libc-bottom-half/cloudlibc/src/libc/dirent/readdir.c

   1 // Copyright (c) 2015-2017 Nuxi, https://nuxi.nl/
   2 //
   3 // SPDX-License-Identifier: BSD-2-Clause
   4
   5 #include <sys/stat.h>
   6
   7 #include <assert.h>
   8 #include <wasi/core.h>
   9 #include <dirent.h>
  10 #include <errno.h>
  11 #include <stddef.h>
  12 #include <stdlib.h>
  13 #include <string.h>
  14
  15 #include "dirent_impl.h"
  16
  17 static_assert(DT_BLK == __WASI_FILETYPE_BLOCK_DEVICE, "Value mismatch");
  18 static_assert(DT_CHR == __WASI_FILETYPE_CHARACTER_DEVICE, "Value mismatch");
  19 static_assert(DT_DIR == __WASI_FILETYPE_DIRECTORY, "Value mismatch");
  20 static_assert(DT_FIFO == __WASI_FILETYPE_SOCKET_STREAM, "Value mismatch");
  21 static_assert(DT_LNK == __WASI_FILETYPE_SYMBOLIC_LINK, "Value mismatch");
  22 static_assert(DT_REG == __WASI_FILETYPE_REGULAR_FILE, "Value mismatch");
  23 static_assert(DT_UNKNOWN == __WASI_FILETYPE_UNKNOWN, "Value mismatch");
  24
  25 // Grows a buffer to be large enough to hold a certain amount of data.
  26 #define GROW(buffer, buffer_size, target_size)      \
  27   do {                                              \
  28     if ((buffer_size) < (target_size)) {            \
  29       size_t new_size = (buffer_size);              \
  30       while (new_size < (target_size))              \
  31         new_size *= 2;                              \
  32       void *new_buffer = realloc(buffer, new_size); \
  33       if (new_buffer == NULL)                       \
  34         return NULL;                                \
  35       (buffer) = new_buffer;                        \
  36       (buffer_size) = new_size;                     \
  37     }                                               \
  38   } while (0)
  39
  40 struct dirent *readdir(DIR *dirp) {
  41   for (;;) {
  42     // Extract the next dirent header.
  43     size_t buffer_left = dirp->buffer_used - dirp->buffer_processed;
  44     if (buffer_left < sizeof(__wasi_dirent_t)) {
  45       // End-of-file.
  46       if (dirp->buffer_used < dirp->buffer_size)
  47         return NULL;
  48       goto read_entries;
  49     }
  50     __wasi_dirent_t entry;
  51     memcpy(&entry, dirp->buffer + dirp->buffer_processed, sizeof(entry));
  52
  53     size_t entry_size = sizeof(__wasi_dirent_t) + entry.d_namlen;
  54     if (entry.d_namlen == 0) {
  55       // Invalid pathname length. Skip the entry.
  56       dirp->buffer_processed += entry_size;
  57       continue;
  58     }
  59
  60     // The entire entry must be present in buffer space. If not, read
  61     // the entry another time. Ensure that the read buffer is large
  62     // enough to fit at least this single entry.
  63     if (buffer_left < entry_size) {
  64       GROW(dirp->buffer, dirp->buffer_size, entry_size);
  65       goto read_entries;
  66     }
  67
  68     // Skip entries having null bytes in the filename.
  69     const char *name = dirp->buffer + dirp->buffer_processed + sizeof(entry);
  70     if (memchr(name, '\0', entry.d_namlen) != NULL) {
  71       dirp->buffer_processed += entry_size;
  72       continue;
  73     }
  74
  75     // Return the next directory entry. Ensure that the dirent is large
  76     // enough to fit the filename.
  77     GROW(dirp->dirent, dirp->dirent_size,
  78          offsetof(struct dirent, d_name) + entry.d_namlen + 1);
  79     struct dirent *dirent = dirp->dirent;
  80     dirent->d_ino = entry.d_ino;
  81     dirent->d_type = entry.d_type;
  82     memcpy(dirent->d_name, name, entry.d_namlen);
  83     dirent->d_name[entry.d_namlen] = '\0';
  84     dirp->cookie = entry.d_next;
  85     dirp->buffer_processed += entry_size;
  86     return dirent;
  87
  88   read_entries:
  89     // Discard data currently stored in the input buffer.
  90     dirp->buffer_used = dirp->buffer_processed = dirp->buffer_size;
  91
  92     // Load more directory entries and continue.
  93     __wasi_errno_t error =
  94 #ifdef __wasilibc_unmodified_upstream
  95         __wasi_file_readdir(dirp->fd, dirp->buffer, dirp->buffer_size,
  96 #else
  97         __wasi_fd_readdir(dirp->fd, dirp->buffer, dirp->buffer_size,
  98 #endif
  99                                   dirp->cookie, &dirp->buffer_used);
 100     if (error != 0) {
 101       errno = error;
 102       return NULL;
 103     }
 104     dirp->buffer_processed = 0;
 105   }
 106 }