Go-ws streaming SDK (#111)

* Added go-ws web streaming SDK.

* Added missing go.sum

* Updated Readme for go-ws

* Renamed Reconnect to ResetConnection to reflect intent!

* Applied fix for Issue #110

* Updated sample code

* Removed test covering volume bug

* Updated code comment.

data-api/go-ws/README.md

@@ -0,0 +1,23 @@
+
+
+## Installation
+
+Install the following dependencies:
+
+```shell
+go mod download github.com/bitly/go-simplejson
+go mod download github.com/shopspring/decimal
+go mod download github.com/gorilla/websocket
+```
+
+
+## Run examples:
+
+```bash
+cd /path/to/workspace
+export GOPATH=/path/to/workspace
+go get -u github.com/CoinAPI/coinapi-sdk/data-api/go-ws
+wget -v https://raw.githubusercontent.com/coinapi/coinapi-sdk/master/go-ws/main.go
+# update api key inside main.go
+go run ./main.go
+```

data-api/go-ws/api/sdk.go

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+package api
+
+import . "go-ws/api/types"
+
+func NewSDK(apiKey string) (sdk SDK) {
+	validateApiKey(apiKey)
+	config := getSDKConfig(apiKey)
+	sdk = getSDK(config)
+	return sdk
+}

data-api/go-ws/api/types/config.go

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+package types
+
+type SdkConfig struct {
+	ApiKey          string
+	ApiVersion      ApiVersion
+	EnvironmentType EnvironmentType
+	ReconnectType   ReconnectType
+}
+
+// WsConfig webservice configuration
+type WsConfig struct {
+	ApiKey             string
+	Endpoint           string
+	WebsocketKeepalive bool
+	WebsocketTimeout   int
+}

data-api/go-ws/api/types/enums.go

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+package types
+
+// ApiVersion custom ENUM for SDK forward compatibility
+type ApiVersion int
+
+const (
+	ApiV1 ApiVersion = iota
+)
+
+// EnvironmentType
+// https://docs.coinapi.io/#endpoints-2
+type EnvironmentType int
+
+const (
+	ProdEncrypted EnvironmentType = iota
+	ProdInsecure
+	TestEncrypted
+	TestInsecure
+)
+
+// MessageType replicates the official incoming message types as (kinda) string enum.
+// https://docs.coinapi.io/#messages
+type MessageType string
+
+const (
+	TRADE          MessageType = "trade"
+	QUOTE          MessageType = "quote"
+	BOOK_L2_FULL   MessageType = "book"    // Orderbook L2 (Full)
+	BOOK_L2_TOP_5  MessageType = "book5"   // Orderbook L2 (5 best Bid / Ask)
+	BOOK_L2_TOP_20 MessageType = "book20"  // Orderbook L2 (20 best Bid / Ask)
+	BOOK_L2_TOP_50 MessageType = "book50"  // Orderbook L2 (50 best Bid / Ask)
+	BOOK_L3_FULL   MessageType = "book_l3" // Orderbook L3 (Full) https://docs.coinapi.io/#orderbook-l3-full-in
+	OHLCV          MessageType = "ohlcv"
+	VOLUME         MessageType = "volume"
+	HEARTBEAT      MessageType = "hearbeat" // DO NOT FIX! it's a typo in the official msg spec!
+	ERROR          MessageType = "error"    // Otherwise processMessage(.) fails to handle heartbeat messages!
+	EXCHANGERATE   MessageType = "exrate"
+	RECONNECT      MessageType = "reconnect"
+)
+
+// ReconnectType defines the reconnect behavior upon receiving a reconnect message
+// https://docs.coinapi.io/#reconnect-in
+type ReconnectType int
+
+const (
+	OnConnectionClose ReconnectType = iota
+	OnReconnectMessage
+)

data-api/go-ws/api/types/functions.go

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+package types
+
+// InvokeFunction is a unified function type for all event handlers.
+// https://yourbasic.org/golang/function-pointer-type-declaration/
+type InvokeFunction func(message *DataMessage) (err error)
+
+// WsHandler handle raw websocket message
+type WsHandler func(message []byte)
+
+// WsErrHandler handles raw websocket errors
+type WsErrHandler func(err error)

data-api/go-ws/api/types/interface.go

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+package types
+
+type SDK interface {
+	SendHello(hello *Hello) (err error)
+	OpenConnection() (err error)
+	CloseConnection() (err error)
+	// ResetConnection hard reset: closes  current connection, opens a new one,
+	// and resends the last hello message. No message buffering!
+	ResetConnection() (err error)
+
+	// sys handlers
+	SetErrorInvoke(function InvokeFunction)
+	SetHeartBeatInvoke(function InvokeFunction)
+	SetReconnectInvoke(function InvokeFunction)
+
+	// Data handlers
+	SetExRateInvoke(function InvokeFunction)
+	SetTradesInvoke(function InvokeFunction)
+	SetQuoteInvoke(function InvokeFunction)
+	SetBookInvoke(function InvokeFunction)
+	SetOHLCVInvoke(function InvokeFunction)
+	SetVolumeInvoke(function InvokeFunction)
+}