Cargo.lock

@@ -14,6 +14,12 @@ version = "2.13.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "3ded4057c258ba199e2d26386d3af3780957ecaee6c4ef4041c6b4b8b97c0b06"
 
+[[package]]
+name = "cfg-if"
+version = "1.0.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4e7648175b45a9a48536d676f68d918270699102aa8dab5496df06904c914600"
+
 [[package]]
 name = "equivalent"
 version = "1.0.2"
@@ -26,6 +32,18 @@ version = "0.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "77ce24cb58228fbb8aa041425bb1050850ac19177686ea6e0f41a70416f56fdb"
 
+[[package]]
+name = "getrandom"
+version = "0.3.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "899def5c37c4fd7b2664648c28120ecec138e4d395b459e5ca34f9cce2dd77fd"
+dependencies = [
+ "cfg-if",
+ "libc",
+ "r-efi",
+ "wasip2",
+]
+
 [[package]]
 name = "hashbrown"
 version = "0.17.1"
@@ -71,6 +89,12 @@ version = "0.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "09edd9e8b54e49e587e4f6295a7d29c3ea94d469cb40ab8ca70b288248a81db2"
 
+[[package]]
+name = "libc"
+version = "0.2.189"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3eaf3ede3fee6db1a4c2ee091bf8a8b4dccdc6d17f656fb07896ee72867612f2"
+
 [[package]]
 name = "log"
 version = "0.4.34"
@@ -98,6 +122,7 @@ checksum = "cf8baf1c55e62ffcace7a9f06f4bd9cd3f0c4beb022d3b367256b91b87513d98"
 name = "memona-plugin-ftp"
 version = "0.1.3"
 dependencies = [
+ "getrandom",
  "memona-plugin-sdk",
  "tokio",
 ]
@@ -106,7 +131,7 @@ dependencies = [
 name = "memona-plugin-sdk"
 version = "0.1.0"
 dependencies = [
- "wit-bindgen",
+ "wit-bindgen 0.62.0",
 ]
 
 [[package]]
@@ -143,6 +168,12 @@ dependencies = [
  "proc-macro2",
 ]
 
+[[package]]
+name = "r-efi"
+version = "5.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "69cdb34c158ceb288df11e18b4bd39de994f6657d83847bdffdbd7f346754b0f"
+
 [[package]]
 name = "semver"
 version = "1.0.28"
@@ -229,6 +260,15 @@ version = "1.0.26"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d245f478577f809a851594d02313b640fb437e0bb33866753cff937863096954"
 
+[[package]]
+name = "wasip2"
+version = "1.0.1+wasi-0.2.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0562428422c63773dad2c345a1882263bbf4d65cf3f42e90921f787ef5ad58e7"
+dependencies = [
+ "wit-bindgen 0.46.0",
+]
+
 [[package]]
 name = "wasm-encoder"
 version = "0.259.0"
@@ -263,6 +303,12 @@ dependencies = [
  "semver",
 ]
 
+[[package]]
+name = "wit-bindgen"
+version = "0.46.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f17a85883d4e6d00e8a97c586de764dabcc06133f7f1d55dce5cdc070ad7fe59"
+
 [[package]]
 name = "wit-bindgen"
 version = "0.62.0"

Cargo.toml

@@ -8,6 +8,7 @@ license = "MIT"
 crate-type = ["cdylib", "rlib"]
 
 [dependencies]
+getrandom = "0.3"
 memona-plugin-sdk = { path = "sdk" }
 
 [dev-dependencies]

src/lib.rs

@@ -32,7 +32,6 @@ const MAX_STAGE_ATTEMPTS: usize = 64;
 thread_local! {
   static CONTROL: RefCell<Option<Control>> = const { RefCell::new(None) };
   static SESSION: RefCell<Option<Session>> = const { RefCell::new(None) };
-  static NEXT_STAGE: Cell<u64> = const { Cell::new(0) };
   /// Raw MLSD listings by path, so later pages of a folder are parsed from
   /// memory instead of downloaded and parsed whole again.
   static LISTINGS: RefCell<HashMap<String, Rc<[u8]>>> = RefCell::new(HashMap::new());
@@ -366,18 +365,27 @@ impl Drop for FtpWriter {
   }
 }
 
-/// Chooses an unused private sibling for one upload. The sequence is local to
-/// the component, and the remote probe prevents reuse after an app restart.
-fn stage_path(target: &str) -> Result<String, ErrorCode> {
+fn random_stage_token() -> Result<u128, ErrorCode> {
+  let mut bytes = [0; 16];
+  getrandom::fill(&mut bytes).map_err(|_| ErrorCode::Internal)?;
+  Ok(u128::from_be_bytes(bytes))
+}
+
+/// Chooses an unused, unguessable private sibling for one upload. The remote
+/// probe remains a collision check, while 128 random bits prevent another
+/// client from racing a predictable name between that probe and `STOR`.
+fn stage_path_with(
+  target: &str,
+  mut next_token: impl FnMut() -> Result<u128, ErrorCode>,
+) -> Result<String, ErrorCode> {
   let (parent, name) =
     target.rsplit_once('/').ok_or(ErrorCode::InvalidInput)?;
   if name.is_empty() {
     return Err(ErrorCode::InvalidInput);
   }
   for _ in 0..MAX_STAGE_ATTEMPTS {
-    let sequence = NEXT_STAGE.get();
-    NEXT_STAGE.set(sequence.wrapping_add(1));
-    let staged = format!("{parent}/.memona-upload-{sequence:016x}");
+    let token = next_token()?;
+    let staged = format!("{parent}/.memona-upload-{token:032x}");
     match with_control(|control| probe(control, &staged)) {
       Err(ErrorCode::NotFound) => return Ok(staged),
       Ok(_) => {}
@@ -387,6 +395,10 @@ fn stage_path(target: &str) -> Result<String, ErrorCode> {
   Err(ErrorCode::Conflict)
 }
 
+fn stage_path(target: &str) -> Result<String, ErrorCode> {
+  stage_path_with(target, random_stage_token)
+}
+
 fn start_writer(target: String) -> Result<FtpWriter, ErrorCode> {
   ready()?;
   let staged = stage_path(&target)?;

src/session_tests.rs

@@ -1,7 +1,7 @@
 //! FTP command recovery against an in-memory protocol transport. Live QA
 //! separately exercises the compiled WASM component over real host sockets.
 
-use super::{Ftp, start_writer, test_host};
+use super::{Ftp, stage_path_with, start_writer, test_host};
 use memona_plugin_sdk::{ErrorCode, Guest, GuestWriter, Locator, Setting};
 
 type TestResult<T = ()> = Result<T, Box<dyn std::error::Error + Send + Sync>>;
@@ -157,3 +157,17 @@ async fn dropping_an_upload_removes_only_its_private_stage() -> TestResult {
   assert_eq!(summary.promotions, 0);
   Ok(())
 }
+
+#[tokio::test]
+async fn a_stage_name_collision_draws_a_fresh_random_token() -> TestResult {
+  let fixture = test_host::install(test_host::Scenario::StageCollision);
+  guest(Ftp::open("ftp".into(), config()))?;
+  let mut tokens = [1, 2].into_iter();
+  let staged = guest(stage_path_with("/target", || {
+    tokens.next().ok_or(ErrorCode::Internal)
+  }))?;
+  assert_eq!(staged, "/.memona-upload-00000000000000000000000000000002");
+  Ftp::close();
+  assert_eq!(fixture.summary().stage_probes, 2);
+  Ok(())
+}

src/test_host.rs

@@ -19,6 +19,7 @@ pub enum Scenario {
   LostUploadData,
   LostMutationReply,
   LostUploadCompletion,
+  StageCollision,
   SuccessfulUpload,
 }
 
@@ -31,6 +32,7 @@ struct State {
   target_upload_commands: usize,
   uploaded_bytes: usize,
   stage_deletes: usize,
+  stage_probes: usize,
   promotions: usize,
 }
 
@@ -48,6 +50,7 @@ pub struct Summary {
   pub target_upload_commands: usize,
   pub uploaded_bytes: usize,
   pub stage_deletes: usize,
+  pub stage_probes: usize,
   pub promotions: usize,
 }
 
@@ -61,6 +64,7 @@ pub fn install(scenario: Scenario) -> Fixture {
     target_upload_commands: 0,
     uploaded_bytes: 0,
     stage_deletes: 0,
+    stage_probes: 0,
     promotions: 0,
   }));
   ACTIVE.set(Some(state.clone()));
@@ -78,6 +82,7 @@ impl Fixture {
       target_upload_commands: state.target_upload_commands,
       uploaded_bytes: state.uploaded_bytes,
       stage_deletes: state.stage_deletes,
+      stage_probes: state.stage_probes,
       promotions: state.promotions,
     }
   }
@@ -196,7 +201,14 @@ impl Tcp {
           return Err(HostError::Unavailable);
         }
         "NOOP" => "200 Still connected\r\n",
+        "MLST /.memona-upload-00000000000000000000000000000001"
+          if matches!(state.scenario, Scenario::StageCollision) =>
+        {
+          state.stage_probes += 1;
+          "250-Begin\r\n type=file;size=3; /.memona-upload-00000000000000000000000000000001\r\n250 End\r\n"
+        }
         command if command.starts_with("MLST /.memona-upload-") => {
+          state.stage_probes += 1;
           "550 Missing\r\n"
         }
         command