Reduce message length limit to 5000 chars (#2615)

- Use the same limit for info: full text can be read in HTML anyway.
- Remove DC_MAX_GET_{TEXT,INFO}_LEN constants from deltachat.h
- Fix a typo: s/DC_ELLIPSE/DC_ELLIPSIS/
- Do not truncate the text when loading from the database.
- Update the documentation: limit is in Rust chars, not bytes

deltachat-ffi/deltachat.h

@@ -3220,10 +3220,6 @@ int64_t          dc_chat_get_remaining_mute_duration (const dc_chat_t* chat);
 #define         DC_STATE_OUT_MDN_RCVD        28
 
 
-#define         DC_MAX_GET_TEXT_LEN          30000 // approx. max. length returned by dc_msg_get_text()
-#define         DC_MAX_GET_INFO_LEN          100000 // approx. max. length returned by dc_get_msg_info()
-
-
 /**
  * Create new message object. Message objects are needed e.g. for sending messages using
  * dc_send_msg().  Moreover, they are returned e.g. from dc_get_msg(),

src/constants.rs

@@ -165,36 +165,18 @@ pub const DC_MSG_ID_MARKER1: u32 = 1;
 pub const DC_MSG_ID_DAYMARKER: u32 = 9;
 pub const DC_MSG_ID_LAST_SPECIAL: u32 = 9;
 
-/// string that indicates sth. is left out or truncated
+/// String that indicates that something is left out or truncated.
-pub const DC_ELLIPSE: &str = "[...]";
+pub const DC_ELLIPSIS: &str = "[...]";
 
-/// to keep bubbles and chat flow usable,
+/// Message length limit.
-/// and to avoid problems with controls using very long texts,
-/// we limit the text length to DC_DESIRED_TEXT_LEN.
-/// if the text is longer, the full text can be retrieved using has_html()/get_html().
 ///
-/// we are using a bit less than DC_MAX_GET_TEXT_LEN to avoid cutting twice
+/// To keep bubbles and chat flow usable and to avoid problems with controls using very long texts,
-/// (a bit less as truncation may not be exact and ellipses may be added).
+/// we limit the text length to `DC_DESIRED_TEXT_LEN`.  If the text is longer, the full text can be
+/// retrieved using has_html()/get_html().
 ///
-/// note, that DC_DESIRED_TEXT_LEN and DC_MAX_GET_TEXT_LEN
+/// Note that for simplicity maximum length is defined as the number of Unicode Scalar Values (Rust
-/// define max. number of bytes, _not_ unicode graphemes.
+/// `char`s), not Unicode Grapheme Clusters.
-/// in general, that seems to be okay for such an upper limit,
+pub const DC_DESIRED_TEXT_LEN: usize = 5000;
-/// esp. as calculating the number of graphemes is not simple
-/// (one graphemes may be a sequence of code points which is a sequence of bytes).
-/// also even if we have the exact number of graphemes,
-/// that would not always help on getting an idea about the screen space used
-/// (to keep bubbles and chat flow usable).
-///
-/// therefore, the number of bytes is only a very rough estimation,
-/// however, the ~30K seems to work okayish for a while,
-/// if it turns out, it is too few for some alphabet, we can still increase.
-pub const DC_DESIRED_TEXT_LEN: usize = 29_000;
-
-/// approx. max. length (number of bytes) returned by dc_msg_get_text()
-pub const DC_MAX_GET_TEXT_LEN: usize = 30_000;
-
-/// approx. max. length returned by dc_get_msg_info()
-pub const DC_MAX_GET_INFO_LEN: usize = 100_000;
 
 pub const DC_CONTACT_ID_UNDEFINED: u32 = 0;
 pub const DC_CONTACT_ID_SELF: u32 = 1;

src/dc_tools.rs

@@ -17,7 +17,7 @@ use chrono::{Local, TimeZone};
 use rand::{thread_rng, Rng};
 
 use crate::chat::{add_device_msg, add_device_msg_with_importance};
-use crate::constants::{Viewtype, DC_ELLIPSE, DC_OUTDATED_WARNING_DAYS};
+use crate::constants::{Viewtype, DC_ELLIPSIS, DC_OUTDATED_WARNING_DAYS};
 use crate::context::Context;
 use crate::events::EventType;
 use crate::message::Message;
@@ -29,7 +29,7 @@ use crate::stock_str;
 #[allow(clippy::indexing_slicing)]
 pub(crate) fn dc_truncate(buf: &str, approx_chars: usize) -> Cow<str> {
     let count = buf.chars().count();
-    if approx_chars > 0 && count > approx_chars + DC_ELLIPSE.len() {
+    if count > approx_chars + DC_ELLIPSIS.len() {
         let end_pos = buf
             .char_indices()
             .nth(approx_chars)
@@ -37,9 +37,9 @@ pub(crate) fn dc_truncate(buf: &str, approx_chars: usize) -> Cow<str> {
             .unwrap_or_default();
 
         if let Some(index) = buf[..end_pos].rfind(|c| c == ' ' || c == '\n') {
-            Cow::Owned(format!("{}{}", &buf[..=index], DC_ELLIPSE))
+            Cow::Owned(format!("{}{}", &buf[..=index], DC_ELLIPSIS))
         } else {
-            Cow::Owned(format!("{}{}", &buf[..end_pos], DC_ELLIPSE))
+            Cow::Owned(format!("{}{}", &buf[..end_pos], DC_ELLIPSIS))
         }
     } else {
         Cow::Borrowed(buf)
@@ -711,10 +711,7 @@ mod tests {
         assert_eq!(dc_truncate("\n  hello \n world", 4), "\n  [...]");
 
         assert_eq!(dc_truncate("𐠈0Aᝮa𫝀®!ꫛa¡0A𐢧00𐹠®A  丽ⷐએ", 1), "𐠈[...]");
-        assert_eq!(
+        assert_eq!(dc_truncate("𐠈0Aᝮa𫝀®!ꫛa¡0A𐢧00𐹠®A  丽ⷐએ", 0), "[...]");
-            dc_truncate("𐠈0Aᝮa𫝀®!ꫛa¡0A𐢧00𐹠®A  丽ⷐએ", 0),
-            "𐠈0Aᝮa𫝀®!ꫛa¡0A𐢧00𐹠®A  丽ⷐએ"
-        );
 
         // 9 characters, so no truncation
         assert_eq!(dc_truncate("𑒀ὐ￠🜀\u{1e01b}A a🟠", 6), "𑒀ὐ￠🜀\u{1e01b}A a🟠",);

src/message.rs

@@ -14,7 +14,7 @@ use crate::chat::{self, Chat, ChatId};
 use crate::config::Config;
 use crate::constants::{
     Blocked, Chattype, VideochatType, Viewtype, DC_CHAT_ID_TRASH, DC_CONTACT_ID_INFO,
-    DC_CONTACT_ID_SELF, DC_MAX_GET_INFO_LEN, DC_MAX_GET_TEXT_LEN, DC_MSG_ID_LAST_SPECIAL,
+    DC_CONTACT_ID_SELF, DC_DESIRED_TEXT_LEN, DC_MSG_ID_LAST_SPECIAL,
 };
 use crate::contact::{Contact, Origin};
 use crate::context::Context;
@@ -541,9 +541,7 @@ impl Message {
     }
 
     pub fn get_text(&self) -> Option<String> {
-        self.text
+        self.text.as_ref().map(|s| s.to_string())
-            .as_ref()
-            .map(|text| dc_truncate(text, DC_MAX_GET_TEXT_LEN).to_string())
     }
 
     pub fn get_subject(&self) -> &str {
@@ -1142,7 +1140,7 @@ pub async fn get_msg_info(context: &Context, msg_id: MsgId) -> Result<String> {
         return Ok(ret);
     }
     let rawtxt = rawtxt.unwrap_or_default();
-    let rawtxt = dc_truncate(rawtxt.trim(), DC_MAX_GET_INFO_LEN);
+    let rawtxt = dc_truncate(rawtxt.trim(), DC_DESIRED_TEXT_LEN);
 
     let fts = dc_timestamp_to_str(msg.get_timestamp());
     ret += &format!("Sent: {}", fts);

src/mimeparser.rs

@@ -10,7 +10,7 @@ use once_cell::sync::Lazy;
 
 use crate::aheader::Aheader;
 use crate::blob::BlobObject;
-use crate::constants::{Viewtype, DC_DESIRED_TEXT_LEN, DC_ELLIPSE};
+use crate::constants::{Viewtype, DC_DESIRED_TEXT_LEN, DC_ELLIPSIS};
 use crate::contact::addr_normalize;
 use crate::context::Context;
 use crate::dc_tools::{dc_get_filemeta, dc_truncate};
@@ -903,13 +903,14 @@ impl MimeMessage {
                             (simplified_txt, top_quote)
                         };
 
-                        let simplified_txt =
+                        let simplified_txt = if simplified_txt.chars().count()
-                            if simplified_txt.len() > DC_DESIRED_TEXT_LEN + DC_ELLIPSE.len() {
+                            > DC_DESIRED_TEXT_LEN + DC_ELLIPSIS.len()
-                                self.is_mime_modified = true;
+                        {
-                                dc_truncate(&*simplified_txt, DC_DESIRED_TEXT_LEN).to_string()
+                            self.is_mime_modified = true;
-                            } else {
+                            dc_truncate(&*simplified_txt, DC_DESIRED_TEXT_LEN).to_string()
-                                simplified_txt
+                        } else {
-                            };
+                            simplified_txt
+                        };
 
                         if !simplified_txt.is_empty() || simplified_quote.is_some() {
                             let mut part = Part {
@@ -1604,7 +1605,6 @@ mod tests {
     #![allow(clippy::indexing_slicing)]
 
     use super::*;
-    use crate::constants::DC_MAX_GET_TEXT_LEN;
     use crate::{
         chatlist::Chatlist,
         config::Config,
@@ -2880,21 +2880,20 @@ On 2020-10-25, Bob wrote:
         let t = TestContext::new().await;
 
         static REPEAT_TXT: &str = "this text with 42 chars is just repeated.\n";
-        static REPEAT_CNT: usize = 2000; // results in a text of 84k, should be more than DC_MAX_GET_TEXT_LEN
+        static REPEAT_CNT: usize = 2000; // results in a text of 84k, should be more than DC_DESIRED_TEXT_LEN
         let long_txt = format!("From: alice@c.de\n\n{}", REPEAT_TXT.repeat(REPEAT_CNT));
-        assert!(DC_DESIRED_TEXT_LEN + DC_ELLIPSE.len() < DC_MAX_GET_TEXT_LEN);
 
         let mimemsg = MimeMessage::from_bytes(&t, long_txt.as_ref())
             .await
             .unwrap();
         assert_eq!(long_txt.matches("just repeated").count(), REPEAT_CNT);
-        assert!(long_txt.len() > DC_MAX_GET_TEXT_LEN);
+        assert!(long_txt.len() > DC_DESIRED_TEXT_LEN);
         assert!(mimemsg.is_mime_modified);
         assert!(
             mimemsg.parts[0].msg.matches("just repeated").count()
-                < DC_MAX_GET_TEXT_LEN / REPEAT_TXT.len()
+                <= DC_DESIRED_TEXT_LEN / REPEAT_TXT.len()
         );
-        assert!(mimemsg.parts[0].msg.len() <= DC_MAX_GET_TEXT_LEN);
+        assert!(mimemsg.parts[0].msg.len() <= DC_DESIRED_TEXT_LEN + DC_ELLIPSIS.len());
     }
 
     #[async_std::test]