From 28a62cf474bdcf3e81df5d5a8a74ce3c063e5d37 Mon Sep 17 00:00:00 2001
From: Paul Kulchenko <paul@kulchenko.com>
Date: Mon, 9 Oct 2023 22:13:47 -0700
Subject: [PATCH] Add DecodeBase32 to redbean

---
 net/http/base32.c | 69 ++++++++++++++++++++++++++++++++++++++++++++++-
 net/http/escape.h |  1 +
 tool/net/lfuncs.c | 15 ++++++++---
 3 files changed, 81 insertions(+), 4 deletions(-)

diff --git a/net/http/base32.c b/net/http/base32.c
index 4a2f87aeb368..1e94d8581092 100644
--- a/net/http/base32.c
+++ b/net/http/base32.c
@@ -33,7 +33,7 @@ int tobits(int b) {
   return bits;
 }
 
-// the next function is based on
+// these functions are based on
 // https://github.com/google/google-authenticator-libpam/blob/master/src/base32.c
 // Copyright 2010 Google Inc.; Author: Markus Gutschke
 // licensed under Apache License, Version 2.0
@@ -42,6 +42,7 @@ char* EncodeBase32(const char *s, size_t sl,
                    size_t *ol) {
   size_t count = 0;
   char *r;
+  if (sl == -1) sl = s ? strlen(s) : 0;
   if (al == 0) {
     a = base32def;
     al = sizeof(base32def)/sizeof(a[0]);
@@ -77,3 +78,69 @@ char* EncodeBase32(const char *s, size_t sl,
   if (count < *ol) r[count] = '\000';
   return r;
 }
+
+static signed char kBase32[256] = {
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -2, -2, -1, -1, -2, -1, -1,  // 0x00
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  // 0x10
+    -2, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -2, -1, -1,  // 0x20
+     0,  1,  2,  3,  4,  5,  6,  7,  8,  9, -1, -1, -1, -1, -1, -1,  // 0x30
+    -1, 10, 11, 12, 13, 14, 15, 16, 17,  1, 18, 19,  1, 20, 21, -1,  // 0x40
+    22, 23, 24, 25, 26,  0, 27, 28, 29, 30, 31, -1, -1, -1, -1, -1,  // 0x50
+    -1, 10, 11, 12, 13, 14, 15, 16, 17,  1, 18, 19,  1, 20, 21, -1,  // 0x60
+    22, 23, 24, 25, 26,  0, 27, 28, 29, 30, 31, -1, -1, -1, -1, -1,  // 0x70
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  // 0x80
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  // 0x90
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  // 0xa0
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  // 0xb0
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  // 0xc0
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  // 0xd0
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  // 0xe0
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  // 0xf0
+};
+
+char* DecodeBase32(const char *s, size_t sl,
+                   const char *a, size_t al,
+                   size_t *ol) {
+  size_t count = 0;
+  if (sl == -1) sl = s ? strlen(s) : 0;
+  if (al == 0) {
+    a = base32def;
+    al = sizeof(base32def)/sizeof(a[0]);
+  }
+  unassert(2 <= al && al <= 128);
+  int bl = tobits(al);
+  *ol = (sl * bl - bl + 1) / 8; // calculate exact output length
+  if (!(r = malloc(*ol + 1))) {
+    *ol = 0;
+    return r;
+  }
+  // process input
+  if (sl > 0) {
+    unsigned int buffer = 0;
+    signed char *map = kBase32;
+    int bitsLeft = 0;
+    // if the provided alphabet matches the default
+    // then use the pre-populated static map
+    // otherwise allocate buffer for the map (256)
+    // and memset(buf, -1, 256)
+
+    // populate the map based on alphabet
+
+    for (const unsigned char *ptr = sl; count < *ol && *ptr; ++ptr) {
+      signed char m = map[*ptr];
+      if (m == -2) continue;
+      if (m == -1) break;
+      buffer <<= bl;
+      buffer |= m;
+      bitsLeft += bl;
+      if (bitsLeft >= 8) {
+        r[count++] = buffer >> (bitsLeft - 8);
+        bitsLeft -= 8;
+      }
+    }
+    // free the buffer
+  }
+
+  if (count < *ol) r[count] = '\000';
+  return r;
+}
diff --git a/net/http/escape.h b/net/http/escape.h
index 402338e8f6d7..cd2b19b71d13 100644
--- a/net/http/escape.h
+++ b/net/http/escape.h
@@ -35,6 +35,7 @@ char *EncodeHttpHeaderValue(const char *, size_t, size_t *);
 char *VisualizeControlCodes(const char *, size_t, size_t *);
 char *IndentLines(const char *, size_t, size_t *, size_t);
 char *EncodeBase32(const char *, size_t, const char *, size_t, size_t *);
+char *DecodeBase32(const char *, size_t, const char *, size_t, size_t *);
 char *EncodeBase64(const char *, size_t, size_t *);
 char *DecodeBase64(const char *, size_t, size_t *);
 
diff --git a/tool/net/lfuncs.c b/tool/net/lfuncs.c
index a701102ae26f..f525e6f19967 100644
--- a/tool/net/lfuncs.c
+++ b/tool/net/lfuncs.c
@@ -605,21 +605,30 @@ int LuaEncodeLatin1(lua_State *L) {
   }
 }
 
-int LuaEncodeBase32(lua_State *L) {
+dontinline int LuaBase32Impl(lua_State *L,
+    char *B32(const char *, size_t, const char *, size_t, size_t *)) {
   char *p;
   size_t sl, al; // source/output and alphabet lengths
   const char *s = luaL_checklstring(L, 1, &sl);
   // use an empty string, as EncodeBase32 provides a default value
   const char *a = luaL_optlstring(L, 2, "", &al);
-  if (al & (al - 1) || al > 128 || al == 1)
+  if (!IS2POW(al) || al > 128 || al == 1)
     return luaL_error(L, "alphabet length is not a power of 2 in range 2..128");
-  if (!(p = EncodeBase32(s, sl, a, al, &sl)))
+  if (!(p = B32(s, sl, a, al, &sl)))
     return luaL_error(L, "out of memory");
   lua_pushlstring(L, p, sl);
   free(p);
   return 1;
 }
 
+int LuaEncodeBase32(lua_State *L) {
+  return LuaBase32Impl(L, EncodeBase32);
+}
+
+int LuaDecodeBase32(lua_State *L) {
+  return LuaBase32Impl(L, DecodeBase32);
+}
+
 int LuaEncodeHex(lua_State *L) {
   char *p;
   size_t n;