CCSDS AOS (Advanced Orbiting Systems) Transfer Frame for satellite downlinks
aos: refactor decode into helpers (merlint E005)
Extract packed_to_header and check_fecf_value from the 65-line decode
function. Now 40 lines.
+43
-42
+43
-42
lib/aos.ml
+43
-42
lib/aos.ml
···
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(* {1 Frame decode/encode via frame_codec} *)
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let packed_to_header pf =
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if pf.pf_version > 1 then Error (Invalid_version pf.pf_version)
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else
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match
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of_packed_header
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{
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version = pf.pf_version;
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scid = pf.pf_scid;
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vcid = pf.pf_vcid;
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vcfc = pf.pf_vcfc;
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replay_flag = pf.pf_replay_flag;
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vc_count_flag = pf.pf_vc_count_flag;
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spare = pf.pf_spare;
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vc_count_cycle = pf.pf_vc_count_cycle;
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}
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with
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| Error `Invalid_scid -> Error (Invalid_scid pf.pf_scid)
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| Error `Invalid_vcid -> Error (Invalid_vcid pf.pf_vcid)
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| Ok header -> Ok header
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+
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let check_fecf_value buf frame_len fecf =
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match fecf with
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| Some actual ->
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let computed = compute_fecf (String.sub buf 0 (frame_len - 2)) in
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if computed <> actual then
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Error (Fecf_mismatch { expected = computed; actual })
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else Ok ()
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| None -> Ok ()
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+
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let decode ?(frame_len = 0) ?(insert_zone_len = 0) ?(expect_ocf = true)
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?(expect_fecf = true) ?(check_fecf = true) buf =
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let buf_len = String.length buf in
···
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else
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match Wire.Codec.decode_with frame_codec env frame_buf 0 with
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| Error _ -> Error (Truncated { need = frame_len; have = buf_len })
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| Ok pf -> (
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if pf.pf_version > 1 then Error (Invalid_version pf.pf_version)
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else
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match
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of_packed_header
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{
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version = pf.pf_version;
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scid = pf.pf_scid;
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vcid = pf.pf_vcid;
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vcfc = pf.pf_vcfc;
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replay_flag = pf.pf_replay_flag;
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vc_count_flag = pf.pf_vc_count_flag;
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spare = pf.pf_spare;
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vc_count_cycle = pf.pf_vc_count_cycle;
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}
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with
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| Error `Invalid_scid -> Error (Invalid_scid pf.pf_scid)
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| Error `Invalid_vcid -> Error (Invalid_vcid pf.pf_vcid)
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| Ok header ->
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let insert_zone =
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if insert_zone_len > 0 then Some pf.pf_insert_zone else None
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in
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let frame =
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{
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header;
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insert_zone;
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data = pf.pf_data;
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ocf = pf.pf_ocf;
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fecf = pf.pf_fecf;
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}
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in
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if expect_fecf && check_fecf then
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match pf.pf_fecf with
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| Some actual ->
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let computed =
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compute_fecf (String.sub buf 0 (frame_len - 2))
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in
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if computed <> actual then
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Error (Fecf_mismatch { expected = computed; actual })
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else Ok frame
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| None -> Ok frame
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else Ok frame)
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| Ok pf ->
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let ( let* ) = Result.bind in
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let* header = packed_to_header pf in
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let insert_zone =
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if insert_zone_len > 0 then Some pf.pf_insert_zone else None
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in
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let frame =
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{ header; insert_zone; data = pf.pf_data; ocf = pf.pf_ocf;
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fecf = pf.pf_fecf }
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in
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if expect_fecf && check_fecf then
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let* () = check_fecf_value buf frame_len pf.pf_fecf in
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Ok frame
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else Ok frame
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let encode_header buf off hdr =
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let packed = to_packed_header hdr in