exchanges/websocket: Implement subscription configuration (#1394)

* Websockets: Move Subscription to its own package

This allows the small type to be imported from both `config` and from
`stream` without an import cycle, so we don't have to repeat ourselves

* Subs: Renamed Currency to Pair

This was being mis-used through much of the code, and since we're
already touching everything, we might as well fix it

* Websockets: Add Subscription configuration

* Binance: Add subscription configuration

* Kucoin: Subscription configuration

* Simplify GenerateDefaultSubs
* Improve TestGenSubs coverage
* Test Candle Sub generation
* Support Candle intervals
* Full responsibility for formatting Channel name on GenerateDefaultSubs
  OR consumer of Subscribe
* Simplify generatePayloads as a result
* Fix test coverage of asset types in processMarketSnapshot

* Exchanges: Abstract ParallelChanOp

* Tests: Generic ws mock instances

* Kucoin: Fix intermittent conflict in test currs

Use isolated test instance for `TestGetOpenInterest`.

`TestGetOpenInterest` would occassionally change pairs before
GenerateDefault Subs.

exchanges/kline/kline.go

@@ -1,9 +1,11 @@
 package kline
 
 import (
+	"bytes"
 	"errors"
 	"fmt"
 	"sort"
+	"strconv"
 	"strings"
 	"time"
 
@@ -143,6 +145,31 @@ func (i Interval) Short() string {
 	return s
 }
 
+// UnmarshalJSON implements the json.Unmarshaler interface for Intervals
+// It does not validate the duration is aligned, only that it is a parsable duration
+func (i *Interval) UnmarshalJSON(text []byte) error {
+	text = bytes.Trim(text, `"`)
+	if len(bytes.TrimLeft(text, `0123456789`)) > 0 { // contains non-numerics, ParseDuration can handle errors
+		d, err := time.ParseDuration(string(text))
+		if err != nil {
+			return err
+		}
+		*i = Interval(d)
+	} else {
+		n, err := strconv.ParseInt(string(text), 10, 64)
+		if err != nil {
+			return err
+		}
+		*i = Interval(n)
+	}
+	return nil
+}
+
+// MarshalText implements the TextMarshaler interface for Intervals
+func (i Interval) MarshalText() ([]byte, error) {
+	return []byte(i.Short()), nil
+}
+
 // addPadding inserts padding time aligned when exchanges do not supply all data
 // when there is no activity in a certain time interval.
 // Start defines the request start and due to potential no activity from this

exchanges/kline/kline_test.go

@@ -10,6 +10,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/stretchr/testify/assert"
 	"github.com/thrasher-corp/gocryptotrader/common"
 	"github.com/thrasher-corp/gocryptotrader/currency"
 	"github.com/thrasher-corp/gocryptotrader/database"
@@ -1396,3 +1397,18 @@ func TestGetIntervalResultLimit(t *testing.T) {
 		t.Errorf("received '%v' expected '%v'", limit, 1337)
 	}
 }
+
+func TestUnmarshalJSON(t *testing.T) {
+	i := new(Interval)
+	err := i.UnmarshalJSON([]byte(`"3m"`))
+	assert.NoError(t, err, "UnmarshalJSON should not error")
+	assert.Equal(t, time.Minute*3, i.Duration(), "Interval should have correct value")
+	err = i.UnmarshalJSON([]byte(`"15s"`))
+	assert.NoError(t, err, "UnmarshalJSON should not error")
+	assert.Equal(t, time.Second*15, i.Duration(), "Interval should have correct value")
+	err = i.UnmarshalJSON([]byte(`720000000000`))
+	assert.NoError(t, err, "UnmarshalJSON should not error")
+	assert.Equal(t, time.Minute*12, i.Duration(), "Interval should have correct value")
+	err = i.UnmarshalJSON([]byte(`"6hedgehogs"`))
+	assert.ErrorContains(t, err, "unknown unit", "UnmarshalJSON should error")
+}