datasize

Golang helpers for data sizes

Usage in flag

var d datasize.ByteSize
fs.Var(&d, "s", "byte size to parse")
fs.Parse([]string{"-s", "2M"})
fmt.Println(d)

Constants

Just like time package provides time.Second, time.Day constants datasize provides:

• datasize.B 1 byte
• datasize.KB 1 kilobyte
• datasize.MB 1 megabyte
• datasize.GB 1 gigabyte
• datasize.TB 1 terabyte
• datasize.PB 1 petabyte
• datasize.EB 1 exabyte

Helpers

Just like time package provides duration.Nanoseconds() uint64 , duration.Hours() float64 helpers datasize has.

• ByteSize.Bytes() uint64
• ByteSize.Kilobytes() float64
• ByteSize.Megabytes() float64
• ByteSize.Gigabytes() float64
• ByteSize.Terabytes() float64
• ByteSize.Petebytes() float64
• ByteSize.Exabytes() float64

Warning: see limitations at the end of this document about a possible precission loss

Parsing strings

datasize.ByteSize implements TextUnmarshaler interface and will automatically parse human readable strings into correct values where it is used:

• "10 MB" -> 10* datasize.MB
• "10240 g" -> 10 * datasize.TB
• "2000" -> 2000 * datasize.B
• "1tB" -> datasize.TB
• "5 peta" -> 5 * datasize.PB
• "28 kilobytes" -> 28 * datasize.KB
• "1 gigabyte" -> 1 * datasize.GB

You can also do it manually:

var v datasize.ByteSize
err := v.UnmarshalText([]byte("100 mb"))

Printing

Bytesize.String() uses largest unit allowing an integer value:

• (102400 * datasize.MB).String() -> "100GB"
• (datasize.MB + datasize.KB).String() -> "1025KB"

Use %d format string to get value in bytes without a unit.

JSON and other encoding

Both TextMarshaler and TextUnmarshaler interfaces are implemented - JSON will just work. Other encoders will work provided they use those interfaces.

Human readable

ByteSize.HumanReadable() or ByteSize.HR() returns a string with 1-3 digits, followed by 1 decimal place, a space and unit big enough to get 1-3 digits

• (102400 * datasize.MB).String() -> "100.0 GB"
• (datasize.MB + 512 * datasize.KB).String() -> "1.5 MB"

Limitations

• The underlying data type for data.ByteSize is uint64, so values outside of 0 to 2^64-1 range will overflow
• size helper functions (like ByteSize.Kilobytes()) return float64, which can't represent all possible values of uint64 accurately:
  • if the returned value is supposed to have no fraction (ie (10 * datasize.MB).Kilobytes()) accuracy loss happens when value is more than 2^53 larger than unit: .Kilobytes() over 8 petabytes, .Megabytes() over 8 exabytes
  • if the returned value is supposed to have a fraction (ie (datasize.PB + datasize.B).Megabytes()) in addition to the above note accuracy loss may occur in fractional part too - larger integer part leaves fewer bytes to store fractional part, the smaller the remainder vs unit the move bytes are required to store the fractional part
• Parsing a string with Mb, Tb, etc units will return a syntax error, because capital followed by lower case is commonly used for bits, not bytes
• Parsing a string with value exceeding 2^64-1 bytes will return 2^64-1 and an out of range error