mirror of https://bitbucket.org/ausocean/av.git
124 lines
3.9 KiB
Go
124 lines
3.9 KiB
Go
/*
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NAME
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helpers.go
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DESCRIPTION
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helpers.go provides functionality for editing and reading bytes slices
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directly in order to insert/read timestamp and location data in psi.
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AUTHOR
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Saxon Milton <saxon@ausocean.org>
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LICENSE
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helpers.go is Copyright (C) 2018 the Australian Ocean Lab (AusOcean)
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It is free software: you can redistribute it and/or modify them
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under the terms of the GNU General Public License as published by the
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Free Software Foundation, either version 3 of the License, or (at your
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option) any later version.
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It is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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for more details.
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You should have received a copy of the GNU General Public License
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along with revid in gpl.txt. If not, see http://www.gnu.org/licenses.
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*/
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package psi
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import (
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"bytes"
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"encoding/binary"
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"errors"
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)
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// TimeBytes takes a timestamp as an uint64 and converts to an 8 byte slice -
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// allows for updating of timestamp in pmt time descriptor.
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func TimeBytes(t uint64) []byte {
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var s [TimeDataSize]byte
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binary.BigEndian.PutUint64(s[:], t)
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return s[:]
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}
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// HasTime takes a psi as a byte slice and checks to see if it has a time descriptor
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// - if so return nil, otherwise return error
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func HasTime(p []byte) bool {
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return p[TimeTagIndx] == TimeDescTag
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}
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// HasLocation takes a psi as a byte slice and checks to see if it has a location descriptor
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// - if so return nil, otherwise return error
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func HasLocation(p []byte) bool {
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return p[LocationTagIndx] == LocationDescTag
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}
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// UpdateTime takes the byte slice representation of a psi-pmt as well as a time
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// as an integer and attempts to update the time descriptor in the pmt with the
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// given time if the time descriptor exists, otherwise an error is returned
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func UpdateTime(dst []byte, t uint64) error {
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if !HasTime(dst) {
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return errors.New("pmt does not have time descriptor, cannot update")
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}
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ts := TimeBytes(uint64(t))
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for i := range dst[TimeDataIndx : TimeDataIndx+TimeDataSize] {
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dst[i+TimeDataIndx] = ts[i]
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}
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updateCrc(dst)
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return nil
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}
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// TimeFrom takes a byte slice representation of a psi-pmt and extracts it's
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// timestamp, returning as a uint64 if it exists, otherwise returning 0 and nil
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// if it does not exist
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func TimeFrom(p []byte) (t uint64, err error) {
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if !HasTime(p) {
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return 0, errors.New("pmt does not have a time descriptor")
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}
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t = binary.BigEndian.Uint64(p[TimeDataIndx : TimeDataIndx+TimeDataSize])
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return t, nil
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}
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// LocationFrom takes a byte slice representation of a psi-pmt and extracts it's
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// timestamp, returning as a uint64 if it exists, otherwise returning 0 and nil
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// if it does not exist
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func LocationFrom(p []byte) (g string, err error) {
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if !HasLocation(p) {
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return "", errors.New("pmt does not have location descriptor")
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}
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gBytes := p[LocationDataIndx : LocationDataIndx+LocationDataSize]
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gBytes = bytes.Trim(gBytes, "\x00")
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g = string(gBytes)
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return g, nil
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}
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// LocationStrBytes take a string of location data and converts to a 32 byte slice -
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// easy update of slice representation of a pmt with location descriptor
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func LocationStrBytes(s string) []byte {
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var b [LocationDataSize]byte
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copy(b[:], s)
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return b[:]
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}
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// UpdateLocation takes a byte slice representation of a psi-pmt containing a location
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// descriptor and attempts to update the location data value with the passed string.
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// If the psi does not contain a location descriptor, and error is returned.
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func UpdateLocation(d []byte, s string) error {
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if !HasLocation(d) {
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return errors.New("pmt does not location descriptor, cannot update")
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}
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gb := LocationStrBytes(s)
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copy(d[LocationDataIndx:LocationDataIndx+LocationDataSize], gb)
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updateCrc(d)
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return nil
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}
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func trimTo(d []byte, t byte) []byte {
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for i, b := range d {
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if b == t {
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return d[:i]
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}
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}
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return d
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}
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