Add XDR schema types

feat: implement XDR (External Data Representation Standard) schema interface

Author: streamich

src/xdr/index.ts

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+/**
+ * XDR (External Data Representation Standard) module
+ *
+ * This module provides TypeScript type definitions for XDR schemas
+ * based on RFC 4506 specification.
+ */
+
+export * from './types';

src/xdr/types.ts

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+/**
+ * XDR (External Data Representation Standard) schema type definitions
+ * based on RFC 4506 specification.
+ * Specification: https://datatracker.ietf.org/doc/html/rfc4506
+ */
+export type XdrSchema = XdrPrimitiveSchema | XdrWidePrimitiveSchema | XdrCompositeSchema;
+
+// Primitive type schemas
+
+export type XdrPrimitiveSchema =
+  | XdrVoidSchema
+  | XdrIntSchema
+  | XdrUnsignedIntSchema
+  | XdrEnumSchema
+  | XdrBooleanSchema
+  | XdrHyperSchema
+  | XdrUnsignedHyperSchema
+  | XdrFloatSchema
+  | XdrDoubleSchema
+  | XdrQuadrupleSchema;
+
+export type XdrVoidSchema = XdrBaseSchema<'void'>;
+export type XdrIntSchema = XdrBaseSchema<'int'>;
+export type XdrUnsignedIntSchema = XdrBaseSchema<'unsigned_int'>;
+export interface XdrEnumSchema extends XdrBaseSchema<'enum'> {
+  values: Record<string, number>;
+}
+export type XdrBooleanSchema = XdrBaseSchema<'boolean'>;
+export type XdrHyperSchema = XdrBaseSchema<'hyper'>;
+export type XdrUnsignedHyperSchema = XdrBaseSchema<'unsigned_hyper'>;
+export type XdrFloatSchema = XdrBaseSchema<'float'>;
+export type XdrDoubleSchema = XdrBaseSchema<'double'>;
+export type XdrQuadrupleSchema = XdrBaseSchema<'quadruple'>;
+
+// Wide primitive type schemas
+
+export type XdrWidePrimitiveSchema = XdrOpaqueSchema | XdrVarlenOpaqueSchema | XdrStringSchema;
+
+export interface XdrOpaqueSchema extends XdrBaseSchema<'opaque'> {
+  size: number;
+}
+
+export interface XdrVarlenOpaqueSchema extends XdrBaseSchema<'vopaque'> {
+  size?: number;
+}
+
+export interface XdrStringSchema extends XdrBaseSchema<'string'> {
+  size?: number;
+}
+
+// Composite type schemas
+
+export type XdrCompositeSchema = XdrArraySchema | XdrVarlenArraySchema | XdrStructSchema | XdrUnionSchema;
+
+export interface XdrArraySchema extends XdrBaseSchema<'array'> {
+  /** Schema of array elements */
+  elements: XdrSchema;
+  /** Fixed number of elements */
+  size: number;
+}
+
+export interface XdrVarlenArraySchema extends XdrBaseSchema<'varray'> {
+  /** Schema of array elements */
+  elements: XdrSchema;
+  /** Optional maximum length constraint */
+  size?: number;
+}
+
+/**
+ * The components of the structure are encoded in the order of their
+ * declaration in the structure.  Each component's size is a multiple of
+ * four bytes, though the components may be different sizes.
+ */
+export interface XdrStructSchema extends XdrBaseSchema<'struct'> {
+  /** Array of field definitions */
+  fields: [schema: XdrSchema, name: string][];
+}
+
+/**
+ * A discriminated union is a type composed of a discriminant followed
+ * by a type selected from a set of prearranged types according to the
+ * value of the discriminant.  The type of discriminant is either "int",
+ * "unsigned int", or an enumerated type, such as "bool".  The component
+ * types are called "arms" of the union and are preceded by the value of
+ * the discriminant that implies their encoding.
+ */
+export interface XdrUnionSchema extends XdrBaseSchema<'union'> {
+  type: 'union';
+  arms: [discriminant: number | string | boolean, schema: XdrSchema][];
+  default?: XdrSchema;
+}
+
+// Base schema
+
+export interface XdrBaseSchema<Type extends string> {
+  /** The schema type */
+  type: Type;
+}