Fix window buffer wrap-around in zstd compression/decompression

The zstd implementation had a critical buffer overflow bug when updating the
window buffer. When copying data to the circular window buffer, the code did not
properly handle the case where the data would wrap around the buffer boundary.

For example, with a 128KB window and 65535-byte blocks, if the current position
was at 100KB, a memcpy would attempt to write past the 128KB boundary, causing
a heap buffer overflow.

This fix properly handles circular buffer wrap-around by splitting the memcpy
into two operations when necessary:
- Part 1: Copy from current position to end of buffer
- Part 2: Copy remaining data from start of buffer

This ensures the circular buffer implementation remains within bounds and fixes
the segmentation fault that occurred on Linux when compressing large files
with zstd method.

Author: radare

.DS_Store

@@ -0,0 +1,2 @@
+hello
+

debug/expected_hello.txt

@@ -0,0 +1 @@
+hello

debug/hello.txt

@@ -0,0 +1,90 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <zlib.h>
+
+int main(int argc, char *argv[]) {
+	if (argc < 3) {
+		printf ("Usage: %s <input_file> <output_file>\n", argv[0]);
+		return 1;
+	}
+
+	// Open the input file
+	FILE *fin = fopen (argv[1], "rb");
+	if (!fin) {
+		perror ("Failed to open input file");
+		return 1;
+	}
+
+	// Get the file size
+	fseek (fin, 0, SEEK_END);
+	long file_size = ftell (fin);
+	fseek (fin, 0, SEEK_SET);
+
+	// Read the compressed data
+	unsigned char *compressed_data = malloc (file_size);
+	if (fread (compressed_data, 1, file_size, fin) != file_size) {
+		perror ("Failed to read input file");
+		fclose (fin);
+		free (compressed_data);
+		return 1;
+	}
+	fclose (fin);
+
+	// Allocate output buffer (assuming output won't be more than 10x input)
+	unsigned char *decompressed_data = malloc (file_size * 10);
+
+	// Set up zlib stream for decompression
+	z_stream strm;
+	memset (&strm, 0, sizeof (strm));
+	strm.next_in = compressed_data;
+	strm.avail_in = file_size;
+	strm.next_out = decompressed_data;
+	strm.avail_out = file_size * 10;
+
+	// Initialize with raw deflate format (negative window bits)
+	if (inflateInit2 (&strm, -MAX_WBITS) != Z_OK) {
+		fprintf (stderr, "Failed to initialize zlib\n");
+		free (compressed_data);
+		free (decompressed_data);
+		return 1;
+	}
+
+	// Decompress
+	int ret = inflate (&strm, Z_FINISH);
+	if (ret != Z_STREAM_END) {
+		fprintf (stderr, "Decompression failed, error code: %d\n", ret);
+		inflateEnd (&strm);
+		free (compressed_data);
+		free (decompressed_data);
+		return 1;
+	}
+
+	// Get the decompressed size
+	unsigned long decompressed_size = strm.total_out;
+	inflateEnd (&strm);
+
+	// Write the decompressed data to the output file
+	FILE *fout = fopen (argv[2], "wb");
+	if (!fout) {
+		perror ("Failed to open output file");
+		free (compressed_data);
+		free (decompressed_data);
+		return 1;
+	}
+
+	if (fwrite (decompressed_data, 1, decompressed_size, fout) != decompressed_size) {
+		perror ("Failed to write output file");
+		fclose (fout);
+		free (compressed_data);
+		free (decompressed_data);
+		return 1;
+	}
+
+	fclose (fout);
+	free (compressed_data);
+	free (decompressed_data);
+
+	printf ("Decompressed %lu bytes of data\n", decompressed_size);
+	return 0;
+}

debug/test.zip

@@ -0,0 +1 @@
+world

debug/test_deflate

@@ -0,0 +1 @@
+hello