we only need to allocate strlen

[toidiu]

Resolved issues:

Resolves #ISSUE-NUMBER1, resolves #ISSUE-NUMBER2, etc.

Description of changes:

Describe s2n’s current behavior and how your code changes that behavior. If there are no issues this PR is resolving, explain why this change is necessary.

Call-outs:

Address any potentially confusing code. Is there code added that needs to be cleaned up later? Is there code that is missing because it’s still in development?

Testing:

How is this change tested (unit tests, fuzz tests, etc.)? Are there any testing steps to be verified by the reviewer?

Is this a refactor change? If so, how have you proved that the intended behavior hasn't changed?

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.