Migrate to govendor to avoid limitations of godep

- over the course of a project history every maintainer needs to update
  its dependency packages, the problem essentially with godep is manipulating
  GOPATH - this manipulation leads to static objects created at different locations
  which end up conflicting with the overall functionality of golang.

  This also leads to broken builds. There is no easier way out of this other than
  asking developers to do 'godep restore' all the time. Which perhaps as a practice
  doesn't sound like a clean solution. On the other hand 'godep restore' has its own
  set of problems.

- govendor is a right tool but a stop gap tool until we wait for golangs official
  1.5 version which fixes this vendoring issue once and for all.

- govendor provides consistency in terms of how import paths should be handled unlike
  manipulation GOPATH.

  This has advantages
    - no more compiled objects being referenced in GOPATH and build time GOPATH
      manging which leads to conflicts.
    - proper import paths referencing the exact package a project is dependent on.

 govendor is simple and provides the minimal necessary tooling to achieve this.

 For now this is the right solution.

internal/github.com/gorilla/rpc/v2/json/client.go

@@ -0,0 +1,61 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Copyright 2012-2013 The Gorilla Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package json
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"math/rand"
+)
+
+// ----------------------------------------------------------------------------
+// Request and Response
+// ----------------------------------------------------------------------------
+
+// clientRequest represents a JSON-RPC request sent by a client.
+type clientRequest struct {
+	// A String containing the name of the method to be invoked.
+	Method string `json:"method"`
+	// Object to pass as request parameter to the method.
+	Params [1]interface{} `json:"params"`
+	// The request id. This can be of any type. It is used to match the
+	// response with the request that it is replying to.
+	Id uint64 `json:"id"`
+}
+
+// clientResponse represents a JSON-RPC response returned to a client.
+type clientResponse struct {
+	Result *json.RawMessage `json:"result"`
+	Error  interface{}      `json:"error"`
+	Id     uint64           `json:"id"`
+}
+
+// EncodeClientRequest encodes parameters for a JSON-RPC client request.
+func EncodeClientRequest(method string, args interface{}) ([]byte, error) {
+	c := &clientRequest{
+		Method: method,
+		Params: [1]interface{}{args},
+		Id:     uint64(rand.Int63()),
+	}
+	return json.Marshal(c)
+}
+
+// DecodeClientResponse decodes the response body of a client request into
+// the interface reply.
+func DecodeClientResponse(r io.Reader, reply interface{}) error {
+	var c clientResponse
+	if err := json.NewDecoder(r).Decode(&c); err != nil {
+		return err
+	}
+	if c.Error != nil {
+		return &Error{Data: c.Error}
+	}
+	if c.Result == nil {
+		return fmt.Errorf("Unexpected null result")
+	}
+	return json.Unmarshal(*c.Result, reply)
+}

internal/github.com/gorilla/rpc/v2/json/doc.go

@@ -0,0 +1,58 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Copyright 2012 The Gorilla Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+/*
+Package gorilla/rpc/json provides a codec for JSON-RPC over HTTP services.
+
+To register the codec in a RPC server:
+
+	import (
+		"http"
+		"github.com/gorilla/rpc/v2"
+		"github.com/gorilla/rpc/v2/json"
+	)
+
+	func init() {
+		s := rpc.NewServer()
+		s.RegisterCodec(json.NewCodec(), "application/json")
+		// [...]
+		http.Handle("/rpc", s)
+	}
+
+A codec is tied to a content type. In the example above, the server will use
+the JSON codec for requests with "application/json" as the value for the
+"Content-Type" header.
+
+This package follows the JSON-RPC 1.0 specification:
+
+	http://json-rpc.org/wiki/specification
+
+Request format is:
+
+	method:
+		The name of the method to be invoked, as a string in dotted notation
+		as in "Service.Method".
+	params:
+		An array with a single object to pass as argument to the method.
+	id:
+		The request id, a uint. It is used to match the response with the
+		request that it is replying to.
+
+Response format is:
+
+	result:
+		The Object that was returned by the invoked method,
+		or null in case there was an error invoking the method.
+	error:
+		An Error object if there was an error invoking the method,
+		or null if there was no error.
+	id:
+		The same id as the request it is responding to.
+
+Check the gorilla/rpc documentation for more details:
+
+	http://gorilla-web.appspot.com/pkg/rpc
+*/
+package json

internal/github.com/gorilla/rpc/v2/json/server.go

@@ -0,0 +1,155 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Copyright 2012 The Gorilla Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package json
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net/http"
+
+	"github.com/minio/minio/internal/github.com/gorilla/rpc/v2"
+)
+
+var null = json.RawMessage([]byte("null"))
+
+// An Error is a wrapper for a JSON interface value. It can be used by either
+// a service's handler func to write more complex JSON data to an error field
+// of a server's response, or by a client to read it.
+type Error struct {
+	Data interface{}
+}
+
+func (e *Error) Error() string {
+	return fmt.Sprintf("%v", e.Data)
+}
+
+// ----------------------------------------------------------------------------
+// Request and Response
+// ----------------------------------------------------------------------------
+
+// serverRequest represents a JSON-RPC request received by the server.
+type serverRequest struct {
+	// A String containing the name of the method to be invoked.
+	Method string `json:"method"`
+	// An Array of objects to pass as arguments to the method.
+	Params *json.RawMessage `json:"params"`
+	// The request id. This can be of any type. It is used to match the
+	// response with the request that it is replying to.
+	Id *json.RawMessage `json:"id"`
+}
+
+// serverResponse represents a JSON-RPC response returned by the server.
+type serverResponse struct {
+	// The Object that was returned by the invoked method. This must be null
+	// in case there was an error invoking the method.
+	Result interface{} `json:"result"`
+	// An Error object if there was an error invoking the method. It must be
+	// null if there was no error.
+	Error interface{} `json:"error"`
+	// This must be the same id as the request it is responding to.
+	Id *json.RawMessage `json:"id"`
+}
+
+// ----------------------------------------------------------------------------
+// Codec
+// ----------------------------------------------------------------------------
+
+// NewCodec returns a new JSON Codec.
+func NewCodec() *Codec {
+	return &Codec{}
+}
+
+// Codec creates a CodecRequest to process each request.
+type Codec struct {
+}
+
+// NewRequest returns a CodecRequest.
+func (c *Codec) NewRequest(r *http.Request) rpc.CodecRequest {
+	return newCodecRequest(r)
+}
+
+// ----------------------------------------------------------------------------
+// CodecRequest
+// ----------------------------------------------------------------------------
+
+// newCodecRequest returns a new CodecRequest.
+func newCodecRequest(r *http.Request) rpc.CodecRequest {
+	// Decode the request body and check if RPC method is valid.
+	req := new(serverRequest)
+	err := json.NewDecoder(r.Body).Decode(req)
+	r.Body.Close()
+	return &CodecRequest{request: req, err: err}
+}
+
+// CodecRequest decodes and encodes a single request.
+type CodecRequest struct {
+	request *serverRequest
+	err     error
+}
+
+// Method returns the RPC method for the current request.
+//
+// The method uses a dotted notation as in "Service.Method".
+func (c *CodecRequest) Method() (string, error) {
+	if c.err == nil {
+		return c.request.Method, nil
+	}
+	return "", c.err
+}
+
+// ReadRequest fills the request object for the RPC method.
+func (c *CodecRequest) ReadRequest(args interface{}) error {
+	if c.err == nil {
+		if c.request.Params != nil {
+			// JSON params is array value. RPC params is struct.
+			// Unmarshal into array containing the request struct.
+			params := [1]interface{}{args}
+			c.err = json.Unmarshal(*c.request.Params, &params)
+		} else {
+			c.err = errors.New("rpc: method request ill-formed: missing params field")
+		}
+	}
+	return c.err
+}
+
+// WriteResponse encodes the response and writes it to the ResponseWriter.
+func (c *CodecRequest) WriteResponse(w http.ResponseWriter, reply interface{}) {
+	if c.request.Id != nil {
+		// Id is null for notifications and they don't have a response.
+		res := &serverResponse{
+			Result: reply,
+			Error:  &null,
+			Id:     c.request.Id,
+		}
+		c.writeServerResponse(w, 200, res)
+	}
+}
+
+func (c *CodecRequest) WriteError(w http.ResponseWriter, _ int, err error) {
+	res := &serverResponse{
+		Result: &null,
+		Id:     c.request.Id,
+	}
+	if jsonErr, ok := err.(*Error); ok {
+		res.Error = jsonErr.Data
+	} else {
+		res.Error = err.Error()
+	}
+	c.writeServerResponse(w, 400, res)
+}
+
+func (c *CodecRequest) writeServerResponse(w http.ResponseWriter, status int, res *serverResponse) {
+	b, err := json.Marshal(res)
+	if err == nil {
+		w.WriteHeader(status)
+		w.Header().Set("Content-Type", "application/json; charset=utf-8")
+		w.Write(b)
+	} else {
+		// Not sure in which case will this happen. But seems harmless.
+		rpc.WriteError(w, 400, err.Error())
+	}
+}