Add a utility routine to do ITU V.250 quoting of strings for AT commands.

BUG=chromium-os:27096,chromium-os:27063
TEST=None
Change-Id: Ic1d24a9e4b7421db7f8d16c52535bd6d2780423e

src/mm-at-serial-port.c

@@ -49,6 +49,32 @@ typedef struct {
 
 /*****************************************************************************/
 
+gchar *
+mm_at_serial_port_quote_string (const char *string)
+{
+    int len, i;
+    gchar *quoted, *pos;
+
+    if (string == NULL)
+        len = 0;
+    else
+        len = strlen (string);
+    quoted = g_malloc (3 + 3 * len); /* worst case */
+
+    pos = quoted;
+    *pos++ = '"';
+    for (i = 0 ; i < len; i++) {
+        if (string[i] < 0x20 || string[i] == '"' || string[i] == '\\')
+            pos += sprintf (pos, "\\%02X", string[i]);
+        else
+            *pos++ = string[i];
+    }
+    *pos++ = '"';
+    *pos++ = '\0';
+
+    return quoted;
+}
+
 void
 mm_at_serial_port_set_response_parser (MMAtSerialPort *self,
                                        MMAtSerialResponseParserFn fn,

src/mm-at-serial-port.h

@@ -104,6 +104,12 @@ void     mm_at_serial_port_queue_command_cached (MMAtSerialPort *self,
                                                  MMAtSerialResponseFn callback,
                                                  gpointer user_data);
 
+/*
+ * Convert a string into a quoted and escaped string. Returns a new
+ * allocated string. Follows ITU V.250 5.4.2.2 "String constants".
+ */
+gchar   *mm_at_serial_port_quote_string (const char *string);
+
 /* Just for unit tests */
 void mm_at_serial_port_remove_echo (GByteArray *response);