b64.bend source

b64.bend on the hub · documented module

# ezhttp/b64: Base64 encoding for HTTP credentials (RFC 4648 §4). The# alphabet is the standard table, with `=` padding. Decoding is not required# for the Authorization helpers.import Base# how many octets of the current quantum are still missingtype Phase is Data:  Need3{}  Need2{first: U32}  Need1{first: U32, second: U32}# RFC 4648 §4 alphabet, index 0 is `A`def b64.table() -> String:  "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"# the character at a 0..63 index, `A` when the index is out of the tabledef b64.char(m: Maybe<&2, Char>) -> Char:  match m:    case None{}:      'A'    case Some{c}:      c# one 6-bit value as an alphabet characterdef b64.at(+n: U32) -> Char:  b64.char(String.get(b64.table(), U32.to_nat(U32.and(n, 63))))# 24 bits from three octetsdef b64.pack(+a: U32, +b: U32, +c: U32) -> U32:  U32.or(U32.or(U32.shln(a, 16n), U32.shln(b, 8n)), c)# the last two characters when the quantum was shortdef b64.tail.more(+n: U32, left: Nat) -> String:  match left:    case 0n:      SCon{b64.at(U32.shrn(n, 6n)), SCon{'=', SNil{}}}    case 1n+k:      SCon{'=', SCon{'=', SNil{}}}# four characters from a packed quantum; pad is how many `=` to writedef b64.tail(+n: U32, pad: Nat) -> String:  match pad:    case 0n:      SCon{b64.at(U32.shrn(n, 6n)), SCon{b64.at(n), SNil{}}}    case 1n+p:      b64.tail.more(n, p)# one quantum as four charactersdef b64.quad(+a: U32, +b: U32, +c: U32, pad: Nat) -> String:  +n = b64.pack(a, b, c)  SCon{b64.at(U32.shrn(n, 18n)), SCon{b64.at(U32.shrn(n, 12n)), b64.tail(n, pad)}}# padding for a quantum that ended earlydef b64.end(phase: Phase) -> String:  match phase:    case Need3{}:      ""    case Need2{first}:      b64.quad(first, 0, 0, 2n)    case Need1{first, second}:      b64.quad(first, second, 0, 1n)# octets to Base64, three at a time (RFC 4648 §4)def b64.go(bs: List<&2, U32>, phase: Phase) -> String:  match bs:    case []:      b64.end(phase)    case h <> t:      match phase:        case Need3{}:          b64.go(t, Need2{h})        case Need2{first}:          b64.go(t, Need1{first, h})        case Need1{first, second}:          b64.quad(first, second, h, 0n) ++ b64.go(t, Need3{})# code points of a string, one octet each (credentials are ASCII)def b64.bytes(s: String) -> List<&2, U32>:  match s:    case SNil{}:      []    case SCon{h, t}:      Char.to_u32(h) <> b64.bytes(t)# Base64 of a string (RFC 4648 §4)def b64.encode(s: String) -> String:  b64.go(b64.bytes(s), Need3{})