add cuscom dialer

[carr123]

hi, i add cuscom dialer to support more underlying transport types.

it's easy to use.

demo :

import ( mqtt "github.com/eclipse/paho.mqtt.golang" )

func main() { mqtt.AddCustomDialer( "haha", func(uri url.URL, tlsc tls.Config, timeout time.Duration, headers http.Header) (net.Conn, error) { return HahaConnect(uri.Host, tlsc, timeout) }, )

  BrokerURL := "haha://127.0.0.1:5883"

}

[MattBrittan]

Thanks for the PR. Unfortunately I cannot progress this until you have signed the ECA (see the commit checks and readme for details).

However I have taken a quick look and am going to suggest a different approach (happy to discuss this!). Please don't take this the wrong way, your approach is fine and would work, but I think the below may be a better fit.

My aims with this suggestion are:

• Minimise the amount of code in this repo (more code = more maintenance/complexity/potential bugs) and this change meets a niche requirement.
• Consistent user experience (currently all configuration is done in ClientOptions so that is where users are likely to look for this kind of setting).
• Avoid init() and globals.
• Maximise flexibility - adding different schema types meets your goal but I suspect it may not meet the needs of others (e.g. some weird proxy requirement, port knocking etc).

I'm also going to suggest that we allow openConnection to be replaced in its entirety rather than just adding in new URL handler types.

So lets start with a ClientOption:

type openConnectionFunc func(uri *url.URL, tlsc *tls.Config, timeout time.Duration, headers http.Header, websocketOptions *WebsocketOptions) (net.Conn, error)
.
.
.
func NewClientOptions() *ClientOptions {
openConnectionFunc: openConnection // default to inbuilt function
.
.
.

// SetOpenConnectionFunc replaces the inbuilt function that establishes a connection with a custom function.
// The passed in function should return an open `net.Conn` or an error (see the existing openConnection function for an example)
func (o *ClientOptions) SetOpenConnectionFunc(fn openConnectionFunc) *ClientOptions {
    o.openConnectionFunc = fn
    return o
}

and then we can replace the call to
conn, err = openConnection(broker, tlsCfg, c.options.ConnectTimeout, c.options.HTTPHeaders, c.options.WebsocketOptions) in client.go with:

c.Options.openConnectionFunc(broker, tlsCfg, c.options.ConnectTimeout, c.options.HTTPHeaders, c.options.WebsocketOptions)

I think that this would meet your needs along with some other potential future requirements whilst limiting the level of change. Thoughts?

[carr123]

i agree with you. your way is much better. i will check what is ECA ,and summit a new PR. :)

[MattBrittan]

OK thanks - I'll close this pull request.