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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 a number of files required for a handful of
test and demo applications which can be accessed via
`index.html`. WASM content cannot, due to XMLHttpRequest security
limitations, be loaded if the containing 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
$ althttpd --enable-sab --max-age 1 --page index.html
```
That will open the system's browser and run the index page, from which
all of the test and demo applications can be accessed.
Note that when serving this app via [althttpd][], it must be a version
from 2022-09-26 or newer so that it recognizes the `--enable-sab`
flag, which causes althttpd to emit two HTTP response headers which
are required to enable JavaScript's `SharedArrayBuffer` and `Atomics`
APIs. Those APIs are required in order to enable the OPFS-related
features in the apps which use them.
# 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][althttpd] from
September 26, 2022 or newer.
* Remote: Install the SQLite source tree. CD to ext/wasm
* Remote: "`make`" to build WASM
* Remote: `althttpd --enable-sab --port 8080 --popup`
* Local: `ssh -L 8180:localhost:8080 remote`
* Local: Point your web-browser at http://localhost:8180/index.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.
[emscripten]: https://emscripten.org
[althttpd]: https://sqlite.org/althttpd
|
