Fetch s3 file list in parallel

s3.go

@@ -7,6 +7,7 @@ import (
 	"path/filepath"
 	"regexp"
 	"strings"
+	"time"
 
 	"github.com/aws/aws-sdk-go/aws"
 	"github.com/aws/aws-sdk-go/service/s3"
@@ -44,59 +45,82 @@ func (s *s3Provider) ListFiles(prefix string) ([]file, error) {
 		return out, err
 	}
 
-	prefixList := []*string{aws.String(path)}
+	processedPrefixes := []string{}
+
+	prefixChan := make(chan *string, 100)
+	outputChan := make(chan file, 100)
+	errChan := make(chan error, 10)
+	syncChan := make(chan bool, 10)
+	doneTimer := time.NewTicker(500 * time.Millisecond)
+
+	prefixChan <- aws.String(path)
 
 	for {
-		fmt.Printf("Scanning prefixes (%d left)...\r", len(prefixList))
-		var p *string
-		p, prefixList = prefixList[0], prefixList[1:]
-		in := &s3.ListObjectsInput{
-			Bucket:    aws.String(bucket),
-			Prefix:    p,
-			MaxKeys:   aws.Long(1000),
-			Delimiter: aws.String("/"),
-		}
-		for {
-			o, err := s.conn.ListObjects(in)
-			if err != nil {
-				return out, err
-			}
-
-			for _, v := range o.Contents {
-				out = append(out, file{
-					Filename: *v.Key,
-					Size:     *v.Size,
-					MD5:      strings.Trim(*v.ETag, "\""), // Wat?
-				})
-			}
-
-			if len(o.CommonPrefixes) > 0 {
-				for _, cp := range o.CommonPrefixes {
-					found := false
-					for _, v := range prefixList {
-						if v == cp.Prefix {
-							found = true
-						}
-					}
-					if !found {
-						prefixList = append(prefixList, cp.Prefix)
+		select {
+		case prefix := <-prefixChan:
+			if len(syncChan) == 10 {
+				prefixChan <- prefix
+			} else {
+				found := false
+				for _, v := range processedPrefixes {
+					if v == *prefix {
+						found = true
 					}
 				}
+				if !found {
+					syncChan <- true
+					go s.readS3FileList(bucket, prefix, outputChan, prefixChan, errChan, syncChan)
+					processedPrefixes = append(processedPrefixes, *prefix)
+				}
 			}
-
-			if !*o.IsTruncated {
-				break
+		case o := <-outputChan:
+			out = append(out, o)
+		case err := <-errChan:
+			return out, err
+		case <-doneTimer.C:
+			fmt.Printf("Scanning prefixes (%d working, %d left)...\r", len(syncChan), len(prefixChan))
+			if len(prefixChan) == 0 && len(syncChan) == 0 {
+				fmt.Printf("\n")
+				return out, nil
 			}
-			in.Marker = o.NextMarker
-		}
-
-		if len(prefixList) == 0 {
-			fmt.Printf("\n")
-			break
 		}
 	}
+}
 
-	return out, nil
+func (s *s3Provider) readS3FileList(bucket string, path *string, outputChan chan file, prefixChan chan *string, errorChan chan error, syncChan chan bool) {
+	defer func() { <-syncChan }()
+	in := &s3.ListObjectsInput{
+		Bucket:    aws.String(bucket),
+		Prefix:    path,
+		MaxKeys:   aws.Long(1000),
+		Delimiter: aws.String("/"),
+	}
+	for {
+		o, err := s.conn.ListObjects(in)
+		if err != nil {
+			errorChan <- err
+			return
+		}
+
+		for _, v := range o.Contents {
+			outputChan <- file{
+				Filename: *v.Key,
+				Size:     *v.Size,
+				MD5:      strings.Trim(*v.ETag, "\""), // Wat?
+			}
+		}
+
+		if len(o.CommonPrefixes) > 0 {
+			for _, cp := range o.CommonPrefixes {
+				prefixChan <- cp.Prefix
+			}
+		}
+
+		if !*o.IsTruncated {
+			break
+		}
+		in.Marker = o.NextMarker
+	}
 }
 
 func (s *s3Provider) WriteFile(path string, content io.ReadSeeker, public bool) error {