Better error reporting for FFI

Previously safe_get(x) where x was null would return an error
about an exception being thrown, instead of a null pointer error.

3 files changed, 18 insertions, 6 deletions

diff --git a/src/lib/ffi/ffi_kdf.cpp b/src/lib/ffi/ffi_kdf.cpp
index 3b907e967..479bf2140 100644
--- a/src/lib/ffi/ffi_kdf.cpp
+++ b/src/lib/ffi/ffi_kdf.cpp
@@ -91,7 +91,7 @@ int botan_bcrypt_generate(uint8_t* out, size_t* out_len,
          return BOTAN_FFI_ERROR_BAD_FLAG;
 
       if(wf < 4 || wf > 18)
-         throw FFI_Error("Bad bcrypt work factor " + std::to_string(wf));
+         throw FFI_Error("Bad bcrypt work factor " + std::to_string(wf), BOTAN_FFI_ERROR_BAD_PARAMETER);
 
       Botan::RandomNumberGenerator& rng = safe_get(rng_obj);
       const std::string bcrypt = Botan::generate_bcrypt(pass, rng, static_cast<uint16_t>(wf));
diff --git a/src/lib/ffi/ffi_mp.cpp b/src/lib/ffi/ffi_mp.cpp
index cbd784d7a..17d5d19c7 100644
--- a/src/lib/ffi/ffi_mp.cpp
+++ b/src/lib/ffi/ffi_mp.cpp
@@ -114,7 +114,7 @@ int botan_mp_to_str(const botan_mp_t mp, uint8_t digit_base, char* out, size_t*
       else if(digit_base == 16)
          base = Botan::BigInt::Hexadecimal;
       else
-         throw FFI_Error("botan_mp_to_str invalid digit base");
+         throw FFI_Error("botan_mp_to_str invalid digit base", BOTAN_FFI_ERROR_BAD_PARAMETER);
 
       std::vector<uint8_t> hex = Botan::BigInt::encode(bn, base);
       hex.push_back(0); // null terminator
diff --git a/src/lib/ffi/ffi_util.h b/src/lib/ffi/ffi_util.h
index 2aa0edd83..623b4bf20 100644
--- a/src/lib/ffi/ffi_util.h
+++ b/src/lib/ffi/ffi_util.h
@@ -18,7 +18,15 @@ namespace Botan_FFI {
 class BOTAN_UNSTABLE_API FFI_Error final : public Botan::Exception
    {
    public:
-      explicit FFI_Error(const std::string& what) : Exception("FFI error", what) {}
+      FFI_Error(const std::string& what, int err_code) :
+         Exception("FFI error", what),
+         m_err_code(err_code)
+         {}
+
+      int error_code() const { return m_err_code; }
+
+   private:
+      int m_err_code;
    };
 
 template<typename T, uint32_t MAGIC>
@@ -50,15 +58,15 @@ template<typename T, uint32_t M>
 T& safe_get(botan_struct<T,M>* p)
    {
    if(!p)
-      throw FFI_Error("Null pointer argument");
+      throw FFI_Error("Null pointer argument", BOTAN_FFI_ERROR_NULL_POINTER);
    if(p->magic_ok() == false)
-      throw FFI_Error("Bad magic in ffi object");
+      throw FFI_Error("Bad magic in ffi object", BOTAN_FFI_ERROR_INVALID_OBJECT);
 
    T* t = p->unsafe_get();
    if(t)
       return *t;
    else
-      throw FFI_Error("Invalid object pointer");
+      throw FFI_Error("Invalid object pointer", BOTAN_FFI_ERROR_INVALID_OBJECT);
    }
 
 template<typename Thunk>
@@ -72,6 +80,10 @@ int ffi_guard_thunk(const char* func_name, Thunk thunk)
       {
       return ffi_error_exception_thrown(func_name, "bad_alloc", BOTAN_FFI_ERROR_OUT_OF_MEMORY);
       }
+   catch(Botan_FFI::FFI_Error& e)
+      {
+      return ffi_error_exception_thrown(func_name, e.what(), e.error_code());
+      }
    catch(Botan::Key_Not_Set& e)
       {
       return ffi_error_exception_thrown(func_name, e.what(), BOTAN_FFI_ERROR_KEY_NOT_SET);