brokenlinks: fix generating relative URL

If the parent URL end with .html or .htm, join the directory of parent
instead of the current path with the relative path.

2 files changed, 59 insertions, 1 deletions

diff --git a/brokenlinks/worker.go b/brokenlinks/worker.go
index 3e089fc..7683730 100644
--- a/brokenlinks/worker.go
+++ b/brokenlinks/worker.go
@@ -12,6 +12,7 @@ import (
 	"net/http"
 	"net/url"
 	"os"
+	"path"
 	"slices"
 	"strings"
 	"time"
@@ -396,7 +397,7 @@ func (wrk *worker) processLink(parentUrl *url.URL, val string, kind int) (
 			newUrl = wrk.baseUrl.JoinPath(newUrl.Path)
 		} else {
 			// val is relative to parent URL.
-			newUrl = parentUrl.JoinPath(`/`, newUrl.Path)
+			newUrl = genURLRelative(parentUrl, newUrl.Path)
 		}
 	}
 	linkq.Url = strings.TrimSuffix(newUrl.String(), `/`)
@@ -405,3 +406,16 @@ func (wrk *worker) processLink(parentUrl *url.URL, val string, kind int) (
 	}
 	return linkq
 }
+
+// genURLRelative generate new URL from parent URL and relative path
+// `relPath`.
+func genURLRelative(parentUrl *url.URL, relPath string) (newUrl *url.URL) {
+	var parentPath = parentUrl.Path
+	var ext = strings.ToLower(path.Ext(parentPath))
+	if ext == `.html` || ext == `.htm` {
+		parentPath = path.Dir(parentPath)
+	}
+	newUrl, _ = url.Parse(parentUrl.String())
+	newUrl.Path = path.Join(parentPath, relPath)
+	return newUrl
+}
diff --git a/brokenlinks/worker_test.go b/brokenlinks/worker_test.go
new file mode 100644
index 0000000..2867338
--- /dev/null
+++ b/brokenlinks/worker_test.go
@@ -0,0 +1,44 @@
+// SPDX-License-Identifier: GPL-3.0-only
+// SPDX-FileCopyrightText: 2026 M. Shulhan <ms@kilabit.info>
+
+package brokenlinks
+
+import (
+	"net/url"
+	"testing"
+
+	"git.sr.ht/~shulhan/pakakeh.go/lib/test"
+)
+
+func TestGenURLRelative(t *testing.T) {
+	listCase := []struct {
+		parentURL string
+		relPath   string
+		expURL    string
+	}{{
+		parentURL: `https://domain/a/b/`,
+		relPath:   `c`,
+		expURL:    `https://domain/a/b/c`,
+	}, {
+		parentURL: `https://domain/a/b`,
+		relPath:   `c`,
+		expURL:    `https://domain/a/b/c`,
+	}, {
+		parentURL: `https://domain/a/b/page.html`,
+		relPath:   `c`,
+		expURL:    `https://domain/a/b/c`,
+	}, {
+		parentURL: `https://domain/a/b/page.htm`,
+		relPath:   `c`,
+		expURL:    `https://domain/a/b/c`,
+	}, {
+		parentURL: `https://domain/a/b/page.HTML`,
+		relPath:   `c`,
+		expURL:    `https://domain/a/b/c`,
+	}}
+	for _, tc := range listCase {
+		parentURL, _ := url.Parse(tc.parentURL)
+		got := genURLRelative(parentURL, tc.relPath)
+		test.Assert(t, ``, tc.expURL, got.String())
+	}
+}