isUtf8 function

bool isUtf8(dynamic value)

Implementation

bool isUtf8(dynamic value) {
  if (value == null) {
    return false;
  }
  // Don't treat HEX as UTF-8.
  if (isHex(value)) {
    return false;
  }
  final u8a = u8aToU8a(value);
  final len = u8a.length;
  int i = 0;

  while (i < len) {
    if (u8a[i] <= 0x7F) /* 00..7F */ {
      i += 1;
    } else if (u8a[i] >= 0xC2 && u8a[i] <= 0xDF) /* C2..DF 80..BF */ {
      if (i + 1 < len) /* Expect a 2nd byte */ {
        if (u8a[i + 1] < 0x80 || u8a[i + 1] > 0xBF) {
          // After a first byte between C2 and DF, expecting a 2nd byte
          // between 80 and BF.
          // faultyBytes = 2;
          return false;
        }
      } else {
        // After a first byte between C2 and DF, expecting a 2nd byte.
        // faultyBytes = 1;
        return false;
      }

      i += 2;
    } else if (u8a[i] == 0xE0) /* E0 A0..BF 80..BF */ {
      if (i + 2 < len) /* Expect a 2nd and 3rd byte */ {
        if (u8a[i + 1] < 0xA0 || u8a[i + 1] > 0xBF) {
          // After a first byte of E0, expecting a 2nd byte between A0 and BF.
          // faultyBytes = 2;
          return false;
        }

        if (u8a[i + 2] < 0x80 || u8a[i + 2] > 0xBF) {
          // After a first byte of E0, expecting a 3nd byte between 80 and BF.
          // faultyBytes = 3;
          return false;
        }
      } else {
        // After a first byte of E0, expecting two following bytes.
        // faultyBytes = 1;
        return false;
      }

      i += 3;
    } else if (u8a[i] >= 0xE1 && u8a[i] <= 0xEC) /* E1..EC 80..BF 80..BF */ {
      if (i + 2 < len) /* Expect a 2nd and 3rd byte */ {
        if (u8a[i + 1] < 0x80 || u8a[i + 1] > 0xBF) {
          // After a first byte between E1 and EC, expecting the 2nd byte
          // between 80 and BF.
          // faultyBytes = 2;
          return false;
        }

        if (u8a[i + 2] < 0x80 || u8a[i + 2] > 0xBF) {
          // After a first byte between E1 and EC, expecting the 3rd byte
          // between 80 and BF.
          // faultyBytes = 3;
          return false;
        }
      } else {
        // After a first byte between E1 and EC, expecting two following bytes.
        // faultyBytes = 1;
        return false;
      }

      i += 3;
    } else if (u8a[i] == 0xED) /* ED 80..9F 80..BF */ {
      if (i + 2 < len) /* Expect a 2nd and 3rd byte */ {
        if (u8a[i + 1] < 0x80 || u8a[i + 1] > 0x9F) {
          // After a first byte of ED, expecting 2nd byte between 80 and 9F.
          // *faultyBytes = 2;
          return false;
        }

        if (u8a[i + 2] < 0x80 || u8a[i + 2] > 0xBF) {
          // After a first byte of ED, expecting 3rd byte between 80 and BF.
          // *faultyBytes = 3;
          return false;
        }
      } else {
        // After a first byte of ED, expecting two following bytes.
        // *faultyBytes = 1;
        return false;
      }

      i += 3;
    } else if (u8a[i] >= 0xEE && u8a[i] <= 0xEF) /* EE..EF 80..BF 80..BF */ {
      if (i + 2 < len) /* Expect a 2nd and 3rd byte */ {
        if (u8a[i + 1] < 0x80 || u8a[i + 1] > 0xBF) {
          // After a first byte between EE and EF, expecting 2nd byte
          // between 80 and BF.
          // faultyBytes = 2;
          return false;
        }

        if (u8a[i + 2] < 0x80 || u8a[i + 2] > 0xBF) {
          // After a first byte between EE and EF, expecting 3rd byte
          // between 80 and BF.
          // faultyBytes = 3;
          return false;
        }
      } else {
        // After a first byte between EE and EF, two following bytes.
        // faultyBytes = 1;
        return false;
      }

      i += 3;
    } else if (u8a[i] == 0xF0) /* F0 90..BF 80..BF 80..BF */ {
      if (i + 3 < len) /* Expect a 2nd, 3rd 3th byte */ {
        if (u8a[i + 1] < 0x90 || u8a[i + 1] > 0xBF) {
          // After a first byte of F0, expecting 2nd byte between 90 and BF.
          // faultyBytes = 2;
          return false;
        }

        if (u8a[i + 2] < 0x80 || u8a[i + 2] > 0xBF) {
          // After a first byte of F0, expecting 3rd byte between 80 and BF.
          // faultyBytes = 3;
          return false;
        }

        if (u8a[i + 3] < 0x80 || u8a[i + 3] > 0xBF) {
          // After a first byte of F0, expecting 4th byte between 80 and BF.
          // faultyBytes = 4;
          return false;
        }
      } else {
        // After a first byte of F0, expecting three following bytes.
        // faultyBytes = 1;
        return false;
      }

      i += 4;
    } else if (u8a[i] >= 0xF1 &&
        u8a[i] <= 0xF3) /* F1..F3 80..BF 80..BF 80..BF */ {
      if (i + 3 < len) /* Expect a 2nd, 3rd 3th byte */ {
        if (u8a[i + 1] < 0x80 || u8a[i + 1] > 0xBF) {
          // After a first byte of F1, F2, or F3, expecting a 2nd byte
          // between 80 and BF.
          // faultyBytes = 2;
          return false;
        }

        if (u8a[i + 2] < 0x80 || u8a[i + 2] > 0xBF) {
          // After a first byte of F1, F2, or F3, expecting a 3rd byte
          // between 80 and BF.
          // faultyBytes = 3;
          return false;
        }

        if (u8a[i + 3] < 0x80 || u8a[i + 3] > 0xBF) {
          // After a first byte of F1, F2, or F3, expecting a 4th byte
          // between 80 and BF.
          // faultyBytes = 4;
          return false;
        }
      } else {
        // After a first byte of F1, F2, or F3, expecting three following bytes.
        // faultyBytes = 1;
        return false;
      }

      i += 4;
    } else if (u8a[i] == 0xF4) /* F4 80..8F 80..BF 80..BF */ {
      if (i + 3 < len) /* Expect a 2nd, 3rd 3th byte */ {
        if (u8a[i + 1] < 0x80 || u8a[i + 1] > 0x8F) {
          // After a first byte of F4, expecting 2nd byte between 80 and 8F.
          // faultyBytes = 2;
          return false;
        }

        if (u8a[i + 2] < 0x80 || u8a[i + 2] > 0xBF) {
          // After a first byte of F4, expecting 3rd byte between 80 and BF.
          // faultyBytes = 3;
          return false;
        }

        if (u8a[i + 3] < 0x80 || u8a[i + 3] > 0xBF) {
          // After a first byte of F4, expecting 4th byte between 80 and BF.
          // faultyBytes = 4;
          return false;
        }
      } else {
        // After a first byte of F4, expecting three following bytes.
        // faultyBytes = 1;
        return false;
      }

      i += 4;
    } else {
      // *message = "Expecting bytes in the following ranges: 00..7F C2..F4.
      // faultyBytes = 1;
      return false;
    }
  }

  return true;
}