Live Scenarios with .NET: How to encode large files into Base64 using c#?

Introduction

Base64 encoding is encoding binary data to string format by translating into using a radix-64 representation.

Contents

How to encode a string into Base64
How to encode large files into Base64 using c#

How to encode a string into Base64

Let us encode a string “ab” into base64

Sring	a								b
ASCII	91								92
Bit wise	0	1	0	1	1	0	1	1	0	1	0	1	1	1	0	0
Grouping Bits (6 bits into one group)	6 bits						6bits						4bits
ASCII	22						53						12
Base64 Encode	W						1						M

Base64 Char set

Value	Char	Value	Char	Value	Char	Value	Char	Value	Char	Value	Char
0	A	11	L	22	W	33	h	44	s	55	3
1	B	12	M	23	X	34	i	45	t	56	4
2	C	13	N	24	Y	35	j	46	u	57	5
3	D	14	O	25	Z	36	k	47	v	58	6
4	E	15	P	26	a	37	l	48	w	59	7
5	F	16	Q	27	b	38	m	49	x	60	8
6	G	17	R	28	c	39	n	50	y	61	9
7	H	18	S	29	d	40	o	51	z	62	+
8	I	19	T	30	e	41	p	52	0	63	/
9	J	20	U	31	f	42	q	53	1
10	K	21	V	32	g	43	r	54	2

How to encode large files into Base64 using c#

.NET has a built-in function to convert a string into Base64 Encoded string. But it may throw an exception (like out of memory) when you are encoding huge data. I am going to create a function which can handle any size file in encoding data to Base64 encoded string

public class Base64Encoder

{

const int SegmentSize = 20 * 1024;

public void Encode(string sourceFile, string destFile)

{

/* Reading a file by segmentwise and encode into Base64string and then write into file During Base64Encoding, 3 characters(3 bytes) will be converted into 4 characters(4 bytes). Hence we need to take segment of size multiples of 3

long actualSegmentSize = 3 * SegmentSize;

long fileLength=0;

using (FileStream sourceStream = new FileStream(sourceFile, FileMode.Open, FileAccess.Read))

{

if (File.Exists(destFile)) File.Delete(destFile);

FileStream destStream = new FileStream(destFile, FileMode.Create, FileAccess.Write);

long filePosition = 0;

fileLength = sourceStream.Length;

byte[] sourceSegment;

byte[] base64EncodeSegment;

while (filePosition < fileLength)

{

if (filePosition + actualSegmentSize > fileLength)

sourceSegment = new byte[fileLength];

else

sourceSegment = new byte[actualSegmentSize];

sourceStream.Read(sourceSegment, 0, sourceSegment.Length);

base64EncodeSegment = System.Text.ASCIIEncoding.ASCII.GetBytes(Convert.ToBase64String(sourceSegment));

destStream.Write(base64EncodeSegment, 0, base64EncodeSegment.Length);

filePosition = sourceStream.Position;

}

destStream.Close();

}

public void Decode(string sourceFile, string destFile)

{

/* Reading Base64Encoded file by segmentwise and decode into string and then write into file During Base64Encoding, 3 characters(3 bytes) will be converted into 4 characters(4 bytes). Hence we need to take segment of size multiples of 4 for decoding

long actualSegmentSize = 4 * SegmentSize;

long fileLength = 0;