From 4d5080388a5da740ce60017728d046c424e1771e Mon Sep 17 00:00:00 2001
From: Sam Atkins <atkinssj@serenityos.org>
Date: Thu, 3 Feb 2022 19:21:51 +0000
Subject: [PATCH] LibCore+Tests: Add SeekableStream::truncate()

---
 Tests/LibCore/TestLibCoreStream.cpp       | 12 ++++++++++++
 Userland/Libraries/LibCore/MemoryStream.h |  2 ++
 Userland/Libraries/LibCore/Stream.cpp     |  5 +++++
 Userland/Libraries/LibCore/Stream.h       |  8 ++++++++
 4 files changed, 27 insertions(+)

diff --git a/Tests/LibCore/TestLibCoreStream.cpp b/Tests/LibCore/TestLibCoreStream.cpp
index e0fcf16aab..37d559bcb0 100644
--- a/Tests/LibCore/TestLibCoreStream.cpp
+++ b/Tests/LibCore/TestLibCoreStream.cpp
@@ -135,6 +135,18 @@ TEST_CASE(file_adopt_invalid_fd)
     EXPECT_EQ(maybe_file.error().code(), EBADF);
 }
 
+TEST_CASE(file_truncate)
+{
+    auto maybe_file = Core::Stream::File::open("/tmp/file-truncate-test.txt", Core::Stream::OpenMode::Write);
+    auto file = maybe_file.release_value();
+
+    EXPECT(!file->truncate(999).is_error());
+    EXPECT_EQ(file->size().release_value(), 999);
+
+    EXPECT(!file->truncate(42).is_error());
+    EXPECT_EQ(file->size().release_value(), 42);
+}
+
 // TCPSocket tests
 
 TEST_CASE(should_error_when_connection_fails)
diff --git a/Userland/Libraries/LibCore/MemoryStream.h b/Userland/Libraries/LibCore/MemoryStream.h
index aee618313a..5eeb066acf 100644
--- a/Userland/Libraries/LibCore/MemoryStream.h
+++ b/Userland/Libraries/LibCore/MemoryStream.h
@@ -26,6 +26,8 @@ public:
     virtual bool is_open() const override { return true; }
     // FIXME: It doesn't make sense to close an memory stream. Therefore, we don't do anything here. Is that fine?
     virtual void close() override { }
+    // FIXME: It doesn't make sense to truncate a memory stream. Therefore, we don't do anything here. Is that fine?
+    virtual ErrorOr<void> truncate(off_t) override { return Error::from_errno(ENOTSUP); }
 
     virtual ErrorOr<size_t> read(Bytes bytes) override
     {
diff --git a/Userland/Libraries/LibCore/Stream.cpp b/Userland/Libraries/LibCore/Stream.cpp
index 0498ab3f46..0fce083488 100644
--- a/Userland/Libraries/LibCore/Stream.cpp
+++ b/Userland/Libraries/LibCore/Stream.cpp
@@ -215,6 +215,11 @@ ErrorOr<off_t> File::seek(i64 offset, SeekMode mode)
     return seek_result;
 }
 
+ErrorOr<void> File::truncate(off_t length)
+{
+    return System::ftruncate(m_fd, length);
+}
+
 ErrorOr<int> Socket::create_fd(SocketDomain domain, SocketType type)
 {
     int socket_domain;
diff --git a/Userland/Libraries/LibCore/Stream.h b/Userland/Libraries/LibCore/Stream.h
index 3757115425..8aba029f45 100644
--- a/Userland/Libraries/LibCore/Stream.h
+++ b/Userland/Libraries/LibCore/Stream.h
@@ -81,6 +81,9 @@ public:
     /// Returns the total size of the stream, or an errno in the case of an
     /// error. May not preserve the original position on the stream on failure.
     virtual ErrorOr<off_t> size();
+    /// Shrinks or extends the stream to the given size. Returns an errno in
+    /// the case of an error.
+    virtual ErrorOr<void> truncate(off_t length) = 0;
 };
 
 /// The Socket class is the base class for all concrete BSD-style socket
@@ -197,6 +200,7 @@ public:
     virtual bool is_open() const override;
     virtual void close() override;
     virtual ErrorOr<off_t> seek(i64 offset, SeekMode) override;
+    virtual ErrorOr<void> truncate(off_t length) override;
 
     virtual ~File() override { close(); }
 
@@ -757,6 +761,10 @@ public:
         m_helper.clear_buffer();
         return result;
     }
+    virtual ErrorOr<void> truncate(off_t length) override
+    {
+        return m_helper.stream().truncate(length);
+    }
 
     ErrorOr<size_t> read_line(Bytes buffer) { return m_helper.read_line(move(buffer)); }
     ErrorOr<size_t> read_until(Bytes buffer, StringView candidate) { return m_helper.read_until(move(buffer), move(candidate)); }