[ECD 10/24] feat: Add support for requiresLength trait

[dayaffe]

Describe the feature

This is the implementation task for #356
SEP: requires-length-trait.md

Use Case

We need to honor Smithy traits. The requiresLength trait further defines the behavior of the SDK when the stream trait is used on a request payload. At the time of writing this SEP, the list of AWS services that use the stream trait in input shapes included

• Lambda InvokeAsync (content-length)
• CloudSearchDomain UploadDocument (content-length)
• S3 PutObject/UploadPart (requiresLength with content-length)
• Glacier UploadArchive/UploadMultipart (requiresLength with content-length)
• Lex PostContent ([Only HTTP/1.1] (transfer-encoding: chunked, content-length if length readily available))
• MediaStore PutObject ([Only HTTP/1.1] (transfer-encoding: chunked, content-length if length readily available))

Proposed Solution

No response

Other Information

• The requiresLength trait is a boolean trait that can only target blob shapes marked with the stream trait.
• The shape should be denoted as a payload member.
• The payload of the request must be signed by default unless the request's operation is explicitly marked as v4-unsigned-body [2] in its authType trait.
• The v4-unsigned-body and requiresLength traits are not mutually exclusive. A given payload shape can be (correctly) marked with both stream and requiresLength, and the associated operation can have authType set to v4-unsigned-body.
• The SDK implementation must fail the request if determined that the content-length header must be set but the length of the payload cannot be calculated.
• If the length is readily available, set the content-length header. If the length is not readily available, requiresLength is not present, and v4-unsigned-body is present on the operation, set the transfer-encoding: chunked header if using HTTP/1.1. In all other cases, fail the request.

Acknowledgements

• I may be able to implement this feature request
• This feature might incur a breaking change

[jbelkins]

Released in AWS SDK for Swift 0.29.0.