Function ResolveLocalImagePaths

shortcuts/mail/draft/patch.go:1029–1066

ResolveLocalImagePaths scans HTML for references, validates each path, generates CIDs, and returns the modified HTML with cid: URIs plus the list of local image references to embed as inline parts. This function handles only the HTML transformation; callers are responsible for

(html string)

// This function handles only the HTML transformation; callers are responsible
// for embedding the actual file data (e.g., via emlbuilder.AddFileInline).
func ResolveLocalImagePaths(html string) (string, []LocalImageRef, error) {
	matches := imgSrcRegexp.FindAllStringSubmatchIndex(html, -1)
	if len(matches) == 0 {
		return html, nil, nil
	}

	// Cache resolved paths so the same file is only attached once.
	pathToCID := make(map[string]string)
	var refs []LocalImageRef

	// Iterate in reverse so that index offsets remain valid after replacement.
	for i := len(matches) - 1; i >= 0; i-- {
		srcStart, srcEnd := matches[i][2], matches[i][3]
		src := html[srcStart:srcEnd]
		if !isLocalFileSrc(src) {
			continue
		}

		resolvedPath, err := validate.SafeInputPath(src)
		if err != nil {
			return "", nil, fmt.Errorf("inline image %q: %w", src, err)
		}

		cid, ok := pathToCID[resolvedPath]
		if !ok {
			cid, err = generateCID()
			if err != nil {
				return "", nil, err
			}
			pathToCID[resolvedPath] = cid
			refs = append(refs, LocalImageRef{FilePath: src, CID: cid})
		}

		html = html[:srcStart] + "cid:" + cid + html[srcEnd:]
	}

	return html, refs, nil
}

// resolveLocalImgSrc scans HTML for <img src="local/path"> references,
// creates MIME inline parts for each local file, and returns the HTML