Include valid spec and headers when calling recover handler for streaming RPCs (#817)

For some reason, this was passing an empty spec and nil headers for
streaming RPCs, though the Go docs don't suggest anything of the sort.

Also simplified the panic recovery to use more intuitive idioms, which
now suffice since this module requires Go 1.21 (which no longer allows
panicking with a nil value).

Author: jhump

recover.go

@@ -22,16 +22,6 @@ import (
 // recoverHandlerInterceptor lets handlers trap panics, perform side effects
 // (like emitting logs or metrics), and present a friendlier error message to
 // clients.
-//
-// This interceptor uses a somewhat unusual strategy to recover from panics.
-// The standard recovery idiom:
-//
-//	if r := recover(); r != nil { ... }
-//
-// isn't robust in the face of user error, because it doesn't handle
-// panic(nil). This occasionally happens by mistake, and it's a beast to debug
-// without a more robust idiom. See https://github.com/golang/go/issues/25448
-// for details.
 type recoverHandlerInterceptor struct {
 	Interceptor
 
@@ -43,10 +33,8 @@ func (i *recoverHandlerInterceptor) WrapUnary(next UnaryFunc) UnaryFunc {
 		if req.Spec().IsClient {
 			return next(ctx, req)
 		}
-		panicked := true
 		defer func() {
-			if panicked {
-				r := recover()
+			if r := recover(); r != nil {
 				// net/http checks for ErrAbortHandler with ==, so we should too.
 				if r == http.ErrAbortHandler { //nolint:errorlint,goerr113
 					panic(r) //nolint:forbidigo
@@ -55,26 +43,22 @@ func (i *recoverHandlerInterceptor) WrapUnary(next UnaryFunc) UnaryFunc {
 			}
 		}()
 		res, err := next(ctx, req)
-		panicked = false
 		return res, err
 	}
 }
 
 func (i *recoverHandlerInterceptor) WrapStreamingHandler(next StreamingHandlerFunc) StreamingHandlerFunc {
 	return func(ctx context.Context, conn StreamingHandlerConn) (retErr error) {
-		panicked := true
 		defer func() {
-			if panicked {
-				r := recover()
+			if r := recover(); r != nil {
 				// net/http checks for ErrAbortHandler with ==, so we should too.
 				if r == http.ErrAbortHandler { //nolint:errorlint,goerr113
 					panic(r) //nolint:forbidigo
 				}
-				retErr = i.handle(ctx, Spec{}, nil, r)
+				retErr = i.handle(ctx, conn.Spec(), conn.RequestHeader(), r)
 			}
 		}()
 		err := next(ctx, conn)
-		panicked = false
 		return err
 	}
 }