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gh-136251: Improvements to WASM demo REPL (GH-136252)

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Co-authored-by: Hood Chatham <roberthoodchatham@gmail.com>
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adam j hartz 2025-07-21 05:56:45 -04:00 • committed by GitHub
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7 changed files with 327 additions and 56 deletions
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4
Makefile.pre.in
View file

@ -1096,7 +1096,7 @@ $(DLLLIBRARY) libpython$(LDVERSION).dll.a: $(LIBRARY_OBJS)
# wasm32-emscripten browser web example
WEBEX_DIR=$(srcdir)/Tools/wasm/emscripten/web_example/
web_example/python.html: $(WEBEX_DIR)/python.html
web_example/index.html: $(WEBEX_DIR)/index.html
@mkdir -p web_example
@cp $< $@
@ -1124,7 +1124,7 @@ web_example/python.mjs web_example/python.wasm: $(BUILDPYTHON)
cp python.wasm web_example/python.wasm
.PHONY: web_example
web_example: web_example/python.mjs web_example/python.worker.mjs web_example/python.html web_example/server.py $(WEB_STDLIB)
web_example: web_example/python.mjs web_example/python.worker.mjs web_example/index.html web_example/server.py $(WEB_STDLIB)
############################################################################
# Header files

1
Misc/NEWS.d/next/Tools-Demos/2025-07-05-15-10-42.gh-issue-136251.GRM6o8.rst Normal file
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@ -0,0 +1 @@
Fixes and usability improvements for ``Tools/wasm/emscripten/web_example``

2
Python/emscripten_syscalls.c
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@ -100,7 +100,7 @@ EM_JS_MACROS(void, _emscripten_promising_main_js, (void), {
return;
}
const origResolveGlobalSymbol = resolveGlobalSymbol;
if (!Module.onExit && process?.exit) {
if (!Module.onExit && globalThis?.process?.exit) {
Module.onExit = (code) => process.exit(code);
}
// * wrap the main symbol with WebAssembly.promising,

8
Tools/wasm/README.md
View file

@ -86,11 +86,11 @@ CLI you will need to write your own alternative to `node_entry.mjs`.
### The Web Example
When building for Emscripten, the web example will be built automatically. It is
in the ``web_example`` directory. To run the web example, ``cd`` into the
When building for Emscripten, the web example will be built automatically. It
is in the ``web_example`` directory. To run the web example, ``cd`` into the
``web_example`` directory, then run ``python server.py``. This will start a web
server; you can then visit ``http://localhost:8000/python.html`` in a browser to
see a simple REPL example.
server; you can then visit ``http://localhost:8000/`` in a browser to see a
simple REPL example.
The web example relies on a bug fix in Emscripten version 3.1.73 so if you build
with earlier versions of Emscripten it may not work. The web example uses

334
Tools/wasm/emscripten/web_example/python.html → Tools/wasm/emscripten/web_example/index.html
View file

@ -1,31 +1,39 @@
<!doctype html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta http-equiv="X-UA-Compatible" content="IE=edge" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<meta name="author" content="Katie Bell" />
<meta name="description" content="Simple REPL for Python WASM" />
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta name="author" content="Katie Bell, Adam Hartz">
<meta name="description" content="Simple REPL for Python WASM">
<title>wasm-python terminal</title>
<link
rel="stylesheet"
href="https://unpkg.com/xterm@4.18.0/css/xterm.css"
crossorigin
integrity="sha384-4eEEn/eZgVHkElpKAzzPx/Kow/dTSgFk1BNe+uHdjHa+NkZJDh5Vqkq31+y7Eycd"
/>
>
<style>
body {
font-family: arial;
max-width: 800px;
margin: 0 auto;
}
#code {
#editor {
padding: 5px;
border: 1px solid black;
width: 100%;
height: 180px;
height: 300px;
}
#info {
padding-top: 20px;
}
.error {
border: 1px solid red;
background-color: #ffd9d9;
padding: 5px;
margin-top: 20px;
}
.button-container {
display: flex;
justify-content: end;
@ -41,8 +49,14 @@
src="https://unpkg.com/xterm@4.18.0/lib/xterm.js"
crossorigin
integrity="sha384-yYdNmem1ioP5Onm7RpXutin5A8TimLheLNQ6tnMi01/ZpxXdAwIm2t4fJMx1Djs+"
/>
></script>
<script
src="https://cdnjs.cloudflare.com/ajax/libs/ace/1.43.1/ace.js"
crossorigin
integrity="sha512-kmA5vhcxOkZI0ReiKJMGNb8/KKbgbExIlnt6aXuPtl86AgHBEi6OHHOz2wsTazBDGZKxe7fmiE+pIuZJQks4+A=="
></script>
<script type="module">
const _magic_ctrlc_string = "__WASM_REPL_CTRLC_" + (Date.now()) + "__";
class WorkerManager {
constructor(
workerURL,
@ -132,11 +146,14 @@
class WasmTerminal {
constructor() {
this.inputBuffer = new BufferQueue();
this.input = "";
this.resolveInput = null;
this.activeInput = false;
this.inputStartCursor = null;
try {
this.history = JSON.parse(sessionStorage.getItem('__python_wasm_repl.history'));
this.historyBuffer = this.history.slice();
} catch(e) {
this.history = [];
this.historyBuffer = [];
}
this.reset();
this.xterm = new Terminal({
scrollback: 10000,
@ -155,6 +172,18 @@
this.xterm.onData(this.handleTermData);
}
reset() {
this.inputBuffer = new BufferQueue();
this.input = "";
this.resolveInput = null;
this.activeInput = false;
this.inputStartCursor = null;
this.cursorPosition = 0;
this.historyIndex = -1;
this.beforeHistoryNav = "";
}
open(container) {
this.xterm.open(container);
}
@ -186,9 +215,34 @@
if (!(ord === 0x1b || ord == 0x7f || ord < 32)) {
this.inputBuffer.addData(data);
}
// TODO: Handle ANSI escape sequences
// TODO: Handle more escape sequences?
} else if (ord === 0x1b) {
// Handle special characters
switch (data.slice(1)) {
case "[A": // up
this.historyBack();
break;
case "[B": // down
this.historyForward();
break;
case "[C": // right
this.cursorRight();
break;
case "[D": // left
this.cursorLeft();
break;
case "[H": // home key
this.cursorHome(true);
break;
case "[F": // end key
this.cursorEnd(true);
break;
case "[3~": // delete key
this.deleteAtCursor();
break;
default:
break;
}
} else if (ord < 32 || ord === 0x7f) {
switch (data) {
case "\x0c": // CTRL+L
@ -201,8 +255,18 @@
this.input + this.writeLine("\n"),
);
this.input = "";
this.cursorPosition = 0;
this.activeInput = false;
break;
case "\x03": // CTRL+C
this.input = "";
this.cursorPosition = 0;
this.historyIndex = -1;
this.resolveInput(_magic_ctrlc_string + "\n");
break;
case "\x09": // TAB
this.handleTab();
break;
case "\x7F": // BACKSPACE
case "\x08": // CTRL+H
this.handleCursorErase(true);
@ -211,14 +275,20 @@
// Send empty input
if (this.input === "") {
this.resolveInput("");
this.cursorPosition = 0;
this.activeInput = false;
}
}
} else {
this.handleCursorInsert(data);
this.updateHistory();
}
};
clearLine() {
this.xterm.write("\x1b[K");
}
writeLine(line) {
this.xterm.write(line.slice(0, -1));
this.xterm.write("\r\n");
@ -226,8 +296,36 @@
}
handleCursorInsert(data) {
this.input += data;
const trailing = this.input.slice(this.cursorPosition);
this.input =
this.input.slice(0, this.cursorPosition) +
data +
trailing;
this.cursorPosition += data.length;
this.xterm.write(data);
if (trailing.length !== 0) {
this.xterm.write(trailing);
this.xterm.write("\x1b[" + trailing.length + "D");
}
this.updateHistory();
}
handleTab() {
// handle tabs: from the current position, add spaces until
// this.cursorPosition is a multiple of 4.
const prefix = this.input.slice(0, this.cursorPosition);
const suffix = this.input.slice(this.cursorPosition);
const count = 4 - (this.cursorPosition % 4);
const toAdd = " ".repeat(count);
this.input = prefix + toAdd + suffix;
this.cursorHome(false);
this.clearLine();
this.xterm.write(this.input);
if (suffix) {
this.xterm.write("\x1b[" + suffix.length + "D");
}
this.cursorPosition += count;
this.updateHistory();
}
handleCursorErase() {
@ -238,9 +336,113 @@
) {
return;
}
this.input = this.input.slice(0, -1);
this.xterm.write("\x1B[D");
this.xterm.write("\x1B[P");
const trailing = this.input.slice(this.cursorPosition);
this.input =
this.input.slice(0, this.cursorPosition - 1) + trailing;
this.cursorLeft();
this.clearLine();
if (trailing.length !== 0) {
this.xterm.write(trailing);
this.xterm.write("\x1b[" + trailing.length + "D");
}
this.updateHistory();
}
deleteAtCursor() {
if (this.cursorPosition < this.input.length) {
const trailing = this.input.slice(
this.cursorPosition + 1,
);
this.input =
this.input.slice(0, this.cursorPosition) + trailing;
this.clearLine();
if (trailing.length !== 0) {
this.xterm.write(trailing);
this.xterm.write("\x1b[" + trailing.length + "D");
}
this.updateHistory();
}
}
cursorRight() {
if (this.cursorPosition < this.input.length) {
this.cursorPosition += 1;
this.xterm.write("\x1b[C");
}
}
cursorLeft() {
if (this.cursorPosition > 0) {
this.cursorPosition -= 1;
this.xterm.write("\x1b[D");
}
}
cursorHome(updatePosition) {
if (this.cursorPosition > 0) {
this.xterm.write("\x1b[" + this.cursorPosition + "D");
if (updatePosition) {
this.cursorPosition = 0;
}
}
}
cursorEnd() {
if (this.cursorPosition < this.input.length) {
this.xterm.write(
"\x1b[" +
(this.input.length - this.cursorPosition) +
"C",
);
this.cursorPosition = this.input.length;
}
}
updateHistory() {
if (this.historyIndex !== -1) {
this.historyBuffer[this.historyIndex] = this.input;
} else {
this.beforeHistoryNav = this.input;
}
}
historyBack() {
if (this.history.length === 0) {
return;
} else if (this.historyIndex === -1) {
// we're not currently navigating the history; store
// the current command and then look at the end of our
// history buffer
this.beforeHistoryNav = this.input;
this.historyIndex = this.history.length - 1;
} else if (this.historyIndex > 0) {
this.historyIndex -= 1;
}
this.input = this.historyBuffer[this.historyIndex];
this.cursorHome(false);
this.clearLine();
this.xterm.write(this.input);
this.cursorPosition = this.input.length;
}
historyForward() {
if (this.history.length === 0 || this.historyIndex === -1) {
// we're not currently navigating the history; NOP.
return;
} else if (this.historyIndex < this.history.length - 1) {
this.historyIndex += 1;
this.input = this.historyBuffer[this.historyIndex];
} else if (this.historyIndex == this.history.length - 1) {
// we're coming back from the last history value; reset
// the input to whatever it was when we started going
// through the history
this.input = this.beforeHistoryNav;
this.historyIndex = -1;
}
this.cursorHome(false);
this.clearLine();
this.xterm.write(this.input);
this.cursorPosition = this.input.length;
}
prompt = async () => {
@ -263,12 +465,29 @@
// Hack to ensure cursor input start doesn't end up after user input
setTimeout(() => {
this.handleCursorInsert(
this.inputBuffer.nextLine(),
this.inputBuffer.nextLine()
);
}, 1);
}
return new Promise((resolve, reject) => {
this.resolveInput = (value) => {
if (
value.replace(/\s/g, "").length != 0 &&
value != _magic_ctrlc_string + "\n"
) {
if (this.historyIndex !== -1) {
this.historyBuffer[this.historyIndex] =
this.history[this.historyIndex];
}
this.history.push(value.slice(0, -1));
this.historyBuffer.push(value.slice(0, -1));
this.historyIndex = -1;
this.cursorPosition = 0;
try {
sessionStorage.setItem('__python_wasm_repl.history', JSON.stringify(this.history));
} catch(e) {
}
}
resolve(value);
};
});
@ -327,8 +546,6 @@
const stopButton = document.getElementById("stop");
const clearButton = document.getElementById("clear");
const codeBox = document.getElementById("codebox");
window.onload = () => {
const terminal = new WasmTerminal();
terminal.open(document.getElementById("terminal"));
@ -362,8 +579,9 @@
runButton.addEventListener("click", (e) => {
terminal.clear();
terminal.reset(); // reset the history
programRunning(true);
const code = codeBox.value;
const code = editor.getValue();
pythonWorkerManager.run({
args: ["main.py"],
files: { "main.py": code },
@ -372,10 +590,28 @@
replButton.addEventListener("click", (e) => {
terminal.clear();
terminal.reset(); // reset the history
const REPL = `
class WASMREPLKeyboardInterrupt(KeyboardInterrupt):
pass
import sys
import code
import builtins
def _interrupt_aware_input(prompt=''):
line = builtins.input(prompt)
if line.strip() == "${_magic_ctrlc_string}":
raise KeyboardInterrupt()
return line
cprt = 'Type "help", "copyright", "credits" or "license" for more information.'
banner = f'Python {sys.version} on {sys.platform}\\n{cprt}'
code.interact(banner=banner, readfunc=_interrupt_aware_input, exitmsg='')
`;
programRunning(true);
// Need to use "-i -" to force interactive mode.
// Looks like isatty always returns false in emscripten
pythonWorkerManager.run({ args: ["-i", "-"], files: {} });
pythonWorkerManager.run({ args: ["-c", REPL], files: {} });
});
stopButton.addEventListener("click", (e) => {
@ -395,6 +631,7 @@
const finishedCallback = () => {
programRunning(false);
pythonWorkerManager.reset();
};
const pythonWorkerManager = new WorkerManager(
@ -404,23 +641,27 @@
finishedCallback,
);
};
var editor;
document.addEventListener("DOMContentLoaded", () => {
editor = ace.edit("editor");
editor.session.setMode("ace/mode/python");
});
</script>
</head>
<body>
<div id="repldemo">
<h1>Simple REPL for Python WASM</h1>
<textarea id="codebox" cols="108" rows="16">
print('Welcome to WASM!')
</textarea
>
<div id="editor">print('Welcome to WASM!')</div>
<div class="button-container">
<button id="run" disabled>Run</button>
<button id="run" disabled>Run code</button>
<button id="repl" disabled>Start REPL</button>
<button id="stop" disabled>Stop</button>
<button id="clear" disabled>Clear</button>
</div>
<div id="terminal"></div>
<div id="info">
The simple REPL provides a limited Python experience in the browser.
The simple REPL provides a limited Python experience in the
browser.
<a
href="https://github.com/python/cpython/blob/main/Tools/wasm/README.md"
>
@ -429,5 +670,34 @@ print('Welcome to WASM!')
contains a list of known limitations and issues. Networking,
subprocesses, and threading are not available.
</div>
</div>
<div id="buffererror" class="error" style="display: none">
<p>
<code>SharedArrayBuffer</code>, which is required for this demo,
is not available in your browser environment. One common cause
of this failure is loading <code>index.html</code> directly in
your browser instead of using <code>server.py</code> as
described in
<a
href="https://github.com/python/cpython/blob/main/Tools/wasm/README.md#the-web-example"
>
Tools/wasm/README.md
</a>.
</p>
<p>
For more details about security requirements for
<code>SharedArrayBuffer</code>, see
<a
href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer#security_requirements"
>this MDN page</a
>.
</p>
<script>
if (typeof SharedArrayBuffer === 'undefined') {
document.getElementById('repldemo').style.display = 'none';
document.getElementById('buffererror').style.display = 'block';
}
</script>
</div>
</body>
</html>

2
configure generated vendored
View file

@ -9603,7 +9603,7 @@ fi
as_fn_append LDFLAGS_NODIST " -sWASM_BIGINT"
as_fn_append LINKFORSHARED " -sFORCE_FILESYSTEM -lidbfs.js -lnodefs.js -lproxyfs.js -lworkerfs.js"
as_fn_append LINKFORSHARED " -sEXPORTED_RUNTIME_METHODS=FS,callMain,ENV"
as_fn_append LINKFORSHARED " -sEXPORTED_RUNTIME_METHODS=FS,callMain,ENV,HEAPU32"
as_fn_append LINKFORSHARED " -sEXPORTED_FUNCTIONS=_main,_Py_Version,__PyRuntime,__PyEM_EMSCRIPTEN_COUNT_ARGS_OFFSET,_PyGILState_GetThisThreadState,__Py_DumpTraceback"
as_fn_append LINKFORSHARED " -sSTACK_SIZE=5MB"
as_fn_append LINKFORSHARED " -sTEXTDECODER=2"

2
configure.ac
View file

@ -2335,7 +2335,7 @@ AS_CASE([$ac_sys_system],
dnl Include file system support
AS_VAR_APPEND([LINKFORSHARED], [" -sFORCE_FILESYSTEM -lidbfs.js -lnodefs.js -lproxyfs.js -lworkerfs.js"])
AS_VAR_APPEND([LINKFORSHARED], [" -sEXPORTED_RUNTIME_METHODS=FS,callMain,ENV"])
AS_VAR_APPEND([LINKFORSHARED], [" -sEXPORTED_RUNTIME_METHODS=FS,callMain,ENV,HEAPU32"])
AS_VAR_APPEND([LINKFORSHARED], [" -sEXPORTED_FUNCTIONS=_main,_Py_Version,__PyRuntime,__PyEM_EMSCRIPTEN_COUNT_ARGS_OFFSET,_PyGILState_GetThisThreadState,__Py_DumpTraceback"])
AS_VAR_APPEND([LINKFORSHARED], [" -sSTACK_SIZE=5MB"])
dnl Avoid bugs in JS fallback string decoding path