From ce0f90d21e6e8ba2da491e6e9ad18f7d7b679eb9 Mon Sep 17 00:00:00 2001
From: MihailRis <mexaruc@gmail.com>
Date: Thu, 11 Jun 2026 00:17:31 +0300
Subject: [PATCH] feat: memory_istream seek support

---
 src/io/memory_istream.hpp  | 52 +++++++++++++++++++++++++++++++++++++-
 test/io/memory_istream.cpp | 11 ++++++++
 2 files changed, 62 insertions(+), 1 deletion(-)

diff --git a/src/io/memory_istream.hpp b/src/io/memory_istream.hpp
index 7c0aded64..84a0c703f 100644
--- a/src/io/memory_istream.hpp
+++ b/src/io/memory_istream.hpp
@@ -15,8 +15,33 @@ public:
     memory_streambuf(const memory_streambuf&) = delete;
     memory_streambuf& operator=(const memory_streambuf&) = delete;
 
+    pos_type seekoff(off_type off, std::ios_base::seekdir way,
+                     std::ios_base::openmode mode = std::ios_base::in) override {
+        if (!(mode & std::ios_base::in)) return pos_type(off_type(-1));
+        char* base = eback();
+        char* end = egptr();
+        if (!base || !end) return pos_type(off_type(-1));
+
+        std::ptrdiff_t current = gptr() - base;
+        std::ptrdiff_t newpos;
+        if (way == std::ios_base::beg) newpos = off;
+        else if (way == std::ios_base::cur) newpos = current + off;
+        else if (way == std::ios_base::end) newpos = (end - base) + off;
+        else return pos_type(off_type(-1));
+
+        if (newpos < 0 || base + newpos > end) return pos_type(off_type(-1));
+        setg(base, base + newpos, end);
+        return pos_type(off_type(newpos));
+    }
+
+    pos_type seekpos(pos_type sp, std::ios_base::openmode mode = std::ios_base::in) override {
+        return seekoff(off_type(sp), std::ios_base::beg, mode);
+    }
 protected:
     int_type underflow() override {
+        if (gptr() < egptr()) {
+            return traits_type::to_int_type(*gptr());
+        }
         return traits_type::eof();
     }
 
@@ -36,7 +61,7 @@ private:
 class memory_view_streambuf : public std::streambuf {
 public:
     explicit memory_view_streambuf(const util::Buffer<char>& buffer)
-        : buffer(std::move(buffer)) {
+        : buffer(buffer) {
         char* base = const_cast<char*>(this->buffer.data());
         char* end = base + this->buffer.size();
         setg(base, base, end);
@@ -45,8 +70,33 @@ public:
     memory_view_streambuf(const memory_view_streambuf&) = delete;
     memory_view_streambuf& operator=(const memory_view_streambuf&) = delete;
 
+    pos_type seekoff(off_type off, std::ios_base::seekdir way,
+                     std::ios_base::openmode mode = std::ios_base::in) override {
+        if (!(mode & std::ios_base::in)) return pos_type(off_type(-1));
+        char* base = eback();
+        char* end = egptr();
+        if (!base || !end) return pos_type(off_type(-1));
+
+        std::ptrdiff_t current = gptr() - base;
+        std::ptrdiff_t newpos;
+        if (way == std::ios_base::beg) newpos = off;
+        else if (way == std::ios_base::cur) newpos = current + off;
+        else if (way == std::ios_base::end) newpos = (end - base) + off;
+        else return pos_type(off_type(-1));
+
+        if (newpos < 0 || base + newpos > end) return pos_type(off_type(-1));
+        setg(base, base + newpos, end);
+        return pos_type(off_type(newpos));
+    }
+
+    pos_type seekpos(pos_type sp, std::ios_base::openmode mode = std::ios_base::in) override {
+        return seekoff(off_type(sp), std::ios_base::beg, mode);
+    }
 protected:
     int_type underflow() override {
+        if (gptr() < egptr()) {
+            return traits_type::to_int_type(*gptr());
+        }
         return traits_type::eof();
     }
 
diff --git a/test/io/memory_istream.cpp b/test/io/memory_istream.cpp
index faabd23cd..674d250fd 100644
--- a/test/io/memory_istream.cpp
+++ b/test/io/memory_istream.cpp
@@ -16,4 +16,15 @@ TEST(io, memory_istream) {
     ASSERT_EQ(text, std::string(data));
     stream.read(text.data(), 1);
     ASSERT_TRUE(stream.eof());
+
+    // seek
+    stream.clear();
+    stream.seekg(0);
+    ASSERT_TRUE(stream.good());
+    stream.read(text.data(), n);
+    ASSERT_EQ(text, std::string(data));
+    stream.seekg(-6, std::ios_base::cur);
+    ASSERT_TRUE(stream.good());
+    stream.read(text.data(), 6);
+    ASSERT_EQ(text.substr(0, 6), "world!");
 }