core: Add a base 64 decoder.

* src/b64dec.c: New. Taken from gnupg.  Prefix function names with
_gpgme_ and change to use standard C malloc functions.
* src/util.h.h (struct b64state): New.
* src/Makefile.am (main_sources): Add file.

--

The file b64dec.c has been taken from gnupg commit
e430ff6ad0b7dcfcebd92b825dd5168205447ff3

Signed-off-by: Werner Koch <wk@gnupg.org>

src/Makefile.am

@@ -74,7 +74,7 @@ endif
 # right linking order with libtool, as the non-installed version has
 # unresolved symbols to the thread module.
 main_sources =								\
-	util.h conversion.c get-env.c context.h ops.h		        \
+	util.h conversion.c b64dec.c get-env.c context.h ops.h		\
 	parsetlv.c parsetlv.h                                           \
 	data.h data.c data-fd.c data-stream.c data-mem.c data-user.c	\
 	data-compat.c data-identify.c					\

src/b64dec.c

@@ -0,0 +1,251 @@
+/* b64dec.c - Simple Base64 decoder.
+ * Copyright (C) 2008, 2011 Free Software Foundation, Inc.
+ * Copyright (C) 2008, 2011, 2016 g10 Code GmbH
+ *
+ * This file is part of GnuPG.
+ *
+ * This file is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as
+ * published by the Free Software Foundation; either version 2.1 of
+ * the License, or (at your option) any later version.
+ *
+ * This file is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <config.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <assert.h>
+
+#include "gpgme.h"
+#include "util.h"
+
+
+/* The reverse base-64 list used for base-64 decoding. */
+static unsigned char const asctobin[128] =
+  {
+    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+    0xff, 0xff, 0xff, 0x3e, 0xff, 0xff, 0xff, 0x3f,
+    0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x3b,
+    0x3c, 0x3d, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+    0xff, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06,
+    0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e,
+    0x0f, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16,
+    0x17, 0x18, 0x19, 0xff, 0xff, 0xff, 0xff, 0xff,
+    0xff, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f, 0x20,
+    0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28,
+    0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f, 0x30,
+    0x31, 0x32, 0x33, 0xff, 0xff, 0xff, 0xff, 0xff
+  };
+
+enum decoder_states
+  {
+    s_init, s_idle, s_lfseen, s_beginseen, s_waitheader, s_waitblank, s_begin,
+    s_b64_0, s_b64_1, s_b64_2, s_b64_3,
+    s_waitendtitle, s_waitend
+  };
+
+
+
+/* Initialize the context for the base64 decoder.  If TITLE is NULL a
+   plain base64 decoding is done.  If it is the empty string the
+   decoder will skip everything until a "-----BEGIN " line has been
+   seen, decoding ends at a "----END " line.  */
+gpg_error_t
+_gpgme_b64dec_start (struct b64state *state, const char *title)
+{
+  memset (state, 0, sizeof *state);
+  if (title)
+    {
+      state->title = strdup (title);
+      if (!state->title)
+        state->lasterr = gpg_error_from_syserror ();
+      else
+        state->idx = s_init;
+    }
+  else
+    state->idx = s_b64_0;
+  return state->lasterr;
+}
+
+
+/* Do in-place decoding of base-64 data of LENGTH in BUFFER.  Stores the
+   new length of the buffer at R_NBYTES. */
+gpg_error_t
+_gpgme_b64dec_proc (struct b64state *state, void *buffer, size_t length,
+                    size_t *r_nbytes)
+{
+  enum decoder_states ds = state->idx;
+  unsigned char val = state->radbuf[0];
+  int pos = state->quad_count;
+  char *d, *s;
+
+  if (state->lasterr)
+    return state->lasterr;
+
+  if (state->stop_seen)
+    {
+      *r_nbytes = 0;
+      state->lasterr = gpg_error (GPG_ERR_EOF);
+      free (state->title);
+      state->title = NULL;
+      return state->lasterr;
+    }
+
+  for (s=d=buffer; length && !state->stop_seen; length--, s++)
+    {
+    again:
+      switch (ds)
+        {
+        case s_idle:
+          if (*s == '\n')
+            {
+              ds = s_lfseen;
+              pos = 0;
+            }
+          break;
+        case s_init:
+          ds = s_lfseen;
+        case s_lfseen:
+          if (*s != "-----BEGIN "[pos])
+            {
+              ds = s_idle;
+              goto again;
+            }
+          else if (pos == 10)
+            {
+              pos = 0;
+              ds = s_beginseen;
+            }
+          else
+            pos++;
+          break;
+        case s_beginseen:
+          if (*s != "PGP "[pos])
+            ds = s_begin; /* Not a PGP armor.  */
+          else if (pos == 3)
+            ds = s_waitheader;
+          else
+            pos++;
+          break;
+        case s_waitheader:
+          if (*s == '\n')
+            ds = s_waitblank;
+          break;
+        case s_waitblank:
+          if (*s == '\n')
+            ds = s_b64_0; /* blank line found.  */
+          else if (*s == ' ' || *s == '\r' || *s == '\t')
+            ; /* Ignore spaces. */
+          else
+            {
+              /* Armor header line.  Note that we don't care that our
+               * FSM accepts a header prefixed with spaces.  */
+              ds = s_waitheader; /* Wait for next header.  */
+            }
+          break;
+        case s_begin:
+          if (*s == '\n')
+            ds = s_b64_0;
+          break;
+        case s_b64_0:
+        case s_b64_1:
+        case s_b64_2:
+        case s_b64_3:
+          {
+            int c;
+
+            if (*s == '-' && state->title)
+              {
+                /* Not a valid Base64 character: assume end
+                   header.  */
+                ds = s_waitend;
+              }
+            else if (*s == '=')
+              {
+                /* Pad character: stop */
+                if (ds == s_b64_1)
+                  *d++ = val;
+                ds = state->title? s_waitendtitle : s_waitend;
+              }
+            else if (*s == '\n' || *s == ' ' || *s == '\r' || *s == '\t')
+              ; /* Skip white spaces. */
+            else if ( (*s & 0x80)
+                      || (c = asctobin[*(unsigned char *)s]) == 255)
+              {
+                /* Skip invalid encodings.  */
+                state->invalid_encoding = 1;
+              }
+            else if (ds == s_b64_0)
+              {
+                val = c << 2;
+                ds = s_b64_1;
+              }
+            else if (ds == s_b64_1)
+              {
+                val |= (c>>4)&3;
+                *d++ = val;
+                val = (c<<4)&0xf0;
+                ds = s_b64_2;
+              }
+            else if (ds == s_b64_2)
+              {
+                val |= (c>>2)&15;
+                *d++ = val;
+                val = (c<<6)&0xc0;
+                ds = s_b64_3;
+              }
+            else
+              {
+                val |= c&0x3f;
+                *d++ = val;
+                ds = s_b64_0;
+              }
+          }
+          break;
+        case s_waitendtitle:
+          if (*s == '-')
+            ds = s_waitend;
+          break;
+        case s_waitend:
+          if ( *s == '\n')
+            state->stop_seen = 1;
+          break;
+        default:
+          assert (!"invalid state");
+        }
+    }
+
+
+  state->idx = ds;
+  state->radbuf[0] = val;
+  state->quad_count = pos;
+  *r_nbytes = (d -(char*) buffer);
+  return 0;
+}
+
+
+/* This function needs to be called before releasing the decoder
+   state.  It may return an error code in case an encoding error has
+   been found during decoding. */
+gpg_error_t
+_gpgme_b64dec_finish (struct b64state *state)
+{
+  if (state->lasterr)
+    return state->lasterr;
+
+  free (state->title);
+  state->title = NULL;
+  return state->invalid_encoding? gpg_error(GPG_ERR_BAD_DATA): 0;
+}

src/util.h

@@ -146,6 +146,26 @@ gpgme_error_t _gpgme_map_gnupg_error (char *err);
 
 int _gpgme_map_pk_algo (int algo, gpgme_protocol_t protocol);
 
+
+/*-- b64dec.c --*/
+
+struct b64state
+{
+  int idx;
+  int quad_count;
+  char *title;
+  unsigned char radbuf[4];
+  int stop_seen:1;
+  int invalid_encoding:1;
+  gpg_error_t lasterr;
+};
+
+gpg_error_t _gpgme_b64dec_start (struct b64state *state, const char *title);
+gpg_error_t _gpgme_b64dec_proc (struct b64state *state,
+                                void *buffer, size_t length, size_t *r_nbytes);
+gpg_error_t _gpgme_b64dec_finish (struct b64state *state);
+
+
 
 /* Retrieve the environment variable NAME and return a copy of it in a
    malloc()'ed buffer in *VALUE.  If the environment variable is not