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// Built-in named entity map (name β replacement string)
// No regex, no {regex,val} objects β just flat key/value pairs.
// ---------------------------------------------------------------------------
import { XML as DEFAULT_XML_ENTITIES } from "./entities.js"
// ---------------------------------------------------------------------------
// Entity hook action constants
// ---------------------------------------------------------------------------
/**
* Action constants for `onExternalEntity` and `onInputEntity` hooks.
*
* Use these instead of raw strings to avoid typos:
*
* @example
* import EntityDecoder, { ENTITY_ACTION } from './EntityDecoder.js';
* const dec = new EntityDecoder({
* onInputEntity: (name, value) => ENTITY_ACTION.BLOCK,
* });
*/
export const ENTITY_ACTION = Object.freeze({
/** Resolve and expand the entity normally. */
ALLOW: 'allow',
/** Silently skip this entity β it will not be registered. */
BLOCK: 'block',
/** Throw an error, aborting entity registration entirely. */
THROW: 'throw',
});
// ---------------------------------------------------------------------------
// Helpers
// ---------------------------------------------------------------------------
const SPECIAL_CHARS = new Set('!?\\\\/[]$%{}^&*()<>|+');
/**
* Validate that an entity name contains no dangerous characters.
* @param {string} name
* @returns {string} the name, unchanged
* @throws {Error} on invalid characters
*/
function validateEntityName(name) {
if (name[0] === '#') {
throw new Error(`[EntityReplacer] Invalid character '#' in entity name: "${name}"`);
}
for (const ch of name) {
if (SPECIAL_CHARS.has(ch)) {
throw new Error(`[EntityReplacer] Invalid character '${ch}' in entity name: "${name}"`);
}
}
return name;
}
/**
* Merge one or more entity maps into a flat nameβstring map.
* Accepts either:
* - plain string values: { amp: '&' }
* - legacy {regex,val} / {regx,val}: { lt: { regex: /.../, val: '<' } }
*
* Values containing '&' are skipped (recursive expansion risk).
*
* @param {...object} maps
* @returns {Record<string, string>}
*/
function mergeEntityMaps(...maps) {
const out = Object.create(null);
for (const map of maps) {
if (!map) continue;
for (const key of Object.keys(map)) {
const raw = map[key];
if (typeof raw === 'string') {
out[key] = raw;
} else if (raw && typeof raw === 'object' && raw.val !== undefined) {
// Legacy {regex,val} or {regx,val} β extract the string val only
const val = raw.val;
if (typeof val === 'string') {
out[key] = val;
}
// function vals are not supported in the scanner β skip
}
}
}
return out;
}
// ---------------------------------------------------------------------------
// applyLimitsTo helpers
// ---------------------------------------------------------------------------
const LIMIT_TIER_EXTERNAL = 'external'; // input/runtime + persistent external maps
const LIMIT_TIER_BASE = 'base'; // DEFAULT_XML_ENTITIES + namedEntities (system) maps
const LIMIT_TIER_ALL = 'all'; // every entity regardless of tier
/**
* Resolve `applyLimitsTo` option into a normalised Set of tier strings.
* Accepted values: 'external' | 'base' | 'all' | string[]
* Default: 'external' (only untrusted injected entities are counted).
* @param {string|string[]|undefined} raw
* @returns {Set<string>}
*/
function parseLimitTiers(raw) {
if (!raw || raw === LIMIT_TIER_EXTERNAL) return new Set([LIMIT_TIER_EXTERNAL]);
if (raw === LIMIT_TIER_ALL) return new Set([LIMIT_TIER_ALL]);
if (raw === LIMIT_TIER_BASE) return new Set([LIMIT_TIER_BASE]);
if (Array.isArray(raw)) return new Set(raw);
return new Set([LIMIT_TIER_EXTERNAL]); // safe default for unrecognised values
}
// ---------------------------------------------------------------------------
// NCR (Numeric Character Reference) classification
// ---------------------------------------------------------------------------
// Severity order β higher number = stricter action.
// Used to enforce minimum action levels for specific codepoint ranges.
const NCR_LEVEL = Object.freeze({ allow: 0, leave: 1, remove: 2, throw: 3 });
// XML 1.0 Β§2.2: allowed chars are #x9 | #xA | #xD | [#x20-#xD7FF] | [#xE000-#xFFFD] | [#x10000-#x10FFFF]
// Restricted C0: U+0001βU+001F excluding U+0009, U+000A, U+000D
const XML10_ALLOWED_C0 = new Set([0x09, 0x0A, 0x0D]);
/**
* Parse the `ncr` constructor option into flat, hot-path-friendly fields.
* @param {object|undefined} ncr
* @returns {{ xmlVersion: number, onLevel: number, nullLevel: number }}
*/
function parseNCRConfig(ncr) {
if (!ncr) {
return { xmlVersion: 1.0, onLevel: NCR_LEVEL.allow, nullLevel: NCR_LEVEL.remove };
}
const xmlVersion = ncr.xmlVersion === 1.1 ? 1.1 : 1.0;
const onLevel = NCR_LEVEL[ncr.onNCR] ?? NCR_LEVEL.allow;
const nullLevel = NCR_LEVEL[ncr.nullNCR] ?? NCR_LEVEL.remove;
// 'allow' is not meaningful for null β clamp to at least 'remove'
const clampedNull = Math.max(nullLevel, NCR_LEVEL.remove);
return { xmlVersion, onLevel, nullLevel: clampedNull };
}
// ---------------------------------------------------------------------------
// EntityReplacer
// ---------------------------------------------------------------------------
/**
* Single-pass, zero-regex entity replacer for XML/HTML content.
*
* Algorithm: scan the string once for '&', read to ';', resolve via map
* or direct codepoint conversion, build output chunks, join once at the end.
*
* Entity lookup priority (highest β lowest):
* 1. input / runtime (DOCTYPE entities for current document)
* 2. persistent external (survive across documents)
* 3. base named map (DEFAULT_XML_ENTITIES + user-supplied namedEntities)
*
* Both input and external resolve as the 'external' tier for limit purposes.
* Base map entities resolve as the 'base' tier.
*
* Numeric / hex references (&#NNN; / &#xHH;) are resolved directly via
* String.fromCodePoint() β no map needed. They count as 'base' tier.
*
* @example
* const replacer = new EntityReplacer({ namedEntities: COMMON_HTML });
* replacer.setExternalEntities({ brand: 'Acme' });
*
* const instance = replacer.reset();
* instance.addInputEntities({ version: '1.0' });
* instance.encode('&brand; v&version; <'); // 'Acme v1.0 <'
*/
export default class EntityDecoder {
/**
* @param {object} [options]
* @param {object|null} [options.namedEntities] β extra named entities merged into base map
* @param {object} [options.limit] β security limits
* @param {number} [options.limit.maxTotalExpansions=0] β 0 = unlimited
* @param {number} [options.limit.maxExpandedLength=0] β 0 = unlimited
* @param {'external'|'base'|'all'|string[]} [options.limit.applyLimitsTo='external']
* Which entity tiers count against the security limits:
* - 'external' (default) β only input/runtime + persistent external entities
* - 'base' β only DEFAULT_XML_ENTITIES + namedEntities
* - 'all' β every entity regardless of tier
* - string[] β explicit combination, e.g. ['external', 'base']
* @param {((resolved: string, original: string) => string)|null} [options.postCheck=null]
* @param {string[]} [options.remove=[]] β entity names (e.g. ['nbsp', '#13']) to delete (replace with empty string)
* @param {string[]} [options.leave=[]] β entity names to keep as literal (unchanged in output)
* @param {object} [options.ncr] β Numeric Character Reference controls
* @param {1.0|1.1} [options.ncr.xmlVersion=1.0]
* XML version governing which codepoint ranges are restricted:
* - 1.0 β C0 controls U+0001βU+001F (except U+0009/000A/000D) are prohibited
* - 1.1 β C0 controls are allowed when written as NCRs; C1 (U+007FβU+009F) decoded as-is
* @param {'allow'|'leave'|'remove'|'throw'} [options.ncr.onNCR='allow']
* Base action for numeric references. Severity order: allow < leave < remove < throw.
* For codepoint ranges that carry a minimum level (surrogates β remove, XML 1.0 C0 β remove),
* the effective action is max(onNCR, rangeMinimum).
* @param {'remove'|'throw'} [options.ncr.nullNCR='remove']
* Action for U+0000 (null). 'allow' and 'leave' are clamped to 'remove' since null is never safe.
* @param {((name: string, value: string) => 'allow'|'block'|'throw')|null} [options.onExternalEntity=null]
* Hook called when an external entity is registered via `setExternalEntities()` or
* `addExternalEntity()`. Return `ENTITY_ACTION.ALLOW` to accept the entity,
* `ENTITY_ACTION.BLOCK` to silently skip it, or `ENTITY_ACTION.THROW` to abort with an error.
* @param {((name: string, value: string) => 'allow'|'block'|'throw')|null} [options.onInputEntity=null]
* Hook called when an input entity is registered via `addInputEntities()`. Return
* `ENTITY_ACTION.ALLOW` to accept, `ENTITY_ACTION.BLOCK` to silently skip, or
* `ENTITY_ACTION.THROW` to abort with an error.
*/
constructor(options = {}) {
this._limit = options.limit || {};
this._maxTotalExpansions = this._limit.maxTotalExpansions || 0;
this._maxExpandedLength = this._limit.maxExpandedLength || 0;
this._postCheck = typeof options.postCheck === 'function' ? options.postCheck : r => r;
this._limitTiers = parseLimitTiers(this._limit.applyLimitsTo ?? LIMIT_TIER_EXTERNAL);
this._numericAllowed = options.numericAllowed ?? true;
// Base map: DEFAULT_XML_ENTITIES + user-supplied extras. Immutable after construction.
this._baseMap = mergeEntityMaps(DEFAULT_XML_ENTITIES, options.namedEntities || null);
// Persistent external entities β survive across documents.
// Stored as a separate map so reset() never touches them.
/** @type {Record<string, string>} */
this._externalMap = Object.create(null);
// Input / runtime entities β current document only, wiped on reset().
/** @type {Record<string, string>} */
this._inputMap = Object.create(null);
// Per-document counters
this._totalExpansions = 0;
this._expandedLength = 0;
// --- New: remove / leave sets ---
/** @type {Set<string>} */
this._removeSet = new Set(options.remove && Array.isArray(options.remove) ? options.remove : []);
/** @type {Set<string>} */
this._leaveSet = new Set(options.leave && Array.isArray(options.leave) ? options.leave : []);
// --- NCR config (parsed into flat fields for hot-path speed) ---
const ncrCfg = parseNCRConfig(options.ncr);
this._ncrXmlVersion = ncrCfg.xmlVersion;
this._ncrOnLevel = ncrCfg.onLevel;
this._ncrNullLevel = ncrCfg.nullLevel;
// --- Registration hooks ---
/** @type {((name: string, value: string) => 'allow'|'block'|'throw')|null} */
this._onExternalEntity = typeof options.onExternalEntity === 'function'
? options.onExternalEntity
: null;
/** @type {((name: string, value: string) => 'allow'|'block'|'throw')|null} */
this._onInputEntity = typeof options.onInputEntity === 'function'
? options.onInputEntity
: null;
}
// -------------------------------------------------------------------------
// Private: registration hook dispatch
// -------------------------------------------------------------------------
/**
* Invoke a registration hook for a single entity name/value pair.
* Returns true when the entity should be accepted, false when it should be
* silently skipped (BLOCK), and throws when the hook returns THROW.
*
* @param {((name: string, value: string) => 'allow'|'block'|'throw')|null} hook
* @param {string} name
* @param {string} value
* @param {string} context β used in error messages ('external' | 'input')
* @returns {boolean} true = accept, false = skip
*/
_applyRegistrationHook(hook, name, value, context) {
if (!hook) return true; // no hook β always accept
const action = hook(name, value);
if (action === ENTITY_ACTION.BLOCK) return false;
if (action === ENTITY_ACTION.THROW) {
throw new Error(
`[EntityDecoder] Registration of ${context} entity "&${name};" was rejected by hook`
);
}
return true; // ALLOW or any unknown return value β accept
}
// -------------------------------------------------------------------------
// Persistent external entity registration
// -------------------------------------------------------------------------
/**
* Replace the full set of persistent external entities.
* All keys are validated β throws on invalid characters.
* If `onExternalEntity` is set, it is called once per entry; entries that
* return `ENTITY_ACTION.BLOCK` are silently omitted, `ENTITY_ACTION.THROW`
* aborts the whole call.
* @param {Record<string, string | { regex?: RegExp, val: string }>} map
*/
setExternalEntities(map) {
if (map) {
for (const key of Object.keys(map)) {
validateEntityName(key);
}
}
if (!this._onExternalEntity) {
this._externalMap = mergeEntityMaps(map);
return;
}
// Hook present β resolve values first, then filter
const flat = mergeEntityMaps(map);
const filtered = Object.create(null);
for (const [name, value] of Object.entries(flat)) {
if (this._applyRegistrationHook(this._onExternalEntity, name, value, 'external')) {
filtered[name] = value;
}
}
this._externalMap = filtered;
}
/**
* Add a single persistent external entity.
* If `onExternalEntity` is set it is called before the entity is stored;
* `ENTITY_ACTION.BLOCK` silently skips storage, `ENTITY_ACTION.THROW` raises.
* @param {string} key
* @param {string} value
*/
addExternalEntity(key, value) {
validateEntityName(key);
if (typeof value === 'string' && value.indexOf('&') === -1) {
if (this._applyRegistrationHook(this._onExternalEntity, key, value, 'external')) {
this._externalMap[key] = value;
}
}
}
// -------------------------------------------------------------------------
// Input / runtime entity registration (per document)
// -------------------------------------------------------------------------
/**
* Inject DOCTYPE entities for the current document.
* Also resets per-document expansion counters.
* If `onInputEntity` is set it is called once per entry; entries returning
* `ENTITY_ACTION.BLOCK` are silently omitted, `ENTITY_ACTION.THROW` aborts.
* @param {Record<string, string | { regx?: RegExp, regex?: RegExp, val: string }>} map
*/
addInputEntities(map) {
this._totalExpansions = 0;
this._expandedLength = 0;
if (!this._onInputEntity) {
this._inputMap = mergeEntityMaps(map);
return;
}
const flat = mergeEntityMaps(map);
const filtered = Object.create(null);
for (const [name, value] of Object.entries(flat)) {
if (this._applyRegistrationHook(this._onInputEntity, name, value, 'input')) {
filtered[name] = value;
}
}
this._inputMap = filtered;
}
// -------------------------------------------------------------------------
// Per-document reset
// -------------------------------------------------------------------------
/**
* Wipe input/runtime entities and reset counters.
* Call this before processing each new document.
* @returns {this}
*/
reset() {
this._inputMap = Object.create(null);
this._totalExpansions = 0;
this._expandedLength = 0;
return this;
}
// -------------------------------------------------------------------------
// XML version (can be set after construction, e.g. once parser reads <?xml?>)
// -------------------------------------------------------------------------
/**
* Update the XML version used for NCR classification.
* Call this as soon as the document's `<?xml version="...">` declaration is parsed.
* @param {1.0|1.1|number} version
*/
setXmlVersion(version) {
this._ncrXmlVersion = version === 1.1 ? 1.1 : 1.0;
}
// -------------------------------------------------------------------------
// Primary API
// -------------------------------------------------------------------------
/**
* Replace all entity references in `str` in a single pass.
*
* @param {string} str
* @returns {string}
*/
decode(str) {
if (typeof str !== 'string' || str.length === 0) return str;
//TODO: check if needed
if (str.indexOf('&') === -1) return str; // fast path β no entities at all
const original = str;
const chunks = [];
const len = str.length;
let last = 0; // start of next unprocessed literal chunk
let i = 0;
const limitExpansions = this._maxTotalExpansions > 0;
const limitLength = this._maxExpandedLength > 0;
const checkLimits = limitExpansions || limitLength;
while (i < len) {
// Scan forward to next '&'
if (str.charCodeAt(i) !== 38 /* '&' */) { i++; continue; }
// --- Found '&' at position i ---
// Scan forward to ';'
let j = i + 1;
while (j < len && str.charCodeAt(j) !== 59 /* ';' */ && (j - i) <= 32) j++;
if (j >= len || str.charCodeAt(j) !== 59) {
// No closing ';' within window β treat '&' as literal
i++;
continue;
}
// Raw token between '&' and ';' (exclusive)
const token = str.slice(i + 1, j);
if (token.length === 0) { i++; continue; }
let replacement;
let tier; // which limit tier this entity belongs to
if (this._removeSet.has(token)) {
// Remove entity: replace with empty string
replacement = '';
// If entity was unknown (replacement undefined), we still need a tier for limits.
// Treat as external tier because it's user-directed removal of an unknown reference.
if (tier === undefined) {
tier = LIMIT_TIER_EXTERNAL;
}
} else if (this._leaveSet.has(token)) {
// Do not replace β keep original &token; as literal
i++;
continue;
} else if (token.charCodeAt(0) === 35 /* '#' */) {
// ---- Numeric / NCR reference ----
// NCR classification always runs first β prohibited codepoints must be
// caught regardless of numericAllowed.
const ncrResult = this._resolveNCR(token);
if (ncrResult === undefined) {
// 'leave' action β keep original &token; as-is
i++;
continue;
}
replacement = ncrResult; // '' for remove, char string for allow
tier = LIMIT_TIER_BASE;
} else {
// ---- Named reference ----
const resolved = this._resolveName(token);
replacement = resolved?.value;
tier = resolved?.tier;
}
if (replacement === undefined) {
// Unknown entity β leave as-is, advance past '&' only
i++;
continue;
}
// Flush literal chunk before this entity
if (i > last) chunks.push(str.slice(last, i));
chunks.push(replacement);
last = j + 1; // skip past ';'
i = last;
// Apply expansion limits only if this tier is being tracked
if (checkLimits && this._tierCounts(tier)) {
if (limitExpansions) {
this._totalExpansions++;
if (this._totalExpansions > this._maxTotalExpansions) {
throw new Error(
`[EntityReplacer] Entity expansion count limit exceeded: ` +
`${this._totalExpansions} > ${this._maxTotalExpansions}`
);
}
}
if (limitLength) {
// delta: replacement.length minus the raw &token; length (token.length + 2 for '&' and ';')
const delta = replacement.length - (token.length + 2);
if (delta > 0) {
this._expandedLength += delta;
if (this._expandedLength > this._maxExpandedLength) {
throw new Error(
`[EntityReplacer] Expanded content length limit exceeded: ` +
`${this._expandedLength} > ${this._maxExpandedLength}`
);
}
}
}
}
}
// Flush trailing literal
if (last < len) chunks.push(str.slice(last));
// If nothing was replaced, chunks is empty β return original
const result = chunks.length === 0 ? str : chunks.join('');
return this._postCheck(result, original);
}
// -------------------------------------------------------------------------
// Private: limit tier check
// -------------------------------------------------------------------------
/**
* Returns true if a resolved entity of the given tier should count
* against the expansion/length limits.
* @param {string} tier β LIMIT_TIER_EXTERNAL | LIMIT_TIER_BASE
* @returns {boolean}
*/
_tierCounts(tier) {
if (this._limitTiers.has(LIMIT_TIER_ALL)) return true;
return this._limitTiers.has(tier);
}
// -------------------------------------------------------------------------
// Private: entity resolution
// -------------------------------------------------------------------------
/**
* Resolve a named entity token (without & and ;).
* Priority: inputMap > externalMap > baseMap
* Returns the resolved value tagged with its limit tier.
*
* @param {string} name
* @returns {{ value: string, tier: string }|undefined}
*/
_resolveName(name) {
// input and external both count as 'external' tier for limit purposes β
// they are injected at runtime and are the untrusted surface.
if (name in this._inputMap) return { value: this._inputMap[name], tier: LIMIT_TIER_EXTERNAL };
if (name in this._externalMap) return { value: this._externalMap[name], tier: LIMIT_TIER_EXTERNAL };
if (name in this._baseMap) return { value: this._baseMap[name], tier: LIMIT_TIER_BASE };
return undefined;
}
/**
* Classify a codepoint and return the minimum action level that must be applied.
* Returns -1 when no minimum is imposed (normal allow path).
*
* Ranges checked (in priority order):
* 1. U+0000 β null, governed by nullNCR (always β₯ remove)
* 2. U+D800βU+DFFF β surrogates, always prohibited (min: remove)
* 3. U+0001βU+001F \ {0x09,0x0A,0x0D} β XML 1.0 restricted C0 (min: remove)
* (skipped in XML 1.1 β C0 controls are allowed when written as NCRs)
*
* @param {number} cp β codepoint
* @returns {number} β minimum NCR_LEVEL value, or -1 for no restriction
*/
_classifyNCR(cp) {
// 1. Null
if (cp === 0) return this._ncrNullLevel;
// 2. Surrogates β always prohibited, minimum 'remove'
if (cp >= 0xD800 && cp <= 0xDFFF) return NCR_LEVEL.remove;
// 3. XML 1.0 restricted C0 controls
if (this._ncrXmlVersion === 1.0) {
if (cp >= 0x01 && cp <= 0x1F && !XML10_ALLOWED_C0.has(cp)) return NCR_LEVEL.remove;
}
return -1; // no restriction
}
/**
* Execute a resolved NCR action.
*
* @param {number} action β NCR_LEVEL value
* @param {string} token β raw token (e.g. '#38') for error messages
* @param {number} cp β codepoint, used only for error messages
* @returns {string|undefined}
* - decoded character string β 'allow'
* - '' β 'remove'
* - undefined β 'leave' (caller must skip past '&' only)
* - throws Error β 'throw'
*/
_applyNCRAction(action, token, cp) {
switch (action) {
case NCR_LEVEL.allow: return String.fromCodePoint(cp);
case NCR_LEVEL.remove: return '';
case NCR_LEVEL.leave: return undefined; // signal: keep literal
case NCR_LEVEL.throw:
throw new Error(
`[EntityDecoder] Prohibited numeric character reference ` +
`&${token}; (U+${cp.toString(16).toUpperCase().padStart(4, '0')})`
);
default: return String.fromCodePoint(cp);
}
}
/**
* Full NCR resolution pipeline for a numeric token.
*
* Steps:
* 1. Parse the codepoint (decimal or hex).
* 2. Validate the raw codepoint range (NaN, <0, >0x10FFFF).
* 3. If numericAllowed is false and no minimum restriction applies β leave as-is.
* 4. Classify the codepoint to find the minimum required action level.
* 5. Resolve effective action = max(onNCR, minimum).
* 6. Apply and return.
*
* @param {string} token β e.g. '#38', '#x26', '#X26'
* @returns {string|undefined}
* - string (incl. '') β replacement ('' = remove)
* - undefined β leave original &token; as-is
*/
_resolveNCR(token) {
// Step 1: parse codepoint
const second = token.charCodeAt(1);
let cp;
if (second === 120 /* x */ || second === 88 /* X */) {
cp = parseInt(token.slice(2), 16);
} else {
cp = parseInt(token.slice(1), 10);
}
// Step 2: out-of-range β leave as-is unconditionally
if (Number.isNaN(cp) || cp < 0 || cp > 0x10FFFF) return undefined;
// Step 3: classify to get minimum action level
const minimum = this._classifyNCR(cp);
// Step 4: if numericAllowed is false and no hard minimum β leave
if (!this._numericAllowed && minimum < NCR_LEVEL.remove) return undefined;
// Step 5: effective action = max(configured onNCR, range minimum)
const effective = minimum === -1
? this._ncrOnLevel
: Math.max(this._ncrOnLevel, minimum);
// Step 6: apply
return this._applyNCRAction(effective, token, cp);
}
} |