Re: [PATCH] basenc: Paddingless input/output for base64url

[Michael Cook]

+          int to_write = BASE_LENGTH (sum);
+          base_encode (inbuf, sum, outbuf, to_write);
+          if (without_padding)
+          {
+            while (*(outbuf+to_write-1) == '=')
+            {
+                --to_write;
+            }
+          }

Probably should make sure `to_write` stays positive:

            while (to_write > 0 && outbuf[to_write - 1] == '=')
            {
                --to_write;
            }


On Tue, Aug 23, 2022 at 4:46 AM Imre Rad <imrer@google.com> wrote:

> * 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.
> * tests/misc/basenc-padding.sh (new test):
> Tests covering the new feature.
> ---
>  src/basenc.c                 | 48 ++++++++++++++++----
>  tests/local.mk               |  1 +
>  tests/misc/basenc-padding.sh | 86 ++++++++++++++++++++++++++++++++++++
>  3 files changed, 127 insertions(+), 8 deletions(-)
>  create mode 100755 tests/misc/basenc-padding.sh
>
> diff --git a/src/basenc.c b/src/basenc.c
> index 04857d59e..9b020eccb 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_OPTION
>  };
>  #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_OPTION},
>    {"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 && inlen == 0) // inlen 0 indicates the final round, see
> do_decode
> +        b = true;
> +    return b;
> +}
>
>  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;
>
> @@ -1122,6 +1149,10 @@ main (int argc, char **argv)
>          break;
>
>  #if BASE_TYPE == 42
> +      case IGNORE_PADDING_OPTION:
> +        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..e3d9d85e2 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/misc/basenc-padding.sh \
>    $(all_root_tests)
>
>  # See tests/factor/create-test.sh.
> diff --git a/tests/misc/basenc-padding.sh b/tests/misc/basenc-padding.sh
> new file mode 100755
> index 000000000..c90f22fa1
> --- /dev/null
> +++ b/tests/misc/basenc-padding.sh
> @@ -0,0 +1,86 @@
> +#!/bin/sh
> +# make sure base64url works fine without paddings
> +
> +# Copyright (C) 2000-2022 Free Software Foundation, Inc.
> +
> +# This program is free software: you can redistribute it and/or modify
> +# it under the terms of the GNU General Public License as published by
> +# the Free Software Foundation, either version 3 of the License, or
> +# (at your option) any later version.
> +
> +# This program is distributed in the hope that it will be useful,
> +# but WITHOUT ANY WARRANTY; without even the implied warranty of
> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> +# GNU General Public License for more details.
> +
> +# You should have received a copy of the GNU General Public License
> +# along with this program.  If not, see <https://www.gnu.org/licenses/>.
> +
> +. "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
> +
> +
> +
> +input='xs?>>>x'
> +
> +# should be fine with wrapped writes
> +b64url_encoded_wo_p="$(echo "$input" | basenc --base64url
> --ignore-padding)"
> +
> +if grep -q "=" <<< "$b64url_encoded_wo_p"; then
> +    echo "Paddings are not supposed to be present"
> +    Exit 1
> +fi
> +
> +
> +# note the 2>&1's, stderr should be clean
> +output="$(echo "$b64url_encoded_wo_p" | basenc --base64url -d
> --ignore-padding 2>&1)"
> +
> +if [ "$input" != "$output" ]; then
> +    echo "Something is wrong without paddings (wrapped writes)"
> +    Exit 1
> +fi
> +
> +# decoding without --ignore-padding
> +output_err="$(echo "$b64url_encoded_wo_p" | basenc --base64url -d 2>&1)"
> +if ! grep -q "invalid input" <<< "$output_err"; then
> +    echo "Decoding without --ignore-padding should still complain"
> +    Exit 1
> +fi
> +
> +# decoding errors anywhere but the last round should still complain,
> even with --ignore-padding
> +known_broken="eHM_Pj4*eAo"
> +output="$(echo "$b64url_encoded_wo_p" | basenc --base64url -d
> --ignore-padding 2>&1)"
> +if ! grep -q "invalid input" <<< "$output_err"; then
> +    echo "Invalid encoding anywhere but the last round should still
> be rejected"
> +    Exit 1
> +fi
> +
> +# should be fine without wrapped writes
> +b64url_encoded_wo_p="$(echo "$input" | basenc --base64url
> --ignore-padding -w0)"
> +
> +# note the 2>&1's, stderr should be clean
> +output="$(echo "$b64url_encoded_wo_p" | basenc --base64url -d
> --ignore-padding 2>&1)"
> +
> +if [ "$input" != "$output" ]; then
> +    echo "Something is wrong without paddings (non-wrapped writes)"
> +    Exit 1
> +fi
> +
> +# should be ok with padding as well
> +b64url_encoded_w_p="$(echo "$input"| basenc --base64url)"
> +
> +# note the 2>&1's, stderr should be clean
> +output="$(echo "$b64url_encoded_w_p" | basenc --base64url -d 2>&1)"
> +
> +if [ "$input" != "$output" ]; then
> +    echo "Something is wrong with paddings"
> +    Exit 1
> +fi
> +
> +if [ "$b64url_encoded_w_p" == "b64url_encoded_wo_p" ]; then
> +   echo "Encoding with and without padding should look different"
> +   Exit 1
> +fi
> +
> +#echo Padding test success
> +
> +Exit 0
> --
> 2.30.2
>
>