Martino Ferrari
106 lines
3.3 KiB
Go
106 lines
3.3 KiB
Go
// Package datasource defines the DataSource interface and shared types used by
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// all data source implementations (EPICS, synthetic, stub, …).
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package datasource
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import (
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"context"
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"errors"
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"time"
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)
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// Quality indicates the reliability of a signal value.
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type Quality uint8
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const (
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QualityGood Quality = iota // value is valid
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QualityUncertain // value may be stale or approximate
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QualityBad // value is invalid
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)
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func (q Quality) String() string {
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switch q {
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case QualityGood:
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return "good"
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case QualityUncertain:
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return "uncertain"
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default:
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return "bad"
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}
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}
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// DataType describes the Go type of a signal's value.
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type DataType uint8
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const (
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TypeFloat64 DataType = iota // scalar float; Data is float64
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TypeFloat64Array // waveform; Data is []float64
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TypeString // Data is string
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TypeInt64 // Data is int64
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TypeBool // Data is bool
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TypeEnum // Data is int64; see Metadata.EnumStrings
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)
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// Value is a timestamped signal reading.
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type Value struct {
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Timestamp time.Time
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Data any // float64 | []float64 | string | int64 | bool
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Quality Quality
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MetaUpdate bool // if true, metadata was refreshed — dispatcher should re-send meta
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}
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// Metadata describes the static properties of a signal.
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type Metadata struct {
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Name string
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Type DataType
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Unit string
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Description string
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DisplayLow float64
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DisplayHigh float64
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DriveLow float64
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DriveHigh float64
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EnumStrings []string // non-nil only for TypeEnum
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Writable bool
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}
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// CancelFunc cancels a subscription started by DataSource.Subscribe.
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type CancelFunc func()
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// DataSource is implemented by every data source plugin.
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type DataSource interface {
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// Name returns the unique short identifier for this source (e.g. "epics").
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Name() string
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// Connect initialises the connection to the underlying system.
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// It should return quickly; actual channel connections are lazy.
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Connect(ctx context.Context) error
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// ListSignals returns metadata for all signals known to this source.
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ListSignals(ctx context.Context) ([]Metadata, error)
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// GetMetadata returns the metadata for a single named signal.
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GetMetadata(ctx context.Context, signal string) (Metadata, error)
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// Subscribe registers ch to receive value updates for the named signal.
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// The first value is delivered as soon as it is available.
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// The returned CancelFunc must be called to release resources.
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Subscribe(ctx context.Context, signal string, ch chan<- Value) (CancelFunc, error)
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// Write sets a new value for a writable signal.
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Write(ctx context.Context, signal string, value any) error
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// History returns up to maxPoints values in [start, end].
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// Returns ErrHistoryUnavailable if the source has no archive.
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History(ctx context.Context, signal string, start, end time.Time, maxPoints int) ([]Value, error)
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}
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var (
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// ErrNotFound is returned when a signal does not exist in the source.
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ErrNotFound = errors.New("signal not found")
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// ErrNotWritable is returned when attempting to write to a read-only signal.
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ErrNotWritable = errors.New("signal is not writable")
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// ErrHistoryUnavailable is returned when the source has no archive backend.
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ErrHistoryUnavailable = errors.New("history unavailable for this data source")
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)
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