INDEX_FILE_EXTENSION}");
+
+                tokio::fs::create_dir_all(
+                    local_index_path
+                        .parent()
+                        .ok_or_else(|| anyhow!("index path without parent"))?,
+                )
+                .await?;
+
+                {
+                    let mut file = tokio::fs::File::create(&local_index_path).await?;
+                    let mut stream = self.get_stream(&remote_index_path).await?.content;
+
+                    tokio::io::copy(&mut stream, &mut file).await?;
+
+                    file.flush().await?;
+                }
+            }
 
-            // when we don't have a locally cached index and many parallel request
-            // we might download the same archive index multiple times here.
-            // So we're storing the content into a temporary file before renaming it
-            // into the final location.
-            let temp_path = tempfile::NamedTempFile::new_in(&self.config.local_archive_cache_path)?
-                .into_temp_path();
-            let mut file = tokio::fs::File::create(&temp_path).await?;
-            file.write_all(&index_content).await?;
-            tokio::fs::rename(temp_path, &local_index_path).await?;
+            _read_guard = _write_guard.downgrade();
         }
 
-        Ok(local_index_path)
+        archive_index::find_in_file(local_index_path, path_in_archive).await
     }
 
     #[instrument]
@@ -420,11 +453,8 @@ impl AsyncStorage {
         path: &str,
         max_size: usize,
     ) -> Result<Blob> {
-        let index_filename = self
-            .download_archive_index(archive_path, latest_build_id)
-            .await?;
-
-        let info = archive_index::find_in_file(index_filename, path)
+        let info = self
+            .find_in_archive_index(archive_path, latest_build_id, path)
             .await?
             .ok_or(PathNotFoundError)?;
 
@@ -454,11 +484,8 @@ impl AsyncStorage {
         latest_build_id: Option<BuildId>,
         path: &str,
     ) -> Result<StreamingBlob> {
-        let index_filename = self
-            .download_archive_index(archive_path, latest_build_id)
-            .await?;
-
-        let info = archive_index::find_in_file(index_filename, path)
+        let info = self
+            .find_in_archive_index(archive_path, latest_build_id, path)
             .await?
             .ok_or(PathNotFoundError)?;
 
@@ -531,7 +558,7 @@ impl AsyncStorage {
             .await?;
 
         let alg = CompressionAlgorithm::default();
-        let remote_index_path = format!("{}.index", &archive_path);
+        let remote_index_path = format!("{}.{ARCHIVE_INDEX_FILE_EXTENSION}", &archive_path);
         let compressed_index_content = {
             let _span = info_span!("create_archive_index", %remote_index_path).entered();
 
@@ -843,17 +870,6 @@ impl Storage {
             .block_on(self.inner.get_range(path, max_size, range, compression))
     }
 
-    pub(super) fn download_index(
-        &self,
-        archive_path: &str,
-        latest_build_id: Option<BuildId>,
-    ) -> Result<PathBuf> {
-        self.runtime.block_on(
-            self.inner
-                .download_archive_index(archive_path, latest_build_id),
-        )
-    }
-
     pub(crate) fn get_from_archive(
         &self,
         archive_path: &str,
@@ -1387,16 +1403,17 @@ mod backend_tests {
             fs::write(path, "data")?;
         }
 
+        let remote_index_filename = format!("folder/test.zip.0.{ARCHIVE_INDEX_FILE_EXTENSION}");
         let local_index_location = storage
             .inner
             .config
             .local_archive_cache_path
-            .join("folder/test.zip.0.index");
+            .join(&remote_index_filename);
 
         let (stored_files, compression_alg) =
             storage.store_all_in_archive("folder/test.zip", dir.path())?;
 
-        assert!(storage.exists("folder/test.zip.index")?);
+        assert!(storage.exists(&remote_index_filename)?);
 
         assert_eq!(compression_alg, CompressionAlgorithm::Bzip2);
         assert_eq!(stored_files.len(), files.len());