Send SMS via the user's default messaging app — a Mob plugin.

Both platforms show a pre-filled composer sheet. The user taps Send inside the system messaging UI for anything to actually go out; the plugin can neither send silently nor bypass the confirmation. This is the sanctioned cross-platform path for "let my app compose an SMS" (invite codes, share a link, tell-a-friend, verification workaround) and requires no permission dialog on either platform.

Usage

MobSms.compose(socket, to: "+15551234567", body: "Join me: https://example.com/i/ABC")

Both :to and :body are optional. Omit :to to let the user pick a recipient from Contacts inside the composer. Omit :body if you want the user to type from scratch (rare — the point of the plugin is usually to seed the message).

Result arrives asynchronously as a message to the calling process:

handle_info({:sms, :sent},             socket)
handle_info({:sms, :cancelled},        socket)
handle_info({:sms, :composer_opened},  socket)
handle_info({:sms, :not_available},    socket)

Per-platform delivery — the asymmetry to know

• iOS — MFMessageComposeViewController is presented as a sheet inside your app. The system delegate reports :sent, :cancelled, or :failed reliably. :not_available is delivered on a device that cannot send SMS (simulator, no cellular / iMessage capability, no SIM).

• Android — Intent.ACTION_SENDTO with smsto: opens the user's default SMS app externally. Android does not reliably tell the host app whether the user tapped Send or cancelled — most SMS apps do not set an activity result. The plugin delivers :composer_opened once the composer is showing (or :not_available if no SMS-capable app is installed) and stops there. If knowing what the user did afterwards matters to your flow, plan around this asymmetry rather than assuming a :sent.

This asymmetry is by design at the platform layer, not something the plugin can paper over — Android intentionally hands the user off to a separate app rather than embedding a sheet.

What the plugin is NOT

Not a silent-send mechanism. iOS has no public API for sending SMS without the user tapping Send; Apple treats that as a bright-line spam surface. Android can do silent send via SmsManager.sendTextMessage under the SEND_SMS runtime permission, but Google Play rejects that permission request for most non-SMS-centric apps (the "Permissions Declaration" gate). If the user has a real reason to bypass the sheet on Android — and can accept iOS being permanently in composer mode — a separate send/2 on this module can land in a later release.