feat: migrate SlowBuffer to Buffer.allocUnsafeSlow() #193

lluisemper · 2025-08-28T20:37:37Z

Add codemod to handle deprecated SlowBuffer API migration covering CommonJS, ES6 imports, and usage patterns

AugustinMauroy

WOW, thank you and congratulations on your first contribution.
Here is the first wave of reviews. Overall, it's good. You've covered a lot of cases except for dynamic imports. For that, you have the getNodeImportCalls function, which allows you to query all nodes that are dynamic imports.
As mentioned in one of the comments, you're using a lot of regex. It's better to base it on the AST for greater stability. Also, as mentioned in a message, you have tools to visualise things, and for query examples, you have utility functions that are quite complex.

AugustinMauroy · 2025-08-29T10:05:50Z

recipes/slow-buffer-to-buffer-alloc-unsafe-slow/README.md

+2. Direct `SlowBuffer` calls to `Buffer.allocUnsafeSlow()`
+3. Import/require statements to use `Buffer` instead of `SlowBuffer`
+
+## Examples


example on rest of codemods use this structure :

## Examples **Before:**  **After:** 

I think your aproach is better in terms of semantics.

@nodejs/userland-migrations what should we do modify this pr or update other codemod ?

I think it’s fine to just update this PR for now. In the future, it might be a good idea to add a script or system at the project root that, when run with
npm run new:codemon --name='slow-buffer-to-buffer-alloc-unsafe-slow',
generates a template project for implementing a new codemon. New contributors and existing ones would benefit from it to have all the basic down.

If this template project would have a different structure, it would be then a good opportunity to correct existing codemons.

Let me know if you find this idea interesting and I can expand on it, or we can discuss how it could be implemented.

oh interesting point.

Codemod CLI ofter a codemod init but it's don't really cover our code style/architecture.

We can have a script that generate the basic of a codemod.

Simple way copy paste a codemod (what I do now)

recipes/slow-buffer-to-buffer-alloc-unsafe-slow/README.md

recipes/slow-buffer-to-buffer-alloc-unsafe-slow/src/workflow.ts

AugustinMauroy · 2025-08-29T10:17:50Z

recipes/slow-buffer-to-buffer-alloc-unsafe-slow/src/workflow.ts

+ * For ESM imports: { SlowBuffer as SB } -> { Buffer as SB }
+ * Preserves original formatting as much as possible
+ */
+function transformDestructuringPattern(originalText: string): string {


Here it's use too much regex, we need to relie on AST for reliability. If you have difficult to visualize the ast you can use Codemod Studio, ast-grep playground or any Tree-sitter sitter visualization tools.

AugustinMauroy · 2025-08-29T10:19:34Z

recipes/slow-buffer-to-buffer-alloc-unsafe-slow/src/workflow.ts

+/**
+ * Process comments mentioning SlowBuffer and update them
+ */
+function processSlowBufferComments(rootNode: SgNode, edits: Edit[]): boolean {


Good idea but in practice we doesn't want to update the user comment. But you can console.warn + file://<path>:<line> where a comment mention this api.

recipes/slow-buffer-to-buffer-alloc-unsafe-slow/workflow.yaml

AugustinMauroy · 2025-08-29T10:27:19Z

for the red ci just run npm I to add your new recipes to the package-lock.json

lluisemper · 2025-08-29T13:53:34Z

@AugustinMauroy thank you very much for the review 💪. I have commited the suggestions and marked the addressed comments with a thums up emoji.

The comments that have a requested change, do not have any emoji. I will aim to commit this over the weekend.

AugustinMauroy · 2025-08-29T14:00:19Z

@AugustinMauroy thank you very much for the review 💪. I have commited the suggestions and marked the addressed comments with a thums up emoji.

The comments that have a requested change, do not have any emoji. I will aim to commit this over the weekend.

Wow super! also any pressure we are open source.

Also for your information you have a button with "resolve conversation" which is collapsing the review 😁

brunocroh · 2025-08-31T19:00:48Z

recipes/slow-buffer-to-buffer-alloc-unsafe-slow/src/workflow.ts

+	if (
+		originalText.includes("SlowBuffer") &&
+		!originalText.includes(",") &&
+		!originalText.includes(":") &&
+		!originalText.includes(" as ")
+	) {
+		return originalText.replace(/SlowBuffer/g, "Buffer");
+	}
+
+	let newText = originalText;
+
+	// Handle aliased patterns (both CommonJS : and ESM as syntax)
+	// { SlowBuffer: SB } -> { Buffer: SB }
+	newText = newText.replace(/SlowBuffer(\s*:\s*\w+)/g, "Buffer$1");
+	// { SlowBuffer as SB } -> { Buffer as SB }
+	newText = newText.replace(/SlowBuffer(\s+as\s+\w+)/g, "Buffer$1");
+
+	// If Buffer is already present in this specific pattern, just remove SlowBuffer
+	if (originalText.includes("Buffer") && originalText.includes("SlowBuffer")) {
+		// Remove non-aliased SlowBuffer references very carefully to preserve spacing
+		newText = newText
+			.replace(/,\s*SlowBuffer(?!\s*[:as])/g, "") // Remove SlowBuffer with leading comma
+			.replace(/SlowBuffer\s*,\s*/g, "") // Remove SlowBuffer with trailing comma and space
+			.replace(/SlowBuffer(?!\s*[:as])/g, ""); // Remove standalone SlowBuffer (not followed by : or as)
+
+		// Clean up any double spaces after opening brace
+		newText = newText.replace(/{\s{2,}/g, "{ ");
+		// Clean up any double commas but preserve spacing
+		newText = newText.replace(/,\s*,/g, ",");
+	}
+	// If Buffer is not present, replace first SlowBuffer with Buffer, remove others
+	else if (originalText.includes("SlowBuffer")) {
+		// Replace the first non-aliased SlowBuffer with Buffer
+		newText = newText.replace(/SlowBuffer(?!\s*[:as])/, "Buffer");
+		// Remove any remaining non-aliased SlowBuffer references
+		newText = newText
+			.replace(/,\s*SlowBuffer\s*(?![\s:as])/g, "")
+			.replace(/SlowBuffer\s*,\s*/g, "")
+			.replace(/SlowBuffer\s*(?![\s:as])/g, "");
+		// Clean up commas
+		newText = newText.replace(/,\s*,/g, ",");
+	}
+
+	return newText;
+}


We have a utility function that resolves these scenarios

please check utils/ast-grep/resolve-binding-path.ts

brunocroh · 2025-08-31T19:31:04Z

recipes/slow-buffer-to-buffer-alloc-unsafe-slow/src/workflow.ts

+	// Find all named_imports that include SlowBuffer aliases (ESM imports)
+	const namedImports = rootNode.findAll({ rule: { kind: "named_imports" } });
+	for (const importNode of namedImports) {
+		const text = importNode.text();
+		// Match patterns like { SlowBuffer as SB } to extract alias "SB"
+		const aliasMatches = text.matchAll(/SlowBuffer\s+as\s+(\w+)/g);
+		for (const match of aliasMatches) {
+			slowBufferAliases.add(match[1]);
+		}
+	}
+
+	// Handle constructor patterns: new SlowBuffer(size) and new SB(size) for aliases
+	const constructorCalls = rootNode.findAll({
+		rule: {
+			kind: "new_expression",
+			has: {
+				field: "constructor",
+				kind: "identifier",
+				regex: "^SlowBuffer$",
+			},
+		},
+	});
+
+	for (const constructorCall of constructorCalls) {
+		const args = constructorCall.field("arguments");
+		if (args) {
+			// Extract the arguments text (without parentheses)
+			const argsText = args.text().slice(1, -1); // Remove ( and )
+			edits.push(constructorCall.replace(`Buffer.allocUnsafeSlow(${argsText})`));
+			hasChanges = true;
+		}
+	}
+
+	// Handle constructor calls with aliases
+	for (const alias of slowBufferAliases) {
+		const aliasConstructorCalls = rootNode.findAll({
+			rule: {
+				kind: "new_expression",
+				has: {
+					field: "constructor",
+					kind: "identifier",
+					regex: `^${alias}$`,
+				},
+			},
+		});
+
+		for (const constructorCall of aliasConstructorCalls) {
+			const args = constructorCall.field("arguments");
+			if (args) {
+				const argsText = args.text().slice(1, -1);
+				edits.push(constructorCall.replace(`${alias}.allocUnsafeSlow(${argsText})`));
+				hasChanges = true;
+			}
+		}
+	}
+
+	// Handle direct function calls: SlowBuffer(size)
+	const directCalls = rootNode.findAll({
+		rule: {
+			kind: "call_expression",
+			has: {
+				field: "function",
+				kind: "identifier",
+				regex: "^SlowBuffer$",
+			},
+		},
+	});
+
+	for (const directCall of directCalls) {
+		const args = directCall.field("arguments");
+		if (args) {
+			// Extract the arguments text (without parentheses)
+			const argsText = args.text().slice(1, -1); // Remove ( and )
+			edits.push(directCall.replace(`Buffer.allocUnsafeSlow(${argsText})`));
+			hasChanges = true;
+		}
+	}
+
+	// Handle direct function calls with aliases
+	for (const alias of slowBufferAliases) {
+		const aliasDirectCalls = rootNode.findAll({
+			rule: {
+				kind: "call_expression",
+				has: {
+					field: "function",
+					kind: "identifier",
+					regex: `^${alias}$`,
+				},
+			},
+		});
+
+		for (const directCall of aliasDirectCalls) {
+			const args = directCall.field("arguments");
+			if (args) {
+				const argsText = args.text().slice(1, -1);
+				edits.push(directCall.replace(`${alias}.allocUnsafeSlow(${argsText})`));
+				hasChanges = true;
+			}
+		}
+	}


This scenario can be simplified using utils/resolve-binding-path, and improving findAll from ast-grep with any and multiple matches.

Suggested change

const objectPatterns = rootNode.findAll({ rule: { kind: "object_pattern" } });

for (const pattern of objectPatterns) {

const text = pattern.text();

// Match patterns like { SlowBuffer: SB } to extract alias "SB"

const aliasMatches = text.matchAll(/SlowBuffer\s*:\s*(\w+)/g);

for (const match of aliasMatches) {

slowBufferAliases.add(match[1]);

}

}

// Find all named_imports that include SlowBuffer aliases (ESM imports)

const namedImports = rootNode.findAll({ rule: { kind: "named_imports" } });

for (const importNode of namedImports) {

const text = importNode.text();

// Match patterns like { SlowBuffer as SB } to extract alias "SB"

const aliasMatches = text.matchAll(/SlowBuffer\s+as\s+(\w+)/g);

for (const match of aliasMatches) {

slowBufferAliases.add(match[1]);

}

}

// Handle constructor patterns: new SlowBuffer(size) and new SB(size) for aliases

const constructorCalls = rootNode.findAll({

rule: {

kind: "new_expression",

has: {

field: "constructor",

kind: "identifier",

regex: "^SlowBuffer$",

},

},

});

for (const constructorCall of constructorCalls) {

const args = constructorCall.field("arguments");

if (args) {

// Extract the arguments text (without parentheses)

const argsText = args.text().slice(1, -1); // Remove ( and )

edits.push(constructorCall.replace(`Buffer.allocUnsafeSlow(${argsText})`));

hasChanges = true;

}

}

// Handle constructor calls with aliases

for (const alias of slowBufferAliases) {

const aliasConstructorCalls = rootNode.findAll({

rule: {

kind: "new_expression",

has: {

field: "constructor",

kind: "identifier",

regex: `^${alias}$`,

},

},

});

for (const constructorCall of aliasConstructorCalls) {

const args = constructorCall.field("arguments");

if (args) {

const argsText = args.text().slice(1, -1);

edits.push(constructorCall.replace(`${alias}.allocUnsafeSlow(${argsText})`));

hasChanges = true;

}

}

}

// Handle direct function calls: SlowBuffer(size)

const directCalls = rootNode.findAll({

rule: {

kind: "call_expression",

has: {

field: "function",

kind: "identifier",

regex: "^SlowBuffer$",

},

},

});

for (const directCall of directCalls) {

const args = directCall.field("arguments");

if (args) {

// Extract the arguments text (without parentheses)

const argsText = args.text().slice(1, -1); // Remove ( and )

edits.push(directCall.replace(`Buffer.allocUnsafeSlow(${argsText})`));

hasChanges = true;

}

}

// Handle direct function calls with aliases

for (const alias of slowBufferAliases) {

const aliasDirectCalls = rootNode.findAll({

rule: {

kind: "call_expression",

has: {

field: "function",

kind: "identifier",

regex: `^${alias}$`,

},

},

});

for (const directCall of aliasDirectCalls) {

const args = directCall.field("arguments");

if (args) {

const argsText = args.text().slice(1, -1);

edits.push(directCall.replace(`${alias}.allocUnsafeSlow(${argsText})`));

hasChanges = true;

}

}

}

var ImportNode // importNode can be fetch with getNodeImportStatement or getNodeRequireCalls

const binding = resolveBindPath(importN, "$.SlowBuffer") //it will resolve the name of the SlowBuffer in this file, independent of the way it was imported.

const aliasConstructorCalls = rootNode.findAll({

rule: {

any: [

{

kind: "new_expression",

pattern: `new ${binding}($$$ARGS)`,

},

{

kind: "call_expression",

pattern: `${binding}($$$ARGS)`,

},

],

},

});

for(const match of matches) {

if(match.kind() === 'new_expression') { // each scenario can be handled by kind here if needed

const args = match.getMultipleMatches() //get args

edits.push(match.replace(/* handle replace */)

}

}

brunocroh · 2025-08-31T19:44:10Z

recipes/slow-buffer-to-buffer-alloc-unsafe-slow/src/workflow.ts

+	if (
+		originalText.includes("SlowBuffer") &&
+		!originalText.includes(",") &&
+		!originalText.includes(":") &&
+		!originalText.includes(" as ")
+	) {
+		return originalText.replace(/SlowBuffer/g, "Buffer");
+	}
+
+	let newText = originalText;
+
+	// Handle aliased patterns (both CommonJS : and ESM as syntax)
+	// { SlowBuffer: SB } -> { Buffer: SB }
+	newText = newText.replace(/SlowBuffer(\s*:\s*\w+)/g, "Buffer$1");
+	// { SlowBuffer as SB } -> { Buffer as SB }
+	newText = newText.replace(/SlowBuffer(\s+as\s+\w+)/g, "Buffer$1");
+
+	// If Buffer is already present in this specific pattern, just remove SlowBuffer
+	if (originalText.includes("Buffer") && originalText.includes("SlowBuffer")) {
+		// Remove non-aliased SlowBuffer references very carefully to preserve spacing
+		newText = newText
+			.replace(/,\s*SlowBuffer(?!\s*[:as])/g, "") // Remove SlowBuffer with leading comma
+			.replace(/SlowBuffer\s*,\s*/g, "") // Remove SlowBuffer with trailing comma and space
+			.replace(/SlowBuffer(?!\s*[:as])/g, ""); // Remove standalone SlowBuffer (not followed by : or as)
+
+		// Clean up any double spaces after opening brace
+		newText = newText.replace(/{\s{2,}/g, "{ ");
+		// Clean up any double commas but preserve spacing
+		newText = newText.replace(/,\s*,/g, ",");
+	}
+	// If Buffer is not present, replace first SlowBuffer with Buffer, remove others
+	else if (originalText.includes("SlowBuffer")) {
+		// Replace the first non-aliased SlowBuffer with Buffer
+		newText = newText.replace(/SlowBuffer(?!\s*[:as])/, "Buffer");
+		// Remove any remaining non-aliased SlowBuffer references
+		newText = newText
+			.replace(/,\s*SlowBuffer\s*(?![\s:as])/g, "")
+			.replace(/SlowBuffer\s*,\s*/g, "")
+			.replace(/SlowBuffer\s*(?![\s:as])/g, "");
+		// Clean up commas
+		newText = newText.replace(/,\s*,/g, ",");
+	}
+
+	return newText;


I think it can be handled with updateBinding utility function #182 , but it hasn’t been merged yet.

@AugustinMauroy Could we check with someone to follow up on the #182 merge?

@AugustinMauroy Could we check with someone to follow up on the #182 merge? yess

lluisemper · 2025-09-13T16:42:15Z

Hey guys! Based on your and suggestiongs I have pushed some changes. I have included some test for dynamic imports and I decided to remove the warning for the comments, with all the suggestions it was increasing the complexity and I was loosing track of what was what.

In addition to this I am not sure if updating this branch with a commit merge from main is fine or if you would prefer to rebase it. I will leave it down to you

AugustinMauroy · 2025-09-13T21:05:09Z

Hey guys! Based on your and suggestiongs I have pushed some changes. I have included some test for dynamic imports and I decided to remove the warning for the comments, with all the suggestions it was increasing the complexity and I was loosing track of what was what.

In addition to this I am not sure if updating this branch with a commit merge from main is fine or if you would prefer to rebase it. I will leave it down to you

It's look good I am still on holiday I am going to review it when I'll be back !

AugustinMauroy

LGMT !

recipes/slow-buffer-to-buffer-alloc-unsafe-slow/src/workflow.ts

recipes/slow-buffer-to-buffer-alloc-unsafe-slow/codemod.yaml

Add codemod to handle deprecated SlowBuffer API migration covering CommonJS, ES6 imports, and usage patterns Closes: nodejs#125 (comment)

lluisemper · 2025-09-17T06:01:18Z

@AugustinMauroy @brunocroh Thank you very much for the reviews! I managed to learn a lot.
By the way, I have commited the change in which I was removing the hasChanged variables which were usseles. This has caused that approval is needed once again. However I will leave this in your hands.

lluisemper force-pushed the main branch 4 times, most recently from b04a60b to d2d54d6 Compare August 28, 2025 20:56

AugustinMauroy reviewed Aug 29, 2025

View reviewed changes

lluisemper force-pushed the main branch 3 times, most recently from a68a702 to 48798a1 Compare August 29, 2025 13:51

brunocroh reviewed Aug 31, 2025

View reviewed changes

lluisemper force-pushed the main branch from 48798a1 to 7c22e79 Compare September 13, 2025 16:35

lluisemper requested review from AugustinMauroy and brunocroh September 13, 2025 16:42

brunocroh approved these changes Sep 15, 2025

View reviewed changes

AugustinMauroy approved these changes Sep 16, 2025

View reviewed changes

feat: migrate SlowBuffer to Buffer.allocUnsafeSlow()

944cbcd

Add codemod to handle deprecated SlowBuffer API migration covering CommonJS, ES6 imports, and usage patterns Closes: nodejs#125 (comment)

lluisemper force-pushed the main branch from 7c22e79 to 944cbcd Compare September 17, 2025 05:58

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feat: migrate SlowBuffer to Buffer.allocUnsafeSlow() #193

Are you sure you want to change the base?

feat: migrate SlowBuffer to Buffer.allocUnsafeSlow() #193

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lluisemper commented Sep 17, 2025

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lluisemper commented Aug 29, 2025 •

edited

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