Fix null values being stored as empty strings

Add subtype method on context

Author: simolus3

Cargo.lock

@@ -28,7 +28,7 @@ inherits = "release"
 inherits = "wasm"
 
 [workspace.package]
-version = "0.4.3"
+version = "0.4.4"
 edition = "2024"
 authors = ["JourneyApps"]
 keywords = ["sqlite", "powersync"]
@@ -37,5 +37,4 @@ homepage = "https://powersync.com"
 repository = "https://github.com/powersync-ja/powersync-sqlite-core"
 
 [workspace.dependencies]
-sqlite_nostd = { path="./sqlite-rs-embedded/sqlite_nostd" }
-
+sqlite_nostd = { path = "./sqlite-rs-embedded/sqlite_nostd" }

Cargo.toml

@@ -13,7 +13,7 @@ plugins {
 }
 
 group = "com.powersync"
-version = "0.4.3"
+version = "0.4.4"
 description = "PowerSync Core SQLite Extension"
 
 val localRepo = uri("build/repository/")

android/build.gradle.kts

@@ -2,5 +2,5 @@
   "name": "powersync_sqlite_core",
   "schema_version": 2,
   "dependencies": [],
-  "version": "0.4.3"
+  "version": "0.4.4"
 }

android/src/prefab/prefab.json

@@ -9,6 +9,8 @@ pub const FULL_GIT_HASH: &'static str = env!("GIT_HASH");
 // we're testing with the minimum version we claim to support.
 pub const MIN_SQLITE_VERSION_NUMBER: c_int = 3044000;
 
+pub const SUBTYPE_JSON: u32 = 'J' as u32;
+
 pub fn short_git_hash() -> &'static str {
     &FULL_GIT_HASH[..8]
 }

crates/core/src/constants.rs

@@ -7,18 +7,20 @@ use sqlite::ResultCode;
 use sqlite_nostd as sqlite;
 use sqlite_nostd::{Connection, Context, Value};
 
-use serde_json as json;
-
+use crate::constants::SUBTYPE_JSON;
 use crate::create_sqlite_text_fn;
 use crate::error::PowerSyncError;
+use serde_json as json;
+use sqlite_nostd::bindings::SQLITE_RESULT_SUBTYPE;
 
 fn powersync_diff_impl(
-    _ctx: *mut sqlite::context,
+    ctx: *mut sqlite::context,
     args: &[*mut sqlite::value],
 ) -> Result<String, PowerSyncError> {
     let data_old = args[0].text();
     let data_new = args[1].text();
 
+    ctx.result_subtype(SUBTYPE_JSON);
     diff_objects(data_old, data_new)
 }
 
@@ -66,7 +68,7 @@ pub fn register(db: *mut sqlite::sqlite3) -> Result<(), ResultCode> {
     db.create_function_v2(
         "powersync_diff",
         2,
-        sqlite::UTF8 | sqlite::DETERMINISTIC,
+        sqlite::UTF8 | sqlite::DETERMINISTIC | SQLITE_RESULT_SUBTYPE,
         None,
         Some(powersync_diff),
         None,

crates/core/src/diff.rs

@@ -3,19 +3,34 @@ extern crate alloc;
 use alloc::string::{String, ToString};
 use core::ffi::c_int;
 
+use crate::constants::SUBTYPE_JSON;
+use crate::create_sqlite_text_fn;
+use crate::error::PowerSyncError;
 use sqlite::ResultCode;
 use sqlite_nostd as sqlite;
+use sqlite_nostd::bindings::{SQLITE_RESULT_SUBTYPE, SQLITE_SUBTYPE};
 use sqlite_nostd::{Connection, Context, Value};
 
-use crate::create_sqlite_text_fn;
-use crate::error::PowerSyncError;
+extern "C" fn powersync_strip_subtype(
+    ctx: *mut sqlite::context,
+    argc: c_int,
+    argv: *mut *mut sqlite::value,
+) {
+    if argc != 1 {
+        return;
+    }
+
+    let arg = unsafe { *argv };
+    ctx.result_value(arg);
+    ctx.result_subtype(0);
+}
 
 /// Given any number of JSON TEXT arguments, merge them into a single JSON object.
 ///
 /// This assumes each argument is a valid JSON object, with no duplicate keys.
 /// No JSON parsing or validation is performed - this performs simple string concatenation.
 fn powersync_json_merge_impl(
-    _ctx: *mut sqlite::context,
+    ctx: *mut sqlite::context,
     args: &[*mut sqlite::value],
 ) -> Result<String, PowerSyncError> {
     if args.is_empty() {
@@ -42,6 +57,7 @@ fn powersync_json_merge_impl(
 
     // Close the outer brace
     result.push('}');
+    ctx.result_subtype(SUBTYPE_JSON);
     Ok(result)
 }
 
@@ -55,13 +71,24 @@ pub fn register(db: *mut sqlite::sqlite3) -> Result<(), ResultCode> {
     db.create_function_v2(
         "powersync_json_merge",
         -1,
-        sqlite::UTF8 | sqlite::DETERMINISTIC,
+        sqlite::UTF8 | sqlite::DETERMINISTIC | SQLITE_RESULT_SUBTYPE,
         None,
         Some(powersync_json_merge),
         None,
         None,
         None,
     )?;
 
+    db.create_function_v2(
+        "powersync_strip_subtype",
+        -1,
+        sqlite::UTF8 | sqlite::DETERMINISTIC | SQLITE_SUBTYPE | SQLITE_RESULT_SUBTYPE,
+        None,
+        Some(powersync_strip_subtype),
+        None,
+        None,
+        None,
+    )?;
+
     Ok(())
 }

crates/core/src/json_merge.rs renamed to crates/core/src/json_util.rs

@@ -23,7 +23,7 @@ mod diff;
 mod error;
 mod ext;
 mod fix_data;
-mod json_merge;
+mod json_util;
 mod kv;
 mod macros;
 mod migrations;
@@ -73,7 +73,7 @@ fn init_extension(db: *mut sqlite::sqlite3) -> Result<(), PowerSyncError> {
     crate::uuid::register(db)?;
     crate::diff::register(db)?;
     crate::fix_data::register(db)?;
-    crate::json_merge::register(db)?;
+    crate::json_util::register(db)?;
     crate::view_admin::register(db)?;
     crate::checkpoint::register(db)?;
     crate::kv::register(db)?;

crates/core/src/lib.rs

@@ -1,23 +1,23 @@
 use core::cell::RefCell;
 use core::ffi::{c_int, c_void};
 
+use super::streaming_sync::SyncClient;
+use super::sync_status::DownloadSyncStatus;
+use crate::constants::SUBTYPE_JSON;
+use crate::error::PowerSyncError;
+use crate::schema::Schema;
+use crate::state::DatabaseState;
 use alloc::borrow::Cow;
 use alloc::boxed::Box;
 use alloc::rc::Rc;
 use alloc::sync::Arc;
 use alloc::{string::String, vec::Vec};
 use serde::{Deserialize, Serialize};
 use sqlite::{ResultCode, Value};
+use sqlite_nostd::bindings::SQLITE_RESULT_SUBTYPE;
 use sqlite_nostd::{self as sqlite, ColumnType};
 use sqlite_nostd::{Connection, Context};
 
-use crate::error::PowerSyncError;
-use crate::schema::Schema;
-use crate::state::DatabaseState;
-
-use super::streaming_sync::SyncClient;
-use super::sync_status::DownloadSyncStatus;
-
 /// Payload provided by SDKs when requesting a sync iteration.
 #[derive(Default, Deserialize)]
 pub struct StartSyncStream {
@@ -186,6 +186,7 @@ pub fn register(db: *mut sqlite::sqlite3, state: Arc<DatabaseState>) -> Result<(
             let formatted =
                 serde_json::to_string(&instructions).map_err(PowerSyncError::internal)?;
             ctx.result_text_transient(&formatted);
+            ctx.result_subtype(SUBTYPE_JSON);
 
             Ok(())
         })();
@@ -206,7 +207,7 @@ pub fn register(db: *mut sqlite::sqlite3, state: Arc<DatabaseState>) -> Result<(
     db.create_function_v2(
         "powersync_control",
         2,
-        sqlite::UTF8 | sqlite::DIRECTONLY,
+        sqlite::UTF8 | sqlite::DIRECTONLY | SQLITE_RESULT_SUBTYPE,
         Some(Box::into_raw(controller).cast()),
         Some(control),
         None,

crates/core/src/sync/interface.rs

@@ -421,7 +421,7 @@ fn json_object_fragment<'a>(
             // function, meaning that it has a JSON subtype active - causing the json_object() call
             // we're about to emit to include it as a subobject instead of a string.
             "TEXT" | "text" => format!(
-                "{:}, concat({:}.{:})",
+                "{:}, powersync_strip_subtype({:}.{:})",
                 QuotedString(name),
                 prefix,
                 quote_identifier(name)