Add code to convert ALB events to http.Request and http.ResponseWriter

core/requestALB.go

@@ -0,0 +1,210 @@
+// Package core provides utility methods that help convert ALB events
+// into an http.Request and http.ResponseWriter
+package core
+
+import (
+	"bytes"
+	"context"
+	"encoding/base64"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"log"
+	"net/http"
+	"net/url"
+	"strings"
+
+	"github.com/aws/aws-lambda-go/events"
+	"github.com/aws/aws-lambda-go/lambdacontext"
+)
+
+const (
+	// ALBContextHeader is the custom header key used to store the
+	// ALB ELB context. To access the Context properties use the
+	// GetALBContext method of the RequestAccessorALB object.
+	ALBContextHeader = "X-GoLambdaProxy-ALB-Context"
+)
+
+// RequestAccessorALB objects give access to custom ALB Target Group properties
+// in the request.
+type RequestAccessorALB struct {
+	stripBasePath string
+}
+
+// GetALBContext extracts the ALB context object from a request's custom header.
+// Returns a populated events.ALBTargetGroupRequestContext object from the request.
+func (r *RequestAccessorALB) GetContextALB(req *http.Request) (events.ALBTargetGroupRequestContext, error) {
+	if req.Header.Get(ALBContextHeader) == "" {
+		return events.ALBTargetGroupRequestContext{}, errors.New("no context header in request")
+	}
+	context := events.ALBTargetGroupRequestContext{}
+	err := json.Unmarshal([]byte(req.Header.Get(ALBContextHeader)), &context)
+	if err != nil {
+		log.Println("Error while unmarshalling context")
+		log.Println(err)
+		return events.ALBTargetGroupRequestContext{}, err
+	}
+	return context, nil
+}
+
+// StripBasePath instructs the RequestAccessor object that the given base
+// path should be removed from the request path before sending it to the
+// framework for routing. This is used when API Gateway is configured with
+// base path mappings in custom domain names.
+func (r *RequestAccessorALB) StripBasePath(basePath string) string {
+	if strings.Trim(basePath, " ") == "" {
+		r.stripBasePath = ""
+		return ""
+	}
+
+	newBasePath := basePath
+	if !strings.HasPrefix(newBasePath, "/") {
+		newBasePath = "/" + newBasePath
+	}
+
+	if strings.HasSuffix(newBasePath, "/") {
+		newBasePath = newBasePath[:len(newBasePath)-1]
+	}
+
+	r.stripBasePath = newBasePath
+
+	return newBasePath
+}
+
+// ProxyEventToHTTPRequest converts an ALB Target Group Request event into a http.Request object.
+// Returns the populated http request with additional custom header for the ALB context.
+// To access these properties use the GetALBContext method of the RequestAccessorALB object.
+func (r *RequestAccessorALB) ProxyEventToHTTPRequest(req events.ALBTargetGroupRequest) (*http.Request, error) {
+	httpRequest, err := r.EventToRequest(req)
+	if err != nil {
+		log.Println(err)
+		return nil, err
+	}
+	return addToHeaderALB(httpRequest, req)
+}
+
+// EventToRequestWithContext converts an ALB Target Group Request event and context into an http.Request object.
+// Returns the populated http request with lambda context, ALB TargetGroup RequestContext as part of its context.
+func (r *RequestAccessorALB) EventToRequestWithContext(ctx context.Context, req events.ALBTargetGroupRequest) (*http.Request, error) {
+	httpRequest, err := r.EventToRequest(req)
+	if err != nil {
+		log.Println(err)
+		return nil, err
+	}
+	return addToContextALB(ctx, httpRequest, req), nil
+}
+
+// EventToRequest converts an ALB TargetGroup event into an http.Request object.
+// Returns the populated request maintaining headers
+func (r *RequestAccessorALB) EventToRequest(req events.ALBTargetGroupRequest) (*http.Request, error) {
+	decodedBody := []byte(req.Body)
+	if req.IsBase64Encoded {
+		base64Body, err := base64.StdEncoding.DecodeString(req.Body)
+		if err != nil {
+			return nil, err
+		}
+		decodedBody = base64Body
+	}
+
+	path := req.Path
+	if r.stripBasePath != "" && len(r.stripBasePath) > 1 {
+		if strings.HasPrefix(path, r.stripBasePath) {
+			path = strings.Replace(path, r.stripBasePath, "", 1)
+		}
+	}
+	if !strings.HasPrefix(path, "/") {
+		path = "/" + path
+	}
+	serverAddress := "https://" + req.Headers["host"]
+	//  if customAddress, ok := os.LookupEnv(CustomHostVariable); ok {
+	//  	serverAddress = customAddress
+	//  }
+	path = serverAddress + path
+
+	if len(req.MultiValueQueryStringParameters) > 0 {
+		queryString := ""
+		for q, l := range req.MultiValueQueryStringParameters {
+			for _, v := range l {
+				if queryString != "" {
+					queryString += "&"
+				}
+				queryString += url.QueryEscape(q) + "=" + url.QueryEscape(v)
+			}
+		}
+		path += "?" + queryString
+	} else if len(req.QueryStringParameters) > 0 {
+		// Support `QueryStringParameters` for backward compatibility.
+		// https://github.com/awslabs/aws-lambda-go-api-proxy/issues/37
+		queryString := ""
+		for q := range req.QueryStringParameters {
+			if queryString != "" {
+				queryString += "&"
+			}
+			queryString += url.QueryEscape(q) + "=" + url.QueryEscape(req.QueryStringParameters[q])
+		}
+		path += "?" + queryString
+	}
+
+	httpRequest, err := http.NewRequest(
+		strings.ToUpper(req.HTTPMethod),
+		path,
+		bytes.NewReader(decodedBody),
+	)
+
+	if err != nil {
+		fmt.Printf("Could not convert request %s:%s to http.Request\n", req.HTTPMethod, req.Path)
+		log.Println(err)
+		return nil, err
+	}
+
+	if req.MultiValueHeaders != nil {
+		for k, values := range req.MultiValueHeaders {
+			for _, value := range values {
+				httpRequest.Header.Add(k, value)
+			}
+		}
+	} else {
+		for h := range req.Headers {
+			httpRequest.Header.Add(h, req.Headers[h])
+		}
+	}
+
+	httpRequest.RequestURI = httpRequest.URL.RequestURI()
+
+	return httpRequest, nil
+}
+
+func addToHeaderALB(req *http.Request, albRequest events.ALBTargetGroupRequest) (*http.Request, error) {
+	albContext, err := json.Marshal(albRequest.RequestContext)
+	if err != nil {
+		log.Println("Could not Marshal ALB context for custom header")
+		return req, err
+	}
+	req.Header.Set(ALBContextHeader, string(albContext))
+	return req, nil
+}
+
+// adds context data to http request so we can pass
+func addToContextALB(ctx context.Context, req *http.Request, albRequest events.ALBTargetGroupRequest) *http.Request {
+	lc, _ := lambdacontext.FromContext(ctx)
+	rc := requestContextALB{lambdaContext: lc, albContext: albRequest.RequestContext}
+	ctx = context.WithValue(ctx, ctxKey{}, rc)
+	return req.WithContext(ctx)
+}
+
+// GetALBTargetGroupRequestFromContext retrieve ALBTargetGroupt from context.Context
+func GetTargetGroupRequetFromContextALB(ctx context.Context) (events.ALBTargetGroupRequestContext, bool) {
+	v, ok := ctx.Value(ctxKey{}).(requestContextALB)
+	return v.albContext, ok
+}
+
+// GetRuntimeContextFromContext retrieve Lambda Runtime Context from context.Context
+func GetRuntimeContextFromContextALB(ctx context.Context) (*lambdacontext.LambdaContext, bool) {
+	v, ok := ctx.Value(ctxKey{}).(requestContextALB)
+	return v.lambdaContext, ok
+}
+
+type requestContextALB struct {
+	lambdaContext *lambdacontext.LambdaContext
+	albContext    events.ALBTargetGroupRequestContext
+}