[wimlib] / src / resource.c

/*
 * resource.c
 *
 * Read uncompressed and compressed metadata and file resources.
 */

/*
 * Copyright (C) 2010 Carl Thijssen
 * Copyright (C) 2012 Eric Biggers
 *
 * This file is part of wimlib, a library for working with WIM files.
 *
 * wimlib is free software; you can redistribute it and/or modify it under the
 * terms of the GNU Lesser General Public License as published by the Free
 * Software Foundation; either version 2.1 of the License, or (at your option)
 * any later version.
 *
 * wimlib is distributed in the hope that it will be useful, but WITHOUT ANY
 * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
 * A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
 * details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with wimlib; if not, see http://www.gnu.org/licenses/.
 */

#include "wimlib_internal.h"
#include "lookup_table.h"
#include "io.h"
#include "lzx.h"
#include "xpress.h"
#include "sha1.h"
#include "dentry.h"
#include "config.h"
#include <unistd.h>
#include <errno.h>


/* 
 * Reads all or part of a compressed resource into an in-memory buffer.
 *
 * @fp:                 The FILE* for the WIM file.
 * @resource_compressed_size:    The compressed size of the resource.  
 * @resource_uncompressed_size:  The uncompressed size of the resource.
 * @resource_offset:             The offset of the start of the resource from
 *                                      the start of the stream @fp.
 * @resource_ctype:     The compression type of the resource. 
 * @len:                The number of bytes of uncompressed data to read from
 *                              the resource.
 * @offset:             The offset of the bytes to read within the uncompressed
 *                              resource.
 * @contents_len:       An array into which the uncompressed data is written.
 *                              It must be at least @len bytes long.
 *
 * Returns zero on success, nonzero on failure.
 */
static int read_compressed_resource(FILE *fp, u64 resource_compressed_size, 
                                    u64 resource_uncompressed_size, 
                                    u64 resource_offset, int resource_ctype, 
                                    u64 len, u64 offset, u8  contents_ret[])
{

        DEBUG2("comp size = %"PRIu64", uncomp size = %"PRIu64", "
               "res offset = %"PRIu64"",
               resource_compressed_size,
               resource_uncompressed_size,
               resource_offset);
        DEBUG2("resource_ctype = %s, len = %"PRIu64", offset = %"PRIu64"",
               wimlib_get_compression_type_string(resource_ctype), len, offset);
        /* Trivial case */
        if (len == 0)
                return 0;

        int (*decompress)(const void *, uint, void *, uint);
        /* Set the appropriate decompress function. */
        if (resource_ctype == WIM_COMPRESSION_TYPE_LZX)
                decompress = lzx_decompress;
        else
                decompress = xpress_decompress;

        /* The structure of a compressed resource consists of a table of chunk
         * offsets followed by the chunks themselves.  Each chunk consists of
         * compressed data, and there is one chunk for each WIM_CHUNK_SIZE =
         * 32768 bytes of the uncompressed file, with the last chunk having any
         * remaining bytes.
         *
         * The chunk offsets are measured relative to the end of the chunk
         * table.  The first chunk is omitted from the table in the WIM file
         * because its offset is implicitly given by the fact that it directly
         * follows the chunk table and therefore must have an offset of 0. 
         */

        /* Calculate how many chunks the resource conists of in its entirety. */
        u64 num_chunks = (resource_uncompressed_size + WIM_CHUNK_SIZE - 1) /
                                                                WIM_CHUNK_SIZE;
        /* As mentioned, the first chunk has no entry in the chunk table. */
        u64 num_chunk_entries = num_chunks - 1;


        /* The index of the chunk that the read starts at. */
        u64 start_chunk = offset / WIM_CHUNK_SIZE;
        /* The byte offset at which the read starts, within the start chunk. */
        u64 start_chunk_offset = offset % WIM_CHUNK_SIZE;

        /* The index of the chunk that contains the last byte of the read. */
        u64 end_chunk   = (offset + len - 1) / WIM_CHUNK_SIZE;
        /* The byte offset of the last byte of the read, within the end chunk */
        u64 end_chunk_offset = (offset + len - 1) % WIM_CHUNK_SIZE;

        /* Number of chunks that are actually needed to read the requested part
         * of the file. */
        u64 num_needed_chunks = end_chunk - start_chunk + 1;

        /* If the end chunk is not the last chunk, an extra chunk entry is
         * needed because we need to know the offset of the chunk after the last
         * chunk read to figure out the size of the last read chunk. */
        if (end_chunk != num_chunks - 1)
                num_needed_chunks++;

        /* Declare the chunk table.  It will only contain offsets for the chunks
         * that are actually needed for this read. */
        u64 chunk_offsets[num_needed_chunks];

        /* Set the implicit offset of the first chunk if it is included in the
         * needed chunks.
         *
         * Note: M$'s documentation includes a picture that shows the first
         * chunk starting right after the chunk entry table, labeled as offset
         * 0x10.  However, in the actual file format, the offset is measured
         * from the end of the chunk entry table, so the first chunk has an
         * offset of 0. */
        if (start_chunk == 0)
                chunk_offsets[0] = 0;

        /* According to M$'s documentation, if the uncompressed size of
         * the file is greater than 4 GB, the chunk entries are 8-byte
         * integers.  Otherwise, they are 4-byte integers. */
        u64 chunk_entry_size = (resource_uncompressed_size >= (u64)1 << 32) ? 
                                                                        8 : 4;

        /* Size of the full chunk table in the WIM file. */
        u64 chunk_table_size = chunk_entry_size * num_chunk_entries;

        /* Read the needed chunk offsets from the table in the WIM file. */

        /* Index, in the WIM file, of the first needed entry in the
         * chunk table. */
        u64 start_table_idx = (start_chunk == 0) ? 0 : start_chunk - 1;

        /* Number of entries we need to actually read from the chunk
         * table (excludes the implicit first chunk). */
        u64 num_needed_chunk_entries = (start_chunk == 0) ? 
                                num_needed_chunks - 1 : num_needed_chunks;

        /* Skip over unneeded chunk table entries. */
        u64 file_offset_of_needed_chunk_entries = resource_offset + 
                                start_table_idx * chunk_entry_size;
        if (fseeko(fp, file_offset_of_needed_chunk_entries, SEEK_SET) != 0) {
                ERROR_WITH_ERRNO("Failed to seek to byte %"PRIu64" to read "
                                 "chunk table of compressed resource",
                                 file_offset_of_needed_chunk_entries);
                return WIMLIB_ERR_READ;
        }

        /* Number of bytes we need to read from the chunk table. */
        size_t size = num_needed_chunk_entries * chunk_entry_size;

        u8 chunk_tab_buf[size];

        if (fread(chunk_tab_buf, 1, size, fp) != size)
                goto err;

        /* Now fill in chunk_offsets from the entries we have read in
         * chunk_tab_buf. */

        u64 *chunk_tab_p = chunk_offsets;
        if (start_chunk == 0)
                chunk_tab_p++;

        if (chunk_entry_size == 4) {
                u32 *entries = (u32*)chunk_tab_buf;
                while (num_needed_chunk_entries--)
                        *chunk_tab_p++ = to_le32(*entries++);
        } else {
                u64 *entries = (u64*)chunk_tab_buf;
                while (num_needed_chunk_entries--)
                        *chunk_tab_p++ = to_le64(*entries++);
        }

        /* Done with the chunk table now.  We must now seek to the first chunk
         * that is needed for the read. */

        u64 file_offset_of_first_needed_chunk = resource_offset + 
                                chunk_table_size + chunk_offsets[0];
        if (fseeko(fp, file_offset_of_first_needed_chunk, SEEK_SET) != 0) {
                ERROR_WITH_ERRNO("Failed to seek to byte %"PRIu64" to read "
                                 "first chunk of compressed resource",
                                 file_offset_of_first_needed_chunk);
                return WIMLIB_ERR_READ;
        }

        /* Pointer to current position in the output buffer for uncompressed
         * data. */
        u8 *out_p = (u8*)contents_ret;

        /* Buffer for compressed data.  While most compressed chunks will have a
         * size much less than WIM_CHUNK_SIZE, WIM_CHUNK_SIZE - 1 is the maximum
         * size in the worst-case.  This assumption is valid only if chunks that
         * happen to compress to more than the uncompressed size (i.e. a
         * sequence of random bytes) are always stored uncompressed. But this seems
         * to be the case in M$'s WIM files, even though it is undocumented. */
        u8 compressed_buf[WIM_CHUNK_SIZE - 1];


        /* Decompress all the chunks. */
        for (u64 i = start_chunk; i <= end_chunk; i++) {

                DEBUG2("Chunk %"PRIu64" (start %"PRIu64", end %"PRIu64").",
                       i, start_chunk, end_chunk);

                /* Calculate the sizes of the compressed chunk and of the
                 * uncompressed chunk. */
                uint compressed_chunk_size, uncompressed_chunk_size;
                if (i != num_chunks - 1) {
                        /* All the chunks except the last one in the resource
                         * expand to WIM_CHUNK_SIZE uncompressed, and the amount
                         * of compressed data for the chunk is given by the
                         * difference of offsets in the chunk offset table. */
                        compressed_chunk_size = chunk_offsets[i + 1 - start_chunk] - 
                                                chunk_offsets[i - start_chunk];
                        uncompressed_chunk_size = WIM_CHUNK_SIZE;
                } else {
                        /* The last compressed chunk consists of the remaining
                         * bytes in the file resource, and the last uncompressed
                         * chunk has size equal to however many bytes are left-
                         * that is, the remainder of the uncompressed size when
                         * divided by WIM_CHUNK_SIZE. 
                         *
                         * Note that the resource_compressed_size includes the
                         * chunk table, so the size of it must be subtracted. */
                        compressed_chunk_size = resource_compressed_size - 
                                                chunk_table_size -
                                                chunk_offsets[i - start_chunk];

                        uncompressed_chunk_size = resource_uncompressed_size % 
                                                                WIM_CHUNK_SIZE;

                        /* If the remainder is 0, the last chunk actually
                         * uncompresses to a full WIM_CHUNK_SIZE bytes. */
                        if (uncompressed_chunk_size == 0)
                                uncompressed_chunk_size = WIM_CHUNK_SIZE;
                }

                DEBUG2("compressed_chunk_size = %u, "
                       "uncompressed_chunk_size = %u",
                       compressed_chunk_size, uncompressed_chunk_size);


                /* Figure out how much of this chunk we actually need to read */
                u64 start_offset;
                if (i == start_chunk)
                        start_offset = start_chunk_offset;
                else
                        start_offset = 0;
                u64 end_offset;
                if (i == end_chunk)
                        end_offset = end_chunk_offset;
                else
                        end_offset = WIM_CHUNK_SIZE - 1;

                u64 partial_chunk_size = end_offset + 1 - start_offset;
                bool is_partial_chunk = (partial_chunk_size != 
                                                uncompressed_chunk_size);

                DEBUG2("start_offset = %u, end_offset = %u", start_offset,
                                        end_offset);
                DEBUG2("partial_chunk_size = %u", partial_chunk_size);

                /* This is undocumented, but chunks can be uncompressed.  This
                 * appears to always be the case when the compressed chunk size
                 * is equal to the uncompressed chunk size. */
                if (compressed_chunk_size == uncompressed_chunk_size) {
                        /* Probably an uncompressed chunk */

                        if (start_offset != 0) {
                                if (fseeko(fp, start_offset, SEEK_CUR) != 0) {
                                        ERROR_WITH_ERRNO("Uncompressed partial "
                                                         "chunk fseek() error");
                                        return WIMLIB_ERR_READ;
                                }
                        }
                        if (fread(out_p, 1, partial_chunk_size, fp) != 
                                        partial_chunk_size)
                                goto err;
                } else {
                        /* Compressed chunk */
                        int ret;

                        /* Read the compressed data into compressed_buf. */
                        if (fread(compressed_buf, 1, compressed_chunk_size, 
                                                fp) != compressed_chunk_size)
                                goto err;

                        /* For partial chunks we must buffer the uncompressed
                         * data because we don't need all of it. */
                        if (is_partial_chunk) {
                                u8 uncompressed_buf[uncompressed_chunk_size];

                                ret = decompress(compressed_buf,
                                                compressed_chunk_size,
                                                uncompressed_buf, 
                                                uncompressed_chunk_size);
                                if (ret != 0)
                                        return WIMLIB_ERR_DECOMPRESSION;
                                memcpy(out_p, uncompressed_buf + start_offset,
                                                partial_chunk_size);
                        } else {
                                ret = decompress(compressed_buf,
                                                compressed_chunk_size,
                                                out_p,
                                                uncompressed_chunk_size);
                                if (ret != 0)
                                        return WIMLIB_ERR_DECOMPRESSION;
                        }
                }

                /* Advance the pointer into the uncompressed output data by the
                 * number of uncompressed bytes that were written.  */
                out_p += partial_chunk_size;
        }

        return 0;

err:
        if (feof(fp))
                ERROR("Unexpected EOF in compressed file resource");
        else
                ERROR_WITH_ERRNO("Error reading compressed file resource");
        return WIMLIB_ERR_READ;
}

/* 
 * Reads uncompressed data from an open file stream.
 */
int read_uncompressed_resource(FILE *fp, u64 offset, u64 len, 
                                        u8 contents_ret[])
{
        if (fseeko(fp, offset, SEEK_SET) != 0) {
                ERROR("Failed to seek to byte %"PRIu64" of input file "
                      "to read uncompressed resource (len = %"PRIu64")",
                      offset, len);
                return WIMLIB_ERR_READ;
        }
        if (fread(contents_ret, 1, len, fp) != len) {
                if (feof(fp)) {
                        ERROR("Unexpected EOF in uncompressed file resource");
                } else {
                        ERROR("Failed to read %"PRIu64" bytes from "
                              "uncompressed resource at offset %"PRIu64,
                              len, offset);
                }
                return WIMLIB_ERR_READ;
        }
        return 0;
}


/* 
 * Reads a WIM resource.
 *
 * @fp:                 The FILE* for the WIM file.
 * @resource_size:              The compressed size of the resource.
 * @resource_original_size:     The uncompressed size of the resource.
 * @resource_offset:            The offset of the resource in the stream @fp.
 * @resource_ctype:             The compression type of the resource.
 *                              (WIM_COMPRESSION_TYPE_*)
 * @len:                How many bytes of the resource should be read.
 * @offset:             The offset within the resource at which the read
 *                              will occur.
 *
 *                      To read the whole file resource, specify offset =
 *                      0 and len = resource_original_size, or call
 *                      read_full_resource().
 *
 * @contents_ret:       An array, that must have length at least @len,
 *                              into which the uncompressed contents of
 *                              the file resource starting at @offset and 
 *                              continuing for @len bytes will be written.
 *
 * @return:             Zero on success, nonzero on failure. Failure may be due to
 *                      being unable to read the data from the WIM file at the
 *                      specified length and offset, or it may be due to the
 *                      compressed data (if the data is compressed) being
 *                      invalid.
 */
int read_resource(FILE *fp, u64 resource_size, u64 resource_original_size,
                  u64 resource_offset, int resource_ctype, u64 len, 
                  u64 offset, void *contents_ret)
{
        if (resource_ctype == WIM_COMPRESSION_TYPE_NONE) {
                if (resource_size != resource_original_size) {
                        ERROR("Resource with original size %"PRIu64" bytes is "
                              "marked as uncompressed, but its actual size is "
                              "%"PRIu64" bytes", 
                              resource_original_size, resource_size);
                        return WIMLIB_ERR_INVALID_RESOURCE_SIZE;
                }
                return read_uncompressed_resource(fp, 
                                resource_offset + offset, 
                                len, contents_ret);
        } else {
                return read_compressed_resource(fp, resource_size,
                                resource_original_size, resource_offset,
                                resource_ctype, len, offset, contents_ret);
        }
}


/* 
 * Extracts the first @size bytes file resource specified by @entry to the open
 * file @fd.  Returns nonzero on error.
 *
 * XXX
 * This function is somewhat redundant with uncompress_resource(). The
 * main difference is that this function writes to a file descriptor using
 * low-level calls to write() rather than to a FILE* with fwrite(); also this
 * function allows only up to @size bytes to be extracted.
 */
int extract_resource_to_fd(WIMStruct *w, const struct resource_entry *entry, 
                           int fd, u64 size)
{
        u64 num_chunks;
        u64 n;
        u8 buf[min(size, WIM_CHUNK_SIZE)];
        int res_ctype;
        u64 offset;
        u64 i;
        int ret;

        errno = 0;

        num_chunks = (size + WIM_CHUNK_SIZE - 1) / WIM_CHUNK_SIZE;
        n = WIM_CHUNK_SIZE;
        res_ctype = wim_resource_compression_type(w, entry);
        offset = 0;
        for (i = 0; i < num_chunks; i++) {
                if (i == num_chunks - 1) {
                        n = size % WIM_CHUNK_SIZE;
                        if (n == 0) {
                                n = WIM_CHUNK_SIZE;
                        }
                }

                ret = read_resource(w->fp, entry->size, entry->original_size,
                                    entry->offset, res_ctype, n, offset, buf);
                if (ret != 0)
                        return ret;

                if (full_write(fd, buf, n) != n)
                        return WIMLIB_ERR_WRITE;
                offset += n;
        }
        return ret;
}

/* 
 * Copies the file resource specified by the lookup table entry @lte from the
 * input WIM, pointed to by the fp field of the WIMStruct, to the output WIM,
 * pointed to by the out_fp field of the WIMStruct.
 *
 * The output_resource_entry, out_refcnt, and part_number fields of @lte are
 * updated.
 *
 * Metadata resources are not copied (they are handled elsewhere for joining and
 * splitting).
 */
int copy_resource(struct lookup_table_entry *lte, void *w)
{
        if ((lte->resource_entry.flags & WIM_RESHDR_FLAG_METADATA) &&
            !((WIMStruct*)w)->write_metadata) {
                return 0;
        }

        FILE *in_fp = ((WIMStruct*)w)->fp;
        FILE *out_fp = ((WIMStruct*)w)->out_fp;
        int ret;
        u64 size = lte->resource_entry.size;
        u64 offset = lte->resource_entry.offset;
        off_t new_offset = ftello(out_fp);

        if (new_offset == -1)
                return WIMLIB_ERR_WRITE;

        ret = copy_between_files(in_fp, offset, out_fp, size);
        if (ret != 0)
                return ret;

        memcpy(&lte->output_resource_entry, &lte->resource_entry, 
                        sizeof(struct resource_entry));

        lte->output_resource_entry.offset = new_offset;
        lte->out_refcnt = lte->refcnt;
        lte->part_number = ((WIMStruct*)w)->hdr.part_number;
        return 0;
}

/* Reads the contents of a struct resource_entry, as represented in the on-disk
 * format, from the memory pointed to by @p, and fills in the fields of @entry.
 * A pointer to the byte after the memory read at @p is returned. */
const u8 *get_resource_entry(const u8 *p, struct resource_entry *entry)
{
        u64 size;
        u8 flags;

        p = get_u56(p, &size);
        p = get_u8(p, &flags);
        entry->size = size;
        entry->flags = flags;
        p = get_u64(p, &entry->offset);
        p = get_u64(p, &entry->original_size);
        return p;
}

/* Copies the struct resource_entry @entry to the memory pointed to by @p in the
 * on-disk format.  A pointer to the byte after the memory written at @p is
 * returned. */
u8 *put_resource_entry(u8 *p, const struct resource_entry *entry)
{
        p = put_u56(p, entry->size);
        p = put_u8(p, entry->flags);
        p = put_u64(p, entry->offset);
        p = put_u64(p, entry->original_size);
        return p;
}

/* Given the compression type for the WIM file as a whole as the flags field of
 * a resource entry, returns the compression type for that resource entry. */
int resource_compression_type(int wim_ctype, int reshdr_flags)
{
        if (wim_ctype != WIM_COMPRESSION_TYPE_NONE &&
             (reshdr_flags & WIM_RESHDR_FLAG_COMPRESSED))
                return wim_ctype;
        else
                return WIM_COMPRESSION_TYPE_NONE;
}



/*
 * Copies bytes between two file streams.
 *
 * Copies @len bytes from @in_fp to @out_fp, at the current position in @out_fp,
 * and at an offset of @in_offset in @in_fp.
 */
int copy_between_files(FILE *in_fp, off_t in_offset, FILE *out_fp, size_t len)
{
        u8 buf[BUFFER_SIZE];
        size_t n;

        if (fseeko(in_fp, in_offset, SEEK_SET) != 0) {
                ERROR_WITH_ERRNO("Failed to seek to byte %"PRIu64" of "
                                 "input file", in_offset);
                return WIMLIB_ERR_READ;
        }
        /* To reduce memory usage and improve speed, read and write BUFFER_SIZE
         * bytes at a time. */
        while (len != 0) {
                n = min(len, BUFFER_SIZE);
                if (fread(buf, 1, n, in_fp) != n) {
                        if (feof(in_fp)) {
                                ERROR("Unexpected EOF when copying data "
                                      "between files");
                        } else {
                                ERROR_WITH_ERRNO("Error copying data between "
                                                 "files");
                        }
                        return WIMLIB_ERR_READ;
                }

                if (fwrite(buf, 1, n, out_fp) != n) {
                        ERROR_WITH_ERRNO("Error copying data between files");
                        return WIMLIB_ERR_WRITE;
                }
                len -= n;
        }
        return 0;
}


/* 
 * Uncompresses a WIM file resource and writes it uncompressed to a file stream.
 *
 * @in_fp:          The file stream that contains the file resource.
 * @size:           The size of the resource in the input file.
 * @original_size:  The original (uncompressed) size of the resource. 
 * @offset:         The offset of the start of the resource in @in.
 * @input_ctype:    The compression type of the resource in @in.
 * @out_fp:         The file stream to write the file resource to.
 */
static int uncompress_resource(FILE *in_fp, u64 size, u64 original_size,
                               off_t offset, int input_ctype, FILE *out_fp)
{
        int ret;
        u8 buf[WIM_CHUNK_SIZE];
        /* Determine how many compressed chunks the file is divided into. */
        u64 num_chunks;
        u64 i;
        u64 uncompressed_offset;
        u64 uncompressed_chunk_size;
        
        num_chunks = (original_size + WIM_CHUNK_SIZE - 1) / WIM_CHUNK_SIZE;

        for (i = 0; i < num_chunks; i++) {

                uncompressed_offset = i * WIM_CHUNK_SIZE;
                uncompressed_chunk_size = min(WIM_CHUNK_SIZE, original_size -
                                              uncompressed_offset);

                ret = read_resource(in_fp, size, original_size, offset,
                                    input_ctype, uncompressed_chunk_size, 
                                    uncompressed_offset, buf);
                if (ret != 0)
                        return ret;

                if (fwrite(buf, 1, uncompressed_chunk_size, out_fp) != 
                      uncompressed_chunk_size) 
                {
                        ERROR_WITH_ERRNO("Failed to write file resource");
                        return WIMLIB_ERR_WRITE;
                }
        }
        return 0;
}

/* 
 * Transfers a file resource between two files, writing it compressed.  The file
 * resource in the input file may be either compressed or uncompressed.
 * Alternatively, the input resource may be in-memory, but it must be
 * uncompressed.
 *
 * @in_fp:                  The file stream that contains the file resource.  Ignored
 *                      if uncompressed_resource != NULL.
 * @uncompressed_resource:      If this pointer is not NULL, it points to an
 *                                      array of @original_size bytes that are
 *                                      the uncompressed input resource.
 * @size:           The size of the resource in the input file.
 * @original_size:  The original (uncompressed) size of the resource. 
 * @offset:         The offset of the start of the resource in @in.  Ignored
 *                      if uncompressed_resource != NULL.
 * @input_ctype:    The compression type of the resource in @in.  Ignored if
 *                      uncompressed_resource != NULL.
 * @out_fp:         The file stream to write the file resource to.
 * @output_type:    The compression type to use when writing the resource to
 *                      @out.
 * @new_size_ret:   A location into which the new compressed size of the file
 *                      resource in returned.
 */
static int recompress_resource(FILE *in_fp, const u8 *uncompressed_resource, 
                               u64 size, u64 original_size,
                               off_t offset, int input_ctype, FILE *out_fp,
                               int output_ctype, u64 *new_size_ret)
{
        int ret;
        int (*compress)(const void *, uint, void *, uint *);
        if (output_ctype == WIM_COMPRESSION_TYPE_LZX)
                compress = lzx_compress;
        else
                compress = xpress_compress;

        u8 uncompressed_buf[WIM_CHUNK_SIZE];
        u8 compressed_buf[WIM_CHUNK_SIZE - 1];

        /* Determine how many compressed chunks the file needs to be divided
         * into. */
        u64 num_chunks = (original_size + WIM_CHUNK_SIZE - 1) / WIM_CHUNK_SIZE;

        u64 num_chunk_entries = num_chunks - 1;

        /* Size of the chunk entries--- 8 bytes for files over 4GB, otherwise 4
         * bytes */
        uint chunk_entry_size = (original_size >= (u64)1 << 32) ? 8 : 4;

        /* Array in which to construct the chunk offset table. */
        u64 chunk_offsets[num_chunk_entries];

        /* Offset of the start of the chunk table in the output file. */
        off_t chunk_tab_offset = ftello(out_fp);

        if (chunk_tab_offset == -1) {
                ERROR_WITH_ERRNO("Failed to get offset of output file");
                return WIMLIB_ERR_WRITE;
        }

        /* Total size of the chunk table (as written to the file) */
        u64 chunk_tab_size = chunk_entry_size * num_chunk_entries;

        /* Reserve space for the chunk table. */
        if (fwrite(chunk_offsets, 1, chunk_tab_size, out_fp) !=
              chunk_tab_size)
        {
                ERROR_WITH_ERRNO("Failed to write chunk offset table");
                return WIMLIB_ERR_WRITE;
        }

        /* Read each chunk of the file, compress it, write it to the output
         * file, and update th chunk offset table. */
        u64 cur_chunk_offset = 0;
        for (u64 i = 0; i < num_chunks; i++) {

                u64 uncompressed_offset = i * WIM_CHUNK_SIZE;
                u64 uncompressed_chunk_size = min(WIM_CHUNK_SIZE, 
                                        original_size - uncompressed_offset);

                const u8 *uncompressed_p;
                if (uncompressed_resource != NULL) {
                        uncompressed_p = uncompressed_resource + 
                                         uncompressed_offset;

                } else {
                        /* Read chunk i of the file into uncompressed_buf. */
                        ret = read_resource(in_fp, size, original_size, offset,
                                            input_ctype,
                                            uncompressed_chunk_size, 
                                            uncompressed_offset, 
                                            uncompressed_buf);
                        if (ret != 0)
                                return ret;
                        uncompressed_p = uncompressed_buf;
                }

                if (i != 0)
                        chunk_offsets[i - 1] = cur_chunk_offset;

                uint compressed_len;

                ret = compress(uncompressed_p, uncompressed_chunk_size, 
                               compressed_buf, &compressed_len);

                /* if compress() returned nonzero, the compressed chunk would
                 * have been at least as large as the uncompressed chunk.  In
                 * this situation, the WIM format requires that the uncompressed
                 * chunk be written instead. */
                const u8 *buf_to_write;
                uint len_to_write;
                if (ret == 0) {
                        buf_to_write = compressed_buf;
                        len_to_write = compressed_len;
                } else {
                        buf_to_write = uncompressed_p;
                        len_to_write = uncompressed_chunk_size;
                }

                if (fwrite(buf_to_write, 1, len_to_write, out_fp) !=
                      len_to_write)
                {
                        ERROR_WITH_ERRNO("Failed to write compressed "
                                         "file resource");
                        return WIMLIB_ERR_WRITE;
                }
                cur_chunk_offset += len_to_write;
        }

        /* The chunk offset after the last chunk, plus the size of the chunk
         * table, gives the total compressed size of the resource. */
        *new_size_ret = cur_chunk_offset + chunk_tab_size;

        /* Now that all entries of the chunk table are determined, rewind the
         * stream to where the chunk table was, and write it back out. */

        if (fseeko(out_fp, chunk_tab_offset, SEEK_SET) != 0) {
                ERROR_WITH_ERRNO("Failed to seek to beginning of chunk table");
                return WIMLIB_ERR_READ;
        }

        if (chunk_entry_size == 8) {
                array_to_le64(chunk_offsets, num_chunk_entries);
        } else {
                for (u64 i = 0; i < num_chunk_entries; i++)
                        ((u32*)chunk_offsets)[i] = to_le32(chunk_offsets[i]);
        }
        if (fwrite(chunk_offsets, 1, chunk_tab_size, out_fp) != chunk_tab_size)
        {
                ERROR_WITH_ERRNO("Failed to write chunk table");
                return WIMLIB_ERR_WRITE;
        }

        if (fseeko(out_fp, 0, SEEK_END) != 0) {
                ERROR_WITH_ERRNO("Failed to seek to end of output file");
                return WIMLIB_ERR_WRITE;
        }

        return 0;
}

int write_resource_from_memory(const u8 resource[], int out_ctype,
                               u64 resource_original_size, FILE *out_fp,
                               u64 *resource_size_ret)
{
        if (out_ctype == WIM_COMPRESSION_TYPE_NONE) {
                if (fwrite(resource, 1, resource_original_size, out_fp) != 
                      resource_original_size)
                {
                        ERROR_WITH_ERRNO("Failed to write resource of length "
                                         "%"PRIu64, resource_original_size);
                        return WIMLIB_ERR_WRITE;
                }
                *resource_size_ret = resource_original_size;
                return 0;
        } else {
                return recompress_resource(NULL, resource,
                                           resource_original_size,
                                           resource_original_size, 0, 0, out_fp,
                                           out_ctype, resource_size_ret);
        }
}


/* 
 * Transfers a file resource from a FILE* opened for reading to a FILE* opened
 * for writing, possibly changing the compression type. 
 *
 * @in_fp:              The FILE* that contains the file resource.
 * @size:               The (compressed) size of the file resource.
 * @original_size:      The uncompressed size of the file resource.
 * @offset:             The offset of the file resource in the input file.
 * @input_ctype:        The compression type of the file resource in the input
 *                              file.
 * @out_fp:             The FILE* for the output file.  The file resource is 
 *                              written at the current position of @out.
 * @output_ctype:       The compression type to which the file resource will be
 *                              converted.
 * @output_res_entry:   A pointer to a resource entry that, upon successful
 *                              return of this function,  will have the size,
 *                              original size, offset, and flags fields filled
 *                              in for the file resource written to the output
 *                              file.
 */
static int transfer_file_resource(FILE *in_fp, u64 size, u64 original_size,
                                  off_t offset, int input_ctype, FILE *out_fp,
                                  int output_ctype,
                                  struct resource_entry *output_res_entry)
{
        int ret;

        /* Handle zero-length files */
        if (original_size == 0) {
                memset(output_res_entry, 0, sizeof(*output_res_entry));
                return 0;
        }

        /* Get current offset in the output file. */
        off_t out_offset = ftello(out_fp);
        if (out_offset == -1) {
                ERROR_WITH_ERRNO("Failed to get output position");
                return WIMLIB_ERR_WRITE;
        }
        output_res_entry->offset = (u64)out_offset;

        if (output_ctype == input_ctype) {
                /* The same compression types; simply copy the resource. */

                ret = copy_between_files(in_fp, offset, out_fp, size);
                if (ret != 0)
                        return ret;
                output_res_entry->size = size;
        } else {
                /* Different compression types. */

                if (output_ctype == WIM_COMPRESSION_TYPE_NONE) {
                        /* Uncompress a compressed file resource */
                        ret = uncompress_resource(in_fp, size,
                                                  original_size, offset, 
                                                  input_ctype, out_fp);
                        if (ret != 0)
                                return ret;
                        output_res_entry->size = original_size;
                } else {
                        u64 new_size;
                        /* Compress an uncompressed file resource, or compress a
                         * compressed file resource using a different
                         * compression type */
                        ret = recompress_resource(in_fp, NULL, size,
                                                  original_size,
                                                  offset, input_ctype, out_fp,
                                                  output_ctype, &new_size);
                        if (ret != 0)
                                return ret;
                        output_res_entry->size = new_size;
                }

        }

        output_res_entry->original_size = original_size;
        if (output_ctype == WIM_COMPRESSION_TYPE_NONE)
                output_res_entry->flags = 0;
        else
                output_res_entry->flags = WIM_RESHDR_FLAG_COMPRESSED;
        return 0;
}

/* 
 * Reads the metadata metadata resource from the WIM file.  The metadata
 * resource consists of the security data, followed by the directory entry for
 * the root directory, followed by all the other directory entries in the
 * filesystem.  The subdir_offset field of each directory entry gives the start
 * of its child entries from the beginning of the metadata resource.  An
 * end-of-directory is signaled by a directory entry of length '0', really of
 * length 8, because that's how long the 'length' field is.
 *
 * @fp:         The FILE* for the input WIM file.
 * @wim_ctype:  The compression type of the WIM file.
 * @imd:        Pointer to the image metadata structure.  Its
 *              `lookup_table_entry' member specifies the lookup table entry for
 *              the metadata resource.  The rest of the image metadata entry
 *              will be filled in by this function.
 *
 * @return:     Zero on success, nonzero on failure.
 */
int read_metadata_resource(FILE *fp, int wim_ctype, struct image_metadata *imd)
{
        u8 *buf;
        int ctype;
        u32 dentry_offset;
        int ret;
        const struct resource_entry *res_entry;
        struct dentry *dentry;
        struct wim_security_data *sd;
        struct link_group_table *lgt;

        res_entry = &imd->metadata_lte->resource_entry;

        DEBUG("Reading metadata resource: length = %"PRIu64", "
              "offset = %"PRIu64"",
              res_entry->original_size, res_entry->offset);

        if (res_entry->original_size < 8) {
                ERROR("Expected at least 8 bytes for the metadata resource");
                return WIMLIB_ERR_INVALID_RESOURCE_SIZE;
        }

        /* Allocate memory for the uncompressed metadata resource. */
        buf = MALLOC(res_entry->original_size);

        if (!buf) {
                ERROR("Failed to allocate %"PRIu64" bytes for uncompressed "
                      "metadata resource", res_entry->original_size);
                return WIMLIB_ERR_NOMEM;
        }

        /* Determine the compression type of the metadata resource. */
        ctype = resource_compression_type(wim_ctype, res_entry->flags);

        /* Read the metadata resource into memory.  (It may be compressed.) */
        ret = read_full_resource(fp, res_entry->size, 
                                 res_entry->original_size, res_entry->offset, 
                                 ctype, buf);
        if (ret != 0)
                goto out_free_buf;

        DEBUG("Finished reading metadata resource into memory.");

        /* The root directory entry starts after security data, on an 8-byte
         * aligned address. 
         *
         * The security data starts with a 4-byte integer giving its total
         * length. */

        /* Read the security data into a wim_security_data structure. */
        ret = read_security_data(buf, res_entry->original_size, &sd);
        if (ret != 0)
                goto out_free_buf;

        dentry = MALLOC(sizeof(struct dentry));
        if (!dentry) {
                ERROR("Failed to allocate %zu bytes for root dentry",
                      sizeof(struct dentry));
                ret = WIMLIB_ERR_NOMEM;
                goto out_free_security_data;
        }

        get_u32(buf, &dentry_offset);
        if (dentry_offset == 0)
                dentry_offset = 8;
        dentry_offset = (dentry_offset + 7) & ~7;
                
        ret = read_dentry(buf, res_entry->original_size, dentry_offset, dentry);
        /* This is the root dentry, so set its pointers correctly. */
        dentry->parent = dentry;
        dentry->next   = dentry;
        dentry->prev   = dentry;
        if (ret != 0)
                goto out_free_dentry_tree;

        /* Now read the entire directory entry tree. */
        ret = read_dentry_tree(buf, res_entry->original_size, dentry);
        if (ret != 0)
                goto out_free_dentry_tree;

        /* Calculate the full paths in the dentry tree. */
        ret = for_dentry_in_tree(dentry, calculate_dentry_full_path, NULL);
        if (ret != 0)
                goto out_free_dentry_tree;

        lgt = new_link_group_table(9001);
        if (!lgt)
                goto out_free_dentry_tree;
        ret = for_dentry_in_tree(dentry, link_group_table_insert, lgt);
        if (ret != 0)
                goto out_free_lgt;

        ret = link_groups_free_duplicate_data(lgt);
        if (ret != 0)
                goto out_free_lgt;

        imd->lgt           = lgt;
        imd->security_data = sd;
        imd->root_dentry   = dentry;
        goto out_free_buf;
out_free_lgt:
        free_link_group_table(lgt);
out_free_dentry_tree:
        free_dentry_tree(dentry, NULL, false);
out_free_security_data:
        free_security_data(sd);
out_free_buf:
        FREE(buf);
        return ret;
}

/* Write the metadata resource for the current image. */
int write_metadata_resource(WIMStruct *w)
{
        FILE *out;
        u8 *buf;
        u8 *p;
        int ret;
        u64 subdir_offset;
        struct dentry *root;
        struct lookup_table_entry *lte;
        struct resource_entry *res_entry;
        off_t metadata_offset;
        u64 metadata_original_size;
        u64 metadata_compressed_size;
        int metadata_ctype;
        u8  hash[WIM_HASH_SIZE];

        DEBUG("Writing metadata resource for image %d", w->current_image);

        out = w->out_fp;
        root = wim_root_dentry(w);
        metadata_ctype = wimlib_get_compression_type(w);
        metadata_offset = ftello(out);
        if (metadata_offset == -1)
                return WIMLIB_ERR_WRITE;

        struct wim_security_data *sd = wim_security_data(w);
        if (sd)
                subdir_offset = sd->total_length + root->length + 8;
        else
                subdir_offset = 8 + root->length + 8;
        calculate_subdir_offsets(root, &subdir_offset);
        metadata_original_size = subdir_offset;
        buf = MALLOC(metadata_original_size);
        if (!buf) {
                ERROR("Failed to allocate %"PRIu64" bytes for "
                      "metadata resource", metadata_original_size);
                return WIMLIB_ERR_NOMEM;
        }

        p = write_security_data(sd, buf);

        DEBUG("Writing dentry tree.");
        p = write_dentry_tree(root, p);

        /* Like file resources, the lookup table entry for a metadata resource
         * uses for the hash code a SHA1 message digest of its uncompressed
         * contents. */
        sha1_buffer(buf, metadata_original_size, hash);

        ret = write_resource_from_memory(buf, 
                                         metadata_ctype,
                                         metadata_original_size, 
                                         out,
                                         &metadata_compressed_size);
        FREE(buf);
        if (ret != 0)
                return ret;

        /* Update the lookup table entry, including the hash and output resource
         * entry fields, for this image's metadata resource.  */
        lte = wim_metadata_lookup_table_entry(w);
        res_entry = &lte->output_resource_entry;
        lte->out_refcnt++;
        if (memcmp(hash, lte->hash, WIM_HASH_SIZE) != 0) {
                lookup_table_unlink(w->lookup_table, lte);
                memcpy(lte->hash, hash, WIM_HASH_SIZE);
                lookup_table_insert(w->lookup_table, lte);
        }
        res_entry->original_size = metadata_original_size;
        res_entry->offset        = metadata_offset;
        res_entry->size          = metadata_compressed_size;
        res_entry->flags         = WIM_RESHDR_FLAG_METADATA;
        if (metadata_ctype != WIM_COMPRESSION_TYPE_NONE)
                res_entry->flags |= WIM_RESHDR_FLAG_COMPRESSED;
        return 0;
}

static int write_file_resource(WIMStruct *w, const u8 hash[])
{
        /* Get the lookup entry for the file resource. */
        struct lookup_table_entry *lte;
        
        lte = __lookup_resource(w->lookup_table, hash);
        if (!lte)
                return 0;

        /* No need to write file resources twice. */
        if (++lte->out_refcnt != 1)
                return 0;

        /* do not write empty resources */
        if (lte->resource_entry.original_size == 0)
                return 0;

        int out_wim_ctype = wimlib_get_compression_type(w);
        struct resource_entry *output_res_entry = &lte->output_resource_entry;
        u64 len;
        FILE *in_fp;
        FILE *out_fp = w->out_fp;
        int ret = 0;

        /* Figure out if we can read the resource from the WIM file, or
         * if we have to read it from the filesystem outside, or if it's a
         * symbolic link with the data already in memory pointed to by a field
         * of the lookup table entry. */
        if (lte->is_symlink) {
                off_t offset = ftello(w->out_fp);
                u64 new_size;

                if (offset == -1) {
                        ERROR_WITH_ERRNO("Could not get position in output "
                                         "file");
                        return WIMLIB_ERR_WRITE;
                }

                wimlib_assert(lte->symlink_buf);

                len = lte->resource_entry.original_size;

                ret = recompress_resource(NULL, lte->symlink_buf, len, len, 0,
                                          0, out_fp, out_wim_ctype, &new_size);
                output_res_entry->size = new_size;
                output_res_entry->original_size = len;
                output_res_entry->offset = offset;
                output_res_entry->flags = (out_wim_ctype == WIM_COMPRESSION_TYPE_NONE)
                                                ? 0 : WIM_RESHDR_FLAG_COMPRESSED;
        } else if (lte->file_on_disk) {

                /* Read from disk (uncompressed) */

                len = lte->resource_entry.original_size;

                in_fp = fopen(lte->file_on_disk, "rb");
                if (!in_fp) {
                        ERROR_WITH_ERRNO("Failed to open the file `%s'",
                                         lte->file_on_disk);
                        return WIMLIB_ERR_OPEN;
                }

                ret = transfer_file_resource(in_fp, len, len, 0,
                                             WIM_COMPRESSION_TYPE_NONE, out_fp,
                                             out_wim_ctype, output_res_entry);
                fclose(in_fp);
        } else {
                int in_wim_ctype;

                /* Read from input WIM (possibly compressed) */

                /* It may be a different WIM file, in the case of
                 * exporting images from one WIM file to another */
                if (lte->other_wim_fp) {
                        /* Different WIM file. */
                        in_fp = lte->other_wim_fp;
                        in_wim_ctype = lte->other_wim_ctype;
                } else {
                        /* Same WIM file. */
                        in_fp = w->fp;
                        in_wim_ctype = out_wim_ctype;
                }
                int input_res_ctype = resource_compression_type(
                                                in_wim_ctype, 
                                                lte->resource_entry.flags);

                ret = transfer_file_resource(in_fp,
                                             lte->resource_entry.size,
                                             lte->resource_entry.original_size, 
                                             lte->resource_entry.offset,
                                             input_res_ctype, 
                                             out_fp,
                                             out_wim_ctype,
                                             output_res_entry);
        }
        return ret;
}

/* 
 * Writes a dentry's resources to the output file. 
 *
 * @dentry:  The dentry for the file resource.
 * @wim_p:   A pointer to the WIMStruct.  The fields of interest to this
 *           function are the input and output file streams and the lookup
 *           table, and the alternate data streams.
 *
 * @return zero on success, nonzero on failure. 
 */
int write_dentry_resources(struct dentry *dentry, void *wim_p)
{
        WIMStruct *w = wim_p;
        int ret;

        /* Directories don't need file resources. */
        if (dentry_is_directory(dentry))
                return 0;

        ret = write_file_resource(w, dentry->hash);
        if (ret != 0)
                return ret;
        for (u16 i = 0; i < dentry->num_ads; i++) {
                ret = write_file_resource(w, dentry->ads_entries[i].hash);
                if (ret != 0)
                        return ret;
        }
        return 0;
}