EllanJiang/GameFramework · error · GameFrameworkException

Stream is not writable.

Error message

Stream is not writable.

What it means

FileSystem.ReadFile throws this when the destination stream exists but its CanWrite property is false. Reading a file copies bytes into the supplied stream, so the stream must be writable. Read-only streams (e.g. a stream opened from a file with FileAccess.Read, or Stream.Null) are rejected.

Solutions

1. Pass a writable stream such as new MemoryStream() or a FileStream opened with FileAccess.Write/ReadWrite.
2. Check stream.CanWrite before calling ReadFile.
3. If you only need the bytes, use the byte[]-oriented overloads (ReadFileSegment) instead of the stream overload.

Example fix

// before
using (var stream = File.OpenRead(path))
{
    fs.ReadFile(name, stream); // throws: CanWrite == false
}

// after
using (var stream = new MemoryStream())
{
    fs.ReadFile(name, stream);
}

if (stream == null || !stream.CanWrite)
    throw new ArgumentException("Stream must be writable to receive file contents", nameof(stream));
int read = fs.ReadFile(name, stream);

static bool IsWritableStream(Stream stream) => stream != null && stream.CanWrite;

try
{
    int read = fs.ReadFile(name, stream);
}
catch (GameFrameworkException ex) when (ex.Message == "Stream is not writable.")
{
    // swap in a MemoryStream / writable FileStream
}

When it happens

Trigger: Calling ReadFile with a stream obtained from File.OpenRead, a read-only FileStream, Stream.Null, or any Stream whose CanWrite returns false.

Common situations: Reusing the same read-only stream that was previously used to feed FileSystem.LoadFileSystem; wrapping a read-only underlying file; passing a readonly MemoryStream created over a fixed buffer (CanWrite is actually true there, so usually it is a read-only FileStream).

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• Stream is not readable.
• Offset is invalid.
• Length is invalid.
• Max file count is invalid.
• Max block count is invalid.

AI-assisted analysis of EllanJiang/GameFramework@d0c010b051 (2026-09-15). Data as JSON: /api/errors/74f614169a710a17. Report an issue: GitHub.

Appendix: source

Thrown at GameFramework/FileSystem/FileSystem.cs:469

        {
            if (m_Access != FileSystemAccess.Read && m_Access != FileSystemAccess.ReadWrite)
            {
                throw new GameFrameworkException("File system is not readable.");
            }

            if (string.IsNullOrEmpty(name))
            {
                throw new GameFrameworkException("Name is invalid.");
            }

            if (stream == null)
            {
                throw new GameFrameworkException("Stream is invalid.");
            }

            if (!stream.CanWrite)
            {
                throw new GameFrameworkException("Stream is not writable.");
            }

            FileInfo fileInfo = GetFileInfo(name);
            if (!fileInfo.IsValid)
            {
                return 0;
            }

            int length = fileInfo.Length;
            if (length > 0)
            {
                m_Stream.Position = fileInfo.Offset;
                return m_Stream.Read(stream, length);
            }

            return 0;
        }

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