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* fix minor typos

* fix another typo

* fix another typo

* Update entry.go

Co-authored-by: Bryan Moffatt <>
9 contributors

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@bmoffatt @yunspace @eraclitux @shogo82148 @moorereason @krak3n @harrisonhjones @dlsniper @efritz
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// Copyright 2017, Inc. or its affiliates. All Rights Reserved.
package lambda
import (
// Start takes a handler and talks to an internal Lambda endpoint to pass requests to the handler. If the
// handler does not match one of the supported types an appropriate error message will be returned to the caller.
// Start blocks, and does not return after being called.
// Rules:
// * handler must be a function
// * handler may take between 0 and two arguments.
// * if there are two arguments, the first argument must satisfy the "context.Context" interface.
// * handler may return between 0 and two arguments.
// * if there are two return values, the second argument must be an error.
// * if there is one return value it must be an error.
// Valid function signatures:
// func ()
// func () error
// func (TIn) error
// func () (TOut, error)
// func (TIn) (TOut, error)
// func (context.Context) error
// func (context.Context, TIn) error
// func (context.Context) (TOut, error)
// func (context.Context, TIn) (TOut, error)
// Where "TIn" and "TOut" are types compatible with the "encoding/json" standard library.
// See for how deserialization behaves
func Start(handler interface{}) {
StartWithContext(context.Background(), handler)
// StartWithContext is the same as Start except sets the base context for the function.
func StartWithContext(ctx context.Context, handler interface{}) {
StartHandlerWithContext(ctx, NewHandler(handler))
// StartHandler takes in a Handler wrapper interface which can be implemented either by a
// custom function or a struct.
// Handler implementation requires a single "Invoke()" function:
// func Invoke(context.Context, []byte) ([]byte, error)
func StartHandler(handler Handler) {
StartHandlerWithContext(context.Background(), handler)
type startFunction struct {
env string
f func(ctx context.Context, envValue string, hander Handler) error
var (
// This allows users to save a little bit of coldstart time in the download, by the dependencies brought in for RPC support.
// The tradeoff is dropping compatibility with the go1.x runtime, functions must be "Custom Runtime" instead.
// To drop the rpc dependencies, compile with `-tags lambda.norpc`
rpcStartFunction = &startFunction{
f: func(c context.Context, p string, h Handler) error {
return errors.New("_LAMBDA_SERVER_PORT was present but the function was compiled without RPC support")
runtimeAPIStartFunction = &startFunction{
f: startRuntimeAPILoop,
startFunctions = []*startFunction{rpcStartFunction, runtimeAPIStartFunction}
// This allows end to end testing of the Start functions, by tests overwriting this function to keep the program alive
logFatalf = log.Fatalf
// StartHandlerWithContext is the same as StartHandler except sets the base context for the function.
// Handler implementation requires a single "Invoke()" function:
// func Invoke(context.Context, []byte) ([]byte, error)
func StartHandlerWithContext(ctx context.Context, handler Handler) {
var keys []string
for _, start := range startFunctions {
config := os.Getenv(start.env)
if config != "" {
// in normal operation, the start function never returns
// if it does, exit!, this triggers a restart of the lambda function
err := start.f(ctx, config, handler)
logFatalf("%v", err)
keys = append(keys, start.env)
logFatalf("expected AWS Lambda environment variables %s are not defined", keys)
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