Add assertion if nullptr is passed to parse function

docs/mkdocs/docs/api/basic_json/accept.md

@@ -64,6 +64,10 @@ Whether the input is valid JSON.
 
 Strong guarantee: if an exception is thrown, there are no changes in the JSON value.
 
+## Exceptions
+
+Throws [`parse_error.116`](../../home/exceptions.md#jsonexceptionparse_error116) if passed `#!cpp FILE` pointer is `#!cpp nullptr`.
+
 ## Complexity
 
 Linear in the length of the input. The parser is a predictive LL(1) parser.

docs/mkdocs/docs/api/basic_json/parse.md

@@ -71,6 +71,14 @@ Deserialized JSON value; in case of a parse error and `allow_exceptions` set to
 
 Strong guarantee: if an exception is thrown, there are no changes in the JSON value.
 
+## Exceptions
+
+- Throws [`parse_error.101`](../../home/exceptions.md#jsonexceptionparse_error101) in case of an unexpected token.
+- Throws [`parse_error.102`](../../home/exceptions.md#jsonexceptionparse_error102) if to_unicode fails or surrogate
+  error.
+- Throws [`parse_error.103`](../../home/exceptions.md#jsonexceptionparse_error103) if to_unicode fails.
+- Throws [`parse_error.116`](../../home/exceptions.md#jsonexceptionparse_error116) if passed `#!cpp FILE` pointer is `#!cpp nullptr`.
+
 ## Complexity
 
 Linear in the length of the input. The parser is a predictive LL(1) parser. The complexity can be higher if the parser

docs/mkdocs/docs/home/exceptions.md

@@ -354,6 +354,16 @@ A UBJSON high-precision number could not be parsed.
     [json.exception.parse_error.115] parse error at byte 5: syntax error while parsing UBJSON high-precision number: invalid number text: 1A
     ```
 
+### json.exception.parse_error.116
+
+A `#!cpp FILE*` pointer passed to the [parse](../api/basic_json/parse.md) function is `#!cpp nullptr`; that is, a previous call to `#!cpp std::fopen` failed.
+
+!!! failure "Example message"
+
+    ```
+    [json.exception.parse_error.116] parse error: input file is invalid
+    ```
+
 ## Iterator errors
 
 This exception is thrown if iterators passed to a library function do not match

include/nlohmann/detail/input/input_adapters.hpp

@@ -24,6 +24,7 @@
 #endif                  // JSON_NO_IO
 
 #include <nlohmann/detail/iterators/iterator_traits.hpp>
+#include <nlohmann/detail/exceptions.hpp>
 #include <nlohmann/detail/macro_scope.hpp>
 
 namespace nlohmann
@@ -48,9 +49,14 @@ class file_input_adapter
     using char_type = char;
 
     JSON_HEDLEY_NON_NULL(2)
-    explicit file_input_adapter(std::FILE* f) noexcept
+    explicit file_input_adapter(std::FILE* f)
         : m_file(f)
-    {}
+    {
+        if (m_file == nullptr)
+        {
+            JSON_THROW(parse_error::create(116, 0, "input file is invalid", nullptr));
+        }
+    }
 
     // make class move-only
     file_input_adapter(const file_input_adapter&) = delete;

single_include/nlohmann/json.hpp

@@ -5909,6 +5909,8 @@ std::size_t hash(const BasicJsonType& j)
 
 // #include <nlohmann/detail/iterators/iterator_traits.hpp>
 
+// #include <nlohmann/detail/exceptions.hpp>
+
 // #include <nlohmann/detail/macro_scope.hpp>
 
 
@@ -5934,9 +5936,14 @@ class file_input_adapter
     using char_type = char;
 
     JSON_HEDLEY_NON_NULL(2)
-    explicit file_input_adapter(std::FILE* f) noexcept
+    explicit file_input_adapter(std::FILE* f)
         : m_file(f)
-    {}
+    {
+        if (m_file == nullptr)
+        {
+            JSON_THROW(parse_error::create(116, 0, "input file is invalid", nullptr));
+        }
+    }
 
     // make class move-only
     file_input_adapter(const file_input_adapter&) = delete;

tests/src/unit-deserialization.cpp

@@ -166,6 +166,21 @@ struct SaxEventLoggerExitAfterStartArray : public SaxEventLogger
 };
 } // namespace
 
+// Passing a NULL pointer to the input adapter violates its NON_NULL attribute which is detected by UBSAN.
+// To still test whether exceptions are thrown, we need to exclude these tests from UBSAN which can only
+// be done with a function attribute. See
+// https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html#disabling-instrumentation-with-attribute-no-sanitize-undefined
+#if defined(__clang__)
+    __attribute__((no_sanitize("undefined")))
+#endif
+void test_file_exception()
+{
+    std::FILE* f = std::fopen("nonexisting_file", "r"); // NOLINT(cppcoreguidelines-owning-memory)
+    json _;
+    CHECK_THROWS_WITH_AS(_ = json::parse(f), "[json.exception.parse_error.116] parse error: input file is invalid", json::parse_error&);
+    CHECK_THROWS_WITH_AS(_ = json::accept(f), "[json.exception.parse_error.116] parse error: input file is invalid", json::parse_error&);
+}
+
 TEST_CASE("deserialization")
 {
     SECTION("successful deserialization")
@@ -332,6 +347,11 @@ TEST_CASE("deserialization")
         {
             CHECK_THROWS_WITH_AS("[\"foo\",1,2,3,false,{\"one\":1}"_json, "[json.exception.parse_error.101] parse error at line 1, column 29: syntax error while parsing array - unexpected end of input; expected ']'", json::parse_error&);
         }
+
+        SECTION("FILE*")
+        {
+            test_file_exception();
+        }
     }
 
     SECTION("contiguous containers")