You can append a custom type label to the supported data types (String, Number, and Binary) to create custom data types. This capability is similar to type traits in programming languages. For example, if you have an application that needs to know which type of number is being sent in the message, then you could create custom types similar to the following: Number.byte, Number.short, Number.int, and Number.float. Another example using the binary data type is to use Binary.gif and Binary.png to distinguish among different image file types in a message or batch of messages. The appended data is optional and opaque to Amazon SQS, which means that the appended data is not interpreted, validated, or used by Amazon SQS. The Custom Type extension has the same restrictions on allowed characters as the message body.

Message Attribute Value

The user-specified message attribute value. For string data types, the value attribute has the same restrictions on the content as the message body. For more information, see SendMessage.

Name, type, and value must not be empty or null. In addition, the message body should not be empty or null. All parts of the message attribute, including name, type, and value, are included in the message size restriction, which is currently 256 KB (262,144 bytes).

The supported message attribute data types are String, Number, and Binary. You can also provide custom information on the type. The data type has the same restrictions on the content as the message body. The data type is case sensitive, and it can be up to 256 bytes long.

http://docs.aws.amazon.com/AWSSimpleQueueService/2012-11-05/APIReference/API_MessageAttributeValue.html

The message attribute name can contain the following characters: A-Z, a-z, 0-9, underscore(_), hyphen(-), and period (.). The name must not start or end with a period, and it should not have successive periods. The name is case sensitive and must be unique among all attribute names for the message. The name can be up to 256 characters long. The name cannot start with "AWS." or "Amazon." (or any variations in casing) because these prefixes are reserved for use by Amazon Web Services.

Message Attribute

Name, type, and value must not be empty or null. In addition, the message body should not be empty or null. All parts of the message attribute, including name, type, and value, are included in the message size restriction, which is currently 256 KB (262,144 bytes).

http://docs.aws.amazon.com/AWSSimpleQueueService/latest/SQSDeveloperGuide/SQSMessageAttributes.html#SQSMessageAttributes.DataTypes

NOTE

The Amazon SQS API reference calls this MessageAttribute. The Haskell bindings use this term for what the Amazon documentation calls just Attributes. In order to limit backward compatibility issues we keep the terminology of the Haskell bindings and call this type UserMessageAttributes.

Delivers a message to the specified queue. With Amazon SQS, you now have the ability to send large payload messages that are up to 256KB (262,144 bytes) in size. To send large payloads, you must use an AWS SDK that supports SigV4 signing. To verify whether SigV4 is supported for an AWS SDK, check the SDK release notes.

IMPORTANT

The following list shows the characters (in Unicode) allowed in your message, according to the W3C XML specification. For more information, go to http://www.w3.org/TR/REC-xml/#charsets If you send any characters not included in the list, your request will be rejected.

#x9 | #xA | #xD | [#x20 to #xD7FF] | [#xE000 to #xFFFD] | [#x10000 to #x10FFFF]

http://docs.aws.amazon.com/AWSSimpleQueueService/2012-11-05/APIReference/API_SendMessage.html

At http://docs.aws.amazon.com/AWSSimpleQueueService/2012-11-05/APIReference/API_SendMessageResult.html all fields of SendMessageResult are denoted as optional. At http://queue.amazonaws.com/doc/2012-11-05/QueueService.wsdl all fields are specified as required.

The actual service seems to treat at least smrMD5OfMessageAttributes as optional.

Deletes the specified message from the specified queue. You specify the message by using the message's receipt handle and not the message ID you received when you sent the message. Even if the message is locked by another reader due to the visibility timeout setting, it is still deleted from the queue. If you leave a message in the queue for longer than the queue's configured retention period, Amazon SQS automatically deletes it.

NOTE

The receipt handle is associated with a specific instance of receiving the message. If you receive a message more than once, the receipt handle you get each time you receive the message is different. When you request DeleteMessage, if you don't provide the most recently received receipt handle for the message, the request will still succeed, but the message might not be deleted.

IMPORTANT

It is possible you will receive a message even after you have deleted it. This might happen on rare occasions if one of the servers storing a copy of the message is unavailable when you request to delete the message. The copy remains on the server and might be returned to you again on a subsequent receive request. You should create your system to be idempotent so that receiving a particular message more than once is not a problem.

http://docs.aws.amazon.com/AWSSimpleQueueService/2012-11-05/APIReference/API_DeleteMessage.html

An Amazon SQS message.

In http://docs.aws.amazon.com/AWSSimpleQueueService/2012-11-05/APIReference/API_Message.html all elements are denoted as optional. In http://queue.amazonaws.com/doc/2012-11-05/QueueService.wsdl all elements except for the attributes are specified as required. At least for the field mMD5OfMessageAttributes the the service is not always returning a value and therefor we make this field optional.

Retrieves one or more messages, with a maximum limit of 10 messages, from the specified queue. Long poll support is enabled by using the WaitTimeSeconds parameter. For more information, see Amazon SQS Long Poll in the Amazon SQS Developer Guide.

Short poll is the default behavior where a weighted random set of machines is sampled on a ReceiveMessage call. This means only the messages on the sampled machines are returned. If the number of messages in the queue is small (less than 1000), it is likely you will get fewer messages than you requested per ReceiveMessage call. If the number of messages in the queue is extremely small, you might not receive any messages in a particular ReceiveMessage response; in which case you should repeat the request.

For each message returned, the response includes the following:

Message body

• MD5 digest of the message body. For information about MD5, go to http://www.faqs.org/rfcs/rfc1321.html.
• Message ID you received when you sent the message to the queue.
• Receipt handle.
• Message attributes.
• MD5 digest of the message attributes.

The receipt handle is the identifier you must provide when deleting the message. For more information, see Queue and Message Identifiers in the Amazon SQS Developer Guide.

You can provide the VisibilityTimeout parameter in your request, which will be applied to the messages that Amazon SQS returns in the response. If you do not include the parameter, the overall visibility timeout for the queue is used for the returned messages. For more information, see Visibility Timeout in the Amazon SQS Developer Guide.

NOTE

Going forward, new attributes might be added. If you are writing code that calls this action, we recommend that you structure your code so that it can handle new attributes gracefully.

http://docs.aws.amazon.com/AWSSimpleQueueService/2012-11-05/APIReference/API_ReceiveMessage.html

Changes the visibility timeout of a specified message in a queue to a new value. The maximum allowed timeout value you can set the value to is 12 hours. This means you can't extend the timeout of a message in an existing queue to more than a total visibility timeout of 12 hours. (For more information visibility timeout, see Visibility Timeout in the Amazon SQS Developer Guide.)

For example, let's say you have a message and its default message visibility timeout is 30 minutes. You could call ChangeMessageVisiblity with a value of two hours and the effective timeout would be two hours and 30 minutes. When that time comes near you could again extend the time out by calling ChangeMessageVisiblity, but this time the maximum allowed timeout would be 9 hours and 30 minutes.

NOTE

There is a 120,000 limit for the number of inflight messages per queue. Messages are inflight after they have been received from the queue by a consuming component, but have not yet been deleted from the queue. If you reach the 120,000 limit, you will receive an OverLimit error message from Amazon SQS. To help avoid reaching the limit, you should delete the messages from the queue after they have been processed. You can also increase the number of queues you use to process the messages.

IMPORTANT

If you attempt to set the VisibilityTimeout to an amount more than the maximum time left, Amazon SQS returns an error. It will not automatically recalculate and increase the timeout to the maximum time remaining.

IMPORTANT

Unlike with a queue, when you change the visibility timeout for a specific message, that timeout value is applied immediately but is not saved in memory for that message. If you don't delete a message after it is received, the visibility timeout for the message the next time it is received reverts to the original timeout value, not the value you set with the ChangeMessageVisibility action.

http://docs.aws.amazon.com/AWSSimpleQueueService/2012-11-05/APIReference/API_ChangeMessageVisibility.html