# parse method

UriData parse (String uri)

Parses a string as a `data` URI.

The string must have the format:

    'data:' (type '/' subtype)? (';' attribute '=' value)* (';base64')? ',' data

where `type`, `subtype`, `attribute` and `value` are specified in RFC-2045, and `data` is a sequence of URI-characters (RFC-2396 `uric`).

This means that all the characters must be ASCII, but the URI may contain percent-escapes for non-ASCII byte values that need an interpretation to be converted to the corresponding string.

Parsing checks that Base64 encoded data is valid, and it normalizes it to use the default Base64 alphabet and to use padding. Non-Base64 data is escaped using percent-escapes as necessary to make it valid, and existing escapes are case normalized.

Accessing the individual parts may fail later if they turn out to have content that can't be decoded successfully as a string, for example if existing percent escapes represent bytes that cannot be decoded by the chosen Encoding (see contentAsString).

A FormatException is thrown if `uri` is not a valid data URI.

## Implementation

    static UriData parse(String uri) {
      if (uri.length >= 5) {
        int dataDelta = _startsWithData(uri, 0);
        if (dataDelta == 0) {
          // Exact match on "data:".
          return _parse(uri, 5, null);
        }
        if (dataDelta == 0x20) {
          // Starts with a non-normalized "data" scheme containing upper-case
          // letters. Parse anyway, but throw away the scheme.
          return _parse(uri.substring(5), 0, null);
        }
      }
      throw FormatException("Does not start with 'data:'", uri, 0);
    }