X-Git-Url: http://git.scottworley.com/overonion/blobdiff_plain/673e2d68a8813804502df1923a6c2f6e727e69a0..f5ec0b4b91687c7a34d4760381f6e7424f981127:/reverse_lib.c

diff --git a/reverse_lib.c b/reverse_lib.c
new file mode 100644
index 0000000..f55bedf
--- /dev/null
+++ b/reverse_lib.c
@@ -0,0 +1,76 @@
+#define _FILE_OFFSET_BITS 64
+
+#include "temp_file.h"
+
+#include <err.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sysexits.h>
+#include <unistd.h>
+
+static off_t ceil_div(off_t dividend, off_t divisor) {
+  return (dividend - 1) / divisor + 1;
+}
+
+void reverse_file(const char* input_filename, FILE* output_stream) {
+  const off_t mmap_chunk_size = 512 << 20;
+
+  int fd = open(input_filename, O_RDONLY);
+  if (fd == -1) err(EX_NOINPUT, "Could not open specified file");
+
+  struct stat stats;
+  if (fstat(fd, &stats) == -1) err(EX_NOINPUT, "Could not stat input");
+
+  long page_size = sysconf(_SC_PAGE_SIZE);
+  off_t num_chunks = ceil_div(stats.st_size, mmap_chunk_size);
+  for (off_t chunk = num_chunks - 1; chunk >= 0; chunk--) {
+    off_t start_offset = chunk * mmap_chunk_size;
+    off_t end_offset = (chunk + 1) * mmap_chunk_size;
+    if (end_offset > stats.st_size) {
+      end_offset = stats.st_size;
+    }
+    off_t pages = ceil_div(end_offset - start_offset, page_size);
+    long map_size = pages * page_size;
+    char *m = mmap(NULL, map_size, PROT_READ, MAP_SHARED, fd, start_offset);
+    if (m == MAP_FAILED) err(EX_NOINPUT, "Could not mmap chunk %lld of %lld", chunk, num_chunks);
+
+    for (off_t p = (end_offset - start_offset) - 1; p >= 0; p--) {
+      if (fputc(m[p], output_stream) == EOF) errx(EX_IOERR, "Could not write");
+    }
+
+    if (munmap(m, map_size) == -1) err(EX_IOERR, "Could not unmap chunk %lld of %lld", chunk, num_chunks);
+  }
+
+  if (close(fd) == -1) err(EX_IOERR, "Could not close input");
+}
+
+/* Copy data from input to output until EOF is reached. */
+static void copy(FILE* input, FILE* output) {
+  for (;;) {
+    int c = fgetc(input);
+    if (c == EOF) {
+      if (ferror(input)) errx(EX_IOERR, "Could not read");
+      if (!feof(input)) errx(EX_IOERR, "Unexpected end of file");
+      break;
+    }
+    if (fputc(c, output) == EOF) errx(EX_IOERR, "Could not write");
+  }
+}
+
+void reverse_stream(FILE* input_stream, FILE* output_stream) {
+  char* temp_filename;
+  FILE* temp_file;
+  make_temporary_file(&temp_filename, &temp_file);
+
+  copy(input_stream, temp_file);
+  if (fclose(temp_file) != 0) err(EX_IOERR, "Could not close temporary file");
+
+  reverse_file(temp_filename, output_stream);
+
+  if (unlink(temp_filename) == -1) err(EX_IOERR, "Could not remove temporary file");
+  free(temp_filename);
+}