Add more specific error message when attempting to parse empty input (#4180)

colbychaskell · web-flow · commit 59da644db4e5 · 2023-10-31T20:17:43.000+01:00
diff --git a/docs/mkdocs/docs/home/exceptions.md b/docs/mkdocs/docs/home/exceptions.md
@@ -139,7 +139,7 @@ This error indicates a syntax error while deserializing a JSON text. The error m
     No input:
 
     ```
-    [json.exception.parse_error.101] parse error at line 1, column 1: syntax error while parsing value - unexpected end of input; expected '[', '{', or a literal
+    [json.exception.parse_error.101] parse error at line 1, column 1: attempting to parse an empty input; check that your input string or stream contains the expected JSON
     ```
 
     Control character was not escaped:
diff --git a/include/nlohmann/detail/input/parser.hpp b/include/nlohmann/detail/input/parser.hpp
@@ -341,13 +341,25 @@ class parser
                                                 m_lexer.get_token_string(),
                                                 parse_error::create(101, m_lexer.get_position(), exception_message(token_type::uninitialized, "value"), nullptr));
                     }
+                    case token_type::end_of_input:
+                    {
+                        if (JSON_HEDLEY_UNLIKELY(m_lexer.get_position().chars_read_total == 1))
+                        {
+                            return sax->parse_error(m_lexer.get_position(),
+                                                    m_lexer.get_token_string(),
+                                                    parse_error::create(101, m_lexer.get_position(),
+                                                            "attempting to parse an empty input; check that your input string or stream contains the expected JSON", nullptr));
+                        }
 
+                        return sax->parse_error(m_lexer.get_position(),
+                                                m_lexer.get_token_string(),
+                                                parse_error::create(101, m_lexer.get_position(), exception_message(token_type::literal_or_value, "value"), nullptr));
+                    }
                     case token_type::uninitialized:
                     case token_type::end_array:
                     case token_type::end_object:
                     case token_type::name_separator:
                     case token_type::value_separator:
-                    case token_type::end_of_input:
                     case token_type::literal_or_value:
                     default: // the last token was unexpected
                     {
diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
@@ -12441,13 +12441,25 @@ class parser
                                                 m_lexer.get_token_string(),
                                                 parse_error::create(101, m_lexer.get_position(), exception_message(token_type::uninitialized, "value"), nullptr));
                     }
+                    case token_type::end_of_input:
+                    {
+                        if (JSON_HEDLEY_UNLIKELY(m_lexer.get_position().chars_read_total == 1))
+                        {
+                            return sax->parse_error(m_lexer.get_position(),
+                                                    m_lexer.get_token_string(),
+                                                    parse_error::create(101, m_lexer.get_position(),
+                                                            "attempting to parse an empty input; check that your input string or stream contains the expected JSON", nullptr));
+                        }
 
+                        return sax->parse_error(m_lexer.get_position(),
+                                                m_lexer.get_token_string(),
+                                                parse_error::create(101, m_lexer.get_position(), exception_message(token_type::literal_or_value, "value"), nullptr));
+                    }
                     case token_type::uninitialized:
                     case token_type::end_array:
                     case token_type::end_object:
                     case token_type::name_separator:
                     case token_type::value_separator:
-                    case token_type::end_of_input:
                     case token_type::literal_or_value:
                     default: // the last token was unexpected
                     {
diff --git a/tests/src/unit-diagnostics.cpp b/tests/src/unit-diagnostics.cpp
@@ -74,7 +74,7 @@ TEST_CASE("Better diagnostics")
     SECTION("Parse error")
     {
         json _;
-        CHECK_THROWS_WITH_AS(_ = json::parse(""), "[json.exception.parse_error.101] parse error at line 1, column 1: syntax error while parsing value - unexpected end of input; expected '[', '{', or a literal", json::parse_error);
+        CHECK_THROWS_WITH_AS(_ = json::parse(""), "[json.exception.parse_error.101] parse error at line 1, column 1: attempting to parse an empty input; check that your input string or stream contains the expected JSON", json::parse_error);
     }
 
     SECTION("Wrong type in update()")
diff --git a/tests/src/unit-regression1.cpp b/tests/src/unit-regression1.cpp
@@ -722,7 +722,7 @@ TEST_CASE("regression tests 1")
     {
         std::ifstream f("file_not_found.json");
         json _;
-        CHECK_THROWS_WITH_AS(_ = json::parse(f), "[json.exception.parse_error.101] parse error at line 1, column 1: syntax error while parsing value - unexpected end of input; expected '[', '{', or a literal", json::parse_error&);
+        CHECK_THROWS_WITH_AS(_ = json::parse(f), "[json.exception.parse_error.101] parse error at line 1, column 1: attempting to parse an empty input; check that your input string or stream contains the expected JSON", json::parse_error&);
     }
 
     SECTION("issue #367 - calling stream at EOF")
@@ -736,7 +736,7 @@ TEST_CASE("regression tests 1")
         // ss is not at EOF; this yielded an error before the fix
         // (threw basic_string::append). No, it should just throw
         // a parse error because of the EOF.
-        CHECK_THROWS_WITH_AS(ss >> j, "[json.exception.parse_error.101] parse error at line 1, column 1: syntax error while parsing value - unexpected end of input; expected '[', '{', or a literal", json::parse_error&);
+        CHECK_THROWS_WITH_AS(ss >> j, "[json.exception.parse_error.101] parse error at line 1, column 1: attempting to parse an empty input; check that your input string or stream contains the expected JSON", json::parse_error&);
     }
 
     SECTION("issue #367 - behavior of operator>> should more closely resemble that of built-in overloads")
@@ -745,7 +745,7 @@ TEST_CASE("regression tests 1")
         {
             std::stringstream ss;
             json j;
-            CHECK_THROWS_WITH_AS(ss >> j, "[json.exception.parse_error.101] parse error at line 1, column 1: syntax error while parsing value - unexpected end of input; expected '[', '{', or a literal", json::parse_error&);
+            CHECK_THROWS_WITH_AS(ss >> j, "[json.exception.parse_error.101] parse error at line 1, column 1: attempting to parse an empty input; check that your input string or stream contains the expected JSON", json::parse_error&);
         }
 
         SECTION("(whitespace)")
@@ -765,7 +765,7 @@ TEST_CASE("regression tests 1")
             CHECK_NOTHROW(ss >> j);
             CHECK(j == 111);
 
-            CHECK_THROWS_WITH_AS(ss >> j, "[json.exception.parse_error.101] parse error at line 1, column 1: syntax error while parsing value - unexpected end of input; expected '[', '{', or a literal", json::parse_error&);
+            CHECK_THROWS_WITH_AS(ss >> j, "[json.exception.parse_error.101] parse error at line 1, column 1: attempting to parse an empty input; check that your input string or stream contains the expected JSON", json::parse_error&);
         }
 
         SECTION("one value + whitespace")
@@ -788,7 +788,7 @@ TEST_CASE("regression tests 1")
             CHECK_NOTHROW(ss >> j);
             CHECK(j == 333);
 
-            CHECK_THROWS_WITH_AS(ss >> j, "[json.exception.parse_error.101] parse error at line 1, column 1: syntax error while parsing value - unexpected end of input; expected '[', '{', or a literal", json::parse_error&);
+            CHECK_THROWS_WITH_AS(ss >> j, "[json.exception.parse_error.101] parse error at line 1, column 1: attempting to parse an empty input; check that your input string or stream contains the expected JSON", json::parse_error&);
         }
 
         SECTION("three values")
@@ -803,7 +803,7 @@ TEST_CASE("regression tests 1")
             CHECK_NOTHROW(ss >> j);
             CHECK(j == 333);
 
-            CHECK_THROWS_WITH_AS(ss >> j, "[json.exception.parse_error.101] parse error at line 1, column 1: syntax error while parsing value - unexpected end of input; expected '[', '{', or a literal", json::parse_error&);
+            CHECK_THROWS_WITH_AS(ss >> j, "[json.exception.parse_error.101] parse error at line 1, column 1: attempting to parse an empty input; check that your input string or stream contains the expected JSON", json::parse_error&);
         }
 
         SECTION("literals without whitespace")
@@ -820,7 +820,7 @@ TEST_CASE("regression tests 1")
             CHECK_NOTHROW(ss >> j);
             CHECK(j == "");
 
-            CHECK_THROWS_WITH_AS(ss >> j, "[json.exception.parse_error.101] parse error at line 1, column 1: syntax error while parsing value - unexpected end of input; expected '[', '{', or a literal", json::parse_error&);
+            CHECK_THROWS_WITH_AS(ss >> j, "[json.exception.parse_error.101] parse error at line 1, column 1: attempting to parse an empty input; check that your input string or stream contains the expected JSON", json::parse_error&);
         }
 
         SECTION("example from #529")
@@ -833,7 +833,7 @@ TEST_CASE("regression tests 1")
             CHECK_NOTHROW(ss >> j);
             CHECK(j == json({{"three", 3}}));
 
-            CHECK_THROWS_WITH_AS(ss >> j, "[json.exception.parse_error.101] parse error at line 1, column 1: syntax error while parsing value - unexpected end of input; expected '[', '{', or a literal", json::parse_error&);
+            CHECK_THROWS_WITH_AS(ss >> j, "[json.exception.parse_error.101] parse error at line 1, column 1: attempting to parse an empty input; check that your input string or stream contains the expected JSON", json::parse_error&);
         }
 
         SECTION("second example from #529")

Original file line number	Diff line number	Diff line change
`@@ -74,7 +74,7 @@ TEST_CASE("Better diagnostics")`
`74`	`74`	`SECTION("Parse error")`
`75`	`75`	`{`
`76`	`76`	`json _;`
`77`		`- CHECK_THROWS_WITH_AS(_ = json::parse(""), "[json.exception.parse_error.101] parse error at line 1, column 1: syntax error while parsing value - unexpected end of input; expected '[', '{', or a literal", json::parse_error);`
	`77`	`+ CHECK_THROWS_WITH_AS(_ = json::parse(""), "[json.exception.parse_error.101] parse error at line 1, column 1: attempting to parse an empty input; check that your input string or stream contains the expected JSON", json::parse_error);`
`78`	`78`	`}`
`79`	`79`
`80`	`80`	`SECTION("Wrong type in update()")`
Original file line number	Diff line number	Diff line change
`@@ -722,7 +722,7 @@ TEST_CASE("regression tests 1")`
`722`	`722`	`{`
`723`	`723`	`std::ifstream f("file_not_found.json");`
`724`	`724`	`json _;`
`725`		`- CHECK_THROWS_WITH_AS(_ = json::parse(f), "[json.exception.parse_error.101] parse error at line 1, column 1: syntax error while parsing value - unexpected end of input; expected '[', '{', or a literal", json::parse_error&);`
	`725`	`+ CHECK_THROWS_WITH_AS(_ = json::parse(f), "[json.exception.parse_error.101] parse error at line 1, column 1: attempting to parse an empty input; check that your input string or stream contains the expected JSON", json::parse_error&);`
`726`	`726`	`}`
`727`	`727`
`728`	`728`	`SECTION("issue #367 - calling stream at EOF")`
`@@ -736,7 +736,7 @@ TEST_CASE("regression tests 1")`
`736`	`736`	`// ss is not at EOF; this yielded an error before the fix`
`737`	`737`	`// (threw basic_string::append). No, it should just throw`
`738`	`738`	`// a parse error because of the EOF.`
`739`		`- CHECK_THROWS_WITH_AS(ss >> j, "[json.exception.parse_error.101] parse error at line 1, column 1: syntax error while parsing value - unexpected end of input; expected '[', '{', or a literal", json::parse_error&);`
	`739`	`+ CHECK_THROWS_WITH_AS(ss >> j, "[json.exception.parse_error.101] parse error at line 1, column 1: attempting to parse an empty input; check that your input string or stream contains the expected JSON", json::parse_error&);`
`740`	`740`	`}`
`741`	`741`
`742`	`742`	`SECTION("issue #367 - behavior of operator>> should more closely resemble that of built-in overloads")`
`@@ -745,7 +745,7 @@ TEST_CASE("regression tests 1")`
`745`	`745`	`{`
`746`	`746`	`std::stringstream ss;`
`747`	`747`	`json j;`
`748`		`- CHECK_THROWS_WITH_AS(ss >> j, "[json.exception.parse_error.101] parse error at line 1, column 1: syntax error while parsing value - unexpected end of input; expected '[', '{', or a literal", json::parse_error&);`
	`748`	`+ CHECK_THROWS_WITH_AS(ss >> j, "[json.exception.parse_error.101] parse error at line 1, column 1: attempting to parse an empty input; check that your input string or stream contains the expected JSON", json::parse_error&);`
`749`	`749`	`}`
`750`	`750`
`751`	`751`	`SECTION("(whitespace)")`
`@@ -765,7 +765,7 @@ TEST_CASE("regression tests 1")`
`765`	`765`	`CHECK_NOTHROW(ss >> j);`
`766`	`766`	`CHECK(j == 111);`
`767`	`767`
`768`		`- CHECK_THROWS_WITH_AS(ss >> j, "[json.exception.parse_error.101] parse error at line 1, column 1: syntax error while parsing value - unexpected end of input; expected '[', '{', or a literal", json::parse_error&);`
	`768`	`+ CHECK_THROWS_WITH_AS(ss >> j, "[json.exception.parse_error.101] parse error at line 1, column 1: attempting to parse an empty input; check that your input string or stream contains the expected JSON", json::parse_error&);`
`769`	`769`	`}`
`770`	`770`
`771`	`771`	`SECTION("one value + whitespace")`
`@@ -788,7 +788,7 @@ TEST_CASE("regression tests 1")`
`788`	`788`	`CHECK_NOTHROW(ss >> j);`
`789`	`789`	`CHECK(j == 333);`
`790`	`790`
`791`		`- CHECK_THROWS_WITH_AS(ss >> j, "[json.exception.parse_error.101] parse error at line 1, column 1: syntax error while parsing value - unexpected end of input; expected '[', '{', or a literal", json::parse_error&);`
	`791`	`+ CHECK_THROWS_WITH_AS(ss >> j, "[json.exception.parse_error.101] parse error at line 1, column 1: attempting to parse an empty input; check that your input string or stream contains the expected JSON", json::parse_error&);`
`792`	`792`	`}`
`793`	`793`
`794`	`794`	`SECTION("three values")`
`@@ -803,7 +803,7 @@ TEST_CASE("regression tests 1")`
`803`	`803`	`CHECK_NOTHROW(ss >> j);`
`804`	`804`	`CHECK(j == 333);`
`805`	`805`
`806`		`- CHECK_THROWS_WITH_AS(ss >> j, "[json.exception.parse_error.101] parse error at line 1, column 1: syntax error while parsing value - unexpected end of input; expected '[', '{', or a literal", json::parse_error&);`
	`806`	`+ CHECK_THROWS_WITH_AS(ss >> j, "[json.exception.parse_error.101] parse error at line 1, column 1: attempting to parse an empty input; check that your input string or stream contains the expected JSON", json::parse_error&);`
`807`	`807`	`}`
`808`	`808`
`809`	`809`	`SECTION("literals without whitespace")`
`@@ -820,7 +820,7 @@ TEST_CASE("regression tests 1")`
`820`	`820`	`CHECK_NOTHROW(ss >> j);`
`821`	`821`	`CHECK(j == "");`
`822`	`822`
`823`		`- CHECK_THROWS_WITH_AS(ss >> j, "[json.exception.parse_error.101] parse error at line 1, column 1: syntax error while parsing value - unexpected end of input; expected '[', '{', or a literal", json::parse_error&);`
	`823`	`+ CHECK_THROWS_WITH_AS(ss >> j, "[json.exception.parse_error.101] parse error at line 1, column 1: attempting to parse an empty input; check that your input string or stream contains the expected JSON", json::parse_error&);`
`824`	`824`	`}`
`825`	`825`
`826`	`826`	`SECTION("example from #529")`
`@@ -833,7 +833,7 @@ TEST_CASE("regression tests 1")`
`833`	`833`	`CHECK_NOTHROW(ss >> j);`
`834`	`834`	`CHECK(j == json({{"three", 3}}));`
`835`	`835`
`836`		`- CHECK_THROWS_WITH_AS(ss >> j, "[json.exception.parse_error.101] parse error at line 1, column 1: syntax error while parsing value - unexpected end of input; expected '[', '{', or a literal", json::parse_error&);`
	`836`	`+ CHECK_THROWS_WITH_AS(ss >> j, "[json.exception.parse_error.101] parse error at line 1, column 1: attempting to parse an empty input; check that your input string or stream contains the expected JSON", json::parse_error&);`
`837`	`837`	`}`
`838`	`838`
`839`	`839`	`SECTION("second example from #529")`