read_resource_prefix(): Remove comment about removed flag
[wimlib] / src / resource.c
index f8f4844..4b91be6 100644 (file)
@@ -1,11 +1,11 @@
 /*
  * resource.c
  *
- * Read uncompressed and compressed metadata and file resources.
+ * Read uncompressed and compressed metadata and file resources from a WIM file.
  */
 
 /*
- * 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; if not, see http://www.gnu.org/licenses/.
  */
 
-#include "config.h"
-
-#include <stdlib.h>
-#include <stdarg.h>
-
-#include "dentry.h"
-
 #include "wimlib_internal.h"
+#include "dentry.h"
 #include "lookup_table.h"
 #include "buffer_io.h"
-#include "lzx.h"
-#include "xpress.h"
 #include "sha1.h"
-#include <unistd.h>
-#include <errno.h>
 
-#ifdef WITH_NTFS_3G
-#include <time.h>
-#include <ntfs-3g/attrib.h>
-#include <ntfs-3g/inode.h>
-#include <ntfs-3g/dir.h>
+#ifdef __WIN32__
+#  include "win32.h"
 #endif
 
+#include <errno.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;
@@ -84,9 +67,9 @@ static int read_compressed_resource(FILE *fp, u64 resource_compressed_size,
        int (*decompress)(const void *, unsigned, void *, unsigned);
        /* Set the appropriate decompress function. */
        if (resource_ctype == WIMLIB_COMPRESSION_TYPE_LZX)
-               decompress = lzx_decompress;
+               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
@@ -100,7 +83,8 @@ static int read_compressed_resource(FILE *fp, u64 resource_compressed_size,
         * 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. */
@@ -127,9 +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.
@@ -165,20 +162,17 @@ static int read_compressed_resource(FILE *fp, u64 resource_compressed_size,
        /* Skip over unneeded chunk table entries. */
        u64 file_offset_of_needed_chunk_entries = resource_offset +
                                start_table_idx * chunk_entry_size;
-       if (fseeko(fp, file_offset_of_needed_chunk_entries, SEEK_SET) != 0) {
-               ERROR_WITH_ERRNO("Failed to seek to byte %"PRIu64" to read "
-                                "chunk table of compressed resource",
-                                file_offset_of_needed_chunk_entries);
-               return WIMLIB_ERR_READ;
-       }
 
        /* Number of bytes we need to read from the chunk table. */
        size_t size = num_needed_chunk_entries * chunk_entry_size;
 
-       u8 chunk_tab_buf[size];
+       /* 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. */
@@ -200,18 +194,16 @@ static int read_compressed_resource(FILE *fp, u64 resource_compressed_size,
        /* 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
@@ -219,15 +211,11 @@ 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. */
                unsigned compressed_chunk_size;
@@ -262,11 +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)
@@ -279,109 +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;
@@ -411,7 +378,8 @@ const u8 *get_resource_entry(const u8 *p, struct resource_entry *entry)
 /* 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);
@@ -420,272 +388,320 @@ u8 *put_resource_entry(u8 *p, const struct resource_entry *entry)
        return p;
 }
 
-#ifdef WITH_FUSE
-static FILE *wim_get_fp(WIMStruct *w)
+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)
 {
-       pthread_mutex_lock(&w->fp_tab_mutex);
-       FILE *fp;
-
-       wimlib_assert(w->filename != NULL);
+       WIMStruct *wim;
+       int in_fd;
+       int ret;
 
-       for (size_t i = 0; i < w->num_allocated_fps; i++) {
-               if (w->fp_tab[i]) {
-                       fp = w->fp_tab[i];
-                       w->fp_tab[i] = NULL;
-                       goto out;
+       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 = 0;
        }
-       DEBUG("Opening extra file descriptor to `%s'", w->filename);
-       fp = fopen(w->filename, "rb");
-       if (!fp)
-               ERROR_WITH_ERRNO("Failed to open `%s'", w->filename);
+       goto out;
+read_error:
+       ERROR_WITH_ERRNO("Error reading data from WIM");
+       ret = WIMLIB_ERR_READ;
 out:
-       pthread_mutex_unlock(&w->fp_tab_mutex);
-       return fp;
+       if (ret) {
+               if (errno == 0)
+                       errno = EIO;
+       }
+       return ret;
+}
+
+
+int
+read_partial_wim_resource_into_buf(const struct wim_lookup_table_entry *lte,
+                                  size_t size, u64 offset, void *buf)
+{
+       return read_partial_wim_resource(lte, size, NULL, buf, 0, offset);
 }
 
-static int wim_release_fp(WIMStruct *w, FILE *fp)
+static int
+read_wim_resource_prefix(const struct wim_lookup_table_entry *lte,
+                        u64 size,
+                        consume_data_callback_t cb,
+                        void *ctx_or_buf,
+                        int flags)
 {
-       int ret = 0;
-       FILE **fp_tab;
+       return read_partial_wim_resource(lte, size, cb, ctx_or_buf, flags, 0);
+}
 
-       pthread_mutex_lock(&w->fp_tab_mutex);
 
-       for (size_t i = 0; i < w->num_allocated_fps; i++) {
-               if (w->fp_tab[i] == NULL) {
-                       w->fp_tab[i] = fp;
-                       goto out;
+#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 tchar *filename = lte->file_on_disk;
+       int ret;
+       int fd;
+       size_t bytes_read;
+
+       fd = open(filename, O_RDONLY);
+       if (fd < 0) {
+               ERROR_WITH_ERRNO("Can't open \"%"TS"\"", filename);
+               return WIMLIB_ERR_OPEN;
+       }
+       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;
        }
+       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
+read_buffer_prefix(const struct wim_lookup_table_entry *lte,
+                  u64 size, consume_data_callback_t cb,
+                  void *ctx_or_buf, int _ignored_flags)
+{
+       const void *inbuf = lte->attached_buffer;
+       int ret;
 
-       fp_tab = REALLOC(w->fp_tab, sizeof(FILE*) * (w->num_allocated_fps + 4));
-       if (!fp_tab) {
-               ret = WIMLIB_ERR_NOMEM;
-               goto out;
+       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 {
+               memcpy(ctx_or_buf, inbuf, size);
        }
-       w->fp_tab = fp_tab;
-       memset(&w->fp_tab[w->num_allocated_fps], 0, 4 * sizeof(FILE*));
-       w->fp_tab[w->num_allocated_fps] = fp;
-       w->num_allocated_fps += 4;
-out:
-       pthread_mutex_unlock(&w->fp_tab_mutex);
-       return ret;
+       return 0;
 }
-#endif
+
+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);
 
 /*
- * Reads some data from the resource corresponding to a WIM lookup table entry.
+ * 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.
  *
- * @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.
+ * 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).
  *
- * Returns zero on success, nonzero on failure.
+ * When using a callback function, it is called with chunks up to 32768 bytes in
+ * size until the resource is exhausted.
+ *
+ * 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.
  */
-int read_wim_resource(const struct lookup_table_entry *lte, u8 buf[],
-                     size_t size, u64 offset, int flags)
+int
+read_resource_prefix(const struct wim_lookup_table_entry *lte,
+                    u64 size, consume_data_callback_t cb, void *ctx_or_buf,
+                    int flags)
 {
-       int ctype;
-       int ret = 0;
-       FILE *fp;
+       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);
+}
 
-       /* We shouldn't be allowing read over-runs in any part of the library.
-        * */
-       if (flags & WIMLIB_RESOURCE_FLAG_RAW)
-               wimlib_assert(offset + size <= lte->resource_entry.size);
-       else
-               wimlib_assert(offset + size <= lte->resource_entry.original_size);
-
-       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 != NULL);
-
-               #ifdef WITH_FUSE
-               if (flags & WIMLIB_RESOURCE_FLAG_MULTITHREADED) {
-                       fp = wim_get_fp(lte->wim);
-                       if (!fp)
-                               return WIMLIB_ERR_OPEN;
-               } else
-               #endif
-               {
-                       wimlib_assert(!(flags & WIMLIB_RESOURCE_FLAG_MULTITHREADED));
-                       wimlib_assert(lte->wim->fp != NULL);
-                       fp = lte->wim->fp;
-               }
+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);
+}
 
-               ctype = wim_resource_compression_type(lte);
+struct extract_ctx {
+       SHA_CTX sha_ctx;
+       consume_data_callback_t extract_chunk;
+       void *extract_chunk_arg;
+};
 
-               wimlib_assert(ctype != WIMLIB_COMPRESSION_TYPE_NONE ||
-                             (lte->resource_entry.original_size ==
-                              lte->resource_entry.size));
+static int
+extract_chunk_sha1_wrapper(const void *chunk, size_t chunk_size,
+                          void *_ctx)
+{
+       struct extract_ctx *ctx = _ctx;
 
-               if ((flags & WIMLIB_RESOURCE_FLAG_RAW)
-                   || ctype == WIMLIB_COMPRESSION_TYPE_NONE)
-                       ret = read_uncompressed_resource(fp,
-                                                        lte->resource_entry.offset + offset,
-                                                        size, buf);
-               else
-                       ret = read_compressed_resource(fp,
-                                                      lte->resource_entry.size,
-                                                      lte->resource_entry.original_size,
-                                                      lte->resource_entry.offset,
-                                                      ctype, size, offset, buf);
-       #ifdef WITH_FUSE
-               if (flags & WIMLIB_RESOURCE_FLAG_MULTITHREADED) {
-                       int ret2 = wim_release_fp(lte->wim, fp);
-                       if (ret == 0)
-                               ret = ret2;
-               }
-       #endif
-               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);
-                               ret = WIMLIB_ERR_OPEN;
-                               break;
+       sha1_update(&ctx->sha_ctx, chunk, chunk_size);
+       return ctx->extract_chunk(chunk, chunk_size, ctx->extract_chunk_arg);
+}
+
+/* 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;
                        }
                }
-               ret = read_uncompressed_resource(fp, offset, size, buf);
-               if (fp != lte->file_on_disk_fp)
-                       fclose(fp);
-               break;
-       case RESOURCE_IN_ATTACHED_BUFFER:
-               /* The resource is directly attached uncompressed in an
-                * in-memory buffer. */
-               wimlib_assert(lte->attached_buffer != NULL);
-               memcpy(buf, lte->attached_buffer + offset, size);
-               break;
-#ifdef WITH_NTFS_3G
-       case RESOURCE_IN_NTFS_VOLUME:
-               wimlib_assert(lte->ntfs_loc != NULL);
-               wimlib_assert(lte->attr != NULL);
-               if (lte->ntfs_loc->is_reparse_point)
-                       offset += 8;
-               if (ntfs_attr_pread(lte->attr, offset, size, buf) != size) {
-                       ERROR_WITH_ERRNO("Error reading NTFS attribute "
-                                        "at `%s'",
-                                        lte->ntfs_loc->path_utf8);
-                       ret = WIMLIB_ERR_NTFS_3G;
-               }
-               break;
-#endif
-       default:
-               wimlib_assert(0);
-               ret = -1;
-               break;
+       } else {
+               /* Don't do SHA1 */
+               ret = read_resource_prefix(lte, size, extract_chunk,
+                                          extract_chunk_arg, 0);
        }
        return ret;
 }
 
-/*
- * 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 flags)
+static int
+extract_wim_chunk_to_fd(const void *buf, size_t len, void *_fd_p)
 {
-       return read_wim_resource(lte, buf, wim_resource_size(lte), 0, flags);
+       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;
+       }
 }
 
-/* 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])
+int
+extract_wim_resource_to_fd(const struct wim_lookup_table_entry *lte,
+                          int fd, u64 size)
 {
-       /* Set up a temporary lookup table entry to 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_out_hash(lte.hash);
-       ret = write_wim_resource(&lte, out_fp, out_ctype, out_res_entry, 0);
-       if (ret != 0)
-               return ret;
-       copy_hash(hash, lte.hash);
-       return 0;
+       return extract_wim_resource(lte, size, extract_wim_chunk_to_fd, &fd);
 }
 
-/*
- * 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)
+
+static int
+sha1_chunk(const void *buf, size_t len, void *ctx)
 {
-       u64 bytes_remaining = size;
-       u8 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, 0);
-               if (ret != 0)
-                       break;
-               sha1_update(&ctx, buf, to_read);
-               if (full_write(fd, buf, to_read) < to_read) {
-                       ERROR_WITH_ERRNO("Error extracting WIM resource");
-                       return WIMLIB_ERR_WRITE;
-               }
-               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;
-       }
+       sha1_update(ctx, buf, len);
        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)
+/* Calculate the SHA1 message digest of a stream. */
+int
+sha1_resource(struct wim_lookup_table_entry *lte)
 {
-       return extract_wim_resource_to_fd(lte, fd, wim_resource_size(lte));
+       int ret;
+       SHA_CTX sha_ctx;
+
+       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;
 }
 
 /*
@@ -695,291 +711,21 @@ int extract_full_wim_resource_to_fd(const struct lookup_table_entry *lte, int fd
  *
  * The output_resource_entry, out_refcnt, and part_number fields of @lte are
  * updated.
+ *
+ * (This function is confusing and should be refactored somehow.)
  */
-int copy_resource(struct lookup_table_entry *lte, void *wim)
+int
+copy_resource(struct wim_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,
+       ret = write_wim_resource(lte, w->out_fd,
                                 wim_resource_compression_type(lte),
                                 &lte->output_resource_entry, 0);
-       if (ret != 0)
-               return ret;
-       lte->out_refcnt = lte->refcnt;
-       lte->part_number = w->hdr.part_number;
-       return 0;
-}
-
-/*
- * Reads the metadata metadata resource from the WIM file.  The metadata
- * resource consists of the security data, followed by the directory entry for
- * the root directory, followed by all the other directory entries in the
- * filesystem.  The subdir_offset field of each directory entry gives the start
- * of its child entries from the beginning of the metadata resource.  An
- * end-of-directory is signaled by a directory entry of length '0', really of
- * length 8, because that's how long the 'length' field is.
- *
- * @fp:                The FILE* for the input WIM file.
- * @wim_ctype: The compression type of the WIM file.
- * @imd:       Pointer to the image metadata structure.  Its `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.
- */
-int read_metadata_resource(WIMStruct *w, struct image_metadata *imd)
-{
-       u8 *buf;
-       u32 dentry_offset;
-       int ret;
-       struct dentry *dentry;
-       struct inode_table inode_tab;
-       const struct lookup_table_entry *metadata_lte;
-       u64 metadata_len;
-       struct hlist_head inode_list;
-
-       metadata_lte = imd->metadata_lte;
-       metadata_len = wim_resource_size(metadata_lte);
-
-       DEBUG("Reading metadata resource: length = %"PRIu64", "
-             "offset = %"PRIu64"", metadata_len,
-             metadata_lte->resource_entry.offset);
-
-       /* There is no way the metadata resource could possibly be less than (8
-        * + WIM_DENTRY_DISK_SIZE) bytes, where the 8 is for security data (with
-        * no security descriptors) and WIM_DENTRY_DISK_SIZE is for the root
-        * dentry. */
-       if (metadata_len < 8 + WIM_DENTRY_DISK_SIZE) {
-               ERROR("Expected at least %u bytes for the metadata resource",
-                     8 + WIM_DENTRY_DISK_SIZE);
-               return WIMLIB_ERR_INVALID_RESOURCE_SIZE;
-       }
-
-       if (sizeof(size_t) < 8 && metadata_len > 0xffffffff) {
-               ERROR("Metadata resource is too large (%"PRIu64" bytes",
-                     metadata_len);
-               return WIMLIB_ERR_INVALID_RESOURCE_SIZE;
+       if (ret == 0) {
+               lte->out_refcnt = lte->refcnt;
+               lte->part_number = w->hdr.part_number;
        }
-
-       /* Allocate memory for the uncompressed metadata resource. */
-       buf = MALLOC(metadata_len);
-
-       if (!buf) {
-               ERROR("Failed to allocate %"PRIu64" bytes for uncompressed "
-                     "metadata resource", metadata_len);
-               return WIMLIB_ERR_NOMEM;
-       }
-
-       /* Read the metadata resource into memory.  (It may be compressed.) */
-       ret = read_full_wim_resource(metadata_lte, buf, 0);
-       if (ret != 0)
-               goto out_free_buf;
-
-       DEBUG("Finished reading metadata resource into memory.");
-
-       /* The root directory entry starts after security data, aligned on an
-        * 8-byte boundary within the metadata resource.
-        *
-        * The security data starts with a 4-byte integer giving its total
-        * length, so if we round that up to an 8-byte boundary that gives us
-        * the offset of the root dentry.
-        *
-        * Here we read the security data into a wim_security_data structure,
-        * and if successful, go ahead and calculate the offset in the metadata
-        * resource of the root dentry. */
-
-       wimlib_assert(imd->security_data == NULL);
-       ret = read_security_data(buf, metadata_len, &imd->security_data);
-       if (ret != 0)
-               goto out_free_buf;
-
-       dentry_offset = (imd->security_data->total_length + 7) & ~7;
-
-       if (dentry_offset == 0) {
-               ERROR("Integer overflow while reading metadata resource");
-               ret = WIMLIB_ERR_INVALID_SECURITY_DATA;
-               goto out_free_security_data;
-       }
-
-       DEBUG("Reading root dentry");
-
-       /* Allocate memory for the root dentry and read it into memory */
-       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 = read_dentry(buf, metadata_len, dentry_offset, dentry);
-
-       /* This is the root dentry, so set its parent to itself. */
-       dentry->parent = dentry;
-
-       if (ret == 0 && dentry->length == 0) {
-               ERROR("Metadata resource cannot begin with end-of-directory entry!");
-               ret = WIMLIB_ERR_INVALID_DENTRY;
-       }
-
-       if (ret != 0) {
-               FREE(dentry);
-               goto out_free_security_data;
-       }
-
-       inode_add_dentry(dentry, dentry->d_inode);
-
-       /* Now read the entire directory entry tree into memory. */
-       DEBUG("Reading dentry tree");
-       ret = read_dentry_tree(buf, metadata_len, dentry);
-       if (ret != 0)
-               goto out_free_dentry_tree;
-
-       /* Calculate the full paths in the dentry tree. */
-       DEBUG("Calculating dentry full paths");
-       ret = for_dentry_in_tree(dentry, calculate_dentry_full_path, NULL);
-       if (ret != 0)
-               goto out_free_dentry_tree;
-
-       /* Build hash table that maps hard link group IDs to dentry sets */
-       DEBUG("Building link group table");
-       ret = init_inode_table(&inode_tab, 9001);
-       if (ret != 0)
-               goto out_free_dentry_tree;
-
-       for_dentry_in_tree(dentry, inode_table_insert, &inode_tab);
-
-       DEBUG("Fixing inconsistencies in the hard link groups");
-       ret = fix_inodes(&inode_tab, &inode_list);
-       destroy_inode_table(&inode_tab);
-       if (ret != 0)
-               goto out_free_dentry_tree;
-
-       if (!w->all_images_verified) {
-               DEBUG("Running miscellaneous verifications on the dentry tree");
-               for_lookup_table_entry(w->lookup_table, lte_zero_real_refcnt, NULL);
-               ret = for_dentry_in_tree(dentry, verify_dentry, w);
-               if (ret != 0)
-                       goto out_free_dentry_tree;
-       }
-
-       DEBUG("Done reading image metadata");
-
-       imd->root_dentry = dentry;
-       imd->inode_list  = inode_list;
-       goto out_free_buf;
-out_free_dentry_tree:
-       free_dentry_tree(dentry, NULL);
-out_free_security_data:
-       free_security_data(imd->security_data);
-       imd->security_data = NULL;
-out_free_buf:
-       FREE(buf);
-       return ret;
-}
-
-static void recalculate_security_data_length(struct wim_security_data *sd)
-{
-       u32 total_length = sizeof(u64) * sd->num_entries + 2 * sizeof(u32);
-       for (u32 i = 0; i < sd->num_entries; i++)
-               total_length += sd->sizes[i];
-       sd->total_length = total_length;
-}
-
-/* Write the metadata resource for the current WIM image. */
-int write_metadata_resource(WIMStruct *w)
-{
-       u8 *buf;
-       u8 *p;
-       int ret;
-       u64 subdir_offset;
-       struct dentry *root;
-       struct lookup_table_entry *lte;
-       u64 metadata_original_size;
-       struct wim_security_data *sd;
-
-       DEBUG("Writing metadata resource for image %d (offset = %"PRIu64")",
-             w->current_image, ftello(w->out_fp));
-
-       root = wim_root_dentry(w);
-       sd = wim_security_data(w);
-
-       /* Offset of first child of the root dentry.  It's equal to:
-        * - The total length of the security data, rounded to the next 8-byte
-        *   boundary,
-        * - plus the total length of the root dentry,
-        * - plus 8 bytes for an end-of-directory entry following the root
-        *   dentry (shouldn't really be needed, but just in case...)
-        */
-       recalculate_security_data_length(sd);
-       subdir_offset = (((u64)sd->total_length + 7) & ~7) +
-                       dentry_correct_total_length(root) + 8;
-
-       /* Calculate the subdirectory offsets for the entire dentry tree. */
-       calculate_subdir_offsets(root, &subdir_offset);
-
-       /* Total length of the metadata resource (uncompressed) */
-       metadata_original_size = subdir_offset;
-
-       /* Allocate a buffer to contain the uncompressed metadata resource */
-       buf = MALLOC(metadata_original_size);
-       if (!buf) {
-               ERROR("Failed to allocate %"PRIu64" bytes for "
-                     "metadata resource", metadata_original_size);
-               return WIMLIB_ERR_NOMEM;
-       }
-
-       /* Write the security data into the resource buffer */
-       p = write_security_data(sd, buf);
-
-       /* Write the dentry tree into the resource buffer */
-       p = write_dentry_tree(root, p);
-
-       /* We MUST have exactly filled the buffer; otherwise we calculated its
-        * size incorrectly or wrote the data incorrectly. */
-       wimlib_assert(p - buf == metadata_original_size);
-
-       /* Get the lookup table entry for the metadata resource so we can update
-        * it. */
-       lte = w->image_metadata[w->current_image - 1].metadata_lte;
-
-       /* Write the metadata resource to the output WIM using the proper
-        * compression type.  The lookup table entry for the metadata resource
-        * is updated. */
-       ret = write_wim_resource_from_buffer(buf, metadata_original_size,
-                                            w->out_fp,
-                                            wimlib_get_compression_type(w),
-                                            &lte->output_resource_entry,
-                                            lte->hash);
-       if (ret != 0)
-               goto out;
-
-       /* It's very likely the SHA1 message digest of the metadata resource
-        * changed, so re-insert the lookup table entry into the lookup table.
-        *
-        * We do not check for other lookup table entries having the same SHA1
-        * message digest.  It's possible for 2 absolutely identical images to
-        * be added, therefore causing 2 identical metadata resources to be in
-        * the WIM.  However, in this case, it's expected for 2 separate lookup
-        * table entries to be created, even though this doesn't make a whole
-        * lot of sense since they will share the same SHA1 message digest.
-        * */
-       lookup_table_unlink(w->lookup_table, lte);
-       lookup_table_insert(w->lookup_table, lte);
-       lte->out_refcnt = 1;
-
-       /* Make sure that the lookup table entry for this metadata resource is
-        * marked with the metadata flag. */
-       lte->output_resource_entry.flags |= WIM_RESHDR_FLAG_METADATA;
-out:
-       /* All the data has been written to the new WIM; no need for the buffer
-        * anymore */
-       FREE(buf);
        return ret;
 }