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ProbeLabs36 findings · 123 requirements
SYS-REQ-062SystemApproved

When ParseString encounters a UTF-16 high surrogate escape followed by a second unicode escape whose value is below the low surrogate range (e.g., '\uD800\u0041'), the parser shall substitute U+FFFD (replacement character) for the malformed surrogate sequence and continue parsing, matching encoding/json behavior, rather than producing corrupted output or returning an error.

PriorityshallTypeguaranteeCategoryfunctionalComponentparserAssuranceEFindingsHighworst open

Specification

The requirement exactly as authored — its complete prose text and, where present, the formal FRETish sentence it compiles to.

Description

When ParseString encounters a UTF-16 high surrogate escape followed by a second unicode escape whose value is below the low surrogate range (e.g., '\uD800\u0041'), the parser shall substitute U+FFFD (replacement character) for the malformed surrogate sequence and continue parsing, matching encoding/json behavior, rather than producing corrupted output or returning an error.

FRETish formula
the parser shall always satisfy !raw_string_has_invalid_low_surrogate | substitutes_replacement_for_invalid_low_surrogate

Rationale & tags

Why this requirement exists, and how it is categorised.

An invalid low surrogate (valid unicode escape but wrong range) exercises a different branch in decodeUnicodeEscape than a completely missing second escape.

parsestringunicodesurrogate

Verification & provenance

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Assurance levelE
Formalizationvalid
Realizabilityrealizable
Vacuitychecked_ok
Strategyfretish

Review

Status
approved
Reviewer
human:buger · lead_engineer
Reviewed
Jul 27, 2026, 11:43 UTC
Surrogate-bug hardening: motivation linked to DEFECT-260727-SNGT

History

Created
Apr 14, 2026, 18:00 UTC · agent:claude
Modified
Jul 27, 2026, 11:43 UTC · human:buger

Obligations

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No obligations recorded for this requirement

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Formula evidence

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FRETish formula

the parser shall always satisfy !raw_string_has_invalid_low_surrogate | substitutes_replacement_for_invalid_low_surrogate

Variables

NameTypeDirectionDescription
raw_string_has_invalid_low_surrogateTrue when ParseString encounters a UTF-16 high surrogate followed by a unicode escape whose value is below the low surrogate range.
substitutes_replacement_for_invalid_low_surrogateTrue when ParseString substitutes U+FFFD for a high surrogate followed by an invalid low surrogate, matching encoding/json behavior.

Witnesses· 2 scenarios total

  • TestInvalidSurrogateLow
    deep_spec_test.go:642
  • TestMCDC_SYS_REQ_062_Row1_TriggerFalse
    mcdc_spec_witnesses_test.go:2833exercises 1 condition scenario
  • TestMCDC_SYS_REQ_062_Row3_InvalidLowSurrogateError
    mcdc_spec_witnesses_test.go:2847exercises 1 condition scenario

Its place

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Trace evidence

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No implementation linked

No source files are traced to this requirement yet.

Impact

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If you change this

Requirements
0
Files
0
Tests
2
At-risk contracts
0

Tests to re-run (2)

  • deep_spec_test.godeep_spec_test.go
  • mcdc_spec_witnesses_test.gomcdc_spec_witnesses_test.go

What this rests on

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