pub type FileOpenMode {
  Append
  Binary
  DelayedWrite(size: Int, delay: Int)
  Encoding(encoding: TextEncoding)
  Exclusive
  Raw
  Read
  ReadAhead(size: Int)
  Write
}

Constructors

• Append

  The file is opened for writing. It is created if it does not exist. Every write operation to a file opened with Append takes place at the end of the file.

• Binary

  Causes read operations on the file stream to return binaries rather than lists.

  This mode is always set by file_stream.open() and does not need to be specified manually.

• DelayedWrite(size: Int, delay: Int)

  Data in subsequent file_stream.write_* calls are buffered until at least size bytes are buffered, or until the oldest buffered data is delay milliseconds old. Then all buffered data is written in one operating system call. The buffered data is also flushed before some other file operations that are not file_stream.write_* calls.

  The purpose of this option is to increase performance by reducing the number of operating system calls. Thus, file_stream.write_* calls must be for sizes significantly less than size, and should not interspersed by too many other file operations.

  When this option is used, the result of file_stream.write_* calls can prematurely be reported as successful, and if a write error occurs, the error is reported as the result of the next file operation, which is not executed.

  For example, when DelayedWrite is used, after a number of file_stream.write_* calls, file_stream.close() can return Error(FileStreamError(Enospc))) as there is not enough space on the device for previously written data. file_stream.close() must be called again, as the file is still open.

• Encoding(encoding: TextEncoding)

  Makes the file stream perform automatic translation of text to and from the specified text encoding when using the file_stream.read_line(), file_stream.read_chars(), and file_stream.write_chars() functions.

  If characters are written that can’t be converted to the specified encoding then an error occurs and the file is closed.

  This option is not allowed when Raw is specified.

  The text encoding of an open file stream can be changed with file_stream.set_encoding() function.

• Exclusive

  The file is opened for writing. It is created if it does not exist. If the file exists, Error(FileStreamError(Eexist)) is returned by file_stream.open().

  This option does not guarantee exclusiveness on file systems not supporting O_EXCL properly, such as NFS. Do not depend on this option unless you know that the file system supports it (in general, local file systems are safe).

• Raw

  Allows much faster access to a file, as no Erlang process is needed to handle the file. However, a file opened in this way has the following limitations:

  • Only the Erlang process that opened the file can use it.
  • The Encoding option can’t be used and text-based reading and writing is always done in UTF-8. This is because other text encodings depend on the io module, which requires an Erlang process to talk to.
  • The file_stream.read_chars() function can’t be used and will return Error(Enotsup).
  • A remote Erlang file server cannot be used. The computer on which the Erlang node is running must have access to the file system (directly or through NFS).

• Read

  The file, which must exist, is opened for reading.

• ReadAhead(size: Int)

  Activates read data buffering. If file_stream.read_* calls are for significantly less than size bytes, read operations to the operating system are still performed for blocks of size bytes. The extra data is buffered and returned in subsequent file_stream.read_* calls, giving a performance gain as the number of operating system calls is reduced.

  If file_stream.read_* calls are for sizes not significantly less than size bytes, or are greater than size bytes, no performance gain can be expected.

• Write

  The file is opened for writing. It is created if it does not exist. If the file exists and Write is not combined with Read, the file is truncated.