ensureValidDid function

void ensureValidDid(String did)

Human-readable constraints:

• valid W3C DID (https://www.w3.org/TR/did-core/#did-syntax)
  • entire URI is ASCII: a-zA-Z0-9._:%-
  • always starts "did:" (lower-case)
  • method name is one or more lower-case letters, followed by ":"
  • remaining identifier can have any of the above chars, but can not end in ":"
  • it seems that a bunch of ":" can be included, and don't need spaces between
  • "%" is used only for "percent encoding" and must be followed by two hex characters (and thus can't end in "%")
  • query ("?") and fragment ("#") stuff is defined for "DID URIs", but not as part of identifier itself
  • "The current specification does not take a position on the maximum length of a DID"
• in current atproto, only allowing did:plc and did:web. But not forcing this at lexicon layer
• hard length limit of 8KBytes
• not going to validate "percent encoding" here

Implementation

void ensureValidDid(final String did) {
  // check that all chars are boring ASCII
  if (!RegExp(r'^[a-zA-Z0-9._:%-]*$').hasMatch(did)) {
    throw InvalidDidError(
      'Disallowed characters in DID (ASCII letters, digits, and a couple '
      'other characters only)',
    );
  }

  final parts = did.split(':');
  if (parts.length < 3) {
    throw InvalidDidError(
      'DID requires prefix, method, and method-specific content',
    );
  }

  if (parts[0] != 'did') {
    throw InvalidDidError('DID requires "did:" prefix');
  }

  if (!RegExp(r'^[a-z]+$').hasMatch(parts[1])) {
    throw InvalidDidError('DID method must be lower-case letters');
  }

  if (did.endsWith(':') || did.endsWith('%')) {
    throw InvalidDidError('DID can not end with ":" or "%"');
  }

  if (did.length > 8 * 1024) {
    throw InvalidDidError('DID is far too long');
  }
}