Matthias Braun Matthias Braun - 24 days ago 10
Scala Question

Bytes in human-readable format with idiomatic Scala

I'm looking for idiomatic Scala code that formats a number of bytes into a human-readable string which is useful when displaying file sizes to users.

For example, 1000 bytes should be formatted to

1.0 kB
and 49134421234 bytes to
49.1 GB
.

Some requirements for the formatting function:


  • As readable and idiomatic as possible

  • Works both with SI (e.g, megabyte) and IEC units (e.g, mebibyte)

  • No dependencies on external libraries

  • Executable in a browser via Scala.js


Answer Source

My version:

/**
  * Converts a number of bytes into a human-readable string
  * such as `2.2 MB` or `8.0 EiB`.
  *
  * @param bytes the number of bytes we want to convert
  * @param si    if true, we use base 10 SI units where 1000 bytes are 1 kB.
  *              If false, we use base 2 IEC units where 1024 bytes are 1 KiB.
  * @return the bytes as a human-readable string
  */
def humanReadableSize(bytes: Long, si: Boolean): String = {

  // See https://en.wikipedia.org/wiki/Byte
  val (baseValue, unitStrings) =
    if (si)
      (1000, Vector("B", "kB", "MB", "GB", "TB", "PB", "EB", "ZB", "YB"))
    else
      (1024, Vector("B", "KiB", "MiB", "GiB", "TiB", "PiB", "EiB", "ZiB", "YiB"))

  def getExponent(curBytes: Long, baseValue: Int, curExponent: Int = 0): Int =
    if (curBytes < baseValue) curExponent
    else {
      val newExponent = 1 + curExponent
      getExponent(curBytes / (baseValue * newExponent), baseValue, newExponent)
    }

  val exponent = getExponent(bytes, baseValue)
  val divisor = Math.pow(baseValue, exponent)
  val unitString = unitStrings(exponent)

  // Divide the bytes and show one digit after the decimal point
  f"${bytes / divisor}%.1f $unitString"
}

Usage examples:

// Result: 1.0 kB
humanReadableSize(1000, si = true)

// Result: 1000.0 B
humanReadableSize(1000, si = false)

// Result: 10.0 kB
humanReadableSize(10000, si = true)

// Result: 9.8 KiB
humanReadableSize(10000, si = false)

// Result: 49.1 GB
humanReadableSize(49134421234L, si = true)

// Result: 45.8 GiB
humanReadableSize(49134421234L, si = false)