grpc: Interceptor to catch panics and convert them to Internal errors.

tokenserver/appengine/frontend/main.go

 // Copyright 2016 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 // Package frontend implements HTTP server that handles requests to 'default'
 // module.
 package frontend
 
 import (
         "net/http"
 
         "github.com/golang/protobuf/proto"
         "golang.org/x/net/context"
         "google.golang.org/grpc"
         "google.golang.org/grpc/codes"
 
         "github.com/luci/luci-go/appengine/gaemiddleware"
         "github.com/luci/luci-go/common/logging"
         "github.com/luci/luci-go/grpc/discovery"
         "github.com/luci/luci-go/grpc/grpcmon"
+        "github.com/luci/luci-go/grpc/grpcutil"
         "github.com/luci/luci-go/grpc/prpc"
         "github.com/luci/luci-go/server/auth"
         "github.com/luci/luci-go/server/router"
 
         "github.com/luci/luci-go/tokenserver/api/admin/v1"
         "github.com/luci/luci-go/tokenserver/api/minter/v1"
 
         "github.com/luci/luci-go/tokenserver/appengine/impl/services/admin/adminsrv"
         "github.com/luci/luci-go/tokenserver/appengine/impl/services/admin/certauthorities"
         "github.com/luci/luci-go/tokenserver/appengine/impl/services/minter/tokenminter"
@@ skipping 17 matching lines @@
         r := router.New()
 
         // Install auth, config and tsmon handlers.
         gaemiddleware.InstallHandlers(r)
 
         // The service has no UI, so just redirect to stock RPC explorer.
         r.GET("/", router.MiddlewareChain{}, func(c *router.Context) {
                 http.Redirect(c.Writer, c.Request, "/rpcexplorer/", http.StatusFound)
         })
 
-        // Install all RPC servers.
+        // Install all RPC servers. Catch panics, report metrics to tsmon (including
+        // panics themselves, as Internal errors).
         api := prpc.Server{
-                UnaryServerInterceptor: grpcmon.NewUnaryServerInterceptor(nil),
+                UnaryServerInterceptor: grpcmon.NewUnaryServerInterceptor(grpcutil.NewUnaryServerPanicCatcher(nil)),
         }
         admin.RegisterCertificateAuthoritiesServer(&api, &admin.DecoratedCertificateAuthorities{
                 Service: certauthorities.NewServer(),
                 Prelude: adminPrelude("admin.CertificateAuthorities"),
         })
         admin.RegisterAdminServer(&api, &admin.DecoratedAdmin{
                 Service: adminsrv.NewServer(),
                 Prelude: adminPrelude("admin.Admin"),
         })
         minter.RegisterTokenMinterServer(&api, tokenminter.NewServer()) // auth inside
         discovery.Enable(&api)
         api.InstallHandlers(r, gaemiddleware.BaseProd())
 
         // Expose all this stuff.
         http.DefaultServeMux.Handle("/", r)
 }