Extend further validation of config values (#8469)

- This PR allows config KVS to be validated properly
  without being affected by ENV overrides, rejects
  invalid values during set operation

- Expands unit tests and refactors the error handling
  for notification targets, returns error instead of
  ignoring targets for invalid KVS

- Does all the prep-work for implementing safe-mode
  style operation for MinIO server, introduces a new
  global variable to toggle safe mode based operations
  NOTE: this PR itself doesn't provide safe mode operations

pkg/net/url.go

@@ -19,6 +19,7 @@ package net
 import (
 	"encoding/json"
 	"errors"
+	"fmt"
 	"net"
 	"net/http"
 	"net/url"
@@ -103,6 +104,21 @@ func (u URL) DialHTTP() error {
 	return nil
 }
 
+// ParseHTTPURL - parses a string into HTTP URL, string is
+// expected to be of form http:// or https://
+func ParseHTTPURL(s string) (u *URL, err error) {
+	u, err = ParseURL(s)
+	if err != nil {
+		return nil, err
+	}
+	switch u.Scheme {
+	default:
+		return nil, fmt.Errorf("unexpected scheme found %s", u.Scheme)
+	case "http", "https":
+		return u, nil
+	}
+}
+
 // ParseURL - parses string into URL.
 func ParseURL(s string) (u *URL, err error) {
 	var uu *url.URL

pkg/net/url_test.go

@@ -133,6 +133,42 @@ func TestURLUnmarshalJSON(t *testing.T) {
 	}
 }
 
+func TestParseHTTPURL(t *testing.T) {
+	testCases := []struct {
+		s           string
+		expectedURL *URL
+		expectErr   bool
+	}{
+		{"http://play", &URL{Scheme: "http", Host: "play"}, false},
+		{"https://play.min.io:0", &URL{Scheme: "https", Host: "play.min.io:0"}, false},
+		{"https://147.75.201.93:9000/", &URL{Scheme: "https", Host: "147.75.201.93:9000", Path: "/"}, false},
+		{"https://s3.amazonaws.com/?location", &URL{Scheme: "https", Host: "s3.amazonaws.com", Path: "/", RawQuery: "location"}, false},
+		{"http://myminio:10000/mybucket//myobject/", &URL{Scheme: "http", Host: "myminio:10000", Path: "/mybucket/myobject/"}, false},
+		{"ftp://myftp.server:10000/myuser", nil, true},
+		{"https://my.server:10000000/myuser", nil, true},
+		{"myserver:1000", nil, true},
+		{"http://:1000/mybucket", nil, true},
+		{"https://147.75.201.93:90000/", nil, true},
+		{"http:/play", nil, true},
+	}
+
+	for _, testCase := range testCases {
+		testCase := testCase
+		t.Run(testCase.s, func(t *testing.T) {
+			url, err := ParseHTTPURL(testCase.s)
+			expectErr := (err != nil)
+			if expectErr != testCase.expectErr {
+				t.Fatalf("error: expected: %v, got: %v", testCase.expectErr, expectErr)
+			}
+			if !testCase.expectErr {
+				if !reflect.DeepEqual(url, testCase.expectedURL) {
+					t.Fatalf("host: expected: %#v, got: %#v", testCase.expectedURL, url)
+				}
+			}
+		})
+	}
+}
+
 func TestParseURL(t *testing.T) {
 	testCases := []struct {
 		s           string