laurentgo commented on code in PR #13879:
URL: https://github.com/apache/iceberg/pull/13879#discussion_r3227896662


##########
open-api/rest-catalog-open-api.yaml:
##########
@@ -3480,6 +3480,309 @@ components:
           additionalProperties:
             type: string
 
+    ReadRestrictions:
+      type: object
+      description: >
+          Read restrictions for a table, including column projections and row 
filter expressions.
+
+          A client MUST enforce the restrictions defined in this object when 
reading data
+          from the table.
+
+          These restrictions apply only to the authenticated principal, user, 
or account
+          associated with the request. They MUST NOT be interpreted as global 
policy and
+          MUST NOT be applied beyond the entity identified by the 
Authentication header
+          (or other applicable authentication mechanism).
+
+          If both properties are absent or empty, the ReadRestrictions object 
imposes no
+          restrictions and is equivalent to the field being absent from the 
response.
+          A server MUST NOT return an action for a column whose type is not 
listed in
+          that action's "Applicable to" set.
+          For all actions, if the input column value is NULL, the output MUST 
be NULL.
+
+          If a column projection targets a struct-typed field, other column 
projections
+          in the same ReadRestrictions MUST NOT target any of that struct's 
subfields
+          (at any depth). This avoids ambiguity about which action governs a 
given
+          leaf value.
+      properties:
+        required-column-projections:
+          description: >
+            A list of columns that require specific actions to be applied when 
reading.
+
+            If this property is absent, a reader MAY access all columns of the 
table as-is
+            without any mandatory transformations.
+
+            If this property is present, each listed column MUST have its 
specified
+            action applied. Columns not listed in required-column-projections
+            are not subject to any read restrictions.
+
+            When this list is present:
+
+            1. For each column listed in required-column-projections, the 
reader MUST apply
+              the specified action before returning values for that column.
+
+            2. The reader MUST replace all output references to the column 
with the result
+              of the action, presenting the result under the original column 
name. For
+              example, if the action for column cc is mask-alphanum, the 
reader MUST
+              return the masked value as cc in the query output.
+
+            3. Columns not listed in required-column-projections MAY be 
projected normally
+              by the reader without any mandatory transformations.
+
+            4. A column MUST appear at most once in 
required-column-projections.
+
+            5. If a projected column's action cannot be evaluated by the reader
+              (including unrecognized action types), the reader MUST fail 
rather than
+              ignore or skip the action.
+
+            6. Each action defines the output type for its column. For all 
predefined
+              actions except apply-expression, the output type matches the 
input column
+              type. For apply-expression, the output type is determined by the 
expression.
+
+          type: array
+          items:
+            $ref: '#/components/schemas/Action'
+        required-row-filter:
+          description: >
+            An expression that filters rows in the table that the 
authenticated principal does not have access to.
+
+            1. The expression MUST evaluate to a boolean. A reader MUST 
discard any row for which
+              the filter evaluates to FALSE, and no information derived from 
discarded rows
+              MAY be included in the query result.
+
+            2. Row filters MUST be evaluated against the original, 
untransformed column values.
+              Required projections MUST be applied only after row filters are 
applied.
+
+            3. If a client cannot interpret or evaluate a provided filter 
expression, it MUST fail.
+
+            4. If this property is absent, null, or always true then no 
mandatory filtering is required.
+          $ref: '#/components/schemas/Expression'
+
+    Action:
+      discriminator:
+        propertyName: action
+        mapping:
+          mask-alphanum: '#/components/schemas/MaskAlphanum'
+          mask-to-fixed-value: '#/components/schemas/MaskToFixedValue'
+          replace-with-null: '#/components/schemas/ReplaceWithNull'
+          show-first-4: '#/components/schemas/ShowFirst4'
+          show-last-4: '#/components/schemas/ShowLast4'
+          truncate-to-year: '#/components/schemas/TruncateToYear'
+          truncate-to-month: '#/components/schemas/TruncateToMonth'
+          sha-256-global: '#/components/schemas/Sha256Global'
+          sha-256-query-local: '#/components/schemas/Sha256QueryLocal'
+          apply-expression: '#/components/schemas/ApplyExpression'
+      type: object
+      required:
+        - action
+        - field-id
+      properties:
+        action:
+          type: string
+        field-id:
+          type: integer
+          description: field id of the column being projected.
+
+    MaskAlphanum:
+      description: >
+        Redacts the column value Unicode code point by code point using the 
following rules:
+
+        - Digits (U+0030–U+0039, 0-9) are replaced with 'n'
+        - The following punctuation characters are kept as-is:
+            U+0028 '('  LEFT PARENTHESIS
+            U+0029 ')'  RIGHT PARENTHESIS
+            U+002C ','  COMMA
+            U+002E '.'  FULL STOP
+            U+002D '-'  HYPHEN-MINUS
+            U+0040 '@'  COMMERCIAL AT
+        - All other Unicode characters (including letters, whitespace, and any 
punctuation
+          not listed above) are replaced with 'x'
+
+        For example: "[email protected]" → "[email protected]"
+
+        Applicable to: string
+      allOf:
+        - $ref: '#/components/schemas/Action'
+      properties:
+        action:
+          type: string
+          const: "mask-alphanum"
+
+    MaskToFixedValue:
+      description: >
+        Replaces the column value with a predefined type-specific fixed value.
+        Engines MUST use exactly the values listed below to ensure consistency
+        across implementations.
+
+        Fixed values by type:
+        - boolean: false
+        - int: 0
+        - long: 0
+        - float: 0.0
+        - double: 0.0
+        - decimal(p, s): 0 (zero with s digits after the decimal point, e.g. 
0.00 for decimal(p,2))
+        - string: "XXXXXXXX"
+        - date: 1970-01-01
+        - time: 00:00:00
+        - timestamp: 1970-01-01T00:00:00
+        - timestamptz: 1970-01-01T00:00:00+00:00
+        - timestamp_ns: 1970-01-01T00:00:00.000000000
+        - timestamptz_ns: 1970-01-01T00:00:00.000000000+00:00
+        - uuid: 00000000-0000-0000-0000-000000000000
+        - fixed(n): n zero bytes
+        - binary: empty byte sequence
+        - variant: {}
+        - geometry: POINT EMPTY
+        - geography: POINT EMPTY
+        - list: empty list []
+        - map: empty map {}
+        - struct: struct with each field set to its type-specific default 
(applied recursively)
+
+        Applicable to: all data types
+      allOf:
+        - $ref: '#/components/schemas/Action'
+      properties:
+        action:
+          type: string
+          const: "mask-to-fixed-value"
+
+    ReplaceWithNull:
+      description: >
+        Replaces the entire column value with NULL.
+
+        Applicable to: all nullable types
+      allOf:
+        - $ref: '#/components/schemas/Action'
+      properties:
+        action:
+          type: string
+          const: "replace-with-null"
+
+    ShowFirst4:
+      description: >
+        Preserves the first 4 Unicode code points of the column value and 
redacts the remainder
+        using mask-alphanum rules (see MaskAlphanum for the exact character 
rules).
+        Values with 4 or fewer Unicode code points are returned unchanged.
+
+        For example: "[email protected]" → "[email protected]"
+
+        Applicable to: string
+      allOf:
+        - $ref: '#/components/schemas/Action'
+      properties:
+        action:
+          type: string
+          const: "show-first-4"
+
+    ShowLast4:
+      description: >
+        Redacts all Unicode code points except the last 4 using mask-alphanum 
rules
+        (see MaskAlphanum for the exact character rules).
+        Values with 4 or fewer Unicode code points are returned unchanged.
+
+        For example: "4111-1111-1111-4444" → "nnnn-nnnn-nnnn-4444"
+
+        Applicable to: string
+      allOf:
+        - $ref: '#/components/schemas/Action'
+      properties:
+        action:
+          type: string
+          const: "show-last-4"
+
+    TruncateToYear:
+      description: >
+        Truncates the column value to year precision, setting month, day, and 
time components
+        to their minimum values. The output type matches the input type.
+
+        For example: 2024-07-15 → 2024-01-01
+        For timestamptz and timestamptz_ns, truncation is performed in UTC.
+
+        Applicable to: date, timestamp, timestamptz, timestamp_ns, 
timestamptz_ns
+      allOf:
+        - $ref: '#/components/schemas/Action'
+      properties:
+        action:
+          type: string
+          const: "truncate-to-year"
+
+    TruncateToMonth:
+      description: >
+        Truncates the column value to year and month precision, setting day 
and time components
+        to their minimum values. The output type matches the input type.
+
+        For example: 2024-07-15 → 2024-07-01
+        For timestamptz and timestamptz_ns, truncation is performed in UTC.
+
+        Applicable to: date, timestamp, timestamptz, timestamp_ns, 
timestamptz_ns
+      allOf:
+        - $ref: '#/components/schemas/Action'
+      properties:
+        action:
+          type: string
+          const: "truncate-to-month"
+
+    Sha256Global:
+      description: |
+        Applies SHA-256 as specified in NIST FIPS 180-4. Deterministic across 
all queries
+        and engines — the same input always produces the same output.
+
+        Input-to-bytes encoding by type:
+        - string: UTF-8 encoded bytes
+        - int: 4 bytes, little-endian
+        - long: 8 bytes, little-endian
+        - binary: raw bytes as-is
+
+        Output encoding by type:
+        - string: 64-character lowercase hexadecimal string
+        - int: first 4 bytes of the digest, read as a signed two's complement 
little-endian int
+        - long: first 8 bytes of the digest, read as a signed two's complement 
little-endian long
+        - binary: the full 32-byte raw SHA-256 digest
+
+        Applicable to: string, int, long, binary
+      allOf:
+        - $ref: '#/components/schemas/Action'
+      properties:
+        action:
+          type: string
+          const: "sha-256-global"
+
+    Sha256QueryLocal:
+      description: |
+        Applies SHA-256 with a per-query random salt, making the output 
non-deterministic
+        across queries while remaining consistent within a single query.
+
+        The engine MUST generate a cryptographically random salt of at least 
16 bytes for each query and apply it as:
+          SHA-256(salt_bytes || canonical_bytes)
+        where canonical_bytes follows the same encoding rules as 
sha-256-global.
+
+        Output encoding follows the same rules as sha-256-global.
+
+        Applicable to: string, int, long, binary
+      allOf:
+        - $ref: '#/components/schemas/Action'
+      properties:
+        action:
+          type: string
+          const: "sha-256-query-local"
+
+    ApplyExpression:
+      description: >
+        Replace the field with the result of an expression. Produce the 
original field name
+        with the expression result.
+
+        Applicable to: all data types
+      allOf:
+        - $ref: '#/components/schemas/Action'
+      required:
+        - action
+        - expression
+      properties:
+        action:
+          type: string
+          const: "apply-expression"
+        expression:
+          $ref: '#/components/schemas/Expression'

Review Comment:
   I thought we always considered the evaluation of FGAC as a view was defined 
on top of the table to be protected. If this is still the case, then it's the 
first point: evaluation is always against raw column values



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