Netdev changes - rebased

README-net.md

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+### Table of Contents
+
+- ["net" Package](#net-package)
+- [Using "net" Package](#using-net-package)
+- [Using "net/http" Package](#using-nethttp-package)
+- [Using "crypto/tls" Package](#using-cryptotls-package)
+- [Using Sockets](#using-sockets)
+
+## "net" Package
+
+TinyGo's "net" package is ported from Go.  The port offers a subset of Go's
+"net" package.  The subset maintains Go 1 compatiblity guarantee.  A Go
+application that uses "net" will most-likey just work on TinyGo if the usage is
+within the subset offered.  (There may be external constraints such as limited
+SRAM on some targets that may limit full "net" functionality).
+
+Continue below for details on using "net" and "net/http" packages.
+
+See src/net/READMD.md in the TinyGo repo for more details on maintaining
+TinyGo's "net" package.
+
+## Using "net" Package
+
+Ideally, TinyGo's "net" package would be Go's "net" package and applications
+using "net" would just work, as-is.  TinyGo's net package is a partial port of
+Go's net package, so some things may not work because they have not been
+ported.
+
+There are a few features excluded during the porting process, in particular:
+
+- No IPv6 support
+- No DualStack support
+
+Run ```go doc -all ./src/net``` in TinyGo repo to see full listing of what has
+been ported.  Here is a list of things known to work.  You can find examples
+of these at [examples/net](examples/net/).
+
+### What is Known to Work
+
+(These are all IPv4 only).
+
+- TCP client and server
+- UDP client
+- TLS client
+- HTTP client and server
+- HTTPS client
+- NTP client (UDP)
+- MQTT client (paho & natiu)
+- WebSocket client and server
+
+Multiple sockets can be opened in a single app.  For example, the app could run
+as an http server listen on port :80 and also use NTP to get the current time
+or send something over MQTT.  There is a practical limit to the number of
+active sockets per app, around 8 or 10, so don't go crazy.
+
+Applications using Go's net package will need a few setup steps to work with
+TinyGo's net package.  The steps are required before using "net".
+
+### Step 1: Probe to Load Network Driver
+
+Call Probe() to load the correct network driver for your target.  Probe()
+allows the app to work on multiple targets.
+
+```go
+package main
+
+import (
+	"tinygo.org/x/drivers/netlink/probe"
+)
+
+func main() {
+
+	// load network driver for target
+	link, dev := probe.Probe()
+
+	...	
+}
+```
+
+Probe() will load the driver with default configuration for the target.  For
+custom configuration, the app can open code Probe() for the target
+requirements.
+
+Probe() returns a [Netlinker](netlink/README.md) and a
+[Netdever](netdev/README.md), interfaces implemented by the network driver.
+Next, we'll use the Netlinker interface to connect the target to an IP network.
+
+### Step 2: Connect to an IP Network
+
+Before the net package is fully functional, we need to connect the target to an
+IP network.
+
+```go
+package main
+
+import (
+	"tinygo.org/x/drivers/netlink"
+	"tinygo.org/x/drivers/netlink/probe"
+)
+
+func main() {
+
+	// load network driver for target
+	link, _ := probe.Probe()
+
+	// Connect target to IP network
+	link.NetConnect(&netlink.ConnectParams{
+		Ssid:       "my SSID",
+		Passphrase: "my passphrase",
+	})
+
+	// OK to use "net" from here on
+	...	
+}
+```
+
+Optionally, get notified of IP network connects and disconnects:
+
+```go
+	link.Notify(func(e netlink.Event) {
+		switch e {
+		case netlink.EventNetUp:   println("Network UP")
+		case netlink.EventNetDown: println("Network DOWN")
+	})
+```
+
+Here is an example of an http server listening on port :8080:
+
+```go
+package main
+
+import (
+	"fmt"
+	"net/http"
+
+	"tinygo.org/x/drivers/netlink"
+	"tinygo.org/x/drivers/netlink/probe"
+)
+
+func HelloServer(w http.ResponseWriter, r *http.Request) {
+	fmt.Fprintf(w, "Hello, %s!", r.URL.Path[1:])
+}
+
+func main() {
+
+	// load network driver for target
+	link, _ := probe.Probe()
+
+	// Connect target to IP network
+	link.NetConnect(&netlink.ConnectParams{
+		Ssid:       "my SSID",
+		Passphrase: "my passphrase",
+	})
+
+	// Serve it up
+	http.HandleFunc("/", HelloServer)
+	http.ListenAndServe(":8080", nil)
+}
+```
+
+## Using "net/http" Package
+
+TinyGo's net/http package is a partial port of Go's net/http package, providing
+a subset of the full net/http package.  There are a few features excluded
+during the porting process, in particular:
+
+- No HTTP/2 support
+- No TLS support for HTTP servers (no https servers)
+- HTTP client request can't be reused
+
+HTTP client methods (http.Get, http.Head, http.Post, and http.PostForm) are
+functional.  Dial clients support both HTTP and HTTPS URLs.
+
+HTTP server methods and objects are mostly ported, but for HTTP only; HTTPS
+servers are not supported.
+
+HTTP request and response handling code is mostly ported, so most the intricacy
+of parsing and writing headers is handled as in the full net/http package.
+
+Run ```go doc -all ./src/net/http``` in TinyGo repo to see full listing.
+
+## Using "crypto/tls" Package
+
+TinyGo's TLS support (crypto/tls) relies on hardware offload of the TLS
+protocol.  This is different from Go's crypto/tls package which handles the TLS
+protocol in software.
+
+TinyGo's TLS support is only available for client applications.  You can
+http.Get() to an https:// address, but you cannot http.ListenAndServeTLS() an
+https server.
+
+The offloading hardware has pre-defined TLS certificates built-in.
+
+## Using Sockets
+
+The Netdever interface is a BSD socket-like interface so an application can make direct
+socket calls, bypassing the "net" package for the lowest overhead.
+
+Here is a simple TCP client application using direct sockets:
+
+```go
+package main
+
+import (
+	"net"  // only need to parse IP address
+
+	"tinygo.org/x/drivers/netdev"
+	"tinygo.org/x/drivers/netlink"
+	"tinygo.org/x/drivers/netlink/probe"
+)
+
+func main() {
+
+	// load network driver for target
+	link, dev := probe.Probe()
+
+	// Connect target to IP network
+	link.NetConnect(&netlink.ConnectParams{
+		Ssid:       "my SSID",
+		Passphrase: "my passphrase",
+	})
+
+	// omit error handling
+
+	sock, _ := dev.Socket(netdev.AF_INET, netdev.SOCK_STREAM, netdev.IPPROTO_TCP)
+
+        dev.Connect(sock, "", net.ParseIP("10.0.0.100"), 8080)
+	dev.Send(sock, []bytes("hello"), 0, 0)
+
+	dev.Close(sock)
+	link.NetDisconnect()
+}
+```