api: add init_transports() for multi-relay onboarding

Closes #8693 and supsersedes #8707 from which the API
and some overall shape of this commit is inspired.

UIs call `init_transports(None)` or `init_transports(qr)`
to initialize a first transport on the fresh profile,
with more transports added in the background later.

deltachat-jsonrpc/src/api.rs

@@ -546,6 +546,18 @@ impl CommandApi {
         ctx.add_transport_from_qr(&qr).await
     }
 
+    /// Adds an initial transport on a randomly chosen chatmail relay
+    /// and lets the profile add further ones in the background.
+    ///
+    /// A `DCACCOUNT:` or `DCLOGIN:` `qr` code adds a single transport
+    /// while securejoin codes add the inviter's relays to the candidates.
+    ///
+    /// Does nothing if the profile already has a transport.
+    async fn init_transports(&self, account_id: u32, qr: Option<String>) -> Result<()> {
+        let ctx = self.get_context(account_id).await?;
+        ctx.init_transports(qr.as_deref()).await
+    }
+
     /// Returns the list of all email accounts that are used as a transport in the current profile.
     /// Use [Self::add_or_update_transport()] to add or change a transport
     /// and [Self::delete_transport()] to remove a transport.

deltachat-rpc-client/src/deltachat_rpc_client/account.py

@@ -139,6 +139,18 @@ class Account:
         """Add a new transport using a QR code."""
         yield self._rpc.add_transport_from_qr.future(self.id, qr)
 
+    @futuremethod
+    def init_transports(self, qr: Optional[str] = None):
+        """Add an initial transport on a randomly chosen chatmail relay.
+
+        The profile then adds further ones in the background.
+        A ``DCACCOUNT:`` or ``DCLOGIN:`` ``qr`` code adds a single transport
+        while securejoin codes add the inviter's relays to the candidates.
+
+        Does nothing if the profile already has a transport.
+        """
+        yield self._rpc.init_transports.future(self.id, qr)
+
     def delete_transport(self, addr: str):
         """Delete a transport."""
         self._rpc.delete_transport(self.id, addr)

deltachat-rpc-client/tests/test_multitransport.py

@@ -24,6 +24,12 @@ def wait_for_imap_message(imap):
         time.sleep(1)
 
 
+def test_init_transports(acf):
+    account = acf.get_unconfigured_account()
+    account.init_transports(acf.get_account_qr())
+    assert len(account.list_transports()) == 1
+
+
 def test_add_second_address(acf) -> None:
     account = acf.new_configured_account()
     assert len(account.list_transports()) == 1

docs/schema.sql

@@ -630,9 +630,12 @@ CREATE TABLE broadcast_secrets(
 
 
 -- Candidate chatmail relays for automatic relay management.
+-- Holds the hosts a QR code contributed and the default relays already tried;
+-- the default list itself lives in `autorelay.rs` and is not stored here.
 CREATE TABLE relay_candidates(
     host TEXT PRIMARY KEY NOT NULL,
-    last_tried INTEGER NOT NULL DEFAULT 0 -- Timestamp of the last connection attempt.
+    -- Timestamp of the last connection attempt, 0 if the host was never tried.
+    last_tried INTEGER NOT NULL DEFAULT 0
 ) STRICT;
 
 CREATE TABLE transports (

src/autorelay.rs

@@ -1,29 +1,22 @@
-//! # Automatic relay handling (experimental, still in development)
+//! # Automatic multi-relay onboarding
 //!
-//! Chatmail relays create an account on first login,
-//! so a profile can add further transports on its own without user interaction.
-//! Candidate hosts come from the `relay_candidates` table,
-//! which migrations seed with a list of known chatmail relays.
-//!
-//! Status of implementation:
-//! Additions are attempted right before going into IMAP IDLE,
-//! i.e. only while connected and with nothing more important to do,
-//! and only if a UI opted in via [`Config::Autorelay`].
-//! Once a profile has reached `NUM_TRANSPORTS_TARGET` transports,
-//! [`Config::AutorelayFinished`] is set and nothing is ever added again,
-//! so deleting a transport later does not pull in a replacement.
+//! Support for automatically onboarding a profile on transport
+//! candidates without the user choosing a relay.
 
+use std::collections::BTreeMap;
 use std::pin::Pin;
 
-use anyhow::Result;
+use anyhow::{Result, format_err};
 use deltachat_contact_tools::addr_normalize;
 use rand::distr::{Alphanumeric, SampleString};
-use rand::seq::IndexedRandom;
+use rand::seq::{IndexedRandom, SliceRandom};
+use rusqlite::Transaction;
 
 use crate::config::{self, Config};
+use crate::configure::{EnteredLoginParam, configure};
 use crate::log::{LogExt, warn};
 use crate::login_param::{EnteredCertificateChecks, EnteredImapLoginParam};
-use crate::{configure::EnteredLoginParam, context::Context, tools::time};
+use crate::{context::Context, tools::time};
 
 /// The target number of transports.
 const NUM_TRANSPORTS_TARGET: usize = 3;
@@ -32,6 +25,65 @@ const AUTOMATIC_ADDITION_DEBOUNCE_SECONDS: i64 = 60 * 60; // one hour
 /// How long we ignore a relay candidate after failing to connect to it:
 const BACKOFF_PERIOD_FOR_NOT_WORKING_RELAY: i64 = 60 * 60 * 24 * 7; // one week
 
+/// Sorted relay list a profile can attempt to onboard on without the user choosing one.
+const DEFAULT_RELAY_CANDIDATES: &[&str] = &[
+    "chat.adminforge.de", // iroh relay 404s
+    "chat.me.ke",
+    "chat.nuvon.app",
+    "chat.tinydispatch.org",
+    "chat.vim.wtf",
+    "chatmail.uk",
+    "chtml.ca",
+    "deltachat.me",
+    "e2e.sus.fr",
+    "e2ee.wang",
+    "mailchat.pl",
+    "nchrcht.la10cy.net",
+    "nine.testrun.org",
+    "sweetfern.net",
+    "tarpit.fun",
+];
+
+/// Records the hosts of `addrs` as relay candidates.
+pub(crate) async fn add_relay_candidates(context: &Context, addrs: &[String]) -> Result<()> {
+    context
+        .sql
+        .transaction(|tx| hosts_of(addrs).try_for_each(|host| save_relay_candidate(tx, host, 0)))
+        .await
+}
+
+/// Adds a first transport on the relay candidate that answers fastest.
+///
+/// All candidates are probed at once with a TCP connection to their HTTPS port
+/// and configured in the order in which the connections complete,
+/// stopping at the first success. Candidates that fail the probe are skipped.
+pub(crate) async fn add_transport_from_candidates(
+    context: &Context,
+    skip_network: bool,
+) -> Result<()> {
+    let mut candidates = triable_relay_candidates(context, time()).await?;
+    candidates.shuffle(&mut rand::rng());
+    let mut last_err = format_err!("No relay candidates");
+
+    // We patiently try each candidate in turn which might take a while
+    // if many hosts are unreachable but eventually succeeds if one candidate works.
+    let mark_as_autorelay = true;
+    for host in &candidates {
+        let param = login_param_from_host(host, mark_as_autorelay);
+        match configure(context, &param, skip_network).await {
+            Ok(()) => {
+                info!(context, "Added a transport on relay {host}.");
+                return Ok(());
+            }
+            Err(err) => {
+                warn!(context, "Failed to add relay {host}: {err:#}.");
+                last_err = err;
+            }
+        }
+    }
+    Err(last_err)
+}
+
 pub(crate) fn maybe_add_additional_relays(
     context: Context,
 ) -> Pin<Box<dyn Future<Output = ()> + Send>> {
@@ -93,10 +145,7 @@ async fn maybe_add_additional_relays_inner(context: &Context, skip_network: bool
             return Ok(relay_added);
         }
 
-        // First, query all candidates that were not tried since `BACKOFF_PERIOD_FOR_NOT_WORKING_RELAY` seconds.
-        // Hosts that are already used are excluded.
-        let candidates = load_relay_candidates(context, now).await?;
-
+        let candidates = triable_relay_candidates(context, now).await?;
         let Some(host) = candidates.choose(&mut rand::rng()) else {
             info!(
                 context,
@@ -113,14 +162,11 @@ async fn maybe_add_additional_relays_inner(context: &Context, skip_network: bool
 
         context
             .sql
-            .execute(
-                "UPDATE relay_candidates SET last_tried=? WHERE host=?",
-                (now, host),
-            )
+            .transaction(|tx| save_relay_candidate(tx, host, now))
             .await?;
         let mark_as_autorelay = true;
         let param = login_param_from_host(host, mark_as_autorelay);
-        let res = crate::configure::configure(context, &param, skip_network).await;
+        let res = configure(context, &param, skip_network).await;
         if let Err(e) = res {
             warn!(
                 context,
@@ -135,30 +181,49 @@ async fn maybe_add_additional_relays_inner(context: &Context, skip_network: bool
     Ok(relay_added)
 }
 
-async fn load_relay_candidates(context: &Context, now: i64) -> Result<Vec<String>, anyhow::Error> {
+async fn triable_relay_candidates(context: &Context, now: i64) -> Result<Vec<String>> {
     let cutoff_timestamp = now.saturating_sub(BACKOFF_PERIOD_FOR_NOT_WORKING_RELAY);
-    let candidates: Vec<String> = context
+    let mut last_tried: BTreeMap<String, i64> = context
         .sql
-        .query_map_vec(
-            // This also selects candidates which have last_tried in the future,
-            // essentially treating them as never tried,
-            // so if some timestamp far in the future is accidentally stored,
-            // we are not stuck never trying the candidate.
-            // After trying the candidate, last_tried will be corrected to the current time.
-            "SELECT host FROM relay_candidates WHERE (last_tried<? OR last_tried>?)
-                AND NOT EXISTS (
-                    SELECT 1
-                    FROM transports
-                    WHERE substr(addr, instr(addr, '@') + 1) = host
-                )",
-            (cutoff_timestamp, now),
-            |row| Ok(row.get::<_, String>(0)?),
-        )
+        .query_map_collect("SELECT host, last_tried FROM relay_candidates", (), |row| {
+            Ok((row.get(0)?, row.get(1)?))
+        })
         .await?;
+    for host in DEFAULT_RELAY_CANDIDATES {
+        last_tried.entry(host.to_string()).or_insert(0);
+    }
+    let self_addrs = context.get_self_addrs().await?;
+    let used_hosts: Vec<&str> = hosts_of(&self_addrs).collect();
+
+    // We also try candidates which have `last_tried` in the future,
+    // which on next failure get `last_tried` reset to the current time.
+    let candidates = last_tried
+        .into_iter()
+        .filter(|(host, last_tried)| {
+            (*last_tried < cutoff_timestamp || *last_tried > now)
+                && !used_hosts.contains(&host.as_str())
+        })
+        .map(|(host, _)| host)
+        .collect();
 
     Ok(candidates)
 }
 
+/// Returns the host of each address in `addrs`.
+fn hosts_of(addrs: &[String]) -> impl Iterator<Item = &str> {
+    addrs.iter().filter_map(|a| Some(a.rsplit_once('@')?.1))
+}
+
+/// Records `host` as a relay candidate, overwriting a stored `last_tried`.
+fn save_relay_candidate(tx: &Transaction, host: &str, last_tried: i64) -> Result<()> {
+    tx.execute(
+        "INSERT INTO relay_candidates (host, last_tried) VALUES (?, ?)
+        ON CONFLICT(host) DO UPDATE SET last_tried=excluded.last_tried",
+        (host, last_tried),
+    )?;
+    Ok(())
+}
+
 pub(crate) fn login_param_from_host(host: &str, mark_as_autorelay: bool) -> EnteredLoginParam {
     let rng = &mut rand::rng();
     let username = Alphanumeric.sample_string(rng, 9);

src/autorelay/autorelay_tests.rs

@@ -1,42 +1,140 @@
 use std::time::Duration;
 
 use super::*;
-use crate::test_utils::TestContext;
+use crate::test_utils::{TestContext, TestContextManager};
 use crate::tools::SystemTime;
 
+/// Tests that the default relays are candidates without a row in the table.
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-async fn test_load_relay_candidates_single() -> Result<()> {
+async fn test_triable_relay_candidates_defaults() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let t = &tcm.unconfigured().await;
+    let now = time();
+
+    assert!(DEFAULT_RELAY_CANDIDATES.is_sorted());
+    let mut candidates = triable_relay_candidates(t, now).await?;
+    candidates.sort();
+    assert_eq!(candidates, DEFAULT_RELAY_CANDIDATES);
+
+    let tried = DEFAULT_RELAY_CANDIDATES[0];
+    save_relay_candidates(t, &[tried], now).await?;
+    let candidates = triable_relay_candidates(t, now).await?;
+    assert_eq!(candidates.len(), DEFAULT_RELAY_CANDIDATES.len() - 1);
+    assert!(!candidates.contains(&tried.to_string()));
+
+    Ok(())
+}
+
+/// Tests that a transport is added on a candidate from the given addresses.
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_add_transport_from_candidates() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let t = &tcm.unconfigured().await;
+    mark_defaults_tried(t, time()).await?;
+    let addrs_from_qr = [
+        "alice@example.org".to_string(),
+        "bob@example.org".to_string(),
+    ];
+    let skip_network = true;
+    add_relay_candidates(t, &addrs_from_qr).await?;
+    add_transport_from_candidates(t, skip_network).await?;
+
+    let transports = t.list_transports().await?;
+    assert_eq!(transports.len(), 1);
+    assert!(transports[0].addr.ends_with("@example.org"));
+    let untried = untried_relay_candidates(t).await?;
+    assert_eq!(untried, ["example.org"]);
+
+    Ok(())
+}
+
+/// Tests correct add_transport_from_candidates error handling.
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_add_transport_from_candidates_failure() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let t = &tcm.unconfigured().await;
+    mark_defaults_tried(t, time()).await?;
+    save_relay_candidates(t, &["bad host", "worse host"], 0).await?;
+
+    let skip_network = false;
+    let err = add_transport_from_candidates(t, skip_network)
+        .await
+        .unwrap_err();
+    assert!(format!("{err:#}").contains("Bad email-address"));
+    assert!(!t.is_configured().await?);
+    let untried = untried_relay_candidates(t).await?;
+    assert_eq!(untried, ["bad host", "worse host"]);
+    t.assert_warns_or_errors(&[
+        "Failed to add relay bad host",
+        "Failed to add relay worse host",
+    ])
+    .await;
+
+    Ok(())
+}
+
+async fn untried_relay_candidates(t: &TestContext) -> Result<Vec<String>> {
+    t.sql
+        .query_map_vec(
+            "SELECT host FROM relay_candidates WHERE last_tried=0 ORDER BY host",
+            (),
+            |row| Ok(row.get(0)?),
+        )
+        .await
+}
+
+async fn save_relay_candidates(t: &TestContext, hosts: &[&str], last_tried: i64) -> Result<()> {
+    t.sql
+        .transaction(|tx| {
+            for host in hosts {
+                save_relay_candidate(tx, host, last_tried)?;
+            }
+            Ok(())
+        })
+        .await
+}
+
+/// Keeps the default relays out of `triable_relay_candidates()`.
+async fn mark_defaults_tried(t: &TestContext, now: i64) -> Result<()> {
+    save_relay_candidates(t, DEFAULT_RELAY_CANDIDATES, now).await
+}
+
+/// Tests that saving a candidate overwrites its stored timestamp.
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_save_relay_candidate() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let t = &tcm.unconfigured().await;
+    let now = time();
+
+    for last_tried in [0, now, 0] {
+        t.sql
+            .transaction(|tx| save_relay_candidate(tx, "relay.example", last_tried))
+            .await?;
+        let stored: Option<i64> = t
+            .sql
+            .query_get_value(
+                "SELECT last_tried FROM relay_candidates WHERE host=?",
+                ("relay.example",),
+            )
+            .await?;
+        assert_eq!(stored, Some(last_tried));
+    }
+
+    Ok(())
+}
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_triable_relay_candidates_single() -> Result<()> {
     let t = &TestContext::new_alice().await;
     enable_config(t).await;
     let now = time();
 
-    t.sql.execute("DELETE FROM relay_candidates", ()).await?;
+    mark_defaults_tried(t, now).await?;
 
-    // This host should be returned by load_relay_candidates():
-    t.sql
-        .execute(
-            "INSERT INTO relay_candidates (host, last_tried) VALUES (?, ?)",
-            ("never_tried.example", 0),
-        )
-        .await?;
+    save_relay_candidates(t, &["never_tried.example", "example.org"], 0).await?;
+    save_relay_candidates(t, &["recent.example"], now).await?;
 
-    // This host was recently tried and should not be returned:
-    t.sql
-        .execute(
-            "INSERT INTO relay_candidates (host, last_tried) VALUES (?, ?)",
-            ("recent.example", now),
-        )
-        .await?;
-
-    // This host is already in use (alice@example.org) and should not be returned:
-    t.sql
-        .execute(
-            "INSERT INTO relay_candidates (host, last_tried) VALUES (?, ?)",
-            ("example.org", 0),
-        )
-        .await?;
-
-    let candidates = load_relay_candidates(t, now).await?;
+    let candidates = triable_relay_candidates(t, now).await?;
 
     assert_eq!(candidates, vec!["never_tried.example".to_string()]);
 
@@ -44,22 +142,15 @@ async fn test_load_relay_candidates_single() -> Result<()> {
 }
 
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-async fn test_load_relay_candidates_multiple() -> Result<()> {
+async fn test_triable_relay_candidates_multiple() -> Result<()> {
     let t = &TestContext::new().await;
     enable_config(t).await;
     let now = time();
 
-    t.sql.execute("DELETE FROM relay_candidates", ()).await?;
-    for host in ["a.example", "b.example", "c.example"] {
-        t.sql
-            .execute(
-                "INSERT INTO relay_candidates (host, last_tried) VALUES (?, ?)",
-                (host, 0),
-            )
-            .await?;
-    }
+    mark_defaults_tried(t, now).await?;
+    save_relay_candidates(t, &["a.example", "b.example", "c.example"], 0).await?;
 
-    let mut candidates = load_relay_candidates(t, now).await?;
+    let mut candidates = triable_relay_candidates(t, now).await?;
     candidates.sort();
 
     assert_eq!(
@@ -160,13 +251,8 @@ async fn test_maybe_add_additional_relays_add_one() -> Result<()> {
     enable_config(t).await;
     let now = time();
 
-    t.sql.execute("DELETE FROM relay_candidates", ()).await?;
-    t.sql
-        .execute(
-            "INSERT INTO relay_candidates (host, last_tried) VALUES (?, ?)",
-            ("relay.example", 0),
-        )
-        .await?;
+    mark_defaults_tried(t, now).await?;
+    save_relay_candidates(t, &["relay.example"], 0).await?;
 
     let transports_before = t.count_transports().await?;
 
@@ -189,15 +275,8 @@ async fn test_maybe_add_additional_relays_add_multiple() -> Result<()> {
     enable_config(t).await;
     let now = time();
 
-    t.sql.execute("DELETE FROM relay_candidates", ()).await?;
-    for host in ["a.example", "b.example", "c.example", "d.example"] {
-        t.sql
-            .execute(
-                "INSERT INTO relay_candidates (host, last_tried) VALUES (?, ?)",
-                (host, 0),
-            )
-            .await?;
-    }
+    mark_defaults_tried(t, now).await?;
+    save_relay_candidates(t, &["a.example", "b.example", "c.example", "d.example"], 0).await?;
 
     let skip_network = true;
     let relay_added = maybe_add_additional_relays_inner(t, skip_network).await?;
@@ -218,14 +297,9 @@ async fn test_maybe_add_additional_relays_failure() -> Result<()> {
     enable_config(t).await;
     let now = time();
 
-    t.sql.execute("DELETE FROM relay_candidates", ()).await?;
+    mark_defaults_tried(t, now).await?;
     for i in 1..10 {
-        t.sql
-            .execute(
-                "INSERT INTO relay_candidates (host, last_tried) VALUES (?, ?)",
-                (format!("{i}.invalid.example"), 0),
-            )
-            .await?;
+        save_relay_candidates(t, &[format!("{i}.invalid.example").as_str()], 0).await?;
     }
 
     let transports_before = t.count_transports().await?;
@@ -254,7 +328,7 @@ async fn test_maybe_add_additional_relays_failure() -> Result<()> {
 
     // ...but not all, because there might be many relay candidates
     // and we don't want to try all of them in a single call:
-    assert_eq!(load_relay_candidates(t, now).await?.is_empty(), false);
+    assert_eq!(triable_relay_candidates(t, now).await?.is_empty(), false);
 
     t.assert_warns_or_errors(&[
         "DNS lookup with memory cache failure",

src/configure.rs

@@ -31,7 +31,7 @@ use crate::login_param::EnteredCertificateChecks;
 pub use crate::login_param::EnteredLoginParam;
 use crate::net::proxy::ProxyConfig;
 use crate::provider::{self, Protocol, Socket};
-use crate::qr::{login_param_from_account_qr, login_param_from_login_qr};
+use crate::qr::{Qr, check_qr, login_param_from_account_qr, login_param_from_login_qr};
 use crate::smtp::Smtp;
 use crate::sync::Sync::Nosync;
 use crate::tools::time;
@@ -40,7 +40,7 @@ use crate::transport::{
     ConnectionCandidate, delete_transport_row, maybe_update_sending_transport,
     purge_transport_caches, send_sync_transports, transport_addrs,
 };
-use crate::{EventType, stock_str};
+use crate::{EventType, autorelay, stock_str};
 
 /// Maximum number of relays.
 ///
@@ -189,6 +189,62 @@ impl Context {
         Ok(())
     }
 
+    /// Adds an initial transport on a randomly chosen chatmail relay
+    /// and lets the profile add further ones in the background.
+    ///
+    /// A `DCACCOUNT:` or `DCLOGIN:` `qr` code adds a single transport
+    /// while securejoin codes add the inviter's relays to the candidates.
+    ///
+    /// Does nothing if the profile already has a transport.
+    pub async fn init_transports(&self, qr: Option<&str>) -> Result<()> {
+        if self.is_configured().await? {
+            return Ok(());
+        }
+        if let Some(qr) = qr {
+            match check_qr(self, qr).await? {
+                Qr::Account { .. } | Qr::Login { .. } => {
+                    return self.add_transport_from_qr(qr).await;
+                }
+                Qr::AskVerifyContact { addrs, .. }
+                | Qr::AskVerifyGroup { addrs, .. }
+                | Qr::AskJoinBroadcast { addrs, .. } => {
+                    autorelay::add_relay_candidates(self, &addrs).await?
+                }
+                _ => bail!("QR code does not contain a relay"),
+            }
+        }
+
+        let cancel_channel = self.alloc_ongoing().await?;
+        let skip_network = false;
+        let res = autorelay::add_transport_from_candidates(self, skip_network)
+            .race(cancel_channel.recv().map(|_| Err(format_err!("Canceled"))))
+            .await;
+        self.free_ongoing().await;
+
+        let configured = self.is_configured().await?;
+        match res {
+            Ok(()) => {}
+            Err(err) if configured => {
+                warn!(
+                    self,
+                    "Onboarding interrupted after adding a transport: {err:#}."
+                );
+            }
+            Err(err) => {
+                let error_msg = stock_str::configuration_failed(self, &format!("{err:#}"));
+                self.emit_event(EventType::ConfigureProgress {
+                    progress: 0,
+                    comment: Some(error_msg.clone()),
+                });
+                bail!(error_msg);
+            }
+        }
+        self.set_config_bool(Config::Autorelay, true).await?;
+        emit_progress(self, 1000);
+        self.start_io().await;
+        Ok(())
+    }
+
     /// Returns the list of all email accounts that are used as a transport in the current profile.
     /// Use [Self::add_or_update_transport()] to add or change a transport
     /// and [Self::delete_transport()] to delete a transport.
@@ -689,6 +745,28 @@ mod tests {
         Ok(())
     }
 
+    /// Tests that init_transports() fails on a bad code
+    /// and does nothing on a profile that already has a transport.
+    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+    async fn test_init_transports() -> Result<()> {
+        let mut tcm = TestContextManager::new();
+        let t = &tcm.unconfigured().await;
+        assert!(t.init_transports(Some("not a qr code")).await.is_err());
+        assert!(!t.is_configured().await?);
+
+        let alice = &tcm.alice().await;
+        let invite = "openpgp4fpr:79252762C34C5096AF57958F4FC3D21A81B0F0A7#a=cli%40invite.example&i=TbnwJ6lSvD5&s=0ejvbdFSQxB";
+        alice.init_transports(Some(invite)).await?;
+        let candidates = alice
+            .sql
+            .count("SELECT COUNT(*) FROM relay_candidates", ())
+            .await?;
+        assert_eq!(candidates, 0);
+        assert_eq!(alice.count_transports().await?, 1);
+
+        Ok(())
+    }
+
     #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
     async fn test_get_configured_param() -> Result<()> {
         let t = &TestContext::new().await;

src/qr.rs

@@ -13,6 +13,7 @@ use serde::Deserialize;
 
 use crate::autorelay::login_param_from_host;
 use crate::config::Config;
+use crate::configure::MAX_RELAYS;
 use crate::contact::{Contact, ContactId, Origin};
 use crate::context::Context;
 use crate::key::Fingerprint;
@@ -500,7 +501,8 @@ async fn decode_openpgp(context: &Context, qr: &str) -> Result<Qr> {
             addrs.push(normalize_address(primary_addr)?);
         };
         if let Some(secondary_addrs_raw) = param.get("r") {
-            for secondary_address in secondary_addrs_raw.split(',') {
+            let max_secondary = MAX_RELAYS.saturating_sub(addrs.len());
+            for secondary_address in secondary_addrs_raw.split(',').take(max_secondary) {
                 addrs.push(normalize_address(secondary_address)?)
             }
         }

src/qr/qr_tests.rs

@@ -361,6 +361,23 @@ async fn test_decode_openpgp_secure_join() -> Result<()> {
         bail!("Wrong QR code type");
     }
 
+    // A bad invite code must not be able to steer us onto arbitrarily many relays.
+    let relays: Vec<String> = (0..20).map(|i| format!("cli%40r{i}.example.org")).collect();
+    let qr = check_qr(
+        &ctx.ctx,
+        &format!(
+            "openpgp4fpr:79252762C34C5096AF57958F4FC3D21A81B0F0A7#a=cli%40deltachat.de&r={}&i=TbnwJ6lSvD5&s=0ejvbdFSQxB",
+            relays.join(",")
+        ),
+    )
+    .await?;
+
+    if let Qr::AskVerifyContact { addrs, .. } = qr {
+        assert_eq!(addrs.len(), MAX_RELAYS);
+    } else {
+        bail!("Wrong QR code type");
+    }
+
     Ok(())
 }
 

src/sql/migrations.rs

@@ -2673,6 +2673,13 @@ CREATE TABLE smtp2 (
         .await?;
     }
 
+    inc_and_check(&mut migration_version, 167)?;
+    if dbversion < migration_version {
+        // The default relay candidates are no longer seeded into the table.
+        sql.execute_migration("DELETE FROM relay_candidates", migration_version)
+            .await?;
+    }
+
     let new_version = sql
         .get_raw_config_int(VERSION_CFG)
         .await?