fixes #7347, asyncfile.getFileSize (#7354)

* fixes #7347

* fixes #7347

lib/pure/asyncfile.nim

@@ -78,7 +78,10 @@ proc getFileSize*(f: AsyncFile): int64 =
       raiseOSError(osLastError())
     result = (high shl 32) or low
   else:
+    let curPos = lseek(f.fd.cint, 0, SEEK_CUR)
     result = lseek(f.fd.cint, 0, SEEK_END)
+    f.offset = lseek(f.fd.cint, curPos, SEEK_SET)
+    assert(f.offset == curPos)
 
 proc newAsyncFile*(fd: AsyncFd): AsyncFile =
   ## Creates `AsyncFile` with a previously opened file descriptor `fd`.
@@ -281,6 +284,7 @@ proc read*(f: AsyncFile, size: int): Future[string] =
           result = false # We still want this callback to be called.
       elif res == 0:
         # EOF
+        f.offset = lseek(fd.cint, 0, SEEK_CUR)
         retFuture.complete("")
       else:
         readBuffer.setLen(res)

tests/async/hello.txt

@@ -0,0 +1 @@
+hello humans!

tests/async/tasyncfile.nim

@@ -1,4 +1,8 @@
 discard """
+  output: '''13
+hello humans!
+13
+'''
   file: "tasyncfile.nim"
   exitcode: 0
 """
@@ -48,5 +52,12 @@ proc main() {.async.} =
     doAssert data == "t3"
     file.close()
 
+  # Issue #7347
+  block:
+    let appDir = getAppDir()
+    var file = openAsync(appDir & DirSep & "hello.txt")
+    echo file.getFileSize()
+    echo await file.readAll()
+    echo file.getFilePos()
 
 waitFor main()