s3: add bucket-lookup parameter to select path or dns style bucket lookup

This is to enable restic working with Alibaba cloud

Fixes #2528

changelog/unreleased/issue-2528

@@ -0,0 +1,20 @@
+Enhancement: support Alibaba/Aliyun OSS with S3 backend
+
+We've added a new flag to the s3 backend `s3.bucket-lookup` which can
+be set to these 3 values:
+
+- `auto` - existing behaviour
+- `dns` - use DNS style bucket access
+- `path` - use path style bucket access
+
+To make the s3 backend work with Alibaba/Aliyun OSS you must set
+`s3.bucket-lookup` to `dns` and set the `s3.region` parameter.  For
+example:
+
+    restic -o s3.bucket-lookup=dns -o s3.region=oss-eu-west-1 -r s3:https://oss-eu-west-1.aliyuncs.com/bucketname init
+
+Note that s3.region must be set otherwise the minio SDK tries to look
+it up and it seems that Alibaba doesn't support that properly.
+
+https://github.com/restic/restic/issues/2528
+https://github.com/restic/restic/pull/2535

doc/030_preparing_a_new_repo.rst

@@ -299,6 +299,46 @@ this command.
     Please note that knowledge of your password is required to access
     the repository. Losing your password means that your data is irrecoverably lost.
 
+Alibaba Cloud (Aliyun) Object Storage System (OSS)
+**************************************************
+
+`Alibaba OSS <https://www.alibabacloud.com/product/oss/>`__ is an
+encrypted, secure, cost-effective, and easy-to-use object storage
+service that enables you to store, back up, and archive large amounts
+of data in the cloud.
+
+Alibaba OSS is S3 compatible so it can be used as a storage provider
+for a restic repository with a couple of extra parameters.
+
+-  Determine the correct `Alibaba OSS region endpoint <https://www.alibabacloud.com/help/doc-detail/31837.htm>`__ - this will be something like ``oss-eu-west-1.aliyuncs.com``
+-  You'll need the region name too - this will be something like ``oss-eu-west-1``
+
+You must first setup the following environment variables with the
+credentials of your Alibaba OSS account.
+
+.. code-block:: console
+
+    $ export AWS_ACCESS_KEY_ID=<YOUR-OSS-ACCESS-KEY-ID>
+    $ export AWS_SECRET_ACCESS_KEY=<YOUR-OSS-SECRET-ACCESS-KEY>
+
+Now you can easily initialize restic to use Alibaba OSS as a backend with
+this command.
+
+.. code-block:: console
+
+    $ ./restic -o s3.bucket-lookup=dns -o s3.region=<OSS-REGION> -r s3:https://<OSS-ENDPOINT>/<OSS-BUCKET-NAME> init
+    enter password for new backend:
+    enter password again:
+    created restic backend xxxxxxxxxx at s3:https://<OSS-ENDPOINT>/<OSS-BUCKET-NAME>
+    Please note that knowledge of your password is required to access
+    the repository. Losing your password means that your data is irrecoverably lost.
+
+For example with an actual endpoint:
+
+.. code-block:: console
+
+    $ restic -o s3.bucket-lookup=dns -o s3.region=oss-eu-west-1 -r s3:https://oss-eu-west-1.aliyuncs.com/bucketname init
+
 OpenStack Swift
 ***************
 

internal/backend/s3/config.go

@@ -23,6 +23,7 @@ type Config struct {
 	Connections  uint   `option:"connections" help:"set a limit for the number of concurrent connections (default: 5)"`
 	MaxRetries   uint   `option:"retries" help:"set the number of retries attempted"`
 	Region       string `option:"region" help:"set region"`
+	BucketLookup string `option:"bucket-lookup" help:"bucket lookup style: 'auto', 'dns', or 'path'."`
 }
 
 // NewConfig returns a new Config with the default values filled in.

internal/backend/s3/s3.go

@@ -2,6 +2,7 @@ package s3
 
 import (
 	"context"
+	"fmt"
 	"io"
 	"io/ioutil"
 	"net/http"
@@ -66,12 +67,26 @@ func open(ctx context.Context, cfg Config, rt http.RoundTripper) (*Backend, erro
 			},
 		},
 	})
-	client, err := minio.New(cfg.Endpoint, &minio.Options{
+
+	options := &minio.Options{
 		Creds:     creds,
 		Secure:    !cfg.UseHTTP,
 		Region:    cfg.Region,
 		Transport: rt,
-	})
+	}
+
+	switch strings.ToLower(cfg.BucketLookup) {
+	case "", "auto":
+		options.BucketLookup = minio.BucketLookupAuto
+	case "dns":
+		options.BucketLookup = minio.BucketLookupDNS
+	case "path":
+		options.BucketLookup = minio.BucketLookupPath
+	default:
+		return nil, fmt.Errorf(`bad bucket-lookup style %q must be "auto", "path" or "dns"`, cfg.BucketLookup)
+	}
+
+	client, err := minio.New(cfg.Endpoint, options)
 	if err != nil {
 		return nil, errors.Wrap(err, "minio.New")
 	}