Answer keyring and GPG prompts

gnome-keyring and pinentry-gnome3 ask a prompter service on the session bus for passphrases and confirmations. Gnoblin can serve them and publish each one as an event. Your config or shell shows the prompt and returns the answer.

This is off by default. Turn it on with gnoblin.configure.prompts:

gnoblin.configure {
    prompts = {enabled = true},
}

Write a handler first. A prompt that nothing answers is cancelled after 120 seconds.

Answer a prompt from Lua

This config uses zenity to ask for a password or a yes or no answer. For a password prompt, zenity --password prints the password to standard output. For a confirmation, zenity --question reports the answer in its exit status. When the prompt window opens, window:present() gives it keyboard focus, so you can type the password without clicking it first.

local prompts = {}

local function text(value, fallback)
    if value == nil or value == "" then
        return fallback
    end
    return value
end

-- Focus the window of a running prompt program.
gnoblin.on("gnoblin.window.created", function(event)
    if prompts[event.window.process] then
        event.window:present()
    end
end)

local function ask(argv, options, answer)
    local prompt = gnoblin.process.spawn(argv, options)
    prompts[prompt.id] = true
    prompt:wait():on_complete(function(exit, err)
        prompts[prompt.id] = nil
        answer(exit, err)
    end)
end

gnoblin.on("gnoblin.prompt.requested", function(event)
    local request = event.request
    local title = text(request.title, "Passphrase")
    local message = text(request.message, title)

    if request.kind == "password" then
        ask({"zenity", "--password", "--title", message}, {stdout = "capture"}, function(exit, err)
            if err or exit.exit_code ~= 0 then
                request:cancel()
                return
            end
            request:answer((exit.stdout:gsub("\n$", "")))
        end)
        return
    end

    ask({"zenity", "--question", "--title", title, "--text", message}, nil, function(exit, err)
        if err or exit.signal then
            request:cancel()
            return
        end
        request:answer(exit.exit_code == 0)
    end)
end)

Run echo test | gpg --symmetric --output /dev/null in a terminal with pinentry-gnome3 as the pinentry program. The prompt appears, and gpg continues after you enter a passphrase.

The request

gnoblin.prompt.requested carries event.request, a Request. Its kind is "password" when the program needs a password, or "confirm" when it needs a yes or no answer. Its fields:

• id: the same for the prompt's events. Gnoblin does not reuse it while it runs.
• title, message, description and warning: text for the user. Any of them can be an empty string.
• password_new: true when the user chooses a new password. Ask for it twice if your prompt program supports it.
• choice_label: the text of an optional checkbox, for example "Automatically unlock this keyring". It is an empty string when there is no checkbox.
• caller_window: the window of the program that asked, in the form the program gave it, or an empty string.
• continue_label and cancel_label: the preferred button texts, or empty strings.

choice is the state of the checkbox that choice_label describes.

The outcome is one of these values:

• "answered": the request got an answer.
• "cancelled": the prompt was cancelled, or the program withdrew it.
• "timeout": nothing answered in 120 seconds.

gnoblin.prompt.finished reports the same outcome as result.

Limits

• Each prompt waits up to 120 seconds for an answer.
• At most 8 prompts wait at the same time. Extra prompts are cancelled.
• Gnoblin cancels every waiting prompt when prompts.enabled becomes false or when the session ends. A prompt that arrives while the Lua runtime is not ready is cancelled at once.
• gcr-prompter must not own the bus names. If it does, the prompt-broker capability is unavailable with the reason name_unavailable. The reason is prompts_disabled while the setting is off. Check it with gnoblinctl capabilities.

Handle the password with care

Gnoblin keeps the password in secure memory while it holds it and wipes that copy when the prompt ends. The password also passes through the Lua runtime, and Lua strings are not wiped.

• Do not log the password or the prompt program's stdout.
• Do not put a password in argv. Other users can read command lines.
• A prompt program that prints the password to standard output keeps it off the command line.
• A keyring password unlocks stored secrets. Show the prompt only for requests that come from your own session.

Answer from a shell process

A shell that connects to the compositor bridge needs API version 1.79 or later. It subscribes to the gnoblin.prompt.* events and answers with these methods, each with request_id:

• prompt.respond, with password or confirmed and optional choice.
• prompt.cancel.

Only a client that received gnoblin.prompt.requested can answer that prompt.