From 0b84905c85ef398d75981fcbe9f5f109412d6f83 Mon Sep 17 00:00:00 2001
From: Damien Elmes <gpg@ankiweb.net>
Date: Sat, 23 Sep 2023 15:43:11 +1000
Subject: [PATCH] Avoid excessive floating point precision when serializing

---
 rslib/src/storage/card/data.rs | 45 +++++++++++++++++++++++++---------
 rslib/src/storage/card/mod.rs  |  8 +++---
 2 files changed, 38 insertions(+), 15 deletions(-)

diff --git a/rslib/src/storage/card/data.rs b/rslib/src/storage/card/data.rs
index a9151b89d..e4d87b5d7 100644
--- a/rslib/src/storage/card/data.rs
+++ b/rslib/src/storage/card/data.rs
@@ -5,9 +5,7 @@ use std::collections::HashMap;
 
 use rusqlite::types::FromSql;
 use rusqlite::types::FromSqlError;
-use rusqlite::types::ToSqlOutput;
 use rusqlite::types::ValueRef;
-use rusqlite::ToSql;
 use serde::Deserialize;
 use serde::Serialize;
 use serde_json::Value;
@@ -78,6 +76,24 @@ impl CardData {
         }
         None
     }
+
+    pub(crate) fn convert_to_json(&mut self) -> Result<String> {
+        if let Some(v) = &mut self.fsrs_stability {
+            round_to_places(v, 1)
+        }
+        if let Some(v) = &mut self.fsrs_difficulty {
+            round_to_places(v, 3)
+        }
+        if let Some(v) = &mut self.fsrs_desired_retention {
+            round_to_places(v, 2)
+        }
+        serde_json::to_string(&self).map_err(Into::into)
+    }
+}
+
+fn round_to_places(value: &mut f32, decimal_places: u32) {
+    let factor = 10_f32.powi(decimal_places as i32);
+    *value = (*value * factor).round() / factor;
 }
 
 impl FromSql for CardData {
@@ -91,17 +107,9 @@ impl FromSql for CardData {
     }
 }
 
-impl ToSql for CardData {
-    fn to_sql(&self) -> Result<ToSqlOutput<'_>, rusqlite::Error> {
-        Ok(ToSqlOutput::Owned(
-            serde_json::to_string(self).unwrap().into(),
-        ))
-    }
-}
-
 /// Serialize the JSON `data` for a card.
 pub(crate) fn card_data_string(card: &Card) -> String {
-    serde_json::to_string(&CardData::from_card(card)).unwrap()
+    CardData::from_card(card).convert_to_json().unwrap()
 }
 
 fn meta_is_empty(s: &str) -> bool {
@@ -143,4 +151,19 @@ mod test {
         assert!(validate_custom_data(r#"{"日本語": 5}"#).is_err());
         assert!(validate_custom_data(&format!(r#"{{"foo": "{}"}}"#, "x".repeat(100))).is_err());
     }
+
+    #[test]
+    fn compact_floats() {
+        let mut data = CardData {
+            original_position: None,
+            fsrs_stability: Some(123.45678),
+            fsrs_difficulty: Some(1.234567),
+            fsrs_desired_retention: Some(0.987654),
+            custom_data: "".to_string(),
+        };
+        assert_eq!(
+            data.convert_to_json().unwrap(),
+            r#"{"s":123.5,"d":1.235,"dr":0.99}"#
+        );
+    }
 }
diff --git a/rslib/src/storage/card/mod.rs b/rslib/src/storage/card/mod.rs
index f9da74d05..22046f88e 100644
--- a/rslib/src/storage/card/mod.rs
+++ b/rslib/src/storage/card/mod.rs
@@ -126,7 +126,7 @@ impl super::SqliteStorage {
             card.original_due,
             card.original_deck_id,
             card.flags,
-            CardData::from_card(card),
+            CardData::from_card(card).convert_to_json()?,
             card.id,
         ])?;
         Ok(())
@@ -153,7 +153,7 @@ impl super::SqliteStorage {
             card.original_due,
             card.original_deck_id,
             card.flags,
-            CardData::from_card(card),
+            CardData::from_card(card).convert_to_json()?,
         ])?;
         card.id = CardId(self.db.last_insert_rowid());
         Ok(())
@@ -181,7 +181,7 @@ impl super::SqliteStorage {
                 card.original_due,
                 card.original_deck_id,
                 card.flags,
-                CardData::from_card(card),
+                CardData::from_card(card).convert_to_json()?,
             ])
             .map(|n_rows| n_rows == 1)
             .map_err(Into::into)
@@ -208,7 +208,7 @@ impl super::SqliteStorage {
             card.original_due,
             card.original_deck_id,
             card.flags,
-            CardData::from_card(card),
+            CardData::from_card(card).convert_to_json()?,
         ])?;
 
         Ok(())