From 86eb98393ab87989cc9752506adba9786c635c5a Mon Sep 17 00:00:00 2001
From: Maksim Denisov <denisov.maksim@huawei.com>
Date: Thu, 20 Feb 2025 10:17:18 +0100
Subject: IncrementalReader: Support reading from memory

---
 src/utils/cpp/incremental_reader.cpp | 38 ++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

(limited to 'src/utils/cpp/incremental_reader.cpp')

diff --git a/src/utils/cpp/incremental_reader.cpp b/src/utils/cpp/incremental_reader.cpp
index c1b5bc3a..a7bcc184 100644
--- a/src/utils/cpp/incremental_reader.cpp
+++ b/src/utils/cpp/incremental_reader.cpp
@@ -72,6 +72,29 @@ auto IncrementalReader::FromFile(std::size_t chunk_size,
     }
 }
 
+auto IncrementalReader::FromMemory(
+    std::size_t chunk_size,
+    gsl::not_null<std::string const*> const& data) noexcept
+    -> expected<IncrementalReader, std::string> {
+    if (chunk_size == 0) {
+        return unexpected<std::string>{
+            "IncrementalReader: the chunk size cannot be 0"};
+    }
+
+    try {
+        // Reading from memory doesn't require a buffer. The resulting chunks
+        // point at the content_ directly.
+        return IncrementalReader{chunk_size,
+                                 /*content_size=*/data->size(),
+                                 data,
+                                 /*buffer=*/std::string{}};
+    } catch (...) {
+        return unexpected<std::string>{
+            "IncrementalReader: Got an unknown exception during creation from "
+            "a string"};
+    }
+}
+
 auto IncrementalReader::ReadChunk(std::size_t offset) const noexcept
     -> expected<std::string_view, std::string> {
     using Result = expected<std::string_view, std::string>;
@@ -79,6 +102,9 @@ auto IncrementalReader::ReadChunk(std::size_t offset) const noexcept
         [this, offset](FileSource const& file) -> Result {
             return ReadFromFile(file, offset);
         },
+        [this, offset](MemorySource const& data) -> Result {
+            return ReadFromMemory(data, offset);
+        },
     };
 
     try {
@@ -119,6 +145,18 @@ auto IncrementalReader::ReadFromFile(FileSource const& file, std::size_t offset)
     return std::string_view{buffer_.data(), read};
 }
 
+auto IncrementalReader::ReadFromMemory(MemorySource const& data,
+                                       std::size_t offset) const
+    -> expected<std::string_view, std::string> {
+    if (data->empty()) {
+        // NOLINTNEXTLINE(bugprone-string-constructor,-warnings-as-errors)
+        return std::string_view{data->data(), 0};
+    }
+
+    std::size_t const read = std::min(chunk_size_, data->size() - offset);
+    return std::string_view{&data->at(offset), read};
+}
+
 IncrementalReader::Iterator::Iterator(
     gsl::not_null<IncrementalReader const*> const& owner,
     std::size_t offset) noexcept
-- 
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