Add controller API client interface (#1467)

This PR adds an interface for controller API client, it allows us to
implement mock API client for unit testing with ease and we are
able to generate spec file without accessing the real Fission server.

pkg/controller/client/rest/client.go

@@ -0,0 +1,126 @@
+/*
+Copyright 2019 The Fission Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package rest
+
+import (
+	"bytes"
+	"context"
+	"io"
+	"io/ioutil"
+	"net/http"
+	"strings"
+
+	"github.com/pkg/errors"
+	"golang.org/x/net/context/ctxhttp"
+)
+
+type (
+	Interface interface {
+		Create(relativeUrl string, contentType string, payload []byte) (*http.Response, error)
+		Put(relativeUrl string, contentType string, payload []byte) (*http.Response, error)
+		Get(relativeUrl string) (*http.Response, error)
+		Delete(relativeUrl string) error
+		Proxy(method string, relativeUrl string, payload []byte) (*http.Response, error)
+		ServerInfo() (*http.Response, error)
+		ServerURL() string
+	}
+
+	RESTClient struct {
+		url string
+	}
+)
+
+func NewRESTClient(serverUrl string) Interface {
+	return &RESTClient{
+		url: strings.TrimSuffix(serverUrl, "/"),
+	}
+}
+
+func (c *RESTClient) Create(relativeUrl string, contentType string, payload []byte) (*http.Response, error) {
+	var reader io.Reader
+	if len(payload) > 0 {
+		reader = bytes.NewReader(payload)
+	}
+	return c.sendRequest(http.MethodPost, c.v2CrdUrl(relativeUrl), map[string]string{"Content-type": contentType}, reader)
+}
+
+func (c *RESTClient) Put(relativeUrl string, contentType string, payload []byte) (*http.Response, error) {
+	var reader io.Reader
+	if len(payload) > 0 {
+		reader = bytes.NewReader(payload)
+	}
+	return c.sendRequest(http.MethodPut, c.v2CrdUrl(relativeUrl), map[string]string{"Content-type": contentType}, reader)
+}
+
+func (c *RESTClient) Get(relativeUrl string) (*http.Response, error) {
+	return c.sendRequest(http.MethodGet, c.v2CrdUrl(relativeUrl), nil, nil)
+}
+
+func (c *RESTClient) Delete(relativeUrl string) error {
+	resp, err := c.sendRequest(http.MethodDelete, c.v2CrdUrl(relativeUrl), nil, nil)
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != 200 {
+		body, err := ioutil.ReadAll(resp.Body)
+		if err != nil {
+			return errors.Wrap(err, "error deleting")
+		} else {
+			return errors.Errorf("failed to delete: %v", string(body))
+		}
+	}
+
+	return nil
+}
+
+func (c *RESTClient) Proxy(method string, relativeUrl string, payload []byte) (*http.Response, error) {
+	var reader io.Reader
+	if len(payload) > 0 {
+		reader = bytes.NewReader(payload)
+	}
+	return c.sendRequest(method, c.proxyUrl(relativeUrl), nil, reader)
+}
+
+func (c *RESTClient) ServerInfo() (*http.Response, error) {
+	return c.sendRequest(http.MethodGet, c.url, nil, nil)
+}
+
+func (c *RESTClient) ServerURL() string {
+	return c.url
+}
+
+func (c *RESTClient) sendRequest(method string, relativeUrl string, headers map[string]string, reader io.Reader) (*http.Response, error) {
+	req, err := http.NewRequest(method, relativeUrl, reader)
+	if err != nil {
+		return nil, err
+	}
+	for k, v := range headers {
+		req.Header.Set(k, v)
+	}
+	// TODO: accept context
+	return ctxhttp.Do(context.Background(), &http.Client{}, req)
+}
+
+func (c *RESTClient) v2CrdUrl(relativeUrl string) string {
+	return c.url + "/v2/" + strings.TrimPrefix(relativeUrl, "/")
+}
+
+func (c *RESTClient) proxyUrl(relativeUrl string) string {
+	return c.url + "/proxy/" + strings.TrimPrefix(relativeUrl, "/")
+}