From 1becd3e0bac788497caf62ecac5a4f99dedc5bb3 Mon Sep 17 00:00:00 2001
From: Konstantin Pastbin <konstantin.pastbin@gmail.com>
Date: Wed, 2 Jul 2025 21:18:29 +0700
Subject: [PATCH] [core] Use dynamic chunk size for downloading maps

Signed-off-by: Konstantin Pastbin <konstantin.pastbin@gmail.com>
---
 .../DownloadResourcesLegacyActivity.cpp       |  2 +-
 platform/chunks_download_strategy.cpp         | 26 ++++++++++++++++++-
 platform/http_request.cpp                     | 13 +++-------
 platform/http_request.hpp                     |  2 +-
 4 files changed, 31 insertions(+), 12 deletions(-)

diff --git a/android/app/src/main/cpp/app/organicmaps/DownloadResourcesLegacyActivity.cpp b/android/app/src/main/cpp/app/organicmaps/DownloadResourcesLegacyActivity.cpp
index 748368a63..1ac953548 100644
--- a/android/app/src/main/cpp/app/organicmaps/DownloadResourcesLegacyActivity.cpp
+++ b/android/app/src/main/cpp/app/organicmaps/DownloadResourcesLegacyActivity.cpp
@@ -171,7 +171,7 @@ extern "C"
           curFile.GetRemoteSize(),
           std::bind(&DownloadFileFinished, ptr, _1),
           std::bind(&DownloadFileProgress, ptr, _1),
-          512 * 1024, false));
+          0, false));
     });
 
     return ERR_FILE_IN_PROGRESS;
diff --git a/platform/chunks_download_strategy.cpp b/platform/chunks_download_strategy.cpp
index 3e895ec1d..87fdc82f3 100644
--- a/platform/chunks_download_strategy.cpp
+++ b/platform/chunks_download_strategy.cpp
@@ -40,7 +40,31 @@ ChunksDownloadStrategy::GetChunk(RangeT const & range)
 
 void ChunksDownloadStrategy::InitChunks(int64_t fileSize, int64_t chunkSize, ChunkStatusT status)
 {
-  m_chunks.reserve(static_cast<size_t>(fileSize / chunkSize + 2));
+  if (chunkSize == 0)
+  {
+    int64_t constexpr kMb = 1024 * 1024;
+    size_t const sizeMb = std::max(fileSize / kMb, static_cast<int64_t>(1));
+
+    size_t constexpr kTargetCount = 40;
+    size_t constexpr kMinMb = 1;
+    size_t constexpr kMaxMb = 16;
+    size_t const chunkMb = std::min(std::max(sizeMb / kTargetCount, kMinMb), kMaxMb);
+
+    size_t chunksCount = sizeMb / chunkMb;
+    if (static_cast<int64_t>(kMb * chunkMb * chunksCount) < fileSize)
+      ++chunksCount;
+    ASSERT_GREATER_OR_EQUAL(static_cast<int64_t>(kMb * chunkMb * chunksCount), fileSize, ());
+
+    LOG(LINFO, ("File size", sizeMb, "MB; chunk size", chunkMb, "MB; chunks count", chunksCount));
+
+    m_chunks.reserve(chunksCount + 1);
+    chunkSize = chunkMb * kMb;
+  }
+  else
+  {
+    m_chunks.reserve(static_cast<size_t>(fileSize / chunkSize + 2));
+  }
+
   for (int64_t i = 0; i < fileSize; i += chunkSize)
     m_chunks.push_back(ChunkT(i, status));
   // The last AUX chunk is just used to hold end of the range (eof) for the previous chunk.
diff --git a/platform/http_request.cpp b/platform/http_request.cpp
index fe675409a..745883ffa 100644
--- a/platform/http_request.cpp
+++ b/platform/http_request.cpp
@@ -136,7 +136,6 @@ class FileHttpRequest : public HttpRequest, public IHttpThreadCallback
   string m_filePath;
   unique_ptr<FileWriter> m_writer;
 
-  size_t m_goodChunksCount;
   bool m_doCleanProgressFiles;
 
   // Starts a thread per each free/available server.
@@ -248,13 +247,9 @@ class FileHttpRequest : public HttpRequest, public IHttpThreadCallback
     else if (result == ChunksDownloadStrategy::EDownloadSucceeded)
       m_status = DownloadStatus::Completed;
 
-    if (isChunkOk)
-    {
-      // save information for download resume
-      ++m_goodChunksCount;
-      if (m_status != DownloadStatus::Completed && m_goodChunksCount % 10 == 0)
-        SaveResumeChunks();
-    }
+    // Save chunks statuses into the resume file.
+    if (isChunkOk && m_status != DownloadStatus::Completed)
+      SaveResumeChunks();
 
     if (m_status == DownloadStatus::InProgress)
       return;
@@ -300,7 +295,7 @@ public:
                   int64_t chunkSize, bool doCleanProgressFiles)
     : HttpRequest(std::move(onFinish), std::move(onProgress)),
       m_strategy(urls), m_filePath(filePath),
-      m_goodChunksCount(0), m_doCleanProgressFiles(doCleanProgressFiles)
+      m_doCleanProgressFiles(doCleanProgressFiles)
   {
     ASSERT ( !urls.empty(), () );
 
diff --git a/platform/http_request.hpp b/platform/http_request.hpp
index d09398a90..04e5187df 100644
--- a/platform/http_request.hpp
+++ b/platform/http_request.hpp
@@ -59,7 +59,7 @@ public:
                                std::string const & filePath, int64_t fileSize,
                                Callback && onFinish,
                                Callback && onProgress = Callback(),
-                               int64_t chunkSize = 512 * 1024,
+                               int64_t chunkSize = 0, // 0 for auto
                                bool doCleanOnCancel = true);
 };
 } // namespace downloader