Fix backup creation for collections > 1 GiB (#2423)

Co-authored-by: Damien Elmes <dae@users.noreply.github.com>

rslib/src/collection/backup.rs

@@ -16,7 +16,7 @@ use itertools::Itertools;
 use tracing::error;
 
 use crate::import_export::package::export_colpkg_from_data;
-use crate::io::read_file;
+use crate::io::read_locked_db_file;
 use crate::pb::config::preferences::BackupLimits;
 use crate::prelude::*;
 
@@ -39,7 +39,7 @@ impl Collection {
         } else {
             let tr = self.tr.clone();
             self.storage.checkpoint()?;
-            let col_data = read_file(&self.col_path)?;
+            let col_data = read_locked_db_file(&self.col_path)?;
             self.update_last_backup_timestamp()?;
             Ok(Some(thread::spawn(move || {
                 backup_inner(&col_data, &backup_folder, limits, &tr)

rslib/src/io.rs

@@ -2,6 +2,8 @@
 // License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
 
 use std::fs::File;
+use std::io::Read;
+use std::io::Seek;
 use std::path::Component;
 use std::path::Path;
 
@@ -63,6 +65,34 @@ pub(crate) fn read_file(path: impl AsRef<Path>) -> Result<Vec<u8>> {
     })
 }
 
+/// Like [read_file], but skips the section that is potentially locked by
+/// SQLite.
+pub(crate) fn read_locked_db_file(path: impl AsRef<Path>) -> Result<Vec<u8>> {
+    read_locked_db_file_inner(&path).context(FileIoSnafu {
+        path: path.as_ref(),
+        op: FileOp::Read,
+    })
+}
+
+const LOCKED_SECTION_START_BYTE: usize = 1024 * 1024 * 1024;
+const LOCKED_SECTION_LEN_BYTES: usize = 512;
+const LOCKED_SECTION_END_BYTE: usize = LOCKED_SECTION_START_BYTE + LOCKED_SECTION_LEN_BYTES;
+
+fn read_locked_db_file_inner(path: impl AsRef<Path>) -> std::io::Result<Vec<u8>> {
+    let size = std::fs::metadata(&path)?.len() as usize;
+    if size < LOCKED_SECTION_END_BYTE {
+        return std::fs::read(path);
+    }
+
+    let mut file = File::open(&path)?;
+    let mut buf = vec![0; size];
+    file.read_exact(&mut buf[..LOCKED_SECTION_START_BYTE])?;
+    file.seek(std::io::SeekFrom::Current(LOCKED_SECTION_LEN_BYTES as i64))?;
+    file.read_exact(&mut buf[LOCKED_SECTION_END_BYTE..])?;
+
+    Ok(buf)
+}
+
 pub(crate) fn new_tempfile() -> Result<NamedTempFile> {
     NamedTempFile::new().context(FileIoSnafu {
         path: std::env::temp_dir(),