transactions: Consolidate transaction and subtransaction errors

Initially, there was no support for subtransactions, so every node could
only cast a single vote for a given transaction. This was later extended
to support subtransactions, where nodes can cast a sequence of votes.

Due to this organic growth, there now is some confusion when it comes to
errors: some errors talk about transactions, while others talk about
subtransactions. This commit thus consolidates the errors to only ever
talk about transactions -- callers needn't be aware of subtransactions,
even less so as they're handled completely transparently.

3 files changed, 10 insertions, 19 deletions

diff --git a/internal/praefect/transactions/manager.go b/internal/praefect/transactions/manager.go
index d77aa5ec3..577cd7b80 100644
--- a/internal/praefect/transactions/manager.go
+++ b/internal/praefect/transactions/manager.go
@@ -229,7 +229,7 @@ func (mgr *Manager) VoteTransaction(ctx context.Context, transactionID uint64, n
 	if err := mgr.voteTransaction(ctx, transactionID, node, hash); err != nil {
 		if errors.Is(err, ErrTransactionStopped) {
 			mgr.counterMetric.WithLabelValues("stopped").Inc()
-		} else if errors.Is(err, ErrTransactionVoteFailed) {
+		} else if errors.Is(err, ErrTransactionFailed) {
 			mgr.counterMetric.WithLabelValues("aborted").Inc()
 
 			mgr.log(ctx).WithFields(logrus.Fields{
diff --git a/internal/praefect/transactions/subtransaction.go b/internal/praefect/transactions/subtransaction.go
index 5f46d55a4..4b836b80b 100644
--- a/internal/praefect/transactions/subtransaction.go
+++ b/internal/praefect/transactions/subtransaction.go
@@ -3,19 +3,10 @@ package transactions
 import (
 	"context"
 	"crypto/sha1"
-	"errors"
 	"fmt"
 	"sync"
 )
 
-var (
-	// ErrTransactionVoteFailed indicates the transaction didn't reach quorum.
-	ErrTransactionVoteFailed = errors.New("transaction did not reach quorum")
-	// ErrTransactionCanceled indicates the transaction was canceled before
-	// reaching quorum.
-	ErrTransactionCanceled = errors.New("transaction was canceled")
-)
-
 // VoteResult represents the outcome of a transaction for a single voter.
 type VoteResult int
 
@@ -230,7 +221,7 @@ func (t *subtransaction) collectVotes(ctx context.Context, node string) error {
 	// exceeding it, we know we're the winner in that case.
 	if t.voteCounts[voter.vote] < t.threshold {
 		voter.result = VoteFailed
-		return fmt.Errorf("%w: got %d/%d votes", ErrTransactionVoteFailed, t.voteCounts[voter.vote], t.threshold)
+		return fmt.Errorf("%w: got %d/%d votes", ErrTransactionFailed, t.voteCounts[voter.vote], t.threshold)
 	}
 
 	voter.result = VoteCommitted
diff --git a/internal/praefect/transactions/transaction.go b/internal/praefect/transactions/transaction.go
index 3f0dd7f97..770a0ac8f 100644
--- a/internal/praefect/transactions/transaction.go
+++ b/internal/praefect/transactions/transaction.go
@@ -16,12 +16,12 @@ var (
 	// invalid threshold that may either allow for multiple different
 	// quorums or none at all.
 	ErrInvalidThreshold = errors.New("transaction has invalid threshold")
-	// ErrSubtransactionFailed indicates a vote was cast on an outcome
-	// which didn't reach majority.
-	ErrSubtransactionFailed = errors.New("subtransaction did not reach majority")
-	// ErrSubtransactionCanceled indicates a vote was cast on a
-	// subtransaction which failed already.
-	ErrSubtransactionCanceled = errors.New("subtransaction has been canceled")
+
+	// ErrTransactionFailed indicates the transaction didn't reach quorum.
+	ErrTransactionFailed = errors.New("transaction did not reach quorum")
+	// ErrTransactionCanceled indicates the transaction was canceled before
+	// reaching quorum.
+	ErrTransactionCanceled = errors.New("transaction has been canceled")
 	// ErrTransactionStopped indicates the transaction was gracefully stopped.
 	ErrTransactionStopped = errors.New("transaction has been stopped")
 )
@@ -206,12 +206,12 @@ func (t *Transaction) getOrCreateSubtransaction(node string) (*subtransaction, e
 			// If a vote was cast on a subtransaction which failed
 			// to reach majority, then we cannot proceed with any
 			// subsequent votes anymore.
-			return nil, ErrSubtransactionFailed
+			return nil, ErrTransactionFailed
 		case VoteCanceled:
 			// If the subtransaction was aborted, then we need to
 			// fail as we cannot proceed if the path leading to the
 			// end result has intermittent failures.
-			return nil, ErrSubtransactionCanceled
+			return nil, ErrTransactionCanceled
 		case VoteStopped:
 			// If the transaction was stopped, then we need to fail
 			// with a graceful error.