add change detection to file fetcher, cleanup code, fix spellings, swap example code to use file fetcher

example/example.sh

@@ -3,17 +3,12 @@
 #NOTE: DONT CTRL+C OR CLEANUP WONT OCCUR
 #      ENSURE PORTS 5001,5002 ARE UNUSED
 
-#http file server
-go get github.com/jpillora/serve
-serve --port 5002 --quiet . &
-SERVEPID=$!
-
 #initial build
-go build -ldflags '-X main.BUILD_ID=1' -o myapp
+go build -ldflags '-X main.BuildID=1' -o my_app
 echo "BUILT APP (1)"
 #run!
 echo "RUNNING APP"
-./myapp &
+./my_app &
 APPPID=$!
 
 sleep 1
@@ -24,7 +19,7 @@ sleep 1
 #request during an update
 curl localhost:5001?d=5s &
 
-go build -ldflags '-X main.BUILD_ID=2' -o myappnew
+go build -ldflags '-X main.BuildID=2' -o my_app_next
 echo "BUILT APP (2)"
 
 sleep 2
@@ -35,7 +30,7 @@ sleep 1
 #request during an update
 curl localhost:5001?d=5s &
 
-go build -ldflags '-X main.BUILD_ID=3' -o myappnew
+go build -ldflags '-X main.BuildID=3' -o my_app_next
 echo "BUILT APP (3)"
 
 sleep 2
@@ -48,28 +43,25 @@ curl localhost:5001
 sleep 1
 
 #end demo - cleanup
-kill $SERVEPID
 kill $APPPID
-rm myapp* 2> /dev/null
+rm my_app* 2> /dev/null
 
-# Expected output:
-# serving . on port 4000
+# Expected output (hashes will vary across OS/arch/go-versions):
 # BUILT APP (1)
 # RUNNING APP
-# app#1 (96015cccdebcec119adad34f49b93e02552f3ad9) listening...
-# app#1 (96015cccdebcec119adad34f49b93e02552f3ad9) says hello
-# app#1 (96015cccdebcec119adad34f49b93e02552f3ad9) says hello
+# app#1 (9ba12be7d6f581835c6947845aa742cc05515365) listening...
+# app#1 (9ba12be7d6f581835c6947845aa742cc05515365) says hello
+# app#1 (9ba12be7d6f581835c6947845aa742cc05515365) says hello
 # BUILT APP (2)
-# app#2 (ccc073a1c8e94fd4f2d76ebefb2bbc96790cb795) listening...
-# app#2 (ccc073a1c8e94fd4f2d76ebefb2bbc96790cb795) says hello
-# app#2 (ccc073a1c8e94fd4f2d76ebefb2bbc96790cb795) says hello
-# app#1 (96015cccdebcec119adad34f49b93e02552f3ad9) says hello
-# app#1 (96015cccdebcec119adad34f49b93e02552f3ad9) exiting...
+# app#2 (180d6284b53f9618b92a2a4c0450521c93d767b7) listening...
+# app#2 (180d6284b53f9618b92a2a4c0450521c93d767b7) says hello
+# app#2 (180d6284b53f9618b92a2a4c0450521c93d767b7) says hello
+# app#1 (9ba12be7d6f581835c6947845aa742cc05515365) says hello
+# app#1 (9ba12be7d6f581835c6947845aa742cc05515365) exiting...
 # BUILT APP (3)
-# app#3 (286848c2aefcd3f7321a65b5e4efae987fb17911) listening...
-# app#3 (286848c2aefcd3f7321a65b5e4efae987fb17911) says hello
-# app#3 (286848c2aefcd3f7321a65b5e4efae987fb17911) says hello
-# app#2 (ccc073a1c8e94fd4f2d76ebefb2bbc96790cb795) says hello
-# app#2 (ccc073a1c8e94fd4f2d76ebefb2bbc96790cb795) exiting...
-# app#3 (286848c2aefcd3f7321a65b5e4efae987fb17911) says hello
-# app#3 (286848c2aefcd3f7321a65b5e4efae987fb17911) exiting...
+# app#3 (df4f68714724a856d24a08e44102fe41bbf9ee9f) listening...
+# app#3 (df4f68714724a856d24a08e44102fe41bbf9ee9f) says hello
+# app#3 (df4f68714724a856d24a08e44102fe41bbf9ee9f) says hello
+# app#3 (df4f68714724a856d24a08e44102fe41bbf9ee9f) says hello
+# app#2 (180d6284b53f9618b92a2a4c0450521c93d767b7) says hello
+# app#2 (180d6284b53f9618b92a2a4c0450521c93d767b7) exiting...

example/main.go

@@ -11,19 +11,20 @@ import (
 
 //see example.sh for the use-case
 
-var BUILD_ID = "0"
+// BuildID is compile-time variable
+var BuildID = "0"
 
 //convert your 'main()' into a 'prog(state)'
 //'prog()' is run in a child process
 func prog(state overseer.State) {
-	fmt.Printf("app#%s (%s) listening...\n", BUILD_ID, state.ID)
+	fmt.Printf("app#%s (%s) listening...\n", BuildID, state.ID)
 	http.Handle("/", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		d, _ := time.ParseDuration(r.URL.Query().Get("d"))
 		time.Sleep(d)
-		fmt.Fprintf(w, "app#%s (%s) says hello\n", BUILD_ID, state.ID)
+		fmt.Fprintf(w, "app#%s (%s) says hello\n", BuildID, state.ID)
 	}))
 	http.Serve(state.Listener, nil)
-	fmt.Printf("app#%s (%s) exiting...\n", BUILD_ID, state.ID)
+	fmt.Printf("app#%s (%s) exiting...\n", BuildID, state.ID)
 }
 
 //then create another 'main' which runs the upgrades
@@ -32,10 +33,7 @@ func main() {
 	overseer.Run(overseer.Config{
 		Program: prog,
 		Address: ":5001",
-		Fetcher: &fetcher.HTTP{
-			URL:      "http://localhost:5002/myappnew",
-			Interval: 1 * time.Second,
-		},
-		Debug: false, //display log of overseer actions
+		Fetcher: &fetcher.File{Path: "my_app_next"},
+		Debug:   false, //display log of overseer actions
 	})
 }

fetcher/fetcher.go

@@ -2,6 +2,7 @@ package fetcher
 
 import "io"
 
+// Interface defines the required fetcher functions
 type Interface interface {
 	//Init should perform validation on fields. For
 	//example, ensure the appropriate URLs or keys
@@ -12,12 +13,12 @@ type Interface interface {
 	//binary to fetch, and then stream it back the
 	//form of an io.Reader. If io.Reader is nil,
 	//then it is assumed there are no updates. Fetch
-	//will be run repeatly and forever. It is up the
+	//will be run repeatedly and forever. It is up the
 	//implementation to throttle the fetch frequency.
 	Fetch() (io.Reader, error)
 }
 
-//Converts a fetch function into interface
+// Func converts a fetch function into the fetcher interface
 func Func(fn func() (io.Reader, error)) Interface {
 	return &fetcher{fn}
 }

fetcher/fetcher_file.go

@@ -1,82 +1,100 @@
 package fetcher
 
 import (
+	"errors"
 	"fmt"
 	"io"
 	"os"
 	"time"
 )
 
-// File is used to check new version
+// File checks the provided Path, at the provided
+// Interval for new Go binaries. When a new binary
+// is found it will replace the currently running
+// binary.
 type File struct {
 	Path     string
 	Interval time.Duration
-	// file modify time and its size makes up its hash
-	uniqHash string
-	delay    bool
+	// hash is the file modify time and its size
+	hash  string
+	delay bool
 }
 
-// Init interval and lastHash
+// Init sets the Path and Interval options
 func (f *File) Init() error {
 	if f.Path == "" {
 		return fmt.Errorf("Path required")
 	}
-	if f.Interval == 0 {
-		f.Interval = 10 * time.Second
+	if f.Interval < 1*time.Second {
+		f.Interval = 1 * time.Second
 	}
-
 	if err := f.updateHash(); err != nil {
 		return err
 	}
-	f.delay = false
-
 	return nil
 }
 
-// Fetch file
+// Fetch file from the specified Path
 func (f *File) Fetch() (io.Reader, error) {
-	//delay fetches after first
+	//only delay after first fetch
 	if f.delay {
 		time.Sleep(f.Interval)
 	}
 	f.delay = true
-
-	lastHash := f.uniqHash
+	lastHash := f.hash
 	if err := f.updateHash(); err != nil {
 		return nil, err
 	}
 	// no change
-	if lastHash == f.uniqHash {
+	if lastHash == f.hash {
 		return nil, nil
 	}
-
+	// changed!
 	file, err := os.Open(f.Path)
 	if err != nil {
 		return nil, err
 	}
-
+	//check every 1/4s for 5s to
+	//ensure its not mid-copy
+	const rate = 250 * time.Millisecond
+	const total = int(5 * time.Second / rate)
+	attempt := 1
+	for {
+		if attempt == total {
+			file.Close()
+			return nil, errors.New("file is currently being changed")
+		}
+		attempt++
+		//sleep
+		time.Sleep(rate)
+		//check hash!
+		if err := f.updateHash(); err != nil {
+			file.Close()
+			return nil, err
+		}
+		//check until no longer changing
+		if lastHash == f.hash {
+			break
+		}
+		lastHash = f.hash
+	}
 	return file, nil
 }
 
 func (f *File) updateHash() error {
 	file, err := os.Open(f.Path)
 	if err != nil {
-		// new version not exist, return
+		//binary does not exist, skip
 		if os.IsNotExist(err) {
 			return nil
 		}
 		return fmt.Errorf("Open file error: %s", err)
 	}
 	defer file.Close()
-
-	state, err := file.Stat()
+	s, err := file.Stat()
 	if err != nil {
-		return fmt.Errorf("Get file state error: %s", err)
+		return fmt.Errorf("Get file stat error: %s", err)
 	}
-
-	n := state.ModTime().UnixNano()
-	s := state.Size()
-	f.uniqHash = fmt.Sprintf("%d%d", n, s)
-
+	f.hash = fmt.Sprintf("%d|%d", s.ModTime().UnixNano(), s.Size())
 	return nil
 }

fetcher/fetcher_github.go

@@ -25,7 +25,7 @@ type Github struct {
 	//By default a file will match if it contains
 	//both GOOS and GOARCH.
 	Asset func(filename string) bool
-	//interal state
+	//internal state
 	releaseURL    string
 	delay         bool
 	lastETag      string
@@ -42,6 +42,7 @@ func (h *Github) defaultAsset(filename string) bool {
 	return strings.Contains(filename, runtime.GOOS) && strings.Contains(filename, runtime.GOARCH)
 }
 
+// Init validates the provided config
 func (h *Github) Init() error {
 	//apply defaults
 	if h.User == "" {
@@ -62,6 +63,7 @@ func (h *Github) Init() error {
 	return nil
 }
 
+// Fetch the binary from the provided Repository
 func (h *Github) Fetch() (io.Reader, error) {
 	//delay fetches after first
 	if h.delay {
@@ -105,7 +107,7 @@ func (h *Github) Fetch() (io.Reader, error) {
 		return nil, fmt.Errorf("release location request failed (status code %d)", resp.StatusCode)
 	}
 	s3URL := resp.Header.Get("Location")
-	//psuedo-HEAD request
+	//pseudo-HEAD request
 	req, err = http.NewRequest("GET", s3URL, nil)
 	if err != nil {
 		return nil, fmt.Errorf("release location url error (%s)", err)

fetcher/fetcher_http.go

@@ -9,7 +9,7 @@ import (
 	"time"
 )
 
-//HTTPFetcher uses HEAD requests to poll the status of a given
+//HTTP fetcher uses HEAD requests to poll the status of a given
 //file. If it detects this file has been updated, it will fetch
 //and return its io.Reader stream.
 type HTTP struct {
@@ -17,7 +17,7 @@ type HTTP struct {
 	URL          string
 	Interval     time.Duration
 	CheckHeaders []string
-	//interal state
+	//internal state
 	delay bool
 	lasts map[string]string
 }
@@ -25,6 +25,7 @@ type HTTP struct {
 //if any of these change, the binary has been updated
 var defaultHTTPCheckHeaders = []string{"ETag", "If-Modified-Since", "Last-Modified", "Content-Length"}
 
+// Init validates the provided config
 func (h *HTTP) Init() error {
 	//apply defaults
 	if h.URL == "" {
@@ -40,6 +41,7 @@ func (h *HTTP) Init() error {
 	return nil
 }
 
+// Fetch the binary from the provided URL
 func (h *HTTP) Fetch() (io.Reader, error) {
 	//delay fetches after first
 	if h.delay {

fetcher/fetcher_s3.go

@@ -31,6 +31,7 @@ type S3 struct {
 	lastETag string
 }
 
+// Init validates the provided config
 func (s *S3) Init() error {
 	if s.Bucket == "" {
 		return errors.New("S3 bucket not set")
@@ -58,6 +59,7 @@ func (s *S3) Init() error {
 	return nil
 }
 
+// Fetch the binary from S3
 func (s *S3) Fetch() (io.Reader, error) {
 	//delay fetches after first
 	if s.delay {

overseer.go

@@ -1,4 +1,5 @@
-// Daemonizable self-upgrading binaries in Go (golang).
+// Package overseer implements daemonizable
+// self-upgrading binaries in Go (golang).
 package overseer
 
 import (
@@ -22,6 +23,7 @@ const (
 	envBinCheckLegacy = "GO_UPGRADE_BIN_CHECK"
 )
 
+// Config defines overseer's run-time configuration
 type Config struct {
 	//Required will prevent overseer from fallback to running
 	//running the program in the main process on failure.
@@ -42,7 +44,7 @@ type Config struct {
 	//This helps to prevent unwieldy fetch.Interfaces from hogging
 	//too many resources. Defaults to 1 second.
 	MinFetchInterval time.Duration
-	//PreUpgrade runs after a binary has been retreived, user defined checks
+	//PreUpgrade runs after a binary has been retrieved, user defined checks
 	//can be run here and returning an error will cancel the upgrade.
 	PreUpgrade func(tempBinaryPath string) error
 	//Debug enables all [overseer] logs.
@@ -91,7 +93,7 @@ func RunErr(c Config) error {
 }
 
 //Run executes overseer, if an error is
-//encounted, overseer fallsback to running
+//encountered, overseer fallsback to running
 //the program directly (unless Required is set).
 func Run(c Config) {
 	err := runErr(&c)

proc_master.go

@@ -394,7 +394,7 @@ func (mp *master) fork() error {
 		}
 		mp.debugf("prog exited with %d", code)
 		//if a restarts are disabled or if it was an
-		//unexpected creash, proxy this exit straight
+		//unexpected crash, proxy this exit straight
 		//through to the main process
 		if mp.NoRestart || !mp.restarting {
 			os.Exit(code)

proc_slave.go

@@ -18,6 +18,7 @@ var (
 	DisabledState = State{Enabled: false}
 )
 
+// State contains the current run-time state of overseer
 type State struct {
 	//whether overseer is running enabled. When enabled,
 	//this program will be running in a child process and

sys_windows.go

@@ -27,7 +27,7 @@ func move(dst, src string) error {
 		return nil
 	}
 	//HACK: we're shelling out to move because windows
-	//throws errors when crossing device boundaryes.
+	//throws errors when crossing device boundaries.
 	// https://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/move.mspx?mfr=true
 
 	// https://blogs.msdn.microsoft.com/twistylittlepassagesallalike/2011/04/23/everyone-quotes-command-line-arguments-the-wrong-way/