[SSDP] add schema(Print &) const

[earlephilhower]

Supercedes #2806

Make SSDP::schema(WiFiClient&) use a by-ref (reduce stack use)

Add a SSDP::schema(Print&)

From @Palatis' original PR:
useful when using AsyncWebServer.

[earlephilhower]

@d-a-v, for the SSDP patch, I'm just the messenger.
I can't think of a good use case for a Printable vs. sending it over the wire, honestly.

However, maybe it makes sense to use just export Print& interface and drop the WiFiClient& one? WiFiClient inherits a Print& interface from Stream...

[earlephilhower]

Err, @devyte I meant to ping!

[devyte]

maybe it makes sense to use just export Print& interface and drop the WiFiClient& one

Exactly why I asked. I suggest picking which of the two bodies looks best and keeping that one with Print arg.
Something that bothers me: the IP printout in both cases, one with the octets the other with IP2STR. I think the IPAddress::toString() method should be used instead, but that means updating the schema string, I think.

[earlephilhower]

Both comments addressed. SSDP will now use ip.toString() instead of octet extraction, and will export only the schema(Print&) which should work for any existing code as WiFiClient has a Print interface..

[earlephilhower]

Well, I guess C++ can't convert silently from a WiFiClient to Print for us. Multiple inheritance C++ classes might have such limitations (not like Java where there's a first-class interface type).

Any ideas?

/home/travis/build/esp8266/Arduino/libraries/ESP8266SSDP/examples/SSDP/SSDP.ino:29:32: error: no matching function for call to 'SSDPClass::schema(esp8266webserver::ESP8266WebServerTemplate<WiFiServer>::ClientType)'

       SSDP.schema(HTTP.client());

                                ^

/home/travis/build/esp8266/Arduino/libraries/ESP8266SSDP/examples/SSDP/SSDP.ino:29:32: note: candidate is:

In file included from /home/travis/build/esp8266/Arduino/libraries/ESP8266SSDP/examples/SSDP/SSDP.ino:3:0:

/home/travis/arduino_ide/hardware/esp8266com/esp8266/libraries/ESP8266SSDP/ESP8266SSDP.h:65:10: note: void SSDPClass::schema(Print&) const

     void schema(Print &print) const;

          ^

/home/travis/arduino_ide/hardware/esp8266com/esp8266/libraries/ESP8266SSDP/ESP8266SSDP.h:65:10: note:   no known conversion for argument 1 from 'esp8266webserver::ESP8266WebServerTemplate<WiFiServer>::ClientType {aka WiFiClient}' to 'Print&'

[devyte]

Might be running into the 1-step implicit casting rule. I'll take a look at some point.

[devyte]

glad to see the crazy forwarder idea worked :)