Make a parse_config_line_from_str variant that gives error messages

Without this patch, there's no way to know what went wrong when we
fail to parse a torrc line entirely (that is, we can't turn it into
a K,V pair.)  This patch introduces a new function that yields an
error message on failure, so we can at least tell the user what to
look for in their nonfunctional torrc.

(Actually, it's the same function as before with a new name:
parse_config_line_from_str is now a wrapper macro that the unit
tests use.)

Fixes bug 7950; fix on 0.2.0.16-alpha (58de695f9062576f) which first
introduced the possibility of a torrc value not parsing correctly.

4 files changed, 27 insertions, 8 deletions

diff --git a/changes/bug7950 b/changes/bug7950
new file mode 100644
index 000000000..e62cca07a
--- /dev/null
+++ b/changes/bug7950
@@ -0,0 +1,4 @@
+  o Minor bugfixes:
+    - When rejecting a configuration because we were unable to parse a
+      quoted string, log an actual error message. Fix for bug 7950;
+      bugfix on 0.2.0.16-alpha.
diff --git a/src/common/util.c b/src/common/util.c
index 6a6963559..5f045d51b 100644
--- a/src/common/util.c
+++ b/src/common/util.c
@@ -2537,10 +2537,13 @@ unescape_string(const char *s, char **result, size_t *size_out)
  * key portion and *<b>value_out</b> to a new string holding the value portion
  * of the line, and return a pointer to the start of the next line.  If we run
  * out of data, return a pointer to the end of the string.  If we encounter an
- * error, return NULL.
+ * error, return NULL and set *<b>err_out</b> (if provided) to an error
+ * message.
  */
 const char *
-parse_config_line_from_str(const char *line, char **key_out, char **value_out)
+parse_config_line_from_str_verbose(const char *line, char **key_out,
+                                   char **value_out,
+                                   const char **err_out)
 {
   /* I believe the file format here is supposed to be:
      FILE = (EMPTYLINE | LINE)* (EMPTYLASTLINE | LASTLINE)?
@@ -2614,12 +2617,18 @@ parse_config_line_from_str(const char *line, char **key_out, char **value_out)
 
   /* Find the end of the line. */
   if (*line == '\"') { // XXX No continuation handling is done here
-    if (!(line = unescape_string(line, value_out, NULL)))
-       return NULL;
+    if (!(line = unescape_string(line, value_out, NULL))) {
+      if (err_out)
+        *err_out = "Invalid escape sequence in quoted string";
+      return NULL;
+    }
     while (*line == ' ' || *line == '\t')
       ++line;
-    if (*line && *line != '#' && *line != '\n')
+    if (*line && *line != '#' && *line != '\n') {
+      if (err_out)
+        *err_out = "Excess data after quoted string";
       return NULL;
+    }
   } else {
     /* Look for the end of the line. */
     while (*line && *line != '\n' && (*line != '#' || continuation)) {
diff --git a/src/common/util.h b/src/common/util.h
index ac88f1ca1..0123a5366 100644
--- a/src/common/util.h
+++ b/src/common/util.h
@@ -375,8 +375,11 @@ char *read_file_to_str(const char *filename, int flags, struct stat *stat_out)
 char *read_file_to_str_until_eof(int fd, size_t max_bytes_to_read,
                                  size_t *sz_out)
   ATTR_MALLOC;
-const char *parse_config_line_from_str(const char *line,
-                                       char **key_out, char **value_out);
+const char *parse_config_line_from_str_verbose(const char *line,
+                                       char **key_out, char **value_out,
+                                       const char **err_out);
+#define parse_config_line_from_str(line,key_out,value_out) \
+  parse_config_line_from_str_verbose((line),(key_out),(value_out),NULL)
 char *expand_filename(const char *filename);
 struct smartlist_t *tor_listdir(const char *dirname);
 int path_is_relative(const char *filename);
diff --git a/src/or/confparse.c b/src/or/confparse.c
index 717d4ac2a..98fde98e7 100644
--- a/src/or/confparse.c
+++ b/src/or/confparse.c
@@ -91,12 +91,15 @@ config_get_lines(const char *string, config_line_t **result, int extended)
 {
   config_line_t *list = NULL, **next;
   char *k, *v;
+  const char *parse_err;
 
   next = &list;
   do {
     k = v = NULL;
-    string = parse_config_line_from_str(string, &k, &v);
+    string = parse_config_line_from_str_verbose(string, &k, &v, &parse_err);
     if (!string) {
+      log_warn(LD_CONFIG, "Error while parsing configuration: %s",
+               parse_err?parse_err:"<unknown>");
       config_free_lines(list);
       tor_free(k);
       tor_free(v);