Netstring

Netstring is a simple data-encoding used to frame strings in network communications. A netstring encodes a string as a decimal length, a colon, the data itself, and a trailing comma: <length>:<data>,. The length indicates the number of bytes in data. For example, 3:abc, encodes the three-byte string abc, while 0:, encodes the empty string. Netstrings are self-delimiting and preserve binary data without escaping.

Because the length is explicit, netstrings are straightforward to parse: a reader collects digits until a colon, interprets the value as the length, reads exactly that many bytes of data, and then consumes the trailing comma. The data portion may include any binary byte values, including colon or comma, since those characters have no special meaning outside the length-delimiter and the final comma.

Advantages of netstrings include simple and predictable parsing, robust framing for streaming I/O, and avoidance of escaping rules for data. They provide a clear boundary between successive messages and can be implemented with minimal state in many programming languages. While not universal, they are used in a variety of lightweight network protocols and inter-process communication schemes where unambiguous string framing is desirable.

Origin and terminology: netstring was proposed by Daniel J. Bernstein as a straightforward, portable way to transmit strings over networks. The format’s name reflects its role as a string-encoding primitive for network protocols. The concept has influenced other length-prefixed framing schemes and remains cited as a simple reference implementation for self-delimiting data.