asn1_dec.c File Reference

Functions
err_t	snmp_asn1_dec_type (struct pbuf *p, u16_t ofs, u8_t *type)
err_t	snmp_asn1_dec_length (struct pbuf *p, u16_t ofs, u8_t *octets_used, u16_t *length)
err_t	snmp_asn1_dec_u32t (struct pbuf *p, u16_t ofs, u16_t len, u32_t *value)
err_t	snmp_asn1_dec_s32t (struct pbuf *p, u16_t ofs, u16_t len, s32_t *value)
err_t	snmp_asn1_dec_oid (struct pbuf *p, u16_t ofs, u16_t len, struct snmp_obj_id *oid)
err_t	snmp_asn1_dec_raw (struct pbuf *p, u16_t ofs, u16_t len, u16_t raw_len, u8_t *raw)

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Detailed Description

Abstract Syntax Notation One (ISO 8824, 8825) decoding

Todo:

not optimised (yet), favor correctness over speed, favor speed over size

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Function Documentation

err_t snmp_asn1_dec_length	(	struct pbuf *	p,
		u16_t	ofs,
		u8_t *	octets_used,
		u16_t *	length
	)

Decodes length field from incoming pbuf chain into host length.

Parameters:

	p	points to a pbuf holding an ASN1 coded length
	ofs	points to the offset within the pbuf chain of the ASN1 coded length
	octets_used	returns number of octets used by the length code
	length	return host order length, upto 64k

Returns:

ERR_OK if successfull, ERR_ARG if we can't (or won't) decode

Todo:

: do we need to accept inefficient codings with many leading zero's?

err_t snmp_asn1_dec_oid	(	struct pbuf *	p,
		u16_t	ofs,
		u16_t	len,
		struct snmp_obj_id *	oid
	)

Decodes object identifier from incoming message into array of s32_t.

Parameters:

	p	points to a pbuf holding an ASN1 coded object identifier
	ofs	points to the offset within the pbuf chain of the ASN1 coded object identifier
	len	length of the coded object identifier
	oid	return object identifier struct

Returns:

ERR_OK if successfull, ERR_ARG if we can't (or won't) decode

err_t snmp_asn1_dec_raw	(	struct pbuf *	p,
		u16_t	ofs,
		u16_t	len,
		u16_t	raw_len,
		u8_t *	raw
	)

Decodes (copies) raw data (ip-addresses, octet strings, opaque encoding) from incoming message into array.

Parameters:

	p	points to a pbuf holding an ASN1 coded raw data
	ofs	points to the offset within the pbuf chain of the ASN1 coded raw data
	len	length of the coded raw data (zero is valid, e.g. empty string!)
	raw_len	length of the raw return value
	raw	return raw bytes

Returns:

ERR_OK if successfull, ERR_ARG if we can't (or won't) decode

err_t snmp_asn1_dec_s32t	(	struct pbuf *	p,
		u16_t	ofs,
		u16_t	len,
		s32_t *	value
	)

Decodes integer into s32_t.

Parameters:

	p	points to a pbuf holding an ASN1 coded integer
	ofs	points to the offset within the pbuf chain of the ASN1 coded integer
	len	length of the coded integer field
	value	return host order integer

Returns:

ERR_OK if successfull, ERR_ARG if we can't (or won't) decode

Note:

ASN coded integers are _always_ signed!

err_t snmp_asn1_dec_type	(	struct pbuf *	p,
		u16_t	ofs,
		u8_t *	type
	)

Retrieves type field from incoming pbuf chain.

Parameters:

	p	points to a pbuf holding an ASN1 coded type field
	ofs	points to the offset within the pbuf chain of the ASN1 coded type field
	type	return ASN1 type

Returns:

ERR_OK if successfull, ERR_ARG if we can't (or won't) decode

err_t snmp_asn1_dec_u32t	(	struct pbuf *	p,
		u16_t	ofs,
		u16_t	len,
		u32_t *	value
	)

Decodes positive integer (counter, gauge, timeticks) into u32_t.

Parameters:

	p	points to a pbuf holding an ASN1 coded integer
	ofs	points to the offset within the pbuf chain of the ASN1 coded integer
	len	length of the coded integer field
	value	return host order integer

Returns:

ERR_OK if successfull, ERR_ARG if we can't (or won't) decode

Note:

ASN coded integers are _always_ signed. E.g. +0xFFFF is coded as 0x00,0xFF,0xFF. Note the leading sign octet. A positive value of 0xFFFFFFFF is preceded with 0x00 and the length is 5 octets!!

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