Support creating a driver directly without registering it

[sirwart]

In some cases it's useful to reuse drivers to prevent leaking drivers every
time a connection is opened. This allows library users to register the driver
themselves and reuse the registered name when necessary.

[tejasmanohar]

Thanks for the 3 PRs! Glad to see someone else is using go-athena. I'll review shortly.

[tejasmanohar]

@sirwart This whole register ordeal feels hacky, but leaking drivers seems like a real problem if your app is connecting to lots of "Athenas" (e.g. a BI platform). Just to clarify, does the following snippet reflect how you intend to use this?

driver := athena.NewDriver()
sql.Register("athena", driver)
// do stuff with driver
// later,
newDriver := athena.NewDriveR() 
*driver = *newDriver

Mind adding a godoc comment about reusing the Driver, as this trick may help others, too?

[f2prateek]

Probably need a different name for that to work, otherwise you'd be calling register twice (once from your snippet and once from the init) twice which panics. https://godoc.org/database/sql#Register

[sirwart]

Thanks Tejas, this driver helped me get going a lot faster than otherwise.

My solution for avoiding leaking is to register as athena-\<configuration hash\>, so there's a driver for every unique configuration rather than for every database connection opened. I've included my code below that's pretty complicated to talk about in the doc string. Pushing this logic into the library would require serializing aws.Config which I wasn't sure about, but now doesn't sound like a terrible idea. What do you think?

func (d athenaDriver) ConnectionStr(timeout int) (driverName, connectionStr string) {
	bytes, err := json.Marshal(d.connConfig)
	if err != nil {
		panic(err)
	}

	h := sha256.New()
	h.Write(bytes)
	hash := hex.EncodeToString(h.Sum(nil))
	driverName = fmt.Sprintf("athena-%s", hash)

	athenaConfigMutex.Lock()
	func() {
		defer athenaConfigMutex.Unlock()

		if athenaConfigs == nil {
			athenaConfigs = map[string]bool{}
		}
		if !athenaConfigs[hash] {
			creds := credentials.NewStaticCredentials(d.connConfig.AwsAccessKeyId, d.connConfig.AwsSecretAccessKey, "")
			session, err := session.NewSession(&aws.Config{
				Region:      d.connConfig.Region,
				Credentials: creds,
			})
			if err != nil {
				panic(err)
			}
			driverConfig := athena.Config{session, d.connConfig.Database, d.connConfig.StagingDir, 1 * time.Second}
			sql.Register(driverName, athena.NewDriver(&driverConfig))
			athenaConfigs[hash] = true
		}
	}()
	return
}

[tejasmanohar]

@sirwart That makes sense. Thanks for the context.

I'm afraid aws.Config has some unserializable options, like custom HTTP transports, but I'd be happy to merge support simple, popular options, like AWS key/secret, in the connection string. That would probably be simplest for your use case.

Regardless, let's go ahead and merge this in.

[sirwart]

Yea, good point. If you decide to go the adding options route, it'd probably be good to include region in addition to the AWS key/secret which would cover all the basics needed to connect to Athena.

The only other thing I can think of are the encryption options, but I haven't had to deal with them yet.