Cowboy2静态文件处理器：能否修改浏览器下载文件名？

Yes, absolutely! You can control the filename that browsers see when downloading static files in Cowboy2, and also fix the unwanted .dms suffix issue. Here's how to do it:

Why the .dms Suffix Appears #

First, let's address the .dms problem: this usually happens when Cowboy serves a file with a generic application/octet-stream Content-Type header. Browsers (especially older Safari versions) may not recognize this type and append .dms as a default extension. Fixing this requires setting the correct Content-Type for your files.

Approach 1: Configure Cowboy's Built-in Static Handler #

Cowboy's cowboy_static module allows you to customize headers like Content-Disposition (which controls the download filename) and Content-Type via callback functions. Here's a sample route configuration:

{"/static/[...]", cowboy_static, [
    {directory, {priv_dir, your_app_name, "static"}},
    % Customize Content-Type to avoid .dms suffix
    {content_type, fun(_Req, Path) ->
        case filename:basename(Path) of
            "123" -> <<"text/plain">>; % Set correct type for your file
            % Fallback to Cowboy's default mimetype detection for other files
            _ -> cowboy_mimetypes:all(_Req, Path)
        end
    end},
    % Set custom download filename
    {content_disposition, fun(_Req, Path) ->
        case filename:basename(Path) of
            "123" -> {attachment, "123.txt"}; % Specify desired filename
            % For other files, use inline display or default attachment
            _ -> inline
        end
    end}
]}

Key Details: #

• {content_disposition, Fun}: The function returns either inline (display in browser), attachment (download with original filename), or {attachment, DesiredFilename} (download with custom name).
• content_type callback: Ensures the browser recognizes the file type, eliminating the .dms guesswork.

Approach 2: Create a Custom Handler for Full Control #

If you need more flexibility (like dynamic filename mappings or additional logic), build a custom handler module:

-module(custom_file_handler).
-export([init/2]).

init(Req0, State) ->
    % Get the requested path
    Path = cowboy_req:path(Req0),
    DiskFilePath = filename:join([code:priv_dir(your_app_name), "static", filename:basename(Path)]),
    
    case file:read_file_info(DiskFilePath) of
        {ok, _FileInfo} ->
            % Map disk filename to desired download name
            DisplayFilename = case filename:basename(DiskFilePath) of
                "123" -> "123.txt";
                % Add more mappings here as needed
                Other -> Other
            end,
            
            % Set correct Content-Type based on display filename
            ContentType = case DisplayFilename of
                "123.txt" -> <<"text/plain">>;
                _ -> cowboy_mimetypes:all(Req0, DisplayFilename)
            end,
            
            % Set response headers
            Req1 = cowboy_req:set_resp_header(<<"content-type">>, ContentType, Req0),
            Req2 = cowboy_req:set_resp_header(<<"content-disposition">>, 
                <<"attachment; filename=\"", DisplayFilename/binary, "\"">>, Req1),
            
            % Send the file to the client
            cowboy_req:reply(200, [], {sendfile, 0, 0, DiskFilePath}, Req2, State);
        
        {error, enoent} ->
            % Handle missing files
            cowboy_req:reply(404, [], <<"File not found">>, Req0, State)
    end.

Then add this handler to your route list:

{"/custom-files/[...]", custom_file_handler, []}

Testing the Solution #

After updating your configuration or adding the custom handler:

1. Start your Cowboy server.
2. Navigate to the file URL (e.g., http://your-server/static/123).
3. The browser should download the file as 123.txt without the .dms suffix.

内容的提问来源于stack exchange，提问作者Andriy Drozdyuk