fix up readme advanced example with updated API

README.md

@@ -23,6 +23,7 @@ will take 2 minutes!
 # Advanced example
 
 TODO going to move to [examples](examples/) too :)
+TODO make these `_example.go` instead of in markdown ;)
 
 ```go
 package main
@@ -41,21 +42,32 @@ func main() {
   fdk.Handle(fdk.HandlerFunc(myHandler))
 }
 
+// TODO make http.Handler example
+
 func myHandler(ctx context.Context, in io.Reader, out io.Writer) {
-  fnctx := fdk.Context(ctx)
+  fnctx, ok := fdk.GetContext(ctx).(fdk.HTTPContext)
+  if !ok {
+    // optionally, this may be a good idea
+    fdk.WriteStatus(out, 400)
+    fdk.SetHeader(out, "Content-Type", "application/json")
+    io.WriteString(out, `{"error":"function not invoked via http trigger"}`)
+    return
+  }
 
-  contentType := fnctx.Header.Get("Content-Type")
+  contentType := fnctx.Header().Get("Content-Type")
   if contentType != "application/json" {
+    // can assert content type for your api this way
     fdk.WriteStatus(out, 400)
     fdk.SetHeader(out, "Content-Type", "application/json")
     io.WriteString(out, `{"error":"invalid content type"}`)
     return
   }
 
-  if fnctx.Method != "PUT" {
+  if fnctx.RequestMethod() != "PUT" {
+    // can assert certain request methods for certain endpoints
     fdk.WriteStatus(out, 404)
     fdk.SetHeader(out, "Content-Type", "application/json")
-    io.WriteString(out, `{"error":"route not found"}`)
+    io.WriteString(out, `{"error":"route not found, method not supported"}`)
     return
   }
 
@@ -64,20 +76,23 @@ func myHandler(ctx context.Context, in io.Reader, out io.Writer) {
   }
   json.NewDecoder(in).Decode(&person)
 
-  // you can write your own headers & status, if you'd like to
-  fdk.WriteStatus(out, 201)
-  fdk.SetHeader(out, "Content-Type", "application/json")
+  // this is where you might insert person into a database or do something else
 
   all := struct {
     Name   string            `json:"name"`
+    URL    string            `json:"url"`
     Header http.Header       `json:"header"`
     Config map[string]string `json:"config"`
   }{
-    Name: person.Name,
-    Header: fnctx.Header,
-    Config: fnctx.Config,
+    Name:   person.Name,
+    URL:    fnctx.RequestURL(),
+    Header: fnctx.Header(),
+    Config: fnctx.Config(),
   }
 
+  // you can write your own headers & status, if you'd like to
+  fdk.SetHeader(out, "Content-Type", "application/json")
+  fdk.WriteStatus(out, 201)
   json.NewEncoder(out).Encode(&all)
 }
 ```