feat: fix mremap on darwin

.github/workflows/test.yml

@@ -4,7 +4,10 @@ on:
 
 jobs:
   go-test:
-    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest]
+    runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v3
       - uses: actions/setup-go@v4
@@ -20,7 +23,7 @@ jobs:
       - name: Use Node.js 18
         uses: actions/setup-node@v3
         with:
-          node-version: '18'
+          node-version: "18"
       - run: npm ci
       - run: npm run build
       - run: npm test

pkg/mmap/mmap.go

@@ -13,6 +13,9 @@ type MemoryMappedFile struct {
 	file  *os.File
 	bytes []byte
 	seek  int64
+
+	// parameters used for remapping.
+	prot, flags int
 }
 
 var _ io.ReadWriteSeeker = &MemoryMappedFile{}
@@ -35,13 +38,13 @@ func NewMemoryMappedFile(f *os.File, prot int) (*MemoryMappedFile, error) {
 		return nil, fmt.Errorf("stat: %v", err)
 	}
 	if fi.Size() == 0 {
-		return &MemoryMappedFile{file: f, bytes: nil, seek: 0}, nil
+		return &MemoryMappedFile{file: f, bytes: nil, seek: 0, prot: prot, flags: unix.MAP_SHARED}, nil
 	}
 	b, err := unix.Mmap(int(fd), 0, int(fi.Size()), prot, unix.MAP_SHARED)
 	if err != nil {
 		return nil, fmt.Errorf("mmap: %v", err)
 	}
-	return &MemoryMappedFile{file: f, bytes: b, seek: 0}, nil
+	return &MemoryMappedFile{file: f, bytes: b, seek: 0, prot: prot, flags: unix.MAP_SHARED}, nil
 }
 
 // Open is a convenience function to open a file and memory map it.
@@ -141,13 +144,13 @@ func (m *MemoryMappedFile) WriteAt(b []byte, off int64) (int, error) {
 			return 0, err
 		}
 		if m.bytes == nil {
-			m.bytes, err = unix.Mmap(int(m.file.Fd()), 0, int(fi.Size()), unix.PROT_READ|unix.PROT_WRITE, unix.MAP_SHARED)
+			m.bytes, err = unix.Mmap(int(m.file.Fd()), 0, int(fi.Size()), m.prot, m.flags)
 			if err != nil {
 				return 0, fmt.Errorf("mmap: %v", err)
 			}
 			return len(b), nil
 		}
-		b, err := unix.Mremap(m.bytes, int(fi.Size()), unix.MREMAP_MAYMOVE)
+		b, err := mremap(m.bytes, int(m.file.Fd()), int(fi.Size()), m.prot, m.flags)
 		if err != nil {
 			return 0, fmt.Errorf("mmap: %v", err)
 		}

pkg/mmap/mremap_darwin.go

@@ -0,0 +1,13 @@
+package mmap
+
+import "golang.org/x/sys/unix"
+
+func mremap(oldAddress []byte, fd, newSize, prot, flags int) ([]byte, error) {
+	// darwin doesn't have mremap, so we have to munmap and mmap the new size
+
+	// unmap the old address
+	if err := unix.Munmap(oldAddress); err != nil {
+		return nil, err
+	}
+	return unix.Mmap(fd, 0, newSize, prot, flags)
+}

pkg/mmap/mremap_linux.go

@@ -0,0 +1,7 @@
+package mmap
+
+import "golang.org/x/sys/unix"
+
+func mremap(oldAddress []byte, fd, newSize, prot, flags int) ([]byte, error) {
+	return unix.Mremap(oldAddress, newSize, unix.MREMAP_MAYMOVE)
+}