Expand description
§Debugging
To debug parsing errors, the debug feature can be used to print any error on stderr:
$ ./fail_debug
asn1_rs::asn1_types::sequence::Sequence ↯ Parsing failed at location:
00000000 30 81 04 00 00 0�...
asn1_rs::asn1_types::sequence::Sequence ↯ T::from_der failed: Parsing requires 2 bytes/chars
In the above example, the parser tries to read a Sequence but input is incomplete (missing at least 2 bytes).
The debug feature will print errors. To add the full trace of all parsing functions, use the trace feature:
$ ./fail_trace
u32 ⤷ T::from_der
u32 ⤷ input (len=3, type=asn1_rs::asn1_types::any::Any)
u32 ⤶ Parsed 3 bytes, 0 remaining
u32 ⤷ Conversion to uint
u32 ↯ T::from_der failed: Parsing Error: UnexpectedTag { expected: Some(Tag(2)), actual: Tag(1) }
bool ↯ T::from_der failed: Parsing Error: DerConstraintFailed(InvalidBoolean)
In this example, the parser tries to read an u32. It is first read as Any with sucess, however the conversion to u32 fails because of a wrong tag. See below for details on how to interpret output.
Note that the trace feature is very verbose, and can generate a huge amount of logs on large inputs.
§Interpretating output
When interpreting the trace output, knowing how asn1-rs works is useful. For most types, the following operations are done when parsing type T:
- first, the object is parsed as
Any: this is a very quick step, header is parsed, and object length is tested - next, DER constraint are tested for type
T(if parsing DER) - finally, object is converted using
T::try_from(any). Other type-depdendant checks are done during this step.
§Examples and
When writing a crate, the feature can be activated without changing the Cargo.toml file.
For example, if you want to run example/print-cert with trace enabled:
$ cargo run --features=asn1-rs/trace --example=print-cert -- ./assets/certificate.der