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use diesel::result::Error;
use diesel::QueryResult;
use scoped_futures::ScopedBoxFuture;
use std::borrow::Cow;
use std::num::NonZeroU32;
use crate::AsyncConnection;
// TODO: refactor this to share more code with diesel
/// Manages the internal transaction state for a connection.
///
/// You will not need to interact with this trait, unless you are writing an
/// implementation of [`AsyncConnection`].
#[async_trait::async_trait]
pub trait TransactionManager<Conn: AsyncConnection>: Send {
/// Data stored as part of the connection implementation
/// to track the current transaction state of a connection
type TransactionStateData;
/// Begin a new transaction or savepoint
///
/// If the transaction depth is greater than 0,
/// this should create a savepoint instead.
/// This function is expected to increment the transaction depth by 1.
async fn begin_transaction(conn: &mut Conn) -> QueryResult<()>;
/// Rollback the inner-most transaction or savepoint
///
/// If the transaction depth is greater than 1,
/// this should rollback to the most recent savepoint.
/// This function is expected to decrement the transaction depth by 1.
async fn rollback_transaction(conn: &mut Conn) -> QueryResult<()>;
/// Commit the inner-most transaction or savepoint
///
/// If the transaction depth is greater than 1,
/// this should release the most recent savepoint.
/// This function is expected to decrement the transaction depth by 1.
async fn commit_transaction(conn: &mut Conn) -> QueryResult<()>;
/// Fetch the current transaction status as mutable
///
/// Used to ensure that `begin_test_transaction` is not called when already
/// inside of a transaction, and that operations are not run in a `InError`
/// transaction manager.
#[doc(hidden)]
fn transaction_manager_status_mut(conn: &mut Conn) -> &mut TransactionManagerStatus;
/// Executes the given function inside of a database transaction
///
/// Each implementation of this function needs to fulfill the documented
/// behaviour of [`AsyncConnection::transaction`]
async fn transaction<'a, F, R, E>(conn: &mut Conn, callback: F) -> Result<R, E>
where
F: for<'r> FnOnce(&'r mut Conn) -> ScopedBoxFuture<'a, 'r, Result<R, E>> + Send + 'a,
E: From<Error> + Send,
R: Send,
{
Self::begin_transaction(conn).await?;
match callback(&mut *conn).await {
Ok(value) => {
Self::commit_transaction(conn).await?;
Ok(value)
}
Err(user_error) => match Self::rollback_transaction(conn).await {
Ok(()) => Err(user_error),
Err(Error::BrokenTransactionManager) => {
// In this case we are probably more interested by the
// original error, which likely caused this
Err(user_error)
}
Err(rollback_error) => Err(rollback_error.into()),
},
}
}
/// This methods checks if the connection manager is considered to be broken
/// by connection pool implementations
///
/// A connection manager is considered to be broken by default if it either
/// contains an open transaction (because you don't want to have connections
/// with open transactions in your pool) or when the transaction manager is
/// in an error state.
#[doc(hidden)]
fn is_broken_transaction_manager(conn: &mut Conn) -> bool {
match Self::transaction_manager_status_mut(conn).transaction_state() {
// all transactions are closed
// so we don't consider this connection broken
Ok(ValidTransactionManagerStatus {
in_transaction: None,
}) => false,
// The transaction manager is in an error state
// Therefore we consider this connection broken
Err(_) => true,
// The transaction manager contains a open transaction
// we do consider this connection broken
// if that transaction was not opened by `begin_test_transaction`
Ok(ValidTransactionManagerStatus {
in_transaction: Some(s),
}) => !s.test_transaction,
}
}
}
/// An implementation of `TransactionManager` which can be used for backends
/// which use ANSI standard syntax for savepoints such as SQLite and PostgreSQL.
#[derive(Default, Debug)]
pub struct AnsiTransactionManager {
pub(crate) status: TransactionManagerStatus,
}
/// Status of the transaction manager
#[derive(Debug)]
pub enum TransactionManagerStatus {
/// Valid status, the manager can run operations
Valid(ValidTransactionManagerStatus),
/// Error status, probably following a broken connection. The manager will no longer run operations
InError,
}
impl Default for TransactionManagerStatus {
fn default() -> Self {
TransactionManagerStatus::Valid(ValidTransactionManagerStatus::default())
}
}
impl TransactionManagerStatus {
/// Returns the transaction depth if the transaction manager's status is valid, or returns
/// [`Error::BrokenTransactionManager`] if the transaction manager is in error.
pub fn transaction_depth(&self) -> QueryResult<Option<NonZeroU32>> {
match self {
TransactionManagerStatus::Valid(valid_status) => Ok(valid_status.transaction_depth()),
TransactionManagerStatus::InError => Err(Error::BrokenTransactionManager),
}
}
/// If in transaction and transaction manager is not broken, registers that the
/// connection can not be used anymore until top-level transaction is rolled back
pub(crate) fn set_top_level_transaction_requires_rollback(&mut self) {
if let TransactionManagerStatus::Valid(ValidTransactionManagerStatus {
in_transaction:
Some(InTransactionStatus {
top_level_transaction_requires_rollback,
..
}),
}) = self
{
*top_level_transaction_requires_rollback = true;
}
}
/// Sets the transaction manager status to InError
///
/// Subsequent attempts to use transaction-related features will result in a
/// [`Error::BrokenTransactionManager`] error
pub fn set_in_error(&mut self) {
*self = TransactionManagerStatus::InError
}
fn transaction_state(&mut self) -> QueryResult<&mut ValidTransactionManagerStatus> {
match self {
TransactionManagerStatus::Valid(valid_status) => Ok(valid_status),
TransactionManagerStatus::InError => Err(Error::BrokenTransactionManager),
}
}
pub(crate) fn set_test_transaction_flag(&mut self) {
if let TransactionManagerStatus::Valid(ValidTransactionManagerStatus {
in_transaction: Some(s),
}) = self
{
s.test_transaction = true;
}
}
}
/// Valid transaction status for the manager. Can return the current transaction depth
#[allow(missing_copy_implementations)]
#[derive(Debug, Default)]
pub struct ValidTransactionManagerStatus {
in_transaction: Option<InTransactionStatus>,
}
#[allow(missing_copy_implementations)]
#[derive(Debug)]
struct InTransactionStatus {
transaction_depth: NonZeroU32,
top_level_transaction_requires_rollback: bool,
test_transaction: bool,
}
impl ValidTransactionManagerStatus {
/// Return the current transaction depth
///
/// This value is `None` if no current transaction is running
/// otherwise the number of nested transactions is returned.
pub fn transaction_depth(&self) -> Option<NonZeroU32> {
self.in_transaction.as_ref().map(|it| it.transaction_depth)
}
/// Update the transaction depth by adding the value of the `transaction_depth_change` parameter if the `query` is
/// `Ok(())`
pub fn change_transaction_depth(
&mut self,
transaction_depth_change: TransactionDepthChange,
) -> QueryResult<()> {
match (&mut self.in_transaction, transaction_depth_change) {
(Some(in_transaction), TransactionDepthChange::IncreaseDepth) => {
// Can be replaced with saturating_add directly on NonZeroU32 once
// <https://github.com/rust-lang/rust/issues/84186> is stable
in_transaction.transaction_depth =
NonZeroU32::new(in_transaction.transaction_depth.get().saturating_add(1))
.expect("nz + nz is always non-zero");
Ok(())
}
(Some(in_transaction), TransactionDepthChange::DecreaseDepth) => {
// This sets `transaction_depth` to `None` as soon as we reach zero
match NonZeroU32::new(in_transaction.transaction_depth.get() - 1) {
Some(depth) => in_transaction.transaction_depth = depth,
None => self.in_transaction = None,
}
Ok(())
}
(None, TransactionDepthChange::IncreaseDepth) => {
self.in_transaction = Some(InTransactionStatus {
transaction_depth: NonZeroU32::new(1).expect("1 is non-zero"),
top_level_transaction_requires_rollback: false,
test_transaction: false,
});
Ok(())
}
(None, TransactionDepthChange::DecreaseDepth) => {
// We screwed up something somewhere
// we cannot decrease the transaction count if
// we are not inside a transaction
Err(Error::NotInTransaction)
}
}
}
}
/// Represents a change to apply to the depth of a transaction
#[derive(Debug, Clone, Copy)]
pub enum TransactionDepthChange {
/// Increase the depth of the transaction (corresponds to `BEGIN` or `SAVEPOINT`)
IncreaseDepth,
/// Decreases the depth of the transaction (corresponds to `COMMIT`/`RELEASE SAVEPOINT` or `ROLLBACK`)
DecreaseDepth,
}
impl AnsiTransactionManager {
fn get_transaction_state<Conn>(
conn: &mut Conn,
) -> QueryResult<&mut ValidTransactionManagerStatus>
where
Conn: AsyncConnection<TransactionManager = Self>,
{
conn.transaction_state().status.transaction_state()
}
/// Begin a transaction with custom SQL
///
/// This is used by connections to implement more complex transaction APIs
/// to set things such as isolation levels.
/// Returns an error if already inside of a transaction.
pub async fn begin_transaction_sql<Conn>(conn: &mut Conn, sql: &str) -> QueryResult<()>
where
Conn: AsyncConnection<TransactionManager = Self>,
{
let state = Self::get_transaction_state(conn)?;
match state.transaction_depth() {
None => {
conn.batch_execute(sql).await?;
Self::get_transaction_state(conn)?
.change_transaction_depth(TransactionDepthChange::IncreaseDepth)?;
Ok(())
}
Some(_depth) => Err(Error::AlreadyInTransaction),
}
}
}
#[async_trait::async_trait]
impl<Conn> TransactionManager<Conn> for AnsiTransactionManager
where
Conn: AsyncConnection<TransactionManager = Self>,
{
type TransactionStateData = Self;
async fn begin_transaction(conn: &mut Conn) -> QueryResult<()> {
let transaction_state = Self::get_transaction_state(conn)?;
let start_transaction_sql = match transaction_state.transaction_depth() {
None => Cow::from("BEGIN"),
Some(transaction_depth) => {
Cow::from(format!("SAVEPOINT diesel_savepoint_{}", transaction_depth))
}
};
conn.batch_execute(&start_transaction_sql).await?;
Self::get_transaction_state(conn)?
.change_transaction_depth(TransactionDepthChange::IncreaseDepth)?;
Ok(())
}
async fn rollback_transaction(conn: &mut Conn) -> QueryResult<()> {
let transaction_state = Self::get_transaction_state(conn)?;
let rollback_sql = match transaction_state.in_transaction {
Some(ref mut in_transaction) => {
match in_transaction.transaction_depth.get() {
1 => Cow::Borrowed("ROLLBACK"),
depth_gt1 => {
if in_transaction.top_level_transaction_requires_rollback {
// There's no point in *actually* rolling back this one
// because we won't be able to do anything until top-level
// is rolled back.
// To make it easier on the user (that they don't have to really look
// at actual transaction depth and can just rely on the number of
// times they have called begin/commit/rollback) we don't mark the
// transaction manager as out of the savepoints as soon as we
// realize there is that issue, but instead we still decrement here:
in_transaction.transaction_depth = NonZeroU32::new(depth_gt1 - 1)
.expect("Depth was checked to be > 1");
return Ok(());
} else {
Cow::Owned(format!(
"ROLLBACK TO SAVEPOINT diesel_savepoint_{}",
depth_gt1 - 1
))
}
}
}
}
None => return Err(Error::NotInTransaction),
};
match conn.batch_execute(&rollback_sql).await {
Ok(()) => {
Self::get_transaction_state(conn)?
.change_transaction_depth(TransactionDepthChange::DecreaseDepth)?;
Ok(())
}
Err(rollback_error) => {
let tm_status = Self::transaction_manager_status_mut(conn);
match tm_status {
TransactionManagerStatus::Valid(ValidTransactionManagerStatus {
in_transaction:
Some(InTransactionStatus {
transaction_depth,
top_level_transaction_requires_rollback,
..
}),
}) if transaction_depth.get() > 1
&& !*top_level_transaction_requires_rollback =>
{
// A savepoint failed to rollback - we may still attempt to repair
// the connection by rolling back top-level transaction.
*transaction_depth = NonZeroU32::new(transaction_depth.get() - 1)
.expect("Depth was checked to be > 1");
*top_level_transaction_requires_rollback = true;
}
_ => tm_status.set_in_error(),
}
Err(rollback_error)
}
}
}
/// If the transaction fails to commit due to a `SerializationFailure` or a
/// `ReadOnlyTransaction` a rollback will be attempted. If the rollback succeeds,
/// the original error will be returned, otherwise the error generated by the rollback
/// will be returned. In the second case the connection will be considered broken
/// as it contains a uncommitted unabortable open transaction.
async fn commit_transaction(conn: &mut Conn) -> QueryResult<()> {
let transaction_state = Self::get_transaction_state(conn)?;
let transaction_depth = transaction_state.transaction_depth();
let commit_sql = match transaction_depth {
None => return Err(Error::NotInTransaction),
Some(transaction_depth) if transaction_depth.get() == 1 => Cow::Borrowed("COMMIT"),
Some(transaction_depth) => Cow::Owned(format!(
"RELEASE SAVEPOINT diesel_savepoint_{}",
transaction_depth.get() - 1
)),
};
match conn.batch_execute(&commit_sql).await {
Ok(()) => {
Self::get_transaction_state(conn)?
.change_transaction_depth(TransactionDepthChange::DecreaseDepth)?;
Ok(())
}
Err(commit_error) => {
if let TransactionManagerStatus::Valid(ValidTransactionManagerStatus {
in_transaction:
Some(InTransactionStatus {
ref mut transaction_depth,
top_level_transaction_requires_rollback: true,
..
}),
}) = conn.transaction_state().status
{
match transaction_depth.get() {
1 => match Self::rollback_transaction(conn).await {
Ok(()) => {}
Err(rollback_error) => {
conn.transaction_state().status.set_in_error();
return Err(Error::RollbackErrorOnCommit {
rollback_error: Box::new(rollback_error),
commit_error: Box::new(commit_error),
});
}
},
depth_gt1 => {
// There's no point in *actually* rolling back this one
// because we won't be able to do anything until top-level
// is rolled back.
// To make it easier on the user (that they don't have to really look
// at actual transaction depth and can just rely on the number of
// times they have called begin/commit/rollback) we don't mark the
// transaction manager as out of the savepoints as soon as we
// realize there is that issue, but instead we still decrement here:
*transaction_depth = NonZeroU32::new(depth_gt1 - 1)
.expect("Depth was checked to be > 1");
}
}
}
Err(commit_error)
}
}
}
fn transaction_manager_status_mut(conn: &mut Conn) -> &mut TransactionManagerStatus {
&mut conn.transaction_state().status
}
}