implement health status endpoint (closes #3)

README.md

@@ -18,6 +18,9 @@ following are supported:
   to the cache. Writing implies being able to read.
 - `ENEX_BIND_ADDRESSES` - comma-separated list of IP addresses to bind the
   service to. If empty the service will bind to all available interfaces.
+- `ENEX_MAX_CACHE_SIZE` - the maximum size of the cache in bytes. If the cache
+  exceeds that size, the least-recently used entries will be pruned to make
+  room.
 
 enex-rcache will try to read a `.env` file at startup in order to set the
 environment. Existing enviroment entries will take precedence over the contents

src/app_state.rs

@@ -1,25 +1,51 @@
-use std::sync::{Arc, Mutex};
+use std::{
+    sync::{Arc, RwLock},
+    time::{Instant, SystemTime},
+};
 
 use tracing::error;
 
 use crate::lru_cache::WeightedLRUCache;
 
+pub struct Stats {
+    pub started_at: Instant,
+    pub cache_size: u64,
+    pub oldest_entry_at: Option<SystemTime>,
+    pub newest_entry_at: Option<SystemTime>,
+    pub successful_writes: usize,
+    pub invalid_writes: usize,
+    pub failed_writes: usize,
+    pub collisions: usize,
+    pub invalid_reads: usize,
+    pub cache_misses: usize,
+    pub cache_hits: usize,
+}
+
+pub struct CacheEntryMeta {
+    pub create_at: SystemTime,
+}
+
+pub struct SharedState {
+    pub lru_cache: WeightedLRUCache<CacheEntryMeta>,
+    pub stats: Stats,
+}
+
 #[derive(Clone)]
 pub struct AppState {
-    pub lru_cache: Arc<Mutex<WeightedLRUCache>>,
     pub config: crate::config::AppConfig,
+    pub shared: Arc<RwLock<SharedState>>,
 }
 
 impl AppState {
     /// little helper to simplify access to the LRU cache
-    pub fn with_lru_cache(&self, f: impl FnOnce(&mut WeightedLRUCache)) {
-        let cache = self.lru_cache.lock();
-        match cache {
-            Ok(mut cache) => {
-                f(&mut cache);
+    pub fn with_shared(&self, f: impl FnOnce(&mut SharedState)) {
+        let shared = self.shared.write();
+        match shared {
+            Ok(mut shared) => {
+                f(&mut shared);
             }
             Err(e) => {
-                error!("Could not promote cache item: {}", e);
+                error!("Could not acquire shared state write lock: {}", e);
             }
         }
     }

src/disk_cache.rs

@@ -2,7 +2,12 @@ use std::{path::PathBuf, sync::mpsc::Receiver};
 
 use tracing::{debug, warn};
 
-use crate::{config::AppConfig, lru_cache::WeightedLRUCache};
+use crate::{
+    app_state::{CacheEntryMeta, Stats},
+    config::AppConfig,
+    helpers::update_boundary_items,
+    lru_cache::WeightedLRUCache,
+};
 
 pub fn get_cache_entry_path(config: &AppConfig, hash: &str) -> PathBuf {
     PathBuf::from(&config.cache_dir).join(hash)
@@ -37,9 +42,10 @@ struct SortableCacheEntry {
 }
 
 /// load the existing files from the cache directory into an LRU cache
-pub fn fill_lru_cache_from_disk(
+pub fn init_from_disk(
     config: &AppConfig,
-    lru_cache: &mut WeightedLRUCache,
+    lru_cache: &mut WeightedLRUCache<CacheEntryMeta>,
+    stats: &mut Stats,
 ) -> std::io::Result<()> {
     let entries = std::fs::read_dir(&config.cache_dir)?;
     let mut cache_entries = vec![];
@@ -48,6 +54,7 @@ pub fn fill_lru_cache_from_disk(
             Ok(entry) => match entry.metadata() {
                 Ok(metadata) => {
                     let weight = metadata.len();
+                    stats.cache_size += weight;
                     let key = entry.file_name().to_string_lossy().to_string();
                     match metadata.created() {
                         Ok(creation_time) => cache_entries.push(SortableCacheEntry {
@@ -70,7 +77,14 @@ pub fn fill_lru_cache_from_disk(
     }
     cache_entries.sort_by(|a, b| b.creation_time.cmp(&a.creation_time));
     for entry in cache_entries {
-        lru_cache.put(entry.key, entry.weight);
+        lru_cache.put(
+            entry.key,
+            entry.weight,
+            CacheEntryMeta {
+                create_at: entry.creation_time,
+            },
+        );
     }
+    update_boundary_items(stats, &lru_cache);
     Ok(())
 }

src/handlers.rs

@@ -1,17 +1,21 @@
-use std::io::Write;
+use std::{
+    time::{Instant, SystemTime},
+    u64,
+};
 
 use actix_web::{
     HttpResponse, Responder, get, put,
     web::{Data, Path, Payload},
 };
 use actix_web_httpauth::extractors::bearer::BearerAuth;
-use futures_util::StreamExt;
-use tracing::{debug, error, trace};
+use serde::Serialize;
+use tracing::{debug, trace};
 
 use crate::{
     access::{AccessLevel, has_access_level},
-    app_state::AppState,
+    app_state::{AppState, CacheEntryMeta},
     disk_cache::get_cache_entry_path,
+    helpers::{StreamingError, stream_to_file, update_boundary_items},
 };
 
 #[get("/v1/cache/{hash}")]
@@ -26,6 +30,7 @@ pub async fn get_cache_item(
             "Tried to read cache item {} without valid read access token.",
             hash.as_str()
         );
+        app_data.with_shared(|shared| shared.stats.invalid_reads += 1);
         return HttpResponse::Unauthorized()
             .content_type("text/plain")
             .body("Please provide a valid access token with at least read-level access.");
@@ -33,10 +38,14 @@ pub async fn get_cache_item(
     let path = get_cache_entry_path(&app_data.config, &hash);
     if !path.exists() {
         trace!("Cache item not found: {}", hash.as_str());
+        app_data.with_shared(|shared| shared.stats.cache_misses += 1);
         HttpResponse::NotFound().body("The record was not found.")
     } else {
         trace!("Returning cache item {}", hash.as_str());
-        app_data.with_lru_cache(|cache| cache.promote(hash.to_string()));
+        app_data.with_shared(|shared| {
+            shared.lru_cache.promote(hash.to_string());
+            shared.stats.cache_hits += 1;
+        });
         HttpResponse::Ok().body(std::fs::read(path).unwrap())
     }
 }
@@ -54,39 +63,94 @@ pub async fn put_cache_item(
             "Tried to write cache item {} without valid read-write access token.",
             hash.as_str()
         );
+        app_data.with_shared(|shared| shared.stats.invalid_writes += 1);
         return HttpResponse::Unauthorized()
             .content_type("text/plain")
             .body("Please provide a valid access token with read-write access.");
     }
-    let path = get_cache_entry_path(&app_data.config, &hash);
-    let file = std::fs::File::create_new(&path);
-    match file {
-        Ok(mut file) => {
-            let mut complete_size = 0u64;
-            while let Some(chunk) = body.next().await {
-                match chunk {
-                    Ok(chunk) => {
-                        complete_size += chunk.len() as u64;
-                        file.write_all(&chunk).expect("This should actually work")
-                    }
-                    Err(e) => {
-                        error!("Could not write cache item chunk: {}", e);
-                        drop(file);
-                        std::fs::remove_file(path).unwrap(); // Clean up to make sure the block doesn't get half-written with the wrong content
-                        complete_size = 0;
-                        break;
-                    }
-                }
-            }
-            if complete_size > 0 {
-                app_data.with_lru_cache(|cache| cache.put(hash.to_string(), complete_size));
-            }
+
+    let stream_result = stream_to_file(&app_data.config, &mut body, &hash).await;
+    match stream_result {
+        Ok(size) => {
+            app_data.with_shared(|shared| {
+                shared.lru_cache.put(
+                    hash.to_string(),
+                    size,
+                    CacheEntryMeta {
+                        create_at: SystemTime::now(),
+                    },
+                );
+                shared.stats.successful_writes += 1;
+                update_boundary_items(&mut shared.stats, &shared.lru_cache);
+            });
             debug!("Created cache item {}", hash.as_str());
             HttpResponse::Accepted().finish()
         }
-        Err(_) => {
-            trace!("Tried to overwrite existing cache item {}", hash.as_str());
+        Err(StreamingError::Collision) => {
+            app_data.with_shared(|shared| shared.stats.collisions += 1);
             HttpResponse::Conflict().body("Cannot overwrite an existing record.")
         }
+        Err(StreamingError::ReadError) => {
+            app_data.with_shared(|shared| shared.stats.failed_writes += 1);
+            HttpResponse::BadRequest().body("Failed fully read payload") // this is technically not in the spec, but BadRequest sounds plausible for an error to read the request payload
+        }
+    }
+}
+
+#[derive(Serialize)]
+pub struct HealthStatus {
+    pub cache_entries: usize,
+    pub cache_size: u64,
+    pub cache_capacity: u64,
+    pub oldest_entry_ms: Option<u64>,
+    pub newest_entry_ms: Option<u64>,
+    pub uptime_ms: u64,
+    pub write_requests: usize,
+    pub invalid_writes: usize,
+    pub collisions: usize,
+    pub read_requests: usize,
+    pub invalid_reads: usize,
+    pub cache_misses: usize,
+    pub cache_hits: usize,
+}
+
+#[get("/health")]
+pub async fn get_heath_status(app_data: Data<AppState>, auth: BearerAuth) -> impl Responder {
+    trace!("Received health status request");
+    if !has_access_level(&app_data.config, auth.token(), AccessLevel::Read) {
+        HttpResponse::Forbidden().body("Need at least read access to get the health status")
+    } else {
+        let now = SystemTime::now();
+        if let Ok(shared) = app_data.shared.read() {
+            HttpResponse::Ok().json(HealthStatus {
+                cache_entries: shared.lru_cache.len(),
+                cache_size: shared.stats.cache_size,
+                cache_capacity: app_data.config.max_cache_size.unwrap_or(u64::MAX),
+                oldest_entry_ms: shared
+                    .stats
+                    .oldest_entry_at
+                    .and_then(|time| now.duration_since(time).ok())
+                    .map(|elapsed| elapsed.as_millis() as u64),
+                newest_entry_ms: shared
+                    .stats
+                    .newest_entry_at
+                    .and_then(|time| now.duration_since(time).ok())
+                    .map(|elapsed| elapsed.as_millis() as u64),
+                uptime_ms: Instant::now()
+                    .duration_since(shared.stats.started_at)
+                    .as_millis() as u64,
+                write_requests: shared.stats.successful_writes,
+                invalid_writes: shared.stats.invalid_writes,
+                collisions: shared.stats.collisions,
+                read_requests: shared.stats.cache_misses
+                    + shared.stats.cache_hits
+                    + shared.stats.invalid_reads,
+                invalid_reads: shared.stats.invalid_reads,
+                cache_misses: shared.stats.cache_misses,
+                cache_hits: shared.stats.cache_hits,
+            })
+        } else {
+            HttpResponse::InternalServerError().body("Could not acquire shared data read lock")
+        }
     }
 }

src/helpers.rs

@@ -0,0 +1,68 @@
+use std::io::Write;
+
+use actix_web::web::Payload;
+use futures_util::StreamExt;
+use tracing::{error, trace};
+
+use crate::{
+    app_state::{CacheEntryMeta, Stats},
+    config::AppConfig,
+    disk_cache::get_cache_entry_path,
+    lru_cache::WeightedLRUCache,
+};
+
+pub enum StreamingError {
+    Collision,
+    ReadError,
+}
+
+pub fn update_boundary_items(stats: &mut Stats, entries: &WeightedLRUCache<CacheEntryMeta>) {
+    for (_, value) in entries.iter() {
+        if stats
+            .oldest_entry_at
+            .is_none_or(|oldest_entry| oldest_entry < value.meta.create_at)
+        {
+            stats.oldest_entry_at = Some(value.meta.create_at);
+        }
+        if stats
+            .newest_entry_at
+            .is_none_or(|newest_entry| newest_entry > value.meta.create_at)
+        {
+            stats.newest_entry_at = Some(value.meta.create_at);
+        }
+    }
+}
+
+pub async fn stream_to_file(
+    config: &AppConfig,
+    body: &mut Payload,
+    hash: &str,
+) -> Result<u64, StreamingError> {
+    let path = get_cache_entry_path(config, &hash);
+    let file = std::fs::File::create_new(&path);
+
+    match file {
+        Ok(mut file) => {
+            let mut complete_size = 0u64;
+            while let Some(chunk) = body.next().await {
+                match chunk {
+                    Ok(chunk) => {
+                        complete_size += chunk.len() as u64;
+                        file.write_all(&chunk).expect("This should actually work") // this might lead to a crash in the service -> not good
+                    }
+                    Err(e) => {
+                        error!("Could not read body chunk: {}", e);
+                        drop(file);
+                        std::fs::remove_file(path).unwrap(); // Clean up to make sure the block doesn't get half-written with the wrong content
+                        return Err(StreamingError::ReadError);
+                    }
+                }
+            }
+            Ok(complete_size)
+        }
+        Err(_) => {
+            trace!("Tried to overwrite existing cache item {}", hash);
+            return Err(StreamingError::Collision);
+        }
+    }
+}

src/lru_cache.rs

@@ -1,24 +1,25 @@
 use std::{
-    collections::{HashMap, VecDeque},
+    collections::{HashMap, VecDeque, hash_map::Iter},
     sync::mpsc::Sender,
 };
 
 use tracing::error;
 
-struct CacheEntry {
-    weight: u64,
+pub struct CacheEntry<TMeta> {
+    pub weight: u64,
+    pub meta: TMeta,
 }
 
-pub struct WeightedLRUCache {
+pub struct WeightedLRUCache<TMeta> {
     current_weight: u64,
     pub max_weight: u64,
-    entries: HashMap<String, CacheEntry>,
+    entries: HashMap<String, CacheEntry<TMeta>>,
     lru_list: VecDeque<String>,
     eviction_notifier: Option<Sender<Vec<String>>>,
 }
 
-impl WeightedLRUCache {
-    pub fn new(max_weight: u64) -> WeightedLRUCache {
+impl<TMeta> WeightedLRUCache<TMeta> {
+    pub fn new(max_weight: u64) -> WeightedLRUCache<TMeta> {
         WeightedLRUCache {
             current_weight: 0,
             max_weight,
@@ -32,9 +33,14 @@ impl WeightedLRUCache {
         self.eviction_notifier = Some(sender);
     }
 
-    pub fn put(&mut self, key: String, weight: u64) {
-        self.entries
-            .insert(key.clone(), CacheEntry { weight: weight });
+    pub fn put(&mut self, key: String, weight: u64, meta: TMeta) {
+        self.entries.insert(
+            key.clone(),
+            CacheEntry {
+                weight: weight,
+                meta,
+            },
+        );
         self.current_weight += weight;
         self.promote(key);
         if self.current_weight > self.max_weight {
@@ -60,6 +66,10 @@ impl WeightedLRUCache {
         self.entries.len()
     }
 
+    pub fn iter<'a>(&'a self) -> Iter<'a, String, CacheEntry<TMeta>> {
+        self.entries.iter()
+    }
+
     fn evict(&mut self) -> Vec<String> {
         let mut removed_keys = Vec::new();
         while self.current_weight > self.max_weight {
@@ -86,11 +96,11 @@ mod tests {
 
     #[test]
     fn fill_lru_cache() {
-        let mut lru_cache = WeightedLRUCache::new(100);
+        let mut lru_cache = WeightedLRUCache::<u8>::new(100);
 
-        lru_cache.put("key1".to_string(), 10);
-        lru_cache.put("key2".to_string(), 20);
-        lru_cache.put("key3".to_string(), 30);
+        lru_cache.put("key1".to_string(), 10, 0);
+        lru_cache.put("key2".to_string(), 20, 0);
+        lru_cache.put("key3".to_string(), 30, 0);
 
         assert!(lru_cache.has_entry("key1"));
         assert!(lru_cache.has_entry("key2"));
@@ -99,11 +109,11 @@ mod tests {
 
     #[test]
     fn overflow_lru_cache() {
-        let mut lru_cache = WeightedLRUCache::new(100);
+        let mut lru_cache = WeightedLRUCache::<u8>::new(100);
 
-        lru_cache.put("key1".to_string(), 10);
-        lru_cache.put("key2".to_string(), 45);
-        lru_cache.put("key3".to_string(), 50);
+        lru_cache.put("key1".to_string(), 10, 0);
+        lru_cache.put("key2".to_string(), 45, 0);
+        lru_cache.put("key3".to_string(), 50, 0);
 
         assert!(!lru_cache.has_entry("key1"));
         assert!(lru_cache.has_entry("key2"));
@@ -112,26 +122,26 @@ mod tests {
 
     #[test]
     fn calls_expunge_cb() {
-        let mut lru_cache = WeightedLRUCache::new(100);
+        let mut lru_cache = WeightedLRUCache::<u8>::new(100);
         let (sender, receiver) = std::sync::mpsc::channel();
         {
             lru_cache.on_eviction(sender);
         }
-        lru_cache.put("key1".to_string(), 10);
-        lru_cache.put("key2".to_string(), 45);
-        lru_cache.put("key3".to_string(), 50);
+        lru_cache.put("key1".to_string(), 10, 0);
+        lru_cache.put("key2".to_string(), 45, 0);
+        lru_cache.put("key3".to_string(), 50, 0);
 
         assert_eq!(receiver.recv().unwrap(), vec!["key1".to_string()]);
     }
 
     #[test]
     fn double_insert_pushes_entries_to_the_back() {
-        let mut lru_cache = WeightedLRUCache::new(100);
+        let mut lru_cache = WeightedLRUCache::<u8>::new(100);
 
-        lru_cache.put("key1".to_string(), 10);
-        lru_cache.put("key2".to_string(), 45);
-        lru_cache.put("key1".to_string(), 20);
-        lru_cache.put("key3".to_string(), 50);
+        lru_cache.put("key1".to_string(), 10, 0);
+        lru_cache.put("key2".to_string(), 45, 0);
+        lru_cache.put("key1".to_string(), 20, 0);
+        lru_cache.put("key3".to_string(), 50, 0);
 
         assert!(lru_cache.has_entry("key1"));
         assert!(!lru_cache.has_entry("key2"));
@@ -140,12 +150,12 @@ mod tests {
 
     #[test]
     fn promote_pushes_entries_to_the_back() {
-        let mut lru_cache = WeightedLRUCache::new(100);
+        let mut lru_cache = WeightedLRUCache::<u8>::new(100);
 
-        lru_cache.put("key1".to_string(), 10);
-        lru_cache.put("key2".to_string(), 45);
+        lru_cache.put("key1".to_string(), 10, 0);
+        lru_cache.put("key2".to_string(), 45, 0);
         lru_cache.promote("key1".to_string());
-        lru_cache.put("key3".to_string(), 50);
+        lru_cache.put("key3".to_string(), 50, 0);
 
         assert!(lru_cache.has_entry("key1"));
         assert!(!lru_cache.has_entry("key2"));
@@ -154,8 +164,8 @@ mod tests {
 
     #[test]
     fn gracefully_fails_with_zero_size() {
-        let mut lru_cache = WeightedLRUCache::new(0);
-        lru_cache.put("key1".to_string(), 10);
+        let mut lru_cache = WeightedLRUCache::<u8>::new(0);
+        lru_cache.put("key1".to_string(), 10, 0);
 
         assert!(!lru_cache.has_entry("key1"));
     }

src/main.rs

@@ -1,21 +1,25 @@
 use std::{
-    sync::{Arc, Mutex, mpsc::Receiver},
+    sync::{Arc, RwLock},
+    time::Instant,
     u64,
 };
 
 use actix_web::{App, HttpServer, web::Data};
 use app_state::AppState;
-use disk_cache::{cache_cleanup, fill_lru_cache_from_disk};
+use disk_cache::{cache_cleanup, init_from_disk};
 use dotenvy::dotenv;
 use lru_cache::WeightedLRUCache;
 use tracing::{Level, debug, warn};
 use tracing_subscriber::FmtSubscriber;
 
+use crate::app_state::{SharedState, Stats};
+
 mod access;
 mod app_state;
 mod config;
 mod disk_cache;
 mod handlers;
+mod helpers;
 mod lru_cache;
 
 #[actix_web::main]
@@ -40,13 +44,26 @@ async fn main() -> std::io::Result<()> {
     }
     let (tx, rx) = std::sync::mpsc::channel();
     lru_cache.on_eviction(tx);
+    let mut stats = Stats {
+        started_at: Instant::now(),
+        cache_size: 0,
+        oldest_entry_at: None,
+        newest_entry_at: None,
+        successful_writes: 0,
+        invalid_writes: 0,
+        failed_writes: 0,
+        collisions: 0,
+        invalid_reads: 0,
+        cache_misses: 0,
+        cache_hits: 0,
+    };
     // Load the existing cache entries from disk
-    fill_lru_cache_from_disk(&config, &mut lru_cache)?;
+    init_from_disk(&config, &mut lru_cache, &mut stats)?;
     debug!("Loaded cache with {} entries", lru_cache.len());
 
     let app_state = AppState {
-        lru_cache: Arc::new(Mutex::new(lru_cache)),
         config: config.clone(),
+        shared: Arc::new(RwLock::new(SharedState { lru_cache, stats })),
     };
 
     let mut server = HttpServer::new({
@@ -56,6 +73,7 @@ async fn main() -> std::io::Result<()> {
                 .wrap(actix_web::middleware::Logger::default())
                 .service(handlers::get_cache_item)
                 .service(handlers::put_cache_item)
+                .service(handlers::get_heath_status)
         }
     })
     .keep_alive(None); // disable HTTP keep-alive because it seems to break NX (at least in version 20.8)