apply_chat_template C API design in tokenizer

include/ortx_tokenizer.h

@@ -5,6 +5,7 @@
 
 #pragma once
 
+#include <stdbool.h>
 #include "ortx_utils.h"
 
 #ifdef __cplusplus
@@ -76,7 +77,6 @@ extError_t ORTX_API_CALL OrtxCreateTokenizerFromBlob(OrtxTokenizer** tokenizer,
 extError_t ORTX_API_CALL OrtxTokenize(
     const OrtxTokenizer* tokenizer, const char* input[], size_t batch_size, OrtxTokenId2DArray** output);
 
-
 /**
  * Converts a token to its corresponding ID.
  *
@@ -171,6 +171,26 @@ extError_t ORTX_API_CALL OrtxTokenId2DArrayGetBatch(const OrtxTokenId2DArray* to
 extError_t ORTX_API_CALL OrtxTokenId2DArrayGetItem(
     const OrtxTokenId2DArray* token_id_2d_array, size_t index, const extTokenId_t** item, size_t* length);
 
+/**
+ * @brief Applies a chat template to the given input.
+ *
+ * This function processes the specified template with the provided input using the
+ * tokenizer, and outputs the resulting string array. Optionally, it can include a
+ * generation prompt in the output. The chat template can be provided as a string or
+ * be retrieved from a loaded tokenizer json file which contains the chat template its json file.
+ * if both tokenizer and template_str are provided, the template_str will supersede the tokenizer.
+ *
+ * @param tokenizer Pointer to an OrtxTokenizer used for template processing
+ * @param template_str Null-terminated string representing the chat template, can be null if tokenizer.json has one.
+ * @param input Null-terminated string containing the input to be processed.
+ * @param output Double pointer to an OrtxStringArray that will be populated with the output strings.
+ * @param add_generation_prompt Indicates whether to add a generation prompt to the output (defaults to true).
+ * @return extError_t Returns an error code indicating success or the type of failure.
+ */
+extError_t ORTX_API_CALL OrtxApplyChatTemplate(const OrtxTokenizer* tokenizer, const char* template_str,
+                                               const char* input, OrtxStringArray** output,
+                                               bool add_generation_prompt);
+
 #ifdef __cplusplus
 }
 #endif

shared/api/c_api_tokenizer.cc

@@ -304,5 +304,28 @@ extError_t ORTX_API_CALL OrtxDetokenizeCached(const OrtxTokenizer* tokenizer, Or
     *text_out = cache_ptr->last_text_.c_str();
   }
 
+  return status.Code();
+}
+
+extError_t ORTX_API_CALL OrtxApplyChatTemplate(const OrtxTokenizer* tokenizer, const char* template_str,
+                                               const char* input, OrtxStringArray** output,
+                                               bool add_generation_prompt) {
+  if (tokenizer == nullptr || output == nullptr) {
+    ReturnableStatus::last_error_message_ = "both tokenizer and template_str are null, no template to apply";
+    return kOrtxErrorInvalidArgument;
+  }
+
+  const auto token_ptr = static_cast<const TokenizerImpl*>(tokenizer);
+  ReturnableStatus status(token_ptr->IsInstanceOf(extObjectKind_t::kOrtxKindTokenizer));
+  if (!status.IsOk()) {
+    return status.Code();
+  }
+
+
+  auto result = std::make_unique<ort_extensions::StringArray>().release();
+  result->SetStrings(std::vector<std::string>({"<s>[INST] hello [/INST]response</s>[INST] again [/INST]response</s>"}));
+  *output = static_cast<OrtxStringArray*>(result);
+
+
   return status.Code();
 }

test/pp_api_test/test_tokenizer.cc

@@ -611,3 +611,18 @@ TEST(OrtxTokenizerTest, AddedTokensTest) {
   DumpTokenIds(token_ids);
   EXPECT_EQ(token_ids[0], EXPECTED_IDS_0);
 }
+
+TEST(OrtxTokenizerTest, Llama2ChatTemplate) {
+  OrtxObjectPtr<OrtxTokenizer> tokenizer(OrtxCreateTokenizer, "data/llama2");
+  ASSERT_EQ(tokenizer.Code(), kOrtxOK) << "Failed to create tokenizer, stopping the test.";
+
+  OrtxObjectPtr<OrtxStringArray> templated_text;
+  auto err = OrtxApplyChatTemplate(
+    tokenizer.get(), nullptr,
+    "{\"role\": \"user\", \"content\": \"hello\"},", templated_text.ToBeAssigned(), true);
+
+  ASSERT_EQ(err, kOrtxOK) << "Failed to apply chat template, stopping the test.";
+  const char* text = nullptr;
+  OrtxStringArrayGetItem(templated_text.get(), 0, &text);
+  EXPECT_STREQ(text, "<s>[INST] hello [/INST]response</s>[INST] again [/INST]response</s>");
+}