crc_32.go

// Copyright 2021 Comcast Cable Communications Management, LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or   implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// SPDX-License-Identifier: Apache-2.0

package scte35

import (
	"errors"

	"github.com/bamiaux/iobit"
)

var (
	// ErrCRC32Invalid indicates that a splice_info_sections CRC_32 is
	// invalid with respect to the binary payload.
	ErrCRC32Invalid = errors.New("CRC_32 not valid")

	// crc32Table provides values for calculating an SCTE35 object's CRC32 value.
	crc32Table = [...]uint{
		0x00000000,
		0x04C11DB7,
		0x09823B6E,
		0x0D4326D9,
		0x130476DC,
		0x17C56B6B,
		0x1A864DB2,
		0x1E475005,
		0x2608EDB8,
		0x22C9F00F,
		0x2F8AD6D6,
		0x2B4BCB61,
		0x350C9B64,
		0x31CD86D3,
		0x3C8EA00A,
		0x384FBDBD,
		0x4C11DB70,
		0x48D0C6C7,
		0x4593E01E,
		0x4152FDA9,
		0x5F15ADAC,
		0x5BD4B01B,
		0x569796C2,
		0x52568B75,
		0x6A1936C8,
		0x6ED82B7F,
		0x639B0DA6,
		0x675A1011,
		0x791D4014,
		0x7DDC5DA3,
		0x709F7B7A,
		0x745E66CD,
		0x9823B6E0,
		0x9CE2AB57,
		0x91A18D8E,
		0x95609039,
		0x8B27C03C,
		0x8FE6DD8B,
		0x82A5FB52,
		0x8664E6E5,
		0xBE2B5B58,
		0xBAEA46EF,
		0xB7A96036,
		0xB3687D81,
		0xAD2F2D84,
		0xA9EE3033,
		0xA4AD16EA,
		0xA06C0B5D,
		0xD4326D90,
		0xD0F37027,
		0xDDB056FE,
		0xD9714B49,
		0xC7361B4C,
		0xC3F706FB,
		0xCEB42022,
		0xCA753D95,
		0xF23A8028,
		0xF6FB9D9F,
		0xFBB8BB46,
		0xFF79A6F1,
		0xE13EF6F4,
		0xE5FFEB43,
		0xE8BCCD9A,
		0xEC7DD02D,
		0x34867077,
		0x30476DC0,
		0x3D044B19,
		0x39C556AE,
		0x278206AB,
		0x23431B1C,
		0x2E003DC5,
		0x2AC12072,
		0x128E9DCF,
		0x164F8078,
		0x1B0CA6A1,
		0x1FCDBB16,
		0x018AEB13,
		0x054BF6A4,
		0x0808D07D,
		0x0CC9CDCA,
		0x7897AB07,
		0x7C56B6B0,
		0x71159069,
		0x75D48DDE,
		0x6B93DDDB,
		0x6F52C06C,
		0x6211E6B5,
		0x66D0FB02,
		0x5E9F46BF,
		0x5A5E5B08,
		0x571D7DD1,
		0x53DC6066,
		0x4D9B3063,
		0x495A2DD4,
		0x44190B0D,
		0x40D816BA,
		0xACA5C697,
		0xA864DB20,
		0xA527FDF9,
		0xA1E6E04E,
		0xBFA1B04B,
		0xBB60ADFC,
		0xB6238B25,
		0xB2E29692,
		0x8AAD2B2F,
		0x8E6C3698,
		0x832F1041,
		0x87EE0DF6,
		0x99A95DF3,
		0x9D684044,
		0x902B669D,
		0x94EA7B2A,
		0xE0B41DE7,
		0xE4750050,
		0xE9362689,
		0xEDF73B3E,
		0xF3B06B3B,
		0xF771768C,
		0xFA325055,
		0xFEF34DE2,
		0xC6BCF05F,
		0xC27DEDE8,
		0xCF3ECB31,
		0xCBFFD686,
		0xD5B88683,
		0xD1799B34,
		0xDC3ABDED,
		0xD8FBA05A,
		0x690CE0EE,
		0x6DCDFD59,
		0x608EDB80,
		0x644FC637,
		0x7A089632,
		0x7EC98B85,
		0x738AAD5C,
		0x774BB0EB,
		0x4F040D56,
		0x4BC510E1,
		0x46863638,
		0x42472B8F,
		0x5C007B8A,
		0x58C1663D,
		0x558240E4,
		0x51435D53,
		0x251D3B9E,
		0x21DC2629,
		0x2C9F00F0,
		0x285E1D47,
		0x36194D42,
		0x32D850F5,
		0x3F9B762C,
		0x3B5A6B9B,
		0x0315D626,
		0x07D4CB91,
		0x0A97ED48,
		0x0E56F0FF,
		0x1011A0FA,
		0x14D0BD4D,
		0x19939B94,
		0x1D528623,
		0xF12F560E,
		0xF5EE4BB9,
		0xF8AD6D60,
		0xFC6C70D7,
		0xE22B20D2,
		0xE6EA3D65,
		0xEBA91BBC,
		0xEF68060B,
		0xD727BBB6,
		0xD3E6A601,
		0xDEA580D8,
		0xDA649D6F,
		0xC423CD6A,
		0xC0E2D0DD,
		0xCDA1F604,
		0xC960EBB3,
		0xBD3E8D7E,
		0xB9FF90C9,
		0xB4BCB610,
		0xB07DABA7,
		0xAE3AFBA2,
		0xAAFBE615,
		0xA7B8C0CC,
		0xA379DD7B,
		0x9B3660C6,
		0x9FF77D71,
		0x92B45BA8,
		0x9675461F,
		0x8832161A,
		0x8CF30BAD,
		0x81B02D74,
		0x857130C3,
		0x5D8A9099,
		0x594B8D2E,
		0x5408ABF7,
		0x50C9B640,
		0x4E8EE645,
		0x4A4FFBF2,
		0x470CDD2B,
		0x43CDC09C,
		0x7B827D21,
		0x7F436096,
		0x7200464F,
		0x76C15BF8,
		0x68860BFD,
		0x6C47164A,
		0x61043093,
		0x65C52D24,
		0x119B4BE9,
		0x155A565E,
		0x18197087,
		0x1CD86D30,
		0x029F3D35,
		0x065E2082,
		0x0B1D065B,
		0x0FDC1BEC,
		0x3793A651,
		0x3352BBE6,
		0x3E119D3F,
		0x3AD08088,
		0x2497D08D,
		0x2056CD3A,
		0x2D15EBE3,
		0x29D4F654,
		0xC5A92679,
		0xC1683BCE,
		0xCC2B1D17,
		0xC8EA00A0,
		0xD6AD50A5,
		0xD26C4D12,
		0xDF2F6BCB,
		0xDBEE767C,
		0xE3A1CBC1,
		0xE760D676,
		0xEA23F0AF,
		0xEEE2ED18,
		0xF0A5BD1D,
		0xF464A0AA,
		0xF9278673,
		0xFDE69BC4,
		0x89B8FD09,
		0x8D79E0BE,
		0x803AC667,
		0x84FBDBD0,
		0x9ABC8BD5,
		0x9E7D9662,
		0x933EB0BB,
		0x97FFAD0C,
		0xAFB010B1,
		0xAB710D06,
		0xA6322BDF,
		0xA2F33668,
		0xBCB4666D,
		0xB8757BDA,
		0xB5365D03,
		0xB1F740B4,
	}
)

// calculateCRC32 takes an byte array Writer containing all of the bytes of a
// Splice Info Section object up to the CRC32 value, calculates a CRC32 value
// matching the bits for those existing bytes, and returns it.
func calculateCRC32(b []byte) uint32 {
	crc := int32(-1)
	for i := range b {
		crc = (crc << 8) ^ int32(crc32Table[((crc>>24)^int32(b[i]))&0xFF])
	}
	return uint32(crc)
}

// verifyCRC32 verifies the base-64 encoded binary string is valid by confirming
// the CRC_32 matches
func verifyCRC32(b []byte) error {
	if len(b) < 4 {
		return ErrCRC32Invalid
	}

	r := iobit.NewReader(b)

	payload := r.Bytes(len(b) - 4)
	crc := r.Uint32(32)

	calculated := calculateCRC32(payload)
	if calculated != crc {
		Logger.Printf("CRC_32 calculated (%d) != reported (%d)\n", calculated, crc)
		return ErrCRC32Invalid
	}

	return nil
}