unsquashfs: add file data extraction

Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>

1 files changed, 97 insertions, 0 deletions

diff --git a/unpack/extract_file.c b/unpack/extract_file.c
new file mode 100644
index 0000000..c18ace8
--- /dev/null
+++ b/unpack/extract_file.c
@@ -0,0 +1,97 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+#include "unsquashfs.h"
+
+int extract_file(file_info_t *fi, compressor_t *cmp, size_t block_size,
+		 frag_reader_t *frag, int sqfsfd, int outfd)
+{
+	size_t i, count, fragsz;
+	bool compressed;
+	void *buffer;
+	uint32_t bs;
+	ssize_t ret;
+
+	buffer = malloc(block_size);
+	if (buffer == NULL) {
+		perror("allocating scratch buffer");
+		return -1;
+	}
+
+	count = fi->size / block_size;
+
+	if (count > 0) {
+		if (lseek(sqfsfd, fi->startblock, SEEK_SET) == (off_t)-1)
+			goto fail_seek;
+
+		for (i = 0; i < count; ++i) {
+			bs = fi->blocksizes[i];
+
+			compressed = (bs & (1 << 24)) == 0;
+			bs &= (1 << 24) - 1;
+
+			if (bs > block_size)
+				goto fail_bs;
+
+			ret = read_retry(sqfsfd, buffer, bs);
+			if (ret < 0)
+				goto fail_rd;
+
+			if ((size_t)ret < bs)
+				goto fail_trunc;
+
+			if (compressed) {
+				ret = cmp->do_block(cmp, buffer, bs);
+				if (ret <= 0)
+					goto fail;
+
+				bs = ret;
+			}
+
+			ret = write_retry(outfd, buffer, bs);
+			if (ret < 0)
+				goto fail_wr;
+
+			if ((size_t)ret < bs)
+				goto fail_wr_trunc;
+		}
+	}
+
+	fragsz = fi->size % block_size;
+
+	if (fragsz > 0) {
+		if (frag_reader_read(frag, fi->fragment, fi->fragment_offset,
+				     buffer, fragsz)) {
+			goto fail;
+		}
+
+		ret = write_retry(outfd, buffer, fragsz);
+		if (ret < 0)
+			goto fail_wr;
+
+		if ((size_t)ret < fragsz)
+			goto fail_wr_trunc;
+	}
+
+	free(buffer);
+	return 0;
+fail_seek:
+	perror("seek on squashfs");
+	goto fail;
+fail_wr:
+	perror("writing uncompressed block");
+	goto fail;
+fail_wr_trunc:
+	fputs("writing uncompressed block: truncated write\n", stderr);
+	goto fail;
+fail_rd:
+	perror("reading from squashfs");
+	goto fail;
+fail_trunc:
+	fputs("reading from squashfs: unexpected end of file\n", stderr);
+	goto fail;
+fail_bs:
+	fputs("found compressed block larger than block size\n", stderr);
+	goto fail;
+fail:
+	free(buffer);
+	return -1;
+}