1 files changed, 211 insertions, 0 deletions
diff --git a/LibGit/Extensions/StreamExtensions.cs b/LibGit/Extensions/StreamExtensions.cs
new file mode 100644
index 0000000..6555783
--- /dev/null
+++ b/LibGit/Extensions/StreamExtensions.cs
@@ -0,0 +1,211 @@
+using System.IO.Compression;
+
+namespace LibGit.Extensions;
+
+public static class StreamExtensions
+{
+    private const bool _debug = false;
+
+    public static long Remaining(this Stream stream)
+    {
+        //if (_debug) Console.WriteLine($"stream pos: {stream.Position}, stream len: {stream.Length}, stream rem: {stream.Length - stream.Position}");
+        return stream.Length - stream.Position;
+    }
+
+    public static int Peek(this Stream stream)
+    {
+        if (!stream.CanRead)
+            throw new InvalidOperationException("Can't peek a non-readable stream");
+        if (!stream.CanSeek)
+            throw new InvalidOperationException("Can't peek a non-seekable stream");
+
+        int peek = stream.ReadByte();
+        if (peek != -1)
+            stream.Seek(-1, SeekOrigin.Current);
+
+        return peek;
+    }
+
+    public static IEnumerable<byte> Peek(this Stream stream, long count)
+    {
+        if (!stream.CanRead)
+            throw new InvalidOperationException("Can't peek a non-readable stream");
+        if (!stream.CanSeek)
+            throw new InvalidOperationException("Can't peek a non-seekable stream");
+        long i;
+        for (i = 0; i < count; i++)
+        {
+            int peek = stream.ReadByte();
+            if (peek == -1)
+            {
+                if(_debug) Console.WriteLine($"Can't peek {count} bytes, only {i} bytes remaining");
+                stream.Seek(-i, SeekOrigin.Current);
+                yield break;
+            }
+
+            yield return (byte)peek;
+        }
+        stream.Seek(-i, SeekOrigin.Current);
+    }
+
+    public static IEnumerable<byte> ReadBytes(this Stream stream, long count)
+    {
+        if (!stream.CanRead)
+            throw new InvalidOperationException("Can't read a non-readable stream");
+        if (!stream.CanSeek)
+            throw new InvalidOperationException("Can't read a non-seekable stream");
+
+        for (long i = 0; i < count; i++)
+        {
+            int read = stream.ReadByte();
+            if (read == -1)
+                yield break;
+            yield return (byte)read;
+        }
+    }
+
+    public static bool StartsWith(this Stream stream, IEnumerable<byte> sequence)
+    {
+        if (!stream.CanRead)
+            throw new InvalidOperationException("Can't read a non-readable stream");
+        if (!stream.CanSeek)
+            throw new InvalidOperationException("Can't read a non-seekable stream");
+
+        if (_debug)
+        {
+            Console.WriteLine($"Expected: {sequence.AsHexString()} ({sequence.AsString()})");
+            Console.WriteLine($"Actual:   {stream.Peek(sequence.Count()).AsHexString()} ({stream.Peek(sequence.Count()).AsString()})");
+        }
+        
+        int readCount = 0;
+        foreach (int b in sequence)
+        {
+            int read = stream.ReadByte();
+            readCount++;
+            if (read == -1)
+            {
+                stream.Seek(-readCount, SeekOrigin.Current);
+                return false;
+            }
+            
+            if (read != b)
+            {
+                if (_debug)
+                {
+                    Console.ForegroundColor = ConsoleColor.Red;
+                    Console.WriteLine("^^".PadLeft(readCount * 3 + 9));
+                    Console.ResetColor();
+                }
+
+                stream.Seek(-readCount, SeekOrigin.Current);
+                return false;
+            }
+        }
+        stream.Seek(-readCount, SeekOrigin.Current);
+        
+        return true;
+    }
+
+    public static bool StartsWith(this Stream stream, string ascii_seq)
+    {
+        return stream.StartsWith(ascii_seq.Select(x => (byte)x));
+    }
+
+    public static Stream Skip(this Stream stream, long count = 1)
+    {
+        if (!stream.CanSeek)
+            throw new InvalidOperationException("Can't skip a non-seekable stream");
+        stream.Seek(count, SeekOrigin.Current);
+        return stream;
+    }
+
+    public static IEnumerable<byte> ReadNullTerminatedField(this Stream stream, IEnumerable<byte>? binaryPrefix = null, string? asciiPrefix = null) => ReadTerminatedField(stream: stream, terminator: 0x00, binaryPrefix: binaryPrefix, asciiPrefix: asciiPrefix);
+    public static IEnumerable<byte> ReadSpaceTerminatedField(this Stream stream, IEnumerable<byte>? binaryPrefix = null, string? asciiPrefix = null) => ReadTerminatedField(stream: stream, terminator: 0x20, binaryPrefix: binaryPrefix, asciiPrefix: asciiPrefix);
+    public static IEnumerable<byte> ReadTerminatedField(this Stream stream, byte terminator, IEnumerable<byte>? binaryPrefix = null, string? asciiPrefix = null)
+    {
+        if (!stream.CanRead)
+            throw new InvalidOperationException("Can't read a non-readable stream");
+        if (binaryPrefix != null)
+            if (!stream.StartsWith(binaryPrefix))
+                throw new InvalidDataException($"Binary prefix {stream.Peek(binaryPrefix.Count()).AsHexString()} does not match expected value of {binaryPrefix.AsHexString()}!");
+            else stream.Skip(binaryPrefix.Count());
+        else if (asciiPrefix != null)
+            if (!stream.StartsWith(asciiPrefix))
+                throw new InvalidDataException($"Text prefix {stream.Peek(asciiPrefix.Length).AsHexString()} ({stream.Peek(asciiPrefix.Length).AsString()}) does not match expected value of {asciiPrefix.AsBytes().AsHexString()} ({asciiPrefix})!");
+            else stream.Skip(asciiPrefix.Length);
+
+        var read = 0;
+        while (stream.Peek() != terminator)
+        {
+            if (_debug) Console.WriteLine($"ReadTerminatedField -- pos: {stream.Position}/+{stream.Remaining()}/{stream.Length} | next: {(char)stream.Peek()} | Length: {read}");
+            if (stream.Peek() == -1)
+            {
+                Console.WriteLine($"Warning: Reached end of stream while reading null-terminated field");
+                yield break;
+            }
+
+            read++;
+            yield return (byte)stream.ReadByte();
+        }
+
+        if (stream.Peek() == terminator) stream.Skip();
+    }
+    
+    public static IEnumerable<byte> ReadToEnd(this Stream stream)
+    {
+        if (!stream.CanRead)
+            throw new InvalidOperationException("Can't read a non-readable stream");
+
+        while (stream.Peek() != -1)
+            yield return (byte)stream.ReadByte();
+    }
+    
+    public static int ReadInt32BE(this Stream stream)
+    {
+        if (!stream.CanRead)
+            throw new InvalidOperationException("Can't read a non-readable stream");
+
+        var bytes = stream.ReadBytes(4).ToArray();
+        
+        if (BitConverter.IsLittleEndian)
+            Array.Reverse(bytes);
+        
+        Console.WriteLine("ReadInt32BE: " + bytes.AsHexString() + " => " + BitConverter.ToInt32(bytes));
+        return BitConverter.ToInt32(bytes);
+    }
+    
+    //read variable length number
+    public static int ReadVLQ(this Stream stream)
+    {
+        if (!stream.CanRead)
+            throw new InvalidOperationException("Can't read a non-readable stream");
+
+        int result = 0;
+        int shift = 0;
+        byte b;
+        do
+        {
+            b = (byte)stream.ReadByte();
+            result |= (b & 0b0111_1111) << shift;
+            shift += 7;
+        } while ((b & 0b1000_0000) != 0);
+
+        return result;
+    }
+    public static int ReadVLQBigEndian(this Stream stream)
+    {
+        if (!stream.CanRead)
+            throw new InvalidOperationException("Can't read a non-readable stream");
+
+        int result = 0;
+        int shift = 0;
+        byte b;
+        do
+        {
+            b = (byte)stream.ReadByte();
+            result = (result << 7) | (b & 0b0111_1111);
+        } while ((b & 0b1000_0000) != 0);
+
+        return result;
+    }
+}
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