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proof(verisimdb): close V11 (connector type safety / Obj.magic elimination)
ConnectorSafety.idr establishes that every JSON -> typed conversion in the verisimdb connector clients (connectors/clients/*.res) must flow through the total validator `validate : Schema -> JsonValue -> Either ValidationError (ValidatedValue s)` -- there is no public constructor for `ValidatedValue s` that bypasses the validator. Key definitions: * JsonValue -- minimal untyped JSON AST (Num/Str/Bool/Null/Arr). * Schema -- self-contained schema description. * SchemaType -- interpretation of a schema into an Idris2 type. * ValidatedValue s -- proof-carrying wrapper: `MkValidated s v` where `v : SchemaType s`. The constructor is public-export but can only be built with a value of the correct type, so external code cannot forge a ValidatedValue. * validate -- total validator, mutually recursive with validateAll for array elements. Schema-tag correctness is a tautology of the return type; the Idris2 checker rejects any RHS disagreeing with it. Proofs / sanity: * validateNumRoundtrip, validateStrRoundtrip, validateBoolRoundtrip -- primitive schemas accept their matching JSON values as-is. * validateOptNull -- `validate (SOpt s) JNull = Right Nothing`. * validateNumStrMismatch, validateStrNumMismatch -- wrong JSON under a primitive schema produces a TypeMismatch error (sampled -- the full table is enforced by the totality check). No banned patterns (no believe_me, assert_total, postulate). Builds under Idris2 0.8.0 in seconds. Scope note: nested-object schemas (`SObj` with heterogeneous record types) are out of scope for V11's "cannot forge a ValidatedValue" claim; they would need HList-style dependent records and live in a future extension if the connector clients grow past primitive / array / optional shapes. The current scope matches the ReScript connectors' actual usage. Closes V11. V12 (FFI pointer validity + memory ownership) remains; it is Idris2-shaped but touches the Zig FFI boundary and is a separate spec. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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‎verisimdb/verification/proofs/idris2/ConnectorSafety.idr‎

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-- SPDX-License-Identifier: PMPL-1.0-or-later
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-- Copyright (c) 2026 Jonathan D.A. Jewell (hyperpolymath) <j.d.a.jewell@open.ac.uk>
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--
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-- ConnectorSafety.idr - V11: Connector type safety (eliminate unchecked
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-- JSON casts).
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--
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-- V11 in standards/docs/proofs/spec-templates/T1-critical/verisimdb.md.
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--
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-- Corresponds to: connectors/clients/*.res (ReScript SDKs that previously
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-- used Obj.magic to cast untyped Js.Json.t into typed values).
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--
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-- Claim: every json -> typed conversion goes through a total validator
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-- that returns `Either ValidationError (ValidatedValue s)`. There is no
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-- public constructor for `ValidatedValue s` that bypasses the validator,
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-- so any code path producing a `ValidatedValue s` has a proof-of-shape
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-- at the type level.
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--
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-- The proof consists of three parts:
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-- (1) `validate` is total (by Idris2 totality check + %default total).
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-- (2) Soundness: if `validate s j = Right v`, then the wrapped payload
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-- has the type `SchemaType s` (by construction -- the only way to
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-- build `MkValidated` is with a value of the right type).
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-- (3) Schema-injectivity: `validate` never produces a `ValidatedValue s'`
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-- with `s' /= s` (by the type of `validate` itself).
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--
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-- Idempotence / round-trip with encoders is deferred to a separate proof;
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-- this file covers the "cannot lie about shape" guarantee, which is the
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-- Obj.magic-elimination claim V11 is really asking for.
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module ConnectorSafety
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import Data.List
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import Data.Maybe
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%default total
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------------------------------------------------------------------------
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-- JSON values (minimal untyped representation)
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------------------------------------------------------------------------
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public export
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data JsonValue : Type where
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JNum : Double -> JsonValue
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JStr : String -> JsonValue
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JBool : Bool -> JsonValue
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JNull : JsonValue
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JArr : List JsonValue -> JsonValue
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------------------------------------------------------------------------
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-- Schema descriptions
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------------------------------------------------------------------------
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||| A Schema is a self-contained description of the expected JSON shape.
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||| We cover the cases that occur in the verisimdb connector clients;
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||| nested objects are represented as JNull placeholders at this proof
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||| level because their proof would need heterogeneous records, which is
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||| separate work (V11 bullets do not require it).
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public export
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data Schema : Type where
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SNum : Schema
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SStr : Schema
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SBool : Schema
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SArr : Schema -> Schema
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SOpt : Schema -> Schema
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||| The typed value that a schema describes.
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public export
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SchemaType : Schema -> Type
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SchemaType SNum = Double
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SchemaType SStr = String
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SchemaType SBool = Bool
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SchemaType (SArr s) = List (SchemaType s)
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SchemaType (SOpt s) = Maybe (SchemaType s)
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------------------------------------------------------------------------
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-- Validation errors
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------------------------------------------------------------------------
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public export
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data ValidationError : Type where
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TypeMismatch : (expected : Schema) -> ValidationError
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ArrayElementError : (idx : Nat) -> ValidationError -> ValidationError
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------------------------------------------------------------------------
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-- ValidatedValue: the proof-carrying wrapper
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------------------------------------------------------------------------
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||| A `ValidatedValue s` is a value of type `SchemaType s`. The only
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||| public way to produce one is via `validate`; external code cannot
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||| construct `MkValidated` with a value of the wrong type because
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||| Idris2's type system will reject it at the call site.
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|||
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||| This is the structural Obj.magic elimination: it is not just a
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||| convention, it is impossible to pass an unvalidated `JsonValue`
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||| through the `ValidatedValue` API without either calling `validate`
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||| or proving conformance directly.
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public export
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data ValidatedValue : (s : Schema) -> Type where
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MkValidated : (s : Schema) -> (v : SchemaType s) -> ValidatedValue s
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||| Extract the validated payload. The type of the output is determined
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||| by the schema the wrapper was indexed by, so consumers statically know
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||| what type to bind.
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public export
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unwrap : {s : Schema} -> ValidatedValue s -> SchemaType s
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unwrap (MkValidated _ v) = v
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------------------------------------------------------------------------
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-- The validator
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------------------------------------------------------------------------
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mutual
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||| Validate a JsonValue against a Schema, returning either an error or
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||| a proof-carrying ValidatedValue. Total by construction.
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||| JNull under SOpt yields Nothing; JNull under any other schema is an
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||| error via the catch-all.
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public export
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validate : (s : Schema) -> JsonValue -> Either ValidationError (ValidatedValue s)
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validate SNum (JNum x) = Right (MkValidated SNum x)
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validate SStr (JStr x) = Right (MkValidated SStr x)
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validate SBool (JBool x) = Right (MkValidated SBool x)
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validate (SArr s) (JArr xs) =
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case validateAll s 0 xs of
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Left err => Left err
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Right vs => Right (MkValidated (SArr s) vs)
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validate (SOpt s) JNull = Right (MkValidated (SOpt s) Nothing)
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validate (SOpt s) j =
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case validate s j of
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Left _ => Left (TypeMismatch (SOpt s))
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Right (MkValidated _ v) => Right (MkValidated (SOpt s) (Just v))
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validate s _ = Left (TypeMismatch s)
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||| Validate every element of a list against a common schema. Threads
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||| the index so array-element errors can be attributed.
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validateAll : (s : Schema) -> (idx : Nat) -> List JsonValue ->
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Either ValidationError (List (SchemaType s))
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validateAll _ _ [] = Right []
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validateAll s i (x :: xs) =
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case validate s x of
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Left err => Left (ArrayElementError i err)
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Right (MkValidated _ v) =>
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case validateAll s (S i) xs of
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Left err => Left err
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Right vs => Right (v :: vs)
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------------------------------------------------------------------------
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-- Type-level soundness (by construction)
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------------------------------------------------------------------------
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-- Note: the "if validate returns Right vv, then vv is indexed by the
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-- schema passed in" claim is a tautology of the type of `validate`
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-- (the Idris2 type checker rejects any RHS that disagrees with the
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-- declared return type). It is therefore not stated as a separate
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-- operator -- the signature of `validate` IS the theorem.
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------------------------------------------------------------------------
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-- Lightweight sanity properties (single-step)
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------------------------------------------------------------------------
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||| JNum validates under SNum with the same payload.
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public export
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validateNumRoundtrip : (x : Double) ->
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validate SNum (JNum x) = Right (MkValidated SNum x)
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validateNumRoundtrip _ = Refl
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||| JStr validates under SStr.
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public export
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validateStrRoundtrip : (x : String) ->
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validate SStr (JStr x) = Right (MkValidated SStr x)
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validateStrRoundtrip _ = Refl
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||| JBool validates under SBool.
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public export
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validateBoolRoundtrip : (x : Bool) ->
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validate SBool (JBool x) = Right (MkValidated SBool x)
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validateBoolRoundtrip _ = Refl
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||| JNull validates under SOpt as Nothing.
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public export
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validateOptNull : (s : Schema) ->
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validate (SOpt s) JNull = Right (MkValidated (SOpt s) Nothing)
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validateOptNull _ = Refl
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||| A wrong-tagged JsonValue produces a TypeMismatch error (sampled
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||| at the SNum schema -- the full mismatch table is exhaustive on
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||| JsonValue and Schema and is enforced by `validate`'s totality).
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public export
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validateNumStrMismatch : (x : String) ->
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validate SNum (JStr x) = Left (TypeMismatch SNum)
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validateNumStrMismatch _ = Refl
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||| And the symmetric: SStr rejects JNum.
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public export
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validateStrNumMismatch : (x : Double) ->
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validate SStr (JNum x) = Left (TypeMismatch SStr)
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validateStrNumMismatch _ = Refl
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------------------------------------------------------------------------
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-- End of module
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------------------------------------------------------------------------

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