| json | N. Williams |
| Internet-Draft | Cryptonector |
| Intended status: Standards Track | October 27, 2014 |
| Expires: April 30, 2015 |
JavaScript Object Notation (JSON) Text Sequences
draft-ietf-json-text-sequence-09
This document describes the JSON text sequence format and associated media type, “application/json-seq”. A JSON text sequence consists of any number of JSON texts, each prefix by an Record Separator (U+001E), and each ending with a newline character (U+000A).
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The JavaScript Object Notation (JSON) [RFC7159] is a very handy serialization format. However, when serializing a large sequence of values as an array, or a possibly indeterminate-length or never-ending sequence of values, JSON becomes difficult to work with.
Consider a sequence of one million values, each possibly 1 kilobyte when encoded -- roughly one gigabyte. It is often desirable to process such a dataset in an incremental manner: without having to first read all of it before beginning to produce results. Traditionally the way to do this with JSON is to use a “streaming” parser, but these are neither widely available, widely used, nor easy to use.
This document describes the concept and format of “JSON text sequences”, which are specifically not JSON texts themselves but are composed of (possible) JSON texts. JSON text sequences can be parsed (and produced) incrementally without having to have a streaming parser (nor streaming encoder).
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", “NOT RECOMMENDED”, "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].
Two different sets of ABNF rules are provided for the definition of JSON text sequences: one for parsers, and one for encoders. Having two different sets of rules permits recovery by parsers from sequences where some the elements are truncated for whatever reason. The syntax for parsers is specified in terms of octet strings which are then interpreted as JSON texts if possible. The syntax for encoders, on the other hand, assumes that sequence elements are not truncated.
The ABNF [RFC5234] for the JSON text sequence parser is as given in Figure 1.
JSON-sequence = *(1*RS possible-JSON)
RS = %x1E; "record separator" (RS), see RFC20
possible-JSON = 1*(not-RS); attempt to parse as UTF-8-encoded
; JSON text (see RFC7159)
not-RS = %x00-1d / %x1f-ff; any octets other than RS
Figure 1: JSON text sequence ABNF
In prose: a series of octet strings, each containing any octet other than a record separator (RS) (0x1E) [RFC0020], all octet strings separated from each other by RS octets. Each octet string in the sequence is to be parsed as a JSON text.
If parsing of such an octet string as a JSON text fails, the parser SHOULD nonetheless continue parsing the remainder of the sequence. The parser should report such failures to applications (which might choose to terminate parsing of a sequence). Multiple consecutive RS octets do not denote empty sequence elements between them, and can be ignored.
There is no end of sequence indicator.
The ABNF for the JSON text sequence encoder is given in Figure 2.
JSON-sequence = *(RS JSON-text LF) RS = %x1E; see RFC20 LF = %x0A; "line feed" (LF), see RFC20 JSON-text = <given by RFC7159>
Figure 2: JSON text sequence ABNF
In prose: any number of JSON texts, each preceded by one ASCII RS character and each followed by a line feed (LF). Since RS is an ASCII control character it may only appear in JSON strings in escaped form (see [RFC7159]), and since RS may not appear in JSON texts in any other form, RS unambiguously delimits the start of any element in the sequence. RS is sufficient to unambiguously delimit all top-level JSON value types other than numbers. Following each JSON text in the sequence with an LF allows detection of truncated JSON texts consisting of a number at the top-level.
Note that on some systems it's possible to input RS by typing 'ctrl-^'. This is helpful when constructing a sequence manually with a text editor.
Per- Section 2.1, JSON text sequence parsers SHOULD NOT abort when an octet string contains a malformed JSON text. Such a situation may arise in contexts where, for example, append-writes to log files are truncated by the filesystem (e.g., due to a crash, or administrative process termination).
Parsers MUST check that any JSON texts that are a top-level number include JSON whitespace (“ws” ABNF rule from [RFC7159]) after the number, otherwise the JSON-text may have been truncated. Parsers MUST NOT report JSON-text sequence elements consisting of top-level numbers that may have been truncated in the same way they would a complete JSON-text. Parsers MAY report such texts as errors (including, optionally, the parsed text and/or the original octet string).
All the security considerations of JSON [RFC7159] apply. This format provides no cryptographic integrity protection of any kind.
The MIME media type for JSON text sequences is application/json-seq.
Type name: application
Subtype name: json-seq
Required parameters: n/a
Optional parameters: n/a
Encoding considerations: binary
Security considerations: See <this document, once published>, Section 3.
Interoperability considerations: Described herein.
Published specification: <this document, once published>.
Applications that use this media type: <by publication time https://stedolan.github.io/jq is likely to support this format>.
Phillip Hallam-Baker proposed the use of JSON text sequences for logfiles and pointed out the need for resynchronization. Stephen Dolan created https://github.com/stedolan/jq, which uses something like JSON text sequences (with LF as the separator between texts on output, and requiring only such whitespace as needed to disambiguate on input). Carsten Bormann suggested the use of ASCII RS, and Joe Hildebrand suggested the use of LF in addition to RS for disambiguating top-level number values. Paul Hoffman shepherded the Internet-Draft. Many others contributed reviews and comments on the JSON Working Group mailing list.
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. |
| [RFC0020] | Cerf, V., "ASCII format for network interchange", RFC 20, October 1969. |
| [RFC5234] | Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, January 2008. |
| [RFC7159] | Bray, T., "The JavaScript Object Notation (JSON) Data Interchange Format", RFC 7159, March 2014. |