Expose and fix bug with assumption of removable 2-char prefix, seemingly meant for ./ (#1345)

Author: rsheeter

server/router.go

@@ -1304,7 +1304,7 @@ func esmRouter(esmStorage storage.Storage, logger *log.Logger) rex.Handle {
 		}
 
 		if buildMeta.CSSEntry != "" {
-			url := strings.Join([]string{origin, esmPath.PackageId(), buildMeta.CSSEntry[2:]}, "/")
+			url := getCSSEntryRedirectURL(origin, esmPath, buildMeta.CSSEntry)			
 			return redirect(ctx, url, isExactVersion)
 		}
 
@@ -1617,3 +1617,7 @@ func errorJS(ctx *rex.Context, message string) any {
 	ctx.SetHeader("Cache-Control", ccImmutable)
 	return buf.Bytes()
 }
+
+func getCSSEntryRedirectURL(origin string, esmPath EsmPath, cssEntry string) string {
+	return origin + "/" + esmPath.PackageId() + utils.NormalizePathname(cssEntry)
+}

server/router_test.go

@@ -0,0 +1,35 @@
+package server
+
+import (
+	"testing"
+)
+
+func TestCSSEntryRedirectURL(t *testing.T) {
+	origin := "https://esm.sh"
+	esmPath := EsmPath{
+		PkgName:    "@material/web",
+		PkgVersion: "2.4.2-nightly.95dd57c.0",
+	}
+
+	tests := []struct {
+		cssEntry string
+		expected string
+	}{
+		{
+			cssEntry: "./labs/gb/components/ripple/ripple.css",
+			expected: "https://esm.sh/@material/web@2.4.2-nightly.95dd57c.0/labs/gb/components/ripple/ripple.css",
+		},
+		{
+			cssEntry: "labs/gb/components/ripple/ripple.css",
+			expected: "https://esm.sh/@material/web@2.4.2-nightly.95dd57c.0/labs/gb/components/ripple/ripple.css",
+		},
+	}
+
+	for _, test := range tests {
+		// Calling the actual helper function from router.go
+		url := getCSSEntryRedirectURL(origin, esmPath, test.cssEntry)
+		if url != test.expected {
+			t.Errorf("For CSSEntry %q, expected %q, but got %q", test.cssEntry, test.expected, url)
+		}
+	}
+}