1 files changed, 150 insertions, 0 deletions
diff --git a/src/restore.c b/src/restore.c
new file mode 100644
index 0000000..c6121c1
--- /dev/null
+++ b/src/restore.c
@@ -0,0 +1,150 @@
+#include "restore.h"
+
+#include "file.h"
+#include "print.h"
+
+#include <errno.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+static bool
+is_reference_file_valid(resources_t *const res, uint32_t sector_size)
+{
+    const long ref_size = file_size(res->ref_file);
+
+    if (ref_size < 0) {
+        print_error("cannot get size of reference file: %s", strerror(errno));
+        return false;
+    } else if (ref_size == 0) {
+        print_error("reference file is empty");
+        return false;
+    } else if ((ref_size % (sizeof(uint64_t) + sector_size)) != 0) {
+        /* The reference file must hold equally sized sectors and the
+         * offset of each of them
+         */
+        print_error(
+            "reference file has size that cannot contain valid diff data");
+        return false;
+    }
+
+    const long out_size = file_size(res->out_file);
+
+    if (out_size < 0) {
+        print_error("cannot get size of output file: %s", strerror(errno));
+        return 1;
+    }
+
+    uint64_t ref_offset = 0;
+    uint64_t prev_out_offset;
+
+    /* Scan the reference file and check  */
+    for (;;) {
+        uint64_t out_offset;
+        /* Read the next offset */
+        const size_t ref_read =
+            fread(&out_offset, sizeof(out_offset), 1U, res->ref_file);
+        out_offset = le64toh(out_offset);
+
+        if (feof(res->ref_file)) {
+            break;
+        } else if ((ref_read != 1U) || ferror(res->ref_file)) {
+            print_error("cannot read from reference file: %s", strerror(errno));
+            return false;
+        } else if (((ref_offset != 0) && (out_offset <= prev_out_offset)) ||
+                   ((out_offset + sector_size) > out_size)) {
+            /* The offset must be higher than the previous one and it
+             * must point into the file
+             */
+            print_error("reference file is not valid");
+            return false;
+        } else if (fseek(res->ref_file, sector_size, SEEK_CUR) != 0) {
+            print_error("cannot seek in reference file: %s", strerror(errno));
+            return false;
+        }
+
+        prev_out_offset = out_offset;
+    }
+
+    if (ftell(res->ref_file) != ref_size) {
+        /* The reference file must be read completely */
+        print_error("reference file is not valid");
+        return false;
+    } else if (fseek(res->ref_file, 0L, SEEK_SET) != 0) {
+        /* The file must be prepared for the restoring */
+        print_error("cannot seek in reference file: %s", strerror(errno));
+        return false;
+    }
+
+    return true;
+}
+
+int
+restore(const options_t *const opts, resources_t *const res)
+{
+    /* Check validity of the reference file */
+    if (!is_reference_file_valid(res, opts->sector_size)) {
+        return 1;
+    }
+
+    const long ref_size = file_size(res->ref_file);
+
+    if (ref_size < 0) {
+        print_error("cannot get size of reference file: %s", strerror(errno));
+        return 1;
+    }
+
+    /* Allocate the buffer for data from the reference file */
+    /* The reference buffer contains also the offsets */
+    const size_t ref_buffer_size =
+        ((opts->buffer_size / opts->sector_size) * sizeof(uint64_t)) +
+        opts->buffer_size;
+
+    if ((res->ref_buffer = (char *)malloc(ref_buffer_size)) == NULL) {
+        print_error("cannot allocate buffer for reference file data");
+        return 1;
+    }
+
+    /* Restore data from the differential image */
+    uint64_t out_offset;
+
+    for (;;) {
+        /* Read data of the offset and the next sector */
+        const size_t ref_read =
+            fread(res->ref_buffer, ref_buffer_size, 1U, res->ref_file);
+
+        if (feof(res->ref_file)) {
+            break;
+        } else if ((ref_read != 1U) || ferror(res->ref_file)) {
+            print_error("cannot read from reference file: %s", strerror(errno));
+            return 1;
+        }
+
+        /* Get offset */
+        out_offset = le64toh(*((uint64_t *)res->ref_buffer));
+
+        if (fseek(res->out_file, out_offset, SEEK_SET) != 0) {
+            print_error("cannot seek in output file: %s", strerror(errno));
+            return 1;
+        }
+
+        /* Write the sector data to the output file */
+        const size_t out_written = fwrite(res->ref_buffer + sizeof(out_offset),
+                                          opts->sector_size, 1U, res->out_file);
+
+        if (out_written != 1U) {
+            print_error("cannot write to output file: %s", strerror(errno));
+            return 1;
+        }
+    }
+
+    /* The reference file must be read completely */
+    if (ftell(res->ref_file) != ref_size) {
+        print_error("reference file is not valid");
+        return 1;
+    }
+
+    return 0;
+}