Patch escape_text_add_tags() crash on empty escaped string

1 files changed, 8 insertions, 5 deletions

diff --git a/src/gemini2html.c b/src/gemini2html.c
index d40a3bd..40621a0 100644
--- a/src/gemini2html.c
+++ b/src/gemini2html.c
@@ -98,6 +98,8 @@ void skip_non_whitespace(const char* str, size_t* pos) {
  * Examples:
  *   escape_text_add_tags("<p>", "5 < 6\n", "</p>", 6) => "<p>5 &lt; 6</p>\n"
  *   escape_text_add_tags("<p>", "5 < 6", "</p>", 5)   => "<p>5 &lt; 6</p>\n"
+ *   escape_text_add_tags("", "", "", 0)               => "\n"
+ *   escape_text_add_tags("", "", "<br/>", 0)          => "<br/>\n"
  */
 char* escape_text_add_tags(const char* opening_tag, const char* unescaped, const char* closing_tag, const size_t unescaped_len) {
     char* escaped = escape_text(unescaped, unescaped_len);
@@ -113,11 +115,12 @@ char* escape_text_add_tags(const char* opening_tag, const char* unescaped, const
     strncpy(escaped_with_tags + index, opening_tag, opening_tag_len);
     index += opening_tag_len;
 
-    /* append escaped text without newline at the end, if one exists */
-    strncpy(escaped_with_tags + index, escaped, escaped_len - 1);
+    /* append escaped text */
+    strncpy(escaped_with_tags + index, escaped, escaped_len);
+
+    /* don't increment index if newline so newline can be overwritten */
     index += escaped_len - 1;
-    bool is_newline = escaped[escaped_len - 1] == '\n';
-    if (!is_newline) escaped_with_tags[index++] = escaped[escaped_len - 1];
+    if (escaped_with_tags[index] != '\n') index++;
 
     /* escaped string is no longer needed */
     free(escaped);
@@ -154,7 +157,7 @@ enum linetype getlinetype(const char* line, const bool pre_is_toggled) {
 }
 
 char* convert_text_line(const char* line, const size_t size) {
-    if (line[0] == '\n') return strdup("<br/>\n");
+    if (line[0] == '\n') return escape_text_add_tags("", "", "<br/>", 0);
     else return escape_text_add_tags("<p>", line, "</p>", size);
 }