Fixed a number of compilation bugs.

entry.go

@@ -13,16 +13,12 @@ type Entry struct {
 }
 
 // LoadEntry loads an entry from disk.
-func LoadEntry(filename string) (*Entry, error) {
+func (e *Entry) LoadEntry(filename string) error {
 	f, err := os.Open(filename)
 	if err != nil {
-		return nil, err
+		return err
 	}
-	e := &Entry{}
-	if err = json.NewDecoder(f).Decode(e); err != nil {
-		return nil, err
-	}
-	return e, nil
+	return json.NewDecoder(f).Decode(e)
 }
 
 // Save writes the entry to disk.

reader.go

@@ -28,7 +28,7 @@ func NewReader(writer *Writer, jsonFilename, dataFilename string) *Reader {
 		status:        StatusNone,
 		statusChanged: make(chan Status),
 	}
-	if r.writer {
+	if r.writer != nil {
 		r.writer.Subscribe(r.statusChanged)
 	}
 	return r
@@ -76,7 +76,7 @@ func (r *Reader) Read(p []byte) (n int, err error) {
 		err = errors.New("writer error")
 		return
 	case StatusDone:
-		err = os.EOF
+		err = io.EOF
 		return
 	default:
 		for n < len(p) {
@@ -84,7 +84,7 @@ func (r *Reader) Read(p []byte) (n int, err error) {
 			bytesRead, err = r.file.Read(p[n:])
 			n += bytesRead
 			if err != nil {
-				if err == os.EOF && r.writer != nil {
+				if err == io.EOF && r.writer != nil {
 					err = nil
 					var watcher *fsnotify.Watcher
 					watcher, err = fsnotify.NewWatcher()

storage.go

@@ -3,7 +3,6 @@ package main
 import (
 	"crypto/md5"
 	"fmt"
-	"io"
 	"os"
 	"path"
 	"sync"
@@ -13,27 +12,46 @@ import (
 // avoid race conditions, adding and testing for entries in the cache are
 // protected by a mutex.
 type Storage struct {
-	Directory string
-	mutex     sync.Mutex
+	directory  string
+	writers    map[string]*Writer
+	writerDone chan *Writer
+	mutex      sync.Mutex
 }
 
-// GetReader returns an io.Reader for the specified URL. If the file does not
+// NewStorage creates a new storage manager.
+func NewStorage(directory string) *Storage {
+	return &Storage{
+		directory:  directory,
+		writers:    make(map[string]*Writer),
+		writerDone: make(chan *Writer),
+	}
+}
+
+// GetReader returns a *Reader for the specified URL. If the file does not
 // exist, both a writer (for downloading the file) and a reader are created.
-func (s *Storage) GetReader(url string) (io.Reader, error) {
+func (s *Storage) GetReader(url string) (*Reader, error) {
 	var (
 		hash         = string(md5.Sum([]byte(url)))
-		jsonFilename = path.Join(s.Directory, fmt.Sprintf("%s.json", hash))
-		dataFilename = path.Join(s.Directory, fmt.Sprintf("%s.data", hash))
+		jsonFilename = path.Join(s.directory, fmt.Sprintf("%s.json", hash))
+		dataFilename = path.Join(s.directory, fmt.Sprintf("%s.data", hash))
 	)
 	s.mutex.Lock()
 	defer s.mutex.Unlock()
-	i, err := os.Stat(jsonFilename)
-	if err != nil {
-		if os.IsNotExist(err) {
-			NewWriter(url, jsonFilename, dataFilename)
+	w, ok := s.writers[hash]
+	if ok {
+		return NewReader(w, jsonFilename, dataFilename), nil
+	} else {
+		_, err := os.Stat(jsonFilename)
+		if err != nil {
+			if os.IsNotExist(err) {
+				w = NewWriter(url, jsonFilename, dataFilename, s.writerDone)
+				s.writers[hash] = w
+				return NewReader(w, jsonFilename, dataFilename), nil
+			} else {
+				return nil, err
+			}
 		} else {
-			return nil, err
+			return NewReader(nil, jsonFilename, dataFilename), nil
 		}
 	}
-	return NewReader(url, jsonFilename, dataFilename)
 }

writer.go

@@ -3,7 +3,6 @@ package main
 import (
 	"container/list"
 	"io"
-	"log"
 	"net/http"
 	"os"
 	"sync"
@@ -27,7 +26,7 @@ type Writer struct {
 	status   Status
 }
 
-func (w *Writer) sendStatus(statusChan chan Status, status Status) {
+func (w *Writer) sendStatus(statusChan chan<- Status, status Status) {
 	statusChan <- status
 }
 
@@ -36,17 +35,16 @@ func (w *Writer) setStatus(status Status) {
 	defer w.mutex.Unlock()
 	w.status = status
 	for e := w.channels.Front(); e != nil; e = e.Next() {
-		go w.sendStatus(e.Value.(chan Status), status)
+		go w.sendStatus(e.Value.(chan<- Status), status)
 	}
 }
 
-// Create a new writer for the given URL. Status information is passed along to
-// subscribed channels. The done channel is used to notify the storage system
-// that the download is complete (either success or an error).
+// NewWriter creates a new writer for the given URL. Status information is
+// passed along to subscribed channels. The done channel is used to notify the
+// storage system that the download is complete (either success or an error).
 func NewWriter(url, jsonFilename, dataFilename string, done chan<- *Writer) *Writer {
 	w := &Writer{
-		channels: make([]chan Status),
-		status:   StatusNone,
+		channels: list.New(),
 	}
 	go func() {
 		r, err := http.Get(url)
@@ -55,8 +53,9 @@ func NewWriter(url, jsonFilename, dataFilename string, done chan<- *Writer) *Wri
 		}
 		defer r.Body.Close()
 		e := &Entry{
-			URL:         url,
-			ContentType: r.Header.Get("Content-Type"),
+			URL:           url,
+			ContentLength: r.ContentLength,
+			ContentType:   r.Header.Get("Content-Type"),
 		}
 		if err = e.Save(jsonFilename); err != nil {
 			goto error
@@ -82,21 +81,23 @@ func NewWriter(url, jsonFilename, dataFilename string, done chan<- *Writer) *Wri
 
 // Subscribe adds a channel to the list to be notified when the writer's status
 // changes. The channel will also immediately receive the current status.
-func (w *Writer) Subscribe(statusChan chan Status) {
+func (w *Writer) Subscribe(statusChan chan<- Status) {
 	w.mutex.Lock()
 	defer w.mutex.Unlock()
-	w.channels = append(w.channels, c)
-	w.sendStatus(c, w.status)
+	w.channels.PushBack(statusChan)
+
+	// TODO: is "go" necessary here?
+	go w.sendStatus(statusChan, w.status)
 }
 
-// Unsubscribe a channel from the list to be notified. This may occur when a
-// client cancels a request, for example.
-func (w *Writer) Unsubscribe(statusChan chan Status) {
+// Unsubscribe removes a channel from the list to be notified. This may occur
+// when a client cancels a request, for example.
+func (w *Writer) Unsubscribe(statusChan chan<- Status) {
 	w.mutex.Lock()
 	defer w.mutex.Unlock()
-	for i, c := range w.channels {
-		if c == statusChan {
-			w.channels = append(w.channels[:i], w.channels[i+1:]...)
+	for e := w.channels.Front(); e != nil; e = e.Next() {
+		if e.Value.(chan<- Status) == statusChan {
+			w.channels.Remove(e)
 		}
 	}
 }