bech32

commit dd25247ba61d75fae3502b51e95766acf47450e4
parent d1583e150f23af9baa923f1aaa17b35b85872a5e
Author: Jared Tobin <jared@jtobin.io>
Date:   Fri,  3 Jan 2025 19:29:33 -0330

lib: decoding

Diffstat:
M
README.md
 | 
6
+++++-
M
flake.nix
 | 
2
+-
M
lib/Data/ByteString/Bech32.hs
 | 
28
++++++++++++++++++++++++++--
M
lib/Data/ByteString/Bech32m.hs
 | 
29
+++++++++++++++++++++++++++--
M
ppad-bech32.cabal
 | 
6
+++---

5 files changed, 62 insertions(+), 9 deletions(-)
diff --git a/README.md b/README.md
@@ -1,6 +1,6 @@
 # ppad-bech32
 
-A pure Haskell implementation of the bech32m and bech32 encodings on
+A pure Haskell implementation of bech32m and bech32 encoding/decoding on
 strict ByteStrings, as specified by [BIP350][bi350] and [BIP173][bi173].
 
 ## Usage
@@ -26,6 +26,10 @@ A sample GHCi session:
   > -- tweaked stuff will obviously fail to verify (s/m/w below)
   > Bech32m.verify "bc1vys8xarpdejxzunyypwk7uny8qsxy7t5v4ehgunfdenswyuz0e"
   False
+  >
+  > -- decode bech32m-encoded input
+  > Bech32m.decode bech32m
+  Just ("bc","a standard word8 bytestring")
 ```
 
 ## Documentation
diff --git a/flake.nix b/flake.nix
@@ -1,5 +1,5 @@
 {
-  description = "Pure Haskell bech32m/bech32 encodings.";
+  description = "Pure Haskell bech32m and bech32 encoding/decoding.";
 
   inputs = {
     nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
diff --git a/lib/Data/ByteString/Bech32.hs b/lib/Data/ByteString/Bech32.hs
@@ -9,11 +9,12 @@
 --
 -- The
 -- [BIP0173](https://github.com/bitcoin/bips/blob/master/bip-0173.mediawiki)
--- bech32 checksummed base32 encoding, with checksum verification.
+-- bech32 checksummed base32 encoding, with decoding and checksum verification.
 
 module Data.ByteString.Bech32 (
-    -- * Encoding
+    -- * Encoding and Decoding
     encode
+  , decode
 
     -- * Checksum
   , verify
@@ -26,6 +27,7 @@ import qualified Data.ByteString.Base32 as B32
 import qualified Data.ByteString.Bech32.Internal as BI
 import qualified Data.ByteString.Builder as BSB
 import qualified Data.ByteString.Builder.Extra as BE
+import qualified Data.ByteString.Internal as BSI
 import qualified Data.Char as C (toLower)
 
 -- realization for small builders
@@ -57,6 +59,28 @@ encode hrp (B32.encode -> dat) = do
   guard (BS.length res < 91)
   pure res
 
+-- | Decode a bech32-encoded 'ByteString' into its human-readable and data
+--   parts.
+--
+--   >>> decode "hi1df6x7cnfdcs8wctnyp5x2un9wed5st"
+--   Just ("hi","jtobin was here")
+--   >>> decode "hey1df6x7cnfdcs8wctnyp5x2un9wed5st" -- s/hi/hey
+--   Nothing
+decode
+  :: BS.ByteString                        -- ^ bech23-encoded bytestring
+  -> Maybe (BS.ByteString, BS.ByteString)
+decode bs@(BSI.PS _ _ l) = do
+  guard (l <= 90)
+  guard (verify bs)
+  sep <- BS.elemIndexEnd 0x31 bs
+  case BS.splitAt sep bs of
+    (hrp, raw) -> do
+      guard (BI.valid_hrp hrp)
+      guard (BS.length raw >= 6)
+      (_, BS.dropEnd 6 -> bech32dat) <- BS.uncons raw
+      dat <- B32.decode bech32dat
+      pure (hrp, dat)
+
 -- | Verify that a bech32 string has a valid checksum.
 --
 --   >>> verify "bc1d4ujqum5wf5kuecmu02w2"
diff --git a/lib/Data/ByteString/Bech32m.hs b/lib/Data/ByteString/Bech32m.hs
@@ -9,11 +9,13 @@
 --
 -- The
 -- [BIP350](https://github.com/bitcoin/bips/blob/master/bip-0350.mediawiki)
--- bech32m checksummed base32 encoding, with checksum verification.
+-- bech32m checksummed base32 encoding, with decoding and checksum
+-- verification.
 
 module Data.ByteString.Bech32m (
-    -- * Encoding
+    -- * Encoding and Decoding
     encode
+  , decode
 
     -- * Checksum
   , verify
@@ -26,6 +28,7 @@ import qualified Data.ByteString.Base32 as B32
 import qualified Data.ByteString.Bech32.Internal as BI
 import qualified Data.ByteString.Builder as BSB
 import qualified Data.ByteString.Builder.Extra as BE
+import qualified Data.ByteString.Internal as BSI
 import qualified Data.Char as C (toLower)
 
 -- realization for small builders
@@ -57,6 +60,28 @@ encode hrp (B32.encode -> dat) = do
   guard (BS.length res < 91)
   pure res
 
+-- | Decode a bech32m-encoded 'ByteString' into its human-readable and data
+--   parts.
+--
+--   >>> decode "hi1df6x7cnfdcs8wctnyp5x2un9m9ac4f"
+--   Just ("hi","jtobin was here")
+--   >>> decode "hey1df6x7cnfdcs8wctnyp5x2un9m9ac4f" -- s/hi/hey
+--   Nothing
+decode
+  :: BS.ByteString                        -- ^ bech23-encoded bytestring
+  -> Maybe (BS.ByteString, BS.ByteString)
+decode bs@(BSI.PS _ _ l) = do
+  guard (l <= 90)
+  guard (verify bs)
+  sep <- BS.elemIndexEnd 0x31 bs
+  case BS.splitAt sep bs of
+    (hrp, raw) -> do
+      guard (BI.valid_hrp hrp)
+      guard (BS.length raw >= 6)
+      (_, BS.dropEnd 6 -> bech32dat) <- BS.uncons raw
+      dat <- B32.decode bech32dat
+      pure (hrp, dat)
+
 -- | Verify that a bech32m string has a valid checksum.
 --
 --   >>> verify "bc1d4ujqum5wf5kuecwqlxtg"
diff --git a/ppad-bech32.cabal b/ppad-bech32.cabal
@@ -1,7 +1,7 @@
 cabal-version:      3.0
 name:               ppad-bech32
 version:            0.1.2
-synopsis:           The bech32 and bech32m encodings, per BIPs 173 & 350.
+synopsis:           bech32 and bech32m encoding/decoding, per BIPs 173 & 350.
 license:            MIT
 license-file:       LICENSE
 author:             Jared Tobin
@@ -11,8 +11,8 @@ build-type:         Simple
 tested-with:        GHC == 9.8.1
 extra-doc-files:    CHANGELOG
 description:
-  The bech32 and bech32m encodings on strict bytestrings, per BIPs 173 &
-  350.
+  bech32 and bech32m encoding/decoding on strict bytestrings, per BIPs
+  173 & 350.
 
 source-repository head
   type:     git