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/*
`Base32` encoding and decoding, as specified in [[ RFC 4648; https://www.rfc-editor.org/rfc/rfc4648.html ]].
A secondary param can be used to supply a custom alphabet to `encode` and a matching decoding table to `decode`.
If none is supplied it just uses the standard Base32 alphabet.
In case your specific version does not use padding, you may
truncate it from the encoded output.
Error represents errors that can occur during base32 decoding operations.
As per RFC 4648:
- Section 3.3: Invalid character handling
- Section 3.2: Padding requirements
- Section 6: Base32 encoding specifics (including block size requirements)
*/
package encoding_base32
Error :: enum {
None,
Invalid_Character, // Input contains characters outside the specified alphabet
Invalid_Length, // Input length is not valid for base32 (must be a multiple of 8 with proper padding)
Malformed_Input, // Input has improper structure (wrong padding position or incomplete groups)
}
Validate_Proc :: #type proc(c: byte) -> bool
@private
_validate_default :: proc(c: byte) -> bool {
return (c >= 'A' && c <= 'Z') || (c >= '2' && c <= '7')
}
@(rodata)
ENC_TABLE := [32]byte {
'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H',
'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',
'Y', 'Z', '2', '3', '4', '5', '6', '7',
}
PADDING :: '='
@(rodata)
DEC_TABLE := [256]u8 {
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 26, 27, 28, 29, 30, 31, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 0, 0, 0, 0, 0,
0, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
}
encode :: proc(data: []byte, ENC_TBL := ENC_TABLE, allocator := context.allocator) -> string {
out_length := (len(data) + 4) / 5 * 8
out := make([]byte, out_length, allocator)
_encode(out, data, ENC_TBL)
return string(out[:])
}
@private
_encode :: proc(out, data: []byte, ENC_TBL := ENC_TABLE, allocator := context.allocator) {
out := out
data := data
for len(data) > 0 {
carry: byte
switch len(data) {
case:
out[7] = ENC_TBL[data[4] & 0x1f]
carry = data[4] >> 5
fallthrough
case 4:
out[6] = ENC_TBL[carry | (data[3] << 3) & 0x1f]
out[5] = ENC_TBL[(data[3] >> 2) & 0x1f]
carry = data[3] >> 7
fallthrough
case 3:
out[4] = ENC_TBL[carry | (data[2] << 1) & 0x1f]
carry = (data[2] >> 4) & 0x1f
fallthrough
case 2:
out[3] = ENC_TBL[carry | (data[1] << 4) & 0x1f]
out[2] = ENC_TBL[(data[1] >> 1) & 0x1f]
carry = (data[1] >> 6) & 0x1f
fallthrough
case 1:
out[1] = ENC_TBL[carry | (data[0] << 2) & 0x1f]
out[0] = ENC_TBL[data[0] >> 3]
}
if len(data) < 5 {
out[7] = byte(PADDING)
if len(data) < 4 {
out[6] = byte(PADDING)
out[5] = byte(PADDING)
if len(data) < 3 {
out[4] = byte(PADDING)
if len(data) < 2 {
out[3] = byte(PADDING)
out[2] = byte(PADDING)
}
}
}
break
}
data = data[5:]
out = out[8:]
}
}
@(optimization_mode="favor_size")
decode :: proc(
data: string,
DEC_TBL := DEC_TABLE,
validate: Validate_Proc = _validate_default,
allocator := context.allocator) -> (out: []byte, err: Error) {
if len(data) == 0 {
return nil, .None
}
// Check minimum length requirement first
if len(data) < 2 {
return nil, .Invalid_Length
}
// Validate characters using provided validation function
for i := 0; i < len(data); i += 1 {
c := data[i]
if c == byte(PADDING) {
break
}
if !validate(c) {
return nil, .Invalid_Character
}
}
// Validate padding and length
data_len := len(data)
padding_count := 0
for i := data_len - 1; i >= 0; i -= 1 {
if data[i] != byte(PADDING) {
break
}
padding_count += 1
}
// Verify no padding in the middle
for i := 0; i < data_len - padding_count; i += 1 {
if data[i] == byte(PADDING) {
return nil, .Malformed_Input
}
}
// Check for proper padding and length combinations
if padding_count > 0 {
content_len := data_len - padding_count
mod8 := content_len % 8
required_padding: int
switch mod8 {
case 2: required_padding = 6 // 2 chars need 6 padding chars
case 4: required_padding = 4 // 4 chars need 4 padding chars
case 5: required_padding = 3 // 5 chars need 3 padding chars
case 7: required_padding = 1 // 7 chars need 1 padding char
case: required_padding = 0
}
if required_padding > 0 {
if padding_count != required_padding {
return nil, .Malformed_Input
}
} else if mod8 != 0 {
return nil, .Malformed_Input
}
} else {
// No padding - must be multiple of 8
if data_len % 8 != 0 {
return nil, .Malformed_Input
}
}
// Calculate decoded length: 5 bytes for every 8 input chars
input_chars := data_len - padding_count
out_len := input_chars * 5 / 8
out = make([]byte, out_len, allocator)
defer if err != .None {
delete(out)
}
// Process input in 8-byte blocks
outi := 0
for i := 0; i < input_chars; i += 8 {
buf: [8]byte
block_size := min(8, input_chars - i)
// Decode block
for j := 0; j < block_size; j += 1 {
buf[j] = DEC_TBL[data[i + j]]
}
// Convert to output bytes based on block size
bytes_to_write := block_size * 5 / 8
switch block_size {
case 8:
out[outi + 4] = (buf[6] << 5) | buf[7]
fallthrough
case 7:
out[outi + 3] = (buf[4] << 7) | (buf[5] << 2) | (buf[6] >> 3)
fallthrough
case 5:
out[outi + 2] = (buf[3] << 4) | (buf[4] >> 1)
fallthrough
case 4:
out[outi + 1] = (buf[1] << 6) | (buf[2] << 1) | (buf[3] >> 4)
fallthrough
case 2:
out[outi] = (buf[0] << 3) | (buf[1] >> 2)
}
outi += bytes_to_write
}
return
}
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