Implement backblaze-b2 gateway support (#5002)

Fixes https://github.com/minio/minio/issues/4072

docs/gateway/README.md

@@ -2,8 +2,8 @@
 Minio Gateway adds Amazon S3 compatibility to third party cloud storage providers.
 - [Microsoft Azure Blob Storage](https://github.com/minio/minio/blob/master/docs/gateway/azure.md)
 - [Google Cloud Storage](https://github.com/minio/minio/blob/master/docs/gateway/gcs.md) _Alpha release_
+- [Backblaze B2](https://github.com/minio/minio/blob/master/docs/gateway/b2.md) _Alpha release_
 
 ## Roadmap
-* Minio & AWS S3
 * Edge Caching - Disk based proxy caching support
 

docs/gateway/b2.md

@@ -0,0 +1,48 @@
+# Minio B2 Gateway [![Slack](https://slack.minio.io/slack?type=svg)](https://slack.minio.io)
+Minio Gateway adds Amazon S3 compatibility to Backblaze B2 Cloud Storage.
+
+## Run Minio Gateway for Backblaze B2 Cloud Storage
+Please follow this [guide](https://www.backblaze.com/b2/docs/quick_account.html) to create an account on backblaze.com to obtain your access credentisals for B2 Cloud storage.
+
+### Using Binary
+Please download the test binary for gateway B2 support https://data.minio.io:10000/minio-b2/linux-amd64/minio-b2
+
+```
+export MINIO_ACCESS_KEY=b2_accound_id
+export MINIO_SECRET_KEY=b2_application_key
+minio gateway b2
+```
+## Test using Minio Browser
+Minio Gateway comes with an embedded web based object browser. Point your web browser to http://127.0.0.1:9000 ensure your server has started successfully.
+
+![Screenshot](https://raw.githubusercontent.com/minio/minio/master/docs/screenshots/minio-browser-gateway.png)
+
+## Test using Minio Client `mc`
+`mc` provides a modern alternative to UNIX commands such as ls, cat, cp, mirror, diff etc. It supports filesystems and Amazon S3 compatible cloud storage services.
+
+### Configure `mc`
+```
+mc config host add myb2 http://gateway-ip:9000 b2_account_id b2_application_key
+```
+
+### List buckets on Backblaze B2
+```
+mc ls myb2
+[2017-02-22 01:50:43 PST]     0B ferenginar/
+[2017-02-26 21:43:51 PST]     0B my-bucket/
+[2017-02-26 22:10:11 PST]     0B test-bucket1/
+```
+
+### Known limitations
+Gateway inherits the following B2 limitations:
+- No support for CopyObject S3 API (There are no equivalent APIs available on Backblaze B2).
+- No support for CopyObjectPart S3 API (There are no equivalent APIs available on Backblaze B2).
+- Only read-only bucket policy supported at bucket level, all other variations will return API Notimplemented error.
+
+Other limitations:
+- Bucket notification APIs are not supported on Gateway.
+
+## Explore Further
+- [`mc` command-line interface](https://docs.minio.io/docs/minio-client-quickstart-guide)
+- [`aws` command-line interface](https://docs.minio.io/docs/aws-cli-with-minio)
+- [`minio-go` Go SDK](https://docs.minio.io/docs/golang-client-quickstart-guide)