sanitize: naive CSS sanitizer implementation

- CSS sanitizer allows a limited set of properties in a style attribute.
- Added a CSS inlined version of the tutsplus responsive test mail.
- Linter fixes in inbucket.go

sanitize/html_test.go

@@ -35,6 +35,7 @@ func TestHTMLSimpleFormatting(t *testing.T) {
 		"<em>emphasis</em>",
 		"<strong>strong</strong>",
 		"<div><span>text</span></div>",
+		"<center>text</center>",
 	}
 	for _, ts := range testStrings {
 		t.Run(ts, func(t *testing.T) {
@@ -75,3 +76,96 @@ func TestHTMLScriptTags(t *testing.T) {
 		})
 	}
 }
+
+func TestSanitizeStyleTags(t *testing.T) {
+	testCases := []struct {
+		name, input, want string
+	}{
+		{
+			"empty",
+			``,
+			``,
+		},
+		{
+			"open",
+			`<div>`,
+			`<div>`,
+		},
+		{
+			"open close",
+			`<div></div>`,
+			`<div></div>`,
+		},
+		{
+			"inner text",
+			`<div>foo bar</div>`,
+			`<div>foo bar</div>`,
+		},
+		{
+			"self close",
+			`<br/>`,
+			`<br/>`,
+		},
+		{
+			"open params",
+			`<div id="me">`,
+			`<div id="me">`,
+		},
+		{
+			"open params squote",
+			`<div id="me" title='best'>`,
+			`<div id="me" title="best">`,
+		},
+		{
+			"open style",
+			`<div id="me" style="color: red;">`,
+			`<div id="me" style="color: red;">`,
+		},
+		{
+			"open style squote",
+			`<div id="me" style='color: red;'>`,
+			`<div id="me" style="color: red;">`,
+		},
+		{
+			"open style mixed case",
+			`<div id="me" StYlE="color: red;">`,
+			`<div id="me" style="color: red;">`,
+		},
+		{
+			"closed style",
+			`<br style="border: 1px solid red;"/>`,
+			`<br style="border: 1px solid red;"/>`,
+		},
+		{
+			"mixed case style",
+			`<br StYlE="border: 1px solid red;"/>`,
+			`<br style="border: 1px solid red;"/>`,
+		},
+		{
+			"mixed case invalid style",
+			`<br StYlE="position: fixed;"/>`,
+			`<br/>`,
+		},
+		{
+			"mixed",
+			`<p id='i' title="cla'zz" style="font-size: 25px;"><b>some text</b></p>`,
+			`<p id="i" title="cla&#39;zz" style="font-size: 25px;"><b>some text</b></p>`,
+		},
+		{
+			"invalid styles",
+			`<div id="me" style='position: absolute;'>`,
+			`<div id="me">`,
+		},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			got, err := sanitize.HTML(tc.input)
+			if err != nil {
+				t.Fatal(err)
+			}
+			if got != tc.want {
+				t.Errorf("input: %s\ngot : %s\nwant: %s", tc.input, got, tc.want)
+			}
+		})
+	}
+}