feat: use environment variables to configure the datadog client

Author: etiennep

README.md

@@ -151,6 +151,24 @@ func main() {
 }
 ```
 
+### Configuring Using Environment Variables
+
+The datadog client can be auto-configured using the following environment variables:
+
+* `STATSD_HOST` - the hostname of the UDP server. Defaults to `localhost`
+* `STATSD_UDP_PORT` - the port of the UDP server. Defaults to `8125`
+* `STATSD_SOCKET` - the path of the unix domain socket of the server.
+
+Note: if the `STATSD_SOCKET` variable is present, the client will be configured to use UDS by default and ignore the UDP settings.
+
+```go
+func main() {
+    stats.Register(datadog.NewClientFromEnv())
+    defer stats.Flush()
+
+    // ...
+```
+
 ### Flushing Metrics
 
 Metrics are stored in a buffer, which will be flushed when it reaches its

datadog/client.go

@@ -14,9 +14,17 @@ import (
 )
 
 const (
+
+	// DefaultHost is the default host to which the datadog client tries to
+	DefaultHost = "localhost"
+
+	// DefaultPort is the default port to which the datadog client tries to
+	// connect to.
+	DefaultPort = "8125"
+
 	// DefaultAddress is the default address to which the datadog client tries
 	// to connect to.
-	DefaultAddress = "localhost:8125"
+	DefaultAddress = DefaultHost + ":" + DefaultPort
 
 	// DefaultBufferSize is the default size for batches of metrics sent to
 	// datadog.
@@ -77,11 +85,19 @@ func NewClient(addr string) *Client {
 	})
 }
 
+// NewClientFromEnv creates and returns a new datadog client publishing metrics
+// to the server running at the address specified in the environment variable.
+// The STATSD_HOST and STATSD_UDP_PORT environment variables are used to
+// determine the address.
+func NewClientFromEnv() *Client {
+	return NewClientWith(ClientConfig{})
+}
+
 // NewClientWith creates and returns a new datadog client configured with the
 // given config.
 func NewClientWith(config ClientConfig) *Client {
 	if len(config.Address) == 0 {
-		config.Address = DefaultAddress
+		config.Address = addressFromEnv()
 	}
 
 	if config.BufferSize == 0 {
@@ -153,6 +169,25 @@ func (c *Client) Close() error {
 	return c.err
 }
 
+// Returns the address to which the client will send metrics by
+// looking at the STATSD_SOCKET, STATSD_HOST and STATSD_UDP_PORT environment variables.
+func addressFromEnv() string {
+	socket := os.Getenv("STATSD_SOCKET")
+	if len(socket) > 0 {
+		return "unixgram://" + socket
+	}
+	hostname := os.Getenv("STATSD_HOST")
+	if len(hostname) == 0 {
+		hostname = DefaultHost
+	}
+	port := os.Getenv("STATSD_UDP_PORT")
+	if len(port) == 0 {
+		port = DefaultPort
+	}
+	addr := hostname + ":" + port
+	return addr
+}
+
 func bufSizeFromFD(f *os.File, sizehint int) (bufsize int, err error) {
 	fd := int(f.Fd())
 

datadog/client_test.go

@@ -16,6 +16,33 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
+// TestDefaultAddressFromEnv tests that the addressFromEnv function returns the
+// default address when the environment variable is not set.
+func TestDefaultAddressFromEnv(t *testing.T) {
+	address := addressFromEnv()
+
+	assert.Equal(t, "localhost:8125", address)
+}
+
+// TestUdpAddressFromEnv tests that the addressFromEnv function returns the
+// address from the environment variable when it is set.
+func TestUdpAddressFromEnv(t *testing.T) {
+	t.Setenv("STATSD_HOST", "not-localhost")
+	t.Setenv("STATSD_UDP_PORT", "1234")
+
+	address := addressFromEnv()
+	assert.Equal(t, "not-localhost:1234", address)
+}
+
+// TestUdsAddressFromEnv tests that the addressFromEnv function returns the
+// address from the environment variable when it is set.
+func TestUdsAddressFromEnv(t *testing.T) {
+	t.Setenv("STATSD_SOCKET", "/dir/file.ext")
+
+	address := addressFromEnv()
+	assert.Equal(t, "unixgram:///dir/file.ext", address)
+}
+
 func TestClient(t *testing.T) {
 	client := NewClient(DefaultAddress)