memory-mapped files for posix and windows

1 files changed, 173 insertions, 30 deletions

diff --git a/lib/pure/memfiles.nim b/lib/pure/memfiles.nim
index ed7deeaa5..7fb73186a 100644
--- a/lib/pure/memfiles.nim
+++ b/lib/pure/memfiles.nim
@@ -9,43 +9,186 @@
 
 ## This module provides support for `memory mapped files`:idx:
 ## (Posix's `mmap`:idx:) on the different operating systems.
-## XXX Currently it is implemented with Nimrod's
-## basic IO facilities and does not use any platform specific code!
-## Oh and currently only ``fmRead`` is supported...
+
+when defined(windows):
+  import windows
+elif defined(posix):
+  import posix
+else:
+  {.error: "the memfiles module is not supported yet on your operating system!".}
+
+## mem
+## a pointer to the memory mapped file `f`. The pointer can be
+## used directly to change the contents of the file, if `f` was opened
+## with write access.
+
+## size
+## size of the memory mapped file `f`.
+
+when defined(windows):
+  type Tsize = int64
+else:
+  type Tsize = int
 
 type
   TMemFile* = object {.pure.} ## represents a memory mapped file
-    file: TFile
-    buffer: pointer
-    fileLen: int
-  
-proc open*(f: var TMemFile, filename: string, mode: TFileMode = fmRead): bool =
+    mem*: pointer # XXX: The compiler won't let me add comments on the next line
+    size*: Tsize
+
+    when defined(windows):
+      fHandle: int
+      mapHandle: int 
+    else:
+      handle: cint
+
+proc open*(
+  f           : var TMemFile,
+  filename    : string,
+  mode        : TFileMode = fmRead,
+  mappedSize  : int       = -1,
+  offset      : Tsize     = 0,
+  newFileSize : Tsize     = -1 ): bool =
   ## open a memory mapped file `f`. Returns true for success.
-  assert mode == fmRead
-  result = open(f.file, filename, mode)
-
-  var len = getFileSize(f.file)
-  if len < high(int):
-    f.fileLen = int(len)
-    f.buffer = alloc(f.fileLen)
-    if readBuffer(f.file, f.buffer, f.fileLen) != f.fileLen:
-      raise newException(EIO, "error while reading from file")
+
+  # The file can be resized only when write mode is used
+  assert newFileSize == -1 or mode != fmRead
+  var readonly = mode == fmRead
+
+  template rollback =
+    f.mem = nil
+    f.size = 0
+
+  when defined(windows):
+    template fail(msg: expr) =
+      rollback()
+      if f.fHandle != 0: discard CloseHandle(f.fHandle)
+      if f.mapHandle != 0: discard CloseHandle(f.mapHandle)
+      # return false
+      raise newException(EIO, msg)
+      
+    f.fHandle = CreateFileA(
+      filename,
+      if readonly: GENERIC_READ else: GENERIC_ALL,
+      FILE_SHARE_READ,
+      nil,
+      if newFileSize != -1: CREATE_ALWAYS else: OPEN_EXISTING,
+      if readonly: FILE_ATTRIBUTE_READONLY else: FILE_ATTRIBUTE_TEMPORARY,
+      0)
+
+    if f.fHandle == INVALID_HANDLE_VALUE:
+      fail "error opening file"
+
+    if newFileSize != -1:
+      var 
+        sizeHigh = int32(newFileSize shr 32)
+        sizeLow  = int32(newFileSize and 0xffffffff)
+
+      var status = SetFilePointer(f.fHandle, sizeLow, addr(sizeHigh), FILE_BEGIN)
+      if (status == INVALID_SET_FILE_POINTER and GetLastError() != NO_ERROR) or
+         (SetEndOfFile(f.fHandle) == 0):
+        fail "error setting file size"
+
+    f.mapHandle = CreateFileMapping(
+      f.fHandle, nil,
+      if readonly: PAGE_READONLY else: PAGE_READWRITE,
+      0, 0, nil)
+
+    if f.mapHandle == 0:
+      fail "error creating mapping"
+
+    f.mem = MapViewOfFileEx(
+      f.mapHandle,
+      if readonly: FILE_MAP_READ else: FILE_MAP_WRITE,
+      int32(offset shr 32),
+      int32(offset and 0xffffffff),
+      if mappedSize == -1: 0 else: mappedSize,
+      nil)
+
+    if f.mem == nil:
+      fail "error mapping view"
+
+    var hi, low: int32
+    low = GetFileSize(f.fHandle, addr(hi))
+    if low == INVALID_FILE_SIZE:
+      fail "error getting file size"
+    else:
+      var fileSize = (int64(hi) shr 32) or low
+      f.size = if mappedSize != -1: min(fileSize, mappedSize) else: fileSize
+
+    result = true
+
   else:
-    raise newException(EIO, "file too big to fit in memory")
+    template fail(msg: expr) =
+      rollback()
+      if f.handle != 0:
+        discard close(f.handle)
+      # return false
+      raise newException(system.EIO, msg)
+  
+    var flags = if readonly: O_RDONLY else: O_RDWR
+
+    if newFileSize != -1:
+      flags = flags or O_CREAT or O_TRUNC
+
+    f.handle = open(filename, flags)
+    if f.handle == -1:
+      # XXX: errno is supposed to be set here
+      # Is there an exception that wraps it?
+      fail "error opening file"
+
+    if newFileSize != -1:
+      if ftruncate(f.handle, newFileSize) == -1:
+        fail "error setting file size"
+
+    if mappedSize != -1:
+      f.size = mappedSize
+    else:
+      var stat: Tstat
+      if fstat(f.handle, stat) != -1:
+        # XXX: Hmm, this could be unsafe
+        # Why is mmap taking int anyway?
+        f.size = int(stat.st_size)
+      else:
+        fail "error getting file size"
+
+    f.mem = mmap(
+      nil,
+      f.size,
+      if readonly: PROT_READ else: PROT_READ or PROT_WRITE,
+      if readonly: MAP_PRIVATE else: MAP_SHARED,
+      f.handle,
+      offset)
+
+    if f.mem == cast[pointer](MAP_FAILED):
+      fail "file mapping failed"
+
+    result = true
 
 proc close*(f: var TMemFile) =
   ## closes the memory mapped file `f`. All changes are written back to the
   ## file system, if `f` was opened with write access.
-  dealloc(f.buffer)
-  close(f.file)
-
-proc mem*(f: var TMemFile): pointer {.inline.} =
-  ## retrives a pointer to the memory mapped file `f`. The pointer can be
-  ## used directly to change the contents of the file, if `f` was opened
-  ## with write access.
-  result = f.buffer
-
-proc size*(f: var TMemFile): int {.inline.} =
-  ## retrives the size of the memory mapped file `f`.
-  result = f.fileLen
+  
+  var error = false
+
+  when defined(windows):
+    if f.fHandle != INVALID_HANDLE_VALUE:
+      error = UnmapViewOfFile(f.mem) == 0
+      error = (CloseHandle(f.mapHandle) == 0) or error
+      error = (CloseHandle(f.fHandle) == 0) or error
+  else:
+    if f.handle != 0:
+      error = munmap(f.mem, f.size) != 0
+      error = (close(f.handle) != 0) or error
+
+  f.size = 0
+  f.mem = nil
+
+  when defined(windows):
+    f.fHandle = 0
+    f.mapHandle = 0
+  else:
+    f.handle = 0
+  
+  if error:
+    raise newException(system.EIO, "error closing file")