Golang opentelemetry-go draft API (incomplete) (#9)

* Work in progress from https://github.com/lightstep/opentelemetry-golang-prototype

* Renames

* Rename

* Finish rename

* Rename packages

* README

example/http/client/client.go

@@ -0,0 +1,57 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+
+	"github.com/open-telemetry/opentelemetry-go/api/tag"
+	"github.com/open-telemetry/opentelemetry-go/api/trace"
+	"github.com/open-telemetry/opentelemetry-go/plugin/httptrace"
+
+	_ "github.com/open-telemetry/opentelemetry-go/exporter/loader"
+)
+
+var (
+	tracer = trace.GlobalTracer().
+		WithService("client").
+		WithComponent("main").
+		WithResources(
+			tag.New("whatevs").String("yesss"),
+		)
+)
+
+func main() {
+	client := http.DefaultClient
+
+	ctx := tag.NewContext(context.Background(),
+		tag.Insert(tag.New("username").String("donuts")),
+	)
+
+	var body []byte
+
+	err := tracer.WithSpan(ctx, "say hello",
+		func(ctx context.Context) error {
+			req, _ := http.NewRequest("GET", "http://localhost:7777/hello", nil)
+
+			ctx, req, inj := httptrace.W3C(ctx, req)
+
+			trace.Inject(ctx, inj)
+
+			res, err := client.Do(req)
+			if err != nil {
+				panic(err)
+			}
+			body, err = ioutil.ReadAll(res.Body)
+			res.Body.Close()
+
+			return err
+		})
+
+	if err != nil {
+		panic(err)
+	}
+
+	fmt.Printf("%s", body)
+}

example/http/server/modd.conf

@@ -0,0 +1,7 @@
+# A basic modd.conf file for Go development.
+
+# Run go test on ALL modules on startup, and subsequently only on modules
+# containing changes.
+server.go {
+    daemon +sigterm: go run server.go
+}

example/http/server/server.go

@@ -0,0 +1,49 @@
+package main
+
+import (
+	"io"
+	"net/http"
+
+	"github.com/open-telemetry/opentelemetry-go/api/core"
+	"github.com/open-telemetry/opentelemetry-go/api/log"
+	"github.com/open-telemetry/opentelemetry-go/api/tag"
+	"github.com/open-telemetry/opentelemetry-go/api/trace"
+	"github.com/open-telemetry/opentelemetry-go/plugin/httptrace"
+
+	_ "github.com/open-telemetry/opentelemetry-go/exporter/loader"
+)
+
+var (
+	tracer = trace.GlobalTracer().
+		WithService("server").
+		WithComponent("main").
+		WithResources(
+			tag.New("whatevs").String("nooooo"),
+		)
+)
+
+func main() {
+	helloHandler := func(w http.ResponseWriter, req *http.Request) {
+		attrs, tags, spanCtx := httptrace.Extract(req)
+
+		req = req.WithContext(tag.WithMap(req.Context(), tag.NewMap(core.KeyValue{}, tags, core.Mutator{}, nil)))
+
+		ctx, span := tracer.Start(
+			req.Context(),
+			"hello",
+			trace.WithAttributes(attrs...),
+			trace.ChildOf(spanCtx),
+		)
+		defer span.Finish()
+
+		log.Log(ctx, "handling this...")
+
+		io.WriteString(w, "Hello, world!\n")
+	}
+
+	http.HandleFunc("/hello", helloHandler)
+	err := http.ListenAndServe(":7777", nil)
+	if err != nil {
+		panic(err)
+	}
+}