Add "append block children" endpoint support

client.go

@@ -261,3 +261,41 @@ func (c *Client) FindBlockChildrenByID(ctx context.Context, blockID string, quer
 
 	return result, nil
 }
+
+// AppendBlockChildren appends child content (blocks) to an existing block.
+// See: https://developers.notion.com/reference/patch-block-children
+func (c *Client) AppendBlockChildren(ctx context.Context, blockID string, children []Block) (block Block, err error) {
+	type PostBody struct {
+		Children []Block `json:"children"`
+	}
+
+	dto := PostBody{children}
+	body := &bytes.Buffer{}
+
+	err = json.NewEncoder(body).Encode(dto)
+	if err != nil {
+		return Block{}, fmt.Errorf("notion: failed to encode body params to JSON: %w", err)
+	}
+
+	req, err := c.newRequest(ctx, http.MethodPatch, fmt.Sprintf("/blocks/%v/children", blockID), body)
+	if err != nil {
+		return Block{}, fmt.Errorf("notion: invalid request: %w", err)
+	}
+
+	res, err := c.httpClient.Do(req)
+	if err != nil {
+		return Block{}, fmt.Errorf("notion: failed to make HTTP request: %w", err)
+	}
+	defer res.Body.Close()
+
+	if res.StatusCode != http.StatusOK {
+		return Block{}, fmt.Errorf("notion: failed to append block children: %w", parseErrorResponse(res))
+	}
+
+	err = json.NewDecoder(res.Body).Decode(&block)
+	if err != nil {
+		return Block{}, fmt.Errorf("notion: failed to parse HTTP response: %w", err)
+	}
+
+	return block, nil
+}