Fix parser when address is empty token

Bug detected by go-fuzz (more fuzzing is required; need larger corpus)

config/config.go

@@ -36,6 +36,9 @@ func Load(filename string, input io.Reader) (Group, error) {
 	if err != nil {
 		return nil, err
 	}
+	if len(serverBlocks) == 0 {
+		return Default()
+	}
 
 	// Each server block represents one or more servers/addresses.
 	// Iterate each server block and make a config for each one,

config/parse/parsing.go

@@ -21,7 +21,9 @@ func (p *parser) parseAll() ([]ServerBlock, error) {
 		if err != nil {
 			return blocks, err
 		}
-		blocks = append(blocks, p.block)
+		if len(p.block.Addresses) > 0 {
+			blocks = append(blocks, p.block)
+		}
 	}
 
 	return blocks, nil
@@ -85,21 +87,23 @@ func (p *parser) addresses() error {
 			break
 		}
 
-		// Trailing comma indicates another address will follow, which
-		// may possibly be on the next line
-		if tkn[len(tkn)-1] == ',' {
-			tkn = tkn[:len(tkn)-1]
-			expectingAnother = true
-		} else {
-			expectingAnother = false // but we may still see another one on this line
-		}
+		if tkn != "" {
+			// Trailing comma indicates another address will follow, which
+			// may possibly be on the next line
+			if tkn[len(tkn)-1] == ',' {
+				tkn = tkn[:len(tkn)-1]
+				expectingAnother = true
+			} else {
+				expectingAnother = false // but we may still see another one on this line
+			}
 
-		// Parse and save this address
-		host, port, err := standardAddress(tkn)
-		if err != nil {
-			return err
+			// Parse and save this address
+			host, port, err := standardAddress(tkn)
+			if err != nil {
+				return err
+			}
+			p.block.Addresses = append(p.block.Addresses, Address{host, port})
 		}
-		p.block.Addresses = append(p.block.Addresses, Address{host, port})
 
 		// Advance token and possibly break out of loop or return error
 		hasNext := p.Next()

config/parse/parsing_test.go

@@ -61,7 +61,7 @@ func TestParseOneAndImport(t *testing.T) {
 
 	testParseOne := func(input string) (ServerBlock, error) {
 		p := testParser(input)
-		p.Next()
+		p.Next() // parseOne doesn't call Next() to start, so we must
 		err := p.parseOne()
 		return p.block, err
 	}
@@ -234,6 +234,10 @@ func TestParseOneAndImport(t *testing.T) {
 			"dir1": 1,
 			"dir2": 2,
 		}},
+
+		{``, false, []Address{}, map[string]int{}},
+
+		{`""`, false, []Address{}, map[string]int{}},
 	} {
 		result, err := testParseOne(test.input)
 
@@ -275,6 +279,62 @@ func TestParseOneAndImport(t *testing.T) {
 	}
 }
 
+func TestParseAll(t *testing.T) {
+	setupParseTests()
+
+	testParseAll := func(input string) ([]ServerBlock, error) {
+		p := testParser(input)
+		return p.parseAll()
+	}
+
+	for i, test := range []struct {
+		input     string
+		shouldErr bool
+		numBlocks int
+	}{
+		{`localhost`, false, 1},
+
+		{`localhost {
+			    dir1
+			  }`, false, 1},
+
+		{`http://localhost https://localhost
+			  dir1 foo bar`, false, 1},
+
+		{`http://localhost, https://localhost {
+			    dir1 foo bar
+			  }`, false, 1},
+
+		{`http://host1.com,
+			  http://host2.com,
+			  https://host3.com`, false, 1},
+
+		{`host1 {
+			}
+			host2 {
+			}`, false, 2},
+
+		{`""`, false, 0},
+
+		{``, false, 0},
+	} {
+		results, err := testParseAll(test.input)
+
+		if test.shouldErr && err == nil {
+			t.Errorf("Test %d: Expected an error, but didn't get one", i)
+		}
+		if !test.shouldErr && err != nil {
+			t.Errorf("Test %d: Expected no error, but got: %v", i, err)
+		}
+
+		if len(results) != test.numBlocks {
+			t.Errorf("Test %d: Expected %d server blocks, got %d",
+				i, test.numBlocks, len(results))
+			continue
+		}
+	}
+}
+
 func setupParseTests() {
 	// Set up some bogus directives for testing
 	ValidDirectives = map[string]struct{}{