chore(blobs): generalised blob storage

cmd/infra/ursrv/serve/serve.go

@@ -26,9 +26,11 @@ import (
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
 	"github.com/puzpuzpuz/xsync/v3"
+	"github.com/syncthing/syncthing/internal/blob"
+	"github.com/syncthing/syncthing/internal/blob/azureblob"
+	"github.com/syncthing/syncthing/internal/blob/s3"
 	"github.com/syncthing/syncthing/lib/build"
 	"github.com/syncthing/syncthing/lib/geoip"
-	"github.com/syncthing/syncthing/lib/s3"
 	"github.com/syncthing/syncthing/lib/ur/contract"
 )
 
@@ -40,11 +42,15 @@ type CLI struct {
 	DumpFile        string        `env:"UR_DUMP_FILE" default:"reports.jsons.gz"`
 	DumpInterval    time.Duration `env:"UR_DUMP_INTERVAL" default:"5m"`
 
-	S3Endpoint    string `name:"s3-endpoint" hidden:"true" env:"UR_S3_ENDPOINT"`
-	S3Region      string `name:"s3-region" hidden:"true" env:"UR_S3_REGION"`
-	S3Bucket      string `name:"s3-bucket" hidden:"true" env:"UR_S3_BUCKET"`
-	S3AccessKeyID string `name:"s3-access-key-id" hidden:"true" env:"UR_S3_ACCESS_KEY_ID"`
-	S3SecretKey   string `name:"s3-secret-key" hidden:"true" env:"UR_S3_SECRET_KEY"`
+	S3Endpoint    string `name:"s3-endpoint" env:"UR_S3_ENDPOINT"`
+	S3Region      string `name:"s3-region" env:"UR_S3_REGION"`
+	S3Bucket      string `name:"s3-bucket" env:"UR_S3_BUCKET"`
+	S3AccessKeyID string `name:"s3-access-key-id" env:"UR_S3_ACCESS_KEY_ID"`
+	S3SecretKey   string `name:"s3-secret-key" env:"UR_S3_SECRET_KEY"`
+
+	AzureBlobAccount   string `name:"azure-blob-account" env:"UR_AZUREBLOB_ACCOUNT"`
+	AzureBlobKey       string `name:"azure-blob-key" env:"UR_AZUREBLOB_KEY"`
+	AzureBlobContainer string `name:"azure-blob-container" env:"UR_AZUREBLOB_CONTAINER"`
 }
 
 var (
@@ -120,19 +126,25 @@ func (cli *CLI) Run() error {
 		go geo.Serve(context.TODO())
 	}
 
-	// s3
+	// Blob storage
 
-	var s3sess *s3.Session
+	var blobs blob.Store
 	if cli.S3Endpoint != "" {
-		s3sess, err = s3.NewSession(cli.S3Endpoint, cli.S3Region, cli.S3Bucket, cli.S3AccessKeyID, cli.S3SecretKey)
+		blobs, err = s3.NewSession(cli.S3Endpoint, cli.S3Region, cli.S3Bucket, cli.S3AccessKeyID, cli.S3SecretKey)
 		if err != nil {
 			slog.Error("Failed to create S3 session", "error", err)
 			return err
 		}
+	} else if cli.AzureBlobAccount != "" {
+		blobs, err = azureblob.NewBlobStore(cli.AzureBlobAccount, cli.AzureBlobKey, cli.AzureBlobContainer)
+		if err != nil {
+			slog.Error("Failed to create Azure blob store", "error", err)
+			return err
+		}
 	}
 
-	if _, err := os.Stat(cli.DumpFile); err != nil && s3sess != nil {
-		if err := cli.downloadDumpFile(s3sess); err != nil {
+	if _, err := os.Stat(cli.DumpFile); err != nil && blobs != nil {
+		if err := cli.downloadDumpFile(blobs); err != nil {
 			slog.Error("Failed to download dump file", "error", err)
 		}
 	}
@@ -154,7 +166,7 @@ func (cli *CLI) Run() error {
 
 	go func() {
 		for range time.Tick(cli.DumpInterval) {
-			if err := cli.saveDumpFile(srv, s3sess); err != nil {
+			if err := cli.saveDumpFile(srv, blobs); err != nil {
 				slog.Error("Failed to write dump file", "error", err)
 			}
 		}
@@ -193,8 +205,8 @@ func (cli *CLI) Run() error {
 	return metricsSrv.Serve(urListener)
 }
 
-func (cli *CLI) downloadDumpFile(s3sess *s3.Session) error {
-	latestKey, err := s3sess.LatestKey()
+func (cli *CLI) downloadDumpFile(blobs blob.Store) error {
+	latestKey, err := blobs.LatestKey(context.Background())
 	if err != nil {
 		return fmt.Errorf("list latest S3 key: %w", err)
 	}
@@ -202,7 +214,7 @@ func (cli *CLI) downloadDumpFile(s3sess *s3.Session) error {
 	if err != nil {
 		return fmt.Errorf("create dump file: %w", err)
 	}
-	if err := s3sess.Download(fd, latestKey); err != nil {
+	if err := blobs.Download(context.Background(), latestKey, fd); err != nil {
 		_ = fd.Close()
 		return fmt.Errorf("download dump file: %w", err)
 	}
@@ -213,7 +225,7 @@ func (cli *CLI) downloadDumpFile(s3sess *s3.Session) error {
 	return nil
 }
 
-func (cli *CLI) saveDumpFile(srv *server, s3sess *s3.Session) error {
+func (cli *CLI) saveDumpFile(srv *server, blobs blob.Store) error {
 	fd, err := os.Create(cli.DumpFile + ".tmp")
 	if err != nil {
 		return fmt.Errorf("creating dump file: %w", err)
@@ -234,13 +246,13 @@ func (cli *CLI) saveDumpFile(srv *server, s3sess *s3.Session) error {
 	}
 	slog.Info("Dump file saved")
 
-	if s3sess != nil {
+	if blobs != nil {
 		key := fmt.Sprintf("reports-%s.jsons.gz", time.Now().UTC().Format("2006-01-02"))
 		fd, err := os.Open(cli.DumpFile)
 		if err != nil {
 			return fmt.Errorf("opening dump file: %w", err)
 		}
-		if err := s3sess.Upload(fd, key); err != nil {
+		if err := blobs.Upload(context.Background(), key, fd); err != nil {
 			return fmt.Errorf("uploading dump file: %w", err)
 		}
 		_ = fd.Close()

cmd/stdiscosrv/database.go

@@ -24,11 +24,11 @@ import (
 	"github.com/puzpuzpuz/xsync/v3"
 	"google.golang.org/protobuf/proto"
 
+	"github.com/syncthing/syncthing/internal/blob"
 	"github.com/syncthing/syncthing/internal/gen/discosrv"
 	"github.com/syncthing/syncthing/internal/protoutil"
 	"github.com/syncthing/syncthing/lib/protocol"
 	"github.com/syncthing/syncthing/lib/rand"
-	"github.com/syncthing/syncthing/lib/s3"
 )
 
 type clock interface {
@@ -51,12 +51,12 @@ type inMemoryStore struct {
 	m             *xsync.MapOf[protocol.DeviceID, *discosrv.DatabaseRecord]
 	dir           string
 	flushInterval time.Duration
-	s3            *s3.Session
+	blobs         blob.Store
 	objKey        string
 	clock         clock
 }
 
-func newInMemoryStore(dir string, flushInterval time.Duration, s3sess *s3.Session) *inMemoryStore {
+func newInMemoryStore(dir string, flushInterval time.Duration, blobs blob.Store) *inMemoryStore {
 	hn, err := os.Hostname()
 	if err != nil {
 		hn = rand.String(8)
@@ -65,16 +65,16 @@ func newInMemoryStore(dir string, flushInterval time.Duration, s3sess *s3.Sessio
 		m:             xsync.NewMapOf[protocol.DeviceID, *discosrv.DatabaseRecord](),
 		dir:           dir,
 		flushInterval: flushInterval,
-		s3:            s3sess,
+		blobs:         blobs,
 		objKey:        hn + ".db",
 		clock:         defaultClock{},
 	}
 	nr, err := s.read()
-	if os.IsNotExist(err) && s3sess != nil {
-		// Try to read from AWS
-		latestKey, cerr := s3sess.LatestKey()
+	if os.IsNotExist(err) && blobs != nil {
+		// Try to read from blob storage
+		latestKey, cerr := blobs.LatestKey(context.Background())
 		if cerr != nil {
-			log.Println("Error finding database from S3:", cerr)
+			log.Println("Error finding database from blob storage:", cerr)
 			return s
 		}
 		fd, cerr := os.Create(path.Join(s.dir, "records.db"))
@@ -82,8 +82,8 @@ func newInMemoryStore(dir string, flushInterval time.Duration, s3sess *s3.Sessio
 			log.Println("Error creating database file:", cerr)
 			return s
 		}
-		if cerr := s3sess.Download(fd, latestKey); cerr != nil {
-			log.Printf("Error downloading database from S3: %v", cerr)
+		if cerr := blobs.Download(context.Background(), latestKey, fd); cerr != nil {
+			log.Printf("Error downloading database from blob storage: %v", cerr)
 		}
 		_ = fd.Close()
 		nr, err = s.read()
@@ -310,16 +310,16 @@ func (s *inMemoryStore) write() (err error) {
 		return err
 	}
 
-	// Upload to S3
-	if s.s3 != nil {
+	// Upload to blob storage
+	if s.blobs != nil {
 		fd, err = os.Open(dbf)
 		if err != nil {
-			log.Printf("Error uploading database to S3: %v", err)
+			log.Printf("Error uploading database to blob storage: %v", err)
 			return nil
 		}
 		defer fd.Close()
-		if err := s.s3.Upload(fd, s.objKey); err != nil {
-			log.Printf("Error uploading database to S3: %v", err)
+		if err := s.blobs.Upload(context.Background(), s.objKey, fd); err != nil {
+			log.Printf("Error uploading database to blob storage: %v", err)
 		}
 		log.Println("Finished uploading database")
 	}

cmd/stdiscosrv/main.go

@@ -21,11 +21,13 @@ import (
 	"github.com/prometheus/client_golang/prometheus/promhttp"
 	"github.com/thejerf/suture/v4"
 
+	"github.com/syncthing/syncthing/internal/blob"
+	"github.com/syncthing/syncthing/internal/blob/azureblob"
+	"github.com/syncthing/syncthing/internal/blob/s3"
 	_ "github.com/syncthing/syncthing/lib/automaxprocs"
 	"github.com/syncthing/syncthing/lib/build"
 	"github.com/syncthing/syncthing/lib/protocol"
 	"github.com/syncthing/syncthing/lib/rand"
-	"github.com/syncthing/syncthing/lib/s3"
 	"github.com/syncthing/syncthing/lib/tlsutil"
 )
 
@@ -74,6 +76,10 @@ type CLI struct {
 	DBS3AccessKeyID string `name:"db-s3-access-key-id" group:"Database (S3 backup)" hidden:"true" help:"S3 access key ID for database" env:"DISCOVERY_DB_S3_ACCESS_KEY_ID"`
 	DBS3SecretKey   string `name:"db-s3-secret-key" group:"Database (S3 backup)" hidden:"true" help:"S3 secret key for database" env:"DISCOVERY_DB_S3_SECRET_KEY"`
 
+	DBAzureBlobAccount   string `name:"db-azure-blob-account" env:"DISCOVERY_DB_AZUREBLOB_ACCOUNT"`
+	DBAzureBlobKey       string `name:"db-azure-blob-key" env:"DISCOVERY_DB_AZUREBLOB_KEY"`
+	DBAzureBlobContainer string `name:"db-azure-blob-container" env:"DISCOVERY_DB_AZUREBLOB_CONTAINER"`
+
 	AMQPAddress string `group:"AMQP replication" hidden:"true" help:"Address to AMQP broker" env:"DISCOVERY_AMQP_ADDRESS"`
 
 	Debug   bool `short:"d" help:"Print debug output" env:"DISCOVERY_DEBUG"`
@@ -117,18 +123,20 @@ func main() {
 		Timeout:           2 * time.Minute,
 	})
 
-	// If configured, use S3 for database backups.
-	var s3c *s3.Session
+	// If configured, use blob storage for database backups.
+	var blobs blob.Store
+	var err error
 	if cli.DBS3Endpoint != "" {
-		var err error
-		s3c, err = s3.NewSession(cli.DBS3Endpoint, cli.DBS3Region, cli.DBS3Bucket, cli.DBS3AccessKeyID, cli.DBS3SecretKey)
-		if err != nil {
-			log.Fatalf("Failed to create S3 session: %v", err)
-		}
+		blobs, err = s3.NewSession(cli.DBS3Endpoint, cli.DBS3Region, cli.DBS3Bucket, cli.DBS3AccessKeyID, cli.DBS3SecretKey)
+	} else if cli.DBAzureBlobAccount != "" {
+		blobs, err = azureblob.NewBlobStore(cli.DBAzureBlobAccount, cli.DBAzureBlobKey, cli.DBAzureBlobContainer)
+	}
+	if err != nil {
+		log.Fatalf("Failed to create blob store: %v", err)
 	}
 
 	// Start the database.
-	db := newInMemoryStore(cli.DBDir, cli.DBFlushInterval, s3c)
+	db := newInMemoryStore(cli.DBDir, cli.DBFlushInterval, blobs)
 	main.Add(db)
 
 	// If we have an AMQP broker for replication, start that

go.mod

@@ -4,6 +4,7 @@ go 1.23.0
 
 require (
 	github.com/AudriusButkevicius/recli v0.0.7-0.20220911121932-d000ce8fbf0f
+	github.com/Azure/azure-sdk-for-go/sdk/storage/azblob v1.6.0
 	github.com/alecthomas/kong v1.10.0
 	github.com/aws/aws-sdk-go v1.55.6
 	github.com/calmh/incontainer v1.0.0
@@ -51,6 +52,8 @@ require (
 )
 
 require (
+	github.com/Azure/azure-sdk-for-go/sdk/azcore v1.17.0 // indirect
+	github.com/Azure/azure-sdk-for-go/sdk/internal v1.10.0 // indirect
 	github.com/Azure/go-ntlmssp v0.0.0-20221128193559-754e69321358 // indirect
 	github.com/beorn7/perks v1.0.1 // indirect
 	github.com/cenkalti/backoff/v4 v4.3.0 // indirect

go.sum

@@ -1,7 +1,19 @@
 github.com/AudriusButkevicius/recli v0.0.7-0.20220911121932-d000ce8fbf0f h1:GmH5lT+moM7PbAJFBq57nH9WJ+wRnBXr/tyaYWbSAx8=
 github.com/AudriusButkevicius/recli v0.0.7-0.20220911121932-d000ce8fbf0f/go.mod h1:Nhfib1j/VFnLrXL9cHgA+/n2O6P5THuWelOnbfPNd78=
+github.com/Azure/azure-sdk-for-go/sdk/azcore v1.17.0 h1:g0EZJwz7xkXQiZAI5xi9f3WWFYBlX1CPTrR+NDToRkQ=
+github.com/Azure/azure-sdk-for-go/sdk/azcore v1.17.0/go.mod h1:XCW7KnZet0Opnr7HccfUw1PLc4CjHqpcaxW8DHklNkQ=
+github.com/Azure/azure-sdk-for-go/sdk/azidentity v1.8.0 h1:B/dfvscEQtew9dVuoxqxrUKKv8Ih2f55PydknDamU+g=
+github.com/Azure/azure-sdk-for-go/sdk/azidentity v1.8.0/go.mod h1:fiPSssYvltE08HJchL04dOy+RD4hgrjph0cwGGMntdI=
+github.com/Azure/azure-sdk-for-go/sdk/internal v1.10.0 h1:ywEEhmNahHBihViHepv3xPBn1663uRv2t2q/ESv9seY=
+github.com/Azure/azure-sdk-for-go/sdk/internal v1.10.0/go.mod h1:iZDifYGJTIgIIkYRNWPENUnqx6bJ2xnSDFI2tjwZNuY=
+github.com/Azure/azure-sdk-for-go/sdk/resourcemanager/storage/armstorage v1.6.0 h1:PiSrjRPpkQNjrM8H0WwKMnZUdu1RGMtd/LdGKUrOo+c=
+github.com/Azure/azure-sdk-for-go/sdk/resourcemanager/storage/armstorage v1.6.0/go.mod h1:oDrbWx4ewMylP7xHivfgixbfGBT6APAwsSoHRKotnIc=
+github.com/Azure/azure-sdk-for-go/sdk/storage/azblob v1.6.0 h1:UXT0o77lXQrikd1kgwIPQOUect7EoR/+sbP4wQKdzxM=
+github.com/Azure/azure-sdk-for-go/sdk/storage/azblob v1.6.0/go.mod h1:cTvi54pg19DoT07ekoeMgE/taAwNtCShVeZqA+Iv2xI=
 github.com/Azure/go-ntlmssp v0.0.0-20221128193559-754e69321358 h1:mFRzDkZVAjdal+s7s0MwaRv9igoPqLRdzOLzw/8Xvq8=
 github.com/Azure/go-ntlmssp v0.0.0-20221128193559-754e69321358/go.mod h1:chxPXzSsl7ZWRAuOIE23GDNzjWuZquvFlgA8xmpunjU=
+github.com/AzureAD/microsoft-authentication-library-for-go v1.3.2 h1:kYRSnvJju5gYVyhkij+RTJ/VR6QIUaCfWeaFm2ycsjQ=
+github.com/AzureAD/microsoft-authentication-library-for-go v1.3.2/go.mod h1:wP83P5OoQ5p6ip3ScPr0BAq0BvuPAvacpEuSzyouqAI=
 github.com/BurntSushi/toml v1.4.0/go.mod h1:ukJfTF/6rtPPRCnwkur4qwRxa8vTRFBF0uk2lLoLwho=
 github.com/alecthomas/assert/v2 v2.11.0 h1:2Q9r3ki8+JYXvGsDyBXwH3LcJ+WK5D0gc5E8vS6K3D0=
 github.com/alecthomas/assert/v2 v2.11.0/go.mod h1:Bze95FyfUr7x34QZrjL+XP+0qgp/zg8yS+TtBj1WA3k=
@@ -65,6 +77,8 @@ github.com/go-task/slim-sprig/v3 v3.0.0 h1:sUs3vkvUymDpBKi3qH1YSqBQk9+9D/8M2mN1v
 github.com/go-task/slim-sprig/v3 v3.0.0/go.mod h1:W848ghGpv3Qj3dhTPRyJypKRiqCdHZiAzKg9hl15HA8=
 github.com/gofrs/flock v0.12.1 h1:MTLVXXHf8ekldpJk3AKicLij9MdwOWkZ+a/jHHZby9E=
 github.com/gofrs/flock v0.12.1/go.mod h1:9zxTsyu5xtJ9DK+1tFZyibEV7y3uwDxPPfbxeeHCoD0=
+github.com/golang-jwt/jwt/v5 v5.2.1 h1:OuVbFODueb089Lh128TAcimifWaLhJwVflnrgM17wHk=
+github.com/golang-jwt/jwt/v5 v5.2.1/go.mod h1:pqrtFR0X4osieyHYxtmOUWsAWrfe1Q5UVIyoH402zdk=
 github.com/golang/protobuf v1.2.0/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
 github.com/golang/protobuf v1.4.0-rc.1/go.mod h1:ceaxUfeHdC40wWswd/P6IGgMaK3YpKi5j83Wpe3EHw8=
 github.com/golang/protobuf v1.4.0-rc.1.0.20200221234624-67d41d38c208/go.mod h1:xKAWHe0F5eneWXFV3EuXVDTCmh+JuBKY0li0aMyXATA=
@@ -176,6 +190,8 @@ github.com/oschwald/maxminddb-golang v1.13.1 h1:G3wwjdN9JmIK2o/ermkHM+98oX5fS+k5
 github.com/oschwald/maxminddb-golang v1.13.1/go.mod h1:K4pgV9N/GcK694KSTmVSDTODk4IsCNThNdTmnaBZ/F8=
 github.com/pierrec/lz4/v4 v4.1.22 h1:cKFw6uJDK+/gfw5BcDL0JL5aBsAFdsIT18eRtLj7VIU=
 github.com/pierrec/lz4/v4 v4.1.22/go.mod h1:gZWDp/Ze/IJXGXf23ltt2EXimqmTUXEy0GFuRQyBid4=
+github.com/pkg/browser v0.0.0-20240102092130-5ac0b6a4141c h1:+mdjkGKdHQG3305AYmdv1U2eRNDiU2ErMBj1gwrq8eQ=
+github.com/pkg/browser v0.0.0-20240102092130-5ac0b6a4141c/go.mod h1:7rwL4CYBLnjLxUqIJNnCWiEdr3bn6IUYi15bNlnbCCU=
 github.com/pkg/errors v0.8.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=
 github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
@@ -205,8 +221,8 @@ github.com/rcrowley/go-metrics v0.0.0-20250401214520-65e299d6c5c9 h1:bsUq1dX0N8A
 github.com/rcrowley/go-metrics v0.0.0-20250401214520-65e299d6c5c9/go.mod h1:bCqnVzQkZxMG4s8nGwiZ5l3QUCyqpo9Y+/ZMZ9VjZe4=
 github.com/riywo/loginshell v0.0.0-20200815045211-7d26008be1ab h1:ZjX6I48eZSFetPb41dHudEyVr5v953N15TsNZXlkcWY=
 github.com/riywo/loginshell v0.0.0-20200815045211-7d26008be1ab/go.mod h1:/PfPXh0EntGc3QAAyUaviy4S9tzy4Zp0e2ilq4voC6E=
-github.com/rogpeppe/go-internal v1.10.0 h1:TMyTOH3F/DB16zRVcYyreMH6GnZZrwQVAoYjRBZyWFQ=
-github.com/rogpeppe/go-internal v1.10.0/go.mod h1:UQnix2H7Ngw/k4C5ijL5+65zddjncjaFoBhdsK/akog=
+github.com/rogpeppe/go-internal v1.12.0 h1:exVL4IDcn6na9z1rAb56Vxr+CgyK3nn3O+epU5NdKM8=
+github.com/rogpeppe/go-internal v1.12.0/go.mod h1:E+RYuTGaKKdloAfM02xzb0FW3Paa99yedzYV+kq4uf4=
 github.com/russross/blackfriday/v2 v2.1.0 h1:JIOH55/0cWyOuilr9/qlrm0BSXldqnqwMsf35Ld67mk=
 github.com/russross/blackfriday/v2 v2.1.0/go.mod h1:+Rmxgy9KzJVeS9/2gXHxylqXiyQDYRxCVz55jmeOWTM=
 github.com/sclevine/spec v1.4.0 h1:z/Q9idDcay5m5irkZ28M7PtQM4aOISzOpj4bUPkDee8=

internal/blob/azureblob/azureblob.go

@@ -0,0 +1,74 @@
+package azureblob
+
+import (
+	"context"
+	"io"
+	"time"
+
+	stblob "github.com/syncthing/syncthing/internal/blob"
+
+	"github.com/Azure/azure-sdk-for-go/sdk/storage/azblob"
+	"github.com/Azure/azure-sdk-for-go/sdk/storage/azblob/blob"
+	"github.com/Azure/azure-sdk-for-go/sdk/storage/azblob/blockblob"
+	"github.com/Azure/azure-sdk-for-go/sdk/storage/azblob/container"
+)
+
+var _ stblob.Store = (*BlobStore)(nil)
+
+type BlobStore struct {
+	client    *azblob.Client
+	container string
+}
+
+func NewBlobStore(accountName, accountKey, containerName string) (*BlobStore, error) {
+	credential, err := azblob.NewSharedKeyCredential(accountName, accountKey)
+	if err != nil {
+		return nil, err
+	}
+	url := "https://" + accountName + ".blob.core.windows.net/"
+	sc, err := azblob.NewClientWithSharedKeyCredential(url, credential, &azblob.ClientOptions{})
+	if err != nil {
+		return nil, err
+	}
+	// This errors when the container already exists, which we ignore.
+	_, _ = sc.CreateContainer(context.Background(), containerName, &container.CreateOptions{})
+	return &BlobStore{
+		client:    sc,
+		container: containerName,
+	}, nil
+}
+
+func (a *BlobStore) Upload(ctx context.Context, key string, data io.Reader) error {
+	_, err := a.client.UploadStream(ctx, a.container, key, data, &blockblob.UploadStreamOptions{})
+	return err
+}
+
+func (a *BlobStore) Download(ctx context.Context, key string, w stblob.Writer) error {
+	resp, err := a.client.DownloadStream(ctx, a.container, key, &blob.DownloadStreamOptions{})
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+	_, err = io.Copy(w, resp.Body)
+	return err
+}
+
+func (a *BlobStore) LatestKey(ctx context.Context) (string, error) {
+	opts := &azblob.ListBlobsFlatOptions{}
+	pager := a.client.NewListBlobsFlatPager(a.container, opts)
+	var latest string
+	var lastModified time.Time
+	for pager.More() {
+		page, err := pager.NextPage(ctx)
+		if err != nil {
+			return "", err
+		}
+		for _, blob := range page.Segment.BlobItems {
+			if latest == "" || blob.Properties.LastModified.After(lastModified) {
+				latest = *blob.Name
+				lastModified = *blob.Properties.LastModified
+			}
+		}
+	}
+	return latest, nil
+}

internal/blob/interface.go

@@ -0,0 +1,17 @@
+package blob
+
+import (
+	"context"
+	"io"
+)
+
+type Store interface {
+	Upload(ctx context.Context, key string, r io.Reader) error
+	Download(ctx context.Context, key string, w Writer) error
+	LatestKey(ctx context.Context) (string, error)
+}
+
+type Writer interface {
+	io.Writer
+	io.WriterAt
+}

lib/s3/s3.go → internal/blob/s3/s3.go

@@ -7,6 +7,7 @@
 package s3
 
 import (
+	"context"
 	"io"
 	"time"
 
@@ -15,8 +16,11 @@ import (
 	"github.com/aws/aws-sdk-go/aws/session"
 	"github.com/aws/aws-sdk-go/service/s3"
 	"github.com/aws/aws-sdk-go/service/s3/s3manager"
+	"github.com/syncthing/syncthing/internal/blob"
 )
 
+var _ blob.Store = (*Session)(nil)
+
 type Session struct {
 	bucket string
 	s3sess *session.Session
@@ -40,7 +44,7 @@ func NewSession(endpoint, region, bucket, accessKeyID, secretKey string) (*Sessi
 	}, nil
 }
 
-func (s *Session) Upload(r io.Reader, key string) error {
+func (s *Session) Upload(_ context.Context, key string, r io.Reader) error {
 	uploader := s3manager.NewUploader(s.s3sess)
 	_, err := uploader.Upload(&s3manager.UploadInput{
 		Bucket: aws.String(s.bucket),
@@ -50,7 +54,31 @@ func (s *Session) Upload(r io.Reader, key string) error {
 	return err
 }
 
-func (s *Session) List(fn func(*Object) bool) error {
+func (s *Session) Download(_ context.Context, key string, w blob.Writer) error {
+	downloader := s3manager.NewDownloader(s.s3sess)
+	_, err := downloader.Download(w, &s3.GetObjectInput{
+		Bucket: aws.String(s.bucket),
+		Key:    aws.String(key),
+	})
+	return err
+}
+
+func (s *Session) LatestKey(_ context.Context) (string, error) {
+	var latestKey string
+	var lastModified time.Time
+	if err := s.list(func(obj *Object) bool {
+		if latestKey == "" || obj.LastModified.After(lastModified) {
+			latestKey = *obj.Key
+			lastModified = *obj.LastModified
+		}
+		return true
+	}); err != nil {
+		return "", err
+	}
+	return latestKey, nil
+}
+
+func (s *Session) list(fn func(*Object) bool) error {
 	svc := s3.New(s.s3sess)
 
 	opts := &s3.ListObjectsV2Input{
@@ -76,27 +104,3 @@ func (s *Session) List(fn func(*Object) bool) error {
 
 	return nil
 }
-
-func (s *Session) LatestKey() (string, error) {
-	var latestKey string
-	var lastModified time.Time
-	if err := s.List(func(obj *Object) bool {
-		if latestKey == "" || obj.LastModified.After(lastModified) {
-			latestKey = *obj.Key
-			lastModified = *obj.LastModified
-		}
-		return true
-	}); err != nil {
-		return "", err
-	}
-	return latestKey, nil
-}
-
-func (s *Session) Download(w io.WriterAt, key string) error {
-	downloader := s3manager.NewDownloader(s.s3sess)
-	_, err := downloader.Download(w, &s3.GetObjectInput{
-		Bucket: aws.String(s.bucket),
-		Key:    aws.String(key),
-	})
-	return err
-}