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+/**
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+ * MIME Source Parser for Attachment Extraction
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+ *
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+ * Parses raw email MIME source to extract attachment metadata and content.
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+ * Used as a fallback when AppleScript's `mail attachments` returns empty
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+ * (which happens across all account types: iCloud, Google, Exchange).
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+ *
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+ * @module utils/mimeParse
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+ */
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+
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+export interface MimeAttachmentInfo {
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+ /** Filename from Content-Disposition or Content-Type name parameter */
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+ name: string;
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+ /** MIME type from Content-Type header */
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+ mimeType: string;
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+ /** Size in bytes from Content-Disposition size parameter, or estimated from base64 */
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+ size: number;
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+}
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+
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+export interface MimeAttachmentData extends MimeAttachmentInfo {
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+ /** Decoded binary content */
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+ data: Buffer;
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+}
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+
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+/**
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+ * Extract the boundary string from a Content-Type header.
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+ */
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+function extractBoundary(source: string): string | null {
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+ const match = source.match(/boundary="?([^";\s\r\n]+)"?/i);
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+ return match ? match[1] : null;
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+}
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+
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+/**
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+ * Extract a header value from a MIME part header block.
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+ * Handles folded headers (continuation lines starting with whitespace).
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+ */
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+function getHeader(headers: string, name: string): string | null {
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+ const regex = new RegExp(`^${name}:\\s*(.+(?:\\r?\\n[ \\t]+.+)*)`, "im");
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+ const match = headers.match(regex);
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+ if (!match) return null;
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+ // Unfold: replace newline+whitespace with single space
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+ return match[1].replace(/\r?\n[ \t]+/g, " ").trim();
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+}
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+
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+/**
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+ * Extract filename from Content-Disposition or Content-Type headers.
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+ */
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+function extractFilename(headers: string): string | null {
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+ // Try Content-Disposition filename first
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+ const dispHeader = getHeader(headers, "Content-Disposition");
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+ if (dispHeader) {
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+ const fnMatch = dispHeader.match(/filename="?([^";\r\n]+)"?/i);
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+ if (fnMatch) return fnMatch[1].trim();
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+ }
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+ // Fall back to Content-Type name parameter
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+ const ctHeader = getHeader(headers, "Content-Type");
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+ if (ctHeader) {
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+ const nameMatch = ctHeader.match(/name="?([^";\r\n]+)"?/i);
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+ if (nameMatch) return nameMatch[1].trim();
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+ }
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+ return null;
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+}
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+
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+/**
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+ * Check if a MIME part has inline disposition (not a real attachment).
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+ */
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+function isInlineDisposition(headers: string): boolean {
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+ const dispHeader = getHeader(headers, "Content-Disposition");
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+ if (!dispHeader) return false;
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+ return dispHeader.toLowerCase().startsWith("inline");
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+}
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+
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+/**
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+ * Extract size from Content-Disposition size parameter.
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+ */
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+function extractSize(headers: string): number {
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+ const dispHeader = getHeader(headers, "Content-Disposition");
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+ if (dispHeader) {
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+ const sizeMatch = dispHeader.match(/size=(\d+)/i);
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+ if (sizeMatch) return parseInt(sizeMatch[1], 10);
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+ }
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+ return 0;
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+}
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+
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+/**
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+ * Extract MIME type from Content-Type header.
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+ */
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+function extractMimeType(headers: string): string {
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+ const ctHeader = getHeader(headers, "Content-Type");
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+ if (!ctHeader) return "application/octet-stream";
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+ const typeMatch = ctHeader.match(/^([^;\s]+)/);
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+ return typeMatch ? typeMatch[1].toLowerCase() : "application/octet-stream";
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+}
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+
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+/**
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+ * Estimate decoded size from base64 content length.
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+ */
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+function estimateBase64Size(base64Body: string): number {
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+ const cleaned = base64Body.replace(/[\s\r\n]/g, "");
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+ return Math.floor((cleaned.length * 3) / 4);
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+}
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+
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+/**
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+ * Split MIME source into parts using the boundary.
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+ */
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+function splitMimeParts(
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+ source: string,
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+ boundary: string
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+): Array<{ headers: string; body: string }> {
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+ const parts: Array<{ headers: string; body: string }> = [];
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+ const boundaryDelim = `--${boundary}`;
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+
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+ const sections = source.split(boundaryDelim);
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+
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+ for (const section of sections) {
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+ const trimmed = section.trim();
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+ if (!trimmed || trimmed.startsWith("--")) continue;
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+
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+ // Split headers from body at first blank line
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+ const blankLineIdx = trimmed.search(/\r?\n\r?\n/);
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+ if (blankLineIdx === -1) continue;
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+
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+ const headers = trimmed.substring(0, blankLineIdx);
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+ const body = trimmed.substring(blankLineIdx).replace(/^\r?\n\r?\n/, "");
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+
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+ parts.push({ headers, body });
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+ }
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+
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+ return parts;
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+}
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+
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+/**
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+ * Parse MIME source and return metadata for all file attachments.
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+ * Skips inline dispositions (signature images, etc.).
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+ *
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+ * @param source - Raw MIME source of the email
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+ * @returns Array of attachment metadata (name, mimeType, size)
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+ */
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+export function parseMimeAttachments(source: string): MimeAttachmentInfo[] {
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+ if (!source || !source.trim()) return [];
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+
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+ const boundary = extractBoundary(source);
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+ if (!boundary) return [];
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+
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+ const parts = splitMimeParts(source, boundary);
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+ const attachments: MimeAttachmentInfo[] = [];
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+
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+ for (const part of parts) {
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+ const filename = extractFilename(part.headers);
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+ if (!filename) continue;
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+
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+ if (isInlineDisposition(part.headers)) continue;
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+
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+ const encoding = getHeader(part.headers, "Content-Transfer-Encoding");
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+ if (!encoding || encoding.toLowerCase() !== "base64") continue;
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+
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+ attachments.push({
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+ name: filename,
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+ mimeType: extractMimeType(part.headers),
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+ size: extractSize(part.headers) || estimateBase64Size(part.body),
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+ });
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+ }
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+
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+ return attachments;
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+}
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+
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+/**
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+ * Extract and decode a specific attachment from MIME source by filename.
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+ *
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+ * @param source - Raw MIME source of the email
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+ * @param attachmentName - Filename to extract
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+ * @returns Decoded attachment data, or null if not found
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+ */
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+export function extractMimeAttachment(
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+ source: string,
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+ attachmentName: string
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+): MimeAttachmentData | null {
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+ if (!source || !source.trim()) return null;
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+
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+ const boundary = extractBoundary(source);
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+ if (!boundary) return null;
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+
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+ const parts = splitMimeParts(source, boundary);
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+
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+ for (const part of parts) {
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+ const filename = extractFilename(part.headers);
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+ if (filename !== attachmentName) continue;
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+
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+ const encoding = getHeader(part.headers, "Content-Transfer-Encoding");
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+ if (!encoding || encoding.toLowerCase() !== "base64") continue;
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+
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+ const base64Clean = part.body.replace(/[\s\r\n]/g, "");
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+ const data = Buffer.from(base64Clean, "base64");
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+
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+ return {
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+ name: filename,
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+ mimeType: extractMimeType(part.headers),
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+ size: extractSize(part.headers) || data.length,
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+ data,
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+ };
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+ }
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+
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+ return null;
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+}
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Kevin May