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kasu
kasu

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Go's template engine “templ” is convenient (it also works with TinyGo)

#go #tinygo #templ #cloudflare

Synopsis

I wanted to run an application in Go that returned plain HTML,
I decided to use Cloudflare Workers, which can convert it to Wasm and deploy it.

I recommend syumai/workers's template for deploying Go applications to Cloudflare Workers.

syumai/workers: Go package to run an HTTP server on Cloudflare Workers.

Go + text/template

First, let's build using text/template in a straightforward manner.

❯ ls -lh . /build
   total 15656
   -rwxr-xr-x 1 ergofriend staff 7.6M 8 8 20:12 app.wasm
   -rw-r--r-- 1 ergofriend staff 1.2K 8 8 20:12 shim.mjs
   -rw-r--r-- 1 ergofriend staff 16K 8 8 20:12 wasm_exec.js
   -rw-r--r-- 1 ergofriend staff 160B 8 8 20:12 worker.mjs
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It was almost 8 MB.

https://developers.cloudflare.com/workers/platform/limits/#account-plan-limits

Cloudflare Workers has worker size limits depending on the plan.

The free slot is 1MB, and the paid slot ($5~) is 10MB.

Even with the final limit based on size after compression, it will be tough to fit into the free quota starting at 8MB.

TinyGo + text/template

So I decided to switch to TinyGo, which is supposed to be for WebAssembly (Wasm).

After building, the size is about 0.75 MB, which seems to fit into the free frame.

❯ ls -lh . /build
total 1160
-rwxr-xr-x 1 ergofriend staff 556K 8 8 20:23 app.wasm
-rw-r--r-- 1 ergofriend staff 1.2K 8 8 20:23 shim.mjs
-rw-r--r-- 1 ergofriend staff 15K 8 8 20:23 wasm_exec.js
-rw-r--r-- 1 ergofriend staff 160B 8 8 20:23 worker.mjs
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Oops!

But here is where tragedy strikes.

When I try to access the built application, I get an error.

[wrangler:inf] GET / 200 OK (35ms)
✘ [ERROR] Uncaught (in response) RuntimeError: unreachable

      at main.runtime._panic (wasm://wasm/main-0022bc46:wasm-function[35]:0x2b4a)
      at main.(*text/template.state).evalField
  (wasm://wasm/main-0022bc46:wasm-function[540]:0x6c5f4)
      at main.(*text/template.state).evalFieldChain
  (wasm://wasm/main-0022bc46:wasm-function[531]:0x697fe)
      at main.(*text/template.state).evalFieldNode
  (wasm://wasm/main-0022bc46:wasm-function[530]:0x6959a)
      at main.(*text/template.state).evalPipeline
  (wasm://wasm/main-0022bc46:wasm-function[535]:0x6a1d2)
      at main.(*text/template.state).walk (wasm://wasm/main-0022bc46:wasm-function[569]:0x72cdd)
      at main.(*text/template.state).walk (wasm://wasm/main-0022bc46:wasm-function[569]:0x730b0)
      at main.main$1 (wasm://wasm/main-0022bc46:wasm-function[261]:0x2ac52)
      at main.(net/http.HandlerFunc).ServeHTTP
  (wasm://wasm/main-0022bc46:wasm-function[463]:0x5973a)
      at
  main.interface:{ServeHTTP:func:{named:net/http.ResponseWriter,pointer:named:net/http.Request}{}}.ServeHTTP$invoke
  (wasm://wasm/main-0022bc46:wasm-function[459]:0x56f72)

panic: unimplemented: (reflect.Value).MethodByName()
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The method MethodByName, which is called when a template variable is passed in template.ExecuteTemplate(), is not yet It seems to be unimplemented.

Since TinyGo is a subset of the original, there are many unsupported features,
I found that text/template was calling unsupported methods.

https://github.com/tinygo-org/tinygo/blob/1154212c15e6e97048e122068730dab5a1a9427f/src/reflect/type.go#L1086-L1088

Now, I would like to be cool and say p-r for TinyGo, but this time I'm going to look for a quick alternative.

TEMPL

So I was looking for another template engine to replace text/template and came across templ.

GitHub logo a-h / templ

A language for writing HTML user interfaces in Go.

templ

An HTML templating language for Go that has great developer tooling.

templ

Documentation

See user documentation at https://templ.guide

Go Reference xc compatible Go Coverage Go Report Card

Tasks

build

Build a local version.

go run ./get-version > .version
cd cmd/templ
go build
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nix-update-gomod2nix

gomod2nix
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install-snapshot

Build and install current version.

# Remove templ from the non-standard ~/bin/templ path
# that this command previously used.
rm -f ~/bin/templ
# Clear LSP logs.
rm -f cmd/templ/lspcmd/*.txt
# Update version.
go run ./get-version > .version
# Install to $GOPATH/bin or $HOME/go/bin
cd cmd/templ && go install
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build-snapshot

Use goreleaser to build the command line binary using goreleaser.

goreleaser build --snapshot --clean
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generate

Run templ generate using local version.

go run ./cmd/templ generate -include-version=false
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test

Run Go tests.

go run ./get-version > .version
go run ./cmd/templ generate -include-version=false
go test ./...
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test-short

Run Go tests.

go run ./get-version > .version
go run ./cmd/templ generate -include-version=false
go test ./... -short
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test-cover

Run…


View on GitHub


Features

Here is a summary of TEMPL.

Own DSL

It is not difficult to write a unique program, but it can be written like templ ≈ Go + JSX.

templ hello() {
  <div>Welcome back!
}
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It looks like a very familiar writing style.

templ login(isLoggedIn bool) {
  if isLoggedIn {
    @hello() <! -- @ to use other components -->.
  } else {
    <input name="login" type="button" value="Log in"/>
  }
}
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When you use it, you call Go functions generated from the DSL by templ generate on a component-by-component basis.

func login(isLoggedIn bool) templ.Component {
  return templruntime.GeneratedTemplate(func(templ_7745c5c3_Input templruntime.GeneratedComponentInput) (templ_7745c5
  ...
}
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Handle("/", templ.Handler(login(false))))
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The function of the generated component inherits the argument types defined in the template, so it can be safely called.
Unlike some ExecuteTemplate, this is safe.

VSCode Extensions

https://marketplace.visualstudio.com/items?itemName=a-h.templ

Syntax Highlight and LSP completion will be very useful.

TinyGo + templ

Just to be sure, I checked and found that it only depends on reflect's TypeOf, which is already implemented in TinyGo.

https://github.com/tinygo-org/tinygo/blob/1154212c15e6e97048e122068730dab5a1a9427f/src/reflect/type.go#L494-L500

Now let's try using templ.
The build seemed to have enough room.

❯ ls -lh . /build
total 1008
-rwxr-xr-x 1 ergofriend staff 477K 8 8 20:35 app.wasm
-rw-r--r-- 1 ergofriend staff 1.2K 8 8 20:35 shim.mjs
-rw-r--r-- 1 ergofriend staff 15K 8 8 20:35 wasm_exec.js
-rw-r--r-- 1 ergofriend staff 160B 8 8 20:35 worker.mjs
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Here is the actual application.

goworkers-demo.ergofriend.workers.dev

When accessed, the HTML can be returned without error.

> wrangler deploy
Total Upload: 493.48 KiB / gzip: 187.91 KiB
Total Upload: 493.48 KiB / gzip: 187.91 KiB
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The final deployed size is also 187.91 KiB, so there is plenty of room to expand the application.

This verification is left in this repository.
ergofriend/goworkers-demo

This article is a translation from Japanese.
https://ergofriend.hatenablog.com/entry/2024/08/08/230603

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