132 lines
4.2 KiB
Markdown
132 lines
4.2 KiB
Markdown
This directory houses the [Web Assembly (WASM)](https://en.wikipedia.org/wiki/WebAssembly)
|
|
parts of the sqlite3 build.
|
|
|
|
It requires [emscripten][] and that the build environment be set up for
|
|
emscripten. A mini-HOWTO for setting that up follows...
|
|
|
|
First, install the Emscripten SDK, as documented
|
|
[here](https://emscripten.org/docs/getting_started/downloads.html) and summarized
|
|
below for Linux environments:
|
|
|
|
```
|
|
# Clone the emscripten repository:
|
|
$ sudo apt install git
|
|
$ git clone https://github.com/emscripten-core/emsdk.git
|
|
$ cd emsdk
|
|
|
|
# Download and install the latest SDK tools:
|
|
$ ./emsdk install latest
|
|
|
|
# Make the "latest" SDK "active" for the current user:
|
|
$ ./emsdk activate latest
|
|
```
|
|
|
|
Those parts only need to be run once, but the SDK can be updated using:
|
|
|
|
```
|
|
$ git pull
|
|
$ ./emsdk install latest
|
|
$ ./emsdk activate latest
|
|
```
|
|
|
|
The following needs to be run for each shell instance which needs the
|
|
`emcc` compiler:
|
|
|
|
```
|
|
# Activate PATH and other environment variables in the current terminal:
|
|
$ source ./emsdk_env.sh
|
|
|
|
$ which emcc
|
|
/path/to/emsdk/upstream/emscripten/emcc
|
|
```
|
|
|
|
Optionally, add that to your login shell's resource file (`~/.bashrc`
|
|
or equivalent).
|
|
|
|
That `env` script needs to be sourced for building this application
|
|
from the top of the sqlite3 build tree:
|
|
|
|
```
|
|
$ make fiddle
|
|
```
|
|
|
|
Or:
|
|
|
|
```
|
|
$ cd ext/wasm
|
|
$ make
|
|
```
|
|
|
|
That will generate the fiddle application under
|
|
[ext/fiddle](/dir/ext/wasm/fiddle), as `fiddle.html`. That application
|
|
cannot, due to XMLHttpRequest security limitations, run if the HTML
|
|
file is opened directly in the browser (i.e. if it is opened using a
|
|
`file://` URL), so it needs to be served via an HTTP server. For
|
|
example, using [althttpd][]:
|
|
|
|
```
|
|
$ cd ext/wasm/fiddle
|
|
$ althttpd -page fiddle.html
|
|
```
|
|
|
|
That will open the system's browser and run the fiddle app's page.
|
|
|
|
Note that when serving this app via [althttpd][], it must be a version
|
|
from 2022-05-17 or newer so that it recognizes the `.wasm` file
|
|
extension and responds with the mimetype `application/wasm`, as the
|
|
WASM loader is pedantic about that detail.
|
|
|
|
# Testing on a remote machine that is accessed via SSH
|
|
|
|
*NB: The following are developer notes, last validated on 2022-08-18*
|
|
|
|
* Remote: Install git, emsdk, and althttpd
|
|
* Use a [version of althttpd](https://sqlite.org/althttpd/timeline?r=enable-atomics)
|
|
that adds HTTP reply header lines to enable SharedArrayBuffers. These header
|
|
lines are required:
|
|
```
|
|
Cross-Origin-Opener-Policy: same-origin
|
|
Cross-Origin-Embedder-Policy: require-corp
|
|
```
|
|
* Remote: Install the SQLite source tree. CD to ext/wasm
|
|
* Remote: "`make`" to build WASM
|
|
* Remote: althttpd --port 8080 --popup
|
|
* Local: ssh -L 8180:localhost:8080 remote
|
|
* Local: Point your web-browser at http://localhost:8180/testing1.html
|
|
|
|
In order to enable [SharedArrayBuffers](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer),
|
|
the web-browser requires that the two extra Cross-Origin lines be present
|
|
in HTTP reply headers and that the request must come from "localhost".
|
|
Since the web-server is on a different machine from
|
|
the web-broser, the localhost requirement means that the connection must be tunneled
|
|
using SSH.
|
|
|
|
|
|
|
|
# Known Quirks and Limitations
|
|
|
|
Some "impedence mismatch" between C and WASM/JavaScript is to be
|
|
expected.
|
|
|
|
## No I/O
|
|
|
|
sqlite3 shell commands which require file I/O or pipes are disabled in
|
|
the WASM build.
|
|
|
|
## `exit()` Triggered from C
|
|
|
|
When C code calls `exit()`, as happens (for example) when running an
|
|
"unsafe" command when safe mode is active, WASM's connection to the
|
|
sqlite3 shell environment has no sensible choice but to shut down
|
|
because `exit()` leaves it in a state we can no longer recover
|
|
from. The JavaScript-side application attempts to recognize this and
|
|
warn the user that restarting the application is necessary. Currently
|
|
the only way to restart it is to reload the page. Restructuring the
|
|
shell code such that it could be "rebooted" without restarting the
|
|
JS app would require some invasive changes which are not currently
|
|
on any TODO list but have not been entirely ruled out long-term.
|
|
|
|
|
|
[emscripten]: https://emscripten.org
|
|
[althttpd]: https://sqlite.org/althttpd
|