add TrimPrefix, ToUpper, and ToLower template funcs

We need TrimPrefix and ToUpper for some links at Tailscale, and might as
well ToLower as well at that point.

Updates #10

Change-Id: Ia101a4a3005adb9118051b3416f5a64a4a45987d
Signed-off-by: Will Norris <[email protected]>

Author: willnorris

golink.go

@@ -651,7 +651,10 @@ func (e expandEnv) User() (string, error) {
 var expandFuncMap = texttemplate.FuncMap{
 	"PathEscape":  url.PathEscape,
 	"QueryEscape": url.QueryEscape,
+	"TrimPrefix":  strings.TrimPrefix,
 	"TrimSuffix":  strings.TrimSuffix,
+	"ToLower":     strings.ToLower,
+	"ToUpper":     strings.ToUpper,
 	"Match":       regexMatch,
 }
 

golink_test.go

@@ -411,12 +411,30 @@ func TestExpandLink(t *testing.T) {
 			remainder: "a/b+c",
 			want:      "http://host.com/a%2Fb%2Bc",
 		},
+		{
+			name:      "template-with-trimprefix-func",
+			long:      `http://host.com/{{TrimPrefix .Path "BUG-"}}`,
+			remainder: "BUG-123",
+			want:      "http://host.com/123",
+		},
 		{
 			name:      "template-with-trimsuffix-func",
 			long:      `http://host.com/{{TrimSuffix .Path "/"}}`,
 			remainder: "a/",
 			want:      "http://host.com/a",
 		},
+		{
+			name:      "template-with-tolower-func",
+			long:      `http://host.com/{{ToLower .Path}}`,
+			remainder: "BUG-123",
+			want:      "http://host.com/bug-123",
+		},
+		{
+			name:      "template-with-toupper-func",
+			long:      `http://host.com/{{ToUpper .Path}}`,
+			remainder: "bug-123",
+			want:      "http://host.com/BUG-123",
+		},
 		{
 			name:      "template-with-match-func",
 			long:      `http://host.com/{{if Match "\\d+" .Path}}id/{{.Path}}{{else}}search/{{.Path}}{{end}}`,

tmpl/help.html

@@ -63,7 +63,10 @@ <h2 id="advanced">Advanced destination links</h2>
 <ul>
   <li><code>PathEscape</code> is the <a href="https://pkg.go.dev/net/url#PathEscape">url.PathEscape</a> function for escaping values inside a URL path.
   <li><code>QueryEscape</code> is the <a href="https://pkg.go.dev/net/url#QueryEscape">url.QueryEscape</a> function for escaping values inside a URL query.
+  <li><code>TrimPrefix</code> is the <a href="https://pkg.go.dev/strings#TrimPrefix">strings.TrimPrefix</a> function for removing a leading prefix.
   <li><code>TrimSuffix</code> is the <a href="https://pkg.go.dev/strings#TrimSuffix">strings.TrimSuffix</a> function for removing a trailing suffix.
+  <li><code>ToLower</code> is the <a href="https://pkg.go.dev/strings#ToLower">strings.ToLower</a> function for mapping all Unicode letters to their lower case.
+  <li><code>ToUpper</code> is the <a href="https://pkg.go.dev/strings#ToUpper">strings.ToUpper</a> function for mapping all Unicode letters to their upper case.
   <li><code>Match</code> is the <a href="https://pkg.go.dev/regexp#MatchString">regexp.MatchString</a> function for matching a regular expression pattern.
 </ul>