CCSDS File Delivery Protocol

Conformance Statement for `pkg/cfdp`, CCSDS 727.0-B-5

A1.1 GENERAL INFORMATION

A1.1.1 Identification of PICS

Field	Value
Date of Statement (DD/MM/YYYY)	23/08/2026
PICS Serial Number	ASTRO-CFDP-PICS-001
System Conformance Statement Cross-Reference	This document

A1.1.2 Identification of Implementation Under Test (IUT)

Field	Value
Implementation Name	astro/pkg/cfdp
Implementation Version	See `go.mod` / latest commit on `main`
Special Configuration	None
Other Information	Go library implementing CFDP Part 1. Full PDU codec set, modular and CRC-32 checksums, an abstract Filestore with in-memory and OS-backed implementations, and caller-pumped Class 1 and Class 2 transaction machines. The library owns no goroutines and no clock: timers and retransmission scheduling belong to the caller, matching the shape of `pkg/cop`'s FOP-1.

A1.1.3 Identification of Supplier

Field	Value
Supplier	Ravi Suhag
Contact Point for Queries	GitHub, github.com/ravisuhag/astro
Implementation Name(s) and Version(s)	astro/pkg/cfdp (Go package)
System Name(s)	Astro

A1.1.4 Identification of Specification

Field	Value
Specification	CCSDS 727.0-B-5 (CCSDS File Delivery Protocol, Blue Book, Issue 5, July 2020)
Have any exceptions been required?	Yes [X] No [ ], see A1.6

A1.2 PROTOCOL DATA UNITS

Feature	Reference	Status	Support
Fixed PDU header	clause 5.1.2, table 5-1	M	Y
Version '001'	table 5-1	M	Y: other versions rejected on decode
PDU type: File Directive / File Data	clause 5.1.6	M	Y
Direction flag	table 5-1	M	Y
Transmission mode flag	table 5-1	M	Y: '0' acknowledged, '1' unacknowledged
CRC flag	table 5-1	M	Y
Large File flag	table 5-1	M	Y: widens every FSS field to 64 bits
PDU data field length	table 5-1	M	Y: includes the CRC when present
Segmentation control	table 5-1	M	Y
Length of entity IDs	table 5-1	M	Y: 1 to 8 octets, encoded as width less one
Segment metadata flag	table 5-1	M	Y
Length of transaction sequence number	table 5-1	M	Y: 1 to 8 octets
Variable-width entity IDs	clause 5.1.4	M	Y
LV objects	clause 5.1.8, table 5-2	M	Y
TLV objects	clause 5.1.9, table 5-3	M	Y
File-Size Sensitive fields	clause 5.1.10	M	Y

A1.3 FILE DIRECTIVE PDUs

Feature	Reference	Status	Support
Directive codes	clause 5.2.1.2, table 5-4	M	Y: reserved codes rejected
Condition codes	clause 5.2.1.3, table 5-5	M	Y: all fourteen the table defines
EOF PDU	clause 5.2.2, table 5-6	M	Y: condition, checksum, file size, fault location
Fault location omitted for 'no error'	table 5-6	M	Y
Finished PDU	clause 5.2.3, table 5-7	M	Y: condition, delivery code, file status, responses
Fault location omitted for 'no error' and 'unsupported checksum type'	table 5-7	M	Y
ACK PDU	clause 5.2.4, table 5-8	M	Y: EOF and Finished only
ACK directive subtype rules	table 5-8	M	Y: '0001' for Finished, '0000' otherwise
Transaction status	clause 5.2.4	M	Y: all four values
Metadata PDU	clause 5.2.5, table 5-9	M	Y
Closure requested	table 5-9	M	Y
Checksum type field	table 5-9	M	Y
Empty filenames for fileless transactions	table 5-9	M	Y
NAK PDU	clause 5.2.6, table 5-10	O	Y
Segment requests	clause 5.2.6.2, table 5-11	O	Y: including the 0..0 metadata request
Prompt PDU	clause 5.2.7, table 5-12	O	Y: answered with NAK or Keep Alive
Keep Alive PDU	clause 5.2.8, table 5-13	O	Y

A1.4 FILE DATA PDUs

Feature	Reference	Status	Support
File Data PDU	clause 5.3, table 5-14	M	Y
Offset field	table 5-14	M	Y: FSS
Record continuation state	clause 5.3	O	Y: all four states, decoded when present
Segment metadata	table 5-14	O	Y: up to 63 octets

A1.5 PROCEDURES

Feature	Reference	Status
CRC at transmitting entity	clause 4.1.1	O
Y
CRC at receiving entity	clause 4.1.2	O
Y: failing PDUs are discarded
CRC algorithm: CCSDS Telecommand CRC	clause 4.1.3.1	M
Y: reuses `pkg/crc`
CRC placement and coverage	clause 4.1.3.2	M
Y: final octets, counted in the data field length
Checksum 32 bits	clause 4.2.1.2	M
Y
Modular checksum	clause 4.2.2.3	M
Y: verified against the Annex F worked example
Null checksum	clause 4.2.2.4	M
Y
Additional checksum algorithms	clause 4.2.2.5	O
Y: CRC-32C (type 2), CRC-32 (type 3)
Class 1 unacknowledged transfer	clause 4.6	M
Y: file data arriving before Metadata is buffered and replayed
Class 2 acknowledged transfer	clause 4.6	O
Y: NAK-driven gap recovery; the last recovered segment triggers the Finished PDU
Check limit	clause 4.6.3.3	O
Y: caller-driven via `ExpireCheckLimit`; closes out Class 1 with closure
Fault handlers: cancel, suspend, ignore, abandon	clause 4.8, table 4-1	M
Y: every condition defaults to cancel; per-condition config overrides
Suspend and resume	clause 4.11	O
Y: state flags; the caller owns the clock
Cancel	clause 4.11	O
Y: sender EOF (cancel) carries progress; receiver `Cancel()` and inbound EOF (cancel) close out with Finished (incomplete)
Filestore requests	clause 5.4.1, table 5-16	O
P: see A1.6
Filestore responses	clause 5.4.2, table 5-17	O
Y: one per request
Messages to user	clause 5.4.3	O
Y: carried, not interpreted
Fault handler override TLV	clause 5.4.4	O
Y: sent from `SenderConfig`, applied by the receiver on arrival
Flow label TLV	clause 5.4.5	O
Y: carried, not interpreted
Entity ID TLV	clause 5.4.6	M
Y: used for fault location

A1.6 EXCEPTIONS AND UNSUPPORTED FEATURES

Feature	Reference	Support
Filestore actions: append, replace	table 5-16	N
Decoded; execution returns status 'not performed' (table 5-18 allows this).
Filestore actions: create/remove directory, deny directory	table 5-16	N
Same. The `Filestore` interface is deliberately file-only.
Adaptive flow control from Keep Alive	clause 4.6	N
Keep Alive and Prompt encode and decode; no rate adaptation.
Part 2 user behaviour	clause 6	N by design
The Part 2 message formats are implemented (see A1.8). What is not is the behaviour around them: which primitive to call on receipt, and how to queue concurrent suspension orders, which clause 6.5.4.1.2 calls "an implementation matter".
Timers and inactivity detection	clause 4.6	N by design
The library owns no clock. Retransmission and timeout scheduling are the caller's, exposed as `ResendEOF`, `RequestNAK`, `ResendFinished`, `ExpireCheckLimit`, and `DeclareFault`. Limit and inactivity faults raised through `DeclareFault` take the table 4-1 route.

A1.7 IMPLEMENTATION LIMITS

Limit	Value	Source
Entity ID width	1 to 8 octets	3-bit length field, table 5-1
Transaction sequence number width	1 to 8 octets	3-bit length field, table 5-1
PDU data field length	65535 octets	16-bit field, table 5-1
LV / TLV value length	255 octets	8-bit length field, tables 5-2 and 5-3
Segment metadata length	63 octets	6-bit length field, table 5-14
File size, small file	2^32 - 1 octets	32-bit FSS, clause 5.1.10
File size, large file	2^64 - 1 octets	64-bit FSS, clause 5.1.10

A1.8 PART 2: USER OPERATIONS

Section 6 carries every User Operation as a Reserved CFDP Message inside a Message to User TLV in an ordinary transaction's metadata (clause 6.1.1), so Part 2 adds no PDU of its own. The message identifier (the ASCII characters cfdp (table 6-1)) is what separates a protocol message from an application one, and UserMessagesFrom uses it to sift a metadata TLV run.

All 20 message types of tables 6-3, 6-14, 6-17, 6-20 and 6-23 are named, and every content table is encoded and decoded.

Message	Reference	Support
Reserved CFDP Message header	table 6-1	Yes
The `cfdp` identifier and the type octet.
Originating Transaction ID	clause 6.1.5, table 6-2	Yes
Common to every operation. The two 3-bit length fields hold the width less one; the reserved bits either side are checked to be zero.
Proxy Put Request	table 6-4	Yes
An omitted file name is a zero-length LV, not an absent field.
Proxy Message to User	table 6-5	Yes

Proxy Filestore Request	table 6-6	Yes
An 8-bit length then a filestore request's TLV value, doing the job the TLV's own length would.
Proxy Fault Handler Override	table 6-7	Yes

Proxy Transmission Mode	table 6-8	Yes
Table 5-1 makes '0' acknowledged, so the flag is inverted on the wire.
Proxy Flow Label	table 6-9	Yes

Proxy Segmentation Control	table 6-10	Yes
'0' means record boundaries respected.
Proxy Put Response	table 6-12	Yes
Condition code, spare bit, delivery code, file status, the Finished PDU's packing.
Proxy Filestore Response	table 6-13	Yes

Proxy Put Cancel	clause 6.2.6.2	Yes
Has no content, and is encoded with none.
Proxy Closure Request	table 6-11	Yes

Directory Listing Request	table 6-15	Yes

Directory Listing Response	table 6-16	Yes
Success is '0' here.
Remote Status Report Request	table 6-18	Yes

Remote Status Report Response	table 6-19	Yes
Success is '1' here, the opposite polarity from table 6-16, and in the low bit rather than the high one.
Remote Suspend Request	table 6-21	Yes
clause 6.5.3.1.2 requires the carrying transaction to be Acknowledged; that is the caller's to arrange.
Remote Suspend Response	table 6-22	Yes
Carries the transaction ID, which is easy to miss because the field list runs onto a second page.
Remote Resume Request	table 6-24	Yes

Remote Resume Response	table 6-25	Yes
Same body as table 6-22. Clause 6.6.4.2 notes a successful resume may not change the suspension state, so the indicator reports state rather than outcome.

The message type numbering has a gap inside the proxy range: 0x0A is the Originating Transaction ID, common to every operation rather than belonging to proxy, so proxy runs 0x00-0x09 and resumes at 0x0B.

Wire test vectors

The octets backing this statement live in the vector corpus — 25 vectors. Each vector names the clause it comes from and carries the derivation that produced it.

File
`cfdp/interop.json`	7 vectors, captured from spacepackets 0.32.0
`cfdp/transaction.json`	4 vectors
`cfdp/wire.json`	14 vectors

These are data files, so any implementation can check itself against the same octets. See CONTRACT.md for how, and how this is verified for what rests on a published vector versus a reading of the clause.