ARROW-8083: [GLib] Add support for Peek() to GIOInputStream

Closes #6589 from kou/glib-gio-input-stream-peek Authored-by: Sutou Kouhei <kou@clear-code.com> Signed-off-by: Yosuke Shiro <yosuke.shiro615@gmail.com>
apache · Mar 12, 2020 · f60c0b1 · f60c0b1
1 parent 52fb3c6
commit f60c0b1
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diff --git a/c_glib/arrow-glib/input-stream.cpp b/c_glib/arrow-glib/input-stream.cpp
@@ -721,6 +721,37 @@ namespace garrow {
       }
     }
 
+    arrow::Result<arrow::util::string_view> Peek(int64_t nbytes) override {
+      if (!G_IS_BUFFERED_INPUT_STREAM(input_stream_)) {
+        std::string message("[gio-input-stream][peek] "
+                            "not peekable input stream: <");
+        message += G_OBJECT_CLASS_NAME(G_OBJECT_GET_CLASS(input_stream_));
+        message += ">";
+        return arrow::Status::NotImplemented(message);
+      }
+
+      auto stream = G_BUFFERED_INPUT_STREAM(input_stream_);
+      auto available_n_bytes = g_buffered_input_stream_get_available(stream);
+      if (available_n_bytes < static_cast<gsize>(nbytes)) {
+        GError *error = NULL;
+        auto filled_size =
+          g_buffered_input_stream_fill(stream, nbytes, NULL, &error);
+        if (filled_size == -1) {
+          return garrow_error_to_status(error,
+                                        arrow::StatusCode::IOError,
+                                        "[gio-input-stream][peek] "
+                                        "failed to fill");
+        }
+      }
+      gsize data_size;
+      auto data = g_buffered_input_stream_peek_buffer(stream, &data_size);
+      if (data_size > static_cast<gsize>(nbytes)) {
+        data_size = nbytes;
+      }
+      return arrow::util::string_view(static_cast<const char *>(data),
+                                      data_size);
+    }
+
     arrow::Status Seek(int64_t position) override {
       if (!G_IS_SEEKABLE(input_stream_)) {
         std::string message("[gio-input-stream][seek] "

diff --git a/c_glib/test/test-gio-input-stream.rb b/c_glib/test/test-gio-input-stream.rb
@@ -60,4 +60,13 @@ def test_getter
     input = Arrow::GIOInputStream.new(input_stream)
     assert_equal(input_stream, input.raw)
   end
+
+  def test_peek
+    input_stream = Gio::MemoryInputStream.new("Hello World")
+    buffered_input_stream = Gio::BufferedInputStream.new(input_stream)
+    input = Arrow::GIOInputStream.new(buffered_input_stream)
+    assert_equal("He", input.peek(2).to_s)
+    assert_equal("Hel", input.read_bytes(3).to_s)
+    assert_equal("lo ", input.peek(3).to_s)
+  end
 end