start: introduce Server type and Shutdown (breaking change)

the main motivation for this change is to be able to run tests.
before this commit, Start, Router and Log operated on global variables,
making automated testing unreasonably hard.

this commit puts all that a server needs in a new Server type,
which also made it possible for a Server.Shutdown - see ShutdownAware
doc comments.

BREAKING CHANGES:
- Relay.OnInitialized takes one argument now, *relayer.Server.
- relayer.Router is now replaced by relayer.Server.Router().
  package users can still hook into the router from OnInitialized
  for custom HTTP routing.
- relayer.Log is gone. apart from another global var, imho this was
  a too opinionated choice for a framework to build a custom relay upon.
  this commit introduces a Logger interface which package users can implement
  for zerolog to make it log like before. see Server.Log for details.

other notable changes: finally added a couple basic tests, for start up
and shutdown. doc comments now explain most of the essentials,
hopefully making it more approachable for newcomers and easier to understand
the relayer package.

the changes in handlers.go are minimal, although git diff goes crazy.
this is because most of the lines are simply shifted indentation back by one
due to go fmt.

before this commit:

    func handleWebsocket(relay Relay) func(http.ResponseWriter, *http.Request)
    func handleNIP11(relay Relay) func(http.ResponseWriter, *http.Request)

after:

    func (s *Server) handleWebsocket(w http.ResponseWriter, r *http.Request)
    func (s *Server) handleNIP11(w http.ResponseWriter, r *http.Request)

basic/main.go

@@ -3,6 +3,7 @@ package main
 import (
 	"encoding/json"
 	"fmt"
+	"log"
 	"time"
 
 	"github.com/fiatjaf/relayer"
@@ -25,7 +26,7 @@ func (r *Relay) Storage() relayer.Storage {
 	return r.storage
 }
 
-func (r *Relay) OnInitialized() {}
+func (r *Relay) OnInitialized(*relayer.Server) {}
 
 func (r *Relay) Init() error {
 	err := envconfig.Process("", r)
@@ -71,11 +72,11 @@ func (r *Relay) AfterSave(evt *nostr.Event) {
 func main() {
 	r := Relay{}
 	if err := envconfig.Process("", &r); err != nil {
-		relayer.Log.Fatal().Err(err).Msg("failed to read from env")
+		log.Fatalf("failed to read from env: %v", err)
 		return
 	}
 	r.storage = &postgresql.PostgresBackend{DatabaseURL: r.PostgresDatabase}
 	if err := relayer.Start(&r); err != nil {
-		relayer.Log.Fatal().Err(err).Msg("server terminated")
+		log.Fatalf("server terminated: %v", err)
 	}
 }

expensive/main.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"encoding/json"
+	"log"
 	"time"
 
 	"github.com/fiatjaf/relayer"
@@ -45,10 +46,10 @@ func (r *Relay) Init() error {
 	return nil
 }
 
-func (r *Relay) OnInitialized() {
+func (r *Relay) OnInitialized(s *relayer.Server) {
 	// special handlers
-	relayer.Router.Path("/").HandlerFunc(handleWebpage)
-	relayer.Router.Path("/invoice").HandlerFunc(handleInvoice)
+	s.Router().Path("/").HandlerFunc(handleWebpage)
+	s.Router().Path("/invoice").HandlerFunc(handleInvoice)
 }
 
 func (r *Relay) AcceptEvent(evt *nostr.Event) bool {
@@ -81,11 +82,11 @@ func (r *Relay) AfterSave(evt *nostr.Event) {
 func main() {
 	r := Relay{}
 	if err := envconfig.Process("", &r); err != nil {
-		relayer.Log.Fatal().Err(err).Msg("failed to read from env")
+		log.Fatalf("failed to read from env: %v", err)
 		return
 	}
 	r.storage = &postgresql.PostgresBackend{DatabaseURL: r.PostgresDatabase}
 	if err := relayer.Start(&r); err != nil {
-		relayer.Log.Fatal().Err(err).Msg("server terminated")
+		log.Fatalf("server terminated: %v", err)
 	}
 }

go.mod

@@ -16,7 +16,6 @@ require (
 	github.com/nbd-wtf/go-nostr v0.9.0
 	github.com/rif/cache2go v1.0.0
 	github.com/rs/cors v1.7.0
-	github.com/rs/zerolog v1.20.0
 	github.com/stevelacy/daz v0.1.4
 	github.com/tidwall/gjson v1.14.1
 )

go.sum

@@ -100,7 +100,6 @@ github.com/coreos/etcd v3.3.10+incompatible/go.mod h1:uF7uidLiAD3TWHmW31ZFd/JWoc
 github.com/coreos/go-etcd v2.0.0+incompatible/go.mod h1:Jez6KQU2B/sWsbdaef3ED8NzMklzPG4d5KIOhIy30Tk=
 github.com/coreos/go-semver v0.2.0/go.mod h1:nnelYz7RCh+5ahJtPPxZlU+153eP4D4r3EedlOD2RNk=
 github.com/coreos/go-semver v0.3.0 h1:wkHLiw0WNATZnSG7epLsujiMCgPAc9xhjJ4tgnAxmfM=
-github.com/coreos/go-systemd v0.0.0-20190321100706-95778dfbb74e/go.mod h1:F5haX7vjVVG0kc13fIWeqUViNPyEJxv/OmvnBo0Yme4=
 github.com/coreos/go-systemd v0.0.0-20190719114852-fd7a80b32e1f h1:JOrtw2xFKzlg+cbHpyrpLDmnN1HqhBfnX7WDiW7eG2c=
 github.com/coreos/go-systemd/v22 v22.3.2 h1:D9/bQk5vlXQFZ6Kwuu6zaiXJ9oTPe68++AzAJc1DzSI=
 github.com/cpuguy83/go-md2man v1.0.10/go.mod h1:SmD6nW6nTyfqj6ABTjUi3V3JVMnlJmwcJI5acqYI6dE=
@@ -353,9 +352,6 @@ github.com/rif/cache2go v1.0.0 h1:DhvZcxXvsuD9ExQ6ZO6f/sOE66OaAQIwB8Mfumap4w4=
 github.com/rif/cache2go v1.0.0/go.mod h1:reDqW0mGufW34CGJ1tvjMobI1BY3dCTxA0ZWdbvm06s=
 github.com/rs/cors v1.7.0 h1:+88SsELBHx5r+hZ8TCkggzSstaWNbDvThkVK8H6f9ik=
 github.com/rs/cors v1.7.0/go.mod h1:gFx+x8UowdsKA9AchylcLynDq+nNFfI8FkUZdN/jGCU=
-github.com/rs/xid v1.2.1/go.mod h1:+uKXf+4Djp6Md1KODXJxgGQPKngRmWyn10oCKFzNHOQ=
-github.com/rs/zerolog v1.20.0 h1:38k9hgtUBdxFwE34yS8rTHmHBa4eN16E4DJlv177LNs=
-github.com/rs/zerolog v1.20.0/go.mod h1:IzD0RJ65iWH0w97OQQebJEvTZYvsCUm9WVLWBQrJRjo=
 github.com/russross/blackfriday v1.5.2/go.mod h1:JO/DiYxRf+HjHt06OyowR9PTA263kcR/rfWxYHBV53g=
 github.com/russross/blackfriday/v2 v2.0.1/go.mod h1:+Rmxgy9KzJVeS9/2gXHxylqXiyQDYRxCVz55jmeOWTM=
 github.com/ryanuber/columnize v2.1.0+incompatible/go.mod h1:sm1tb6uqfes/u+d4ooFouqFdy9/2g9QGwK3SQygK0Ts=
@@ -553,7 +549,6 @@ golang.org/x/tools v0.0.0-20190311212946-11955173bddd/go.mod h1:LCzVGOaR6xXOjkQ3
 golang.org/x/tools v0.0.0-20190327201419-c70d86f8b7cf/go.mod h1:LCzVGOaR6xXOjkQ3onu1FJEFr0SW1gC7cKk1uF8kGRs=
 golang.org/x/tools v0.0.0-20190328211700-ab21143f2384/go.mod h1:LCzVGOaR6xXOjkQ3onu1FJEFr0SW1gC7cKk1uF8kGRs=
 golang.org/x/tools v0.0.0-20190524140312-2c0ae7006135/go.mod h1:RgjU9mgBXZiqYHBnxXauZ1Gv1EHHAz9KjViQ78xBX0Q=
-golang.org/x/tools v0.0.0-20190828213141-aed303cbaa74/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
 golang.org/x/tools v0.0.0-20191012152004-8de300cfc20a/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
 golang.org/x/tools v0.0.0-20191119224855-298f0cb1881e/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
 golang.org/x/tools v0.0.0-20200207183749-b753a1ba74fa/go.mod h1:TB2adYChydJhpapKDTa4BR/hXlZSLoq2Wpct/0txZ28=