feat: convert fs to use core

Convert the fs module and its example(s) to use the recently-introduced core
module.

pkg/fs/package.json

@@ -4,7 +4,8 @@
 	"dependencies": {
 		"@slangroom/deps": "workspace:*",
 		"@slangroom/shared": "workspace:*",
-		"@slangroom/ignored": "workspace:*"
+		"@slangroom/ignored": "workspace:*",
+		"@slangroom/core": "workspace:*"
 	},
 	"repository": "https://github.com/dyne/slangroom",
 	"license": "AGPL-3.0-only",

pkg/fs/src/plugins.ts

@@ -0,0 +1,39 @@
+import { visit } from '@slangroom/fs/visitor';
+import { AfterPlugin } from '@slangroom/core/plugin';
+import * as path from 'node:path';
+import * as fs from 'node:fs/promises';
+
+/**
+ * A directory that is safe to write to and read from.
+ *
+ * Care must be taken to not allow writes and reads outside of this directory.
+ */
+export const SandboxDir = '/tmp/slangroom';
+
+export const ThenISaveStringIntoTheFile = new AfterPlugin(async ({ statement, result }) => {
+	const ast = visit(statement);
+	// TODO: if `visit()` fails, exit (return)
+
+	const filename = result[ast.filename] as string;
+	const content = result[ast.content] as string;
+	const normalized = path.normalize(filename);
+	// "/" and ".." prevents directory traversal
+	const does_directory_traversal = normalized.startsWith('/') || normalized.startsWith('..');
+	// "." ensures that "foo/bar" or "./foo" is valid, while "." isn't
+	// (that is, no "real" filepath is provided)
+	const doesnt_provide_file = normalized.startsWith('.');
+	if (does_directory_traversal || doesnt_provide_file) return; // TODO: instead of ignoring, do we wanna error out?
+	// here onward, we're sure `filepath` is under `SandboxDir`
+	const filepath = path.join(SandboxDir, normalized);
+
+	// these following two lines allow subdirs to be created if
+	// `normalized` contains any (or `SandboxDir` to be created if it
+	// doesn't exist already)
+	const dirname = path.dirname(filepath);
+	await fs.mkdir(dirname, { recursive: true });
+
+	const fhandle = await fs.open(filepath, 'wx');
+	await fhandle.write(content);
+});
+
+export const allPlugins = new Set([ThenISaveStringIntoTheFile]);

pkg/fs/test/plugins.ts

@@ -0,0 +1,53 @@
+import test from 'ava';
+import { allPlugins, SandboxDir } from '@slangroom/fs/plugins';
+import { Slangroom } from '@slangroom/core';
+import * as fs from 'node:fs/promises';
+import * as path from 'node:path';
+
+test('requires a real path', async (t) => {
+	const slang = new Slangroom(allPlugins);
+	const contract = `Rule unknown ignore
+Given I have a 'string' named 'nameOfTheFile'
+
+When I create the random object of '64' bits
+When I rename the 'random_object' to 'stringToWrite'
+
+Then I save the 'stringToWrite' into the file 'nameOfTheFile'
+Then I print the 'stringToWrite'
+Then I print the 'nameOfTheFile'
+`;
+	{
+		const params = { data: { nameOfTheFile: '../trying/to/h4ck' } };
+		const zout = await slang.execute(contract, params);
+		const nameOfTheFile = zout.result['nameOfTheFile'] as string;
+		await t.throwsAsync(fs.readFile(path.resolve(SandboxDir, nameOfTheFile)));
+	}
+
+	{
+		const params = { data: { nameOfTheFile: '/trying/to/h4ck' } };
+		const zout = await slang.execute(contract, params);
+		const nameOfTheFile = zout.result['nameOfTheFile'] as string;
+		await t.throwsAsync(fs.readFile(path.resolve(SandboxDir, nameOfTheFile)));
+	}
+});
+
+test('keyholder works', async (t) => {
+	const slang = new Slangroom(allPlugins);
+	const contract = `Rule unknown ignore
+Given I have a 'string' named 'nameOfTheFile'
+
+When I create the random object of '64' bits
+When I rename the 'random_object' to 'stringToWrite'
+
+Then I save the 'stringToWrite' into the file 'nameOfTheFile'
+Then I print the 'stringToWrite'
+Then I print the 'nameOfTheFile'
+`;
+	const randomStr = (Math.random() + 1).toString(36).substring(7);
+	const params = { data: { nameOfTheFile: randomStr } };
+	const zout = await slang.execute(contract, params);
+	const nameOfTheFile = zout.result['nameOfTheFile'] as string;
+	const stringToWrite = zout.result['stringToWrite'] as string;
+	const buf = await fs.readFile(path.resolve(SandboxDir, nameOfTheFile));
+	t.is(buf.toString(), stringToWrite);
+});

pkg/fs/test/visitor.ts

@@ -1,9 +1,6 @@
 import test from 'ava';
 import { visit } from '@slangroom/fs/visitor';
 import { getIgnoredStatements } from '@slangroom/ignored';
-import { zencodeExec } from '@slangroom/shared';
-import * as fs from 'node:fs/promises';
-import * as path from 'node:path';
 
 test('ast is correct with one statement', async (t) => {
 	// Given I have a contract with one filesystems statement in it
@@ -99,38 +96,3 @@ Then I save the 'stringToWrite2' into the file 'nameOfTheFile2'
 	// And the value indexed by its filename in data must be data's nameOfTheFile2
 	t.is(data[third?.filename as 'nameOfTheFile2'], data.nameOfTheFile2);
 });
-
-test('keyholder works', async (t) => {
-	// Given I have a contract with one filesystems statement in it
-	const contract = `Rule unknown ignore
-Given I have a 'string' named 'nameOfTheFile'
-
-When I create the random object of '64' bits
-When I rename the 'random_object' to 'stringToWrite'
-
-Then I save the 'stringToWrite' into the file 'nameOfTheFile'
-Then I print the 'stringToWrite'
-Then I print the 'nameOfTheFile'
-`;
-	// And the params used in the contract
-	const params = { data: { nameOfTheFile: 'hello-world.txt' } };
-	// When I get the ignored statement of it
-	const ignoreds = await getIgnoredStatements(contract, params);
-	// eslint-disable-next-line @typescript-eslint/no-non-null-assertion
-	const ast = visit(ignoreds[0]!);
-	// And execute the contract
-	const zout = await zencodeExec(contract, params);
-	// And get the values of the identifiers pointed by filename and content of
-	// the ignored statement
-	const nameOfTheFile = zout.result[ast.filename] as string;
-	const stringToWrite = zout.result[ast.content] as string;
-	// And create /tmp/slangroom
-	await fs.mkdir('/tmp/slangroom/', { recursive: true });
-	// And open file named after nameOfTheFile for writing (and create if it
-	// doesn't already exists
-	const fh = await fs.open(path.resolve('/tmp/slangroom/', nameOfTheFile), 'w');
-	// And write the value of stringToWrite to the file
-	const { buffer } = await fh.write(stringToWrite);
-	// Then the content of the file must be stringToWrite
-	t.is(buffer, stringToWrite);
-});