Add -s3-force-path-style flag and config option (#157)

This option forces path-style addressing instead of using a subdomain.
This appears to be needed by Minio.

README.md

@@ -60,7 +60,7 @@ The following storage backends are available:
 |Name|Options|Notes
 |----|-------|-----
 |LocalFS|```-filespath files/``` -- Path to store uploads (default is files/)<br />```-metapath meta/``` -- Path to store information about uploads (default is meta/)|Enabled by default, this backend uses the filesystem|
-|S3|```-s3-endpoint https://...``` -- S3 endpoint<br>```-s3-region us-east-1``` -- S3 region<br>```-s3-bucket mybucket``` -- S3 bucket to use for files and metadata<br><br>Environment variables to provide:<br>```AWS_ACCESS_KEY_ID``` -- the S3 access key<br>```AWS_SECRET_ACCESS_KEY ``` -- the S3 secret key<br>```AWS_SESSION_TOKEN``` (optional) -- the S3 session token|Use with any S3-compatible provider.<br> This implementation will stream files through the linx instance (every download will request and stream the file from the S3 bucket).<br><br>For high-traffic environments, one might consider using an external caching layer such as described [in this article](https://blog.sentry.io/2017/03/01/dodging-s3-downtime-with-nginx-and-haproxy.html).|
+|S3|```-s3-endpoint https://...``` -- S3 endpoint<br>```-s3-region us-east-1``` -- S3 region<br>```-s3-bucket mybucket``` -- S3 bucket to use for files and metadata<br>```-s3-use-path-style``` -- force path-style addresing (e.g. https://s3.amazonaws.com/linx/example.txt)<br><br>Environment variables to provide:<br>```AWS_ACCESS_KEY_ID``` -- the S3 access key<br>```AWS_SECRET_ACCESS_KEY ``` -- the S3 secret key<br>```AWS_SESSION_TOKEN``` (optional) -- the S3 session token|Use with any S3-compatible provider.<br> This implementation will stream files through the linx instance (every download will request and stream the file from the S3 bucket).<br><br>For high-traffic environments, one might consider using an external caching layer such as described [in this article](https://blog.sentry.io/2017/03/01/dodging-s3-downtime-with-nginx-and-haproxy.html).|
 
 
 #### SSL with built-in server 

backends/s3/s3.go

@@ -177,7 +177,7 @@ func (b S3Backend) List() ([]string, error) {
 	return output, nil
 }
 
-func NewS3Backend(bucket string, region string, endpoint string) S3Backend {
+func NewS3Backend(bucket string, region string, endpoint string, forcePathStyle bool) S3Backend {
 	awsConfig := &aws.Config{}
 	if region != "" {
 		awsConfig.Region = aws.String(region)
@@ -185,6 +185,9 @@ func NewS3Backend(bucket string, region string, endpoint string) S3Backend {
 	if endpoint != "" {
 		awsConfig.Endpoint = aws.String(endpoint)
 	}
+	if forcePathStyle == true {
+		awsConfig.S3ForcePathStyle = aws.Bool(true)
+	}
 
 	sess := session.Must(session.NewSession(awsConfig))
 	svc := s3.New(sess)

server.go

@@ -64,6 +64,7 @@ var Config struct {
 	s3Endpoint                string
 	s3Region                  string
 	s3Bucket                  string
+	s3ForcePathStyle          bool
 }
 
 var Templates = make(map[string]*pongo2.Template)
@@ -138,7 +139,7 @@ func setup() *web.Mux {
 	}
 
 	if Config.s3Bucket != "" {
-		storageBackend = s3.NewS3Backend(Config.s3Bucket, Config.s3Region, Config.s3Endpoint)
+		storageBackend = s3.NewS3Backend(Config.s3Bucket, Config.s3Region, Config.s3Endpoint, Config.s3ForcePathStyle)
 	} else {
 		storageBackend = localfs.NewLocalfsBackend(Config.metaDir, Config.filesDir)
 	}
@@ -265,6 +266,8 @@ func main() {
 		"S3 region")
 	flag.StringVar(&Config.s3Bucket, "s3-bucket", "",
 		"S3 bucket to use for files and metadata")
+	flag.BoolVar(&Config.s3ForcePathStyle, "s3-force-path-style", false,
+		"Force path-style addressing for S3 (e.g. https://s3.amazonaws.com/linx/example.txt)")
 
 	iniflags.Parse()