tools: Add a quoted-printable encoding function.

* tools/mime-maker.c (mime_maker_qp_encode): New.
* tools/t-mime-maker.c: New.
* tools/Makefile.am (TESTS): New.
(module_tests): Add the first test.

tools/Makefile.am

@@ -51,6 +51,12 @@ gpg-wks-client-w32info.o     : gpg-wks-client.w32-manifest \
 
 endif
 
+if DISABLE_TESTS
+TESTS =
+else
+TESTS = $(module_tests)
+endif
+
 AM_CFLAGS = $(LIBGCRYPT_CFLAGS) $(GPG_ERROR_CFLAGS) $(LIBASSUAN_CFLAGS)
 
 sbin_SCRIPTS = addgnupghome applygnupgdefaults
@@ -76,7 +82,7 @@ if !HAVE_W32_SYSTEM
 libexec_PROGRAMS += gpg-auth
 endif
 
-noinst_PROGRAMS = clean-sat make-dns-cert
+noinst_PROGRAMS = clean-sat make-dns-cert $(module_tests)
 
 if BUILD_GPGTAR
   bin_PROGRAMS += gpgtar
@@ -216,6 +222,24 @@ gpg_auth_LDADD = $(common_libs) \
                  $(GPG_ERROR_LIBS) \
                  $(LIBINTL) $(NETLIBS) $(LIBICONV)
 
+#
+# Module tests
+#
+module_tests = t-mime-maker
+
+t_extra_src =
+t_common_cflags = $(LIBGCRYPT_CFLAGS) $(GPG_ERROR_CFLAGS) $(INCICONV)
+t_common_ldadd  = $(libcommon) \
+		  $(LIBGCRYPT_LIBS) $(GPG_ERROR_LIBS) \
+                  $(LIBINTL) $(LIBICONV)
+
+t_mime_maker_SOURCES = t-mime-maker.c \
+		       rfc822parse.c rfc822parse.h \
+		       mime-maker.c mime-maker.h $(t_extra_src)
+t_mime_maker_LDADD = $(t_common_ldadd)
+
+
+
 # Instead of a symlink we install a simple wrapper script for the new
 # gpg-wks-client location.  We assume bin is a sibling of libexec.
 install-exec-local:

tools/mime-maker.c

@@ -1,5 +1,5 @@
 /* mime-maker.c - Create MIME structures
- * Copyright (C) 2016 g10 Code GmbH
+ * Copyright (C) 2016, 2025 g10 Code GmbH
  * Copyright (C) 2016 Bundesamt für Sicherheit in der Informationstechnik
  *
  * This file is part of GnuPG.
@@ -16,6 +16,7 @@
  *
  * You should have received a copy of the GNU Lesser General Public License
  * along with this program; if not, see <https://www.gnu.org/licenses/>.
+ * SPDX-License-Identifier: LGPL-2.1-or-later
  */
 
 #include <config.h>
@@ -348,6 +349,89 @@ add_header (part_t part, const char *name, const char *value)
 }
 
 
+/* Return a new string which is QP encoded.  Also encodes the F in a
+ * leading "From " and a line with a single dot.  Return NULL and sets
+ * ERRNO on error.  */
+char *
+mime_maker_qp_encode (const char *string)
+{
+  /* Check whether the current character is followed by a line ending.
+   * The end of the string also considered a line ending. */
+#define nextislf(a) (*a && ((a[1] == '\r' && a[2] == '\n') \
+                            || a[1] == '\n' || !a[1]))
+
+#define tohex(n) ((n) < 10 ? ((n) + '0') : (((n) - 10) + 'A'))
+
+  char *buffer, *p;
+  const unsigned char *s;
+  int lastwaslf;
+  size_t n;
+
+  /* Count the required length.  */
+  for (lastwaslf=1, n=0, s = string; *s; s++)
+    {
+      if (*s == '.' && nextislf (s))
+        {
+          n += 3;
+        }
+      else if (!strncmp (s, "From ", 5))
+        {
+          n += 3 + 4;
+          s += 4;
+        }
+      else if (*s == '=')
+        {
+          n += 3;
+        }
+      else if (strchr ("\r\n\t", *s) || (*s >= 0x20 && *s <= 0x7e))
+        n++;
+      else
+        n += 3;
+    }
+  n++;
+
+  /* Now encode.  */
+  p = buffer = xtrymalloc (n);
+  if (!buffer)
+    return NULL;
+  for (lastwaslf=1, s = string; *s; s++)
+    {
+      if (lastwaslf && *s == '.' && nextislf (s))
+        {
+          *p++ = '=';
+          *p++ = '2';
+          *p++ = 'E';
+        }
+      else if (lastwaslf && !strncmp (s, "From ", 5))
+        {
+          memcpy (p, "=46rom ", 7);
+          p += 7;
+          s += 4;
+        }
+      else if (*s == '=')
+        {
+          *p++ = '=';
+          *p++ = '3';
+          *p++ = 'D';
+        }
+      else if (strchr ("\r\n\t", *s) || (*s >= 0x20 && *s <= 0x7e))
+        *p++ = *s;
+      else
+        {
+          *p++ = '=';
+          *p++ = tohex ((*s>>4)&15);
+          *p++ = tohex (*s&15);
+        }
+      lastwaslf = (*s == '\n');
+    }
+  *p = 0;
+
+  return buffer;
+#undef tohex
+#undef nextislf
+}
+
+
 /* Add a header with NAME and VALUE to the current mail.  A LF in the
  * VALUE will be handled automagically.  If NULL is used for VALUE it
  * is expected that the NAME has the format "NAME=VALUE" and VALUE is

tools/mime-maker.h

@@ -31,6 +31,7 @@ void mime_maker_set_verbose (mime_maker_t ctx, int level);
 
 void mime_maker_dump_tree (mime_maker_t ctx);
 
+char *mime_maker_qp_encode (const char *string);
 gpg_error_t mime_maker_add_header (mime_maker_t ctx,
                                    const char *name, const char *value);
 gpg_error_t mime_maker_add_body (mime_maker_t ctx, const char *string);

tools/t-mime-maker.c

@@ -0,0 +1,116 @@
+/* t-mime-maker.c - Module test for mime-maker.c
+ * Copyright (C) 2025 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 Lesser 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 <https://www.gnu.org/licenses/>.
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ */
+
+#include <config.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <errno.h>
+
+#include "../common/util.h"
+#include "../common/init.h"
+#include "mime-maker.h"
+
+
+static int verbose;
+
+
+
+static void
+test_qp_encode (void)
+{
+  static struct
+  {
+    const char *plain;
+    const char *encoded;
+  } samples[] =
+    {
+      { "",
+        ""
+      },{
+        "From someone\n"
+        " I received this mail\n",
+        "=46rom someone\n"
+        " I received this mail\n"
+      },{
+        " From someone\n",
+        " From someone\n"
+      },{
+        "Foo\n"
+        ".\n",
+        "Foo\n"
+        "=2E\n"
+      },{
+        "Foo\n"
+        ".",
+        "Foo\n"
+        "=2E"
+      },{
+        "Hello ÄÖܧäöüß my dear umlauts",
+        "Hello =C3=84=C3=96=C3=9C=C2=A7=C3=A4=C3=B6=C3=BC=C3=9F "
+        "my dear umlauts"
+      },{
+        "👀\tⒶ",
+        "=F0=9F=91=80\t=E2=92=B6"
+      }
+    };
+  int idx;
+  char *result;
+  int oops = 0;
+
+  for (idx=0; idx < DIM (samples); idx++)
+    {
+      result = mime_maker_qp_encode (samples[idx].plain);
+      if (!result)
+        {
+          log_error ("%s:test %d: error: %s\n",
+                     __func__, idx, strerror (errno));
+          exit (1);
+        }
+      if (strcmp (samples[idx].encoded, result))
+        {
+          log_error ("%s:test %d: error\nwant ===>%s<===\n got ===>%s<===\n",
+                     __func__, idx, samples[idx].plain, result);
+          oops = 1;
+        }
+    }
+
+  if (oops)
+    exit (1);
+}
+
+
+int
+main (int argc, char **argv)
+{
+  log_set_prefix ("t-mime-maker", GPGRT_LOG_WITH_PREFIX);
+  init_common_subsystems (&argc, &argv);
+
+  if (argc)
+    { argc--; argv++; }
+  if (argc && !strcmp (argv[0], "--verbose"))
+    {
+      verbose = 1;
+      argc--; argv++;
+    }
+
+  test_qp_encode ();
+
+  return 0;
+}