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🐳 mmap: migrate to unix.MmapPtr & unix.MunmapPtr
While here, improve the API and add a fallback path for files on unsupported filesystems.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,48 @@ | ||
| package mmap | ||
|
|
||
| import ( | ||
| "errors" | ||
| "io" | ||
| "os" | ||
| "unsafe" | ||
| ) | ||
|
|
||
| // ReadFile maps the named file into memory for reading. | ||
| // On success, it returns the mapped data as a byte slice or a string, | ||
| // and a function that unmaps the data. | ||
| func ReadFile[T ~[]byte | ~string](name string) (data T, close func() error, err error) { | ||
| f, err := os.Open(name) | ||
| if err != nil { | ||
| return | ||
| } | ||
| defer f.Close() | ||
|
|
||
| fs, err := f.Stat() | ||
| if err != nil { | ||
| return | ||
| } | ||
|
|
||
| size := fs.Size() | ||
| if size == 0 { | ||
| return | ||
| } | ||
|
|
||
| addr, close, err := readFile(f, uintptr(size)) | ||
| if err != nil { | ||
| if errors.Is(err, errors.ErrUnsupported) { | ||
| return readFileFallback[T](f, size) | ||
| } | ||
| return | ||
| } | ||
|
|
||
| b := unsafe.Slice((*byte)(addr), size) | ||
| return *(*T)(unsafe.Pointer(&b)), close, nil | ||
| } | ||
|
|
||
| func readFileFallback[T ~[]byte | ~string](f *os.File, size int64) (data T, close func() error, err error) { | ||
| b := make([]byte, size) | ||
| if _, err = io.ReadFull(f, b); err != nil { | ||
| return | ||
| } | ||
| return *(*T)(unsafe.Pointer(&b)), func() error { return nil }, nil | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,23 @@ | ||
| //go:build !unix && !windows | ||
|
|
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| package mmap | ||
|
|
||
| import ( | ||
| "errors" | ||
| "os" | ||
| "unsafe" | ||
| ) | ||
|
|
||
| type mmapUnsupportError struct{} | ||
|
|
||
| func (mmapUnsupportError) Error() string { | ||
| return "mmap is not supported on this platform" | ||
| } | ||
|
|
||
| func (mmapUnsupportError) Is(target error) bool { | ||
| return target == errors.ErrUnsupported | ||
| } | ||
|
|
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| func readFile(_ *os.File, _ uintptr) (addr unsafe.Pointer, close func() error, err error) { | ||
| return nil, nil, mmapUnsupportError{} | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,31 @@ | ||
| //go:build unix | ||
|
|
||
| package mmap | ||
|
|
||
| import ( | ||
| "os" | ||
| "unsafe" | ||
|
|
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| "golang.org/x/sys/unix" | ||
| ) | ||
|
|
||
| func readFile(f *os.File, size uintptr) (addr unsafe.Pointer, close func() error, err error) { | ||
| rawConn, err := f.SyscallConn() | ||
| if err != nil { | ||
| return nil, nil, err | ||
| } | ||
|
|
||
| if cerr := rawConn.Control(func(fd uintptr) { | ||
| addr, err = unix.MmapPtr(int(fd), 0, nil, size, unix.PROT_READ, unix.MAP_SHARED) | ||
| }); cerr != nil { | ||
| return nil, nil, cerr | ||
| } | ||
|
|
||
| if err != nil { | ||
| return nil, nil, err | ||
| } | ||
|
|
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| return addr, func() error { | ||
| return unix.MunmapPtr(addr, size) | ||
| }, nil | ||
| } |
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