injectBuildIdMeta function

String injectBuildIdMeta(String html, String buildId)

Inserts the build-ID meta tag just before </head>, removing any previous one first.

Throws a FormatException when html has no </head>.

Implementation

String injectBuildIdMeta(String html, String buildId) {
  final String clean = removeBuildIdMeta(html);
  final Match? head = _headClose.firstMatch(clean);
  if (head == null) {
    throw const FormatException('index.html has no </head> tag');
  }
  final String tag =
      '<meta name="$buildIdMetaName" content="${_escapeAttr(buildId)}">';
  final int lineStart = head.start == 0
      ? 0
      : clean.lastIndexOf('\n', head.start - 1) + 1;
  final String before = clean.substring(lineStart, head.start);
  if (before.trim().isEmpty) {
    // `</head>` starts its own line: add the tag as a line of its own.
    final String newline = clean.contains('\r\n') ? '\r\n' : '\n';
    return '${clean.substring(0, lineStart)}$before  $tag$newline'
        '${clean.substring(lineStart)}';
  }
  return '${clean.substring(0, head.start)}$tag${clean.substring(head.start)}';
}