Update documentation

README.md

@@ -1,31 +1,49 @@
 # dd-lambda-go
 
+Datadog's Lambda Go client library enables distributed tracing between serverful and serverless environments.
+
+## Installation
+
+```bash
+go get github.com/DataDog/dd-lambda-go
+```
+
 ## Usage
 
-Datadog needs to be able to read headers from the incoming Lambda event, in order to add datadog metadata to the go context.
-Wrap your lambda handler like so.
+Datadog needs to be able to read headers from the incoming Lambda event. Wrap your Lambda handler function like so:
 
 ```go
 package main
 
 import (
-	"github.com/aws/aws-lambda-go/lambda"
-	"github.com/DataDog/dd-lambda-go"
+  "github.com/aws/aws-lambda-go/lambda"
+  "github.com/DataDog/dd-lambda-go"
 )
 
 func main() {
-	// Wrap your lambda handler like this
-    lambda.Start( ddlambda.WrapHandler(myHandler))
+  // Wrap your lambda handler like this
+  lambda.Start( ddlambda.WrapHandler(myHandler))
 }
 
 func myHandler(ctx context.Context, event MyEvent) (string, error) {
-	// Add headers to outbound using the context object
-	req, err := http.NewRequest("GET", "http://api.youcompany.com/status")
-	ddlambda.AddTraceHeaders(ctx)
+  // ...
+}
+```
 
-	client := http.Client{}
-	client.Do(req)
+Make sure any outbound requests have Datadog's tracing headers.
 
-	return "Success", nil
+```go
+  req, err := http.NewRequest("GET", "http://api.youcompany.com/status")
+  // Use the same Context object given to your lambda handler.
+  ddlambda.AddTraceHeaders(ctx, req)
+
+  client := http.Client{}
+  client.Do(req)
 }
-```
+```
+
+## Non-proxy integration
+
+If your Lambda function is triggered by API Gateway via the non-proxy integration, then you have to set up a mapping template, which passes the Datadog trace context from the incoming HTTP request headers to the Lambda function via the event object.
+
+If your Lambda function is deployed by the Serverless Framework, such a mapping template gets created by default.

ddlambda.go

@@ -21,8 +21,8 @@ func GetTraceHeaders(ctx context.Context) map[string]string {
 }
 
 // AddTraceHeaders adds DataDog trace headers to a HTTP Request
-func AddTraceHeaders(req *http.Request) {
-	headers := GetTraceHeaders(req.Context())
+func AddTraceHeaders(ctx context.Context, req *http.Request) {
+	headers := GetTraceHeaders(ctx)
 	for key, value := range headers {
 		req.Header.Add(key, value)
 	}

internal/trace/context.go

@@ -116,7 +116,7 @@ func unmarshalEventForTraceContext(ev json.RawMessage) (map[string]string, bool)
 func convertTraceContextFromXRay(ctx context.Context) (map[string]string, error) {
 	traceContext := map[string]string{}
 
-	header := getLambdaTraceHeaderFromContext(ctx)
+	header := getXrayTraceHeaderFromContext(ctx)
 	if header == nil {
 		return traceContext, fmt.Errorf("xray segment doesn't exist, couldn't read trace context")
 	}
@@ -137,10 +137,10 @@ func convertTraceContextFromXRay(ctx context.Context) (map[string]string, error)
 	return traceContext, nil
 }
 
-// getLambdaTraceHeaderFromContext is used to extract xray segment metadata from the lambda context object.
+// getXrayTraceHeaderFromContext is used to extract xray segment metadata from the lambda context object.
 // By default, the context object won't have any Segment, (xray.GetSegment(ctx) will return nil). However it
 // will have the "LambdaTraceHeader" object, which contains the traceID/parentID/sampling info.
-func getLambdaTraceHeaderFromContext(ctx context.Context) *header.Header {
+func getXrayTraceHeaderFromContext(ctx context.Context) *header.Header {
 	var traceHeader string
 
 	if traceHeaderValue := ctx.Value(xray.LambdaTraceHeaderKey); traceHeaderValue != nil {