func (h *Handler) WithClient(c *http.Client) *Handler {
	h.client = c
	return h
}
WithClient allows user to specify a custom `http.Client`
package serverlessplus
import (
	"bytes"
	"context"
	"encoding/base64"
	"fmt"
	"io/ioutil"
	"net/http"
	"net/url"
	"strings"
	"github.com/tencentyun/scf-go-lib/functioncontext"
)
const (
	Host = "127.0.0.1"
)
type APIGatewayRequestContext struct {
	ServiceID string `json:"serviceId"`
	RequestID string `json:"requestId"`
	Method    string `json:"httpMethod"`
	Path      string `json:"path"`
	SourceIP  string `json:"sourceIp"`
	Stage     string `json:"stage"`
	Identity  struct {
		SecretID *string `json:"secretId"`
	} `json:"identity"`
}
type APIGatewayRequest struct {
	Headers     map[string]string        `json:"headers"`
	Method      string                   `json:"httpMethod"`
	Path        string                   `json:"path"`
	QueryString map[string]interface{}   `json:"queryString"`
	Body        string                   `json:"body"`
	Context     APIGatewayRequestContext `json:"requestContext"`
}
type APIGatewayResponse struct {
	IsBase64Encoded bool              `json:"isBase64Encoded"`
	StatusCode      int               `json:"statusCode"`
	Headers         map[string]string `json:"headers"`
	Body            string            `json:"body"`
}
type Handler struct {
	client          *http.Client
	host            string
	port            int
	binaryMIMETypes map[string]struct{}
}
func NewHandler(port int) *Handler {
	return &Handler{
		client: http.DefaultClient,
		host:   Host,
		port:   port,
	}
}