Return error from ParseRemainingChunksFromNonce

ads/ads.go

@@ -7,6 +7,7 @@ package ads
 import (
 	"encoding/binary"
 	"encoding/hex"
+	"errors"
 	"log/slog"
 	"sync"
 	"time"
@@ -258,23 +259,29 @@ func LookupStreamTypeByRPCMethod(rpcMethod string) (StreamType, bool) {
 	}
 }
 
+var (
+	invalidNonceEncodingErr = errors.New("nonce isn't in hex encoding")
+	invalidNonceLengthErr   = errors.New("decoded nonce did not have expected length")
+)
+
 // ParseRemainingChunksFromNonce checks whether the Diderot server implementation chunked the delta
 // responses because not all resources could fit in the same response without going over the default
 // max gRPC message size of 4MB. A nonce from Diderot always starts with the 64-bit nanosecond
 // timestamp of when the response was generated on the server. Then the number of remaining chunks as
 // a 32-bit integer. The sequence of integers is binary encoded with [binary.BigEndian] then hex
-// encoded. If the given nonce does not match the expected format, this function simply returns 0, as
-// it means the nonce was not created by Diderot server implementation, and therefore does not
-// contain the expected information.
-func ParseRemainingChunksFromNonce(nonce string) (remainingChunks int) {
+// encoded. If the given nonce does not match the expected format, this function simply returns 0
+// along with an error describing why it does not match. If the error isn't nil, it means the nonce
+// was not created by a Diderot server implementation, and therefore does not contain the expected
+// information.
+func ParseRemainingChunksFromNonce(nonce string) (remainingChunks int, err error) {
 	decoded, err := hex.DecodeString(nonce)
 	if err != nil {
-		return 0
+		return 0, invalidNonceEncodingErr
 	}
 
 	if len(decoded) != 12 {
-		return 0
+		return 0, invalidNonceLengthErr
 	}
 
-	return int(binary.BigEndian.Uint32(decoded[8:12]))
+	return int(binary.BigEndian.Uint32(decoded[8:12])), nil
 }

internal/server/handlers_delta.go

@@ -92,7 +92,7 @@ type deltaSender struct {
 	queuedUpdates []queuedResourceUpdate
 	// The minimum size an encoded chunk will serialize to, in bytes. Used to check whether a given
 	// update can _ever_ be sent, and as the initial size of a chunk. Note that this value only depends
-	// on utils.MaxNonceLength and the length of typeURL.
+	// on utils.NonceLength and the length of typeURL.
 	minChunkSize int
 }