-extern int try_fgetc(FILE * file, char * f);
-extern char * try_fgets(char * line, int size, FILE * file, char * f);
+extern int try_fgetc(FILE * file, const char * f);
+extern char * try_fgets(char * line, int size, FILE * file, const char * f);
+
+/* Return "path" + suffix "_tmp". Value is malloc'd, must be freed externally.*/
+extern char * build_temp_path(char * path);
+
+/* Write to "path_tmp" "path" + "_tmp" and return a new file at that "path_tmp"
+ * open for writing. "path_tmp" is malloc()'d, must be freed externally.
+*/
+extern FILE * atomic_write_start(char * path, char ** path_tmp);
+
+/* Finish atomic writing started in atomic_write_start(). Wraps successive calls
+ * of fclose() on "file", then unlink() on file at path "path" if it exists,
+ * then rename() from "path_tmp" to "path", then free() on "path_tmp".
+ */
+extern void atomic_write_finish(FILE * file, char * path, char * path_tmp);
+
+/* Check for temp file leftover of atomic writing of "path", abort if found. */
+extern void detect_atomic_leftover(char * path);
+
+/* Return largest line length from "file" (including newline chars). */
+extern uint32_t textfile_width(FILE * file);