From 58b66b75f1d5e18e78852720c2a1651afd7aa6ac Mon Sep 17 00:00:00 2001
From: Nuno Cruces <ncruces@users.noreply.github.com>
Date: Thu, 19 Dec 2024 13:19:10 +0000
Subject: [PATCH] Improved assertions.

---
 vfs/lock.go      | 19 ++++++++-----------
 vfs/shm_bsd.go   |  2 +-
 vfs/shm_memlk.go | 16 +++++++---------
 vfs/shm_ofd.go   | 10 ++++++----
 4 files changed, 22 insertions(+), 25 deletions(-)

diff --git a/vfs/lock.go b/vfs/lock.go
index 8828662..b28d832 100644
--- a/vfs/lock.go
+++ b/vfs/lock.go
@@ -20,12 +20,10 @@ const (
 )
 
 func (f *vfsFile) Lock(lock LockLevel) error {
-	// Argument check. SQLite never explicitly requests a pending lock.
-	if lock != LOCK_SHARED && lock != LOCK_RESERVED && lock != LOCK_EXCLUSIVE {
-		panic(util.AssertErr())
-	}
-
 	switch {
+	case lock != LOCK_SHARED && lock != LOCK_RESERVED && lock != LOCK_EXCLUSIVE:
+		// Argument check. SQLite never explicitly requests a pending lock.
+		panic(util.AssertErr())
 	case f.lock < LOCK_NONE || f.lock > LOCK_EXCLUSIVE:
 		// Connection state check.
 		panic(util.AssertErr())
@@ -87,13 +85,12 @@ func (f *vfsFile) Lock(lock LockLevel) error {
 }
 
 func (f *vfsFile) Unlock(lock LockLevel) error {
-	// Argument check.
-	if lock != LOCK_NONE && lock != LOCK_SHARED {
+	switch {
+	case lock != LOCK_NONE && lock != LOCK_SHARED:
+		// Argument check.
 		panic(util.AssertErr())
-	}
-
-	// Connection state check.
-	if f.lock < LOCK_NONE || f.lock > LOCK_EXCLUSIVE {
+	case f.lock < LOCK_NONE || f.lock > LOCK_EXCLUSIVE:
+		// Connection state check.
 		panic(util.AssertErr())
 	}
 
diff --git a/vfs/shm_bsd.go b/vfs/shm_bsd.go
index fd9d3df..5f4f5d1 100644
--- a/vfs/shm_bsd.go
+++ b/vfs/shm_bsd.go
@@ -208,7 +208,7 @@ func (s *vfsShm) shmLock(offset, n int32, flags _ShmFlag) _ErrorCode {
 		panic(util.AssertErr())
 	}
 
-	// Reacquire the local lock.
+	// Release the local lock we had acquired.
 	if rc != _OK {
 		s.shmMemLock(offset, n, flags^(_SHM_UNLOCK|_SHM_LOCK))
 	}
diff --git a/vfs/shm_memlk.go b/vfs/shm_memlk.go
index 4040196..5c8071e 100644
--- a/vfs/shm_memlk.go
+++ b/vfs/shm_memlk.go
@@ -10,9 +10,6 @@ func (s *vfsShm) shmMemLock(offset, n int32, flags _ShmFlag) _ErrorCode {
 	case flags&_SHM_UNLOCK != 0:
 		for i := offset; i < offset+n; i++ {
 			if s.lock[i] {
-				if s.vfsShmParent.lock[i] == 0 {
-					panic(util.AssertErr())
-				}
 				if s.vfsShmParent.lock[i] <= 0 {
 					s.vfsShmParent.lock[i] = 0
 				} else {
@@ -23,20 +20,21 @@ func (s *vfsShm) shmMemLock(offset, n int32, flags _ShmFlag) _ErrorCode {
 		}
 	case flags&_SHM_SHARED != 0:
 		for i := offset; i < offset+n; i++ {
-			if s.lock[i] {
-				panic(util.AssertErr())
-			}
-			if s.vfsShmParent.lock[i]+1 <= 0 {
+			if !s.lock[i] &&
+				s.vfsShmParent.lock[i]+1 <= 0 {
 				return _BUSY
 			}
 		}
 		for i := offset; i < offset+n; i++ {
-			s.vfsShmParent.lock[i]++
-			s.lock[i] = true
+			if !s.lock[i] {
+				s.vfsShmParent.lock[i]++
+				s.lock[i] = true
+			}
 		}
 	case flags&_SHM_EXCLUSIVE != 0:
 		for i := offset; i < offset+n; i++ {
 			if s.lock[i] {
+				// SQLite never requests an exclusive lock that it already holds.
 				panic(util.AssertErr())
 			}
 			if s.vfsShmParent.lock[i] != 0 {
diff --git a/vfs/shm_ofd.go b/vfs/shm_ofd.go
index d335a85..dd36111 100644
--- a/vfs/shm_ofd.go
+++ b/vfs/shm_ofd.go
@@ -110,7 +110,12 @@ func (s *vfsShm) shmMap(ctx context.Context, mod api.Module, id, size int32, ext
 
 func (s *vfsShm) shmLock(offset, n int32, flags _ShmFlag) _ErrorCode {
 	// Argument check.
-	if n <= 0 || offset < 0 || offset+n > _SHM_NLOCK {
+	switch {
+	case n <= 0:
+		panic(util.AssertErr())
+	case offset < 0 || offset+n > _SHM_NLOCK:
+		panic(util.AssertErr())
+	case n != 1 && flags&_SHM_EXCLUSIVE == 0:
 		panic(util.AssertErr())
 	}
 	switch flags {
@@ -123,9 +128,6 @@ func (s *vfsShm) shmLock(offset, n int32, flags _ShmFlag) _ErrorCode {
 	default:
 		panic(util.AssertErr())
 	}
-	if n != 1 && flags&_SHM_EXCLUSIVE == 0 {
-		panic(util.AssertErr())
-	}
 
 	var timeout time.Duration
 	if s.blocking {