[PATCH] basenc: Paddingless input/output for base64url

[Imre Rad]

* src/basenc.c (ignore-padding):
Padding is optional for base64url encoding and many web
services produce and expect payload without padding.
New command line argument (--ignore-padding) for basenc
allows generating paddingless base64url outputs and
you can also use it for decoding without scary
warnings on stderr.
* tests/local.mk (reference to new test):
Reference to the new test.
---
 src/basenc.c   | 50 +++++++++++++++++++++++++++++++++++++++++---------
 tests/local.mk |  1 +
 2 files changed, 42 insertions(+), 9 deletions(-)

diff --git a/src/basenc.c b/src/basenc.c
index 04857d59e..52bd66054 100644
--- a/src/basenc.c
+++ b/src/basenc.c
@@ -68,7 +68,8 @@ enum
   BASE16_OPTION,
   BASE2MSBF_OPTION,
   BASE2LSBF_OPTION,
-  Z85_OPTION
+  Z85_OPTION,
+  IGNORE_PADDING
 };
 #endif

@@ -78,6 +79,7 @@ static struct option const long_options[] =
   {"wrap", required_argument, 0, 'w'},
   {"ignore-garbage", no_argument, 0, 'i'},
 #if BASE_TYPE == 42
+  {"ignore-padding", no_argument, 0, IGNORE_PADDING},
   {"base64",    no_argument, 0, BASE64_OPTION},
   {"base64url", no_argument, 0, BASE64URL_OPTION},
   {"base32",    no_argument, 0, BASE32_OPTION},
@@ -146,6 +148,8 @@ Base%d encode or decode FILE, or standard input, to
standard output.\n\
 "), stdout);
 #if BASE_TYPE == 42
       fputs (_("\
+      --ignore-padding  base64url only: ignore missing padding at
decoding,\n\
+                        don't pad at encoding\n\
       --z85             ascii85-like encoding (ZeroMQ spec:32/Z85);\n\
                         when encoding, input length must be a multiple of
4;\n\
                         when decoding, input length must be a multiple of
5\n\
@@ -335,7 +339,6 @@ base64url_decode_ctx_init_wrapper (struct
base_decode_context *ctx)
   init_inbuf (ctx);
 }

-
 static bool
 base64url_decode_ctx_wrapper (struct base_decode_context *ctx,
                               char const *restrict in, idx_t inlen,
@@ -368,7 +371,16 @@ base64url_decode_ctx_wrapper (struct
base_decode_context *ctx,
   return b;
 }

-
+static bool
+base64url_decode_ctx_wrapper_no_padding (struct base_decode_context *ctx,
+                              char const *restrict in, idx_t inlen,
+                              char *restrict out, idx_t *outlen)
+{
+    bool b = base64url_decode_ctx_wrapper(ctx, in, inlen, out, outlen);
+    if (!b && ctx->i <= 2)
+        b = true;
+    return true;
+}

 static int
 base32_length_wrapper (int len)
@@ -964,7 +976,7 @@ finish_and_exit (FILE *in, char const *infile)
 }

 static _Noreturn void
-do_encode (FILE *in, char const *infile, FILE *out, idx_t wrap_column)
+do_encode (FILE *in, char const *infile, FILE *out, idx_t wrap_column,
bool without_padding)
 {
   idx_t current_column = 0;
   char *inbuf, *outbuf;
@@ -989,9 +1001,17 @@ do_encode (FILE *in, char const *infile, FILE *out,
idx_t wrap_column)
         {
           /* Process input one block at a time.  Note that ENC_BLOCKSIZE
              is sized so that no pad chars will appear in output. */
-          base_encode (inbuf, sum, outbuf, BASE_LENGTH (sum));
+          int to_write = BASE_LENGTH (sum);
+          base_encode (inbuf, sum, outbuf, to_write);
+          if (without_padding)
+          {
+            while (*(outbuf+to_write-1) == '=')
+            {
+                --to_write;
+            }
+          }

-          wrap_write (outbuf, BASE_LENGTH (sum), wrap_column,
+          wrap_write (outbuf, to_write, wrap_column,
                       &current_column, out);
         }
     }
@@ -1084,6 +1104,13 @@ main (int argc, char **argv)
   bool decode = false;
   /* True if we should ignore non-base-alphabetic characters. */
   bool ignore_garbage = false;
+
+  /* True if we should ignore padding (base64url only). */
+#if BASE_TYPE == 42
+  bool o_ignore_padding = false;
+#endif
+  bool ignore_padding = false;
+
   /* Wrap encoded data around the 76th column, by default. */
   idx_t wrap_column = 76;

@@ -1099,7 +1126,7 @@ main (int argc, char **argv)

   atexit (close_stdout);

-  while ((opt = getopt_long (argc, argv, "diw:", long_options, NULL)) !=
-1)
+  while ((opt = getopt_long (argc, argv, "dipw:", long_options, NULL)) !=
-1)
     switch (opt)
       {
       case 'd':
@@ -1122,6 +1149,10 @@ main (int argc, char **argv)
         break;

 #if BASE_TYPE == 42
+      case IGNORE_PADDING:
+        o_ignore_padding = true;
+        break;
+
       case BASE64_OPTION:
       case BASE64URL_OPTION:
       case BASE32_OPTION:
@@ -1155,11 +1186,12 @@ main (int argc, char **argv)
       break;

     case BASE64URL_OPTION:
+      ignore_padding = o_ignore_padding;
       base_length = base64_length_wrapper;
       isbase = isbase64url;
       base_encode = base64url_encode;
       base_decode_ctx_init = base64url_decode_ctx_init_wrapper;
-      base_decode_ctx = base64url_decode_ctx_wrapper;
+      base_decode_ctx = ignore_padding ?
base64url_decode_ctx_wrapper_no_padding : base64url_decode_ctx_wrapper;
       break;

     case BASE32_OPTION:
@@ -1244,5 +1276,5 @@ main (int argc, char **argv)
   if (decode)
     do_decode (input_fh, infile, stdout, ignore_garbage);
   else
-    do_encode (input_fh, infile, stdout, wrap_column);
+    do_encode (input_fh, infile, stdout, wrap_column, ignore_padding);
 }
diff --git a/tests/local.mk b/tests/local.mk
index 0496c2873..a7703998a 100644
--- a/tests/local.mk
+++ b/tests/local.mk
@@ -728,6 +728,7 @@ all_tests = \
   tests/touch/read-only.sh \
   tests/touch/relative.sh \
   tests/touch/trailing-slash.sh \
+  tests/base64url/padding.sh \
   $(all_root_tests)

 # See tests/factor/create-test.sh.
-- 
2.30.2