Preventing panic after cancelled context

[josgba]

Hello!

I'm noticing that when request context is cancelled during operation, the thunk related to that request panics when it is resolved.

This seems to be due to the thunk not having a value property when the return value in this block is hit (in dataloader.go):

thunk := func() (interface{}, error) {
    result.mu.RLock()
    resultNotSet := result.value == nil
    result.mu.RUnlock()

    if resultNotSet {
        result.mu.Lock()
        if v, ok := <-c; ok {
            result.value = v
        }
        result.mu.Unlock()
    }
    result.mu.RLock()
    defer result.mu.RUnlock()
    return result.value.Data, result.value.Error
}

When this thunk is cached, it then results in a panic in subsequent requests until the cache is cleared.

Is there a suggested way to guard against this? I've tried the following in my cache implementation to attempt to guard against caching these 'invalid' thunks, but it results in a deadlock:

func (c *Cache) Set(ctx context.Context, key dataloader.Key, value dataloader.Thunk) {
    defer func() {
        if r := recover(); r != nil {
            c.C.Clear()
        }
     }()
     value()
    c.C.SetWithTTL(key.String(), value, 0, time.Duration(c.MaxAge*int(time.Hour)))
}

[vivek-ng]

I merged a fix for this back in April but we haven't published a new version 😞 https://github.com/graph-gophers/dataloader/blob/69412165eb30a45d7933e953c719217a2a25c96a/dataloader.go#L235

@tonyghita @pavelnikolov Can we please publish a new version?

[pavelnikolov]

Thank you @vivek-ng I just cut a new release version https://github.com/graph-gophers/dataloader/releases/tag/v7.1.0