1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
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
    }
}