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policy-document.ts
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policy-document.ts
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import { IConstruct } from 'constructs';
import { PolicyStatement, deriveEstimateSizeOptions } from './policy-statement';
import { mergeStatements } from './private/merge-statements';
import { PostProcessPolicyDocument } from './private/postprocess-policy-document';
import * as cdk from '../../core';
import * as cxapi from '../../cx-api';
/**
* Properties for a new PolicyDocument
*/
export interface PolicyDocumentProps {
/**
* Automatically assign Statement Ids to all statements
*
* @default false
*/
readonly assignSids?: boolean;
/**
* Initial statements to add to the policy document
*
* @default - No statements
*/
readonly statements?: PolicyStatement[];
/**
* Try to minimize the policy by merging statements
*
* To avoid overrunning the maximum policy size, combine statements if they produce
* the same result. Merging happens according to the following rules:
*
* - The Effect of both statements is the same
* - Neither of the statements have a 'Sid'
* - Combine Principals if the rest of the statement is exactly the same.
* - Combine Resources if the rest of the statement is exactly the same.
* - Combine Actions if the rest of the statement is exactly the same.
* - We will never combine NotPrincipals, NotResources or NotActions, because doing
* so would change the meaning of the policy document.
*
* @default - false, unless the feature flag `@aws-cdk/aws-iam:minimizePolicies` is set
*/
readonly minimize?: boolean;
}
/**
* A PolicyDocument is a collection of statements
*/
export class PolicyDocument implements cdk.IResolvable {
/**
* Creates a new PolicyDocument based on the object provided.
* This will accept an object created from the `.toJSON()` call
* @param obj the PolicyDocument in object form.
*/
public static fromJson(obj: any): PolicyDocument {
const newPolicyDocument = new PolicyDocument();
const statement = obj.Statement ?? [];
if (statement && !Array.isArray(statement)) {
throw new Error('Statement must be an array');
}
newPolicyDocument.addStatements(...obj.Statement.map((s: any) => PolicyStatement.fromJson(s)));
return newPolicyDocument;
}
public readonly creationStack: string[];
private readonly statements = new Array<PolicyStatement>();
private readonly autoAssignSids: boolean;
private readonly minimize?: boolean;
constructor(props: PolicyDocumentProps = {}) {
this.creationStack = cdk.captureStackTrace();
this.autoAssignSids = !!props.assignSids;
this.minimize = props.minimize;
this.addStatements(...props.statements || []);
}
public resolve(context: cdk.IResolveContext): any {
this.freezeStatements();
this._maybeMergeStatements(context.scope);
// In the previous implementation of 'merge', sorting of actions/resources on
// a statement always happened, even on singular statements. In the new
// implementation of 'merge', sorting only happens when actually combining 2
// statements. This affects all test snapshots, so we need to put in mechanisms
// to avoid having to update all snapshots.
//
// To do sorting in a way compatible with the previous implementation of merging,
// (so we don't have to update snapshots) do it after rendering, but only when
// merging is enabled.
const sort = this.shouldMerge(context.scope);
context.registerPostProcessor(new PostProcessPolicyDocument(this.autoAssignSids, sort));
return this.render();
}
/**
* Whether the policy document contains any statements.
*/
public get isEmpty(): boolean {
return this.statements.length === 0;
}
/**
* The number of statements already added to this policy.
* Can be used, for example, to generate unique "sid"s within the policy.
*/
public get statementCount(): number {
return this.statements.length;
}
/**
* Adds a statement to the policy document.
*
* @param statement the statement to add.
*/
public addStatements(...statement: PolicyStatement[]) {
this.statements.push(...statement);
}
/**
* Encode the policy document as a string
*/
public toString() {
return cdk.Token.asString(this, {
displayHint: 'PolicyDocument',
});
}
/**
* JSON-ify the document
*
* Used when JSON.stringify() is called
*/
public toJSON() {
return this.render();
}
/**
* Validate that all policy statements in the policy document satisfies the
* requirements for any policy.
*
* @see https://docs.aws.amazon.com/IAM/latest/UserGuide/access_policies.html#access_policies-json
*
* @returns An array of validation error messages, or an empty array if the document is valid.
*/
public validateForAnyPolicy(): string[] {
const errors = new Array<string>();
for (const statement of this.statements) {
errors.push(...statement.validateForAnyPolicy());
}
return errors;
}
/**
* Validate that all policy statements in the policy document satisfies the
* requirements for a resource-based policy.
*
* @see https://docs.aws.amazon.com/IAM/latest/UserGuide/access_policies.html#access_policies-json
*
* @returns An array of validation error messages, or an empty array if the document is valid.
*/
public validateForResourcePolicy(): string[] {
const errors = new Array<string>();
for (const statement of this.statements) {
errors.push(...statement.validateForResourcePolicy());
}
return errors;
}
/**
* Validate that all policy statements in the policy document satisfies the
* requirements for an identity-based policy.
*
* @see https://docs.aws.amazon.com/IAM/latest/UserGuide/access_policies.html#access_policies-json
*
* @returns An array of validation error messages, or an empty array if the document is valid.
*/
public validateForIdentityPolicy(): string[] {
const errors = new Array<string>();
for (const statement of this.statements) {
errors.push(...statement.validateForIdentityPolicy());
}
return errors;
}
/**
* Perform statement merging (if enabled and not done yet)
*
* @internal
*/
public _maybeMergeStatements(scope: IConstruct): void {
if (this.shouldMerge(scope)) {
const result = mergeStatements(this.statements, { scope });
this.statements.splice(0, this.statements.length, ...result.mergedStatements);
}
}
/**
* Split the statements of the PolicyDocument into multiple groups, limited by their size
*
* We do a round of size-limited merging first (making sure to not produce statements too
* large to fit into standalone policies), so that we can most accurately estimate total
* policy size. Another final round of minimization will be done just before rendering to
* end up with minimal policies that look nice to humans.
*
* Return a map of the final set of policy documents, mapped to the ORIGINAL (pre-merge)
* PolicyStatements that ended up in the given PolicyDocument.
*
* @internal
*/
public _splitDocument(scope: IConstruct, selfMaximumSize: number, splitMaximumSize: number): Map<PolicyDocument, PolicyStatement[]> {
const self = this;
const newDocs: PolicyDocument[] = [];
// Maps final statements to original statements
this.freezeStatements();
let statementsToOriginals = new Map(this.statements.map(s => [s, [s]]));
// We always run 'mergeStatements' to minimize the policy before splitting.
// However, we only 'merge' when the feature flag is on. If the flag is not
// on, we only combine statements that are *exactly* the same. We must do
// this before splitting, otherwise we may end up with the statement set [X,
// X, X, X, X] being split off into [[X, X, X], [X, X]] before being reduced
// to [[X], [X]] (but should have been just [[X]]).
const doActualMerging = this.shouldMerge(scope);
const result = mergeStatements(this.statements, { scope, limitSize: true, mergeIfCombinable: doActualMerging });
this.statements.splice(0, this.statements.length, ...result.mergedStatements);
statementsToOriginals = result.originsMap;
const sizeOptions = deriveEstimateSizeOptions(scope);
// Cache statement sizes to avoid recomputing them based on the fields
const statementSizes = new Map<PolicyStatement, number>(this.statements.map(s => [s, s._estimateSize(sizeOptions)]));
// Keep some size counters so we can avoid recomputing them based on the statements in each
let selfSize = 0;
const polSizes = new Map<PolicyDocument, number>();
// Getter with a default to save some syntactic noise
const polSize = (x: PolicyDocument) => polSizes.get(x) ?? 0;
let i = 0;
while (i < this.statements.length) {
const statement = this.statements[i];
const statementSize = statementSizes.get(statement) ?? 0;
if (selfSize + statementSize < selfMaximumSize) {
// Fits in self
selfSize += statementSize;
i++;
continue;
}
// Split off to new PolicyDocument. Find the PolicyDocument we can add this to,
// or add a fresh one.
const addToDoc = findDocWithSpace(statementSize);
addToDoc.addStatements(statement);
polSizes.set(addToDoc, polSize(addToDoc) + statementSize);
this.statements.splice(i, 1);
}
// Return the set of all policy document and original statements
const ret = new Map<PolicyDocument, PolicyStatement[]>();
ret.set(this, this.statements.flatMap(s => statementsToOriginals.get(s) ?? [s]));
for (const newDoc of newDocs) {
ret.set(newDoc, newDoc.statements.flatMap(s => statementsToOriginals.get(s) ?? [s]));
}
return ret;
function findDocWithSpace(size: number) {
let j = 0;
while (j < newDocs.length && polSize(newDocs[j]) + size > splitMaximumSize) {
j++;
}
if (j < newDocs.length) {
return newDocs[j];
}
const newDoc = new PolicyDocument({
assignSids: self.autoAssignSids,
minimize: self.minimize,
});
newDocs.push(newDoc);
return newDoc;
}
}
private render(): any {
if (this.isEmpty) {
return undefined;
}
const doc = {
Statement: this.statements.map(s => s.toStatementJson()),
Version: '2012-10-17',
};
return doc;
}
private shouldMerge(scope: IConstruct) {
return this.minimize ?? cdk.FeatureFlags.of(scope).isEnabled(cxapi.IAM_MINIMIZE_POLICIES) ?? false;
}
/**
* Freeze all statements
*/
private freezeStatements() {
for (const statement of this.statements) {
statement.freeze();
}
}
}