Add WASM Support

[theosirian]

Adds WASM support to DIDKit using wasm-pack/wasm-bindgen.

Added a wasm feature on DIDKit to prevent compiling C and Java integration on the wasm-pack build.
Added DIDKitLoader for web targets to facilitate working with the WASM code on browsers.
Added a test for all current methods on DIDKit using DIDKitLoader and the WASM build.

This is a substitute for #15.

[theosirian]

@clehner the build failed because of the issue with how default-features work on workspaces. Do you have any ideas on how to work around it?

[clehner]

Looks good. @theosirian I think this might fix the issue with features: spruceid/ssi#85

Also looks like we must make the didkit crate also not depend on ssi's default-features:

diff --git a/lib/Cargo.toml b/lib/Cargo.toml
index 954ccc6..4b3a3a8 100644
--- a/lib/Cargo.toml
+++ b/lib/Cargo.toml
@@ -9 +9 @@ edition = "2018"
-ssi = { path = "../../ssi" }
+ssi = { path = "../../ssi", default-features = false }

[clehner]

Works for me:

[    ok: should get library version] index.test.js:4:13
[    ok: should generate ed25519 key] index.test.js:4:13
[    ok: should produce did] index.test.js:4:13
[    ok: should produce verificationMethod] index.test.js:4:13
[    ok: should fail if parameters are empty objects] index.test.js:4:13
[    ok: should verify issued credential] index.test.js:4:13
[    ok: should fail if parameters are empty objects] index.test.js:4:13
[    ok: should verify issued presentation]

I had to use wasm-pack build --target web instead of just wasm-pack build. Should that be noted in the readme?

I can build and run it with #55 and the following merged:

diff --git a/lib/Cargo.toml b/lib/Cargo.toml
index 341b4ab..03c543b 100644
--- a/lib/Cargo.toml
+++ b/lib/Cargo.toml
@@ -9,2 +9,3 @@ default = ["ring"]
 ring = ["ssi/ring"]
+wasm = []
 
@@ -24,5 +25 @@ lazy_static = "1.4"
 crate-type = ["lib", "staticlib", "cdylib"]
-
-[features]
-default = []
-wasm = []
diff --git a/wasm/Cargo.toml b/wasm/Cargo.toml
index 18793e3..ac0a460 100644
--- a/wasm/Cargo.toml
+++ b/wasm/Cargo.toml
@@ -18,2 +18,3 @@ chrono = { version = "0.4", features = ["wasmbind"] }
 path = "../lib"
+default-features = false
 features = ["wasm"]

I see more of what you mean about the behavior of workspace features. i.e. "Features in a workspace are unified across all roots selected on the command-line." rust-lang/cargo#8366 (comment)
It seems to mean we can't build didkit-wasm in the same CLI invocation as other crates depending on non-WASM implementations of the crypto. But by using --exclude, we can split the invocations into multiple invocations with different feature selections, like this:

diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index ed1b1a3..3cbb0ae 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -53,6 +53,9 @@ jobs:
     - name: Build
-      run: cargo build --verbose --workspace
+      run: cargo build --verbose --workspace --exclude didkit-wasm
 
-    - name: Test
-      run: cargo test --verbose --workspace
+    - name: Test (non-WASM)
+      run: cargo test --verbose --workspace --exclude didkit-wasm
+
+    - name: Test (WASM)
+      run: cargo test --verbose -p didkit-wasm

Also, what about testing didkit-wasm in CI? There is a wasm-pack test command which runs tests in Node or in a browser. Some other projects are doing this:
https://github.com/search?q=wasm-pack+path%3A%2F.github%2Fworkflows&type=Code&ref=advsearch
https://rustwasm.github.io/wasm-pack/book/tutorials/npm-browser-packages/testing-your-project.html
But it looks like that is for running Rust tests in the WASM environment, not JS tests using the built WASM module. I don't see any typical way of testing JS tests from wasm-pack output... https://stackoverflow.com/questions/65710914/is-it-possible-to-test-wasm-pack-generated-webassembly-from-a-javascript-context

[theosirian]

Building correctly for me as well.

I also didn't find anything on testing from the JS side. We could try manually running wasm/loader/test/index.test.js on a headless browser, but I'm not sure how much work that would involve.

[clehner]

Reopened because accidentally auto-closed by spruceid/ssi#85 (comment).

[clehner]

Maybe it would be possible to have tests run by wasm-pack test load and run the JS tests from Rust code.

Or we could just do the build only, and manually test it in the browser when preparing releases.

[theosirian]

Something like selenium-rs to load the webpage with the test?
Or more like instantiating a JS engine like V8 to run the code?

For now, maybe manually testing is okay.

[theosirian]

Rebased onto current main, moved the WASM package into lib/ and added targets on Makefile and Github Actions.

[clehner]

Thanks @theosirian. Looks good; waiting for CI now.