s3cache: expose add'l config options as URL params

this should allow using at least some s3-compatible services like minio.

Ref #120, #147

README.md

@@ -108,12 +108,25 @@ enabled using the `-cache` flag.  It supports the following values:
    cache items no longer than 4 hours.
  - directory on local disk (e.g. `/tmp/imageproxy`) - will cache images
    on disk
+
  - s3 URL (e.g. `s3://region/bucket-name/optional-path-prefix`) - will cache
    images on Amazon S3.  This requires either an IAM role and instance profile
    with access to your your bucket or `AWS_ACCESS_KEY_ID` and `AWS_SECRET_KEY`
    environmental variables be set. (Additional methods of loading credentials
    are documented in the [aws-sdk-go session
    package](https://docs.aws.amazon.com/sdk-for-go/api/aws/session/)).
+
+   Additional configuration options may be specified as URL query string
+   parameters, which are mostly useful when working with s3-compatible services:
+   - "endpoint" - specify an alternate API endpoint
+   - "disableSSL" - set to "1" to disable SSL when calling the API
+   - "s3ForcePathStyle" - set to "1" to force the request to use path-style addressing
+
+   For example, when working with [minio](https://minio.io), which doesn't use
+   regions, provide a dummy region value and custom endpoint value:
+
+       s3://fake-region/bucket/folder?endpoint=minio:9000&disableSSL=1&s3ForcePathStyle=1
+
  - gcs URL (e.g. `gcs://bucket-name/optional-path-prefix`) - will cache images
    on Google Cloud Storage. Authentication is documented in Google's
    [Application Default Credentials
@@ -127,6 +140,8 @@ enabled using the `-cache` flag.  It supports the following values:
    Rather than specify password in the URI, use the `REDIS_PASSWORD`
    environment variable.
 
+[s3compat]: https://github.com/willnorris/imageproxy/pull/147#issuecomment-473362058
+
 For example, to cache files on disk in the `/tmp/imageproxy` directory:
 
     imageproxy -cache /tmp/imageproxy

internal/s3cache/s3cache.go

@@ -97,7 +97,23 @@ func New(s string) (*cache, error) {
 		prefix = path[1]
 	}
 
-	sess, err := session.NewSession(&aws.Config{Region: &region})
+	config := &aws.Config{
+		Region: &region,
+	}
+
+	// allow overriding some additional config options, mostly useful when
+	// working with s3-compatible services other than AWS.
+	if v := u.Query().Get("endpoint"); v != "" {
+		config.Endpoint = &v
+	}
+	if v := u.Query().Get("disableSSL"); v == "1" {
+		config.DisableSSL = aws.Bool(true)
+	}
+	if v := u.Query().Get("s3ForcePathStyle"); v == "1" {
+		config.S3ForcePathStyle = aws.Bool(true)
+	}
+
+	sess, err := session.NewSession(config)
 	if err != nil {
 		return nil, err
 	}