pkg/html: split off URL helpers

The existing pkg/html package transitively takes too many dependencies,
which complicates the reuse of some of its methods.

Split off a pkg/html/urlutil package.

2 files changed, 105 insertions, 0 deletions

diff --git a/pkg/html/urlutil/urls.go b/pkg/html/urlutil/urls.go
new file mode 100644
index 000000000..42ab505c8
--- /dev/null
+++ b/pkg/html/urlutil/urls.go
@@ -0,0 +1,56 @@
+// Copyright 2025 syzkaller project authors. All rights reserved.
+// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
+
+package urlutil
+
+import "net/url"
+
+// SetParam overrides the specific key from the URL.
+// It does not take into account that there may be multiple parameters with the same name.
+func SetParam(baseURL, key, value string) string {
+	return TransformParam(baseURL, key, func(_ []string) []string {
+		if value == "" {
+			return nil
+		}
+		return []string{value}
+	})
+}
+
+// DropParam removes the specific key=value pair from the URL
+// (it's possible to have many of parameters with the same name).
+// Set value="" to remove the key regardless of the value.
+func DropParam(baseURL, key, value string) string {
+	return TransformParam(baseURL, key, func(oldValues []string) []string {
+		if value == "" {
+			return nil
+		}
+		var newValues []string
+		for _, iterVal := range oldValues {
+			if iterVal != value {
+				newValues = append(newValues, iterVal)
+			}
+		}
+		return newValues
+	})
+}
+
+// TransformParam is a generic method that transforms the set of values
+// for the specified URL parameter key.
+func TransformParam(baseURL, key string, f func([]string) []string) string {
+	if baseURL == "" {
+		return ""
+	}
+	parsed, err := url.Parse(baseURL)
+	if err != nil {
+		return ""
+	}
+	values := parsed.Query()
+	ret := f(values[key])
+	if len(ret) == 0 {
+		values.Del(key)
+	} else {
+		values[key] = ret
+	}
+	parsed.RawQuery = values.Encode()
+	return parsed.String()
+}
diff --git a/pkg/html/urlutil/urls_test.go b/pkg/html/urlutil/urls_test.go
new file mode 100644
index 000000000..a8782c35e
--- /dev/null
+++ b/pkg/html/urlutil/urls_test.go
@@ -0,0 +1,49 @@
+// Copyright 2023 syzkaller project authors. All rights reserved.
+// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
+
+package urlutil
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestDropParam(t *testing.T) {
+	tests := []struct {
+		in    string
+		key   string
+		value string
+		out   string
+	}{
+		{
+			in:    `/upstream?first=a&second=b`,
+			key:   `first`,
+			value: ``,
+			out:   `/upstream?second=b`,
+		},
+		{
+			in:    `/upstream?first=a&first=b&second=c`,
+			key:   `second`,
+			value: ``,
+			out:   `/upstream?first=a&first=b`,
+		},
+		{
+			in:    `/upstream?first=a&first=b&second=c`,
+			key:   `first`,
+			value: ``,
+			out:   `/upstream?second=c`,
+		},
+		{
+			in:    `/upstream?first=a&first=b&second=c`,
+			key:   `first`,
+			value: `b`,
+			out:   `/upstream?first=a&second=c`,
+		},
+	}
+
+	for _, test := range tests {
+		got := DropParam(test.in, test.key, test.value)
+		assert.Equal(t, test.out, got)
+	}
+}