Revert "Revert "Pull fedclient interface over from dendrite (#366)" (#370)"

This reverts commit 3724c73.

Author: devonh

fclient/client.go

@@ -60,6 +60,7 @@ type clientOptions struct {
 	skipVerify   bool
 	keepAlives   bool
 	wellKnownSRV bool
+	userAgent    string
 }
 
 // ClientOption are supplied to NewClient or NewFederationClient.
@@ -88,6 +89,7 @@ func NewClient(options ...ClientOption) *Client {
 			Transport: clientOpts.transport,
 			Timeout:   clientOpts.timeout,
 		},
+		userAgent: clientOpts.userAgent,
 	}
 	return client
 }
@@ -143,6 +145,13 @@ func WithWellKnownSRVLookups(wellKnownSRV bool) ClientOption {
 	}
 }
 
+// WithUserAgent enables specifying the user agent for the http client.
+func WithUserAgent(userAgent string) ClientOption {
+	return func(options *clientOptions) {
+		options.userAgent = userAgent
+	}
+}
+
 const destinationTripperLifetime = time.Minute * 5 // how long to keep an entry
 const destinationTripperReapInterval = time.Minute // how often to check for dead entries