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RFC 7464 / JSON TEXT SEQUENCES

Detect possibly truncated scalars

04

Numbers, true, false and null need trailing JSON whitespace so a parser can reject potentially truncated values.

DIAGRAMRead RFC section 2.4 ↗
RFC 7464 · § 2.4EXAMPLE
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Detect possibly truncated scalarsThree independent comparisons: 123 without whitespace must be dropped; 123 with LF is accepted; truefalse with LF remains invalid JSON. RS alone does not delimit a complete number safely.Check the trailing whitespace canaryIndependent comparisons · not consecutive recordsRStruefalseLFRSNext boundaryvalidate candidateREJECTWhitespace does not repair invalid JSONtruefalse is one invalid text, not two JSON values
03
Reject invalid JSON despite whitespace.

A trailing LF cannot turn truefalse into one valid JSON text.

Source for this drawing: RFC 7464 · Read RFC section 2.4 ↗

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RFC 8259 JSON

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Terms in this drawing
Canary byte
A trailing byte whose absence can signal possible truncation.
Self-delimited
A value whose closing syntax identifies its end, such as a closing quote or brace.
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KEY POINT

Require a whitespace canary for non-self-delimited values.

  • Parsers MUST check that a top-level number, or text that might be true, false or null, has at least one JSON whitespace byte after that value. The encoder’s LF satisfies this check.
  • Parsers MUST drop non-self-delimited top-level elements that lack that whitespace and may have been truncated. For example, RS 123 RS might be a truncated 1234; a boundary alone is insufficient.
  • Whitespace does not repair invalid JSON: truefalse is not two values and is not a valid JSON text. Objects, arrays and strings are self-delimited; incremental parsers may produce these without consuming another byte. Detecting truncation still depends on encoders receiving or producing complete JSON texts.
DETAILS

Three independent comparisons are shown, not consecutive requests: 123 without trailing whitespace is dropped; 123 followed by LF passes this check and parses; truefalse followed by LF still fails JSON parsing. The acceptance example is a format-level result, not authentication or a promise of intact transport.

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