[WIP] Drop the deprecated binary format.

include/xgboost/learner.h

@@ -1,5 +1,5 @@
 /**
- * Copyright 2015-2023 by XGBoost Contributors
+ * Copyright 2015-2025, XGBoost Contributors
  * \file learner.h
  * \brief Learner interface that integrates objective, gbm and evaluation together.
  *  This is the user facing XGBoost training module.
@@ -151,9 +151,6 @@ class Learner : public Model, public Configurable, public dmlc::Serializable {
   void LoadModel(Json const& in) override = 0;
   void SaveModel(Json* out) const override = 0;
 
-  virtual void LoadModel(dmlc::Stream* fi) = 0;
-  virtual void SaveModel(dmlc::Stream* fo) const = 0;
-
   /*!
    * \brief Set multiple parameters at once.
    *

include/xgboost/model.h

@@ -1,15 +1,12 @@
-/*!
- * Copyright (c) 2019 by Contributors
- * \file model.h
- * \brief Defines the abstract interface for different components in XGBoost.
+/**
+ * Copyright 2019-2025, XGBoost Contributors
+ *
+ * @file model.h
+ * @brief Defines the abstract interface for different components in XGBoost.
  */
 #ifndef XGBOOST_MODEL_H_
 #define XGBOOST_MODEL_H_
 
-namespace dmlc {
-class Stream;
-}  // namespace dmlc
-
 namespace xgboost {
 
 class Json;

include/xgboost/tree_model.h

@@ -365,17 +365,6 @@ class RegTree : public Model {
     return stats_[nid];
   }
 
-  /*!
-   * \brief load model from stream
-   * \param fi input stream
-   */
-  void Load(dmlc::Stream* fi);
-  /*!
-   * \brief save model to stream
-   * \param fo output stream
-   */
-  void Save(dmlc::Stream* fo) const;
-
   void LoadModel(Json const& in) override;
   void SaveModel(Json* out) const override;
 

src/c_api/c_api.cc

@@ -1368,7 +1368,38 @@ XGB_DLL int XGBoosterPredictFromCUDAColumnar(BoosterHandle handle, char const *,
 }
 #endif  // !defined(XGBOOST_USE_CUDA)
 
-XGB_DLL int XGBoosterLoadModel(BoosterHandle handle, const char* fname) {
+namespace {
+template <typename Buffer, typename Iter = typename Buffer::const_iterator>
+Json DispatchModelType(Buffer const &buffer, StringView ext, bool warn) {
+  auto first_non_space = [&](Iter beg, Iter end) {
+    for (auto i = beg; i != end; ++i) {
+      if (!std::isspace(*i)) {
+        return i;
+      }
+    }
+    return end;
+  };
+
+  Json model;
+  auto it = first_non_space(buffer.cbegin() + 1, buffer.cend());
+  if (it != buffer.cend() && *it == '"') {
+    if (warn) {
+      LOG(WARNING) << "Unknown file format: `" << ext << "`. Using JSON as a guess.";
+    }
+    model = Json::Load(StringView{buffer.data(), buffer.size()});
+  } else if (it != buffer.cend() && std::isalpha(*it)) {
+    if (warn) {
+      LOG(WARNING) << "Unknown file format: `" << ext << "`. Using UBJ as a guess.";
+    }
+    model = Json::Load(StringView{buffer.data(), buffer.size()}, std::ios::binary);
+  } else {
+    LOG(FATAL) << "Invalid model format";
+  }
+  return model;
+}
+}  // namespace
+
+XGB_DLL int XGBoosterLoadModel(BoosterHandle handle, const char *fname) {
   API_BEGIN();
   CHECK_HANDLE();
   xgboost_CHECK_C_ARG_PTR(fname);
@@ -1378,28 +1409,23 @@ XGB_DLL int XGBoosterLoadModel(BoosterHandle handle, const char* fname) {
     CHECK_EQ(str[0], '{');
     return str;
   };
-  if (common::FileExtension(fname) == "json") {
+  auto ext = common::FileExtension(fname);
+  if (ext == "json") {
     auto buffer = read_file();
     Json in{Json::Load(StringView{buffer.data(), buffer.size()})};
-    static_cast<Learner*>(handle)->LoadModel(in);
-  } else if (common::FileExtension(fname) == "ubj") {
+    static_cast<Learner *>(handle)->LoadModel(in);
+  } else if (ext == "ubj") {
     auto buffer = read_file();
     Json in = Json::Load(StringView{buffer.data(), buffer.size()}, std::ios::binary);
     static_cast<Learner *>(handle)->LoadModel(in);
   } else {
-    std::unique_ptr<dmlc::Stream> fi(dmlc::Stream::Create(fname, "r"));
-    static_cast<Learner*>(handle)->LoadModel(fi.get());
+    auto buffer = read_file();
+    auto in = DispatchModelType(buffer, ext, true);
+    static_cast<Learner *>(handle)->LoadModel(in);
   }
   API_END();
 }
 
-namespace {
-void WarnOldModel() {
-  LOG(WARNING) << "Saving into deprecated binary model format, please consider using `json` or "
-                  "`ubj`. Model format is default to UBJSON in XGBoost 2.1 if not specified.";
-}
-}  // anonymous namespace
-
 XGB_DLL int XGBoosterSaveModel(BoosterHandle handle, const char *fname) {
   API_BEGIN();
   CHECK_HANDLE();
@@ -1419,13 +1445,9 @@ XGB_DLL int XGBoosterSaveModel(BoosterHandle handle, const char *fname) {
     save_json(std::ios::out);
   } else if (common::FileExtension(fname) == "ubj") {
     save_json(std::ios::binary);
-  } else if (common::FileExtension(fname) == "deprecated") {
-    WarnOldModel();
-    auto *bst = static_cast<Learner *>(handle);
-    bst->SaveModel(fo.get());
   } else {
     LOG(WARNING) << "Saving model in the UBJSON format as default.  You can use file extension:"
-                    " `json`, `ubj` or `deprecated` to choose between formats.";
+                    " `json` or `ubj` to choose between formats.";
     save_json(std::ios::binary);
   }
   API_END();
@@ -1436,9 +1458,11 @@ XGB_DLL int XGBoosterLoadModelFromBuffer(BoosterHandle handle, const void *buf,
   API_BEGIN();
   CHECK_HANDLE();
   xgboost_CHECK_C_ARG_PTR(buf);
-
+  auto buffer = common::Span<char const>{static_cast<char const *>(buf), len};
+  // Don't warn, we have to guess the format with buffer input.
+  auto in = DispatchModelType(buffer, "", false);
   common::MemoryFixSizeBuffer fs((void *)buf, len);  // NOLINT(*)
-  static_cast<Learner *>(handle)->LoadModel(&fs);
+  static_cast<Learner *>(handle)->LoadModel(in);
   API_END();
 }
 
@@ -1471,15 +1495,6 @@ XGB_DLL int XGBoosterSaveModelToBuffer(BoosterHandle handle, char const *json_co
     save_json(std::ios::out);
   } else if (format == "ubj") {
     save_json(std::ios::binary);
-  } else if (format == "deprecated") {
-    WarnOldModel();
-    auto &raw_str = learner->GetThreadLocal().ret_str;
-    raw_str.clear();
-    common::MemoryBufferStream fo(&raw_str);
-    learner->SaveModel(&fo);
-
-    *out_dptr = dmlc::BeginPtr(raw_str);
-    *out_len = static_cast<xgboost::bst_ulong>(raw_str.size());
   } else {
     LOG(FATAL) << "Unknown format: `" << format << "`";
   }

src/gbm/gblinear.cc

@@ -101,13 +101,6 @@ class GBLinear : public GradientBooster {
 
   bool ModelFitted() const override { return BoostedRounds() != 0; }
 
-  void Load(dmlc::Stream* fi) override {
-    model_.Load(fi);
-  }
-  void Save(dmlc::Stream* fo) const override {
-    model_.Save(fo);
-  }
-
   void SaveModel(Json* p_out) const override {
     auto& out = *p_out;
     out["name"] = String{"gblinear"};

src/gbm/gblinear_model.cc

@@ -1,9 +1,8 @@
-/*!
- * Copyright 2019-2022 by Contributors
+/**
+ * Copyright 2019-2025, XGBoost Contributors
  */
 #include <algorithm>
 #include <utility>
-#include <limits>
 #include "xgboost/json.h"
 #include "gblinear_model.h"
 

src/gbm/gblinear_model.h

@@ -71,17 +71,6 @@ class GBLinearModel : public Model {
   void SaveModel(Json *p_out) const override;
   void LoadModel(Json const &in) override;
 
-  // save the model to file
-  void Save(dmlc::Stream *fo) const {
-    fo->Write(&param_, sizeof(param_));
-    fo->Write(weight);
-  }
-  // load model from file
-  void Load(dmlc::Stream *fi) {
-    CHECK_EQ(fi->Read(&param_, sizeof(param_)), sizeof(param_));
-    fi->Read(&weight);
-  }
-
   // model bias
   inline bst_float *Bias() {
     return &weight[learner_model_param->num_feature *

src/gbm/gbtree.h

@@ -188,11 +188,6 @@ class GBTree : public GradientBooster {
 
   [[nodiscard]] GBTreeTrainParam const& GetTrainParam() const { return tparam_; }
 
-  void Load(dmlc::Stream* fi) override { model_.Load(fi); }
-  void Save(dmlc::Stream* fo) const override {
-    model_.Save(fo);
-  }
-
   void LoadConfig(Json const& in) override;
   void SaveConfig(Json* p_out) const override;
 

src/gbm/gbtree_model.cc

@@ -50,62 +50,6 @@ void Validate(GBTreeModel const& model) {
 }
 }  // namespace
 
-void GBTreeModel::Save(dmlc::Stream* fo) const {
-  CHECK_EQ(param.num_trees, static_cast<int32_t>(trees.size()));
-
-  if (DMLC_IO_NO_ENDIAN_SWAP) {
-    fo->Write(&param, sizeof(param));
-  } else {
-    auto x = param.ByteSwap();
-    fo->Write(&x, sizeof(x));
-  }
-  for (const auto & tree : trees) {
-    tree->Save(fo);
-  }
-  if (tree_info.size() != 0) {
-    if (DMLC_IO_NO_ENDIAN_SWAP) {
-      fo->Write(dmlc::BeginPtr(tree_info), sizeof(int32_t) * tree_info.size());
-    } else {
-      for (const auto& e : tree_info) {
-        auto x = e;
-        dmlc::ByteSwap(&x, sizeof(x), 1);
-        fo->Write(&x, sizeof(x));
-      }
-    }
-  }
-}
-
-void GBTreeModel::Load(dmlc::Stream* fi) {
-  CHECK_EQ(fi->Read(&param, sizeof(param)), sizeof(param))
-      << "GBTree: invalid model file";
-  if (!DMLC_IO_NO_ENDIAN_SWAP) {
-    param = param.ByteSwap();
-  }
-  trees.clear();
-  trees_to_update.clear();
-  for (int32_t i = 0; i < param.num_trees; ++i) {
-    std::unique_ptr<RegTree> ptr(new RegTree());
-    ptr->Load(fi);
-    trees.push_back(std::move(ptr));
-  }
-  tree_info.resize(param.num_trees);
-  if (param.num_trees != 0) {
-    if (DMLC_IO_NO_ENDIAN_SWAP) {
-      CHECK_EQ(
-          fi->Read(dmlc::BeginPtr(tree_info), sizeof(int32_t) * param.num_trees),
-          sizeof(int32_t) * param.num_trees);
-    } else {
-      for (auto& info : tree_info) {
-        CHECK_EQ(fi->Read(&info, sizeof(int32_t)), sizeof(int32_t));
-        dmlc::ByteSwap(&info, sizeof(info), 1);
-      }
-    }
-  }
-
-  MakeIndptr(this);
-  Validate(*this);
-}
-
 void GBTreeModel::SaveModel(Json* p_out) const {
   auto& out = *p_out;
   CHECK_EQ(param.num_trees, static_cast<int>(trees.size()));

src/gbm/gbtree_model.h

@@ -106,9 +106,6 @@ struct GBTreeModel : public Model {
     }
   }
 
-  void Load(dmlc::Stream* fi);
-  void Save(dmlc::Stream* fo) const;
-
   void SaveModel(Json* p_out) const override;
   void LoadModel(Json const& p_out) override;