Make downloadText work on native

src/app/components/KeyDownload.svelte

@@ -39,7 +39,7 @@
       .replace(/NEWLINE/g, "\n\n")
       .trim()
 
-  const downloadKey = () => {
+  const downloadKey = async () => {
     const sharedCopy = `
     Most online services keep track of users by giving them a username and password. This gives the
     service total control over their users, allowing them to ban them at any time, or sell their activity.
@@ -52,6 +52,8 @@
     account.
     `
 
+    let instructions: string
+
     if (usePassword) {
       if (password.length < 12) {
         return pushToast({
@@ -61,7 +63,7 @@
       }
 
       const ncryptsec = encrypt(hexToBytes(secret), password)
-      const instructions = `
+      instructions = `
       This file contains a backup of your Nostr secret key, downloaded from ${PLATFORM_NAME} and encrypted using
       a password you chose when you signed up.
 
@@ -74,11 +76,9 @@
       To use it to log in to other Nostr apps, find a Nostr Signer app (https://nostrapps.com/#signers is a good
       place to look), and import your key.
       `
-
-      downloadText("Nostr Secret Key.txt", cleanupCopy(instructions))
     } else {
       const nsec = nsecEncode(hexToBytes(secret))
-      const instructions = `
+      instructions = `
       This file contains a backup of your Nostr secret key, downloaded from ${PLATFORM_NAME}.
 
       ${sharedCopy}
@@ -90,11 +90,23 @@
       To use it to log in to other Nostr apps, find a Nostr Signer app (https://nostrapps.com/#signers is a good
       place to look), and import your key.
       `
-
-      downloadText("Nostr Secret Key.txt", cleanupCopy(instructions))
     }
 
-    didDownload = true
+    try {
+      await downloadText("Nostr Secret Key.txt", cleanupCopy(instructions))
+
+      didDownload = true
+    } catch (e) {
+      // Dismissing the native share sheet rejects with "Share canceled" — leave
+      // the flow gated so the user can try again rather than showing an error.
+      if (
+        !String((e as any)?.message || e)
+          .toLowerCase()
+          .includes("cancel")
+      ) {
+        pushToast({theme: "error", message: "We couldn't save your key. Please try again."})
+      }
+    }
   }
 
   const onPasswordChange = () => {

src/lib/html.ts

@@ -1,4 +1,5 @@
 import {sleep, randomId} from "@welshman/lib"
+import {Capacitor} from "@capacitor/core"
 export {preventDefault, stopPropagation} from "svelte/legacy"
 
 // Anchors an @svelte-plugins/datepicker popup with fixed positioning so it
@@ -127,7 +128,28 @@ export const createScroller = ({
 
 export const isMobile = "ontouchstart" in document.documentElement
 
-export const downloadText = (filename: string, text: string) => {
+export const downloadText = async (filename: string, text: string) => {
+  // The <a download> blob trick is a no-op in native WebViews (Android in
+  // particular never triggers a download), so on device we write the file and
+  // hand it to the native share sheet, letting the user save it to Files,
+  // Drive, a password manager, etc. Cache is the directory our FileProvider
+  // (android/app/src/main/res/xml/file_paths.xml) is configured to serve.
+  if (Capacitor.isNativePlatform()) {
+    const {Filesystem, Directory, Encoding} = await import("@capacitor/filesystem")
+    const {Share} = await import("@capacitor/share")
+
+    const {uri} = await Filesystem.writeFile({
+      path: filename,
+      data: text,
+      directory: Directory.Cache,
+      encoding: Encoding.UTF8,
+    })
+
+    await Share.share({title: filename, files: [uri]})
+
+    return
+  }
+
   const blob = new Blob([text], {type: "text/plain"})
   const url = URL.createObjectURL(blob)
   const a = document.createElement("a")