extdesc Struct Reference

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Detailed Description

An extension descriptor.

The extension block is structured thustly:

• <.................len.......................>
• <..headlen.><..........paylen...............>
• +-----------+-------------------------------+
• | header | extension payload |
• +-----------+-------------------------------+
• ^ ^
• base payload

The "<headlen>" part is simply "<len>" - "<paylen>" so it is not stored. Likewise, we store only the beginning of the payload, the base can be computed if needed.

All those pointers refer DIRECTLY to the message we received, so naturally one MUST NOT alter the data we can read or we would corrupt the messages before forwarding them.

There is a slight complication introduced with GGEP extensions, since the data there can be COBS encoded, and even deflated. Therefore, reading directly data from ext_phys_payload could yield compressed data, not something really usable.

Therefore, the extension structure is mostly private, and routines are provided to access the data. Decompression and decoding of COBS is lazily performed when they wish to access the extension data.

The ext_phys_xxx fields refer to the physical information about the extension. The ext_xxx() routines allow access to the virtual information after decompression and COBS decoding. Naturally, if the extension is not compressed nor COBS-encoded, the ext_xxx() routine will return the physical data.

The structure here refers to the opaque data that is dynamically allocated each time a new extension is found.

Data Fields
gchar *	ext_phys_payload
	Start of payload buffer.
gchar *	ext_payload
	"virtual" payload
guint16	ext_phys_len
	Extension length (header + payload).
guint16	ext_phys_paylen
	Extension payload length.
guint16	ext_paylen
	"virtual" payload length
guint16	ext_rpaylen
	Length of buffer for "virtual" payload.
union {
struct {
gboolean   extu_cobs
gboolean   extu_deflate
const gchar *   extu_id
}   extu_ggep
}	ext_u

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Field Documentation

guint16 extdesc::ext_paylen

"virtual" payload length

gchar* extdesc::ext_payload

"virtual" payload

guint16 extdesc::ext_phys_len

Extension length (header + payload).

guint16 extdesc::ext_phys_paylen

Extension payload length.

gchar* extdesc::ext_phys_payload

Start of payload buffer.

guint16 extdesc::ext_rpaylen

Length of buffer for "virtual" payload.

union { ... } extdesc::ext_u

gboolean extdesc::extu_cobs

Payload is COBS-encoded.

gboolean extdesc::extu_deflate

Payload is deflated.

struct { ... } extdesc::extu_ggep

const gchar* extdesc::extu_id

Extension ID.

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The documentation for this struct was generated from the following file:

• extensions.c

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