From 40b397a3d43ed3ad84957abc62012afafe1c8a0e Mon Sep 17 00:00:00 2001
From: Daniel Lemire <daniel@lemire.me>
Date: Tue, 19 Jul 2022 15:17:12 -0400
Subject: [PATCH] Fixing issue 1870 (#1871)

---
 include/simdjson/arm64/stringparsing.h    |  2 --
 include/simdjson/fallback/stringparsing.h |  2 --
 include/simdjson/generic/stringparsing.h  |  0
 include/simdjson/haswell/stringparsing.h  |  2 --
 include/simdjson/icelake/stringparsing.h  |  2 --
 include/simdjson/ppc64/stringparsing.h    |  2 --
 include/simdjson/westmere/stringparsing.h |  2 --
 src/generic/stage2/stringparsing.h        | 11 ++++++++++-
 tests/ondemand/ondemand_misc_tests.cpp    | 12 ++++++++++++
 9 files changed, 22 insertions(+), 13 deletions(-)
 delete mode 100644 include/simdjson/generic/stringparsing.h

diff --git a/include/simdjson/arm64/stringparsing.h b/include/simdjson/arm64/stringparsing.h
index 8f56efc27..82197e30c 100644
--- a/include/simdjson/arm64/stringparsing.h
+++ b/include/simdjson/arm64/stringparsing.h
@@ -48,6 +48,4 @@ simdjson_inline backslash_and_quote backslash_and_quote::copy_and_find(const uin
 } // namespace SIMDJSON_IMPLEMENTATION
 } // namespace simdjson
 
-#include "simdjson/generic/stringparsing.h"
-
 #endif // SIMDJSON_ARM64_STRINGPARSING_H
diff --git a/include/simdjson/fallback/stringparsing.h b/include/simdjson/fallback/stringparsing.h
index ab501a6d9..c4bdbab13 100644
--- a/include/simdjson/fallback/stringparsing.h
+++ b/include/simdjson/fallback/stringparsing.h
@@ -31,6 +31,4 @@ simdjson_inline backslash_and_quote backslash_and_quote::copy_and_find(const uin
 } // namespace SIMDJSON_IMPLEMENTATION
 } // namespace simdjson
 
-#include "simdjson/generic/stringparsing.h"
-
 #endif // SIMDJSON_FALLBACK_STRINGPARSING_H
diff --git a/include/simdjson/generic/stringparsing.h b/include/simdjson/generic/stringparsing.h
deleted file mode 100644
index e69de29bb..000000000
diff --git a/include/simdjson/haswell/stringparsing.h b/include/simdjson/haswell/stringparsing.h
index b6028d8f2..88a4d0c8c 100644
--- a/include/simdjson/haswell/stringparsing.h
+++ b/include/simdjson/haswell/stringparsing.h
@@ -43,6 +43,4 @@ simdjson_inline backslash_and_quote backslash_and_quote::copy_and_find(const uin
 } // namespace SIMDJSON_IMPLEMENTATION
 } // namespace simdjson
 
-#include "simdjson/generic/stringparsing.h"
-
 #endif // SIMDJSON_HASWELL_STRINGPARSING_H
diff --git a/include/simdjson/icelake/stringparsing.h b/include/simdjson/icelake/stringparsing.h
index c4c664360..a617735f1 100644
--- a/include/simdjson/icelake/stringparsing.h
+++ b/include/simdjson/icelake/stringparsing.h
@@ -43,6 +43,4 @@ simdjson_inline backslash_and_quote backslash_and_quote::copy_and_find(const uin
 } // namespace SIMDJSON_IMPLEMENTATION
 } // namespace simdjson
 
-#include "simdjson/generic/stringparsing.h"
-
 #endif // SIMDJSON_ICELAKE_STRINGPARSING_H
diff --git a/include/simdjson/ppc64/stringparsing.h b/include/simdjson/ppc64/stringparsing.h
index b187919e0..9a60e449b 100644
--- a/include/simdjson/ppc64/stringparsing.h
+++ b/include/simdjson/ppc64/stringparsing.h
@@ -60,6 +60,4 @@ backslash_and_quote::copy_and_find(const uint8_t *src, uint8_t *dst) {
 } // namespace SIMDJSON_IMPLEMENTATION
 } // namespace simdjson
 
-#include "simdjson/generic/stringparsing.h"
-
 #endif // SIMDJSON_PPC64_STRINGPARSING_H
diff --git a/include/simdjson/westmere/stringparsing.h b/include/simdjson/westmere/stringparsing.h
index 98e0fc5b2..6725fcf1d 100644
--- a/include/simdjson/westmere/stringparsing.h
+++ b/include/simdjson/westmere/stringparsing.h
@@ -41,6 +41,4 @@ simdjson_inline backslash_and_quote backslash_and_quote::copy_and_find(const uin
 } // namespace SIMDJSON_IMPLEMENTATION
 } // namespace simdjson
 
-#include "simdjson/generic/stringparsing.h"
-
 #endif // SIMDJSON_WESTMERE_STRINGPARSING_H
diff --git a/src/generic/stage2/stringparsing.h b/src/generic/stage2/stringparsing.h
index 696fb1110..97e0fa154 100644
--- a/src/generic/stage2/stringparsing.h
+++ b/src/generic/stage2/stringparsing.h
@@ -47,7 +47,12 @@ simdjson_inline bool handle_unicode_codepoint(const uint8_t **src_ptr,
   // multilingual plane check
   uint32_t code_point = jsoncharutils::hex_to_u32_nocheck(*src_ptr + 2);
   *src_ptr += 6;
-  // check for low surrogate for characters outside the Basic
+  if (code_point >= 0xd800 && code_point < 0xdc00) {
+  }
+
+  // If we found a high surrogate, we must
+  // check for low surrogate for characters
+  // outside the Basic
   // Multilingual Plane.
   if (code_point >= 0xd800 && code_point < 0xdc00) {
     if (((*src_ptr)[0] != '\\') || (*src_ptr)[1] != 'u') {
@@ -67,6 +72,10 @@ simdjson_inline bool handle_unicode_codepoint(const uint8_t **src_ptr,
     code_point =
         (((code_point - 0xd800) << 10) | (code_point_2 - 0xdc00)) + 0x10000;
     *src_ptr += 6;
+  } else if (code_point >= 0xdc00 && code_point <= 0xdfff) {
+      // If we encounter a low surrogate (not preceded by a high surrogate)
+      // then we have an error.
+      return false;
   }
   size_t offset = jsoncharutils::codepoint_to_utf8(code_point, *dst_ptr);
   *dst_ptr += offset;
diff --git a/tests/ondemand/ondemand_misc_tests.cpp b/tests/ondemand/ondemand_misc_tests.cpp
index b29d26c02..7325e5b44 100644
--- a/tests/ondemand/ondemand_misc_tests.cpp
+++ b/tests/ondemand/ondemand_misc_tests.cpp
@@ -52,6 +52,17 @@ namespace misc_tests {
     TEST_SUCCEED();
   }
 
+  bool issue1870() {
+    TEST_START();
+    ondemand::parser parser;
+    auto json = R"("\uDC00")"_padded;
+    ondemand::document doc;
+    ASSERT_SUCCESS(parser.iterate(json).get(doc));
+    std::string_view view;
+    ASSERT_ERROR( doc.get_string().get(view), STRING_ERROR );
+    TEST_SUCCEED();
+  }
+
   bool issue1660() {
     TEST_START();
     ondemand::parser parser;
@@ -447,6 +458,7 @@ namespace misc_tests {
 
   bool run() {
     return
+           issue1870() &&
            is_alive_root_array() &&
            is_alive_root_object() &&
            is_alive_array() &&