streaming with custom reader and multiple client functionality

internal/cache/get_stream.go

@@ -0,0 +1,50 @@
+package cache
+
+import (
+	"os"
+	"path/filepath"
+)
+
+func (c *Cache) getStream(relPath string) (*inFlight, *os.File, error) {
+
+	// lock the map
+	c.inFlightMu.Lock()
+	defer c.inFlightMu.Unlock()
+
+	// download in progress connect new stream to existing download
+	if flight, ok := c.inFlight[relPath]; ok {
+		f, err := c.cr.Open(flight.tmpPath)
+		if err != nil {
+			return nil, nil, err
+		}
+		return flight, f, nil
+	}
+
+	// download not in progress, setup new download and stream
+
+	// make sure the dir structure exists
+	if err := c.cr.MkdirAll(filepath.Dir(relPath), 0750); err != nil {
+		return nil, nil, err
+	}
+	// use a tmp file for the initial fetch in case it fails
+	tmpPath := relPath + ".tmp"
+	tmpFile, err := c.cr.Create(tmpPath)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	flight := &inFlight{
+		tmpPath: tmpPath,
+	}
+
+	c.inFlight[relPath] = flight
+
+	// spin off a downloading func so we can return the file handler
+	// downloadWrangle takes ownership of tmpFile and closes it.
+	go c.downloadWrangle(relPath, flight, tmpFile)
+	f, err := c.cr.Open(flight.tmpPath)
+	if err != nil {
+		return nil, nil, err
+	}
+	return flight, f, nil
+}