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/qr.rs

@@ -556,10 +556,14 @@ async fn decode_openpgp(context: &Context, qr: &str) -> Result<Qr> {
 fn decode_name(param: &BTreeMap<&str, &str>, key: &str) -> Result<Option<String>> {
     if let Some(encoded_name) = param.get(key) {
         let encoded_name = encoded_name.replace('+', "%20"); // sometimes spaces are encoded as `+`
-        match percent_decode_str(&encoded_name).decode_utf8() {
-            Ok(name) => Ok(Some(name.to_string())),
+        let mut name = match percent_decode_str(&encoded_name).decode_utf8() {
+            Ok(name) => name.to_string(),
             Err(err) => bail!("Invalid QR param {key}: {err}"),
+        };
+        if let Some(n) = name.strip_suffix('_') {
+            name = format!("{n}…");
         }
+        Ok(Some(name))
     } else {
         Ok(None)
     }

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}",
         )
     };
 

src/securejoin/securejoin_tests.rs

@@ -1070,3 +1070,46 @@ async fn test_rejoin_group() -> Result<()> {
 
     Ok(())
 }
+
+/// To make invite links a little bit nicer, we put the readable part at the end and encode spaces by `+` instead of `%20`.
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_get_securejoin_qr_name_is_last() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+    alice
+        .set_config(Config::Displayname, Some("Alice Axe"))
+        .await?;
+    let qr = get_securejoin_qr(alice, None).await?;
+    assert!(qr.ends_with("Alice+Axe"));
+
+    let alice_chat_id = chat::create_group(alice, "The Chat").await?;
+    let qr = get_securejoin_qr(alice, Some(alice_chat_id)).await?;
+    assert!(qr.ends_with("The+Chat"));
+
+    Ok(())
+}
+
+/// QR codes should not get arbitrary big because of long names.
+/// The truncation, however, should not let the url end with a `.`, which is a call for trouble in linkfiers.
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_get_securejoin_qr_name_is_truncated() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+    alice
+        .set_config(
+            Config::Displayname,
+            Some("Alice Axe Has A Very Long Family Name Really Indeed"),
+        )
+        .await?;
+    let qr = get_securejoin_qr(alice, None).await?;
+    assert!(qr.ends_with("Alice+Axe+Has+A+Very+Lon_"));
+    assert!(!qr.ends_with("."));
+
+    let alice_chat_id =
+        chat::create_group(alice, "The Chat With One Of The Longest Titles Around").await?;
+    let qr = get_securejoin_qr(alice, Some(alice_chat_id)).await?;
+    assert!(qr.ends_with("The+Chat+With+One+Of+The_"));
+    assert!(!qr.ends_with("."));
+
+    Ok(())
+}