CorDebugStringValue internally returning HRESULT.E_INVALID_ARG - triggering error flow

[christophediericx]

Trying to call public HRESULT TryGetString(out string szStringResult) goes off the rails in the following snippet:

int cchString = 0;
int pcchString;
char[] szString;
HRESULT hr = Raw.GetString(cchString, out pcchString, null);

if (hr != HRESULT.S_FALSE && hr != HRESULT.ERROR_INSUFFICIENT_BUFFER && hr != HRESULT.S_OK)
  goto fail;

Raw.GetString returns HRESULT E_INVALIDARG (because of the null?), thus triggering the "fail" path.

This happens with the latest build as was provided in #13

[lordmilko]

Which interface is this for? ICorDebugStringValue?

[christophediericx]

Yes, that is correct.

[lordmilko]

ClrDebug assumes that anything that is an array can be retrieved via a two stage process, asking for the length and then creating a buffer with the required length. Some APIs don't actually allow for a two stage query, and require you to figure out the length yourself. I fix rare methods like this as I encounter them. I have confirmed from the implementation of CordbObjectValue::GetString that it requires a valid buffer be specified in the first place, using a length retrieved from ICorDebugStringValue.GetLength. I will update this method to use manual query semantics

[christophediericx]

Playing around with the interface it looks like the two stage process approach would still work as long as what is being passed in is not null initially, e.g., the following works fine.

CorDebugStringValue stringVal = val.As<CorDebugStringValue>();
char[] charBuff = Array.Empty<char>();
stringVal.Raw.GetString(1024, out int len, charBuff);
charBuff = new char[len];
stringVal.Raw.GetString(len, out int _len, charBuff);
string v = new(charBuff, 0, _len);

But as you mentioned, since Length is correctly populated on ICorDebugStringValue anyway there is probably not even a need for a second pass.

[lordmilko]

Hi @christophediericx,

Please try the latest build

Regards,
lordmilko

[christophediericx]

Works like a charm - thank you!