From ef94f4ba3ca35d063807fff62a9766769d067202 Mon Sep 17 00:00:00 2001
From: Dmitry Bochkarev <dimabochkarev@gmail.com>
Date: Thu, 15 Dec 2016 18:09:10 +0500
Subject: [PATCH] Fix segmentations failure in error.c
 gumbo_caret_diagnostic_to_string

Without this patch method find_last_newline returns value bigger than
find_next_newline and in line `original_line.length = line_end -
line_start;`
overflow happens.

Before changes newly added test failed with segmentation failure:
```
./test-driver: line 107: 12171 Segmentation fault      (core dumped)
"$@" > $log_file 2>&1
```

This slightly changed copy of code used in nokogumbo gem.
[Link](https://github.com/rubys/nokogumbo/blob/8b4446847dea5c614759684ebcae4c580c47f4ad/ext/nokogumboc/nokogumbo.c#L230)
---
 Makefile.am    |  3 ++-
 src/error.c    |  2 +-
 tests/error.cc | 41 +++++++++++++++++++++++++++++++++++++++++
 3 files changed, 44 insertions(+), 2 deletions(-)
 create mode 100644 tests/error.cc

diff --git a/Makefile.am b/Makefile.am
index cb624591..b0cfc33c 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -93,7 +93,8 @@ gumbo_test_SOURCES = \
 				tests/tokenizer.cc \
 				tests/test_utils.cc \
 				tests/utf8.cc \
-				tests/vector.cc
+				tests/vector.cc \
+				tests/error.cc
 gumbo_test_DEPENDENCIES = libgumbo.la
 gumbo_test_LDADD = libgumbo.la
 
diff --git a/src/error.c b/src/error.c
index 6b184ed4..3bf56aab 100644
--- a/src/error.c
+++ b/src/error.c
@@ -140,7 +140,7 @@ static const char* find_last_newline(
     // There may be an error at EOF, which would be a nul byte.
     assert(*c || c == error_location);
   }
-  return c == original_text ? c : c + 1;
+  return c == original_text || c == error_location ? c : c + 1;
 }
 
 // Finds the next newline in the original source buffer from a given byte
diff --git a/tests/error.cc b/tests/error.cc
new file mode 100644
index 00000000..879b26d3
--- /dev/null
+++ b/tests/error.cc
@@ -0,0 +1,41 @@
+#include "gumbo.h"
+#include "parser.h"
+#include "error.h"
+
+#include <string>
+
+#include "gtest/gtest.h"
+#include "test_utils.h"
+
+namespace {
+
+class GumboErrorTest : public ::testing::Test {
+ protected:
+  GumboErrorTest() {}
+
+  virtual ~GumboErrorTest() {
+
+  }
+};
+
+TEST_F(GumboErrorTest, NewlineAfterLessThanSymbol) {
+  const GumboOptions *options = &kGumboDefaultOptions;
+  const char *input = "<\n";
+  size_t input_len = strlen(input);
+  GumboOutput *output = gumbo_parse_with_options(options, input, input_len);
+  GumboVector *errors = &output->errors;
+  GumboParser parser = { ._options = options };
+  GumboStringBuffer msg;
+
+  gumbo_string_buffer_init(&parser, &msg);
+  for (size_t i=0; i < errors->length; i++) {
+    GumboError *err = (GumboError *)errors->data[i];
+    gumbo_string_buffer_clear(&parser, &msg);
+    gumbo_caret_diagnostic_to_string(&parser, err, input, &msg);
+  }
+  gumbo_string_buffer_destroy(&parser, &msg);
+
+  gumbo_destroy_output(options, output);
+}
+
+}