Improve read_whole_file()

Move into os.c, declare and document in os.h

os.c

@@ -162,3 +162,24 @@ ssize_t read_symlink(const char *path, char *buf, size_t len)
   buf[nr] = '\0';
   return nr;
 }
+
+ssize_t read_whole_file(const char *path, unsigned char *buffer, size_t buffer_size)
+{
+  int fd = open(path, O_RDONLY);
+  if (fd == -1)
+    return WHYF_perror("open(%d,%s,O_RDONLY)", fd, alloca_str_toprint(path));
+  ssize_t ret;
+  struct stat stat;
+  if (fstat(fd, &stat) == -1)
+    ret = WHYF_perror("fstat(%d)", fd);
+  else if ((size_t)stat.st_size > buffer_size)
+    ret = WHYF("file %s (size %zu) is larger than available buffer (%zu)", alloca_str_toprint(path), (size_t)stat.st_size, buffer_size);
+  else {
+    ret = read(fd, buffer, buffer_size);
+    if (ret == -1)
+      ret = WHYF_perror("read(%d,%s,%zu)", fd, alloca_str_toprint(path), buffer_size);
+  }
+  if (close(fd) == -1)
+    ret = WHYF_perror("close(%d)", fd);
+  return ret;
+}

os.h

@@ -125,4 +125,12 @@ int urandombytes(unsigned char *buf, size_t len);
  */
 ssize_t read_symlink(const char *path, char *buf, size_t len);
 
+/* Read the whole file into the given buffer.  If the file will not fit into
+ * the buffer or if there is an error opening or reading the file, logs an
+ * error and returns -1.  Otherwise, returns the number of bytes read.
+ *
+ * @author Andrew Bettison <andrew@servalproject.com>
+ */
+ssize_t read_whole_file(const char *path, unsigned char *buffer, size_t buffer_size);
+
 #endif //__SERVAL_DNA__OS_H

rhizome_bundle.c

@@ -399,19 +399,6 @@ int rhizome_manifest_verify(rhizome_manifest *m)
   return 1;
 }
 
-ssize_t read_whole_file(const char *path, unsigned char *buffer, size_t buffer_size)
-{
-  int fd = open(path, O_RDONLY);
-  if (fd == -1)
-    return WHYF_perror("open(%s,O_RDONLY)", alloca_str_toprint(path));
-  ssize_t ret = read(fd, buffer, buffer_size);
-  if (ret == -1)
-    ret = WHYF_perror("read(%s,%zu)", alloca_str_toprint(path), buffer_size);
-  if (close(fd) == -1)
-    ret = WHY_perror("close");
-  return ret;
-}
-
 static void rhizome_manifest_clear(rhizome_manifest *m)
 {
   while (m->var_count) {