fix https://github.com/nim-lang/RFCs/issues/286: add FileInfo.blockSize (#16023)

changelog.md

@@ -38,6 +38,8 @@
 - Added `asyncdispatch.activeDescriptors` that returns the number of currently
   active async event handles/file descriptors
 
+- `os.FileInfo` (returned by `getFileInfo`) now contains `blockSize`,
+  determining preferred I/O block size for this file object.
 
 ## Language changes
 

lib/pure/os.nim

@@ -1550,40 +1550,6 @@ proc sameFile*(path1, path2: string): bool {.rtl, extern: "nos$1",
     else:
       result = a.st_dev == b.st_dev and a.st_ino == b.st_ino
 
-proc sameFileContent*(path1, path2: string): bool {.rtl, extern: "nos$1",
-  tags: [ReadIOEffect], noWeirdTarget.} =
-  ## Returns true if both pathname arguments refer to files with identical
-  ## binary content.
-  ##
-  ## See also:
-  ## * `sameFile proc <#sameFile,string,string>`_
-  const
-    bufSize = 8192 # 8K buffer
-  var
-    a, b: File
-  if not open(a, path1): return false
-  if not open(b, path2):
-    close(a)
-    return false
-  var bufA = alloc(bufSize)
-  var bufB = alloc(bufSize)
-  while true:
-    var readA = readBuffer(a, bufA, bufSize)
-    var readB = readBuffer(b, bufB, bufSize)
-    if readA != readB:
-      result = false
-      break
-    if readA == 0:
-      result = true
-      break
-    result = equalMem(bufA, bufB, readA)
-    if not result: break
-    if readA != bufSize: break # end of file
-  dealloc(bufA)
-  dealloc(bufB)
-  close(a)
-  close(b)
-
 type
   FilePermission* = enum   ## File access permission, modelled after UNIX.
     ##
@@ -3074,6 +3040,8 @@ type
     lastAccessTime*: times.Time       ## Time file was last accessed.
     lastWriteTime*: times.Time        ## Time file was last modified/written to.
     creationTime*: times.Time         ## Time file was created. Not supported on all systems!
+    blockSize*: int                   ## Preferred I/O block size for this object.
+                                      ## In some filesystems, this may vary from file to file.
 
 template rawToFormalFileInfo(rawInfo, path, formalInfo): untyped =
   ## Transforms the native file info structure into the one nim uses.
@@ -3088,6 +3056,7 @@ template rawToFormalFileInfo(rawInfo, path, formalInfo): untyped =
     formalInfo.lastAccessTime = fromWinTime(rdFileTime(rawInfo.ftLastAccessTime))
     formalInfo.lastWriteTime = fromWinTime(rdFileTime(rawInfo.ftLastWriteTime))
     formalInfo.creationTime = fromWinTime(rdFileTime(rawInfo.ftCreationTime))
+    formalInfo.blockSize = 8192 # xxx use windows API instead of hardcoding
 
     # Retrieve basic permissions
     if (rawInfo.dwFileAttributes and FILE_ATTRIBUTE_READONLY) != 0'i32:
@@ -3114,6 +3083,7 @@ template rawToFormalFileInfo(rawInfo, path, formalInfo): untyped =
     formalInfo.lastAccessTime = rawInfo.st_atim.toTime
     formalInfo.lastWriteTime = rawInfo.st_mtim.toTime
     formalInfo.creationTime = rawInfo.st_ctim.toTime
+    formalInfo.blockSize = rawInfo.st_blksize
 
     formalInfo.permissions = {}
     checkAndIncludeMode(S_IRUSR, fpUserRead)
@@ -3217,6 +3187,39 @@ proc getFileInfo*(path: string, followSymlink = true): FileInfo {.noWeirdTarget.
         raiseOSError(osLastError(), path)
     rawToFormalFileInfo(rawInfo, path, result)
 
+proc sameFileContent*(path1, path2: string): bool {.rtl, extern: "nos$1",
+  tags: [ReadIOEffect], noWeirdTarget.} =
+  ## Returns true if both pathname arguments refer to files with identical
+  ## binary content.
+  ##
+  ## See also:
+  ## * `sameFile proc <#sameFile,string,string>`_
+  var
+    a, b: File
+  if not open(a, path1): return false
+  if not open(b, path2):
+    close(a)
+    return false
+  let bufSize = getFileInfo(a).blockSize
+  var bufA = alloc(bufSize)
+  var bufB = alloc(bufSize)
+  while true:
+    var readA = readBuffer(a, bufA, bufSize)
+    var readB = readBuffer(b, bufB, bufSize)
+    if readA != readB:
+      result = false
+      break
+    if readA == 0:
+      result = true
+      break
+    result = equalMem(bufA, bufB, readA)
+    if not result: break
+    if readA != bufSize: break # end of file
+  dealloc(bufA)
+  dealloc(bufB)
+  close(a)
+  close(b)
+
 proc isHidden*(path: string): bool {.noWeirdTarget.} =
   ## Determines whether ``path`` is hidden or not, using `this
   ## reference <https://en.wikipedia.org/wiki/Hidden_file_and_hidden_directory>`_.