Accept streams as input. Use a temp file

[overonion] / reverse_lib.c

diff --git a/reverse_lib.c b/reverse_lib.c
index dad7e0d733304ad1d7587dbc9dd006934c58bc27..20837ee5f65fe95b237436b0d1685fd2d497a69d 100644 (file)
--- a/reverse_lib.c
+++ b/reverse_lib.c
@@ -1,26 +1,17 @@
+#define _GNU_SOURCE
 #define _FILE_OFFSET_BITS 64
 
-#define BUFFER_SIZE 4096
-
 #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 void write_all(int fd, const void *buf, size_t count) {
-  const char* cbuf = buf;
-  size_t written = 0;
-  while (written < count) {
-    int ret = write(fd, &cbuf[written], count - written);
-    if (ret == -1) err(EX_IOERR, "Could not write");
-    written += ret;
-  }
-}
-
-void reverse_file(const char* input_filename, int output_fd) {
+void reverse_file(const char* input_filename, FILE* output_stream) {
   int fd = open(input_filename, O_RDONLY);
   if (fd == -1) err(EX_NOINPUT, "Could not open specified file");
 
@@ -33,19 +24,54 @@ void reverse_file(const char* input_filename, int output_fd) {
   char *m = mmap(NULL, map_size, PROT_READ, MAP_SHARED, fd, 0);
   if (m == MAP_FAILED) err(EX_NOINPUT, "Could not mmap input");
 
-  char buf[BUFFER_SIZE];
-  off_t buf_offset = 0;
   for (off_t p = stats.st_size - 1; p >= 0; p--) {
-    buf[buf_offset++] = m[p];
-    if (buf_offset >= BUFFER_SIZE) {
-      write_all(output_fd, buf, buf_offset);
-      buf_offset = 0;
-    }
-  }
-  if (buf_offset) {
-    write_all(output_fd, buf, buf_offset);
+    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 input");
   if (close(fd) == -1) err(EX_IOERR, "Could not close input");
 }
+
+/* Create a temporary file in $TMPDIR, or /tmp if TMPDIR is not set.
+ * Caller must free temp_filename and fclose temp_file.  Succeeds or terminates
+ * the process. */
+static void make_temporary_file(char** temp_filename, FILE** temp_file) {
+  char* TMPDIR = getenv("TMPDIR");
+  if (TMPDIR == NULL) {
+    TMPDIR = "/tmp";
+  }
+  if (asprintf(temp_filename, "%s/reverse.XXXXXX", TMPDIR) == -1) {
+    errx(EX_OSERR, "Could not assemble temporary filename");
+  }
+  int fd = mkstemp(*temp_filename);
+  if (fd == -1) err(EX_IOERR, "Could not make a temporary file");
+  *temp_file = fdopen(fd, "w");
+  if (*temp_file == NULL) err(EX_IOERR, "Could not open temporary file");
+}
+
+/* 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);
+}