Add meta data reader implementation

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

2 files changed, 125 insertions, 1 deletions

diff --git a/lib/Makemodule.am b/lib/Makemodule.am
index 026e3f1..5cadf58 100644
--- a/lib/Makemodule.am
+++ b/lib/Makemodule.am
@@ -11,7 +11,8 @@ libsquashfs_a_SOURCES = include/meta_writer.h include/squashfs.h
 libsquashfs_a_SOURCES += lib/sqfs/meta_writer.c lib/sqfs/super.c
 libsquashfs_a_SOURCES += lib/sqfs/id_table.c include/id_table.h
 libsquashfs_a_SOURCES += lib/sqfs/table.c include/table.h
-libsquashfs_a_SOURCES += lib/sqfs/read_super.c
+libsquashfs_a_SOURCES += lib/sqfs/read_super.c lib/sqfs/meta_reader.c
+libsquashfs_a_SOURCES += include/meta_reader.h
 
 libutil_a_SOURCES = lib/util/canonicalize_name.c lib/util/write_retry.c
 libutil_a_SOURCES += lib/util/read_retry.c include/util.h
diff --git a/lib/sqfs/meta_reader.c b/lib/sqfs/meta_reader.c
new file mode 100644
index 0000000..8cd7c8f
--- /dev/null
+++ b/lib/sqfs/meta_reader.c
@@ -0,0 +1,123 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+#include "meta_reader.h"
+#include "util.h"
+
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include <stdio.h>
+
+meta_reader_t *meta_reader_create(int fd, compressor_t *cmp)
+{
+	meta_reader_t *m = calloc(1, sizeof(*m));
+
+	if (m == NULL) {
+		perror("creating meta data reader");
+		return NULL;
+	}
+
+	m->fd = fd;
+	m->cmp = cmp;
+	return m;
+}
+
+void meta_reader_destroy(meta_reader_t *m)
+{
+	free(m);
+}
+
+int meta_reader_seek(meta_reader_t *m, uint64_t block_start, size_t offset)
+{
+	bool compressed;
+	uint16_t header;
+	ssize_t ret;
+	size_t size;
+
+	if (offset >= sizeof(m->data)) {
+		fputs("Tried to seek past end of meta data block.\n", stderr);
+		return -1;
+	}
+
+	if (block_start == m->block_offset) {
+		m->offset = offset;
+		return 0;
+	}
+
+	if (lseek(m->fd, block_start, SEEK_SET) == (off_t)-1) {
+		perror("seek on image file");
+		return -1;
+	}
+
+	ret = read_retry(m->fd, &header, 2);
+	if (ret < 0)
+		goto fail_rd;
+
+	if ((size_t)ret < 2)
+		goto fail_trunc;
+
+	header = le16toh(header);
+	compressed = (header & 0x8000) == 0;
+	size = header & 0x7FFF;
+
+	if (size > sizeof(m->data)) {
+		fputs("found meta data block larger than maximum size\n",
+		      stderr);
+		return -1;
+	}
+
+	m->block_offset = block_start;
+	m->offset = offset;
+	m->next_block = block_start + size + 2;
+
+	memset(m->data, 0, sizeof(m->data));
+
+	ret = read_retry(m->fd, m->data, size);
+	if (ret < 0)
+		goto fail_rd;
+
+	if ((size_t)ret < size)
+		goto fail_trunc;
+
+	if (compressed) {
+		ret = m->cmp->do_block(m->cmp, m->data, size);
+
+		if (ret <= 0) {
+			fputs("error uncompressing meta data block\n", stderr);
+			return -1;
+		}
+	}
+
+	return 0;
+fail_trunc:
+	fputs("reading meta data: unexpected end of file\n", stderr);
+	return -1;
+fail_rd:
+	perror("reading meta data");
+	return -1;
+}
+
+int meta_reader_read(meta_reader_t *m, void *data, size_t size)
+{
+	size_t diff;
+
+	while (size != 0) {
+		diff = sizeof(m->data) - m->offset;
+
+		if (diff == 0) {
+			if (meta_reader_seek(m, m->next_block, 0))
+				return -1;
+			diff = sizeof(m->data);
+		}
+
+		if (diff > size)
+			diff = size;
+
+		memcpy(data, m->data + m->offset, diff);
+
+		m->offset += diff;
+		data = (char *)data + diff;
+		size -= diff;
+	}
+
+	return 0;
+}