Fix RAW_CHUNKS reads

[wimlib] / src / resource.c

/*
 * resource.c
 *
 * Code for reading streams and resources, including compressed WIM resources.
 */

/*
 * Copyright (C) 2012, 2013 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 General Public License as published by the Free Software
 * Foundation; either version 3 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along with
 * wimlib; if not, see http://www.gnu.org/licenses/.
 */

#ifdef HAVE_CONFIG_H
#  include "config.h"
#endif

#include "wimlib.h"
#include "wimlib/endianness.h"
#include "wimlib/error.h"
#include "wimlib/file_io.h"
#include "wimlib/lookup_table.h"
#include "wimlib/resource.h"
#include "wimlib/sha1.h"

#ifdef __WIN32__
/* for read_win32_file_prefix(), read_win32_encrypted_file_prefix() */
#  include "wimlib/win32.h"
#endif

#ifdef WITH_NTFS_3G
/* for read_ntfs_file_prefix() */
#  include "wimlib/ntfs_3g.h"
#endif

#ifdef HAVE_ALLOCA_H
#  include <alloca.h>
#endif
#include <errno.h>
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>

/*
 *                         Compressed WIM resources
 *
 * A compressed resource in a WIM consists of a number of compressed chunks,
 * each of which decompresses to a fixed chunk size (given in the WIM header;
 * usually 32768) except possibly the last, which always decompresses to any
 * remaining bytes.  In addition, immediately before the chunks, a table (the
 * "chunk table") provides the offset, in bytes relative to the end of the chunk
 * table, of the start of each compressed chunk, except for the first chunk
 * which is omitted as it always has an offset of 0.  Therefore, a compressed
 * resource with N chunks will have a chunk table with N - 1 entries.
 *
 * Additional information:
 *
 * - Entries in the chunk table are 4 bytes each, except if the uncompressed
 *   size of the resource is greater than 4 GiB, in which case the entries in
 *   the chunk table are 8 bytes each.  In either case, the entries are unsigned
 *   little-endian integers.
 *
 * - The chunk table is included in the compressed size of the resource provided
 *   in the corresponding entry in the WIM's stream lookup table.
 *
 * - The compressed size of a chunk is never greater than the uncompressed size.
 *   From the compressor's point of view, chunks that would have compressed to a
 *   size greater than or equal to their original size are in fact stored
 *   uncompressed.  From the decompresser's point of view, chunks with
 *   compressed size equal to their uncompressed size are in fact uncompressed.
 *
 * Furthermore, wimlib supports its own "pipable" WIM format, and for this the
 * structure of compressed resources was modified to allow piped reading and
 * writing.  To make sequential writing possible, the chunk table is placed
 * after the chunks rather than before the chunks, and to make sequential
 * reading possible, each chunk is prefixed with a 4-byte header giving its
 * compressed size as a 32-bit, unsigned, little-endian integer.  Otherwise the
 * details are the same.
 */


/* Decompress the specified chunk that uses the specified compression type
 * @ctype, part of a WIM with default chunk size @wim_chunk_size.  For LZX the
 * separate @wim_chunk_size is needed because it determines the window size used
 * for LZX compression.  */
static int
decompress(const void *cchunk, unsigned clen, void *uchunk, unsigned ulen,
           int ctype, u32 wim_chunk_size)
{
        switch (ctype) {
        case WIMLIB_COMPRESSION_TYPE_LZX:
                return wimlib_lzx_decompress2(cchunk, clen,
                                              uchunk, ulen, wim_chunk_size);
        case WIMLIB_COMPRESSION_TYPE_XPRESS:
                return wimlib_xpress_decompress(cchunk, clen,
                                                uchunk, ulen);
        case WIMLIB_COMPRESSION_TYPE_LZMS:
                return wimlib_lzms_decompress(cchunk, clen, uchunk, ulen);
        default:
                ERROR("Invalid compression format (%d)", ctype);
                return -1;
        }
}

struct data_range {
        u64 offset;
        u64 size;
};

/* Alternate chunk table format for resources with
 * WIM_RESHDR_FLAG_PACKED_STREAMS set.  */
struct alt_chunk_table_header_disk {
        /* Uncompressed size of the resource in bytes.  */
        le64 res_usize;

        /* Number of bytes each compressed chunk decompresses into, except
         * possibly the last which decompresses into the remainder.  */
        le32 chunk_size;

        /* Compression format used for compressed chunks:
         * 0 = None
         * 1 = LZX
         * 2 = XPRESS
         * 3 = LZMS  */
        le32 compression_format;

        /* This header is directly followed by a table of compressed sizes of
         * the chunks.  */
} _packed_attribute;

/*
 * read_compressed_wim_resource() -
 *
 * Read data from a compressed WIM resource.
 *
 * @rspec
 *      Specification of the compressed WIM resource to read from.
 * @ranges
 *      Nonoverlapping, nonempty ranges of the uncompressed resource data to
 *      read, sorted by increasing offset.
 * @num_ranges
 *      Number of ranges in @ranges; must be at least 1.
 * @cb
 *      Callback function to feed the data being read.  Each call provides the
 *      next chunk of the requested data.  Each chunk will be of nonzero size
 *      and will not cross range boundaries, but otherwise is of unspecified
 *      size.
 * @cb_ctx
 *      Parameter to pass to @cb_ctx.
 * @raw_chunks_mode
 *      If %true, this function will provide the raw compressed chunks of the
 *      resource rather than the uncompressed data.  In this mode, only a single
 *      data range can be requested, and it must cover the entire uncompressed
 *      resource.
 *
 * Possible return values:
 *
 *      WIMLIB_ERR_SUCCESS (0)
 *      WIMLIB_ERR_READ                   (errno set)
 *      WIMLIB_ERR_UNEXPECTED_END_OF_FILE (errno set to 0)
 *      WIMLIB_ERR_NOMEM                  (errno set to ENOMEM)
 *      WIMLIB_ERR_DECOMPRESSION          (errno set to EINVAL)
 *
 *      or other error code returned by the @cb function.
 */
static int
read_compressed_wim_resource(const struct wim_resource_spec * const rspec,
                             const struct data_range * const ranges,
                             const size_t num_ranges,
                             const consume_data_callback_t cb,
                             void * const cb_ctx,
                             const bool raw_chunks_mode)
{
        int ret;
        int errno_save;

        u64 *chunk_offsets = NULL;
        u8 *ubuf = NULL;
        void *cbuf = NULL;
        bool chunk_offsets_malloced = false;
        bool ubuf_malloced = false;
        bool cbuf_malloced = false;

        /* Sanity checks  */
        wimlib_assert(rspec != NULL);
        wimlib_assert(resource_is_compressed(rspec));
        wimlib_assert(cb != NULL);
        wimlib_assert(num_ranges != 0);
        for (size_t i = 0; i < num_ranges; i++) {
                DEBUG("Range %zu/%zu: %"PRIu64"@+%"PRIu64" / %"PRIu64,
                      i + 1, num_ranges, ranges[i].size, ranges[i].offset,
                      rspec->uncompressed_size);
                wimlib_assert(ranges[i].size != 0);
                wimlib_assert(ranges[i].offset + ranges[i].size >= ranges[i].size);
                wimlib_assert(ranges[i].offset + ranges[i].size <= rspec->uncompressed_size);
        }
        for (size_t i = 0; i < num_ranges - 1; i++)
                wimlib_assert(ranges[i].offset + ranges[i].size <= ranges[i + 1].offset);

        if (raw_chunks_mode) {
                wimlib_assert(num_ranges == 1);
                wimlib_assert(ranges[0].offset == 0);
                wimlib_assert(ranges[0].size == rspec->uncompressed_size);
        }

        /* Get the offsets of the first and last bytes of the read.  */
        const u64 first_offset = ranges[0].offset;
        const u64 last_offset = ranges[num_ranges - 1].offset + ranges[num_ranges - 1].size - 1;

        /* Get the file descriptor for the WIM.  */
        struct filedes * const in_fd = &rspec->wim->in_fd;

        /* Determine if we're reading a pipable resource from a pipe or not.  */
        const bool is_pipe_read = !filedes_is_seekable(in_fd);

        /* Determine if the chunk table is in an altenate format.  */
        const bool alt_chunk_table = (rspec->flags & WIM_RESHDR_FLAG_PACKED_STREAMS)
                                        && !is_pipe_read;

        /* Get the maximum size of uncompressed chunks in this resource, which
         * we require be a power of 2.  */
        u32 chunk_size;
        u64 cur_read_offset = rspec->offset_in_wim;
        int ctype;
        if (alt_chunk_table) {
                /* Alternate chunk table format.  Its header specifies the chunk
                 * size and compression format.  */
                struct alt_chunk_table_header_disk hdr;

                ret = full_pread(in_fd, &hdr, sizeof(hdr), cur_read_offset);
                if (ret)
                        goto read_error;
                cur_read_offset += sizeof(hdr);

                chunk_size = le32_to_cpu(hdr.chunk_size);
                ctype = le32_to_cpu(hdr.compression_format);

                /* Format numbers must be the same as in WIMGAPI to be
                 * compatible.  */
                BUILD_BUG_ON(WIMLIB_COMPRESSION_TYPE_NONE != 0);
                BUILD_BUG_ON(WIMLIB_COMPRESSION_TYPE_LZX != 1);
                BUILD_BUG_ON(WIMLIB_COMPRESSION_TYPE_XPRESS != 2);
                BUILD_BUG_ON(WIMLIB_COMPRESSION_TYPE_LZMS != 3);
        } else {
                /* "Normal" format: the maximum uncompressed chunk size and the
                 * compression format default to those of the WIM itself.  */
                chunk_size = rspec->wim->chunk_size;
                ctype = rspec->wim->compression_type;
        }
        if (!is_power_of_2(chunk_size)) {
                ERROR("Invalid compressed resource: "
                      "expected power-of-2 chunk size (got %u)", chunk_size);
                ret = WIMLIB_ERR_INVALID_CHUNK_SIZE;
                goto out_free_memory;
        }

        const u32 chunk_order = bsr32(chunk_size);

        /* Calculate the total number of chunks the resource is divided into.  */
        const u64 num_chunks = (rspec->uncompressed_size + chunk_size - 1) >> chunk_order;

        /* Calculate the 0-based indices of the first and last chunks containing
         * data that needs to be passed to the callback.  */
        const u64 first_needed_chunk = first_offset >> chunk_order;
        const u64 last_needed_chunk = last_offset >> chunk_order;

        /* Calculate the 0-based index of the first chunk that actually needs to
         * be read.  This is normally first_needed_chunk, but for pipe reads we
         * must always start from the 0th chunk.  */
        const u64 read_start_chunk = (is_pipe_read ? 0 : first_needed_chunk);

        /* Calculate the number of chunk offsets that are needed for the chunks
         * being read.  */
        const u64 num_needed_chunk_offsets =
                last_needed_chunk - read_start_chunk + 1 +
                (last_needed_chunk < num_chunks - 1);

        /* Calculate the number of entries in the chunk table.  Normally, it's
         * one less than the number of chunks, since the first chunk has no
         * entry.  But in the alternate chunk table format, the chunk entries
         * contain chunk sizes, not offsets, and there is one per chunk.  */
        const u64 num_chunk_entries = (alt_chunk_table ? num_chunks : num_chunks - 1);

        /* Set the size of each chunk table entry based on the resource's
         * uncompressed size.  XXX:  Does the alternate chunk table really
         * always have 4-byte entries?  */
        const u64 chunk_entry_size =
                (rspec->uncompressed_size > (1ULL << 32) && !alt_chunk_table)
                        ? 8 : 4;

        /* Calculate the size of the chunk table in bytes.  */
        const u64 chunk_table_size = num_chunk_entries * chunk_entry_size;

        /* Calculate the size of the chunk table in bytes, including the header
         * in the case of the alternate chunk table format.  */
        const u64 chunk_table_full_size =
                (alt_chunk_table) ? chunk_table_size + sizeof(struct alt_chunk_table_header_disk)
                                  : chunk_table_size;

        if (!is_pipe_read) {
                /* Read the needed chunk table entries into memory and use them
                 * to initialize the chunk_offsets array.  */

                u64 first_chunk_entry_to_read;
                u64 last_chunk_entry_to_read;

                if (alt_chunk_table) {
                        /* The alternate chunk table contains chunk sizes, not
                         * offsets, so we always must read all preceding entries
                         * in order to determine offsets.  */
                        first_chunk_entry_to_read = 0;
                        last_chunk_entry_to_read = last_needed_chunk;
                } else {
                        /* Here we must account for the fact that the first
                         * chunk has no explicit chunk table entry.  */

                        if (read_start_chunk == 0)
                                first_chunk_entry_to_read = 0;
                        else
                                first_chunk_entry_to_read = read_start_chunk - 1;

                        if (last_needed_chunk == 0)
                                last_chunk_entry_to_read = 0;
                        else
                                last_chunk_entry_to_read = last_needed_chunk - 1;

                        if (last_needed_chunk < num_chunks - 1)
                                last_chunk_entry_to_read++;
                }

                const u64 num_chunk_entries_to_read =
                        last_chunk_entry_to_read - first_chunk_entry_to_read + 1;

                const u64 chunk_offsets_alloc_size =
                        max(num_chunk_entries_to_read,
                            num_needed_chunk_offsets) * sizeof(chunk_offsets[0]);

                if ((size_t)chunk_offsets_alloc_size != chunk_offsets_alloc_size)
                        goto oom;

                if (chunk_offsets_alloc_size <= STACK_MAX) {
                        chunk_offsets = alloca(chunk_offsets_alloc_size);
                } else {
                        chunk_offsets = MALLOC(chunk_offsets_alloc_size);
                        if (chunk_offsets == NULL)
                                goto oom;
                        chunk_offsets_malloced = true;
                }

                const size_t chunk_table_size_to_read =
                        num_chunk_entries_to_read * chunk_entry_size;

                const u64 file_offset_of_needed_chunk_entries =
                        cur_read_offset
                        + (first_chunk_entry_to_read * chunk_entry_size)
                        + (rspec->is_pipable ? (rspec->size_in_wim - chunk_table_size) : 0);

                void * const chunk_table_data =
                        (u8*)chunk_offsets +
                        chunk_offsets_alloc_size -
                        chunk_table_size_to_read;

                ret = full_pread(in_fd, chunk_table_data, chunk_table_size,
                                 file_offset_of_needed_chunk_entries);
                if (ret)
                        goto read_error;

                /* Now fill in chunk_offsets from the entries we have read in
                 * chunk_tab_data.  We break aliasing rules here to avoid having
                 * to allocate yet another array.  */
                typedef le64 __attribute__((may_alias)) aliased_le64_t;
                typedef le32 __attribute__((may_alias)) aliased_le32_t;
                u64 * chunk_offsets_p = chunk_offsets;

                if (alt_chunk_table) {
                        u64 cur_offset = 0;
                        aliased_le32_t *raw_entries = chunk_table_data;

                        for (size_t i = 0; i < num_chunk_entries_to_read; i++) {
                                u32 entry = le32_to_cpu(raw_entries[i]);
                                if (i >= read_start_chunk)
                                        *chunk_offsets_p++ = cur_offset;
                                cur_offset += entry;
                        }
                        if (last_needed_chunk < num_chunks - 1)
                                *chunk_offsets_p = cur_offset;
                } else {
                        if (read_start_chunk == 0)
                                *chunk_offsets_p++ = 0;

                        if (chunk_entry_size == 4) {
                                aliased_le32_t *raw_entries = chunk_table_data;
                                for (size_t i = 0; i < num_chunk_entries_to_read; i++)
                                        *chunk_offsets_p++ = le32_to_cpu(raw_entries[i]);
                        } else {
                                aliased_le64_t *raw_entries = chunk_table_data;
                                for (size_t i = 0; i < num_chunk_entries_to_read; i++)
                                        *chunk_offsets_p++ = le64_to_cpu(raw_entries[i]);
                        }
                }

                /* Set offset to beginning of first chunk to read.  */
                cur_read_offset += chunk_offsets[0];
                if (rspec->is_pipable)
                        cur_read_offset += read_start_chunk * sizeof(struct pwm_chunk_hdr);
                else
                        cur_read_offset += chunk_table_size;
        }

        /* Allocate buffer for holding the uncompressed data of each chunk.  */
        if (chunk_size <= STACK_MAX) {
                ubuf = alloca(chunk_size);
        } else {
                ubuf = MALLOC(chunk_size);
                if (ubuf == NULL)
                        goto oom;
                ubuf_malloced = true;
        }

        /* Unless the raw compressed data was requested, allocate a temporary
         * buffer for reading compressed chunks, each of which can be at most
         * @chunk_size - 1 bytes.  This excludes compressed chunks that are a
         * full @chunk_size bytes, which are actually stored uncompressed.  */
        if (!raw_chunks_mode) {
                if (chunk_size - 1 <= STACK_MAX) {
                        cbuf = alloca(chunk_size - 1);
                } else {
                        cbuf = MALLOC(chunk_size - 1);
                        if (cbuf == NULL)
                                goto oom;
                        cbuf_malloced = true;
                }
        }

        /* Set current data range.  */
        const struct data_range *cur_range = ranges;
        const struct data_range * const end_range = &ranges[num_ranges];
        u64 cur_range_pos = cur_range->offset;
        u64 cur_range_end = cur_range->offset + cur_range->size;

        /* Read and process each needed chunk.  */
        for (u64 i = read_start_chunk; i <= last_needed_chunk; i++) {

                /* Calculate uncompressed size of next chunk.  */
                u32 chunk_usize;
                if ((i == num_chunks - 1) && (rspec->uncompressed_size & (chunk_size - 1)))
                        chunk_usize = (rspec->uncompressed_size & (chunk_size - 1));
                else
                        chunk_usize = chunk_size;

                /* Calculate compressed size of next chunk.  */
                u32 chunk_csize;
                if (is_pipe_read) {
                        struct pwm_chunk_hdr chunk_hdr;

                        ret = full_pread(in_fd, &chunk_hdr,
                                         sizeof(chunk_hdr), cur_read_offset);
                        if (ret)
                                goto read_error;
                        chunk_csize = le32_to_cpu(chunk_hdr.compressed_size);
                } else {
                        if (i == num_chunks - 1) {
                                chunk_csize = rspec->size_in_wim -
                                              chunk_table_full_size -
                                              chunk_offsets[i - read_start_chunk];
                                if (rspec->is_pipable)
                                        chunk_csize -= num_chunks * sizeof(struct pwm_chunk_hdr);
                        } else {
                                chunk_csize = chunk_offsets[i + 1 - read_start_chunk] -
                                              chunk_offsets[i - read_start_chunk];
                        }
                }
                if (chunk_csize == 0 || chunk_csize > chunk_usize) {
                        ERROR("Invalid chunk size in compressed resource!");
                        errno = EINVAL;
                        ret = WIMLIB_ERR_DECOMPRESSION;
                        goto out_free_memory;
                }
                if (rspec->is_pipable)
                        cur_read_offset += sizeof(struct pwm_chunk_hdr);

                /* Offsets in the uncompressed resource at which this chunk
                 * starts and ends.  */
                const u64 chunk_start_offset = i << chunk_order;
                const u64 chunk_end_offset = chunk_start_offset + chunk_usize;

                if (chunk_end_offset <= cur_range_pos) {

                        /* The next range does not require data in this chunk,
                         * so skip it.  */
                        cur_read_offset += chunk_csize;
                        if (is_pipe_read) {
                                u8 dummy;

                                ret = full_pread(in_fd, &dummy, 1, cur_read_offset - 1);
                                if (ret)
                                        goto read_error;
                        }
                } else {

                        /* Read the chunk and feed data to the callback
                         * function.  */
                        u8 *read_buf;

                        if (chunk_csize == chunk_usize || raw_chunks_mode)
                                read_buf = ubuf;
                        else
                                read_buf = cbuf;

                        ret = full_pread(in_fd,
                                         read_buf,
                                         chunk_csize,
                                         cur_read_offset);
                        if (ret)
                                goto read_error;

                        if (read_buf == cbuf) {
                                DEBUG("Decompressing chunk %"PRIu64" "
                                      "(csize=%"PRIu64" usize=%"PRIu64"",
                                      i, chunk_csize, chunk_usize);
                                ret = decompress(cbuf,
                                                 chunk_csize,
                                                 ubuf,
                                                 chunk_usize,
                                                 ctype,
                                                 chunk_size);
                                if (ret) {
                                        ERROR("Failed to decompress data!");
                                        ret = WIMLIB_ERR_DECOMPRESSION;
                                        errno = EINVAL;
                                        goto out_free_memory;
                                }
                        }
                        cur_read_offset += chunk_csize;

                        /* At least one range requires data in this chunk.  */
                        do {
                                size_t start, end, size;

                                /* Calculate how many bytes of data should be
                                 * sent to the callback function, taking into
                                 * account that data sent to the callback
                                 * function must not overlap range boundaries.
                                 */
                                start = cur_range_pos - chunk_start_offset;
                                end = min(cur_range_end, chunk_end_offset) - chunk_start_offset;
                                size = end - start;

                                if (raw_chunks_mode)
                                        ret = (*cb)(&ubuf[0], chunk_csize, cb_ctx);
                                else
                                        ret = (*cb)(&ubuf[start], size, cb_ctx);

                                if (ret)
                                        goto out_free_memory;

                                cur_range_pos += size;
                                if (cur_range_pos == cur_range_end) {
                                        /* Advance to next range.  */
                                        if (++cur_range == end_range) {
                                                cur_range_pos = ~0ULL;
                                        } else {
                                                cur_range_pos = cur_range->offset;
                                                cur_range_end = cur_range->offset + cur_range->size;
                                        }
                                }
                        } while (cur_range_pos < chunk_end_offset);
                }
        }

        if (is_pipe_read &&
            last_offset == rspec->uncompressed_size - 1 &&
            chunk_table_size)
        {
                u8 dummy;
                /* If reading a pipable resource from a pipe and the full data
                 * was requested, skip the chunk table at the end so that the
                 * file descriptor is fully clear of the resource after this
                 * returns.  */
                cur_read_offset += chunk_table_size;
                ret = full_pread(in_fd, &dummy, 1, cur_read_offset - 1);
                if (ret)
                        goto read_error;
        }
        ret = 0;
out_free_memory:
        errno_save = errno;
        if (chunk_offsets_malloced)
                FREE(chunk_offsets);
        if (ubuf_malloced)
                FREE(ubuf);
        if (cbuf_malloced)
                FREE(cbuf);
        errno = errno_save;
        return ret;

oom:
        ERROR("Not enough memory available to read size=%"PRIu64" bytes "
              "from compressed WIM resource!", last_offset - first_offset + 1);
        errno = ENOMEM;
        ret = WIMLIB_ERR_NOMEM;
        goto out_free_memory;

read_error:
        ERROR_WITH_ERRNO("Error reading compressed WIM resource!");
        goto out_free_memory;
}

/* Read raw data from a file descriptor at the specified offset, feeding the
 * data it in chunks into the specified callback function.  */
static int
read_raw_file_data(struct filedes *in_fd, u64 size,
                   consume_data_callback_t cb, void *cb_ctx, u64 offset)
{
        u8 buf[BUFFER_SIZE];
        size_t bytes_to_read;
        int ret;

        while (size) {
                bytes_to_read = min(sizeof(buf), size);
                ret = full_pread(in_fd, buf, bytes_to_read, offset);
                if (ret) {
                        ERROR_WITH_ERRNO("Read error");
                        return ret;
                }
                ret = cb(buf, bytes_to_read, cb_ctx);
                if (ret)
                        return ret;
                size -= bytes_to_read;
                offset += bytes_to_read;
        }
        return 0;
}

/* A consume_data_callback_t implementation that simply concatenates all chunks
 * into a buffer.  */
static int
bufferer_cb(const void *chunk, size_t size, void *_ctx)
{
        u8 **buf_p = _ctx;

        *buf_p = mempcpy(*buf_p, chunk, size);
        return 0;
}

/*
 * read_partial_wim_resource()-
 *
 * Read a range of data from an uncompressed or compressed resource in a WIM
 * file.  Data is fed chunk-by-chunk into the callback function @cb, passing it
 * the argument @cb_ctx.  The chunks are of unspecified size unless the
 * RAW_CHUNKS mode is requested.
 *
 * By default, this function provides the uncompressed data of the resource, and
 * @offset and @size and interpreted relative to the uncompressed contents of
 * the resource.  This behavior can be modified by either of the following
 * flags:
 *
 * WIMLIB_READ_RESOURCE_FLAG_RAW_FULL:
 *      Read @size bytes at @offset of the raw contents of the compressed
 *      resource.  In the case of pipable resources, this excludes the stream
 *      header.  Exclusive with WIMLIB_READ_RESOURCE_FLAG_RAW_CHUNKS.
 *
 * WIMLIB_READ_RESOURCE_FLAG_RAW_CHUNKS:
 *      Read the raw compressed chunks of the compressed resource.  @size must
 *      be the full uncompressed size, @offset must be 0, and @cb_chunk_size
 *      must be the resource chunk size.
 *
 * Return values:
 *      WIMLIB_ERR_SUCCESS (0)
 *      WIMLIB_ERR_READ                   (errno set)
 *      WIMLIB_ERR_UNEXPECTED_END_OF_FILE (errno set to 0)
 *      WIMLIB_ERR_NOMEM                  (errno set to ENOMEM)
 *      WIMLIB_ERR_DECOMPRESSION          (errno set to EINVAL)
 *
 *      or other error code returned by the @cb function.
 */
static int
read_partial_wim_resource(const struct wim_resource_spec *rspec,
                          u64 offset, u64 size, consume_data_callback_t cb,
                          void *cb_ctx, int flags)
{
        /* Sanity checks.  */
        if (flags & WIMLIB_READ_RESOURCE_FLAG_RAW_FULL) {
                wimlib_assert(!(flags & WIMLIB_READ_RESOURCE_FLAG_RAW_CHUNKS));
                wimlib_assert(offset + size >= offset);
                wimlib_assert(offset + size <= rspec->size_in_wim);
        } else if (flags & WIMLIB_READ_RESOURCE_FLAG_RAW_CHUNKS) {
                wimlib_assert(offset == 0);
                wimlib_assert(size == rspec->uncompressed_size);
        } else {
                wimlib_assert(offset + size >= offset);
                wimlib_assert(offset + size <= rspec->uncompressed_size);
        }

        DEBUG("Reading %"PRIu64" @ %"PRIu64" from WIM resource  "
              "%"PRIu64" => %"PRIu64" @ %"PRIu64" (flags 0x%08x)",
              size, offset, rspec->uncompressed_size,
              rspec->size_in_wim, rspec->offset_in_wim, flags);

        /* Trivial case.  */
        if (size == 0)
                return 0;

        if ((flags & WIMLIB_READ_RESOURCE_FLAG_RAW_FULL) ||
            !resource_is_compressed(rspec))
        {
                return read_raw_file_data(&rspec->wim->in_fd,
                                          size,
                                          cb,
                                          cb_ctx,
                                          rspec->offset_in_wim + offset);
        } else {
                bool raw_chunks = (flags & WIMLIB_READ_RESOURCE_FLAG_RAW_CHUNKS);
                struct data_range range = {
                        .offset = offset,
                        .size = size,
                };
                return read_compressed_wim_resource(rspec, &range, 1,
                                                    cb, cb_ctx, raw_chunks);
        }
}

/* Read the specified range of uncompressed data from the specified stream,
 * which must be located into a WIM file, into the specified buffer.  */
int
read_partial_wim_stream_into_buf(const struct wim_lookup_table_entry *lte,
                                 size_t size, u64 offset, void *_buf)
{
        u8 *buf = _buf;

        wimlib_assert(lte->resource_location == RESOURCE_IN_WIM);

        return read_partial_wim_resource(lte->rspec,
                                         lte->offset_in_res + offset,
                                         size,
                                         bufferer_cb,
                                         &buf,
                                         0);
}

/* A consume_data_callback_t implementation that simply ignores the data
 * received.  */
static int
skip_chunk_cb(const void *chunk, size_t size, void *_ctx)
{
        return 0;
}

/* Skip over the data of the specified stream, which must correspond to a full
 * WIM resource.  */
int
skip_wim_stream(struct wim_lookup_table_entry *lte)
{
        wimlib_assert(lte->resource_location == RESOURCE_IN_WIM);
        wimlib_assert(!lte_is_partial(lte));
        return read_partial_wim_resource(lte->rspec,
                                         0,
                                         lte->rspec->uncompressed_size,
                                         skip_chunk_cb,
                                         NULL,
                                         WIMLIB_READ_RESOURCE_FLAG_RAW_CHUNKS);
}

static int
read_wim_stream_prefix(const struct wim_lookup_table_entry *lte, u64 size,
                       consume_data_callback_t cb, void *cb_ctx, int flags)
{
        return read_partial_wim_resource(lte->rspec,
                                         lte->offset_in_res,
                                         size,
                                         cb,
                                         cb_ctx,
                                         flags);
}

#ifndef __WIN32__
/* This function handles reading stream data that is located in an external
 * file,  such as a file that has been added to the WIM image through execution
 * of a wimlib_add_command.
 *
 * This assumes the file can be accessed using the standard POSIX open(),
 * read(), and close().  On Windows this will not necessarily be the case (since
 * the file may need FILE_FLAG_BACKUP_SEMANTICS to be opened, or the file may be
 * encrypted), so Windows uses its own code for its equivalent case.  */
static int
read_file_on_disk_prefix(const struct wim_lookup_table_entry *lte, u64 size,
                         consume_data_callback_t cb, void *cb_ctx,
                         int _ignored_flags)
{
        int ret;
        int raw_fd;
        struct filedes fd;

        wimlib_assert(size <= lte->size);

        DEBUG("Reading %"PRIu64" bytes from \"%"TS"\"", size, lte->file_on_disk);

        raw_fd = open(lte->file_on_disk, O_BINARY | O_RDONLY);
        if (raw_fd < 0) {
                ERROR_WITH_ERRNO("Can't open \"%"TS"\"", lte->file_on_disk);
                return WIMLIB_ERR_OPEN;
        }
        filedes_init(&fd, raw_fd);
        ret = read_raw_file_data(&fd, size, cb, cb_ctx, 0);
        filedes_close(&fd);
        return ret;
}
#endif /* !__WIN32__ */

/* This function handles the trivial case of reading stream data that is, in
 * fact, already located in an in-memory buffer.  */
static int
read_buffer_prefix(const struct wim_lookup_table_entry *lte,
                   u64 size, consume_data_callback_t cb,
                   void *cb_ctx, int _ignored_flags)
{
        wimlib_assert(size <= lte->size);
        return (*cb)(lte->attached_buffer, size, cb_ctx);
}

typedef int (*read_stream_prefix_handler_t)(const struct wim_lookup_table_entry *lte,
                                            u64 size,
                                            consume_data_callback_t cb,
                                            void *cb_ctx, int flags);

/*
 * read_stream_prefix()-
 *
 * Reads the first @size bytes from a generic "stream", which may be located in
 * any one of several locations, such as in a WIM file (compressed or
 * uncompressed), in an external file, or directly in an in-memory buffer.
 *
 * This function feeds the data to a callback function @cb in chunks of
 * unspecified size.
 *
 * If the stream is located in a WIM file, @flags can be set as documented in
 * read_partial_wim_resource().  Otherwise @flags are ignored.
 *
 * Returns 0 on success; nonzero on error.  A nonzero value will be returned if
 * the stream data cannot be successfully read (for a number of different
 * reasons, depending on the stream location), or if @cb returned nonzero in
 * which case that error code will be returned.
 */
int
read_stream_prefix(const struct wim_lookup_table_entry *lte, u64 size,
                   consume_data_callback_t cb, void *cb_ctx, int flags)
{
        static const read_stream_prefix_handler_t handlers[] = {
                [RESOURCE_IN_WIM]             = read_wim_stream_prefix,
        #ifdef __WIN32__
                [RESOURCE_IN_FILE_ON_DISK]    = read_win32_file_prefix,
        #else
                [RESOURCE_IN_FILE_ON_DISK]    = read_file_on_disk_prefix,
        #endif
                [RESOURCE_IN_ATTACHED_BUFFER] = read_buffer_prefix,
        #ifdef WITH_FUSE
                [RESOURCE_IN_STAGING_FILE]    = read_file_on_disk_prefix,
        #endif
        #ifdef WITH_NTFS_3G
                [RESOURCE_IN_NTFS_VOLUME]     = read_ntfs_file_prefix,
        #endif
        #ifdef __WIN32__
                [RESOURCE_WIN32_ENCRYPTED]    = read_win32_encrypted_file_prefix,
        #endif
        };
        wimlib_assert(lte->resource_location < ARRAY_LEN(handlers)
                      && handlers[lte->resource_location] != NULL);
        return handlers[lte->resource_location](lte, size, cb, cb_ctx, flags);
}

/* Read the full uncompressed data of the specified stream into the specified
 * buffer, which must have space for at least lte->size bytes.  */
int
read_full_stream_into_buf(const struct wim_lookup_table_entry *lte, void *_buf)
{
        u8 *buf = _buf;
        return read_stream_prefix(lte, lte->size, bufferer_cb, &buf, 0);
}

/* Retrieve the full uncompressed data of the specified stream.  A buffer large
 * enough hold the data is allocated and returned in @buf_ret.  */
int
read_full_stream_into_alloc_buf(const struct wim_lookup_table_entry *lte,
                                void **buf_ret)
{
        int ret;
        void *buf;

        if ((size_t)lte->size != lte->size) {
                ERROR("Can't read %"PRIu64" byte stream into "
                      "memory", lte->size);
                return WIMLIB_ERR_NOMEM;
        }

        buf = MALLOC(lte->size);
        if (buf == NULL)
                return WIMLIB_ERR_NOMEM;

        ret = read_full_stream_into_buf(lte, buf);
        if (ret) {
                FREE(buf);
                return ret;
        }

        *buf_ret = buf;
        return 0;
}

/* Retrieve the full uncompressed data of the specified WIM resource.  A buffer
 * large enough hold the data is allocated and returned in @buf_ret.  */
static int
wim_resource_spec_to_data(struct wim_resource_spec *rspec, void **buf_ret)
{
        int ret;
        struct wim_lookup_table_entry *lte;

        lte = new_lookup_table_entry();
        if (lte == NULL)
                return WIMLIB_ERR_NOMEM;

        lte->unhashed = 1;
        lte_bind_wim_resource_spec(lte, rspec);
        lte->flags = rspec->flags;
        lte->size = rspec->uncompressed_size;
        lte->offset_in_res = 0;

        ret = read_full_stream_into_alloc_buf(lte, buf_ret);

        lte_unbind_wim_resource_spec(lte);
        free_lookup_table_entry(lte);
        return ret;
}

/* Retrieve the full uncompressed data of a WIM resource specified as a raw
 * `wim_reshdr' and the corresponding WIM file.  A large enough hold the data is
 * allocated and returned in @buf_ret.  */
int
wim_reshdr_to_data(const struct wim_reshdr *reshdr, WIMStruct *wim, void **buf_ret)
{
        DEBUG("offset_in_wim=%"PRIu64", size_in_wim=%"PRIu64", "
              "uncompressed_size=%"PRIu64,
              reshdr->offset_in_wim, reshdr->size_in_wim,
              reshdr->uncompressed_size);

        struct wim_resource_spec rspec;
        wim_res_hdr_to_spec(reshdr, wim, &rspec);
        return wim_resource_spec_to_data(&rspec, buf_ret);
}

struct streamifier_context {
        struct read_stream_list_callbacks cbs;
        struct wim_lookup_table_entry *cur_stream;
        u64 cur_stream_offset;
        struct wim_lookup_table_entry *final_stream;
        size_t list_head_offset;
};

/* A consume_data_callback_t implementation that translates raw resource data
 * into streams, calling the begin_stream, consume_chunk, and end_stream
 * callback functions as appropriate.  */
static int
streamifier_cb(const void *chunk, size_t size, void *_ctx)
{
        struct streamifier_context *ctx = _ctx;
        int ret;

        DEBUG("%zu bytes passed to streamifier", size);

        wimlib_assert(ctx->cur_stream != NULL);
        wimlib_assert(size <= ctx->cur_stream->size - ctx->cur_stream_offset);

        if (ctx->cur_stream_offset == 0) {
                /* Starting a new stream.  */
                DEBUG("Begin new stream (size=%"PRIu64").",
                      ctx->cur_stream->size);
                ret = (*ctx->cbs.begin_stream)(ctx->cur_stream, true,
                                               ctx->cbs.begin_stream_ctx);
                if (ret)
                        return ret;
        }

        /* Consume the chunk.  */
        ret = (*ctx->cbs.consume_chunk)(chunk, size,
                                        ctx->cbs.consume_chunk_ctx);
        if (ret)
                return ret;
        ctx->cur_stream_offset += size;

        if (ctx->cur_stream_offset == ctx->cur_stream->size) {
                /* Finished reading all the data for a stream.  */
                DEBUG("End stream (size=%"PRIu64").", ctx->cur_stream->size);
                ret = (*ctx->cbs.end_stream)(ctx->cur_stream, 0,
                                             ctx->cbs.end_stream_ctx);
                if (ret)
                        return ret;

                if (ctx->cur_stream != ctx->final_stream) {
                        /* Advance to next stream.  */
                        struct list_head *cur, *next;

                        cur = (struct list_head *)
                                ((u8*)ctx->cur_stream + ctx->list_head_offset);
                        next = cur->next;

                        ctx->cur_stream = (struct wim_lookup_table_entry *)
                                        ((u8*)next - ctx->list_head_offset);

                        ctx->cur_stream_offset = 0;
                } else {
                        /* No more streams.  */
                        ctx->cur_stream = NULL;
                }
        }
        return 0;
}

struct hasher_context {
        SHA_CTX sha_ctx;
        struct read_stream_list_callbacks cbs;
};

/* Callback for starting to read a stream while calculating its SHA1 message
 * digest.  */
static int
hasher_begin_stream(struct wim_lookup_table_entry *lte, bool is_partial_res,
                    void *_ctx)
{
        struct hasher_context *ctx = _ctx;

        sha1_init(&ctx->sha_ctx);

        if (ctx->cbs.begin_stream == NULL)
                return 0;
        else
                return (*ctx->cbs.begin_stream)(lte, is_partial_res,
                                                ctx->cbs.begin_stream_ctx);
}

/* A consume_data_callback_t implementation that continues calculating the SHA1
 * message digest of the stream being read, then optionally passes the data on
 * to another consume_data_callback_t implementation.  This allows checking the
 * SHA1 message digest of a stream being extracted, for example.  */
static int
hasher_consume_chunk(const void *chunk, size_t size, void *_ctx)
{
        struct hasher_context *ctx = _ctx;

        sha1_update(&ctx->sha_ctx, chunk, size);
        if (ctx->cbs.consume_chunk == NULL)
                return 0;
        else
                return (*ctx->cbs.consume_chunk)(chunk, size, ctx->cbs.consume_chunk_ctx);
}

/* Callback for finishing reading a stream while calculating its SHA1 message
 * digest.  */
static int
hasher_end_stream(struct wim_lookup_table_entry *lte, int status, void *_ctx)
{
        struct hasher_context *ctx = _ctx;
        u8 hash[SHA1_HASH_SIZE];
        int ret;

        if (status) {
                /* Error occurred; the full stream may not have been read.  */
                ret = status;
                goto out_next_cb;
        }

        /* Retrieve the final SHA1 message digest.  */
        sha1_final(hash, &ctx->sha_ctx);

        if (lte->unhashed) {
                /* No SHA1 message digest was previously present for the stream.
                 * Set it to the one just calculated.  */
                DEBUG("Set SHA1 message digest for stream (size=%"PRIu64").", lte->size);
                copy_hash(lte->hash, hash);
        } else {
                /* The stream already had a SHA1 message digest present.  Verify
                 * that it is the same as the calculated value.  */
                if (!hashes_equal(hash, lte->hash)) {
                        if (wimlib_print_errors) {
                                ERROR("Invalid SHA1 message digest "
                                      "on the following WIM stream:");
                                print_lookup_table_entry(lte, stderr);
                                if (lte->resource_location == RESOURCE_IN_WIM)
                                        ERROR("The WIM file appears to be corrupt!");
                        }
                        ret = WIMLIB_ERR_INVALID_RESOURCE_HASH;
                        errno = EINVAL;
                        goto out_next_cb;
                }
                DEBUG("SHA1 message digest okay for stream (size=%"PRIu64").", lte->size);
        }
        ret = 0;
out_next_cb:
        if (ctx->cbs.end_stream == NULL)
                return ret;
        else
                return (*ctx->cbs.end_stream)(lte, ret, ctx->cbs.end_stream_ctx);
}

/* Read the full data of the specified stream, passing the data into the
 * specified callbacks (all of which are optional) and either checking or
 * computing the SHA1 message digest of the stream.  */
static int
read_full_stream_with_sha1(struct wim_lookup_table_entry *lte,
                           const struct read_stream_list_callbacks *cbs)
{
        int ret;

        struct hasher_context hasher_ctx = {
                .cbs = *cbs,
        };

        ret = hasher_begin_stream(lte, false, &hasher_ctx);
        if (ret)
                return ret;

        ret = read_stream_prefix(lte, lte->size, hasher_consume_chunk,
                                 &hasher_ctx, 0);

        return hasher_end_stream(lte, ret, &hasher_ctx);
}

struct rechunkifier_context {
        u8 *buffer;
        u32 buffer_filled;
        u32 cb_chunk_size;

        const struct data_range *ranges;
        size_t num_ranges;
        size_t cur_range;
        u64 range_bytes_remaining;

        consume_data_callback_t cb;
        void *cb_ctx;
};

/* Wrapper callback for adjusting the data chunk size.  */
static int
rechunkifier_cb(const void *chunk, size_t size, void *_ctx)
{
        struct rechunkifier_context *ctx = _ctx;
        const u8 *chunkptr = chunk;
        size_t bytes_to_copy;
        int ret;

        wimlib_assert(ctx->cur_range != ctx->num_ranges);

        while (size) {

                /* Append more data to the buffer.  */
                bytes_to_copy = size;

                if (bytes_to_copy > ctx->cb_chunk_size - ctx->buffer_filled)
                        bytes_to_copy = ctx->cb_chunk_size - ctx->buffer_filled;

                if (bytes_to_copy > ctx->range_bytes_remaining - ctx->buffer_filled)
                        bytes_to_copy = ctx->range_bytes_remaining - ctx->buffer_filled;

                memcpy(&ctx->buffer[ctx->buffer_filled], chunkptr, bytes_to_copy);

                ctx->buffer_filled += bytes_to_copy;
                chunkptr += bytes_to_copy;
                size -= bytes_to_copy;
                ctx->range_bytes_remaining -= bytes_to_copy;

                if (ctx->buffer_filled == ctx->cb_chunk_size ||
                    ctx->range_bytes_remaining == 0)
                {
                        /* Maximum chunk size reached, or current range ended.
                         * Call the next consume_data_callback_t and empty the
                         * buffer  */
                        ret = (*ctx->cb)(ctx->buffer, ctx->buffer_filled, ctx->cb_ctx);
                        if (ret)
                                return ret;
                        ctx->buffer_filled = 0;

                        if (ctx->range_bytes_remaining == 0 &&
                            ++ctx->cur_range != ctx->num_ranges)
                                ctx->range_bytes_remaining = ctx->ranges[ctx->cur_range].size;
                }
        }
        return 0;
}

/*
 * Read a list of streams, each of which may be in any supported location (e.g.
 * in a WIM or in an external file).  Unlike read_stream_prefix() or the
 * functions which call it, this function optimizes the case where multiple
 * streams are packed into a single compressed WIM resource and reads them all
 * consecutively, only decompressing the data one time.
 *
 * @stream_list
 *      List of streams (represented as `struct wim_lookup_table_entry's) to
 *      read.
 * @list_head_offset
 *      Offset of the `struct list_head' within each `struct
 *      wim_lookup_table_entry' that makes up the @stream_list.
 * @cb_chunk_size
 *      Size of chunks to provide to @consume_chunk.  For a given stream, all
 *      the chunks will be this size, except possibly the last which will be the
 *      remainder.  If @
 * @cbs TODO
 *
 * Returns 0 on success; a nonzero error code on failure.  Failure can occur due
 * to an error reading the data or due to an error status being returned by any
 * of the callback functions.
 */
int
read_stream_list(struct list_head *stream_list,
                 size_t list_head_offset,
                 u32 cb_chunk_size,
                 const struct read_stream_list_callbacks *cbs)
{
        int ret;
        struct list_head *cur, *next;
        struct wim_lookup_table_entry *lte;

        ret = sort_stream_list_by_sequential_order(stream_list, list_head_offset);
        if (ret)
                return ret;

        for (cur = stream_list->next, next = cur->next;
             cur != stream_list;
             cur = next, next = cur->next)
        {
                lte = (struct wim_lookup_table_entry*)((u8*)cur - list_head_offset);

                if (lte_is_partial(lte)) {

                        struct wim_lookup_table_entry *lte_next, *lte_last;
                        struct list_head *next2;
                        size_t stream_count;

                        /* The next stream is a proper sub-sequence of a WIM
                         * resource.  See if there are other streams in the same
                         * resource that need to be read.  Since
                         * sort_stream_list_by_sequential_order() sorted the
                         * streams by offset in the WIM, this can be determined
                         * by simply scanning forward in the list.  */

                        lte_last = lte;
                        stream_count = 1;
                        for (next2 = next;
                             next2 != stream_list
                             && (lte_next = (struct wim_lookup_table_entry*)
                                                ((u8*)next2 - list_head_offset),
                                 lte_next->resource_location == RESOURCE_IN_WIM
                                 && lte_next->rspec == lte->rspec);
                             next2 = next2->next)
                        {
                                lte_last = lte_next;
                                stream_count++;
                        }
                        if (stream_count > 1) {
                                /* Reading multiple streams combined into a
                                 * single WIM resource.  They are in the stream
                                 * list, sorted by offset; @lte specifies the
                                 * first stream in the resource that needs to be
                                 * read and @lte_last specifies the last stream
                                 * in the resource that needs to be read.  */

                                DEBUG("Reading %zu streams combined in same "
                                      "WIM resource", stream_count);

                                next = next2;

                                struct data_range ranges[stream_count];

                                {
                                        struct list_head *next3;
                                        size_t i;
                                        struct wim_lookup_table_entry *lte_cur;

                                        next3 = cur;
                                        for (i = 0; i < stream_count; i++) {
                                                lte_cur = (struct wim_lookup_table_entry*)
                                                        ((u8*)next3 - list_head_offset);
                                                ranges[i].offset = lte_cur->offset_in_res;
                                                ranges[i].size = lte_cur->size;
                                                next3 = next3->next;
                                        }
                                }

                                /* Set up a chain of callbacks.
                                 *
                                 * The first level is the
                                 * streamifier_cb,
                                 * which takes in chunks of data and divides
                                 * them into the constituent streams.
                                 *
                                 * The second level are the SHA1 message digest
                                 * callbacks, which checksum each stream.
                                 *
                                 * rechunkifier_cb handles dividing the read
                                 * data into chunks of maximum size
                                 * @cb_chunk_size.  If @cb_chunk_size is 0, then
                                 * this callback is not needed.
                                 *
                                 * Finally, the last level of callbacks are
                                 * @cbs, passed as arguments to this function.
                                 */

                                struct rechunkifier_context *rechunkifier_ctx = NULL;
                                consume_data_callback_t last_cb;
                                void *last_cb_ctx;

                                if (cb_chunk_size != 0) {
                                        rechunkifier_ctx = alloca(sizeof(*rechunkifier_ctx));
                                        *rechunkifier_ctx = (struct rechunkifier_context) {
                                                .buffer                 = MALLOC(cb_chunk_size),
                                                .buffer_filled          = 0,
                                                .cb_chunk_size          = cb_chunk_size,
                                                .ranges                 = ranges,
                                                .num_ranges             = stream_count,
                                                .cur_range              = 0,
                                                .range_bytes_remaining  = ranges[0].size,
                                                .cb                     = cbs->consume_chunk,
                                                .cb_ctx                 = cbs->consume_chunk_ctx,
                                        };

                                        if (rechunkifier_ctx->buffer == NULL)
                                                return WIMLIB_ERR_NOMEM;
                                        last_cb = rechunkifier_cb;
                                        last_cb_ctx = rechunkifier_ctx;
                                } else {
                                        rechunkifier_ctx = NULL;
                                        last_cb = cbs->consume_chunk;
                                        last_cb_ctx = cbs->consume_chunk_ctx;
                                }

                                struct hasher_context hasher_ctx = {
                                        .cbs = {
                                                .begin_stream           = cbs->begin_stream,
                                                .begin_stream_ctx       = cbs->begin_stream_ctx,
                                                .consume_chunk          = last_cb,
                                                .consume_chunk_ctx      = last_cb_ctx,
                                                .end_stream             = cbs->end_stream,
                                                .end_stream_ctx         = cbs->end_stream_ctx,
                                        },
                                };

                                struct streamifier_context streamifier_ctx = {
                                        .cbs = {
                                                .begin_stream           = hasher_begin_stream,
                                                .begin_stream_ctx       = &hasher_ctx,
                                                .consume_chunk          = hasher_consume_chunk,
                                                .consume_chunk_ctx      = &hasher_ctx,
                                                .end_stream             = hasher_end_stream,
                                                .end_stream_ctx         = &hasher_ctx,
                                        },
                                        .cur_stream             = lte,
                                        .cur_stream_offset      = 0,
                                        .final_stream           = lte_last,
                                        .list_head_offset       = list_head_offset,
                                };

                                ret = read_compressed_wim_resource(lte->rspec,
                                                                   ranges,
                                                                   stream_count,
                                                                   streamifier_cb,
                                                                   &streamifier_ctx,
                                                                   false);
                                if (rechunkifier_ctx != NULL)
                                        FREE(rechunkifier_ctx->buffer);

                                if (ret) {
                                        if (streamifier_ctx.cur_stream_offset != 0) {
                                                ret = (*streamifier_ctx.cbs.end_stream)
                                                        (streamifier_ctx.cur_stream,
                                                         ret,
                                                         streamifier_ctx.cbs.end_stream_ctx);
                                        }
                                        return ret;
                                }
                                continue;
                        }
                }

                ret = read_full_stream_with_sha1(lte, cbs);
                if (ret > 0)
                        return ret;
        }
        return 0;
}

/* Extract the first @size bytes of the specified stream.
 *
 * If @size specifies the full uncompressed size of the stream, then the SHA1
 * message digest of the uncompressed stream is checked while being extracted.
 *
 * The uncompressed data of the resource is passed in chunks of unspecified size
 * to the @extract_chunk function, passing it @extract_chunk_arg.  */
int
extract_stream(struct wim_lookup_table_entry *lte, u64 size,
               consume_data_callback_t extract_chunk, void *extract_chunk_arg)
{
        if (size == lte->size) {
                /* Do SHA1.  */
                struct read_stream_list_callbacks cbs = {
                        .consume_chunk          = extract_chunk,
                        .consume_chunk_ctx      = extract_chunk_arg,
                };
                return read_full_stream_with_sha1(lte, &cbs);
        } else {
                /* Don't do SHA1.  */
                return read_stream_prefix(lte, size, extract_chunk,
                                          extract_chunk_arg, 0);
        }
}

/* A consume_data_callback_t implementation that writes the chunk of data to a
 * file descriptor.  */
int
extract_chunk_to_fd(const void *chunk, size_t size, void *_fd_p)
{
        struct filedes *fd = _fd_p;

        int ret = full_write(fd, chunk, size);
        if (ret) {
                ERROR_WITH_ERRNO("Error writing to file descriptor");
                return ret;
        }
        return 0;
}

/* Extract the first @size bytes of the specified stream to the specified file
 * descriptor.  */
int
extract_stream_to_fd(struct wim_lookup_table_entry *lte,
                     struct filedes *fd, u64 size)
{
        return extract_stream(lte, size, extract_chunk_to_fd, fd);
}

/* Calculate the SHA1 message digest of a stream and store it in @lte->hash.  */
int
sha1_stream(struct wim_lookup_table_entry *lte)
{
        wimlib_assert(lte->unhashed);
        struct read_stream_list_callbacks cbs = {
        };
        return read_full_stream_with_sha1(lte, &cbs);
}

/* Convert a short WIM resource header to a stand-alone WIM resource
 * specification.  */
void
wim_res_hdr_to_spec(const struct wim_reshdr *reshdr, WIMStruct *wim,
                    struct wim_resource_spec *spec)
{
        spec->wim = wim;
        spec->offset_in_wim = reshdr->offset_in_wim;
        spec->size_in_wim = reshdr->size_in_wim;
        spec->uncompressed_size = reshdr->uncompressed_size;
        INIT_LIST_HEAD(&spec->stream_list);
        spec->flags = reshdr->flags;
        spec->is_pipable = wim_is_pipable(wim);
}

/* Convert a stand-alone resource specification to a WIM resource header.  */
void
wim_res_spec_to_hdr(const struct wim_resource_spec *rspec,
                    struct wim_reshdr *reshdr)
{
        reshdr->offset_in_wim     = rspec->offset_in_wim;
        reshdr->size_in_wim       = rspec->size_in_wim;
        reshdr->flags             = rspec->flags;
        reshdr->uncompressed_size = rspec->uncompressed_size;
}

/* Translates a WIM resource header from the on-disk format into an in-memory
 * format.  */
int
get_wim_reshdr(const struct wim_reshdr_disk *disk_reshdr,
               struct wim_reshdr *reshdr)
{
        reshdr->offset_in_wim = le64_to_cpu(disk_reshdr->offset_in_wim);
        reshdr->size_in_wim = (((u64)disk_reshdr->size_in_wim[0] <<  0) |
                               ((u64)disk_reshdr->size_in_wim[1] <<  8) |
                               ((u64)disk_reshdr->size_in_wim[2] << 16) |
                               ((u64)disk_reshdr->size_in_wim[3] << 24) |
                               ((u64)disk_reshdr->size_in_wim[4] << 32) |
                               ((u64)disk_reshdr->size_in_wim[5] << 40) |
                               ((u64)disk_reshdr->size_in_wim[6] << 48));
        reshdr->uncompressed_size = le64_to_cpu(disk_reshdr->uncompressed_size);
        reshdr->flags = disk_reshdr->flags;

        /* Avoid possible overflows.  */
        if (reshdr->offset_in_wim & 0xc000000000000000ULL)
                return WIMLIB_ERR_INVALID_LOOKUP_TABLE_ENTRY;

        if (reshdr->uncompressed_size & 0xc000000000000000ULL)
                return WIMLIB_ERR_INVALID_LOOKUP_TABLE_ENTRY;

        return 0;
}

/* Translates a WIM resource header from an in-memory format into the on-disk
 * format.  */
void
put_wim_reshdr(const struct wim_reshdr *reshdr,
               struct wim_reshdr_disk *disk_reshdr)
{
        disk_reshdr->size_in_wim[0] = reshdr->size_in_wim  >>  0;
        disk_reshdr->size_in_wim[1] = reshdr->size_in_wim  >>  8;
        disk_reshdr->size_in_wim[2] = reshdr->size_in_wim  >> 16;
        disk_reshdr->size_in_wim[3] = reshdr->size_in_wim  >> 24;
        disk_reshdr->size_in_wim[4] = reshdr->size_in_wim  >> 32;
        disk_reshdr->size_in_wim[5] = reshdr->size_in_wim  >> 40;
        disk_reshdr->size_in_wim[6] = reshdr->size_in_wim  >> 48;
        disk_reshdr->flags = reshdr->flags;
        disk_reshdr->offset_in_wim = cpu_to_le64(reshdr->offset_in_wim);
        disk_reshdr->uncompressed_size = cpu_to_le64(reshdr->uncompressed_size);
}