context.Set() doesn't lock the map for writing

[polds]

So I'm sure this was done on purpose for speed issues but recently ran into an issue where we had a middleware issuing unique Request IDs and saving them using context.Set(). Under high concurrency we found that requests began to start sharing request ids and found it was caused by the underlying map for the store not locking.

[vishr]

Each request runs in a separate goroutine so unless you introduce goroutines within, there shouldn't be any problem. Further the underlying map get reset for every new request.

[polds]

That must have been my problem then. We were introducing additional goroutines within a request. What was happening was the goroutine for Request 1 was receiving the request ID assigned by the middleware of Request 2.

[vishr]

In that case, you must acquire a lock while accessing Context#Set and Context#Get APIs.

[polds]

With the storage being unexported and no mutex added to the struct how would you recommend to obtain the lock without creating a copy of the Context?

[vishr]

For an incoming request, a sync.Mutex should be created and used to access the storage in Context. This lock could be part of Context itself, stored in golang.org/x/net/context. For reference: http://labstack.com/echo/guide/request

Update: You can also store your own synchronized map in net/Context.

[polds]

Using the withValue seems to work. I'm wondering now what the difference in using the store in the echo.Context vs storing things in the net.Context?

example:

What's the difference between:

c.Set("key", "val")
c.Get("key").(string)

and

c.Context = context.WithValue(nil, "key", "val")
c.Value("key").(string)

[vishr]

net/Context was added recently. The only difference now is that internal storage for echo.Context is a map, so you can store multiple key/val pair but with net/Context, by default its just one key val, although val can be a map again 😄. There is another solution as I mentioned earlier, have a synchronized map and store it in net.Context.

[polds]

Appreciate the responses. Closing this.