read_resource_prefix(): Remove comment about removed flag
[wimlib] / src / resource.c
index 7ae7e81..4b91be6 100644 (file)
@@ -1,83 +1,75 @@
 /*
  * resource.c
  *
- * Read uncompressed and compressed metadata and file resources.
+ * Read uncompressed and compressed metadata and file resources from a WIM file.
  */
 
 /*
- * Copyright (C) 2010 Carl Thijssen
- * Copyright (C) 2012 Eric Biggers
+ * 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 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.
+ * 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 Lesser General Public License for more
- * details.
+ * A PARTICULAR PURPOSE. See the GNU 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/.
+ * You should have received a copy of the GNU General Public License along with
+ * wimlib; if not, see http://www.gnu.org/licenses/.
  */
 
 #include "wimlib_internal.h"
+#include "dentry.h"
 #include "lookup_table.h"
-#include "io.h"
-#include "lzx.h"
-#include "xpress.h"
+#include "buffer_io.h"
 #include "sha1.h"
-#include "dentry.h"
-#include "config.h"
-#include <unistd.h>
+
+#ifdef __WIN32__
+#  include "win32.h"
+#endif
+
 #include <errno.h>
-#include <alloca.h>
+#include <stdarg.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <fcntl.h>
 
+#ifdef HAVE_ALLOCA_H
+#  include <alloca.h>
+#endif
 
-/* 
- * 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.
+/*
+ * Reads all or part of a compressed WIM resource.
  *
  * 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[])
+static int
+read_compressed_resource(int in_fd,
+                        u64 resource_compressed_size,
+                        u64 resource_uncompressed_size,
+                        u64 resource_offset,
+                        int resource_ctype,
+                        u64 len,
+                        u64 offset,
+                        consume_data_callback_t cb,
+                        void *ctx_or_buf)
 {
+       int 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);
+       int (*decompress)(const void *, unsigned, void *, unsigned);
        /* Set the appropriate decompress function. */
-       if (resource_ctype == WIM_COMPRESSION_TYPE_LZX)
-               decompress = lzx_decompress;
+       if (resource_ctype == WIMLIB_COMPRESSION_TYPE_LZX)
+               decompress = wimlib_lzx_decompress;
        else
-               decompress = xpress_decompress;
+               decompress = wimlib_xpress_decompress;
 
        /* The structure of a compressed resource consists of a table of chunk
         * offsets followed by the chunks themselves.  Each chunk consists of
@@ -88,10 +80,11 @@ static int read_compressed_resource(FILE *fp, u64 resource_compressed_size,
         * 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. 
+        * follows the chunk table and therefore must have an offset of 0.
         */
 
-       /* Calculate how many chunks the resource conists of in its entirety. */
+       /* Calculate how many chunks the resource consists 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. */
@@ -118,9 +111,22 @@ static int read_compressed_resource(FILE *fp, u64 resource_compressed_size,
        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];
+       /* Allocate the chunk table.  It will only contain offsets for the
+        * chunks that are actually needed for this read. */
+       u64 *chunk_offsets;
+       bool chunk_offsets_malloced;
+       if (num_needed_chunks < 1000) {
+               chunk_offsets = alloca(num_needed_chunks * sizeof(u64));
+               chunk_offsets_malloced = false;
+       } else {
+               chunk_offsets = malloc(num_needed_chunks * sizeof(u64));
+               if (!chunk_offsets) {
+                       ERROR("Failed to allocate chunk table "
+                             "with %"PRIu64" entries", num_needed_chunks);
+                       return WIMLIB_ERR_NOMEM;
+               }
+               chunk_offsets_malloced = true;
+       }
 
        /* Set the implicit offset of the first chunk if it is included in the
         * needed chunks.
@@ -136,7 +142,7 @@ static int read_compressed_resource(FILE *fp, u64 resource_compressed_size,
        /* 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) ? 
+       u64 chunk_entry_size = (resource_uncompressed_size >= (u64)1 << 32) ?
                                                                        8 : 4;
 
        /* Size of the full chunk table in the WIM file. */
@@ -150,26 +156,23 @@ static int read_compressed_resource(FILE *fp, u64 resource_compressed_size,
 
        /* 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) ? 
+       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 + 
+       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];
+       /* Read the raw data into the end of the chunk_offsets array to
+        * avoid allocating another array. */
+       void *chunk_tab_buf = (void*)&chunk_offsets[num_needed_chunks] - size;
 
-       if (fread(chunk_tab_buf, 1, size, fp) != size)
-               goto err;
+       if (full_pread(in_fd, chunk_tab_buf, size,
+                      file_offset_of_needed_chunk_entries) != size)
+               goto read_error;
 
        /* Now fill in chunk_offsets from the entries we have read in
         * chunk_tab_buf. */
@@ -181,28 +184,26 @@ static int read_compressed_resource(FILE *fp, u64 resource_compressed_size,
        if (chunk_entry_size == 4) {
                u32 *entries = (u32*)chunk_tab_buf;
                while (num_needed_chunk_entries--)
-                       *chunk_tab_p++ = to_le32(*entries++);
+                       *chunk_tab_p++ = le32_to_cpu(*entries++);
        } else {
                u64 *entries = (u64*)chunk_tab_buf;
                while (num_needed_chunk_entries--)
-                       *chunk_tab_p++ = to_le64(*entries++);
+                       *chunk_tab_p++ = le64_to_cpu(*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;
-       }
+       u64 cur_read_offset = resource_offset + chunk_table_size + chunk_offsets[0];
 
        /* Pointer to current position in the output buffer for uncompressed
-        * data. */
-       u8 *out_p = (u8*)contents_ret;
+        * data.  Alternatively, if using a callback function, we repeatedly
+        * fill a temporary buffer to feed data into the callback function.  */
+       u8 *out_p;
+       if (cb)
+               out_p = alloca(WIM_CHUNK_SIZE);
+       else
+               out_p = ctx_or_buf;
 
        /* 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
@@ -210,24 +211,21 @@ static int read_compressed_resource(FILE *fp, u64 resource_compressed_size,
         * 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];
-
+       void *compressed_buf = alloca(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;
+               unsigned compressed_chunk_size;
+               unsigned 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] - 
+                       compressed_chunk_size = chunk_offsets[i + 1 - start_chunk] -
                                                chunk_offsets[i - start_chunk];
                        uncompressed_chunk_size = WIM_CHUNK_SIZE;
                } else {
@@ -235,15 +233,15 @@ static int read_compressed_resource(FILE *fp, u64 resource_compressed_size,
                         * 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. 
+                        * 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 - 
+                       compressed_chunk_size = resource_compressed_size -
                                                chunk_table_size -
                                                chunk_offsets[i - start_chunk];
 
-                       uncompressed_chunk_size = resource_uncompressed_size % 
+                       uncompressed_chunk_size = resource_uncompressed_size %
                                                                WIM_CHUNK_SIZE;
 
                        /* If the remainder is 0, the last chunk actually
@@ -252,11 +250,6 @@ static int read_compressed_resource(FILE *fp, u64 resource_compressed_size,
                                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)
@@ -269,109 +262,93 @@ static int read_compressed_resource(FILE *fp, u64 resource_compressed_size,
                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);
+               unsigned partial_chunk_size = end_offset + 1 - start_offset;
+               bool is_partial_chunk = (partial_chunk_size != uncompressed_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;
-                               }
+                       /* Uncompressed chunk */
+                       if (full_pread(in_fd,
+                                      cb ? out_p + start_offset : out_p,
+                                      partial_chunk_size,
+                                      cur_read_offset + start_offset) != partial_chunk_size)
+                       {
+                               goto read_error;
                        }
-                       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;
+                       if (full_pread(in_fd,
+                                      compressed_buf,
+                                      compressed_chunk_size,
+                                      cur_read_offset) != compressed_chunk_size)
+                       {
+                               goto read_error;
+                       }
 
-                       /* For partial chunks we must buffer the uncompressed
-                        * data because we don't need all of it. */
-                       if (is_partial_chunk) {
+                       /* For partial chunks and when writing directly to a
+                        * buffer, we must buffer the uncompressed data because
+                        * we don't need all of it. */
+                       if (is_partial_chunk && !cb) {
                                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;
+                                                compressed_chunk_size,
+                                                uncompressed_buf,
+                                                uncompressed_chunk_size);
+                               if (ret) {
+                                       ret = WIMLIB_ERR_DECOMPRESSION;
+                                       goto out;
+                               }
                                memcpy(out_p, uncompressed_buf + start_offset,
-                                               partial_chunk_size);
+                                      partial_chunk_size);
                        } else {
                                ret = decompress(compressed_buf,
-                                               compressed_chunk_size,
-                                               out_p,
-                                               uncompressed_chunk_size);
-                               if (ret != 0)
-                                       return WIMLIB_ERR_DECOMPRESSION;
+                                                compressed_chunk_size,
+                                                out_p,
+                                                uncompressed_chunk_size);
+                               if (ret) {
+                                       ret = WIMLIB_ERR_DECOMPRESSION;
+                                       goto out;
+                               }
                        }
                }
-
-               /* 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");
+               if (cb) {
+                       /* Feed the data to the callback function */
+                       ret = cb(out_p + start_offset,
+                                partial_chunk_size, ctx_or_buf);
+                       if (ret)
+                               goto out;
                } else {
-                       ERROR("Failed to read %"PRIu64" bytes from "
-                             "uncompressed resource at offset %"PRIu64,
-                             len, offset);
+                       /* No callback function provided; we are writing
+                        * directly to a buffer.  Advance the pointer into this
+                        * buffer by the number of uncompressed bytes that were
+                        * written.  */
+                       out_p += partial_chunk_size;
                }
-               return WIMLIB_ERR_READ;
+               cur_read_offset += compressed_chunk_size;
        }
-       return 0;
-}
-
 
+       ret = 0;
+out:
+       if (chunk_offsets_malloced)
+               FREE(chunk_offsets);
+       return ret;
 
+read_error:
+       ERROR_WITH_ERRNO("Error reading compressed file resource");
+       ret = WIMLIB_ERR_READ;
+       goto out;
+}
 
 /* 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)
+const void *
+get_resource_entry(const void *p, struct resource_entry *entry)
 {
        u64 size;
        u8 flags;
@@ -380,15 +357,29 @@ const u8 *get_resource_entry(const u8 *p, struct resource_entry *entry)
        p = get_u8(p, &flags);
        entry->size = size;
        entry->flags = flags;
+
+       /* offset and original_size are truncated to 62 bits to avoid possible
+        * overflows, when converting to a signed 64-bit integer (off_t) or when
+        * adding size or original_size.  This is okay since no one would ever
+        * actually have a WIM bigger than 4611686018427387903 bytes... */
        p = get_u64(p, &entry->offset);
+       if (entry->offset & 0xc000000000000000ULL) {
+               WARNING("Truncating offset in resource entry");
+               entry->offset &= 0x3fffffffffffffffULL;
+       }
        p = get_u64(p, &entry->original_size);
+       if (entry->original_size & 0xc000000000000000ULL) {
+               WARNING("Truncating original_size in resource entry");
+               entry->original_size &= 0x3fffffffffffffffULL;
+       }
        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)
+void *
+put_resource_entry(void *p, const struct resource_entry *entry)
 {
        p = put_u56(p, entry->size);
        p = put_u8(p, entry->flags);
@@ -397,743 +388,344 @@ u8 *put_resource_entry(u8 *p, const struct resource_entry *entry)
        return p;
 }
 
-/*
- * Reads some data from a WIM resource.
- *
- * If %raw is true, compressed data is read literally rather than being
- * decompressed first.
- *
- * Returns zero on success, nonzero on failure.
- */
-static int __read_wim_resource(const struct lookup_table_entry *lte,
-                              u8 buf[], size_t size, u64 offset, bool raw)
+static int
+read_partial_wim_resource(const struct wim_lookup_table_entry *lte,
+                         u64 size,
+                         consume_data_callback_t cb,
+                         void *ctx_or_buf,
+                         int flags,
+                         u64 offset)
 {
-       /* We shouldn't be allowing read over-runs in any part of the library.
-        * */
-       if (raw)
-               wimlib_assert(offset + size <= lte->resource_entry.size);
-       else
-               wimlib_assert(offset + size <= lte->resource_entry.original_size);
-
-       int ctype;
+       WIMStruct *wim;
+       int in_fd;
        int ret;
-       FILE *fp;
-       switch (lte->resource_location) {
-       case RESOURCE_IN_WIM:
-               /* The resource is in a WIM file, and its WIMStruct is given by
-                * the lte->wim member.  The resource may be either compressed
-                * or uncompressed. */
-               wimlib_assert(lte->wim);
-               wimlib_assert(lte->wim->fp);
-               ctype = wim_resource_compression_type(lte);
-
-               /* XXX This check should be moved elsewhere */
-               if (ctype == WIM_COMPRESSION_TYPE_NONE &&
-                    lte->resource_entry.original_size !=
-                     lte->resource_entry.size) {
-                       ERROR("WIM resource at offset %"PRIu64", size %"PRIu64
-                             "has an original size of %"PRIu64", but is "
-                             "uncompressed",
-                             lte->resource_entry.offset,
-                             lte->resource_entry.size,
-                             lte->resource_entry.original_size);
-                       return WIMLIB_ERR_INVALID_RESOURCE_SIZE;
-               }
 
-               if (raw || ctype == WIM_COMPRESSION_TYPE_NONE)
-                       return read_uncompressed_resource(lte->wim->fp,
-                                                         lte->resource_entry.offset + offset,
-                                                         size, buf);
-               else
-                       return read_compressed_resource(lte->wim->fp,
-                                                       lte->resource_entry.size,
-                                                       lte->resource_entry.original_size,
-                                                       lte->resource_entry.offset,
-                                                       ctype, size, offset, buf);
-               break;
-       case RESOURCE_IN_STAGING_FILE:
-               /* The WIM FUSE implementation needs to handle multiple open
-                * file descriptors per lookup table entry so it does not
-                * currently work with this function. */
-               wimlib_assert(lte->staging_file_name);
-               wimlib_assert(0);
-               break;
-       case RESOURCE_IN_FILE_ON_DISK:
-               /* The resource is in some file on the external filesystem and
-                * needs to be read uncompressed */
-               wimlib_assert(lte->file_on_disk);
-               /* Use existing file pointer if available; otherwise open one
-                * temporarily */
-               if (lte->file_on_disk_fp) {
-                       fp = lte->file_on_disk_fp;
-               } else {
-                       fp = fopen(lte->file_on_disk, "rb");
-                       if (!fp) {
-                               ERROR_WITH_ERRNO("Failed to open the file "
-                                                "`%s'", lte->file_on_disk);
+       wimlib_assert(lte->resource_location == RESOURCE_IN_WIM);
+
+       wim = lte->wim;
+       in_fd = wim->in_fd;
+
+       if (lte->resource_entry.flags & WIM_RESHDR_FLAG_COMPRESSED &&
+           !(flags & WIMLIB_RESOURCE_FLAG_RAW))
+       {
+               ret = read_compressed_resource(in_fd,
+                                              lte->resource_entry.size,
+                                              lte->resource_entry.original_size,
+                                              lte->resource_entry.offset,
+                                              wimlib_get_compression_type(wim),
+                                              size,
+                                              offset,
+                                              cb,
+                                              ctx_or_buf);
+       } else {
+               offset += lte->resource_entry.offset;
+               if (cb) {
+                       /* Send data to callback function */
+                       u8 buf[min(WIM_CHUNK_SIZE, size)];
+                       while (size) {
+                               size_t bytes_to_read = min(WIM_CHUNK_SIZE, size);
+                               size_t bytes_read = full_pread(in_fd, buf,
+                                                              bytes_to_read, offset);
+                               if (bytes_read != bytes_to_read)
+                                       goto read_error;
+                               ret = cb(buf, bytes_read, ctx_or_buf);
+                               if (ret)
+                                       goto out;
+                               size -= bytes_read;
+                               offset += bytes_read;
                        }
+               } else {
+                       /* Send data directly to a buffer */
+                       if (full_pread(in_fd, ctx_or_buf, size, offset) != size)
+                               goto read_error;
                }
-               ret = read_uncompressed_resource(fp, offset, size, buf);
-               if (fp != lte->file_on_disk_fp)
-                       fclose(fp);
-               return ret;
-               break;
-       case RESOURCE_IN_ATTACHED_BUFFER:
-               /* The resource is directly attached uncompressed in an
-                * in-memory buffer. */
-               wimlib_assert(lte->attached_buffer);
-               memcpy(buf, lte->attached_buffer + offset, size);
-               return 0;
-               break;
-       default:
-               assert(0);
+               ret = 0;
+       }
+       goto out;
+read_error:
+       ERROR_WITH_ERRNO("Error reading data from WIM");
+       ret = WIMLIB_ERR_READ;
+out:
+       if (ret) {
+               if (errno == 0)
+                       errno = EIO;
        }
+       return ret;
 }
 
-/* 
- * Reads some data from the resource corresponding to a WIM lookup table entry.
- *
- * @lte:       The WIM lookup table entry for the resource.
- * @buf:       Buffer into which to write the data.
- * @size:      Number of bytes to read.
- * @offset:    Offset at which to start reading the resource.
- *
- * Returns 0 on success; nonzero on failure.
- */
-int read_wim_resource(const struct lookup_table_entry *lte, u8 buf[],
-                     size_t size, u64 offset)
-{
-       return __read_wim_resource(lte, buf, size, offset, false);
-}
 
-/* 
- * Reads all the data from the resource corresponding to a WIM lookup table
- * entry.
- *
- * @lte:       The WIM lookup table entry for the resource.
- * @buf:       Buffer into which to write the data.  It must be at least
- *             wim_resource_size(lte) bytes long.
- *
- * Returns 0 on success; nonzero on failure.
- */
-int read_full_wim_resource(const struct lookup_table_entry *lte, u8 buf[])
+int
+read_partial_wim_resource_into_buf(const struct wim_lookup_table_entry *lte,
+                                  size_t size, u64 offset, void *buf)
 {
-       return __read_wim_resource(lte, buf, wim_resource_size(lte), 0, false);
+       return read_partial_wim_resource(lte, size, NULL, buf, 0, offset);
 }
 
-struct chunk_table {
-       off_t file_offset;
-       u64 num_chunks;
-       u64 original_resource_size;
-       u64 bytes_per_chunk_entry;
-       u64 table_disk_size;
-       u64 cur_offset;
-       u64 *cur_offset_p;
-       u64 offsets[0];
-};
-
 static int
-begin_wim_resource_chunk_tab(const struct lookup_table_entry *lte,
-                            FILE *out_fp,
-                            off_t file_offset,
-                            struct chunk_table **chunk_tab_ret)
+read_wim_resource_prefix(const struct wim_lookup_table_entry *lte,
+                        u64 size,
+                        consume_data_callback_t cb,
+                        void *ctx_or_buf,
+                        int flags)
 {
-       u64 size = wim_resource_size(lte);
-       u64 num_chunks = (size + WIM_CHUNK_SIZE - 1) / WIM_CHUNK_SIZE;
-       struct chunk_table *chunk_tab = MALLOC(sizeof(struct chunk_table) +
-                                              num_chunks * sizeof(u64));
-       int ret = 0;
-
-       wimlib_assert(size != 0);
-
-       if (!chunk_tab) {
-               ERROR("Failed to allocate chunk table for %"PRIu64" byte "
-                     "resource", size);
-               ret = WIMLIB_ERR_NOMEM;
-               goto out;
-       }
-       chunk_tab->file_offset = file_offset;
-       chunk_tab->num_chunks = num_chunks;
-       chunk_tab->original_resource_size = size;
-       chunk_tab->bytes_per_chunk_entry = (size >= (1ULL << 32)) ? 8 : 4;
-       chunk_tab->table_disk_size = chunk_tab->bytes_per_chunk_entry *
-                                    (num_chunks - 1);
-       chunk_tab->cur_offset = 0;
-       chunk_tab->cur_offset_p = chunk_tab->offsets;
-
-       if (fwrite(chunk_tab, 1, chunk_tab->table_disk_size, out_fp) !=
-                  chunk_tab->table_disk_size) {
-               ERROR_WITH_ERRNO("Failed to write chunk table in compressed "
-                                "file resource");
-               ret = WIMLIB_ERR_WRITE;
-               goto out;
-       }
-
-       *chunk_tab_ret = chunk_tab;
-out:
-       return ret;
+       return read_partial_wim_resource(lte, size, cb, ctx_or_buf, flags, 0);
 }
 
-static int compress_chunk(const u8 chunk[], unsigned chunk_size,
-                         u8 compressed_chunk[],
-                         unsigned *compressed_chunk_len_ret,
-                         int ctype)
-{
-       unsigned compressed_chunk_sz;
-       int (*compress)(const void *, unsigned, void *, unsigned *);
-       switch (ctype) {
-       case WIM_COMPRESSION_TYPE_LZX:
-               compress = lzx_compress;
-               break;
-       case WIM_COMPRESSION_TYPE_XPRESS:
-               compress = xpress_compress;
-               break;
-       default:
-               wimlib_assert(0);
-               break;
-       }
-       return (*compress)(chunk, chunk_size, compressed_chunk,
-                          compressed_chunk_len_ret);
-}
 
-static int write_wim_resource_chunk(const u8 chunk[], unsigned chunk_size,
-                                   FILE *out_fp, int out_ctype,
-                                   struct chunk_table *chunk_tab)
+#ifndef __WIN32__
+static int
+read_file_on_disk_prefix(const struct wim_lookup_table_entry *lte,
+                        u64 size,
+                        consume_data_callback_t cb,
+                        void *ctx_or_buf,
+                        int _ignored_flags)
 {
-       const u8 *out_chunk;
-       unsigned out_chunk_size;
-
-       if (!chunk_tab) {
-               out_chunk = chunk;
-               out_chunk_size = chunk_size;
-       } else {
-               u8 *compressed_chunk = alloca(chunk_size);
-               int ret;
-               unsigned compressed_chunk_len;
+       const tchar *filename = lte->file_on_disk;
+       int ret;
+       int fd;
+       size_t bytes_read;
 
-               ret = compress_chunk(chunk, chunk_size, compressed_chunk,
-                                    &out_chunk_size, out_ctype);
-               if (ret == 0) {
-                       out_chunk = compressed_chunk;
-               } else {
-                       out_chunk = chunk;
-                       out_chunk_size = chunk_size;
-               }
-               *chunk_tab->cur_offset_p++ = chunk_tab->cur_offset;
-               chunk_tab->cur_offset += out_chunk_size;
+       fd = open(filename, O_RDONLY);
+       if (fd < 0) {
+               ERROR_WITH_ERRNO("Can't open \"%"TS"\"", filename);
+               return WIMLIB_ERR_OPEN;
        }
-       
-       if (fwrite(out_chunk, 1, out_chunk_size, out_fp) != out_chunk_size) {
-               ERROR_WITH_ERRNO("Failed to write WIM resource chunk");
-               return WIMLIB_ERR_WRITE;
+       if (cb) {
+               /* Send data to callback function */
+               u8 buf[min(WIM_CHUNK_SIZE, size)];
+               size_t bytes_to_read;
+               while (size) {
+                       bytes_to_read = min(WIM_CHUNK_SIZE, size);
+                       bytes_read = full_read(fd, buf, bytes_to_read);
+                       if (bytes_read != bytes_to_read)
+                               goto read_error;
+                       ret = cb(buf, bytes_read, ctx_or_buf);
+                       if (ret)
+                               goto out_close;
+                       size -= bytes_read;
+               }
+       } else {
+               /* Send data directly to a buffer */
+               bytes_read = full_read(fd, ctx_or_buf, size);
+               if (bytes_read != size)
+                       goto read_error;
        }
-       return 0;
+       ret = 0;
+       goto out_close;
+read_error:
+       ERROR_WITH_ERRNO("Error reading \"%"TS"\"", filename);
+       ret = WIMLIB_ERR_READ;
+out_close:
+       close(fd);
+       return ret;
 }
+#endif /* !__WIN32__ */
 
 static int
-finish_wim_resource_chunk_tab(struct chunk_table *chunk_tab,
-                             FILE *out_fp, u64 *compressed_size_p)
+read_buffer_prefix(const struct wim_lookup_table_entry *lte,
+                  u64 size, consume_data_callback_t cb,
+                  void *ctx_or_buf, int _ignored_flags)
 {
-       size_t bytes_written;
-       if (fseeko(out_fp, chunk_tab->file_offset, SEEK_SET) != 0) {
-               ERROR_WITH_ERRNO("Failed to seek to byte "PRIu64" of output "
-                                "WIM file", chunk_tab->file_offset);
-               return WIMLIB_ERR_WRITE;
-       }
+       const void *inbuf = lte->attached_buffer;
+       int ret;
 
-       if (chunk_tab->bytes_per_chunk_entry == 8) {
-               array_to_le64(chunk_tab->offsets, chunk_tab->num_chunks);
+       if (cb) {
+               while (size) {
+                       size_t chunk_size = min(WIM_CHUNK_SIZE, size);
+                       ret = cb(inbuf, chunk_size, ctx_or_buf);
+                       if (ret)
+                               return ret;
+                       size -= chunk_size;
+                       inbuf += chunk_size;
+               }
        } else {
-               for (u64 i = 0; i < chunk_tab->num_chunks; i++)
-                       ((u32*)chunk_tab->offsets)[i] =
-                               to_le32(chunk_tab->offsets[i]);
-       }
-       bytes_written = fwrite((u8*)chunk_tab->offsets +
-                                       chunk_tab->bytes_per_chunk_entry,
-                              1, chunk_tab->table_disk_size, out_fp);
-       if (bytes_written != chunk_tab->table_disk_size) {
-               ERROR_WITH_ERRNO("Failed to write chunk table in compressed "
-                                "file resource");
-               return WIMLIB_ERR_WRITE;
+               memcpy(ctx_or_buf, inbuf, size);
        }
-       if (fseeko(out_fp, 0, SEEK_END) != 0) {
-               ERROR_WITH_ERRNO("Failed to seek to end of output WIM file");
-               return WIMLIB_ERR_WRITE;
-       }
-       *compressed_size_p = chunk_tab->cur_offset + chunk_tab->table_disk_size;
        return 0;
 }
 
+typedef int (*read_resource_prefix_handler_t)(const struct wim_lookup_table_entry *lte,
+                                             u64 size,
+                                             consume_data_callback_t cb,
+                                             void *ctx_or_buf,
+                                             int flags);
+
 /*
- * Writes a WIM resource to a FILE * opened for writing.  The resource may be
- * written uncompressed or compressed depending on the @out_ctype parameter.
+ * Read the first @size bytes from a generic "resource", which may be located in
+ * the WIM (compressed or uncompressed), in an external file, or directly in an
+ * in-memory buffer.
+ *
+ * Feed the data either to a callback function (cb != NULL, passing it
+ * ctx_or_buf), or write it directly into a buffer (cb == NULL, ctx_or_buf
+ * specifies the buffer, which must have room for @size bytes).
  *
- * @lte:       The lookup table entry for the WIM resource.
- * @out_fp:    The FILE * to write the resource to.
- * @out_ctype:  The compression type of the resource to write.  Note: if this is
- *                     the same as the compression type of the WIM resource we
- *                     need to read, we simply copy the data (i.e. we do not
- *                     uncompress it, then compress it again).
- * @out_res_entry:  If non-NULL, a resource entry that is filled in with the 
- *                 offset, original size, compressed size, and compression flag
- *                 of the output resource.
+ * When using a callback function, it is called with chunks up to 32768 bytes in
+ * size until the resource is exhausted.
  *
- * Returns 0 on success; nonzero on failure.
+ * If the resource is located in a WIM file, @flags can be:
+ *   * WIMLIB_RESOURCE_FLAG_RAW if the raw compressed data is to be supplied
+ *     instead of the uncompressed data.
+ * Otherwise, the @flags are ignored.
  */
-static int write_wim_resource(struct lookup_table_entry *lte,
-                             FILE *out_fp, int out_ctype,
-                             struct resource_entry *out_res_entry)
+int
+read_resource_prefix(const struct wim_lookup_table_entry *lte,
+                    u64 size, consume_data_callback_t cb, void *ctx_or_buf,
+                    int flags)
 {
-       u64 bytes_remaining;
-       u64 original_size;
-       u64 old_compressed_size;
-       u64 new_compressed_size;
-       u64 offset = 0;
-       int ret = 0;
-       struct chunk_table *chunk_tab = NULL;
-       bool raw;
-       off_t file_offset;
-
-       original_size = wim_resource_size(lte);
-       old_compressed_size = wim_resource_compressed_size(lte);
-
-       file_offset = ftello(out_fp);
-       if (file_offset == -1) {
-               ERROR_WITH_ERRNO("Failed to get offset in output "
-                                "stream");
-               return WIMLIB_ERR_WRITE;
-       }
-       
-       raw = (wim_resource_compression_type(lte) == out_ctype
-              && out_ctype != WIM_COMPRESSION_TYPE_NONE);
-       if (raw)
-               bytes_remaining = old_compressed_size;
-       else
-               bytes_remaining = original_size;
+       static const read_resource_prefix_handler_t handlers[] = {
+               [RESOURCE_IN_WIM]             = read_wim_resource_prefix,
+       #ifndef __WIN32__
+               [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]              = read_win32_file_prefix,
+               [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, ctx_or_buf, flags);
+}
 
-       if (bytes_remaining == 0)
-               return 0;
+int
+read_full_resource_into_buf(const struct wim_lookup_table_entry *lte,
+                           void *buf)
+{
+       return read_resource_prefix(lte, wim_resource_size(lte), NULL, buf, 0);
+}
 
-       char buf[min(WIM_CHUNK_SIZE, bytes_remaining)];
+struct extract_ctx {
+       SHA_CTX sha_ctx;
+       consume_data_callback_t extract_chunk;
+       void *extract_chunk_arg;
+};
 
-       if (out_ctype != WIM_COMPRESSION_TYPE_NONE && !raw) {
-               ret = begin_wim_resource_chunk_tab(lte, out_fp, file_offset,
-                                                  &chunk_tab);
-               if (ret != 0)
-                       goto out;
-       }
-       if (lte->resource_location == RESOURCE_IN_FILE_ON_DISK
-            && !lte->file_on_disk_fp)
-       {
-               wimlib_assert(lte->file_on_disk);
-               lte->file_on_disk_fp = fopen(lte->file_on_disk, "rb");
-               if (!lte->file_on_disk_fp) {
-                       ERROR_WITH_ERRNO("Failed to open the file `%s' for "
-                                        "reading", lte->file_on_disk);
-                       ret = WIMLIB_ERR_OPEN;
-                       goto out;
-               }
-       }
-       SHA_CTX ctx;
-       if (!raw)
-               sha1_init(&ctx);
-
-       do {
-               u64 to_read = min(bytes_remaining, WIM_CHUNK_SIZE);
-               ret = __read_wim_resource(lte, buf, to_read, offset, raw);
-               if (ret != 0)
-                       goto out_fclose;
-               if (!raw)
-                       sha1_update(&ctx, buf, to_read);
-               ret = write_wim_resource_chunk(buf, to_read, out_fp,
-                                              out_ctype, chunk_tab);
-               if (ret != 0)
-                       goto out_fclose;
-               bytes_remaining -= to_read;
-               offset += to_read;
-       } while (bytes_remaining);
-       if (out_ctype != WIM_COMPRESSION_TYPE_NONE && !raw) {
-               ret = finish_wim_resource_chunk_tab(chunk_tab, out_fp,
-                                                   &new_compressed_size);
-               if (ret != 0)
-                       goto out_fclose;
-       } else {
-               new_compressed_size = old_compressed_size;
-       }
+static int
+extract_chunk_sha1_wrapper(const void *chunk, size_t chunk_size,
+                          void *_ctx)
+{
+       struct extract_ctx *ctx = _ctx;
 
-       if (!raw) {
-               u8 md[SHA1_HASH_SIZE];
-               sha1_final(md, &ctx);
-               if (!hashes_equal(md, lte->hash)) {
-                       ERROR("WIM resource has incorrect hash!");
-                       if (lte->resource_location == RESOURCE_IN_FILE_ON_DISK) {
-                               ERROR("We were reading it from `%s'; maybe it changed "
-                                     "while we were reading it.",
-                                     lte->file_on_disk);
-                       }
-                       ret = WIMLIB_ERR_INTEGRITY;
-                       goto out_fclose;
-               }
-       }
+       sha1_update(&ctx->sha_ctx, chunk, chunk_size);
+       return ctx->extract_chunk(chunk, chunk_size, ctx->extract_chunk_arg);
+}
 
-       if (new_compressed_size > original_size) {
-               /* Oops!  We compressed the resource to larger than the original
-                * size.  Write the resource uncompressed instead. */
-               if (fseeko(out_fp, file_offset, SEEK_SET) != 0) {
-                       ERROR_WITH_ERRNO("Failed to seek to byte "PRIu64" "
-                                        "of output WIM file", file_offset);
-                       ret = WIMLIB_ERR_WRITE;
-                       goto out_fclose;
-               }
-               ret = write_wim_resource(lte, out_fp, WIM_COMPRESSION_TYPE_NONE,
-                                        out_res_entry);
-               if (ret != 0)
-                       goto out_fclose;
-               if (fflush(out_fp) != 0) {
-                       ERROR_WITH_ERRNO("Failed to flush output WIM file");
-                       ret = WIMLIB_ERR_WRITE;
-                       goto out_fclose;
-               }
-               if (ftruncate(fileno(out_fp), file_offset + out_res_entry->size) != 0) {
-                       ERROR_WITH_ERRNO("Failed to truncate output WIM file");
-                       ret = WIMLIB_ERR_WRITE;
+/* Extracts the first @size bytes of a WIM resource to somewhere.  In the
+ * process, the SHA1 message digest of the resource is checked if the full
+ * resource is being extracted.
+ *
+ * @extract_chunk is a function that is called to extract each chunk of the
+ * resource. */
+int
+extract_wim_resource(const struct wim_lookup_table_entry *lte,
+                    u64 size,
+                    consume_data_callback_t extract_chunk,
+                    void *extract_chunk_arg)
+{
+       int ret;
+       if (size == wim_resource_size(lte)) {
+               /* Do SHA1 */
+               struct extract_ctx ctx;
+               ctx.extract_chunk = extract_chunk;
+               ctx.extract_chunk_arg = extract_chunk_arg;
+               sha1_init(&ctx.sha_ctx);
+               ret = read_resource_prefix(lte, size,
+                                          extract_chunk_sha1_wrapper,
+                                          &ctx, 0);
+               if (ret == 0) {
+                       u8 hash[SHA1_HASH_SIZE];
+                       sha1_final(hash, &ctx.sha_ctx);
+                       if (!hashes_equal(hash, lte->hash)) {
+                       #ifdef ENABLE_ERROR_MESSAGES
+                               ERROR("Invalid SHA1 message digest "
+                                     "on the following WIM resource:");
+                               print_lookup_table_entry(lte, stderr);
+                               if (lte->resource_location == RESOURCE_IN_WIM)
+                                       ERROR("The WIM file appears to be corrupt!");
+                       #endif
+                               ret = WIMLIB_ERR_INVALID_RESOURCE_HASH;
+                       }
                }
-               goto out_fclose;
-       }
-       wimlib_assert(new_compressed_size <= original_size);
-       if (out_res_entry) {
-               out_res_entry->size          = new_compressed_size;
-               out_res_entry->original_size = original_size;
-               out_res_entry->offset        = file_offset;
-               if (out_ctype == WIM_COMPRESSION_TYPE_NONE)
-                       out_res_entry->flags = 0;
-               else
-                       out_res_entry->flags = WIM_RESHDR_FLAG_COMPRESSED;
-               if (lte->resource_entry.flags & WIM_RESHDR_FLAG_METADATA)
-                       out_res_entry->flags |= WIM_RESHDR_FLAG_METADATA;
-       }
-out_fclose:
-       if (lte->resource_location == RESOURCE_IN_FILE_ON_DISK
-            && lte->file_on_disk_fp) {
-               fclose(lte->file_on_disk_fp);
-               lte->file_on_disk_fp = NULL;
+       } else {
+               /* Don't do SHA1 */
+               ret = read_resource_prefix(lte, size, extract_chunk,
+                                          extract_chunk_arg, 0);
        }
-out:
-       FREE(chunk_tab);
        return ret;
 }
 
-static int write_wim_resource_from_buffer(const u8 *buf, u64 buf_size,
-                                         u8 buf_hash[SHA1_HASH_SIZE],
-                                         FILE *out_fp, int out_ctype,
-                                         struct resource_entry *out_res_entry)
-{
-       struct lookup_table_entry lte;
-       lte.resource_entry.flags         = 0;
-       lte.resource_entry.original_size = buf_size;
-       lte.resource_entry.size          = buf_size;
-       lte.resource_entry.offset        = 0;
-       lte.resource_location            = RESOURCE_IN_ATTACHED_BUFFER;
-       lte.attached_buffer              = (u8*)buf;
-       copy_hash(lte.hash, buf_hash);
-       return write_wim_resource(&lte, out_fp, out_ctype, out_res_entry);
-}
-
-/* 
- * Extracts the first @size bytes of the resource specified by @lte to the open
- * file @fd.  Returns nonzero on error.
- */
-int extract_wim_resource_to_fd(const struct lookup_table_entry *lte, int fd,
-                              u64 size)
+static int
+extract_wim_chunk_to_fd(const void *buf, size_t len, void *_fd_p)
 {
-       u64 bytes_remaining = size;
-       char buf[min(WIM_CHUNK_SIZE, bytes_remaining)];
-       u64 offset = 0;
-       int ret = 0;
-
-       while (bytes_remaining) {
-               u64 to_read = min(bytes_remaining, WIM_CHUNK_SIZE);
-               ret = read_wim_resource(lte, buf, to_read, offset);
-               if (ret != 0)
-                       break;
-               if (full_write(fd, buf, to_read) < 0) {
-                       ERROR_WITH_ERRNO("Error extracting WIM resource");
-                       return WIMLIB_ERR_WRITE;
-               }
-               bytes_remaining -= to_read;
-               offset += to_read;
+       int fd = *(int*)_fd_p;
+       ssize_t ret = full_write(fd, buf, len);
+       if (ret < len) {
+               ERROR_WITH_ERRNO("Error writing to file descriptor");
+               return WIMLIB_ERR_WRITE;
+       } else {
+               return 0;
        }
-       return 0;
 }
 
-int extract_full_wim_resource_to_fd(const struct lookup_table_entry *lte, int fd)
+int
+extract_wim_resource_to_fd(const struct wim_lookup_table_entry *lte,
+                          int fd, u64 size)
 {
-       return extract_wim_resource_to_fd(lte, fd, wim_resource_size(lte));
+       return extract_wim_resource(lte, size, extract_wim_chunk_to_fd, &fd);
 }
 
-/* 
- * 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 *wim)
-{
-       WIMStruct *w = wim;
-       int ret;
-
-       if ((lte->resource_entry.flags & WIM_RESHDR_FLAG_METADATA) &&
-           !w->write_metadata)
-               return 0;
 
-       ret = write_wim_resource(lte, w->out_fp,
-                                wim_resource_compression_type(lte), 
-                                &lte->output_resource_entry);
-       if (ret != 0)
-               return ret;
-       lte->out_refcnt = lte->refcnt;
-       lte->part_number = w->hdr.part_number;
+static int
+sha1_chunk(const void *buf, size_t len, void *ctx)
+{
+       sha1_update(ctx, buf, len);
        return 0;
 }
 
-/* 
- * Writes a dentry's resources, including the main file resource as well as all
- * alternate data streams, to the output file. 
- *
- * @dentry:  The dentry for the file.
- * @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.
- *
- * @return zero on success, nonzero on failure. 
- */
-int write_dentry_resources(struct dentry *dentry, void *wim_p)
+/* Calculate the SHA1 message digest of a stream. */
+int
+sha1_resource(struct wim_lookup_table_entry *lte)
 {
-       WIMStruct *w = wim_p;
-       int ret = 0;
-       struct lookup_table_entry *lte;
-       int ctype = wimlib_get_compression_type(w);
-
-       if (w->write_flags & WIMLIB_WRITE_FLAG_VERBOSE) {
-               wimlib_assert(dentry->full_path_utf8);
-               printf("Writing streams for `%s'\n", dentry->full_path_utf8);
-       }
+       int ret;
+       SHA_CTX sha_ctx;
 
-       for (unsigned i = 0; i <= dentry->num_ads; i++) {
-               lte = dentry_stream_lte(dentry, i, w->lookup_table);
-               if (lte && ++lte->out_refcnt == 1) {
-                       ret = write_wim_resource(lte, w->out_fp, ctype,
-                                                &lte->output_resource_entry);
-                       if (ret != 0)
-                               break;
-               }
-       }
+       sha1_init(&sha_ctx);
+       ret = read_resource_prefix(lte, wim_resource_size(lte),
+                                  sha1_chunk, &sha_ctx, 0);
+       if (ret == 0)
+               sha1_final(lte->hash, &sha_ctx);
        return ret;
 }
 
-/* 
- * 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.
+/*
+ * Copies the file resource specified by the lookup table entry @lte from the
+ * input WIM to the output WIM that has its FILE * given by
+ * ((WIMStruct*)wim)->out_fp.
  *
- * @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.
+ * The output_resource_entry, out_refcnt, and part_number fields of @lte are
+ * updated.
  *
- * @return:    Zero on success, nonzero on failure.
+ * (This function is confusing and should be refactored somehow.)
  */
-int read_metadata_resource(FILE *fp, int wim_ctype, struct image_metadata *imd)
+int
+copy_resource(struct wim_lookup_table_entry *lte, void *wim)
 {
-       u8 *buf;
-       int ctype;
-       u32 dentry_offset;
+       WIMStruct *w = wim;
        int ret;
-       struct dentry *dentry;
-       struct wim_security_data *sd;
-       struct link_group_table *lgt;
-       const struct lookup_table_entry *metadata_lte;
-       const struct resource_entry *res_entry;
-
-       metadata_lte = imd->metadata_lte;
-       res_entry = &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. */
-
-       /* Read the metadata resource into memory.  (It may be compressed.) */
-       ret = read_full_wim_resource(metadata_lte, 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;
+       ret = write_wim_resource(lte, w->out_fd,
+                                wim_resource_compression_type(lte),
+                                &lte->output_resource_entry, 0);
+       if (ret == 0) {
+               lte->out_refcnt = lte->refcnt;
+               lte->part_number = w->hdr.part_number;
        }
-
-       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;
-
-       DEBUG("Reading 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;
-
-       DEBUG("Calculating dentry full paths");
-       /* 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;
-
-       DEBUG("Building link group table");
-       /* Build hash table that maps hard link group IDs to dentry sets */
-       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;
-
-       DEBUG("Freeing duplicate ADS entries in link group table");
-       ret = link_groups_free_duplicate_data(lgt);
-       if (ret != 0)
-               goto out_free_lgt;
-       DEBUG("Done reading image metadata");
-
-       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);
-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;
-       off_t metadata_offset;
-       u64 metadata_original_size;
-       u64 metadata_compressed_size;
-       int metadata_ctype;
-       u8  hash[SHA1_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);
-
-
-       lte = wim_metadata_lookup_table_entry(w);
-
-       ret = write_wim_resource_from_buffer(buf, metadata_original_size,
-                                            hash, out, metadata_ctype,
-                                            &lte->output_resource_entry);
-
-       lookup_table_unlink(w->lookup_table, lte);
-       copy_hash(lte->hash, hash);
-       lookup_table_insert(w->lookup_table, lte);
-       lte->out_refcnt++;
-       lte->output_resource_entry.flags |= WIM_RESHDR_FLAG_METADATA;
-       FREE(buf);
-       if (ret != 0)
-               return ret;
-
-       return 0;
-}