slightly nicer and shorter QR and invite codes (#7390)

- sort garbage to the beginning, readable text to the end
- instead of `%20`, make use of `+` to encode spaces
- shorter invite links and smaller QR codes by truncation of the names

the truncation of the name uses chars() which does not respect grapheme clusters, so
that last character may be wrong. not sure if there is a nice and easy
alternative, but maybe it's good engoug - the real, full name will come
over the wire (exiting truncate() truncates on word boundaries, which is
maybe too soft here - names may be long, depending on the language, and
not contain any space)

moreover, this resolves the "name too long" issue from
https://github.com/chatmail/core/issues/7015

---------

Co-authored-by: Hocuri <hocuri@gmx.de>

src/securejoin.rs

@@ -2,7 +2,7 @@
 
 use anyhow::{Context as _, Error, Result, bail, ensure};
 use deltachat_contact_tools::ContactAddress;
-use percent_encoding::{NON_ALPHANUMERIC, utf8_percent_encode};
+use percent_encoding::{AsciiSet, utf8_percent_encode};
 
 use crate::chat::{self, Chat, ChatId, ChatIdBlocked, get_chat_id_by_grpid};
 use crate::config::Config;
@@ -42,6 +42,8 @@ use crate::token::Namespace;
 // when Delta Chat v2.22.0 is sufficiently rolled out
 const VERIFICATION_TIMEOUT_SECONDS: i64 = 7 * 24 * 3600;
 
+const DISALLOWED_CHARACTERS: &AsciiSet = &NON_ALPHANUMERIC_WITHOUT_DOT.remove(b'_');
+
 fn inviter_progress(
     context: &Context,
     contact_id: ContactId,
@@ -60,6 +62,17 @@ fn inviter_progress(
     Ok(())
 }
 
+/// Shorten name to max. 25 characters.
+/// This is to not make QR codes or invite links arbitrary long.
+fn shorten_name(name: &str) -> String {
+    if name.chars().count() > 25 {
+        // We use _ rather than ... to avoid dots at the end of the URL, which would confuse linkifiers
+        format!("{}_", &name.chars().take(24).collect::<String>())
+    } else {
+        name.to_string()
+    }
+}
+
 /// Generates a Secure Join QR code.
 ///
 /// With `chat` set to `None` this generates a setup-contact QR code, with `chat` set to a
@@ -108,18 +121,10 @@ pub async fn get_securejoin_qr(context: &Context, chat: Option<ChatId>) -> Resul
     let auth = create_id();
     token::save(context, Namespace::Auth, grpid, &auth, time()).await?;
 
+    let fingerprint = get_self_fingerprint(context).await?.hex();
+
     let self_addr = context.get_primary_self_addr().await?;
-    let self_name = context
-        .get_config(Config::Displayname)
-        .await?
-        .unwrap_or_default();
-
-    let fingerprint = get_self_fingerprint(context).await?;
-
-    let self_addr_urlencoded =
-        utf8_percent_encode(&self_addr, NON_ALPHANUMERIC_WITHOUT_DOT).to_string();
-    let self_name_urlencoded =
-        utf8_percent_encode(&self_name, NON_ALPHANUMERIC_WITHOUT_DOT).to_string();
+    let self_addr_urlencoded = utf8_percent_encode(&self_addr, DISALLOWED_CHARACTERS).to_string();
 
     let qr = if let Some(chat) = chat {
         if sync_token {
@@ -130,42 +135,36 @@ pub async fn get_securejoin_qr(context: &Context, chat: Option<ChatId>) -> Resul
         }
 
         let chat_name = chat.get_name();
-        let chat_name_urlencoded = utf8_percent_encode(chat_name, NON_ALPHANUMERIC).to_string();
+        let chat_name_shortened = shorten_name(chat_name);
+        let chat_name_urlencoded = utf8_percent_encode(&chat_name_shortened, DISALLOWED_CHARACTERS)
+            .to_string()
+            .replace("%20", "+");
+        let grpid = &chat.grpid;
         if chat.typ == Chattype::OutBroadcast {
             // For historic reansons, broadcasts currently use j instead of i for the invitenumber.
             format!(
-                "https://i.delta.chat/#{}&a={}&b={}&x={}&j={}&s={}",
-                fingerprint.hex(),
-                self_addr_urlencoded,
-                &chat_name_urlencoded,
-                &chat.grpid,
-                &invitenumber,
-                &auth,
+                "https://i.delta.chat/#{fingerprint}&x={grpid}&j={invitenumber}&s={auth}&a={self_addr_urlencoded}&b={chat_name_urlencoded}",
             )
         } else {
             format!(
-                "https://i.delta.chat/#{}&a={}&g={}&x={}&i={}&s={}",
-                fingerprint.hex(),
-                self_addr_urlencoded,
-                &chat_name_urlencoded,
-                &chat.grpid,
-                &invitenumber,
-                &auth,
+                "https://i.delta.chat/#{fingerprint}&x={grpid}&i={invitenumber}&s={auth}&a={self_addr_urlencoded}&g={chat_name_urlencoded}",
             )
         }
     } else {
-        // parameters used: a=n=i=s=
+        let self_name = context
+            .get_config(Config::Displayname)
+            .await?
+            .unwrap_or_default();
+        let self_name_shortened = shorten_name(&self_name);
+        let self_name_urlencoded = utf8_percent_encode(&self_name_shortened, DISALLOWED_CHARACTERS)
+            .to_string()
+            .replace("%20", "+");
         if sync_token {
             context.sync_qr_code_tokens(None).await?;
             context.scheduler.interrupt_inbox().await;
         }
         format!(
-            "https://i.delta.chat/#{}&a={}&n={}&i={}&s={}",
-            fingerprint.hex(),
-            self_addr_urlencoded,
-            self_name_urlencoded,
-            &invitenumber,
-            &auth,
+            "https://i.delta.chat/#{fingerprint}&i={invitenumber}&s={auth}&a={self_addr_urlencoded}&n={self_name_urlencoded}",
         )
     };