Merge pull request #28699 from hashicorp/jbardin/plugin-output-monitor

monitor plugin std outputs for unexpected data

command/meta_providers.go

@@ -351,6 +351,8 @@ func providerFactory(meta *providercache.CachedProvider) providers.Factory {
 			Cmd:              exec.Command(execFile),
 			AutoMTLS:         enableProviderAutoMTLS,
 			VersionedPlugins: tfplugin.VersionedPlugins,
+			SyncStdout:       logging.PluginOutputMonitor(fmt.Sprintf("%s:stdout", meta.Provider)),
+			SyncStderr:       logging.PluginOutputMonitor(fmt.Sprintf("%s:stderr", meta.Provider)),
 		}
 
 		client := plugin.NewClient(config)
@@ -406,6 +408,8 @@ func unmanagedProviderFactory(provider addrs.Provider, reattach *plugin.Reattach
 			AllowedProtocols: []plugin.Protocol{plugin.ProtocolGRPC},
 			Managed:          false,
 			Reattach:         reattach,
+			SyncStdout:       logging.PluginOutputMonitor(fmt.Sprintf("%s:stdout", provider)),
+			SyncStderr:       logging.PluginOutputMonitor(fmt.Sprintf("%s:stderr", provider)),
 		}
 		// TODO: we probably shouldn't hardcode the protocol version
 		// here, but it'll do for now, because only one protocol

command/plugins.go

@@ -163,6 +163,8 @@ func provisionerFactory(meta discovery.PluginMeta) provisioners.Factory {
 			Logger:           logging.NewLogger("provisioner"),
 			AllowedProtocols: []plugin.Protocol{plugin.ProtocolGRPC},
 			AutoMTLS:         enableProviderAutoMTLS,
+			SyncStdout:       logging.PluginOutputMonitor(fmt.Sprintf("%s:stdout", meta.Name)),
+			SyncStderr:       logging.PluginOutputMonitor(fmt.Sprintf("%s:stderr", meta.Name)),
 		}
 		client := plugin.NewClient(cfg)
 		return newProvisionerClient(client)

internal/logging/logging.go

@@ -187,3 +187,35 @@ func isValidLogLevel(level string) bool {
 
 	return false
 }
+
+// PluginOutputMonitor creates an io.Writer that will warn about any writes in
+// the default logger. This is used to catch unexpected output from plugins,
+// notifying them about the problem as well as surfacing the lost data for
+// context.
+func PluginOutputMonitor(source string) io.Writer {
+	return pluginOutputMonitor{
+		source: source,
+		log:    logger,
+	}
+}
+
+// pluginOutputMonitor is an io.Writer that logs all writes as
+// "unexpected data" with the source name.
+type pluginOutputMonitor struct {
+	source string
+	log    hclog.Logger
+}
+
+func (w pluginOutputMonitor) Write(d []byte) (int, error) {
+	// Limit the write size to 1024 bytes We're not expecting any data to come
+	// through this channel, so accidental writes will usually be stray fmt
+	// debugging statements and the like, but we want to provide context to the
+	// provider to indicate what the unexpected data might be.
+	n := len(d)
+	if n > 1024 {
+		d = append(d[:1024], '.', '.', '.')
+	}
+
+	w.log.Warn("unexpected data", w.source, strings.TrimSpace(string(d)))
+	return n, nil
+}