Module Netasn1

module Netasn1: sig .. end

ASN.1 support functions

exception Out_of_range

exception Parse_error of int

Byte position in string

module Type_name: sig .. end

module Value: sig .. end

val decode_ber : ?pos:int -> ?len:int -> string -> int * Value.value

Decodes a BER-encoded ASN.1 value. Note that DER is a subset of BER, and can also be decoded.

pos and len may select a substring for the decoder. By default, pos=0, and len as large as necessary to reach to the end of the string.

The function returns the number of interpreted bytes, and the value. It is not considered as an error if less than len bytes are consumed.

The returned value represents implicitly tagged values as Tagptr(class,tag,pc,pos,len). pos and len denote the substring containting the contents. Use Netasn1.decode_ber_contents to further decode the value. You can use Tag to put the decoded value back into the tree.

val decode_ber_contents : ?pos:int ->
       ?len:int ->
       ?indefinite:bool ->
       string ->
       Value.pc -> Type_name.type_name -> int * Value.value

Decodes the BER-encoded contents of a data field. The contents are assumed to have the type denoted by type_name.

pos and len may select a substring for the decoder. By default, pos=0, and len as large as necessary to reach to the end of the string.

If indefinite, the extent of the contents region is considered as indefinite, and the special end marker is required. This is only allowed when pc = Constructed.

The function returns the number of interpreted bytes, and the value. It is not considered as an error if less than len bytes are consumed.

You need to use this function to recursively decode tagged values. If you get a Tagptr(class,tag,pc,s,pos,len) value, it depends on the kind of the tag how to proceed:

For explicit tags just invoke Netasn1.decode_ber again with the given pos and len parameters.
For implicit tags you need to know the type of the field. Now call Netasn1.decode_ber_contents with the right type name.

The BER encoding doesn't include whether the tag is implicit or explicit, so the decode cannot do by itself the right thing here.

val decode_ber_length : ?pos:int -> ?len:int -> string -> int

Like decode_ber, but returns only the length.

This function skips many consistency checks.

val decode_ber_header : ?pos:int ->
       ?len:int ->
       ?skip_length_check:bool ->
       string -> int * Value.tag_class * Value.pc * int * int option

let (hdr_len, tc, pc, tag, len_opt) = decode_ber_header s: Decodes only the header:

hdr_len will be the length of the header in bytes
tc is the tag class
pc whether primitive or constructed
tag is the numeric tag value
len_opt is the length field, or None if the header selects indefinite length

If skip_length_check is set, the function does not check whether the string is long enough to hold the whole data part.

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