Readonly WAL.

Author: ncruces

internal/util/mmap.go

@@ -1,4 +1,4 @@
-//go:build (darwin || linux || illumos) && (amd64 || arm64) && !sqlite3_flock && !sqlite3_noshm && !sqlite3_nosys
+//go:build (darwin || linux || illumos) && (amd64 || arm64 || riscv64) && !sqlite3_flock && !sqlite3_noshm && !sqlite3_nosys
 
 package util
 
@@ -69,10 +69,10 @@ type MappedRegion struct {
 	used bool
 }
 
-func MapRegion(ctx context.Context, mod api.Module, f *os.File, offset int64, size int32) (*MappedRegion, error) {
+func MapRegion(ctx context.Context, mod api.Module, f *os.File, offset int64, size int32, prot int) (*MappedRegion, error) {
 	s := ctx.Value(moduleKey{}).(*moduleState)
 	r := s.new(ctx, mod, size)
-	err := r.mmap(f, offset)
+	err := r.mmap(f, offset, prot)
 	if err != nil {
 		return nil, err
 	}
@@ -90,9 +90,9 @@ func (r *MappedRegion) Unmap() error {
 	return err
 }
 
-func (r *MappedRegion) mmap(f *os.File, offset int64) error {
+func (r *MappedRegion) mmap(f *os.File, offset int64, prot int) error {
 	_, err := mmap(r.addr, uintptr(r.size),
-		unix.PROT_READ|unix.PROT_WRITE, unix.MAP_SHARED|unix.MAP_FIXED,
+		prot, unix.MAP_SHARED|unix.MAP_FIXED,
 		int(f.Fd()), offset)
 	r.used = err == nil
 	return err

internal/util/mmap_other.go

@@ -1,4 +1,4 @@
-//go:build !(darwin || linux || illumos) || !(amd64 || arm64) || sqlite3_flock || sqlite3_noshm || sqlite3_nosys
+//go:build !(darwin || linux || illumos) || !(amd64 || arm64 || riscv64) || sqlite3_flock || sqlite3_noshm || sqlite3_nosys
 
 package util
 

tests/wal_test.go

@@ -1,10 +1,12 @@
 package tests
 
 import (
+	"os"
 	"path/filepath"
 	"testing"
 
 	"github.com/ncruces/go-sqlite3"
+	"github.com/ncruces/go-sqlite3/vfs"
 )
 
 func TestWAL_enter_exit(t *testing.T) {
@@ -32,6 +34,36 @@ func TestWAL_enter_exit(t *testing.T) {
 	}
 }
 
+func TestWAL_readonly(t *testing.T) {
+	if !vfs.SupportsSharedMemory {
+		t.Skip("skipping without shared memory")
+	}
+
+	t.Parallel()
+
+	tmp := filepath.Join(t.TempDir(), "test.db")
+	err := os.WriteFile(tmp, waldb, 0666)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	db, err := sqlite3.OpenFlags(tmp, sqlite3.OPEN_READONLY)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer db.Close()
+
+	stmt, _, err := db.Prepare(`SELECT * FROM sqlite_master`)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer stmt.Close()
+
+	if stmt.Step() {
+		t.Error("want no rows")
+	}
+}
+
 func TestConn_WalCheckpoint(t *testing.T) {
 	t.Parallel()
 

vfs/README.md

@@ -49,19 +49,18 @@ On 64-bit Linux, macOS and illumos, this module uses `mmap` to implement
 [shared-memory for the WAL-index](https://sqlite.org/wal.html#implementation_of_shared_memory_for_the_wal_index),
 like SQLite.
 
-To allow `mmap` to work, each connection needs to reserve a lot of address space.\
+To allow `mmap` to work, each connection needs to reserve up to 4GB of address space.\
 To limit the amount of address space each connection needs,
 use [`WithMemoryLimitPages`](../tests/parallel/parallel_test.go#L21).
 
 On all other platforms, [WAL](https://sqlite.org/wal.html) support is
 [limited](https://sqlite.org/wal.html#noshm).
 
-To work around that limitation, SQLite is [patched](sqlite3/locking_mode.patch)
+To work around this limitation, SQLite is [patched](sqlite3/locking_mode.patch)
 to automatically use `EXCLUSIVE` locking mode for WAL databases on such platforms.
 
-Because connection pooling is incompatible with `EXCLUSIVE` locking mode,
-to use the [`database/sql`](https://pkg.go.dev/database/sql) driver
-with WAL mode databases you should disable connection pooling by calling
+To use the [`database/sql`](https://pkg.go.dev/database/sql) driver
+with `EXCLUSIVE` locking mode you should disable connection pooling by calling
 [`db.SetMaxOpenConns(1)`](https://pkg.go.dev/database/sql#DB.SetMaxOpenConns).
 
 You can use [`vfs.SupportsSharedMemory`](https://pkg.go.dev/github.com/ncruces/go-sqlite3/vfs#SupportsSharedMemory)

vfs/shm.go

@@ -1,4 +1,4 @@
-//go:build (linux || darwin) && (amd64 || arm64) && !sqlite3_flock && !sqlite3_noshm && !sqlite3_nosys
+//go:build (darwin || linux || illumos) && (amd64 || arm64 || riscv64) && !sqlite3_flock && !sqlite3_noshm && !sqlite3_nosys
 
 package vfs
 
@@ -42,11 +42,12 @@ func (f *vfsFile) shmMap(ctx context.Context, mod api.Module, id, size int32, ex
 	if f.shm.File == nil {
 		var flag int
 		if f.readOnly {
-			flag = unix.O_RDONLY | unix.O_NOFOLLOW
+			flag = unix.O_RDONLY
 		} else {
-			flag = unix.O_RDWR | unix.O_CREAT | unix.O_NOFOLLOW
+			flag = unix.O_RDWR
 		}
-		s, err := os.OpenFile(f.Name()+"-shm", flag, 0666)
+		s, err := os.OpenFile(f.Name()+"-shm",
+			flag|unix.O_CREAT|unix.O_NOFOLLOW, 0666)
 		if err != nil {
 			return 0, _CANTOPEN
 		}
@@ -88,7 +89,13 @@ func (f *vfsFile) shmMap(ctx context.Context, mod api.Module, id, size int32, ex
 		}
 	}
 
-	r, err := util.MapRegion(ctx, mod, f.shm.File, int64(id)*int64(size), size)
+	var prot int
+	if f.readOnly {
+		prot = unix.PROT_READ
+	} else {
+		prot = unix.PROT_READ | unix.PROT_WRITE
+	}
+	r, err := util.MapRegion(ctx, mod, f.shm.File, int64(id)*int64(size), size, prot)
 	if err != nil {
 		return 0, err
 	}

vfs/shm_other.go

@@ -1,4 +1,4 @@
-//go:build !(linux || darwin) || !(amd64 || arm64) || sqlite3_flock || sqlite3_noshm || sqlite3_nosys
+//go:build !(darwin || linux || illumos) || !(amd64 || arm64 || riscv64) || sqlite3_flock || sqlite3_noshm || sqlite3_nosys
 
 package vfs