fix(Slack Node): Do not try to parse block if it's already object

packages/core/src/NodeExecuteFunctions.ts

@@ -100,6 +100,7 @@ import type {
 	WorkflowExecuteMode,
 	CallbackManager,
 	INodeParameters,
+	EnsureTypeOptions,
 } from 'n8n-workflow';
 import {
 	ExpressionError,
@@ -2329,6 +2330,99 @@ export const validateValueAgainstSchema = (
 	return validationResult.newValue;
 };
 
+export function ensureType(
+	toType: EnsureTypeOptions,
+	parameterValue: any,
+	parameterName: string,
+	errorOptions?: { itemIndex?: number; runIndex?: number; nodeCause?: string },
+): string | number | boolean | object {
+	let returnData = parameterValue;
+
+	if (returnData === null) {
+		throw new ExpressionError(`Parameter '${parameterName}' must not be null`, errorOptions);
+	}
+
+	if (returnData === undefined) {
+		throw new ExpressionError(
+			`Parameter '${parameterName}' could not be 'undefined'`,
+			errorOptions,
+		);
+	}
+
+	if (['object', 'array', 'json'].includes(toType)) {
+		if (typeof returnData !== 'object') {
+			// if value is not an object and is string try to parse it, else throw an error
+			if (typeof returnData === 'string' && returnData.length) {
+				try {
+					const parsedValue = JSON.parse(returnData);
+					returnData = parsedValue;
+				} catch (error) {
+					throw new ExpressionError(`Parameter '${parameterName}' could not be parsed`, {
+						...errorOptions,
+						description: error.message,
+					});
+				}
+			} else {
+				throw new ExpressionError(
+					`Parameter '${parameterName}' must be an ${toType}, but we got '${String(parameterValue)}'`,
+					errorOptions,
+				);
+			}
+		} else if (toType === 'json') {
+			// value is an object, make sure it is valid JSON
+			try {
+				JSON.stringify(returnData);
+			} catch (error) {
+				throw new ExpressionError(`Parameter '${parameterName}' is not valid JSON`, {
+					...errorOptions,
+					description: error.message,
+				});
+			}
+		}
+
+		if (toType === 'array' && !Array.isArray(returnData)) {
+			// value is not an array, but has to be
+			throw new ExpressionError(
+				`Parameter '${parameterName}' must be an array, but we got object`,
+				errorOptions,
+			);
+		}
+	}
+
+	try {
+		if (toType === 'string') {
+			if (typeof returnData === 'object') {
+				returnData = JSON.stringify(returnData);
+			} else {
+				returnData = String(returnData);
+			}
+		}
+
+		if (toType === 'number') {
+			returnData = Number(returnData);
+			if (Number.isNaN(returnData)) {
+				throw new ExpressionError(
+					`Parameter '${parameterName}' must be a number, but we got '${parameterValue}'`,
+					errorOptions,
+				);
+			}
+		}
+
+		if (toType === 'boolean') {
+			returnData = Boolean(returnData);
+		}
+	} catch (error) {
+		if (error instanceof ExpressionError) throw error;
+
+		throw new ExpressionError(`Parameter '${parameterName}' could not be converted to ${toType}`, {
+			...errorOptions,
+			description: error.message,
+		});
+	}
+
+	return returnData;
+}
+
 /**
  * Returns the requested resolved (all expressions replaced) node parameters.
  *
@@ -2399,6 +2493,15 @@ export function getNodeParameter(
 		returnData = extractValue(returnData, parameterName, node, nodeType, itemIndex);
 	}
 
+	// Make sure parameter value is the type specified in the ensureType option, if needed convert it
+	if (options?.ensureType) {
+		returnData = ensureType(options.ensureType, returnData, parameterName, {
+			itemIndex,
+			runIndex,
+			nodeCause: node.name,
+		});
+	}
+
 	// Validate parameter value if it has a schema defined(RMC) or validateType defined
 	returnData = validateValueAgainstSchema(
 		node,

packages/core/test/NodeExecuteFunctions.test.ts

@@ -2,6 +2,7 @@ import type { SecureContextOptions } from 'tls';
 import {
 	cleanupParameterData,
 	copyInputItems,
+	ensureType,
 	getBinaryDataBuffer,
 	parseIncomingMessage,
 	parseRequestObject,
@@ -25,6 +26,7 @@ import type {
 	Workflow,
 	WorkflowHooks,
 } from 'n8n-workflow';
+import { ExpressionError } from 'n8n-workflow';
 import { BinaryDataService } from '@/BinaryData/BinaryData.service';
 import nock from 'nock';
 import { tmpdir } from 'os';
@@ -583,4 +585,81 @@ describe('NodeExecuteFunctions', () => {
 			},
 		);
 	});
+
+	describe('ensureType', () => {
+		it('throws error for null value', () => {
+			expect(() => ensureType('string', null, 'myParam')).toThrowError(
+				new ExpressionError("Parameter 'myParam' must not be null"),
+			);
+		});
+
+		it('throws error for undefined value', () => {
+			expect(() => ensureType('string', undefined, 'myParam')).toThrowError(
+				new ExpressionError("Parameter 'myParam' could not be 'undefined'"),
+			);
+		});
+
+		it('returns string value without modification', () => {
+			const value = 'hello';
+			const expectedValue = value;
+			const result = ensureType('string', value, 'myParam');
+			expect(result).toBe(expectedValue);
+		});
+
+		it('returns number value without modification', () => {
+			const value = 42;
+			const expectedValue = value;
+			const result = ensureType('number', value, 'myParam');
+			expect(result).toBe(expectedValue);
+		});
+
+		it('returns boolean value without modification', () => {
+			const value = true;
+			const expectedValue = value;
+			const result = ensureType('boolean', value, 'myParam');
+			expect(result).toBe(expectedValue);
+		});
+
+		it('converts object to string if toType is string', () => {
+			const value = { name: 'John' };
+			const expectedValue = JSON.stringify(value);
+			const result = ensureType('string', value, 'myParam');
+			expect(result).toBe(expectedValue);
+		});
+
+		it('converts string to number if toType is number', () => {
+			const value = '10';
+			const expectedValue = 10;
+			const result = ensureType('number', value, 'myParam');
+			expect(result).toBe(expectedValue);
+		});
+
+		it('throws error for invalid conversion to number', () => {
+			const value = 'invalid';
+			expect(() => ensureType('number', value, 'myParam')).toThrowError(
+				new ExpressionError("Parameter 'myParam' must be a number, but we got 'invalid'"),
+			);
+		});
+
+		it('parses valid JSON string to object if toType is object', () => {
+			const value = '{"name": "Alice"}';
+			const expectedValue = JSON.parse(value);
+			const result = ensureType('object', value, 'myParam');
+			expect(result).toEqual(expectedValue);
+		});
+
+		it('throws error for invalid JSON string to object conversion', () => {
+			const value = 'invalid_json';
+			expect(() => ensureType('object', value, 'myParam')).toThrowError(
+				new ExpressionError("Parameter 'myParam' could not be parsed"),
+			);
+		});
+
+		it('throws error for non-array value if toType is array', () => {
+			const value = { name: 'Alice' };
+			expect(() => ensureType('array', value, 'myParam')).toThrowError(
+				new ExpressionError("Parameter 'myParam' must be an array, but we got object"),
+			);
+		});
+	});
 });

packages/nodes-base/nodes/Slack/V2/GenericFunctions.ts

@@ -8,7 +8,7 @@ import type {
 	IWebhookFunctions,
 } from 'n8n-workflow';
 
-import { NodeOperationError, jsonParse } from 'n8n-workflow';
+import { NodeOperationError } from 'n8n-workflow';
 
 import get from 'lodash/get';
 
@@ -162,7 +162,7 @@ export function getMessageContent(
 			};
 			break;
 		case 'block':
-			content = jsonParse(this.getNodeParameter('blocksUi', i) as string);
+			content = this.getNodeParameter('blocksUi', i, {}, { ensureType: 'object' }) as IDataObject;
 
 			if (includeLinkToWorkflow && Array.isArray(content.blocks)) {
 				content.blocks.push({

packages/workflow/src/Interfaces.ts

@@ -622,8 +622,11 @@ export interface IN8nRequestOperationPaginationOffset extends IN8nRequestOperati
 	};
 }
 
+export type EnsureTypeOptions = 'string' | 'number' | 'boolean' | 'object' | 'array' | 'json';
 export interface IGetNodeParameterOptions {
 	contextNode?: INode;
+	// make sure that returned value would be of specified type, converts it if needed
+	ensureType?: EnsureTypeOptions;
 	// extract value from regex, works only when parameter type is resourceLocator
 	extractValue?: boolean;
 	// get raw value of parameter with unresolved expressions