Adds cataloger for Azure blob storage (#1313)

* Adds cataloger for Azure Blob storage

* Revert "Adds cataloger for Azure Blob storage"

This reverts commit 9476c9e256.

* Implements Cataloger interface for Azure blob storage. Fixes #995.

* Upgraded azblob version to v0.7.0

* Upgrades azblob version to v0.7.0

* Fix formatting

* Fix formatting issues

* Use keyed field for comp literal

* reorder import pkgs

go.mod

@@ -5,7 +5,7 @@ go 1.12
 require (
 	cloud.google.com/go v0.26.0
 	contrib.go.opencensus.io/exporter/stackdriver v0.6.0
-	github.com/Azure/azure-storage-blob-go v0.0.0-20181022225951-5152f14ace1c
+	github.com/Azure/azure-storage-blob-go v0.7.0
 	github.com/BurntSushi/toml v0.3.1
 	github.com/DataDog/datadog-go v0.0.0-20180822151419-281ae9f2d895 // indirect
 	github.com/DataDog/opencensus-go-exporter-datadog v0.0.0-20180917103902-e6c7f767dc57

pkg/storage/azureblob/cataloger.go

@@ -0,0 +1,61 @@
+package azureblob
+
+import (
+	"context"
+	"fmt"
+	"strings"
+
+	"github.com/Azure/azure-storage-blob-go/azblob"
+	"github.com/gomods/athens/pkg/config"
+	"github.com/gomods/athens/pkg/errors"
+	"github.com/gomods/athens/pkg/observ"
+	"github.com/gomods/athens/pkg/paths"
+)
+
+// Catalog implements the (./pkg/storage).Catalog interface
+// It returns a list of versions, if any, for a given module
+func (s *Storage) Catalog(ctx context.Context, token string, pageSize int) ([]paths.AllPathParams, string, error) {
+	const op errors.Op = "azblob.Catalog"
+	ctx, span := observ.StartSpan(ctx, op.String())
+	defer span.End()
+
+	res := make([]paths.AllPathParams, 0)
+
+	// one module@version consists of 3 pieces - info, mod, zip
+	objCount := 3 * pageSize
+
+	marker := azblob.Marker{
+		Val: &token,
+	}
+	blobs, err := s.client.containerURL.ListBlobsFlatSegment(ctx, marker, azblob.ListBlobsSegmentOptions{
+		MaxResults: int32(objCount),
+	})
+	if err != nil {
+		return nil, "", errors.E(op, err)
+	}
+
+	nextToken := *blobs.NextMarker.Val
+
+	for _, blob := range blobs.Segment.BlobItems {
+		if strings.HasSuffix(blob.Name, ".info") {
+			p, err := parsModVer(blob.Name)
+			if err != nil {
+				continue
+			}
+			res = append(res, p)
+		}
+	}
+
+	return res, nextToken, nil
+}
+
+func parsModVer(p string) (paths.AllPathParams, error) {
+	const op errors.Op = "azureblob.parseS3Key"
+	// github.com/gomods/testCatalogModule/@v/v1.2.0976.info
+	m, v := config.ModuleVersionFromPath(p)
+
+	if m == "" || v == "" {
+		return paths.AllPathParams{}, errors.E(op, fmt.Errorf("invalid object key format %s", p))
+	}
+	return paths.AllPathParams{Module: m, Version: v}, nil
+}