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# AWS Rule Set Extension
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The `AwsRuleSetExtension` is the main integration point for AWS-specific functionality in the Smithy rules engine. It provides AWS built-in parameters, library functions, and authentication validators.
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## Capabilities
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### AwsRuleSetExtension Class
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The primary extension class that implements `EndpointRuleSetExtension` to integrate AWS-specific functionality into the Smithy rules engine.
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```java { .api }
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/**
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 * AWS-specific extensions to smithy-rules-engine.
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 */
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public final class AwsRuleSetExtension implements EndpointRuleSetExtension {
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    /**
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     * Returns the AWS-specific built-in parameters available to endpoint rules
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     * @return List of AWS built-in parameters including region, dual-stack, FIPS, etc.
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     */
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    public List<Parameter> getBuiltIns();
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    /**
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     * Returns the AWS-specific library functions available to endpoint rules
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     * @return List of AWS library functions for partition resolution, ARN parsing, etc.
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     */
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    public List<FunctionDefinition> getLibraryFunctions();
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    /**
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     * Returns the AWS-specific authentication scheme validators
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     * @return List of authentication validators for SigV4, SigV4a, etc.
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     */
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    public List<AuthSchemeValidator> getAuthSchemeValidators();
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}
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```
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### Service Registration
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The extension is automatically registered through the Java Service Provider Interface:
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```
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META-INF/services/software.amazon.smithy.rulesengine.language.EndpointRuleSetExtension
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```
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**Usage Examples:**
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```java
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import software.amazon.smithy.rulesengine.aws.language.functions.AwsRuleSetExtension;
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import software.amazon.smithy.rulesengine.language.EndpointRuleSetExtension;
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// Extension is automatically loaded by the rules engine
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// You typically don't instantiate this directly
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EndpointRuleSetExtension extension = new AwsRuleSetExtension();
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// Get AWS built-in parameters
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List<Parameter> awsBuiltIns = extension.getBuiltIns();
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// Includes: REGION, DUALSTACK, FIPS, ACCOUNT_ID, S3_ACCELERATE, etc.
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// Get AWS library functions  
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List<FunctionDefinition> awsFunctions = extension.getLibraryFunctions();
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// Includes: aws.partition, aws.parseArn, aws.isVirtualHostableS3Bucket
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// Get authentication validators
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List<AuthSchemeValidator> authValidators = extension.getAuthSchemeValidators();
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// Includes validators for SigV4, SigV4a, SigV4 sub-schemes, and beta schemes
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```
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### Integration with Rules Engine
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The extension integrates seamlessly with Smithy's rules engine to provide AWS-specific capabilities:
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```java
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// The rules engine automatically discovers and loads this extension
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// Built-ins become available as parameters in endpoint rules
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// Functions become available for use in rule expressions  
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// Validators ensure proper AWS authentication configuration
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```
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## Built-in Parameters Provided
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The extension provides the following AWS-specific built-in parameters:
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- `DUALSTACK` - UseDualStack boolean parameter
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- `FIPS` - UseFIPS boolean parameter  
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- `REGION` - Region string parameter
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- `ACCOUNT_ID` - AccountId string parameter
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- `ACCOUNT_ID_ENDPOINT_MODE` - AccountIdEndpointMode string parameter
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- `CREDENTIAL_SCOPE` - CredentialScope string parameter
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- `S3_ACCELERATE` - S3 Accelerate boolean parameter
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- `S3_DISABLE_MRAP` - S3 DisableMultiRegionAccessPoints boolean parameter
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- `S3_FORCE_PATH_STYLE` - S3 ForcePathStyle boolean parameter
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- `S3_USE_ARN_REGION` - S3 UseArnRegion boolean parameter
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- `S3_USE_GLOBAL_ENDPOINT` - S3 UseGlobalEndpoint boolean parameter
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- `S3_CONTROL_USE_ARN_REGION` - S3Control UseArnRegion boolean parameter
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- `STS_USE_GLOBAL_ENDPOINT` - STS UseGlobalEndpoint boolean parameter
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## Library Functions Provided
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The extension provides these AWS-specific functions:
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- `aws.partition` - Maps region to partition information
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- `aws.parseArn` - Parses AWS ARN into component parts
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- `aws.isVirtualHostableS3Bucket` - Validates S3 bucket for virtual hosting
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## Authentication Validators Provided
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The extension provides validators for AWS authentication schemes:
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- `SigV4SchemeValidator` - Validates SigV4 authentication configuration
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- `SigV4aSchemeValidator` - Validates SigV4a authentication configuration  
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- `SigV4SubSchemeValidator` - Validates SigV4 sub-scheme authentication
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- `BetaSchemeValidator` - Validates beta authentication schemes