]> wimlib.net Git - wimlib/blobdiff - src/resource.c
NTFS capture updates
[wimlib] / src / resource.c
index 731bd1c0c3ebb258cbd8462b33ae1aaf5456ab79..73cea71c2de7b264671e5c4629650176d6478814 100644 (file)
 #include "config.h"
 #include <unistd.h>
 #include <errno.h>
+#include <alloca.h>
 
+#ifdef WITH_NTFS_3G
+#include <ntfs-3g/attrib.h>
+#include <ntfs-3g/inode.h>
+#include <ntfs-3g/dir.h>
+#endif
 
 /* 
  * Reads all or part of a compressed resource into an in-memory buffer.
@@ -342,8 +348,8 @@ err:
 /* 
  * Reads uncompressed data from an open file stream.
  */
-int read_uncompressed_resource(FILE *fp, u64 offset, u64 len, 
-                                       u8 contents_ret[])
+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 "
@@ -365,144 +371,7 @@ int read_uncompressed_resource(FILE *fp, u64 offset, u64 len,
 }
 
 
-/* 
- * Reads a WIM resource.
- *
- * @fp:                The FILE* for the WIM file.
- * @resource_size:             The compressed size of the resource.
- * @resource_original_size:    The uncompressed size of the resource.
- * @resource_offset:           The offset of the resource in the stream @fp.
- * @resource_ctype:            The compression type of the resource.
- *                             (WIM_COMPRESSION_TYPE_*)
- * @len:               How many bytes of the resource should be read.
- * @offset:            The offset within the resource at which the read
- *                             will occur.
- *
- *                     To read the whole file resource, specify offset =
- *                     0 and len = resource_original_size, or call
- *                     read_full_resource().
- *
- * @contents_ret:      An array, that must have length at least @len,
- *                             into which the uncompressed contents of
- *                             the file resource starting at @offset and 
- *                             continuing for @len bytes will be written.
- *
- * @return:            Zero on success, nonzero on failure. Failure may be due to
- *                     being unable to read the data from the WIM file at the
- *                     specified length and offset, or it may be due to the
- *                     compressed data (if the data is compressed) being
- *                     invalid.
- */
-int read_resource(FILE *fp, u64 resource_size, u64 resource_original_size,
-                 u64 resource_offset, int resource_ctype, u64 len, 
-                 u64 offset, void *contents_ret)
-{
-       if (resource_ctype == WIM_COMPRESSION_TYPE_NONE) {
-               if (resource_size != resource_original_size) {
-                       ERROR("Resource with original size %"PRIu64" bytes is "
-                             "marked as uncompressed, but its actual size is "
-                             "%"PRIu64" bytes", 
-                             resource_original_size, resource_size);
-                       return WIMLIB_ERR_INVALID_RESOURCE_SIZE;
-               }
-               return read_uncompressed_resource(fp, 
-                               resource_offset + offset, 
-                               len, contents_ret);
-       } else {
-               return read_compressed_resource(fp, resource_size,
-                               resource_original_size, resource_offset,
-                               resource_ctype, len, offset, contents_ret);
-       }
-}
-
-
-/* 
- * Extracts the first @size bytes file resource specified by @entry to the open
- * file @fd.  Returns nonzero on error.
- *
- * XXX
- * This function is somewhat redundant with uncompress_resource(). The
- * main difference is that this function writes to a file descriptor using
- * low-level calls to write() rather than to a FILE* with fwrite(); also this
- * function allows only up to @size bytes to be extracted.
- */
-int extract_resource_to_fd(WIMStruct *w, const struct resource_entry *entry, 
-                          int fd, u64 size)
-{
-       u64 num_chunks;
-       u64 n;
-       u8 buf[min(size, WIM_CHUNK_SIZE)];
-       int res_ctype;
-       u64 offset;
-       u64 i;
-       int ret;
-
-       errno = 0;
-
-       num_chunks = (size + WIM_CHUNK_SIZE - 1) / WIM_CHUNK_SIZE;
-       n = WIM_CHUNK_SIZE;
-       res_ctype = wim_resource_compression_type(w, entry);
-       offset = 0;
-       for (i = 0; i < num_chunks; i++) {
-               if (i == num_chunks - 1) {
-                       n = size % WIM_CHUNK_SIZE;
-                       if (n == 0) {
-                               n = WIM_CHUNK_SIZE;
-                       }
-               }
-
-               ret = read_resource(w->fp, entry->size, entry->original_size,
-                                   entry->offset, res_ctype, n, offset, buf);
-               if (ret != 0)
-                       return ret;
-
-               if (full_write(fd, buf, n) != n)
-                       return WIMLIB_ERR_WRITE;
-               offset += n;
-       }
-       return ret;
-}
-
-/* 
- * Copies the file resource specified by the lookup table entry @lte from the
- * input WIM, pointed to by the fp field of the WIMStruct, to the output WIM,
- * pointed to by the out_fp field of the WIMStruct.
- *
- * The output_resource_entry, out_refcnt, and part_number fields of @lte are
- * updated.
- *
- * Metadata resources are not copied (they are handled elsewhere for joining and
- * splitting).
- */
-int copy_resource(struct lookup_table_entry *lte, void *w)
-{
-       if ((lte->resource_entry.flags & WIM_RESHDR_FLAG_METADATA) &&
-           !((WIMStruct*)w)->write_metadata) {
-               return 0;
-       }
 
-       FILE *in_fp = ((WIMStruct*)w)->fp;
-       FILE *out_fp = ((WIMStruct*)w)->out_fp;
-       int ret;
-       u64 size = lte->resource_entry.size;
-       u64 offset = lte->resource_entry.offset;
-       off_t new_offset = ftello(out_fp);
-
-       if (new_offset == -1)
-               return WIMLIB_ERR_WRITE;
-
-       ret = copy_between_files(in_fp, offset, out_fp, size);
-       if (ret != 0)
-               return ret;
-
-       memcpy(&lte->output_resource_entry, &lte->resource_entry, 
-                       sizeof(struct resource_entry));
-
-       lte->output_resource_entry.offset = new_offset;
-       lte->out_refcnt = lte->refcnt;
-       lte->part_number = ((WIMStruct*)w)->hdr.part_number;
-       return 0;
-}
 
 /* Reads the contents of a struct resource_entry, as represented in the on-disk
  * format, from the memory pointed to by @p, and fills in the fields of @entry.
@@ -533,369 +402,677 @@ u8 *put_resource_entry(u8 *p, const struct resource_entry *entry)
        return p;
 }
 
-/* Given the compression type for the WIM file as a whole as the flags field of
- * a resource entry, returns the compression type for that resource entry. */
-int resource_compression_type(int wim_ctype, int reshdr_flags)
-{
-       if (wim_ctype != WIM_COMPRESSION_TYPE_NONE &&
-            (reshdr_flags & WIM_RESHDR_FLAG_COMPRESSED))
-               return wim_ctype;
-       else
-               return WIM_COMPRESSION_TYPE_NONE;
-}
-
-
-
 /*
- * Copies bytes between two file streams.
+ * Reads some data from the resource corresponding to a WIM lookup table entry.
  *
- * Copies @len bytes from @in_fp to @out_fp, at the current position in @out_fp,
- * and at an offset of @in_offset in @in_fp.
+ * @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.
+ * @raw:       If %true, compressed data is read literally rather than being
+ *                     decompressed first.
+ *
+ * Returns zero on success, nonzero on failure.
  */
-int copy_between_files(FILE *in_fp, off_t in_offset, FILE *out_fp, size_t len)
+int read_wim_resource(const struct lookup_table_entry *lte, u8 buf[],
+                     size_t size, u64 offset, bool raw)
 {
-       u8 buf[BUFFER_SIZE];
-       size_t n;
+       /* 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);
 
-       if (fseeko(in_fp, in_offset, SEEK_SET) != 0) {
-               ERROR_WITH_ERRNO("Failed to seek to byte %"PRIu64" of "
-                                "input file", in_offset);
-               return WIMLIB_ERR_READ;
-       }
-       /* To reduce memory usage and improve speed, read and write BUFFER_SIZE
-        * bytes at a time. */
-       while (len != 0) {
-               n = min(len, BUFFER_SIZE);
-               if (fread(buf, 1, n, in_fp) != n) {
-                       if (feof(in_fp)) {
-                               ERROR("Unexpected EOF when copying data "
-                                     "between files");
-                       } else {
-                               ERROR_WITH_ERRNO("Error copying data between "
-                                                "files");
+       int ctype;
+       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);
+
+               wimlib_assert(ctype != WIM_COMPRESSION_TYPE_NONE ||
+                             (lte->resource_entry.original_size ==
+                              lte->resource_entry.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:
+       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);
+               wimlib_assert(&lte->file_on_disk == &lte->staging_file_name);
+               /* 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);
                        }
-                       return WIMLIB_ERR_READ;
                }
-
-               if (fwrite(buf, 1, n, out_fp) != n) {
-                       ERROR_WITH_ERRNO("Error copying data between files");
-                       return WIMLIB_ERR_WRITE;
+               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;
+#ifdef WITH_NTFS_3G
+       case RESOURCE_IN_NTFS_VOLUME:
+               if (lte->attr) {
+                       if (ntfs_attr_pread(lte->attr, offset, size, buf) == size) {
+                               return 0;
+                       } else {
+                               ERROR_WITH_ERRNO("Error reading NTFS attribute "
+                                                "at `%s'",
+                                                lte->ntfs_loc->path_utf8);
+                               return WIMLIB_ERR_NTFS_3G;
+                       }
+               } else {
+                       wimlib_assert(0);
                }
-               len -= n;
+               break;
+#endif
+       default:
+               assert(0);
        }
-       return 0;
 }
 
-
 /* 
- * Uncompresses a WIM file resource and writes it uncompressed to a file stream.
+ * Reads all the data from the resource corresponding to a WIM lookup table
+ * entry.
  *
- * @in_fp:          The file stream that contains the file resource.
- * @size:           The size of the resource in the input file.
- * @original_size:  The original (uncompressed) size of the resource. 
- * @offset:        The offset of the start of the resource in @in.
- * @input_ctype:    The compression type of the resource in @in.
- * @out_fp:        The file stream to write the file resource to.
+ * @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.
  */
-static int uncompress_resource(FILE *in_fp, u64 size, u64 original_size,
-                              off_t offset, int input_ctype, FILE *out_fp)
+int read_full_wim_resource(const struct lookup_table_entry *lte, u8 buf[])
 {
-       int ret;
-       u8 buf[WIM_CHUNK_SIZE];
-       /* Determine how many compressed chunks the file is divided into. */
-       u64 num_chunks;
-       u64 i;
-       u64 uncompressed_offset;
-       u64 uncompressed_chunk_size;
-       
-       num_chunks = (original_size + WIM_CHUNK_SIZE - 1) / WIM_CHUNK_SIZE;
+       return read_wim_resource(lte, buf, wim_resource_size(lte), 0, false);
+}
 
-       for (i = 0; i < num_chunks; i++) {
+/* Chunk table that's located at the beginning of each compressed resource in
+ * the WIM.  (This is not the on-disk format; the on-disk format just has an
+ * array of offsets.) */
+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];
+};
 
-               uncompressed_offset = i * WIM_CHUNK_SIZE;
-               uncompressed_chunk_size = min(WIM_CHUNK_SIZE, original_size -
-                                             uncompressed_offset);
+/* 
+ * Allocates and initializes a chunk table, and reserves space for it in the
+ * output file.
+ */
+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)
+{
+       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;
 
-               ret = read_resource(in_fp, size, original_size, offset,
-                                   input_ctype, uncompressed_chunk_size, 
-                                   uncompressed_offset, buf);
-               if (ret != 0)
-                       return ret;
+       wimlib_assert(size != 0);
 
-               if (fwrite(buf, 1, uncompressed_chunk_size, out_fp) != 
-                     uncompressed_chunk_size) 
-               {
-                       ERROR_WITH_ERRNO("Failed to write file resource");
-                       return WIMLIB_ERR_WRITE;
-               }
+       if (!chunk_tab) {
+               ERROR("Failed to allocate chunk table for %"PRIu64" byte "
+                     "resource", size);
+               ret = WIMLIB_ERR_NOMEM;
+               goto out;
        }
-       return 0;
+       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;
 }
 
 /* 
- * Transfers a file resource between two files, writing it compressed.  The file
- * resource in the input file may be either compressed or uncompressed.
- * Alternatively, the input resource may be in-memory, but it must be
- * uncompressed.
+ * Compresses a chunk of a WIM resource.
+ *
+ * @chunk:             Uncompressed data of the chunk.
+ * @chunk_size:                Size of the uncompressed chunk in bytes.
+ * @compressed_chunk:  Pointer to output buffer of size at least
+ *                             (@chunk_size - 1) bytes.
+ * @compressed_chunk_len_ret:  Pointer to an unsigned int into which the size
+ *                                     of the compressed chunk will be
+ *                                     returned.
+ * @ctype:     Type of compression to use.  Must be WIM_COMPRESSION_TYPE_LZX
+ *             or WIM_COMPRESSION_TYPE_XPRESS.
  *
- * @in_fp:                 The file stream that contains the file resource.  Ignored
- *                     if uncompressed_resource != NULL.
- * @uncompressed_resource:     If this pointer is not NULL, it points to an
- *                                     array of @original_size bytes that are
- *                                     the uncompressed input resource.
- * @size:           The size of the resource in the input file.
- * @original_size:  The original (uncompressed) size of the resource. 
- * @offset:        The offset of the start of the resource in @in.  Ignored
- *                     if uncompressed_resource != NULL.
- * @input_ctype:    The compression type of the resource in @in.  Ignored if
- *                     uncompressed_resource != NULL.
- * @out_fp:        The file stream to write the file resource to.
- * @output_type:    The compression type to use when writing the resource to
- *                     @out.
- * @new_size_ret:   A location into which the new compressed size of the file
- *                     resource in returned.
+ * Returns zero if compressed succeeded, and nonzero if the chunk could not be
+ * compressed to any smaller than @chunk_size.  This function cannot fail for
+ * any other reasons.
  */
-static int recompress_resource(FILE *in_fp, const u8 *uncompressed_resource, 
-                              u64 size, u64 original_size,
-                              off_t offset, int input_ctype, FILE *out_fp,
-                              int output_ctype, u64 *new_size_ret)
+static int compress_chunk(const u8 chunk[], unsigned chunk_size,
+                         u8 compressed_chunk[],
+                         unsigned *compressed_chunk_len_ret,
+                         int ctype)
 {
-       int ret;
-       int (*compress)(const void *, uint, void *, uint *);
-       if (output_ctype == WIM_COMPRESSION_TYPE_LZX)
+       unsigned compressed_chunk_sz;
+       int (*compress)(const void *, unsigned, void *, unsigned *);
+       switch (ctype) {
+       case WIM_COMPRESSION_TYPE_LZX:
                compress = lzx_compress;
-       else
+               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);
+}
 
-       u8 uncompressed_buf[WIM_CHUNK_SIZE];
-       u8 compressed_buf[WIM_CHUNK_SIZE - 1];
-
-       /* Determine how many compressed chunks the file needs to be divided
-        * into. */
-       u64 num_chunks = (original_size + WIM_CHUNK_SIZE - 1) / WIM_CHUNK_SIZE;
-
-       u64 num_chunk_entries = num_chunks - 1;
+/*
+ * Writes a chunk of a WIM resource to an output file.
+ *
+ * @chunk:       Uncompressed data of the chunk.
+ * @chunk_size:          Size of the chunk (<= WIM_CHUNK_SIZE)
+ * @out_fp:      FILE * to write tho chunk to.
+ * @out_ctype:   Compression type to use when writing the chunk (ignored if no 
+ *                     chunk table provided)
+ * @chunk_tab:   Pointer to chunk table being created.  It is updated with the
+ *                     offset of the chunk we write.
+ *
+ * Returns 0 on success; nonzero on failure.
+ */
+static int write_wim_resource_chunk(const u8 chunk[], unsigned chunk_size,
+                                   FILE *out_fp, int out_ctype,
+                                   struct chunk_table *chunk_tab)
+{
+       const u8 *out_chunk;
+       unsigned out_chunk_size;
 
-       /* Size of the chunk entries--- 8 bytes for files over 4GB, otherwise 4
-        * bytes */
-       uint chunk_entry_size = (original_size >= (u64)1 << 32) ? 8 : 4;
+       wimlib_assert(chunk_size <= WIM_CHUNK_SIZE);
 
-       /* Array in which to construct the chunk offset table. */
-       u64 chunk_offsets[num_chunk_entries];
+       if (!chunk_tab) {
+               out_chunk = chunk;
+               out_chunk_size = chunk_size;
+       } else {
+               u8 *compressed_chunk = alloca(chunk_size);
+               int ret;
+               unsigned compressed_chunk_len;
 
-       /* Offset of the start of the chunk table in the output file. */
-       off_t chunk_tab_offset = ftello(out_fp);
+               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;
+       }
+       
+       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;
+       }
+       return 0;
+}
 
-       if (chunk_tab_offset == -1) {
-               ERROR_WITH_ERRNO("Failed to get offset of output file");
+/* 
+ * Finishes a WIM chunk tale and writes it to the output file at the correct
+ * offset.
+ *
+ * The final size of the full compressed resource is returned in the
+ * @compressed_size_p.
+ */
+static int
+finish_wim_resource_chunk_tab(struct chunk_table *chunk_tab,
+                             FILE *out_fp, u64 *compressed_size_p)
+{
+       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;
        }
 
-       /* Total size of the chunk table (as written to the file) */
-       u64 chunk_tab_size = chunk_entry_size * num_chunk_entries;
+       if (chunk_tab->bytes_per_chunk_entry == 8) {
+               array_to_le64(chunk_tab->offsets, chunk_tab->num_chunks);
+       } 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;
+       }
+       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;
+}
 
-       /* Reserve space for the chunk table. */
-       if (fwrite(chunk_offsets, 1, chunk_tab_size, out_fp) !=
-             chunk_tab_size)
-       {
-               ERROR_WITH_ERRNO("Failed to write chunk offset table");
+/*
+ * Writes a WIM resource to a FILE * opened for writing.  The resource may be
+ * written uncompressed or compressed depending on the @out_ctype parameter.
+ *
+ * If by chance the resource compresses to more than the original size (this may
+ * happen with random data or files than are pre-compressed), the resource is
+ * instead written uncompressed (and this is reflected in the @out_res_entry by
+ * removing the WIM_RESHDR_FLAG_COMPRESSED flag).
+ *
+ * @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.
+ *
+ * Returns 0 on success; nonzero on failure.
+ */
+static int write_wim_resource(struct lookup_table_entry *lte,
+                             FILE *out_fp, int out_ctype,
+                             struct resource_entry *out_res_entry)
+{
+       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;
+#ifdef WITH_NTFS_3G
+       ntfs_inode *ni;
+#endif
+
+       /* Original size of the resource */
+       original_size = wim_resource_size(lte);
+
+       /* Compressed size of the resource (as it exists now) */
+       old_compressed_size = wim_resource_compressed_size(lte);
+
+       /* Current offset in output file */
+       file_offset = ftello(out_fp);
+       if (file_offset == -1) {
+               ERROR_WITH_ERRNO("Failed to get offset in output "
+                                "stream");
                return WIMLIB_ERR_WRITE;
        }
+       
+       /* Are the compression types the same?  If so, do a raw copy (copy
+        * without decompressing and recompressing the data). */
+       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;
 
-       /* Read each chunk of the file, compress it, write it to the output
-        * file, and update th chunk offset table. */
-       u64 cur_chunk_offset = 0;
-       for (u64 i = 0; i < num_chunks; i++) {
+       /* Empty resource; nothing needs to be done, so just return success. */
+       if (bytes_remaining == 0)
+               return 0;
 
-               u64 uncompressed_offset = i * WIM_CHUNK_SIZE;
-               u64 uncompressed_chunk_size = min(WIM_CHUNK_SIZE, 
-                                       original_size - uncompressed_offset);
+       /* Buffer for reading chunks for the resource */
+       char buf[min(WIM_CHUNK_SIZE, bytes_remaining)];
 
-               const u8 *uncompressed_p;
-               if (uncompressed_resource != NULL) {
-                       uncompressed_p = uncompressed_resource + 
-                                        uncompressed_offset;
+       /* If we are writing a compressed resource and not doing a raw copy, we
+        * need to initialize the chunk table */
+       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;
+       }
 
-               } else {
-                       /* Read chunk i of the file into uncompressed_buf. */
-                       ret = read_resource(in_fp, size, original_size, offset,
-                                           input_ctype,
-                                           uncompressed_chunk_size, 
-                                           uncompressed_offset, 
-                                           uncompressed_buf);
-                       if (ret != 0)
-                               return ret;
-                       uncompressed_p = uncompressed_buf;
+       /* If the WIM resource is in an external file, open a FILE * to it so we
+        * don't have to open a temporary one in read_wim_resource() for each
+        * chunk. */
+       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;
                }
-
-               if (i != 0)
-                       chunk_offsets[i - 1] = cur_chunk_offset;
-
-               uint compressed_len;
-
-               ret = compress(uncompressed_p, uncompressed_chunk_size, 
-                              compressed_buf, &compressed_len);
-
-               /* if compress() returned nonzero, the compressed chunk would
-                * have been at least as large as the uncompressed chunk.  In
-                * this situation, the WIM format requires that the uncompressed
-                * chunk be written instead. */
-               const u8 *buf_to_write;
-               uint len_to_write;
-               if (ret == 0) {
-                       buf_to_write = compressed_buf;
-                       len_to_write = compressed_len;
-               } else {
-                       buf_to_write = uncompressed_p;
-                       len_to_write = uncompressed_chunk_size;
+       }
+#ifdef WITH_NTFS_3G
+       else if (lte->resource_location == RESOURCE_IN_NTFS_VOLUME
+                  && !lte->attr)
+       {
+               struct ntfs_location *loc = lte->ntfs_loc;
+               wimlib_assert(loc);
+               ni = ntfs_pathname_to_inode(*loc->ntfs_vol_p, NULL, loc->path_utf8);
+               if (!ni) {
+                       ERROR_WITH_ERRNO("Failed to open inode `%s' in NTFS "
+                                        "volume", loc->path_utf8);
                }
-
-               if (fwrite(buf_to_write, 1, len_to_write, out_fp) !=
-                     len_to_write)
-               {
-                       ERROR_WITH_ERRNO("Failed to write compressed "
-                                        "file resource");
-                       return WIMLIB_ERR_WRITE;
+               lte->attr = ntfs_attr_open(ni,
+                                          loc->is_reparse_point ? AT_REPARSE_POINT : AT_DATA,
+                                          (ntfschar*)loc->stream_name_utf16,
+                                          loc->stream_name_utf16_num_chars);
+               if (!lte->attr) {
+                       ntfs_inode_close(ni);
+                       ERROR_WITH_ERRNO("Failed to open attribute of `%s' in "
+                                        "NTFS volume", loc->path_utf8);
                }
-               cur_chunk_offset += len_to_write;
+       }
+#endif
+
+       /* If we aren't doing a raw copy, we will compute the SHA1 message
+        * digest of the resource as we read it, and verify it's the same as the
+        * hash given in the lookup table entry once we've finished reading the
+        * resource. */
+       SHA_CTX ctx;
+       if (!raw)
+               sha1_init(&ctx);
+
+       /* While there are still bytes remaining in the WIM resource, read a
+        * chunk of the resource, update SHA1, then write that chunk using the
+        * desired compression type. */
+       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 writing a compressed resource and not doing a raw copy, write the
+        * chunk table, and finish_wim_resource_chunk_tab() will provide the
+        * compressed size of the resource we wrote.  Otherwise, the compressed
+        * size of the written resource is the same as the compressed size of
+        * the existing resource. */
+       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;
        }
 
-       /* The chunk offset after the last chunk, plus the size of the chunk
-        * table, gives the total compressed size of the resource. */
-       *new_size_ret = cur_chunk_offset + chunk_tab_size;
-
-       /* Now that all entries of the chunk table are determined, rewind the
-        * stream to where the chunk table was, and write it back out. */
-
-       if (fseeko(out_fp, chunk_tab_offset, SEEK_SET) != 0) {
-               ERROR_WITH_ERRNO("Failed to seek to beginning of chunk table");
-               return WIMLIB_ERR_READ;
+       /* Verify SHA1 message digest of the resource, unless we are doing a raw
+        * write (in which case we never even saw the uncompressed data).  Or,
+        * if the hash we had before is all 0's, just re-set it to be the new
+        * hash. */
+       if (!raw) {
+               u8 md[SHA1_HASH_SIZE];
+               sha1_final(md, &ctx);
+               if (is_zero_hash(lte->hash)) {
+                       copy_hash(lte->hash, md);
+               } else 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_INVALID_RESOURCE_HASH;
+                       goto out_fclose;
+               }
        }
 
-       if (chunk_entry_size == 8) {
-               array_to_le64(chunk_offsets, num_chunk_entries);
-       } else {
-               for (u64 i = 0; i < num_chunk_entries; i++)
-                       ((u32*)chunk_offsets)[i] = to_le32(chunk_offsets[i]);
+       if (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;
+               }
+               goto out_fclose;
        }
-       if (fwrite(chunk_offsets, 1, chunk_tab_size, out_fp) != chunk_tab_size)
-       {
-               ERROR_WITH_ERRNO("Failed to write chunk table");
-               return WIMLIB_ERR_WRITE;
+       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;
+               out_res_entry->flags         = lte->resource_entry.flags
+                                               & ~WIM_RESHDR_FLAG_COMPRESSED;
+               if (out_ctype != WIM_COMPRESSION_TYPE_NONE)
+                       out_res_entry->flags |= WIM_RESHDR_FLAG_COMPRESSED;
        }
-
-       if (fseeko(out_fp, 0, SEEK_END) != 0) {
-               ERROR_WITH_ERRNO("Failed to seek to end of output file");
-               return WIMLIB_ERR_WRITE;
+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;
        }
+#ifdef WITH_NTFS_3G
+       else if (lte->resource_location == RESOURCE_IN_NTFS_VOLUME
+                && lte->attr) {
+               ntfs_attr_close(lte->attr);
+               ntfs_inode_close(ni);
+       }
+#endif
+out:
+       FREE(chunk_tab);
+       return ret;
+}
 
+/* Like write_wim_resource(), but the resource is specified by a buffer of
+ * uncompressed data rather a lookup table entry; also writes the SHA1 hash of
+ * the buffer to @hash.  */
+static int write_wim_resource_from_buffer(const u8 *buf, u64 buf_size,
+                                         FILE *out_fp, int out_ctype,
+                                         struct resource_entry *out_res_entry,
+                                         u8 hash[SHA1_HASH_SIZE])
+{
+       /* Set up a temporary lookup table entry that we provide to
+        * write_wim_resource(). */
+       struct lookup_table_entry lte;
+       int ret;
+       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;
+
+       zero_hash(lte.hash);
+       ret = write_wim_resource(&lte, out_fp, out_ctype, out_res_entry);
+       if (ret != 0)
+               return ret;
+       copy_hash(hash, lte.hash);
        return 0;
 }
 
-int write_resource_from_memory(const u8 resource[], int out_ctype,
-                              u64 resource_original_size, FILE *out_fp,
-                              u64 *resource_size_ret)
+/* 
+ * Extracts the first @size bytes of the WIM resource specified by @lte to the
+ * open file descriptor @fd.
+ * 
+ * Returns 0 on success; nonzero on failure.
+ */
+int extract_wim_resource_to_fd(const struct lookup_table_entry *lte, int fd,
+                              u64 size)
 {
-       if (out_ctype == WIM_COMPRESSION_TYPE_NONE) {
-               if (fwrite(resource, 1, resource_original_size, out_fp) != 
-                     resource_original_size)
-               {
-                       ERROR_WITH_ERRNO("Failed to write resource of length "
-                                        "%"PRIu64, resource_original_size);
+       u64 bytes_remaining = size;
+       char buf[min(WIM_CHUNK_SIZE, bytes_remaining)];
+       u64 offset = 0;
+       int ret = 0;
+       u8 hash[SHA1_HASH_SIZE];
+
+       SHA_CTX ctx;
+       sha1_init(&ctx);
+
+       while (bytes_remaining) {
+               u64 to_read = min(bytes_remaining, WIM_CHUNK_SIZE);
+               ret = read_wim_resource(lte, buf, to_read, offset, false);
+               if (ret != 0)
+                       break;
+               sha1_update(&ctx, buf, to_read);
+               if (full_write(fd, buf, to_read) < 0) {
+                       ERROR_WITH_ERRNO("Error extracting WIM resource");
                        return WIMLIB_ERR_WRITE;
                }
-               *resource_size_ret = resource_original_size;
-               return 0;
-       } else {
-               return recompress_resource(NULL, resource,
-                                          resource_original_size,
-                                          resource_original_size, 0, 0, out_fp,
-                                          out_ctype, resource_size_ret);
+               bytes_remaining -= to_read;
+               offset += to_read;
+       }
+       sha1_final(hash, &ctx);
+       if (!hashes_equal(hash, lte->hash)) {
+               ERROR("Invalid checksum on a WIM resource "
+                     "(detected when extracting to external file)");
+               ERROR("The following WIM resource is invalid:");
+               print_lookup_table_entry(lte);
+               return WIMLIB_ERR_INVALID_RESOURCE_HASH;
        }
+       return 0;
 }
 
+/* 
+ * Extracts the WIM resource specified by @lte to the open file descriptor @fd.
+ * 
+ * Returns 0 on success; nonzero on failure.
+ */
+int extract_full_wim_resource_to_fd(const struct lookup_table_entry *lte, int fd)
+{
+       return extract_wim_resource_to_fd(lte, fd, wim_resource_size(lte));
+}
 
 /* 
- * Transfers a file resource from a FILE* opened for reading to a FILE* opened
- * for writing, possibly changing the compression type. 
+ * 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.
  *
- * @in_fp:             The FILE* that contains the file resource.
- * @size:              The (compressed) size of the file resource.
- * @original_size:     The uncompressed size of the file resource.
- * @offset:            The offset of the file resource in the input file.
- * @input_ctype:       The compression type of the file resource in the input
- *                             file.
- * @out_fp:            The FILE* for the output file.  The file resource is 
- *                             written at the current position of @out.
- * @output_ctype:      The compression type to which the file resource will be
- *                             converted.
- * @output_res_entry:  A pointer to a resource entry that, upon successful
- *                             return of this function,  will have the size,
- *                             original size, offset, and flags fields filled
- *                             in for the file resource written to the output
- *                             file.
+ * 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).
  */
-static int transfer_file_resource(FILE *in_fp, u64 size, u64 original_size,
-                                 off_t offset, int input_ctype, FILE *out_fp,
-                                 int output_ctype,
-                                 struct resource_entry *output_res_entry)
+int copy_resource(struct lookup_table_entry *lte, void *wim)
 {
+       WIMStruct *w = wim;
        int ret;
 
-       /* Handle zero-length files */
-       if (original_size == 0) {
-               memset(output_res_entry, 0, sizeof(*output_res_entry));
+       if ((lte->resource_entry.flags & WIM_RESHDR_FLAG_METADATA) &&
+           !w->write_metadata)
                return 0;
-       }
 
-       /* Get current offset in the output file. */
-       off_t out_offset = ftello(out_fp);
-       if (out_offset == -1) {
-               ERROR_WITH_ERRNO("Failed to get output position");
-               return WIMLIB_ERR_WRITE;
-       }
-       output_res_entry->offset = (u64)out_offset;
+       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;
+       return 0;
+}
 
-       if (output_ctype == input_ctype) {
-               /* The same compression types; simply copy the resource. */
+/* 
+ * 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 containing @dentry.
+ *
+ * @return zero on success, nonzero on failure. 
+ */
+int write_dentry_resources(struct dentry *dentry, void *wim_p)
+{
+       WIMStruct *w = wim_p;
+       int ret = 0;
+       struct lookup_table_entry *lte;
+       int ctype = wimlib_get_compression_type(w);
 
-               ret = copy_between_files(in_fp, offset, out_fp, size);
-               if (ret != 0)
-                       return ret;
-               output_res_entry->size = size;
-       } else {
-               /* Different compression types. */
+       if (w->write_flags & WIMLIB_WRITE_FLAG_VERBOSE) {
+               wimlib_assert(dentry->full_path_utf8);
+               printf("Writing streams for `%s'\n", dentry->full_path_utf8);
+       }
 
-               if (output_ctype == WIM_COMPRESSION_TYPE_NONE) {
-                       /* Uncompress a compressed file resource */
-                       ret = uncompress_resource(in_fp, size,
-                                                 original_size, offset, 
-                                                 input_ctype, out_fp);
+       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)
-                               return ret;
-                       output_res_entry->size = original_size;
-               } else {
-                       u64 new_size;
-                       /* Compress an uncompressed file resource, or compress a
-                        * compressed file resource using a different
-                        * compression type */
-                       ret = recompress_resource(in_fp, NULL, size,
-                                                 original_size,
-                                                 offset, input_ctype, out_fp,
-                                                 output_ctype, &new_size);
-                       if (ret != 0)
-                               return ret;
-                       output_res_entry->size = new_size;
+                               break;
                }
-
        }
-
-       output_res_entry->original_size = original_size;
-       if (output_ctype == WIM_COMPRESSION_TYPE_NONE)
-               output_res_entry->flags = 0;
-       else
-               output_res_entry->flags = WIM_RESHDR_FLAG_COMPRESSED;
-       return 0;
+       return ret;
 }
 
 /* 
@@ -909,10 +1086,10 @@ static int transfer_file_resource(FILE *in_fp, u64 size, u64 original_size,
  *
  * @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.
+ * @imd:       Pointer to the image metadata structure.  Its `metadata_lte'
+ *             member specifies the lookup table entry for the metadata
+ *             resource.  The rest of the image metadata entry will be filled
+ *             in by this function.
  *
  * @return:    Zero on success, nonzero on failure.
  */
@@ -922,12 +1099,14 @@ int read_metadata_resource(FILE *fp, int wim_ctype, struct image_metadata *imd)
        int ctype;
        u32 dentry_offset;
        int ret;
-       const struct resource_entry *res_entry;
        struct dentry *dentry;
        struct wim_security_data *sd;
        struct link_group_table *lgt;
+       const struct lookup_table_entry *metadata_lte;
+       const struct resource_entry *res_entry;
 
-       res_entry = &imd->metadata_lte->resource_entry;
+       metadata_lte = imd->metadata_lte;
+       res_entry = &metadata_lte->resource_entry;
 
        DEBUG("Reading metadata resource: length = %"PRIu64", "
              "offset = %"PRIu64"",
@@ -948,12 +1127,9 @@ int read_metadata_resource(FILE *fp, int wim_ctype, struct image_metadata *imd)
        }
 
        /* Determine the compression type of the metadata resource. */
-       ctype = resource_compression_type(wim_ctype, res_entry->flags);
 
        /* Read the metadata resource into memory.  (It may be compressed.) */
-       ret = read_full_resource(fp, res_entry->size, 
-                                res_entry->original_size, res_entry->offset, 
-                                ctype, buf);
+       ret = read_full_wim_resource(metadata_lte, buf);
        if (ret != 0)
                goto out_free_buf;
 
@@ -991,16 +1167,20 @@ int read_metadata_resource(FILE *fp, int wim_ctype, struct image_metadata *imd)
        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;
@@ -1008,6 +1188,12 @@ int read_metadata_resource(FILE *fp, int wim_ctype, struct image_metadata *imd)
        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;
@@ -1015,7 +1201,7 @@ int read_metadata_resource(FILE *fp, int wim_ctype, struct image_metadata *imd)
 out_free_lgt:
        free_link_group_table(lgt);
 out_free_dentry_tree:
-       free_dentry_tree(dentry, NULL, false);
+       free_dentry_tree(dentry, NULL);
 out_free_security_data:
        free_security_data(sd);
 out_free_buf:
@@ -1023,39 +1209,35 @@ out_free_buf:
        return ret;
 }
 
-/* Write the metadata resource for the current image. */
+/* Write the metadata resource for the current WIM image. */
 int write_metadata_resource(WIMStruct *w)
 {
-       FILE *out;
        u8 *buf;
        u8 *p;
        int ret;
        u64 subdir_offset;
        struct dentry *root;
-       struct lookup_table_entry *lte;
-       struct resource_entry *res_entry;
-       off_t metadata_offset;
+       struct lookup_table_entry *lte, *duplicate_lte;
        u64 metadata_original_size;
-       u64 metadata_compressed_size;
-       int metadata_ctype;
-       u8  hash[WIM_HASH_SIZE];
+
+       /* 
+        * We append 20 random bytes to the metadata resource so that we don't
+        * have identical metadata resources if we happen to append exactly the
+        * same image twice without any changes in timestamps.  If this were to
+        * happen, it would cause confusion about the number and order of images
+        * in the WIM.
+        */
+       const unsigned random_tail_len = 20;
 
        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;
+       const struct wim_security_data *sd = wim_security_data(w);
+       wimlib_assert(sd);
+       subdir_offset = sd->total_length + root->length + 8;
        calculate_subdir_offsets(root, &subdir_offset);
-       metadata_original_size = subdir_offset;
+       metadata_original_size = subdir_offset + random_tail_len;
        buf = MALLOC(metadata_original_size);
        if (!buf) {
                ERROR("Failed to allocate %"PRIu64" bytes for "
@@ -1067,165 +1249,22 @@ int write_metadata_resource(WIMStruct *w)
 
        DEBUG("Writing dentry tree.");
        p = write_dentry_tree(root, p);
+       randomize_byte_array(p, random_tail_len);
+       wimlib_assert(p - buf + random_tail_len == metadata_original_size);
 
-       /* Like file resources, the lookup table entry for a metadata resource
-        * uses for the hash code a SHA1 message digest of its uncompressed
-        * contents. */
-       sha1_buffer(buf, metadata_original_size, hash);
-
-       ret = write_resource_from_memory(buf, 
-                                        metadata_ctype,
-                                        metadata_original_size, 
-                                        out,
-                                        &metadata_compressed_size);
-       FREE(buf);
-       if (ret != 0)
-               return ret;
-
-       /* Update the lookup table entry, including the hash and output resource
-        * entry fields, for this image's metadata resource.  */
        lte = wim_metadata_lookup_table_entry(w);
-       res_entry = &lte->output_resource_entry;
-       lte->out_refcnt++;
-       if (memcmp(hash, lte->hash, WIM_HASH_SIZE) != 0) {
-               lookup_table_unlink(w->lookup_table, lte);
-               memcpy(lte->hash, hash, WIM_HASH_SIZE);
-               lookup_table_insert(w->lookup_table, lte);
-       }
-       res_entry->original_size = metadata_original_size;
-       res_entry->offset        = metadata_offset;
-       res_entry->size          = metadata_compressed_size;
-       res_entry->flags         = WIM_RESHDR_FLAG_METADATA;
-       if (metadata_ctype != WIM_COMPRESSION_TYPE_NONE)
-               res_entry->flags |= WIM_RESHDR_FLAG_COMPRESSED;
-       return 0;
-}
-
-static int write_file_resource(WIMStruct *w, const u8 hash[])
-{
-       /* Get the lookup entry for the file resource. */
-       struct lookup_table_entry *lte;
-       
-       lte = __lookup_resource(w->lookup_table, hash);
-       if (!lte)
-               return 0;
-
-       /* No need to write file resources twice. */
-       if (++lte->out_refcnt != 1)
-               return 0;
-
-       /* do not write empty resources */
-       if (lte->resource_entry.original_size == 0)
-               return 0;
-
-       int out_wim_ctype = wimlib_get_compression_type(w);
-       struct resource_entry *output_res_entry = &lte->output_resource_entry;
-       u64 len;
-       FILE *in_fp;
-       FILE *out_fp = w->out_fp;
-       int ret = 0;
 
-       /* Figure out if we can read the resource from the WIM file, or
-        * if we have to read it from the filesystem outside, or if it's a
-        * symbolic link with the data already in memory pointed to by a field
-        * of the lookup table entry. */
-       if (lte->is_symlink) {
-               off_t offset = ftello(w->out_fp);
-               u64 new_size;
-
-               if (offset == -1) {
-                       ERROR_WITH_ERRNO("Could not get position in output "
-                                        "file");
-                       return WIMLIB_ERR_WRITE;
-               }
-
-               wimlib_assert(lte->symlink_buf);
-
-               len = lte->resource_entry.original_size;
-
-               ret = recompress_resource(NULL, lte->symlink_buf, len, len, 0,
-                                         0, out_fp, out_wim_ctype, &new_size);
-               output_res_entry->size = new_size;
-               output_res_entry->original_size = len;
-               output_res_entry->offset = offset;
-               output_res_entry->flags = (out_wim_ctype == WIM_COMPRESSION_TYPE_NONE)
-                                               ? 0 : WIM_RESHDR_FLAG_COMPRESSED;
-       } else if (lte->file_on_disk) {
-
-               /* Read from disk (uncompressed) */
-
-               len = lte->resource_entry.original_size;
-
-               in_fp = fopen(lte->file_on_disk, "rb");
-               if (!in_fp) {
-                       ERROR_WITH_ERRNO("Failed to open the file `%s'",
-                                        lte->file_on_disk);
-                       return WIMLIB_ERR_OPEN;
-               }
-
-               ret = transfer_file_resource(in_fp, len, len, 0,
-                                            WIM_COMPRESSION_TYPE_NONE, out_fp,
-                                            out_wim_ctype, output_res_entry);
-               fclose(in_fp);
-       } else {
-               int in_wim_ctype;
-
-               /* Read from input WIM (possibly compressed) */
-
-               /* It may be a different WIM file, in the case of
-                * exporting images from one WIM file to another */
-               if (lte->other_wim_fp) {
-                       /* Different WIM file. */
-                       in_fp = lte->other_wim_fp;
-                       in_wim_ctype = lte->other_wim_ctype;
-               } else {
-                       /* Same WIM file. */
-                       in_fp = w->fp;
-                       in_wim_ctype = out_wim_ctype;
-               }
-               int input_res_ctype = resource_compression_type(
-                                               in_wim_ctype, 
-                                               lte->resource_entry.flags);
-
-               ret = transfer_file_resource(in_fp,
-                                            lte->resource_entry.size,
-                                            lte->resource_entry.original_size, 
-                                            lte->resource_entry.offset,
-                                            input_res_ctype, 
-                                            out_fp,
-                                            out_wim_ctype,
-                                            output_res_entry);
-       }
+       ret = write_wim_resource_from_buffer(buf, metadata_original_size,
+                                            w->out_fp,
+                                            wimlib_get_compression_type(w),
+                                            &lte->output_resource_entry,
+                                            lte->hash);
+       lookup_table_unlink(w->lookup_table, lte);
+       lookup_table_insert(w->lookup_table, lte);
+       wimlib_assert(lte->out_refcnt == 0);
+       lte->out_refcnt = 1;
+       lte->output_resource_entry.flags |= WIM_RESHDR_FLAG_METADATA;
+out:
+       FREE(buf);
        return ret;
 }
-
-/* 
- * Writes a dentry's resources to the output file. 
- *
- * @dentry:  The dentry for the file resource.
- * @wim_p:   A pointer to the WIMStruct.  The fields of interest to this
- *          function are the input and output file streams and the lookup
- *          table, and the alternate data streams.
- *
- * @return zero on success, nonzero on failure. 
- */
-int write_dentry_resources(struct dentry *dentry, void *wim_p)
-{
-       WIMStruct *w = wim_p;
-       int ret;
-
-       /* Directories don't need file resources. */
-       if (dentry_is_directory(dentry))
-               return 0;
-
-       ret = write_file_resource(w, dentry->hash);
-       if (ret != 0)
-               return ret;
-       for (u16 i = 0; i < dentry->num_ads; i++) {
-               ret = write_file_resource(w, dentry->ads_entries[i].hash);
-               if (ret != 0)
-                       return ret;
-       }
-       return 0;
-}
-