add error message formatting functions

3 files changed, 72 insertions, 2 deletions

diff --git a/include/aesni/error.h b/include/aesni/error.h
index 54d3d34..47bd0d6 100644
--- a/include/aesni/error.h
+++ b/include/aesni/error.h
@@ -8,6 +8,8 @@
 
 #pragma once
 
+#include <stdlib.h>
+
 #ifdef __cplusplus
 extern "C"
 {
@@ -41,6 +43,13 @@ typedef struct
 }
 AesNI_ErrorDetails;
 
+static __inline AesNI_ErrorCode aesni_get_error_code(const AesNI_ErrorDetails* err_details)
+{
+    return err_details->ec;
+}
+
+size_t aesni_format_error(const AesNI_ErrorDetails*, char*, size_t);
+
 void aesni_make_error_success(AesNI_ErrorDetails*);
 void aesni_make_error_null_argument(AesNI_ErrorDetails*, const char* arg_name);
 void aesni_make_error_invalid_pkcs7_padding(AesNI_ErrorDetails*);
diff --git a/src/error.c b/src/error.c
index c4af82c..e52cd4d 100644
--- a/src/error.c
+++ b/src/error.c
@@ -8,6 +8,8 @@
 
 #include <aesni/all.h>
 
+#include <assert.h>
+#include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
@@ -23,6 +25,56 @@ const char* aesni_strerror(AesNI_ErrorCode ec)
     return err_msgs[ec];
 }
 
+static size_t aesni_format_error_simple(
+    const AesNI_ErrorDetails* err_details,\
+    char* dest,
+    size_t dest_size)
+{
+    const AesNI_ErrorCode ec = aesni_get_error_code(err_details);
+    const char* const msg = aesni_strerror(ec);
+
+    if (dest == NULL && dest_size == 0)
+        return strlen(msg) + 1;
+
+    strncpy(dest, msg, dest_size);
+    dest[dest_size - 1] = '\0';
+    return strlen(dest);
+}
+
+static size_t aesni_format_error_null_argument(
+    const AesNI_ErrorDetails* err_details,
+    char* dest,
+    size_t dest_size)
+{
+    static const char* const fmt = "Invalid argument value NULL (argument name: '%s')";
+    const char* const arg_name = err_details->params.null_arg.arg_name;
+
+    if (dest == NULL && dest_size == 0)
+        return _snprintf(NULL, 0, fmt, arg_name) + 1;
+
+    _snprintf(dest, dest_size, fmt, arg_name);
+    return strlen(dest);
+}
+
+typedef size_t (*AesNI_ErrorFormatter)(const AesNI_ErrorDetails*, char*, size_t);
+
+static AesNI_ErrorFormatter err_formatters[] =
+{
+    &aesni_format_error_simple,
+    &aesni_format_error_null_argument,
+    &aesni_format_error_simple,
+};
+
+size_t aesni_format_error(
+    const AesNI_ErrorDetails* err_details,
+    char* dest,
+    size_t dest_size)
+{
+    assert(err_details);
+
+    return err_formatters[err_details->ec](err_details, dest, dest_size);
+}
+
 static void aesni_make_error(
     AesNI_ErrorDetails* err_details,
     AesNI_ErrorCode ec)
diff --git a/utils/cxx/include/aesnixx/error.hpp b/utils/cxx/include/aesnixx/error.hpp
index af61a32..db390ea 100644
--- a/utils/cxx/include/aesnixx/error.hpp
+++ b/utils/cxx/include/aesnixx/error.hpp
@@ -10,7 +10,11 @@
 
 #include <aesni/all.h>
 
+#include <cstdlib>
+
 #include <stdexcept>
+#include <string>
+#include <vector>
 
 namespace aesni
 {
@@ -24,8 +28,13 @@ namespace aesni
 
         ~ErrorDetailsThrowsInDestructor()
         {
-            if (m_impl.ec != AESNI_ERROR_SUCCESS)
-                throw std::runtime_error(aesni_strerror(m_impl.ec));
+            if (aesni_get_error_code(get()) != AESNI_ERROR_SUCCESS)
+            {
+                std::vector<char> msg;
+                msg.resize(aesni_format_error(get(), NULL, 0));
+                aesni_format_error(get(), msg.data(), msg.size());
+                throw std::runtime_error(std::string(msg.begin(), msg.end()));
+            }
         }
 
         AesNI_ErrorDetails* get() { return &m_impl; }