Mongo PubSub issue

[vladbucur1]

Returning a typed nil from NewHTTPError causes err != nil to be true, leading to panics

Context
In the codebase, we have:

func (m *mongoPubSub) Publish(ctx context.Context, _ types.RealmID, tenant string, event EventMessage) error {
// ...
return types.NewHTTPError(http.StatusInternalServerError, err)
}

The NewHTTPError function is defined as:

func NewHTTPError(code int, e error) *HTTPError {
if e == nil {
return nil
}
// ...
}

So, when e is nil, NewHTTPError returns a *HTTPError that is nil (typed nil pointer).
However, when Publish returns this value, it is assigned to an error interface in the caller:

err := s.inner.Publish(ctx, realm, tenant, event)
return otel.RecordOutcome(err, span)

Problem

• Inside Publish, error is a *types.HTTPError and is <nil>.
• When returned, it is assigned to an error interface, which now has a non-nil type (*types.HTTPError) but a nil value.
• This means err != nil evaluates to true, even though the value is nil.
• This leads to code like err.Error() panicking, since it tries to call a method on a nil pointer.

Solution:
Handle Mongo similar to GCP:

func (m *mongoPubSub) Publish(ctx context.Context, _ types.RealmID, tenant string, event EventMessage) error {
// ...
_, err = collection.InsertOne(ctx, me)
if err != nil {
return types.NewHTTPError(http.StatusInternalServerError, err)
}
return nil
}

@Imperiopolis, what do you think?

[Imperiopolis]

seems reasonable if you want to make a PR