Proof of concept C host by ohAitch · Pull Request #334 · bytecodealliance/component-docs

ohAitch · 2026-03-05T11:14:37Z

cd component-model/examples/example-c-host
gcc -o host host.c -lwasmtime && ./host 6 7 adder.wasm

Previous discussion in bytecodealliance/wasmtime#6987 (comment)

Documentation in particular needs work.

vados-cosmonic · 2026-03-05T11:57:13Z

I'm not a C expert so it's probably going to take a while (and we probably need a set of different eyes on this) but thanks for this1

vados-cosmonic · 2026-03-25T15:23:52Z

A bit late but looking some more at this, to get this across the line we would need to:

Update the C "run the component from ..." section (here we can likely have a C section and a C++ section)
Replace the TODOs in the PR
Add the C host to CI to catch if it breaks
Fix the wording around embeddings, hosts and WASI runtimes (C/C++ & JS can have embeddings of hosts, and other langauges just run wasmtime from CLI which is NOT an embedding... wasmtime is a host and has a WASI runtime)

We will definitely step in to help finish this up @ohAitch so no need to worry about it -- after chatting it looks like there are a few more changes that need to be made documentation wise to make everything coherent.

kate-goldenring

Thank you for putting this together! I put copilot to work to help make this pretty close to ready, filling in the docs and making the Dockerfile cross arch. I PR'd it into your branch here ohAitch#1 for you to review. Feel free to pull that in instead of directly resolving my suggestions.

kate-goldenring · 2026-04-15T19:32:56Z

@@ -0,0 +1,2 @@
+@_default:


Can you change this to a Makefile since those are used more broadly? Maybe add build and run targets. Or we remove it for now

kate-goldenring · 2026-04-15T19:42:41Z

this file is more than the example host -- it is all in one, building the guest and the host, which i think is great, but a host-only one where you could pass in your adder.wasm may also be useful. I'll PR in a suggestion

Yep with #333 in it should totally just use the checked in one.

ohAitch · 2026-04-15T21:04:29Z

Oh thanks for looking into this, I totally missed the first update comment.

TODO deduplicate with add.wasm see bytecodealliance#333 ```sh cd component-model/examples/example-c-host gcc -o host host.c -lwasmtime && ./host 6 7 adder.wasm ``` Co-authored-by: Shelley <shelley@exe.dev>

I had some difficulty setting up the C toolchains, here's everything pinned down as a sanity check ```sh docker build -t example-c-host . docker run example-c-host ``` Co-authored-by: Shelley <shelley@exe.dev>

Documentation is not my forté but the current "running things from C is impossible due to #issue (closed)" is _definitely_ out of date. Needs revision into a more helpful pointer to the code introduced in this PR, whatever its project name and contents shall end up being. Possibly broken out into a separate .md fragments like the rust one, possibly that was only necessary to share instructions with rust.md and the existence of the c/c++ host can stay local to this file.

- Fills in documentation on how to use the C host - Updates Dockerfile to be cross architecture - Adds a new Dockerfile that is just the host Signed-off-by: Kate Goldenring <kgoldenr@akamai.com>

Signed-off-by: Kate Goldenring <kgoldenr@akamai.com>

…volume mount - Delete Dockerfile.guest_and_host (broken wasi-sdk arch mapping; unnecessary now that upstream add.wasm is available via rebase) - Rename Dockerfile.host → Dockerfile - Fix missing trailing newline - Update c.md: remove guest_and_host references, fix Docker instructions to use volume mount with $(pwd)-relative path Co-authored-by: Shelley <shelley@exe.dev>

Tests both the native build (gcc + wasmtime C API) and the Docker workflow against the checked-in add.wasm. Co-authored-by: Shelley <shelley@exe.dev>

kate-goldenring

@ohAitch thank you for getting these docs updated. This LGTM but I'll wait for your final thumbs up before merging

ohAitch · 2026-04-15T23:14:31Z

Changes incorporated and rebased, no more TODOs in files I've touched, host-only cross-platform dockerfile, tyvm kate. CI green though you may wish to drop one of the two. Seems like a good time to unDraft this.

How are we doing on

wording around embeddings, hosts and WASI runtimes

kate-goldenring · 2026-04-16T17:03:36Z

@ohAitch switching to an "embedding" wording would be a nice add -- we've been misusing the word "host" throughout the docs. See an example in this pr which will likely be closed thanks to this one #337

kate-goldenring

some suggestions of how to avoid "host" wording

kate-goldenring · 2026-04-16T17:07:33Z

+wasmtime --invoke 'add(2,2)' adder.wasm
+```
+
+## 7. Run the component from the example C host


Suggested change

## 7. Run the component from the example C host

## 7. Run the component from C/C++ Applications

kate-goldenring · 2026-04-16T17:08:00Z

+
+You can either use a Dockerfile to execute your add component with the C application or directly run the application.
+
+### Option A: Compile and run the host directly


Suggested change

### Option A: Compile and run the host directly

### Option A: Run the C application directly

kate-goldenring · 2026-04-16T17:08:10Z

+### Option A: Compile and run the host directly
+
+If the Wasmtime C API headers and library are installed on your system,
+you can compile and run the host directly:


Suggested change

you can compile and run the host directly:

you can compile and run the application directly:

kate-goldenring · 2026-04-16T17:09:18Z

can the "host" wording here be renamed "application" both in file naming and in content

kate-goldenring · 2026-04-16T17:10:36Z

@@ -0,0 +1,127 @@
+/**
+ * C host for the adder WebAssembly component.


Suggested change

* C host for the adder WebAssembly component.

* C application that embeds Wasmtime and executes a component that does addition

kate-goldenring · 2026-04-16T17:11:02Z

+## 6. Run the component with `wasmtime --invoke`

-The following section requires you to have [a Rust toolchain][rust] installed.
+If you want to quickly run the `add` export without writing a host application that embeds Wasmtime,


Suggested change

If you want to quickly run the `add` export without writing a host application that embeds Wasmtime,

If you want to quickly run the `add` export without writing an application that embeds Wasmtime,

kate-goldenring · 2026-04-16T17:12:05Z

+## 7. Run the component from the example C host
+
+This repository includes a C application that can execute components that implement the add interface. This application embeds Wasmtime using the Wasmtime C API:
+`component-model/examples/example-c-host/host.c`.


Suggested change

`component-model/examples/example-c-host/host.c`.

`component-model/examples/example-c-application/app.c`.

kate-goldenring · 2026-04-16T17:12:14Z

+The application expects three arguments: the two numbers to add and the Wasm component that executed the addition. For example:
+
+```sh
+./adder-host <x> <y> <path-to-component.wasm>


Suggested change

./adder-host <x> <y> <path-to-component.wasm>

./app <x> <y> <path-to-component.wasm>

kate-goldenring · 2026-04-16T17:12:45Z

+cd component-model/examples/example-c-host
+gcc -o adder-host host.c -lwasmtime
+./adder-host 1 2 /absolute/path/to/adder.wasm


Suggested change

cd component-model/examples/example-c-host

gcc -o adder-host host.c -lwasmtime

./adder-host 1 2 /absolute/path/to/adder.wasm

cd component-model/examples/example-c-application

gcc -o app app.c -lwasmtime

./app 1 2 /absolute/path/to/adder.wasm

ohAitch force-pushed the example-c-host branch from bf6b34c to aa3e99d Compare March 5, 2026 12:07

kate-goldenring mentioned this pull request Apr 15, 2026

fix: mention Wasmtime C API in C tutorial #337

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kate-goldenring reviewed Apr 15, 2026

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ohAitch and others added 5 commits April 15, 2026 23:06

Proof of concept C host

e84d1b4

TODO deduplicate with add.wasm see bytecodealliance#333 ```sh cd component-model/examples/example-c-host gcc -o host host.c -lwasmtime && ./host 6 7 adder.wasm ``` Co-authored-by: Shelley <shelley@exe.dev>

(reproducibility) add Dockerfile

83b78d8

I had some difficulty setting up the C toolchains, here's everything pinned down as a sanity check ```sh docker build -t example-c-host . docker run example-c-host ``` Co-authored-by: Shelley <shelley@exe.dev>

Suggested updates to proof of concept C host documentation

db5a342

- Fills in documentation on how to use the C host - Updates Dockerfile to be cross architecture - Adds a new Dockerfile that is just the host Signed-off-by: Kate Goldenring <kgoldenr@akamai.com>

Add wasmtime invoke to the C docs

b5c1f11

Signed-off-by: Kate Goldenring <kgoldenr@akamai.com>

ohAitch force-pushed the example-c-host branch from 0eb2548 to b5c1f11 Compare April 15, 2026 23:06

kate-goldenring marked this pull request as ready for review April 15, 2026 23:10

kate-goldenring requested a review from vados-cosmonic as a code owner April 15, 2026 23:10

exe.dev user and others added 2 commits April 15, 2026 23:11

Add CI workflow for C host example

9f9b3d8

Tests both the native build (gcc + wasmtime C API) and the Docker workflow against the checked-in add.wasm. Co-authored-by: Shelley <shelley@exe.dev>

kate-goldenring approved these changes Apr 15, 2026

View reviewed changes

kate-goldenring reviewed Apr 16, 2026

View reviewed changes

	## 7. Run the component from the example C host
	## 7. Run the component from C/C++ Applications


		You can either use a Dockerfile to execute your add component with the C application or directly run the application.

		### Option A: Compile and run the host directly

	### Option A: Compile and run the host directly
	### Option A: Run the C application directly

	you can compile and run the host directly:
	you can compile and run the application directly:

		@@ -0,0 +1,127 @@
		/**
		* C host for the adder WebAssembly component.

	* C host for the adder WebAssembly component.
	* C application that embeds Wasmtime and executes a component that does addition

	If you want to quickly run the `add` export without writing a host application that embeds Wasmtime,
	If you want to quickly run the `add` export without writing an application that embeds Wasmtime,

	`component-model/examples/example-c-host/host.c`.
	`component-model/examples/example-c-application/app.c`.

	./adder-host <x> <y> <path-to-component.wasm>
	./app <x> <y> <path-to-component.wasm>

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