lix/src/libutil/json-utils.cc
Felix Uhl 3fefc2b284 Fix derivation load assertion errors
When loading a derivation from a JSON, malformed input would trigger
cryptic "assertion failed" errors. Simply replacing calls to `operator []`
with calls to `.at()` was not enough, as this would cause json.execptions
to be printed verbatim.

Display nice error messages instead and give some indication where the
error happened.

*Before:*

```
$ echo 4 | nix derivation add
error: [json.exception.type_error.305] cannot use operator[] with a string argument with number

$ nix derivation show nixpkgs#hello | nix derivation add
Assertion failed: (it != m_value.object->end()), function operator[], file /nix/store/8h9pxgq1776ns6qi5arx08ifgnhmgl22-nlohmann_json-3.11.2/include/nlohmann/json.hpp, line 2135.

$ nix derivation show nixpkgs#hello | jq '.[] | .name = 5' | nix derivation add
error: [json.exception.type_error.302] type must be string, but is object

$ nix derivation show nixpkgs#hello | jq '.[] | .outputs = { out: "/nix/store/8j3f8j-hello" }' | nix derivation add
error: [json.exception.type_error.302] type must be object, but is string

```

*After:*

```
$ echo 4 | nix derivation add
error: Expected JSON of derivation to be of type 'object', but it is of type 'number'

$ nix derivation show nixpkgs#hello | nix derivation add
error: Expected JSON object to contain key 'name' but it doesn't

$ nix derivation show nixpkgs#hello | jq '.[] | .name = 5' | nix derivation add
error: Expected JSON value to be of type 'string' but it is of type 'number'

$ nix derivation show nixpkgs#hello | jq '.[] | .outputs = { out: "/nix/store/8j3f8j-hello" }' | nix derivation add
error:
       … while reading key 'outputs'

       error: Expected JSON value to be of type 'object' but it is of type 'string'
```
2023-08-05 01:34:30 +02:00

44 lines
988 B
C++

#include "json-utils.hh"
#include "error.hh"
namespace nix {
const nlohmann::json * get(const nlohmann::json & map, const std::string & key)
{
auto i = map.find(key);
if (i == map.end()) return nullptr;
return &*i;
}
nlohmann::json * get(nlohmann::json & map, const std::string & key)
{
auto i = map.find(key);
if (i == map.end()) return nullptr;
return &*i;
}
const nlohmann::json & valueAt(
const nlohmann::json & map,
const std::string & key)
{
if (!map.contains(key))
throw Error("Expected JSON object to contain key '%s' but it doesn't", key);
return map[key];
}
const nlohmann::json & ensureType(
const nlohmann::json & value,
nlohmann::json::value_type expectedType
)
{
if (value.type() != expectedType)
throw Error(
"Expected JSON value to be of type '%s' but it is of type '%s'",
nlohmann::json(expectedType).type_name(),
value.type_name());
return value;
}
}