aws-sdk-for-zig/README.md

# AWS SDK for Zig

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This SDK currently supports all AWS services except EC2 and S3. These two
services only support XML, and zig 0.8.0 and master both trigger compile
errors while incorporating the XML parser. S3 also requires some plumbing
tweaks in the signature calculation, which is planned for a zig version
(probably self-hosted 0.9.0) that no longer has an error triggered. Examples
of usage are in src/main.zig.

This is designed to be built statically using the `aws_c_*` libraries, so
we inherit a lot of the goodness of the work going on there. Current
executable size is 9.7M, about half of which is due to the SSL library.
Running strip on the executable after compilation (it seems zig strip
only goes so far), reduces this to 4.3M. This is for x86_linux,
(which is all that's tested at the moment).

# 2022-01-10 SDK Update

To get smaller executable size and better portability with faster compilation,
my intent is to rework the http communications using
[requestz](https://github.com/ducdetronquito/requestz).  This relies on a
couple other projects, and will require the creation of a zig implementation
for [Signature Version 4](https://docs.aws.amazon.com/general/latest/gr/signature-version-4.html),
along with support for some S3 quirks, etc. It will also reduce compatibility
with some edge cases. Long term I think this is a better approach, however and
will remove (or replace) a ton of the C dependencies as well as avoid a bunch
of complexity such as the event loop C implementation found in the AWS
libraries, which eventually could be replaced by zig async. I have created a
[new branch](https://github.com/elerch/aws-sdk-for-zig/tree/zig-native)
for this work as master is currently working fairly well. I'd also love to have
an official package manager in zig, but I know this is high on the priority
list for the foundation. In the meantime I will depend on git commands executed
by build.zig to handle packages.

## Building

I am assuming here that if you're playing with zig, you pretty much know
what you're doing, so I will stay brief.

First, the dependencies are required. Use the Dockerfile to build these.
a `docker build` will do, but be prepared for it to run a while. The
Dockerfile has been tested on x86_64 linux, but I do hope to get arm64
supported as well.

Once that's done, you'll have an alpine image with all dependencies ready
to go and zig master installed. There are some build-related things still
broken in 0.8.0 and hopefully 0.8.1 will address those and we can be on
a standard release.

* `zig build` should work. It will build the code generation project, run
  the code generation, then build the main project with the generated code.
  There is also a Makefile included, but this hasn't been used in a while
  and I'm not sure that works at the moment.

## Running

This library uses the aws c libraries for it's work, so it operates like most
other 'AWS things'. Note that I tested by setting the appropriate environment
variables, so config files haven't gotten a run through.
main.zig gives you a handful of examples for working with services.
For local testing or alternative endpoints, there's no real standard, so
there is code to look for `AWS_ENDPOINT_URL` environment variable that will
supercede all other configuration.

## Dependencies


Full dependency tree:
aws-c-auth
   * s2n
      * aws-lc
   * aws-c-common
   * aws-c-compression
     * aws-c-common
   * aws-c-http
     * s2n
     * aws-c-common
     * aws-c-io
       * aws-c-common
       * s2n
         * aws-lc
       * aws-c-cal
         * aws-c-common
         * aws-lc
     * aws-c-compression
       * aws-c-common
   * aws-c-cal
     * aws-c-common
     * aws-lc

Build order based on above:

1. aws-c-common
1. aws-lc
2. s2n
2. aws-c-cal
2. aws-c-compression
3. aws-c-io
4. aws-c-http
5. aws-c-auth

Dockerfile in this repo will manage this

TODO List:

* Implement jitter/exponential backoff. This appears to be configuration of
  `aws_c_io` and should therefore be trivial
* Implement timeouts and other TODO's in the code
* Switch to aws-c-cal upstream once [PR for full static musl build support is merged](https://github.com/awslabs/aws-c-cal/pull/89)
  (see Dockerfile)
* Implement [AWS restXml protocol](https://awslabs.github.io/smithy/1.0/spec/aws/aws-restxml-protocol.html).
  Includes S3. Total service count 4. This may be blocked due to the same issue as EC2.
* Implement [AWS EC2 query protocol](https://awslabs.github.io/smithy/1.0/spec/aws/aws-ec2-query-protocol.html).
  Includes EC2. Total service count 1. This is currently blocked, probably on
  self-hosted compiler coming in zig 0.9.0 (January 2022) due to compiler bug
  discovered. More details and llvm ir log can be found in the
  [XML branch](https://git.lerch.org/lobo/aws-sdk-for-zig/src/branch/xml).

Compiler wishlist/watchlist:

* [Merge PR to allow stripping -static](https://github.com/ziglang/zig/pull/8248)
* [comptime allocations](https://github.com/ziglang/zig/issues/1291) so we can read files, etc (or is there another way)