Class ALambdaFunction

ALambdaFunction is the abstract base class for all AWS Lambda functions. This class takes care of initializing the function from environment variables, before invoking ProcessMessageStreamAsync(Stream).

Inheritance

System.Object

ALambdaFunction

ALambdaFunction<TRequest, TResponse>

Implements

ILambdaSharpLogger

Namespace: LambdaSharp

Assembly: LambdaSharp.dll

Syntax

public abstract class ALambdaFunction : ILambdaSharpLogger

Constructors

ALambdaFunction()

Initializes a new ALambdaFunction instance using the default implementation of ILambdaFunctionDependencyProvider.

Declaration

protected ALambdaFunction()

ALambdaFunction(ILambdaFunctionDependencyProvider)

Initializes a new ALambdaFunction instance using a custom implementation of ILambdaFunctionDependencyProvider.

Declaration

protected ALambdaFunction(ILambdaFunctionDependencyProvider provider)

Parameters

Type	Name	Description
ILambdaFunctionDependencyProvider	provider	Custom implementation of ILambdaFunctionDependencyProvider.

Exceptions

Type	Condition
System.ArgumentNullException	Thrown when provider is null.

Properties

CurrentContext

Retrieve the current Amazon.Lambda.Core.ILambdaContext for the request.

Declaration

protected ILambdaContext CurrentContext { get; }

Property Value

Type	Description
Amazon.Lambda.Core.ILambdaContext	The Amazon.Lambda.Core.ILambdaContext instance.

Remarks

This property is only set during the invocation of ProcessMessageStreamAsync(Stream). Otherwise, it returns null.

DebugLoggingEnabled

The DebugLoggingEnabled property indicates if the requests received and responses emitted by this Lambda function should be shown in the CloudWatch logs. This can be useful to determine check for issues caused by inconsistencies in serialization or deserialization.

Declaration

protected virtual bool DebugLoggingEnabled { get; }

Property Value

Type	Description
System.Boolean	Boolean indicating if requests and responses are logged

ErrorReportGenerator

Retrieve the ErrorReportGenerator instance used to generate error reports.

Declaration

protected ILambdaErrorReportGenerator ErrorReportGenerator { get; }

Property Value

Type	Description
ILambdaErrorReportGenerator	The ErrorReportGenerator instance.

HttpClient

The HttpClient property holds a HttpClient instance that is initialized with X-Ray support.

Declaration

protected HttpClient HttpClient { get; set; }

Property Value

Type	Description
System.Net.Http.HttpClient	The HttpClient instance.

Info

Retrieve the Lambda function initialization settings.

Declaration

protected ALambdaFunction.FunctionInfo Info { get; }

Property Value

Type	Description
ALambdaFunction.FunctionInfo	The ALambdaFunction.FunctionInfo value.

Logger

Retrieve the ILambdaSharpLogger instance.

Declaration

protected ILambdaSharpLogger Logger { get; }

Property Value

Type	Description
ILambdaSharpLogger	The ILambdaSharpLogger instance.

Provider

The ILambdaFunctionDependencyProvider instance used by the Lambda function to satisfy its required dependencies.

Declaration

protected ILambdaFunctionDependencyProvider Provider { get; }

Property Value

Type	Description
ILambdaFunctionDependencyProvider	The ILambdaFunctionDependencyProvider instance.

UtcNow

Retrieves the current date-time in UTC timezone.

Declaration

protected DateTime UtcNow { get; }

Property Value

Type	Description
System.DateTime	Current date-time in UTC timezone.

Methods

AddPendingTask(Task)

The AddPendingTask(Task) method adds the specified task to the list of pending tasks. The Lambda function waits until all pendings tasks have completed before responding to the active invocation.

Declaration

protected void AddPendingTask(Task task)

Parameters

Type	Name	Description
System.Threading.Tasks.Task	task	A task to wait for before responding to the active invocation.

DecryptSecretAsync(String, Dictionary<String, String>, CancellationToken)

The DecryptSecretAsync(String, Dictionary<String, String>, CancellationToken) method decrypts a Base64-encoded string with an optional encryption context. The Lambda function requires permission to use the kms:Decrypt operation on the KMS key used to encrypt the original message.

Declaration

protected async Task<string> DecryptSecretAsync(string secret, Dictionary<string, string> encryptionContext = null, CancellationToken cancellationToken = default(CancellationToken))

Parameters

Type	Name	Description
System.String	secret	Base64-encoded string of the encrypted value.
System.Collections.Generic.Dictionary<System.String, System.String>	encryptionContext	An optional encryption context. Can be null.
System.Threading.CancellationToken	cancellationToken	The token to monitor for cancellation requests.

Returns

Type	Description
System.Threading.Tasks.Task<System.String>	The task object representing the asynchronous operation.

EncryptSecretAsync(String, String, Dictionary<String, String>, CancellationToken)

The EncryptSecretAsync(String, String, Dictionary<String, String>, CancellationToken) encrypts a sequence of bytes using the specified KMS key. The Lambda function requires permission to use the kms:Encrypt opeartion on the specified KMS key.

Declaration

protected async Task<string> EncryptSecretAsync(string text, string encryptionKeyId, Dictionary<string, string> encryptionContext = null, CancellationToken cancellationToken = default(CancellationToken))

Parameters

Type	Name	Description
System.String	text	The plaintext string to encrypt.
System.String	encryptionKeyId	The KMS key ID used encrypt the plaintext bytes.
System.Collections.Generic.Dictionary<System.String, System.String>	encryptionContext	An optional encryption context. Can be null.
System.Threading.CancellationToken	cancellationToken	The token to monitor for cancellation requests.

Returns

Type	Description
System.Threading.Tasks.Task<System.String>	The task object representing the asynchronous operation.

ForceLambdaColdStart(String)

The ForceLambdaColdStart(String) method causes the Lambda runtime to re-initialize as if a cold start had occurred. This methos is useful when the global environment is corrupted and only a restart can fix it.

Declaration

protected void ForceLambdaColdStart(string reason)

Parameters

Type	Name	Description
System.String	reason

FunctionHandlerAsync(Stream, ILambdaContext)

The FunctionHandlerAsync(Stream, ILambdaContext) method is the entry point for the Lambda function. It is responsible for initializing the Lambda function on first invocation, then invoking ProcessMessageStreamAsync(Stream) and handling any failures that occur.

Declaration

[LambdaSerializer(typeof(LambdaSystemTextJsonSerializer))]
public async Task<Stream> FunctionHandlerAsync(Stream stream, ILambdaContext context)

Parameters

Type	Name	Description
System.IO.Stream	stream	The request stream.
Amazon.Lambda.Core.ILambdaContext	context	The Amazon.Lambda.Core.ILambdaContext instance associated with this request. The instance can be retrieved using the CurrentContext property.

Returns

Type	Description
System.Threading.Tasks.Task<System.IO.Stream>	The task object representing the asynchronous operation.

HandleFailedInitializationAsync(Stream)

The HandleFailedInitializationAsync(Stream) method is only invoked when an error occurs during the Lambda function initialization. This method can be overridden to provide custom behavior for how to handle such failures more gracefully.

Declaration

protected virtual async Task HandleFailedInitializationAsync(Stream stream)

Parameters

Type	Name	Description
System.IO.Stream	stream	The stream with the request payload.

Returns

Type	Description
System.Threading.Tasks.Task	The task object representing the asynchronous operation.

Remarks

Regardless of what this method does. Once completed, the Lambda function exits by rethrowing the original exception that occurred during initialization.

InitializeAsync(LambdaConfig)

The InitializeAsync(LambdaConfig) method is invoke on first request. It is responsible for initializing the Lambda function using the provided LambdaConfig instance.

Declaration

public abstract Task InitializeAsync(LambdaConfig config)

Parameters

Type	Name	Description
LambdaConfig	config	The LambdaConfig instance to use.

Returns

Type	Description
System.Threading.Tasks.Task	The task object representing the asynchronous operation.

InitializeEpilogueAsync()

The InitializeEpilogueAsync() method is invoked to complet the initialization of the Lambda function. This is the last of three methods that are invoked to initialize the Lambda function.

Declaration

protected virtual async Task InitializeEpilogueAsync()

Returns

Type	Description
System.Threading.Tasks.Task	The task object representing the asynchronous operation.

InitializePrologueAsync(ILambdaConfigSource)

The InitializePrologueAsync(ILambdaConfigSource) method is invoked to prepare the Lambda function for initialization. This is the first of three methods that are invoked to initialize the Lambda function.

Declaration

protected virtual async Task InitializePrologueAsync(ILambdaConfigSource envSource)

Parameters

Type	Name	Description
ILambdaConfigSource	envSource	The ILambdaConfigSource instance from which to read the configuration settings.

Returns

Type	Description
System.Threading.Tasks.Task	The task object representing the asynchronous operation.

LogDebug(String, Object[])

Log a debugging message. This message will only appear in the log when debug logging is enabled and will not be forwarded to an error aggregator.

Declaration

protected void LogDebug(string format, params object[] arguments)

Parameters

Type	Name	Description
System.String	format	The message format string. If not arguments are supplied, the message format string will be printed as a plain string.
System.Object[]	arguments	Optional arguments for the message string.

LogError(Exception)

Log an exception as an error. This message will be reported if an error aggregator is configured for the LambdaSharp.Core module.

Declaration

protected void LogError(Exception exception)

Parameters

Type	Name	Description
System.Exception	exception	The exception to log. The exception is logged with its message, stacktrace, and any nested exceptions.

LogError(Exception, String, Object[])

Log an exception with a custom message as an error. This message will be reported if an error aggregator is configured for the LambdaSharp.Core module.

Declaration

protected void LogError(Exception exception, string format, params object[] arguments)

Parameters

Type	Name	Description
System.Exception	exception	The exception to log. The exception is logged with its message, stacktrace, and any nested exceptions.
System.String	format	Optional message to use instead of Exception.Message. This parameter can be null.
System.Object[]	arguments	Optional arguments for the format parameter.

LogErrorAsInfo(Exception)

Log an exception as an information message. This message will only appear in the log and not be forwarded to an error aggregator.

Declaration

protected void LogErrorAsInfo(Exception exception)

Parameters

Type	Name	Description
System.Exception	exception	The exception to log. The exception is logged with its message, stacktrace, and any nested exceptions.

Remarks

Only use this method when the exception has no operational impact. Otherwise, either use LogError(Exception) or LogErrorAsWarning(Exception).

LogErrorAsInfo(Exception, String, Object[])

Log an exception with a custom message as an information message. This message will only appear in the log and not be forwarded to an error aggregator.

Declaration

protected void LogErrorAsInfo(Exception exception, string format, params object[] arguments)

Parameters

Type	Name	Description
System.Exception	exception	The exception to log. The exception is logged with its message, stacktrace, and any nested exceptions.
System.String	format	Optional message to use instead of Exception.Message. This parameter can be null.
System.Object[]	arguments	Optional arguments for the format parameter.

Remarks

Only use this method when the exception has no operational impact. Otherwise, either use LogError(Exception) or LogErrorAsWarning(Exception).

LogErrorAsWarning(Exception)

Log an exception as a warning. This message will be reported if an error aggregator is configured for the LambdaSharp.Core module.

Declaration

protected void LogErrorAsWarning(Exception exception)

Parameters

Type	Name	Description
System.Exception	exception	The exception to log. The exception is logged with its message, stacktrace, and any nested exceptions.

Remarks

Only use this method when the exception has no operational impact. Otherwise, either use LogError(Exception).

LogErrorAsWarning(Exception, String, Object[])

Log an exception with a custom message as a warning. This message will be reported if an error aggregator is configured for the LambdaSharp.Core module.

Declaration

protected void LogErrorAsWarning(Exception exception, string format, params object[] arguments)

Parameters

Type	Name	Description
System.Exception	exception	The exception to log. The exception is logged with its message, stacktrace, and any nested exceptions.
System.String	format	Optional message to use instead of Exception.Message. This parameter can be null.
System.Object[]	arguments	Optional arguments for the format parameter.

Remarks

Only use this method when the exception has no operational impact. Otherwise, either use LogError(Exception).

LogEvent<T>(T, IEnumerable<String>)

Send a CloudWatch event with optional event details and resources it applies to. This event is forwarded to the configured EventBridge. The 'detail-type' property is set to the full type name of the detail value.

Declaration

protected void LogEvent<T>(T detail, IEnumerable<string> resources = null)

Parameters

Type	Name	Description
T	detail	Data-structure to serialize as a JSON string. If value is already a string , it is sent as-is. There is no other schema imposed. The data-structure may contain fields and nested subobjects.
System.Collections.Generic.IEnumerable<System.String>	resources	Optional AWS or custom resources, identified by unique identifier (e.g. ARN), which the event primarily concerns. Any number, including zero, may be present.

Type Parameters

Name	Description
T

LogEvent<T>(String, T, IEnumerable<String>)

Send a CloudWatch event with optional event details and resources it applies to. This event is forwarded to the configured EventBridge. The 'detail-type' property is set to the full type name of the detail value.

Declaration

protected void LogEvent<T>(string source, T detail, IEnumerable<string> resources = null)

Parameters

Type	Name	Description
System.String	source	Name of the event source.
T	detail	Data-structure to serialize as a JSON string. If value is already a string , it is sent as-is. There is no other schema imposed. The data-structure may contain fields and nested subobjects.
System.Collections.Generic.IEnumerable<System.String>	resources	Optional AWS or custom resources, identified by unique identifier (e.g. ARN), which the event primarily concerns. Any number, including zero, may be present.

Type Parameters

Name	Description
T

LogEvent<T>(String, String, T, IEnumerable<String>)

Send a CloudWatch event with optional event details and resources it applies to. This event is forwarded to the configured EventBridge.

Declaration

protected void LogEvent<T>(string source, string detailType, T detail, IEnumerable<string> resources = null)

Parameters

Type	Name	Description
System.String	source	Name of the event source.
System.String	detailType	Free-form string used to decide what fields to expect in the event detail.
T	detail	Data-structure to serialize as a JSON string using System.Text.Json.JsonSerializer. If value is already a string , it is sent as-is. There is no other schema imposed. The data-structure may contain fields and nested subobjects.
System.Collections.Generic.IEnumerable<System.String>	resources	Optional AWS or custom resources, identified by unique identifier (e.g. ARN), which the event primarily concerns. Any number, including zero, may be present.

Type Parameters

Name	Description
T

LogFatal(Exception, String, Object[])

Log an exception with a custom message as a fatal error. This message will be reported if an error aggregator is configured for the LambdaSharp.Core module.

Declaration

protected void LogFatal(Exception exception, string format, params object[] arguments)

Parameters

Type	Name	Description
System.Exception	exception	The exception to log. The exception is logged with its message, stacktrace, and any nested exceptions.
System.String	format	Optional message to use instead of Exception.Message. This parameter can be null.
System.Object[]	arguments	Optional arguments for the format parameter.

LogInfo(String, Object[])

Log an informational message. This message will only appear in the log and not be forwarded to an error aggregator.

Declaration

protected void LogInfo(string format, params object[] arguments)

Parameters

Type	Name	Description
System.String	format	The message format string. If not arguments are supplied, the message format string will be printed as a plain string.
System.Object[]	arguments	Optional arguments for the message string.

LogMetric(IEnumerable<LambdaMetric>)

Log a CloudWatch metric. The metric is picked up by CloudWatch logs and automatically ingested as a CloudWatch metric.

Declaration

protected void LogMetric(IEnumerable<LambdaMetric> metrics)

Parameters

Type	Name	Description
System.Collections.Generic.IEnumerable<LambdaMetric>	metrics	Enumeration of metrics, including their name, value, and unit.

LogMetric(IEnumerable<LambdaMetric>, IEnumerable<String>, Dictionary<String, String>)

Log a CloudWatch metric. The metric is picked up by CloudWatch logs and automatically ingested as a CloudWatch metric.

Declaration

protected virtual void LogMetric(IEnumerable<LambdaMetric> metrics, IEnumerable<string> dimensionNames, Dictionary<string, string> dimensionValues)

Parameters

Type	Name	Description
System.Collections.Generic.IEnumerable<LambdaMetric>	metrics	Enumeration of metrics, including their name, value, and unit.
System.Collections.Generic.IEnumerable<System.String>	dimensionNames	Metric dimensions as comma-separated list (e.g. [ "A", "A,B" ]).
System.Collections.Generic.Dictionary<System.String, System.String>	dimensionValues	Dictionary of dimesion name-value pairs.

LogMetric(String, Double, LambdaMetricUnit)

Log a CloudWatch metric. The metric is picked up by CloudWatch logs and automatically ingested as a CloudWatch metric.

Declaration

protected void LogMetric(string name, double value, LambdaMetricUnit unit)

Parameters

Type	Name	Description
System.String	name	Metric name.
System.Double	value	Metric value.
LambdaMetricUnit	unit	Metric unit.

LogMetric(String, Double, LambdaMetricUnit, IEnumerable<String>, Dictionary<String, String>)

Log a CloudWatch metric. The metric is picked up by CloudWatch logs and automatically ingested as a CloudWatch metric.

Declaration

protected void LogMetric(string name, double value, LambdaMetricUnit unit, IEnumerable<string> dimensionNames, Dictionary<string, string> dimensionValues)

Parameters

Type	Name	Description
System.String	name	Metric name.
System.Double	value	Metric value.
LambdaMetricUnit	unit	Metric unit.
System.Collections.Generic.IEnumerable<System.String>	dimensionNames	Metric dimensions as comma-separated list (e.g. [ "A", "A,B" ]).
System.Collections.Generic.Dictionary<System.String, System.String>	dimensionValues	Dictionary of dimesion name-value pairs.

LogWarn(String, Object[])

Log a warning message. This message will be reported if an error aggregator is configured for the LambdaSharp.Core module.

Declaration

protected void LogWarn(string format, params object[] arguments)

Parameters

Type	Name	Description
System.String	format	The message format string. If not arguments are supplied, the message format string will be printed as a plain string.
System.Object[]	arguments	Optional arguments for the message string.

ProcessMessageStreamAsync(Stream)

The ProcessMessageStreamAsync(Stream) method is invoked for every received request. It is responsible for deserializing the stream and processing the received message. The return stream is sent as response.

Declaration

public abstract Task<Stream> ProcessMessageStreamAsync(Stream stream)

Parameters

Type	Name	Description
System.IO.Stream	stream	The stream with the request payload.

Returns

Type	Description
System.Threading.Tasks.Task<System.IO.Stream>	The task object representing the asynchronous operation.

RecordErrorReport(LambdaErrorReport)

The RecordErrorReport(LambdaErrorReport) method is invoked record errors for later reporting.

Declaration

protected virtual void RecordErrorReport(LambdaErrorReport report)

Parameters

Type	Name	Description
LambdaErrorReport	report	The LambdaErrorReport to record.

RecordException(Exception)

The RecordException(Exception) method is only invoked when Lambda function ErrorReportGenerator instance has not yet been initialized of if an exception occurred while invoking RecordErrorReport(LambdaErrorReport).

Declaration

protected virtual void RecordException(Exception exception)

Parameters

Type	Name	Description
System.Exception	exception	Exception to record.

RecordFailedMessageAsync(LambdaLogLevel, ALambdaFunction.FailedMessageOrigin, String, Exception)

The RecordFailedMessageAsync(LambdaLogLevel, ALambdaFunction.FailedMessageOrigin, String, Exception) method is invoked when a permanent failure is detected during processing and the message should be sent to the dead-letter queue if possible. If no dead-letter queue is configured, the original exception is rethrown instead.

Declaration

protected virtual async Task RecordFailedMessageAsync(LambdaLogLevel level, ALambdaFunction.FailedMessageOrigin origin, string message, Exception exception)

Parameters

Type	Name	Description
LambdaLogLevel	level	The severity level of the failure. This should either be ERROR or FATAL.
ALambdaFunction.FailedMessageOrigin	origin	The origin of the failed message.
System.String	message	The failed message.
System.Exception	exception	The exception that was triggered by the failed message.

Returns

Type	Description
System.Threading.Tasks.Task	The task object representing the asynchronous operation.

RunTask(Action, CancellationToken)

The RunTask(Action, CancellationToken) method queues the specified work for background execution. The Lambda function waits until all queued background work has completed before completing the active invocation.

Declaration

protected void RunTask(Action action, CancellationToken cancellationToken = default(CancellationToken))

Parameters

Type	Name	Description
System.Action	action	The work to execute asynchronously.
System.Threading.CancellationToken	cancellationToken	An optional cancellation token that can be used to cancel the work.

RunTask(Func<Task>, CancellationToken)

The RunTask(Func<Task>, CancellationToken) method queues the specified work for background execution. The Lambda function waits until all queued background work has completed before completing the active invocation.

Declaration

protected void RunTask(Func<Task> function, CancellationToken cancellationToken = default(CancellationToken))

Parameters

Type	Name	Description
System.Func<System.Threading.Tasks.Task>	function	The work to execute asynchronously.
System.Threading.CancellationToken	cancellationToken	An optional cancellation token that can be used to cancel the work.

TerminateLambdaInstance(String)

The TerminateLambdaInstance(String) method forces the Lambda instance to terminate and perform a cold start on next invocation. This method should only be used when the processing environment has become corrupted beyond repair.

Declaration

protected void TerminateLambdaInstance(string reason = null)

Parameters

Type	Name	Description
System.String	reason	Optional message shown as reason for terminating the Lambda instance.

Explicit Interface Implementations

ILambdaSharpLogger.DebugLoggingEnabled

Declaration

bool ILambdaSharpLogger.DebugLoggingEnabled { get; }

Returns

Type	Description
System.Boolean

ILambdaSharpLogger.Info

Declaration

ILambdaSharpInfo ILambdaSharpLogger.Info { get; }

Returns

Type	Description
ILambdaSharpInfo

ILambdaSharpLogger.Log(LambdaLogLevel, Exception, String, Object[])

Declaration

void ILambdaSharpLogger.Log(LambdaLogLevel level, Exception exception, string format, params object[] arguments)

Parameters

Type	Name	Description
LambdaLogLevel	level
System.Exception	exception
System.String	format
System.Object[]	arguments

ILambdaSharpLogger.LogRecord(ALambdaLogRecord)

Declaration

void ILambdaSharpLogger.LogRecord(ALambdaLogRecord record)

Parameters

Type	Name	Description
ALambdaLogRecord	record

Implements

ILambdaSharpLogger