fix(Basic LLM Chain Node): Use correct mimetype for binary data (#12978)

packages/@n8n/nodes-langchain/nodes/chains/ChainLLM/utils.ts

@@ -0,0 +1,12 @@
+import type { IBinaryData } from 'n8n-workflow';
+import { ApplicationError } from 'n8n-workflow';
+
+export class UnsupportedMimeTypeError extends ApplicationError {}
+
+export function dataUriFromImageData(binaryData: IBinaryData, bufferData: Buffer) {
+	if (!binaryData.mimeType?.startsWith('image/'))
+		throw new UnsupportedMimeTypeError(
+			`${binaryData.mimeType} is not a supported type of binary data. Only images are supported.`,
+		);
+	return `data:${binaryData.mimeType};base64,${bufferData.toString('base64')}`;
+}