goshs is a SimpleHTTPServer written in Go. Prior to version 2.1.0, `ShareHandler` reads the share token's `DownloadLimit` under `RLock`, releases the lock, serves the file, then re-acquires the lock to increment the counter. Concurrent requests all read the same `Downloaded`/`DownloadLimit` snapshot, all pass the check, and all are served — exceeding the operator's intended cap. Version 2.1.0 patches the issue.

Affected: Go: goshs.de/goshs/v2

# Share-link `?token=…` redemption races past download limit

**Ecosystem:** Go **Package:** `goshs.de/goshs/v2` (`github.com/patrickhener/goshs`) **Affected:** `<= v2.0.9` (every release that shipped the share-link feature)

## Summary

`ShareHandler` reads the share token's `DownloadLimit` under `RLock`, releases the lock, serves the file, then re-acquires the lock to increment the counter. Concurrent requests all read the same `Downloaded`/`DownloadLimit` snapshot, all pass the check, and all are served — exceeding the operator's intended cap.

## Details

[`httpserver/handler.go:968-1018`](https://github.com/patrickhener/goshs/blob/v2.0.9/httpserver/handler.go#L968-L1018):

```go fs.sharedLinksMu.RLock() entry, ok := fs.SharedLinks[token] fs.sharedLinksMu.RUnlock() // <-- released here

if entry.DownloadLimit > 0 || entry.DownloadLimit == -1 { // ...serve file... // <-- whole transfer happens unlocked }

fs.sharedLinksMu.Lock() // <-- re-acquired only now current.Downloaded++ if current.Downloaded >= current.DownloadLimit { delete(fs.SharedLinks, token) } fs.sharedLinksMu.Unlock() ```

Between line 978 (`RUnlock`) and line 1008 (`Lock`), any number of goroutines can interleave and each observes the same pre-increment limit.

## Proof of concept

```bash goshs -p 18000 -d /tmp/r -b admin:pw & echo data > /tmp/r/f.txt

# operator issues a one-shot share SHARE=$(curl -su admin:pw "http://localhost:1…