net/url: add Values.Has

Adds a method within Values for detecting whether a query parameter is set.

Fixes #45100

Change-Id: I6bb49417e8547e11cc7e8d55c5211d24ee436ec1
GitHub-Last-Rev: 0b27cda
GitHub-Pull-Request: #45835
Reviewed-on: https://go-review.googlesource.com/c/go/+/314850
Run-TryBot: Ian Lance Taylor <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
Trust: Cherry Zhang <[email protected]>

Author: iann0036

src/net/url/url.go

@@ -909,6 +909,12 @@ func (v Values) Del(key string) {
 	delete(v, key)
 }
 
+// Has checks whether a given key is set.
+func (v Values) Has(key string) bool {
+	_, ok := v[key]
+	return ok
+}
+
 // ParseQuery parses the URL-encoded query string and returns
 // a map listing the values specified for each key.
 // ParseQuery always returns a non-nil map containing all the

src/net/url/url_test.go

@@ -1295,10 +1295,10 @@ func TestResolveReference(t *testing.T) {
 }
 
 func TestQueryValues(t *testing.T) {
-	u, _ := Parse("http://x.com?foo=bar&bar=1&bar=2")
+	u, _ := Parse("http://x.com?foo=bar&bar=1&bar=2&baz")
 	v := u.Query()
-	if len(v) != 2 {
-		t.Errorf("got %d keys in Query values, want 2", len(v))
+	if len(v) != 3 {
+		t.Errorf("got %d keys in Query values, want 3", len(v))
 	}
 	if g, e := v.Get("foo"), "bar"; g != e {
 		t.Errorf("Get(foo) = %q, want %q", g, e)
@@ -1313,6 +1313,18 @@ func TestQueryValues(t *testing.T) {
 	if g, e := v.Get("baz"), ""; g != e {
 		t.Errorf("Get(baz) = %q, want %q", g, e)
 	}
+	if h, e := v.Has("foo"), true; h != e {
+		t.Errorf("Has(foo) = %t, want %t", h, e)
+	}
+	if h, e := v.Has("bar"), true; h != e {
+		t.Errorf("Has(bar) = %t, want %t", h, e)
+	}
+	if h, e := v.Has("baz"), true; h != e {
+		t.Errorf("Has(baz) = %t, want %t", h, e)
+	}
+	if h, e := v.Has("noexist"), false; h != e {
+		t.Errorf("Has(noexist) = %t, want %t", h, e)
+	}
 	v.Del("bar")
 	if g, e := v.Get("bar"), ""; g != e {
 		t.Errorf("second Get(bar) = %q, want %q", g, e)