# std/asyncfile

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This module implements asynchronous file reading and writing.

    import std/[asyncfile, asyncdispatch, os]

    proc main() {.async.} =
      var file = openAsync(getTempDir() / "foobar.txt", fmReadWrite)
      await file.write("test")
      file.setFilePos(0)
      let data = await file.readAll()
      doAssert data == "test"
      file.close()

    waitFor main()

# Imports

asyncdispatch, os, winlean

# Types

    AsyncFile = ref object

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# Procs

    proc close(f: AsyncFile) {....raises: [OSError], tags: [], forbids: [].}

  Closes the file specified. Source Edit

    proc getFilePos(f: AsyncFile): int64 {....raises: [], tags: [], forbids: [].}

  Retrieves the current position of the file pointer that is used to read from the specified file. The file's first byte has the index zero. Source Edit

    proc getFileSize(f: AsyncFile): int64 {....raises: [OSError], tags: [], forbids: [].}

  Retrieves the specified file's size. Source Edit

    proc newAsyncFile(fd: AsyncFD): AsyncFile {....raises: [OSError], tags: [],
        forbids: [].}

  Creates `AsyncFile` with a previously opened file descriptor `fd`. Source Edit

    proc openAsync(filename: string; mode = fmRead): AsyncFile {....raises: [OSError],
        tags: [], forbids: [].}

  Opens a file specified by the path in `filename` using the specified FileMode `mode` asynchronously. Source Edit

    proc read(f: AsyncFile; size: int): Future[string] {.
        ...raises: [ValueError, Exception], tags: [RootEffect], forbids: [].}

  Read `size` bytes from the specified file asynchronously starting at the current position of the file pointer. `size` should be greater than zero.

  If the file pointer is past the end of the file then an empty string is returned.

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    proc readAll(f: AsyncFile): Future[string] {....stackTrace: false,
        raises: [Exception, ValueError], tags: [RootEffect], forbids: [].}

  Reads all data from the specified file. Source Edit

    proc readBuffer(f: AsyncFile; buf: pointer; size: int): Future[int] {.
        ...raises: [ValueError, Exception], tags: [RootEffect], forbids: [].}

  Read `size` bytes from the specified file asynchronously starting at the current position of the file pointer.

  If the file pointer is past the end of the file then zero is returned and no bytes are read into `buf`

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    proc readLine(f: AsyncFile): Future[string] {....stackTrace: false,
        raises: [Exception, ValueError], tags: [RootEffect], forbids: [].}

  Reads a single line from the specified file asynchronously. Source Edit

    proc readToStream(f: AsyncFile; fs: FutureStream[string]): owned(
        Future[void]) {....stackTrace: false, raises: [Exception, ValueError],
                        tags: [RootEffect], forbids: [].}

  Writes data to the specified future stream as the file is read. Source Edit

    proc setFilePos(f: AsyncFile; pos: int64) {....raises: [], tags: [], forbids: [].}

  Sets the position of the file pointer that is used for read/write operations. The file's first byte has the index zero. Source Edit

    proc setFileSize(f: AsyncFile; length: int64) {....raises: [OSError], tags: [],
        forbids: [].}

  Set a file length. Source Edit

    proc write(f: AsyncFile; data: string): Future[void] {....raises: [Exception],
        tags: [RootEffect], forbids: [].}

  Writes `data` to the file specified asynchronously.

  The returned Future will complete once all data has been written to the specified file.

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    proc writeBuffer(f: AsyncFile; buf: pointer; size: int): Future[void] {.
        ...raises: [Exception], tags: [RootEffect], forbids: [].}

  Writes `size` bytes from `buf` to the file specified asynchronously.

  The returned Future will complete once all data has been written to the specified file.

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    proc writeFromStream(f: AsyncFile; fs: FutureStream[string]): owned(
        Future[void]) {....stackTrace: false, raises: [Exception, ValueError],
                        tags: [RootEffect], forbids: [].}

  Reads data from the specified future stream until it is completed. The data which is read is written to the file immediately and freed from memory.

  This procedure is perfect for saving streamed data to a file without wasting memory.

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