feat: atomic writes for entries, and better collision security

src/entries.rs

@@ -1,6 +1,32 @@
+use rand::Rng;
 use serde::{Deserialize, Serialize};
+use std::io::Write;
 use std::path::Path;
 
+pub fn write_atomic(path: &Path, contents: &[u8]) -> std::io::Result<()> {
+    let parent = path.parent().ok_or_else(|| {
+        std::io::Error::new(std::io::ErrorKind::InvalidInput, "path has no parent")
+    })?;
+    let filename = path
+        .file_name()
+        .and_then(|n| n.to_str())
+        .ok_or_else(|| std::io::Error::new(std::io::ErrorKind::InvalidInput, "bad filename"))?;
+    let suffix: u32 = rand::rng().random();
+    let tmp = parent.join(format!(".{filename}.{suffix:08x}.tmp"));
+    let mut f = std::fs::File::create(&tmp)?;
+    f.write_all(contents)?;
+    f.sync_all()?;
+    drop(f);
+    if let Err(e) = std::fs::rename(&tmp, path) {
+        let _ = std::fs::remove_file(&tmp);
+        return Err(e);
+    }
+    if let Ok(dir) = std::fs::File::open(parent) {
+        let _ = dir.sync_all();
+    }
+    Ok(())
+}
+
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
 #[serde(rename_all = "lowercase")]
 pub enum Status {
@@ -149,17 +175,16 @@ pub fn append_reply(dir: &Path, id: &str, reply: &str) -> Result<String, String>
     entry.body.push_str("\n\n");
     entry.body.push_str(&quoted);
     let path = dir.join(format!("{}.txt", entry.id));
-    std::fs::write(&path, entry.to_file_contents()).map_err(|e| e.to_string())?;
+    write_atomic(&path, entry.to_file_contents().as_bytes()).map_err(|e| e.to_string())?;
     Ok(entry.meta.name.clone())
 }
 
 #[cfg(any(feature = "telegram", test))]
-/// Find an entry file by ID and update its status.
 pub fn set_status(dir: &Path, short_id: &str, status: Status) -> Result<String, String> {
     let mut entry = find_entry(dir, short_id)?;
     entry.meta.status = status;
     let path = dir.join(format!("{}.txt", entry.id));
-    std::fs::write(&path, entry.to_file_contents()).map_err(|e| e.to_string())?;
+    write_atomic(&path, entry.to_file_contents().as_bytes()).map_err(|e| e.to_string())?;
     Ok(entry.meta.name.clone())
 }
 

src/web.rs

@@ -49,13 +49,20 @@ pub fn router(state: Arc<AppState>) -> Router {
         .with_state(state)
 }
 
-fn generate_id(entries_dir: &std::path::Path) -> String {
+fn generate_id(entries_dir: &std::path::Path) -> std::io::Result<String> {
     const CHARS: &[u8] = b"0123456789abcdefghijklmnopqrstuvwxyz";
     let mut rng = rand::rng();
     loop {
         let id: String = (0..4).map(|_| CHARS[rng.random_range(0..36)] as char).collect();
-        if !entries_dir.join(format!("{id}.txt")).exists() {
-            return id;
+        let path = entries_dir.join(format!("{id}.txt"));
+        match std::fs::OpenOptions::new()
+            .write(true)
+            .create_new(true)
+            .open(&path)
+        {
+            Ok(_) => return Ok(id),
+            Err(e) if e.kind() == std::io::ErrorKind::AlreadyExists => continue,
+            Err(e) => return Err(e),
         }
     }
 }
@@ -272,19 +279,33 @@ async fn submit(
 
     let now = chrono::Utc::now();
     let date = now.format("%Y-%m-%dT%H:%M:%S").to_string();
-    let id = generate_id(&state.config.data_dir.join("entries"));
-    let filename = format!("{id}.txt");
 
-    // Save drawing with the same ID as the entry
+    let entries_dir = state.config.data_dir.join("entries");
+    if let Err(e) = std::fs::create_dir_all(&entries_dir) {
+        tracing::error!("failed to create entries directory: {e}");
+        return Html(render_error_page(&state.config, "Something went wrong. Please try again."));
+    }
+    let id = match generate_id(&entries_dir) {
+        Ok(id) => id,
+        Err(e) => {
+            tracing::error!("failed to reserve entry id: {e}");
+            return Html(render_error_page(&state.config, "Something went wrong. Please try again."));
+        }
+    };
+    let filename = format!("{id}.txt");
+    let path = entries_dir.join(&filename);
+
     let drawing_filename = if let Some(ref bytes) = drawing_bytes {
         let drawing_name = format!("{id}.png");
         let drawings_dir = state.config.data_dir.join("drawings");
         if let Err(e) = std::fs::create_dir_all(&drawings_dir) {
             tracing::error!("failed to create drawings directory: {e}");
+            let _ = std::fs::remove_file(&path);
             return Html(render_error_page(&state.config, "Something went wrong. Please try again."));
         }
-        if let Err(e) = std::fs::write(drawings_dir.join(&drawing_name), bytes) {
+        if let Err(e) = entries::write_atomic(&drawings_dir.join(&drawing_name), bytes) {
             tracing::error!("failed to write drawing: {e}");
+            let _ = std::fs::remove_file(&path);
             return Html(render_error_page(&state.config, "Something went wrong. Please try again."));
         }
         drawing_name
@@ -297,10 +318,18 @@ async fn submit(
         let vn_dir = state.config.data_dir.join("voice_notes");
         if let Err(e) = std::fs::create_dir_all(&vn_dir) {
             tracing::error!("failed to create voice notes directory: {e}");
+            let _ = std::fs::remove_file(&path);
+            if !drawing_filename.is_empty() {
+                let _ = std::fs::remove_file(state.config.data_dir.join("drawings").join(&drawing_filename));
+            }
             return Html(render_error_page(&state.config, "Something went wrong. Please try again."));
         }
-        if let Err(e) = std::fs::write(vn_dir.join(&vn_name), bytes) {
+        if let Err(e) = entries::write_atomic(&vn_dir.join(&vn_name), bytes) {
             tracing::error!("failed to write voice note: {e}");
+            let _ = std::fs::remove_file(&path);
+            if !drawing_filename.is_empty() {
+                let _ = std::fs::remove_file(state.config.data_dir.join("drawings").join(&drawing_filename));
+            }
             return Html(render_error_page(&state.config, "Something went wrong. Please try again."));
         }
         vn_name
@@ -314,22 +343,22 @@ async fn submit(
             name,
             date,
             website,
-            drawing: drawing_filename,
-            voice_note: voice_note_filename,
+            drawing: drawing_filename.clone(),
+            voice_note: voice_note_filename.clone(),
             status: Status::Pending,
         },
         body: message,
     };
 
-    // Write to disk
-    let entries_dir = state.config.data_dir.join("entries");
-    if let Err(e) = std::fs::create_dir_all(&entries_dir) {
-        tracing::error!("failed to create entries directory: {e}");
-        return Html(render_error_page(&state.config, "Something went wrong. Please try again."));
-    }
-    let path = entries_dir.join(&filename);
-    if let Err(e) = std::fs::write(&path, entry.to_file_contents()) {
+    if let Err(e) = entries::write_atomic(&path, entry.to_file_contents().as_bytes()) {
         tracing::error!("failed to write entry: {e}");
+        let _ = std::fs::remove_file(&path);
+        if !drawing_filename.is_empty() {
+            let _ = std::fs::remove_file(state.config.data_dir.join("drawings").join(&drawing_filename));
+        }
+        if !voice_note_filename.is_empty() {
+            let _ = std::fs::remove_file(state.config.data_dir.join("voice_notes").join(&voice_note_filename));
+        }
         return Html(render_error_page(&state.config, "Something went wrong. Please try again."));
     }