Fix NewPaginationTokenFromString, define unit test for it

syncapi/types/types.go

@@ -16,6 +16,7 @@ package types
 
 import (
 	"encoding/json"
+	"errors"
 	"fmt"
 	"strconv"
 	"strings"
@@ -29,6 +30,9 @@ var (
 	// new instance of PaginationToken with an invalid type (i.e. neither "s"
 	// nor "t").
 	ErrInvalidPaginationTokenType = fmt.Errorf("Pagination token has an unknown prefix (should be either s or t)")
+	// ErrInvalidPaginationTokenLen is returned when the pagination token is an
+	// invalid length
+	ErrInvalidPaginationTokenLen = fmt.Errorf("Pagination token has an invalid length")
 )
 
 // StreamPosition represents the offset in the sync stream a client is at.
@@ -71,27 +75,28 @@ type PaginationToken struct {
 // isn't a known type (returns ErrInvalidPaginationTokenType in the latter
 // case).
 func NewPaginationTokenFromString(s string) (token *PaginationToken, err error) {
+	if len(s) == 0 {
+		return nil, ErrInvalidPaginationTokenLen
+	}
+
 	token = new(PaginationToken)
+	var positions []string
 
-	// Check if the type is among the known ones.
-	token.Type = PaginationTokenType(s[:1])
-	if token.Type != PaginationTokenTypeStream && token.Type != PaginationTokenTypeTopology {
-		if pduPos, perr := strconv.ParseInt(s, 10, 64); perr != nil {
-			return nil, ErrInvalidPaginationTokenType
-		} else {
+	switch t := PaginationTokenType(s[:1]); t {
+	case PaginationTokenTypeStream, PaginationTokenTypeTopology:
+		token.Type = t
+		positions = strings.Split(s[1:], "_")
+	default:
 		token.Type = PaginationTokenTypeStream
-			token.PDUPosition = StreamPosition(pduPos)
-			return
+		positions = strings.Split(s, "_")
 	}
-	}
-
-	// Parse the token (aka position).
-	positions := strings.Split(s[1:], "_")
 
 	// Try to get the PDU position.
 	if len(positions) >= 1 {
 		if pduPos, err := strconv.ParseInt(positions[0], 10, 64); err != nil {
 			return nil, err
+		} else if pduPos < 0 {
+			return nil, errors.New("negative PDU position not allowed")
 		} else {
 			token.PDUPosition = StreamPosition(pduPos)
 		}
@@ -101,6 +106,8 @@ func NewPaginationTokenFromString(s string) (token *PaginationToken, err error)
 	if len(positions) >= 2 {
 		if typPos, err := strconv.ParseInt(positions[1], 10, 64); err != nil {
 			return nil, err
+		} else if typPos < 0 {
+			return nil, errors.New("negative EDU typing position not allowed")
 		} else {
 			token.EDUTypingPosition = StreamPosition(typPos)
 		}

syncapi/types/types_test.go

@@ -0,0 +1,52 @@
+package types
+
+import "testing"
+
+func TestNewPaginationTokenFromString(t *testing.T) {
+	shouldPass := map[string]PaginationToken{
+		"2": PaginationToken{
+			Type:        PaginationTokenType("s"),
+			PDUPosition: 2,
+		},
+		"s4": PaginationToken{
+			Type:        PaginationTokenType("s"),
+			PDUPosition: 4,
+		},
+		"s3_1": PaginationToken{
+			Type:              PaginationTokenType("s"),
+			PDUPosition:       3,
+			EDUTypingPosition: 1,
+		},
+		"t3_1_4": PaginationToken{
+			Type:              PaginationTokenType("t"),
+			PDUPosition:       3,
+			EDUTypingPosition: 1,
+		},
+	}
+
+	shouldFail := []string{
+		"",
+		"s_1",
+		"s_",
+		"a3_4",
+		"b",
+		"b-1",
+		"-4",
+	}
+
+	for test, expected := range shouldPass {
+		result, err := NewPaginationTokenFromString(test)
+		if err != nil {
+			t.Error(err)
+		}
+		if *result != expected {
+			t.Errorf("expected %v but got %v", expected.String(), result.String())
+		}
+	}
+
+	for _, test := range shouldFail {
+		if _, err := NewPaginationTokenFromString(test); err == nil {
+			t.Errorf("input '%v' should have errored but didn't", test)
+		}
+	}
+}