add license banner for GNU AGPLv3 (#15178)

Bonus: rewrite subnet re-use of Transport

internal/config/subnet/subnet.go

@@ -0,0 +1,76 @@
+// Copyright (c) 2015-2022 MinIO, Inc.
+//
+// This file is part of MinIO Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package subnet
+
+import (
+	"bytes"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"net/http"
+	"time"
+
+	xhttp "github.com/minio/minio/internal/http"
+)
+
+const (
+	respBodyLimit = 1 << 20 // 1 MiB
+)
+
+// Post submit 'payload' to specified URL
+func (c Config) Post(reqURL string, payload interface{}) (string, error) {
+	if len(c.APIKey) == 0 {
+		return "", errors.New("Deployment is not registered with SUBNET. Please register the deployment via 'mc support register ALIAS'")
+	}
+	body, err := json.Marshal(payload)
+	if err != nil {
+		return "", err
+	}
+	r, err := http.NewRequest(http.MethodPost, reqURL, bytes.NewReader(body))
+	if err != nil {
+		return "", err
+	}
+
+	r.Header.Set("Authorization", c.APIKey)
+	r.Header.Set("Content-Type", "application/json")
+
+	client := &http.Client{
+		Timeout:   10 * time.Second,
+		Transport: c.transport,
+	}
+
+	resp, err := client.Do(r)
+	if err != nil {
+		return "", err
+	}
+	defer xhttp.DrainBody(resp.Body)
+
+	respBytes, err := ioutil.ReadAll(io.LimitReader(resp.Body, respBodyLimit))
+	if err != nil {
+		return "", err
+	}
+	respStr := string(respBytes)
+
+	if resp.StatusCode == http.StatusOK {
+		return respStr, nil
+	}
+
+	return respStr, fmt.Errorf("SUBNET request failed with code %d and error: %s", resp.StatusCode, respStr)
+}