asn1Coding(1) a CHOICE

[Ivan Shmakov]

>>>>> Nikos Mavrogiannopoulos <address@hidden> writes:
>>>>> On 10/04/2012 08:09 AM, Ivan Shmakov wrote:

[…]

 >> Also, the documentation doesn't seem to mention on how to encode a
 >> CHOICE with asn1Coding(1) [3], and just omitting the “unused”
 >> element(s) leads to a failure.

 > I also noticed.  The asn1Coding tool is pretty primitive and needs a
 > lot of changes to be of any use.

        Fortunately, it's only a minor documentation issue, as the
        asn1Coding documentation fails to mention that may use
        “'' field-name” to choose a field from a CHOICE.

        It follows from the fragments of the asn1_write_value ()
        documentation and the asn1Coding.c source quoted below.

--cut: http://www.gnu.org/software/libtasn1/manual/libtasn1.html --
    CHOICE: if NAME indicates a choice type, VALUE must specify one of
    the alternatives with a null terminated string.  LEN != 0.  Using
    “pkix.asn”:

    result
        = asn1_write_value (cert,
                            "certificate1.tbsCertificate.subject",
                            "rdnSequence", 1);
--cut: http://www.gnu.org/software/libtasn1/manual/libtasn1.html --

$ nl -ba < asn1Coding.c 
…
    69  static int
    70  readAssignment (FILE * file, char *varName, char *value)
    71  {
…
    78    if (!strcmp (varName, "''"))
    79      varName[0] = 0;
    80  
    81    ret = fscanf (file, "%s", value);
    82    if (ret == EOF)
    83      return ASSIGNMENT_ERROR;
    84  
    85    return ASSIGNMENT_SUCCESS;
    86  }
…
$ 

        Thus:

$ asn1Coding -o /dev/null asn.1 \
      <(printf %s\\n 'x Example.Foo' "'' bar" 'bar 42') 
Parse: done.

var=x, value=Example.Foo
var=, value=bar
var=bar, value=42

name:NULL  type:CHOICE
  name:bar  type:INTEGER  value:0x2a

Coding: SUCCESS

-----------------
Number of bytes=3
02 01 2a 
-----------------

OutputFile=/dev/null

Writing: done.
$ cat < asn.1 
Example { } DEFINITIONS EXPLICIT TAGS ::=

BEGIN

Null ::= NULL

Foo ::= CHOICE {
    bar     INTEGER,
    baz     GeneralString
}

END
$ 

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