pan: isolate Rains resolver context handling

The rains.Query function takes a timeout value instead of a context, use a default timeout if the context has no deadline.

Author: FR4NK-W

pkg/pan/hosts.go

@@ -93,10 +93,9 @@ func (resolvers resolverList) Resolve(ctx context.Context, name string) (scionAd
 			continue
 		}
 		// check ctx to avoid unnecessary calls with already expired context
-		select {
-		case <-ctx.Done():
+		if err := ctx.Err(); err != nil {
+			rerr = err
 			break
-		default:
 		}
 		addr, err := resolver.Resolve(ctx, name)
 		if err == nil {

pkg/pan/pan.go

@@ -110,7 +110,6 @@ import (
 // ResolveUDPAddr parses the address and resolves the hostname.
 // The address can be of the form of a SCION address (i.e. of the form "ISD-AS,[IP]:port")
 // or in the form of "hostname:port".
-// Default timeout is 1 second, use ResolveUDPAddrContext to provide an explicit context.
 // If the address is in the form of a hostname, the the following sources will
 // be used to resolve a name, in the given order of precedence.
 //

pkg/pan/rains.go

@@ -21,6 +21,7 @@ import (
 	"context"
 	"fmt"
 	"io/ioutil"
+	"net"
 	"os"
 	"strings"
 	"time"
@@ -64,7 +65,7 @@ func readRainsConfig() (UDPAddr, error) {
 	return address, nil
 }
 
-func rainsQuery(ctx context.Context, server UDPAddr, hostname string) (addr scionAddr, err error) {
+func rainsQuery(ctx context.Context, server UDPAddr, hostname string) (scionAddr, error) {
 	const (
 		rainsCtx = "."                    // use global context
 		qType    = rains.OTScionAddr      // request SCION addresses
@@ -73,40 +74,48 @@ func rainsQuery(ctx context.Context, server UDPAddr, hostname string) (addr scio
 	)
 	qOpts := []rains.Option{} // no options
 
-	// TODO(matzf): check that this actually works
-	// - return error on timeout, network problems, invalid format, ...
-	// - return HostNotFoundError error if all went well, but host not found
 	// TODO(chaehni): This call can sometimes cause a timeout even though the server is reachable (see issue #221)
-	// The timeout value has been decreased to counter this behavior until the problem is resolved.
+	// The (default) timeout value has been decreased to counter this behavior until the problem is resolved.
 	srv := server.snetUDPAddr()
 
+	reply, err := rainsQueryChecked(ctx, hostname, rainsCtx, []rains.Type{qType}, qOpts, expire, timeout, srv)
+	if err != nil {
+		return scionAddr{}, err
+	}
+	addrStr, ok := reply[qType]
+	if !ok {
+		return scionAddr{}, &HostNotFoundError{hostname}
+	}
+	addr, err := parseSCIONAddr(addrStr)
+	if err != nil {
+		return scionAddr{}, fmt.Errorf("address for host %q invalid: %w", hostname, err)
+	}
+	return addr, nil
+}
+
+func rainsQueryChecked(ctx context.Context, name, rainsCtx string, types []rains.Type, opts []rains.Option,
+	expire, timeout time.Duration, addr net.Addr) (res map[rains.Type]string, err error) {
+
+	var contextTimeout time.Duration
+	deadline, finite := ctx.Deadline()
+	if finite {
+		contextTimeout = time.Until(deadline)
+		if contextTimeout < 0 {
+			return res, context.DeadlineExceeded
+		}
+	} else {
+		contextTimeout = timeout
+	}
+
 	done := make(chan struct{})
 	go func() {
 		defer close(done)
-		var reply map[rains.Type]string
-		reply, err = rains.Query(hostname, rainsCtx, []rains.Type{qType}, qOpts, expire, timeout, srv)
-		if err != nil {
-			err = fmt.Errorf("address for host %q not found: %w", hostname, err)
-			return
-		}
-		addrStr, ok := reply[qType]
-		if !ok {
-			err = &HostNotFoundError{hostname}
-			return
-		}
-		addr, err = parseSCIONAddr(addrStr)
-		if err != nil {
-			err = fmt.Errorf("address for host %q invalid: %w", hostname, err)
-			addr = scionAddr{}
-		}
+		res, err = rains.Query(name, rainsCtx, types, opts, expire, contextTimeout, addr)
 	}()
 	select {
 	case <-ctx.Done():
-		return scionAddr{}, context.DeadlineExceeded
+		return res, ctx.Err()
 	case <-done:
 	}
-	if err != nil {
-		return scionAddr{}, err
-	}
-	return addr, nil
+	return
 }