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NetworkReader/Writer: all types of collections are now encoded via count-offsetting (null=0, []=1) for consistency and to prepare for VarUInt compression (this way we won't need zig zag VarInt) (#3869)

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* better comments about count offsetting

* NetworkReader/Writer: all types of collections are now encoded via count-offsetting (null=0, []=1) for consistency and to prepare for VarUInt compression (this way we won't need zig zag VarInt)

---------

Co-authored-by: mischa <info@noobtuts.com>
This commit is contained in:
mischa 2024-07-23 17:15:26 +02:00 committed by MrGadget
parent 14f387f752
commit 9bb17e67bc
3 changed files with 61 additions and 35 deletions
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42
Assets/Mirror/Core/NetworkReaderExtensions.cs
View File

@ -97,8 +97,9 @@ public static byte[] ReadBytes(this NetworkReader reader, int count)
/// <exception cref="T:OverflowException">if count is invalid</exception>
public static byte[] ReadBytesAndSize(this NetworkReader reader)
{
// count = 0 means the array was null
// otherwise count -1 is the length of the array
// we offset count by '1' to easily support null without writing another byte.
// encoding null as '0' instead of '-1' also allows for better compression
// (ushort vs. short / varuint vs. varint) etc.
uint count = reader.ReadUInt();
// Use checked() to force it to throw OverflowException if data is invalid
return count == 0 ? null : reader.ReadBytes(checked((int)(count - 1u)));
@ -107,8 +108,9 @@ public static byte[] ReadBytesAndSize(this NetworkReader reader)
/// <exception cref="T:OverflowException">if count is invalid</exception>
public static ArraySegment<byte> ReadArraySegmentAndSize(this NetworkReader reader)
{
// count = 0 means the array was null
// otherwise count - 1 is the length of the array
// we offset count by '1' to easily support null without writing another byte.
// encoding null as '0' instead of '-1' also allows for better compression
// (ushort vs. short / varuint vs. varint) etc.
uint count = reader.ReadUInt();
// Use checked() to force it to throw OverflowException if data is invalid
return count == 0 ? default : reader.ReadBytesSegment(checked((int)(count - 1u)));
@ -264,10 +266,12 @@ public static GameObject ReadGameObject(this NetworkReader reader)
// note that Weaver/Readers/GenerateReader() handles this manually.
public static List<T> ReadList<T>(this NetworkReader reader)
{
int length = reader.ReadInt();
// 'null' is encoded as '-1'
if (length < 0) return null;
// we offset count by '1' to easily support null without writing another byte.
// encoding null as '0' instead of '-1' also allows for better compression
// (ushort vs. short / varuint vs. varint) etc.
uint length = reader.ReadUInt();
if (length == 0) return null;
length -= 1;
// prevent allocation attacks with a reasonable limit.
// server shouldn't allocate too much on client devices.
@ -278,7 +282,7 @@ public static List<T> ReadList<T>(this NetworkReader reader)
throw new EndOfStreamException($"NetworkReader attempted to allocate a List<{typeof(T)}> {length} elements, which is larger than the allowed limit of {NetworkReader.AllocationLimit}.");
}
List<T> result = new List<T>(length);
List<T> result = new List<T>((checked((int)length)));
for (int i = 0; i < length; i++)
{
result.Add(reader.Read<T>());
@ -294,9 +298,13 @@ public static List<T> ReadList<T>(this NetworkReader reader)
/*
public static HashSet<T> ReadHashSet<T>(this NetworkReader reader)
{
int length = reader.ReadInt();
if (length < 0)
return null;
// we offset count by '1' to easily support null without writing another byte.
// encoding null as '0' instead of '-1' also allows for better compression
// (ushort vs. short / varuint vs. varint) etc.
uint length = reader.ReadUInt();
if (length == 0) return null;
length -= 1;
HashSet<T> result = new HashSet<T>();
for (int i = 0; i < length; i++)
{
@ -308,10 +316,12 @@ public static HashSet<T> ReadHashSet<T>(this NetworkReader reader)
public static T[] ReadArray<T>(this NetworkReader reader)
{
int length = reader.ReadInt();
// 'null' is encoded as '-1'
if (length < 0) return null;
// we offset count by '1' to easily support null without writing another byte.
// encoding null as '0' instead of '-1' also allows for better compression
// (ushort vs. short / varuint vs. varint) etc.
uint length = reader.ReadUInt();
if (length == 0) return null;
length -= 1;
// prevent allocation attacks with a reasonable limit.
// server shouldn't allocate too much on client devices.

51
Assets/Mirror/Core/NetworkWriterExtensions.cs
View File

@ -51,10 +51,9 @@ public static class NetworkWriterExtensions
public static void WriteString(this NetworkWriter writer, string value)
{
// write 0 for null support, increment real size by 1
// (note: original HLAPI would write "" for null strings, but if a
// string is null on the server then it should also be null
// on the client)
// we offset count by '1' to easily support null without writing another byte.
// encoding null as '0' instead of '-1' also allows for better compression
// (ushort vs. short / varuint vs. varint) etc.
if (value == null)
{
writer.WriteUShort(0);
@ -94,9 +93,10 @@ public static void WriteBytesAndSize(this NetworkWriter writer, byte[] buffer)
// (like an inventory with different items etc.)
public static void WriteBytesAndSize(this NetworkWriter writer, byte[] buffer, int offset, int count)
{
// null is supported because [SyncVar]s might be structs with null byte[] arrays
// write 0 for null array, increment normal size by 1 to save bandwidth
// (using size=-1 for null would limit max size to 32kb instead of 64kb)
// null is supported because [SyncVar]s might be structs with null byte[] arrays.
// we offset count by '1' to easily support null without writing another byte.
// encoding null as '0' instead of '-1' also allows for better compression
// (ushort vs. short / varuint vs. varint) etc.
if (buffer == null)
{
writer.WriteUInt(0u);
@ -115,9 +115,17 @@ public static void WriteArraySegmentAndSize(this NetworkWriter writer, ArraySegm
// writes ArraySegment of any type, and size header
public static void WriteArraySegment<T>(this NetworkWriter writer, ArraySegment<T> segment)
{
int length = segment.Count;
writer.WriteInt(length);
for (int i = 0; i < length; i++)
// we offset count by '1' to easily support null without writing another byte.
// encoding null as '0' instead of '-1' also allows for better compression
// (ushort vs. short / varuint vs. varint) etc.
//
// ArraySegment technically can't be null, but users may call:
// - WriteArraySegment
// - ReadArray
// in which case ReadArray needs null support. both need to be compatible.
int count = segment.Count;
writer.WriteUInt(checked((uint)count) + 1u);
for (int i = 0; i < count; i++)
{
writer.Write(segment.Array[segment.Offset + i]);
}
@ -315,10 +323,12 @@ public static void WriteGameObject(this NetworkWriter writer, GameObject value)
// note that Weaver/Writers/GenerateWriter() handles this manually.
public static void WriteList<T>(this NetworkWriter writer, List<T> list)
{
// 'null' is encoded as '-1'
// we offset count by '1' to easily support null without writing another byte.
// encoding null as '0' instead of '-1' also allows for better compression
// (ushort vs. short / varuint vs. varint) etc.
if (list is null)
{
writer.WriteInt(-1);
writer.WriteUInt(0);
return;
}
@ -326,7 +336,7 @@ public static void WriteList<T>(this NetworkWriter writer, List<T> list)
if (list.Count > NetworkReader.AllocationLimit)
throw new IndexOutOfRangeException($"NetworkWriter.WriteList - List<{typeof(T)}> too big: {list.Count} elements. Limit: {NetworkReader.AllocationLimit}");
writer.WriteInt(list.Count);
writer.WriteUInt(checked((uint)list.Count) + 1u);
for (int i = 0; i < list.Count; i++)
writer.Write(list[i]);
}
@ -339,12 +349,15 @@ public static void WriteList<T>(this NetworkWriter writer, List<T> list)
/*
public static void WriteHashSet<T>(this NetworkWriter writer, HashSet<T> hashSet)
{
// we offset count by '1' to easily support null without writing another byte.
// encoding null as '0' instead of '-1' also allows for better compression
// (ushort vs. short / varuint vs. varint) etc.
if (hashSet is null)
{
writer.WriteInt(-1);
writer.WriteUInt(0);
return;
}
writer.WriteInt(hashSet.Count);
writer.WriteUInt(checked((uint)hashSet.Count) + 1u);
foreach (T item in hashSet)
writer.Write(item);
}
@ -352,10 +365,12 @@ public static void WriteHashSet<T>(this NetworkWriter writer, HashSet<T> hashSet
public static void WriteArray<T>(this NetworkWriter writer, T[] array)
{
// 'null' is encoded as '-1'
// we offset count by '1' to easily support null without writing another byte.
// encoding null as '0' instead of '-1' also allows for better compression
// (ushort vs. short / varuint vs. varint) etc.
if (array is null)
{
writer.WriteInt(-1);
writer.WriteUInt(0);
return;
}
@ -363,7 +378,7 @@ public static void WriteArray<T>(this NetworkWriter writer, T[] array)
if (array.Length > NetworkReader.AllocationLimit)
throw new IndexOutOfRangeException($"NetworkWriter.WriteArray - Array<{typeof(T)}> too big: {array.Length} elements. Limit: {NetworkReader.AllocationLimit}");
writer.WriteInt(array.Length);
writer.WriteUInt(checked((uint)array.Length) + 1u);
for (int i = 0; i < array.Length; i++)
writer.Write(array[i]);
}

3
Assets/Mirror/Tests/Editor/NetworkReaderWriter/NetworkWriterTest.cs
View File

@ -1404,7 +1404,8 @@ public void TestArrayThrowsIfLengthIsWrong(int badLength)
void WriteBadArray()
{
writer.WriteInt(badLength);
// Reader/Writer encode null as count=0 and [] as count=1 (+1 offset)
writer.WriteUInt((uint)(badLength+1));
int[] array = new int[testArraySize] { 1, 2, 3, 4 };
for (int i = 0; i < array.Length; i++)
writer.Write(array[i]);