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In the parsing of a value assignment, such as:
value INTEGER ::= 42
there is call to a function called lookahead_assignment/1 that
will ensure that the sequence of tokens that follows the value
is a valid assignment. The problem is that if the next assignment
is a value assignment, that too will look ahead to the next
assignment. That means that the complexity will be quadratic
if there are many value assignments following each other.
The reason for the test in the first place is unclear; my guess
is that it was an attempt to provide better error reporting.
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Errors were reported using a throw like this:
throw({asn1_error,{get_line(hd(Tokens)),get(asn1_module),
[got,get_token(hd(Tokens)),expected,typereference]}}).
The attempt to tell the user what was expected was often mis-leading.
It is time-consuming and non-trival to provide correct information
of what is expected. Therefore, we will not even try. Instead we will
spend more effort to report the token where the error was discovered.
We will replace each throw with a function call:
parse_error(Tokens).
Also add the syntax_SUITE test suite to test error reporting and to
cover all error reporting code. Remove the old c_syntax/1 test case.
Also remove all out-commented code.
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Responsibilities for parse error handling were split between
asn1ct and asn1ct_parser2 in a confusing way. Let asn1ct_parser2
return structured_error tuples in the same way as the check
pass.
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Most uses of 'catch' are not necessary. For example,
parse_or/2 is typically called like this:
case catch parse_or(Tokens, Flist) of
{'EXIT',Reason} ->
exit(Reason);
{asn1_error,_}=AsnErr ->
throw(AsnErr);
Result ->
Result
end.
Since {asn1_error,_} is always thrown (never returned) and
a successful is always returned (never thrown), the 'case' and
the 'catch' are not necessary. The code can be simplified too:
parse_or(Tokens, Flist)
In a few cases, we will need to replace the 'catch' with
'try'...'catch'.
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Use try...catch instead of catch.
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The first position in a token tuple is always an atom, the second
the line number. The code tested the third position.
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In a future commit, we want to tighten what we catch. Therefore,
legitimate parsing errors should always throw a controlled exception,
instead of arbitrarily crashing.
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The parse_Type/1 calls various type parse functions. Most of those
functions return a #type record, but not all of them. If a #type{}
record is not returned, parse_Type/1 will wrap the return value in a
We can simplify the code in parse_Type/1 if we make sure that the
type parsing functions called by parse_Type/1 always return
a #type{} record.
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The TypeFromObject and ValueSetFromObjects grammar productions cannot
be distinguished by the parser without the help of type information
(which the parser does not have). Since the parser attempts to
parse TypeFromObject before ValueSetFromObjects, the parsing of
ValueSetFromObjects will always fail.
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To keep the error reporting code in asn1ct_parser2 simple, we
only want to handle pure syntactic errors. Therefore, move the check
that UNIQUE and DEFAULT are not applied to the same field to
asn1ct_check.
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The internal representation for constraints (and object sets)
as produced by the parser was awkward, making further processing
convoluted. Here follows some examples of the old representation
for INTEGER constraints.
The constraint 1..2 is represented as:
{'ValueRange',{1,2}}
If we extend the constraint like this:
1..2, ...,
or like this:
1..2, ..., 3
the representation would be:
{{'ValueRange',{1,2}},[]}
and
{{'ValueRange',{1,2}},{'SingleValue',3}}
respectively. Note that the pattern {A,B} will match all these
constraints.
When combining constraints using set operators:
1..2 | 3..4 ^ 5..6
the representation will no longer be a tuple but a list:
[{'ValueRange',{1..2}} union
{'ValueRange',{3..4}} intersection
{'ValueRange',{5..6}}]
The parse has full knowledge of the operator precedence; unfortunately,
the following pass (asn1ct_check) must also have the same knowledge
in order to correctly evaluate the constraints.
If we would change the order of the evaulation with round brackets:
(1..2 | 3..4) ^ 5..6
there would be a nested listed in the representation:
[[{'ValueRange',{1..2}} union {'ValueRange',{3..4}}]
intersection {'ValueRange',{5..6}}]
We will change the representation to make it more explicit.
At the outer level, a constraint is always represented as
{element_set,Root,Extension}
Extension will be 'none' if there is no extension, and 'empty' if
there is an empty extension. Root may also be 'empty' in an object set
if there are no objects in the root. Thus the constraints:
1..2
1..2, ...
1..2, ..., 3
will be represented as:
{element_set,{'ValueRange',{1,2}},none}
{element_set,{'ValueRange',{1,2}},empty}
{element_set,{'ValueRange',{1,2}},{'SingleValue',3}}
We will change the set operators too. This constraint:
1..2 | 3..4 ^ 5..6
will be represented as:
{element_set,
{union,
{'ValueRange',{1,2}},
{intersection,
{'ValueRange',{3,4}},
{'ValueRange',{5,6}}},
none}}
which is trivial to understand and evaluate. Similarly:
(1..2 | 3..4) ^ 5..6
will be represented as:
{element_set,
{intersection,
{union,{'ValueRange',{1,2}},{'ValueRange',{3,4}}},
{'ValueRange',{5,6}}},
none}
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The parser handled the builtin ABSTRACT-SYNTAX and TYPE-IDENTIFIER
classes specially, which caused problems. It turns out that there
is no longer any need to handle those classes specially.
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Before classes were fully implemented, there was support for
ABSTRACT-SYNTAX and TYPE-IDENTIFIER. Some of that code is still
there and is no longer used. Get rid of it and correct comments.
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If we want construct an #'Externaltypereference'{} from
a #classdef{} record, we will need the module name.
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The only remaining use of #identifier{} in asn1ct_check was in a
temporary packaging of a value that would be ultimately be put
into #valuedef{}.
Therefore we can eliminate that last usage but putting the value
directly into a #valuedef{} and we can move the record definition
into asn1ct_parser2.
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When parsing ASN.1, certain constructs can only be understood in
the full context of the entire ASN.1 module.
For instance, the value following ID in this simplified excerpt
from MTSAbstractService88:
administration-88 PORT ::= {
ID {id-pt-administration 88}
}
the value following "ID" can be interpreted either as value
for:
SEQUENCE {
id-pt-administration INTEGER
}
or as an OBJECT IDENTIFIER.
Our ASN.1 parser assumes that a SEQUENCE is meant, and if that
later turns out to be wrong, the SEQUENCE value is rewritten to
an OBJECT IDENTIFIER. The problem is that at the time of the
rewrite, we no longer know in which ASN.1 module id-pt-administration
was defined in, and we have to use the module name in the state{}
record. Unfortunately, the module name in the state{} record may
not always be correct.
While there are attempts in the code to keep the module name
up-to-date when checking imported types, it is not done consistently,
and it seems to be a difficult and error-prone task to attempt
to make it consistent.
A safer and less error-prone approach is to make sure that we
don't lose the module name while parsing. To make it clear what
we are doing, we will introduce a new #seqtag{} record that
are used for tags in SEQUENCE values. The name is based on its
primary use. The record also contains the module in case it happens
to be an OBJECT IDENTIFIER.
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EXPORTS ALL is the same as leaving out the EXPORTS statement.
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Apart from cleanliness, the test suite runs many tests cases in
parallel, so it never hurts to reduce the memory pressure.
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The record #constraint{} is almost unused outside of the parser
except for two places in asn1ct_check.
The only correct usage of the record is in instance_of_constraints/2.
Eliminate that usage by updating the parser to pass that constraint
in the same way as all other constraints.
In check_integer_range/2, the record is used incorrectly. A
constraint for an integer will never be a list of #constraint{}
records. Therefore, the list comprehension will always produce
an empty list, and check_constr/2 will not actually check anything
(which is kind of lucky, since the 'ValueRange' range constraint
is incorrectly written - the lower and upper bounds should be in
a tuple).
For now, we will not attempt to actually start validating integer
ranges. Firstly (obviously) we will need to be sure that we
correctly handles all forms of constraints, and secondly we will
need to consider whether we need to produce a warning rather than an
error for compatibility reasons.
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The record #typereference{} is only used internally within
the asn1ct_parser2 module (the parser translates it to
an #'Externaltypereference{} record).
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UNION and "|" are synonyms, as are INTERSECTION and "^". Use the same
parsing code for the synonyms.
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- Refactor and clean up asn1_db process
- Remove unused stop function in asn1ct.erl
- Remove infinite loop possibilites in asn1ct_check.erl
- test/1,2,3 now run in separate process
- Update documentation for new test options
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added.
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