feat: Add ability to provide dynamic query parameters

stream.go

@@ -6,6 +6,7 @@ import (
 	"io"
 	"io/ioutil"
 	"net/http"
+	"net/url"
 	"sync"
 	"time"
 )
@@ -14,11 +15,12 @@ import (
 // It will try and reconnect if the connection is lost, respecting both
 // received retry delays and event id's.
 type Stream struct {
-	c           *http.Client
-	req         *http.Request
-	lastEventID string
-	readTimeout time.Duration
-	retryDelay  *retryDelayStrategy
+	c               *http.Client
+	req             *http.Request
+	queryParamsFunc *func() url.Values
+	lastEventID     string
+	readTimeout     time.Duration
+	retryDelay      *retryDelayStrategy
 	// Events emits the events received by the stream
 	Events chan Event
 	// Errors emits any errors encountered while reading events from the stream.
@@ -187,6 +189,10 @@ func newStream(request *http.Request, configuredOptions streamOptions) *Stream {
 		closer:       make(chan struct{}),
 	}
 
+	if configuredOptions.queryParamsFunc != nil {
+		stream.queryParamsFunc = configuredOptions.queryParamsFunc
+	}
+
 	if configuredOptions.errorHandler == nil {
 		// The Errors channel is only used if there is no error handler.
 		stream.Errors = make(chan error)
@@ -231,6 +237,9 @@ func (stream *Stream) connect() (io.ReadCloser, error) {
 		stream.req.Header.Set("Last-Event-ID", stream.lastEventID)
 	}
 	req := *stream.req
+	if stream.queryParamsFunc != nil {
+		req.URL.RawQuery = (*stream.queryParamsFunc)().Encode()
+	}
 
 	// All but the initial connection will need to regenerate the body
 	if stream.connections > 0 && req.GetBody != nil {

stream_options.go

@@ -2,6 +2,7 @@ package eventsource
 
 import (
 	"net/http"
+	"net/url"
 	"time"
 )
 
@@ -16,6 +17,7 @@ type streamOptions struct {
 	retryResetInterval  time.Duration
 	initialRetryTimeout time.Duration
 	errorHandler        StreamErrorHandler
+	queryParamsFunc     *func() url.Values
 }
 
 // StreamOption is a common interface for optional configuration parameters that can be
@@ -24,6 +26,22 @@ type StreamOption interface {
 	apply(s *streamOptions) error
 }
 
+type dynamicQueryParamsOption struct {
+	queryParamsFunc func() url.Values
+}
+
+func (o dynamicQueryParamsOption) apply(s *streamOptions) error {
+	s.queryParamsFunc = &o.queryParamsFunc
+	return nil
+}
+
+// StreamOptionDynamicQueryParams returns an option that sets a function to
+// generate query parameters each time the stream needs to make a fresh
+// connection.
+func StreamOptionDynamicQueryParams(f func() url.Values) StreamOption {
+	return dynamicQueryParamsOption{queryParamsFunc: f}
+}
+
 type readTimeoutOption struct {
 	timeout time.Duration
 }

stream_requests_test.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"net/http"
 	"net/http/httptest"
+	"net/url"
 	"testing"
 	"time"
 
@@ -45,6 +46,29 @@ func TestStreamSendsLastEventID(t *testing.T) {
 	assert.Equal(t, lastID, r0.Request.Header.Get("Last-Event-ID"))
 }
 
+func TestCanSetStreamQueryParameters(t *testing.T) {
+	streamHandler, streamControl := httphelpers.SSEHandler(nil)
+	defer streamControl.Close()
+	handler, requestsCh := httphelpers.RecordingHandler(streamHandler)
+
+	httpServer := httptest.NewServer(handler)
+	defer httpServer.Close()
+
+	option := StreamOptionDynamicQueryParams(func() url.Values {
+		return url.Values{
+			"filter": []string{"my-custom-filter"},
+			"basis":  []string{"last-known-basis"},
+		}
+	})
+
+	stream := mustSubscribe(t, httpServer.URL, option)
+	defer stream.Close()
+
+	r0 := <-requestsCh
+	assert.Equal(t, "my-custom-filter", r0.Request.URL.Query().Get("filter"))
+	assert.Equal(t, "last-known-basis", r0.Request.URL.Query().Get("basis"))
+}
+
 func TestStreamReconnectWithRequestBodySendsBodyTwice(t *testing.T) {
 	body := []byte("my-body")