small adjustments

core/error.rs

@@ -59,6 +59,8 @@ pub enum LimboError {
     ReadOnly,
     #[error("Database is busy")]
     Busy,
+    #[error("Conflict: {0}")]
+    Conflict(String)
 }
 
 #[macro_export]

core/lib.rs

@@ -809,10 +809,14 @@ impl Connection {
         self.pager.borrow().wal_get_frame(frame_no, frame)
     }
 
+    /// Insert `frame` (header included) at the position `frame_no` in the WAL
+    /// If WAL already has frame at that position - turso-db will compare content of the page and either report conflict or return OK
+    /// If attempt to write frame at the position `frame_no` will create gap in the WAL - method will return error
     pub fn wal_insert_frame(&self, frame_no: u32, frame: &[u8]) -> Result<()> {
         self.pager.borrow().wal_insert_frame(frame_no, frame)
     }
 
+    /// Start WAL session by initiating read+write transaction for this connection
     pub fn wal_insert_begin(&self) -> Result<()> {
         let pager = self.pager.borrow();
         match pager.io.block(|| pager.begin_read_tx())? {
@@ -829,6 +833,8 @@ impl Connection {
         Ok(())
     }
 
+    /// Finish WAL session by ending read+write transaction taken in the [Self::wal_insert_begin] method
+    /// All frames written after last commit frame (db_size > 0) within the session will be rolled back
     pub fn wal_insert_end(&self) -> Result<()> {
         let pager = self.pager.borrow();
         let mut wal = pager.wal.borrow_mut();

core/storage/wal.rs

@@ -705,7 +705,7 @@ impl Wal for WalFile {
             )?;
             self.io.wait_for_completion(c)?;
             return if conflict.get() {
-                Err(LimboError::InvalidArgument(format!(
+                Err(LimboError::Conflict(format!(
                     "frame content differs from the WAL: frame_id={frame_id}"
                 )))
             } else {

sqlite3/src/lib.rs

@@ -3,7 +3,7 @@
 
 use std::ffi::{self, CStr, CString};
 use tracing::trace;
-use turso_core::Value;
+use turso_core::{LimboError, Value};
 
 use std::sync::{Arc, Mutex};
 
@@ -1218,6 +1218,7 @@ pub unsafe extern "C" fn libsql_wal_insert_frame(
     frame_no: u32,
     p_frame: *const u8,
     frame_len: u32,
+    p_conflict: *mut i32,
 ) -> ffi::c_int {
     if db.is_null() {
         return SQLITE_MISUSE;
@@ -1227,6 +1228,12 @@ pub unsafe extern "C" fn libsql_wal_insert_frame(
     let frame = std::slice::from_raw_parts(p_frame, frame_len as usize);
     match db.conn.wal_insert_frame(frame_no, frame) {
         Ok(()) => SQLITE_OK,
+        Err(LimboError::Conflict(..)) => {
+            if !p_conflict.is_null() {
+                *p_conflict = 1;
+            }
+            SQLITE_ERROR
+        }
         Err(_) => SQLITE_ERROR,
     }
 }