support file picking and uploads on web

crates/nip4e/src/lib.rs

@@ -221,25 +221,38 @@ impl DeviceRegistry {
         cx.emit(DeviceEvent::Set);
     }
 
-    /// Backup the encryption's secret key to a file
-    pub fn backup(&self, path: PathBuf, cx: &App) -> Task<Result<(), Error>> {
+    /// Backup the encryption's secret key, returning the `nsec1...` content
+    pub fn backup_bytes(&self, cx: &App) -> Task<Result<String, Error>> {
         let nostr = NostrRegistry::global(cx);
         let client = nostr.read(cx).client();
         let signer = nostr.read(cx).signer();
 
         cx.background_spawn(async move {
             let keys = get_keys(&client, &signer).await?;
-            let content = keys.secret_key().to_bech32()?;
+            Ok(keys.secret_key().to_bech32()?)
+        })
+    }
 
-            if cfg!(target_arch = "wasm32") {
-                return Err(anyhow!("Not supported"));
-            }
+    /// Backup the encryption's secret key to a file
+    pub fn backup(&self, path: PathBuf, cx: &App) -> Task<Result<(), Error>> {
+        let backup = self.backup_bytes(cx);
 
-            #[cfg(not(target_arch = "wasm32"))]
+        #[cfg(not(target_arch = "wasm32"))]
+        return cx.background_spawn(async move {
+            let content = backup.await?;
             smol::fs::write(path, &content).await?;
 
             Ok(())
-        })
+        });
+
+        #[cfg(target_arch = "wasm32")]
+        {
+            let _ = path;
+            cx.background_spawn(async move {
+                backup.await?;
+                Err(anyhow!("File backups are not supported on web; copy the key from the backup panel instead."))
+            })
+        }
     }
 
     /// Get device announcement for current user