AK: Lower the requirements for InputStream::eof and rename it.

Consider the following snippet:

    void foo(InputStream& stream) {
        if(!stream.eof()) {
            u8 byte;
            stream >> byte;
        }
    }

There is a very subtle bug in this snippet, for some input streams eof()
might return false even if no more data can be read. In this case an
error flag would be set on the stream.

Until now I've always ensured that this is not the case, but this made
the implementation of eof() unnecessarily complicated.
InputFileStream::eof had to keep a ByteBuffer around just to make this
possible. That meant a ton of unnecessary copies just to get a reliable
eof().

In most cases it isn't actually necessary to have a reliable eof()
implementation.

In most other cases a reliable eof() is avaliable anyways because in
some cases like InputMemoryStream it is very easy to implement.

Libraries/LibCompress/Deflate.cpp

@@ -290,7 +290,7 @@ bool DeflateDecompressor::discard_or_error(size_t count)
 
     size_t ndiscarded = 0;
     while (ndiscarded < count) {
-        if (eof()) {
+        if (unreliable_eof()) {
             set_fatal_error();
             return false;
         }
@@ -301,7 +301,7 @@ bool DeflateDecompressor::discard_or_error(size_t count)
     return true;
 }
 
-bool DeflateDecompressor::eof() const { return m_state == State::Idle && m_read_final_bock; }
+bool DeflateDecompressor::unreliable_eof() const { return m_state == State::Idle && m_read_final_bock; }
 
 Optional<ByteBuffer> DeflateDecompressor::decompress_all(ReadonlyBytes bytes)
 {
@@ -310,7 +310,7 @@ Optional<ByteBuffer> DeflateDecompressor::decompress_all(ReadonlyBytes bytes)
     OutputMemoryStream output_stream;
 
     u8 buffer[4096];
-    while (!deflate_stream.has_any_error() && !deflate_stream.eof()) {
+    while (!deflate_stream.has_any_error() && !deflate_stream.unreliable_eof()) {
         const auto nread = deflate_stream.read({ buffer, sizeof(buffer) });
         output_stream.write_or_error({ buffer, nread });
     }

Libraries/LibCompress/Deflate.h

@@ -92,7 +92,8 @@ public:
     size_t read(Bytes) override;
     bool read_or_error(Bytes) override;
     bool discard_or_error(size_t) override;
-    bool eof() const override;
+
+    bool unreliable_eof() const override;
 
     static Optional<ByteBuffer> decompress_all(ReadonlyBytes);
 

Libraries/LibCompress/Gzip.cpp

@@ -68,7 +68,7 @@ GzipDecompressor::~GzipDecompressor()
 // FIXME: Again, there are surely a ton of bugs because the code doesn't check for read errors.
 size_t GzipDecompressor::read(Bytes bytes)
 {
-    if (has_any_error())
+    if (has_any_error() || m_eof)
         return 0;
 
     if (m_current_member.has_value()) {
@@ -99,12 +99,14 @@ size_t GzipDecompressor::read(Bytes bytes)
 
         return nread;
     } else {
-        if (m_input_stream.eof())
-            return 0;
-
         BlockHeader header;
         m_input_stream >> Bytes { &header, sizeof(header) };
 
+        if (m_input_stream.handle_any_error()) {
+            m_eof = true;
+            return 0;
+        }
+
         if (!header.valid_magic_number() || !header.supported_by_implementation()) {
             set_fatal_error();
             return 0;
@@ -147,7 +149,7 @@ bool GzipDecompressor::discard_or_error(size_t count)
 
     size_t ndiscarded = 0;
     while (ndiscarded < count) {
-        if (eof()) {
+        if (unreliable_eof()) {
             set_fatal_error();
             return false;
         }
@@ -165,7 +167,7 @@ Optional<ByteBuffer> GzipDecompressor::decompress_all(ReadonlyBytes bytes)
     OutputMemoryStream output_stream;
 
     u8 buffer[4096];
-    while (!gzip_stream.has_any_error() && !gzip_stream.eof()) {
+    while (!gzip_stream.has_any_error() && !gzip_stream.unreliable_eof()) {
         const auto nread = gzip_stream.read({ buffer, sizeof(buffer) });
         output_stream.write_or_error({ buffer, nread });
     }
@@ -176,15 +178,6 @@ Optional<ByteBuffer> GzipDecompressor::decompress_all(ReadonlyBytes bytes)
     return output_stream.copy_into_contiguous_buffer();
 }
 
-bool GzipDecompressor::eof() const
-{
-    if (m_current_member.has_value()) {
-        // FIXME: There is an ugly edge case where we read the whole deflate block
-        //        but haven't read CRC32 and ISIZE.
-        return current_member().m_stream.eof() && m_input_stream.eof();
-    } else {
-        return m_input_stream.eof();
-    }
-}
+bool GzipDecompressor::unreliable_eof() const { return m_eof; }
 
 }

Libraries/LibCompress/Gzip.h

@@ -39,7 +39,8 @@ public:
     size_t read(Bytes) override;
     bool read_or_error(Bytes) override;
     bool discard_or_error(size_t) override;
-    bool eof() const override;
+
+    bool unreliable_eof() const override;
 
     static Optional<ByteBuffer> decompress_all(ReadonlyBytes);
 
@@ -87,6 +88,8 @@ private:
 
     InputStream& m_input_stream;
     Optional<Member> m_current_member;
+
+    bool m_eof { false };
 };
 
 }

Libraries/LibCore/FileStream.h

@@ -68,25 +68,8 @@ public:
         if (has_any_error())
             return 0;
 
-        auto nread = m_buffered.bytes().copy_trimmed_to(bytes);
-
-        m_buffered.bytes().slice(nread, m_buffered.size() - nread).copy_to(m_buffered);
-        m_buffered.trim(m_buffered.size() - nread);
-
-        while (nread < bytes.size()) {
-            if (m_file->eof())
-                return nread;
-
-            if (m_file->has_error()) {
-                set_fatal_error();
-                return 0;
-            }
-
-            const auto buffer = m_file->read(bytes.size() - nread);
-            nread += buffer.bytes().copy_to(bytes.slice(nread));
-        }
-
-        return nread;
+        const auto buffer = m_file->read(bytes.size());
+        return buffer.bytes().copy_to(bytes);
     }
 
     bool read_or_error(Bytes bytes) override
@@ -99,34 +82,9 @@ public:
         return true;
     }
 
-    bool discard_or_error(size_t count) override
-    {
-        u8 buffer[4096];
+    bool discard_or_error(size_t count) override { return m_file->seek(count, IODevice::SeekMode::FromCurrentPosition); }
 
-        size_t ndiscarded = 0;
-        while (ndiscarded < count && !eof())
-            ndiscarded += read({ buffer, min<size_t>(count - ndiscarded, sizeof(buffer)) });
-
-        if (eof()) {
-            set_fatal_error();
-            return false;
-        }
-
-        return true;
-    }
-
-    bool eof() const override
-    {
-        if (m_buffered.size() > 0)
-            return false;
-
-        if (m_file->eof())
-            return true;
-
-        m_buffered = m_file->read(4096);
-
-        return m_buffered.size() == 0;
-    }
+    bool unreliable_eof() const override { return m_file->eof(); }
 
     void close()
     {
@@ -137,8 +95,7 @@ public:
 private:
     InputFileStream() = default;
 
-    mutable NonnullRefPtr<File> m_file;
-    mutable ByteBuffer m_buffered;
+    NonnullRefPtr<File> m_file;
 };
 
 class OutputFileStream : public OutputStream {