lib/std: fix ByteWriter.read_from method (#793)

* lib/std: fix ByteWriter.read_from method

When reading from a stream which does not have an available method,
ByteWriter would not make any progress if its buffer was empty.

Signed-off-by: Pierre Curto <pierre.curto@gmail.com>

* test/unit/stdlib/io: use separate module for TestReader

Signed-off-by: Pierre Curto <pierre.curto@gmail.com>

---------

Signed-off-by: Pierre Curto <pierre.curto@gmail.com>

lib/std/io/stream/bytewriter.c3

@@ -79,19 +79,21 @@ fn void! ByteWriter.write_byte(ByteWriter* writer, char c)
  **/
 fn usz! ByteWriter.read_from(ByteWriter* writer, Stream* reader)
 {
+	usz start_index = writer.index;
 	if (reader.supports_available())
 	{
-		usz total_read = 0;
 		while (usz available = reader.available()!)
 		{
 			writer.ensure_capacity(writer.index + available)!;
-			usz len = reader.read(writer.bytes[writer.index..])!;
-			total_read += len;
-			writer.index += len;
+			usz read = reader.read(writer.bytes[writer.index..])!;
+			writer.index += read;
 		}
-		return total_read;
+		return writer.index - start_index;
+	}
+	if (writer.bytes.len == 0)
+	{
+		writer.ensure_capacity(16)!;
 	}
-	usz total_read = 0;
 	while (true)
 	{
 		// See how much we can read.
@@ -100,12 +102,13 @@ fn usz! ByteWriter.read_from(ByteWriter* writer, Stream* reader)
 		if (len_to_read < 16)
 		{
 			writer.ensure_capacity(writer.bytes.len * 2)!;
+			len_to_read = writer.bytes.len - writer.index;
 		}
 		// Read into the rest of the buffer
 		usz read = reader.read(writer.bytes[writer.index..])!;
 		writer.index += read;
 		// Ok, we reached the end.
-		if (read < len_to_read) return total_read;
+		if (read < len_to_read) return writer.index - start_index;
 		// Otherwise go another round
 	}
 }
@@ -116,4 +119,4 @@ StreamInterface bytewriter_interface = {
 	.write_fn = fn (s, char[] bytes) => ((ByteWriter*)s.data).write(bytes),
 	.write_byte_fn = fn (s, char c) => ((ByteWriter*)s.data).write_byte(c),
 	.read_stream_fn = fn (s, reader) => ((ByteWriter*)s.data).read_from(reader),
-};
+};

test/unit/stdlib/io/bytestream.c3

@@ -35,3 +35,44 @@ fn void! bytewriter_buffer()
 	assert(o == "hello");
 	assert(@catchof(s.write("xxxx")));
 }
+
+fn void! bytewriter_read_from()
+{
+    char[] data = "Lorem ipsum dolor sit amet biam.";
+    TestReader r = { .bytes = data };
+    Stream s = r.as_stream();
+
+    ByteWriter bw;
+    bw.tinit();
+    bw.read_from(&s)!;
+
+    assert(bw.as_str() == data);
+}
+
+module std::io;
+// TestReader only has the read method to trigger the path
+// in ByteWriter.read_from that does not rely on the available method.
+struct TestReader
+{
+    char[] bytes;
+    usz index;
+}
+
+fn Stream TestReader.as_stream(TestReader *r)
+{
+    return { .fns = &testReader_interface, .data = r };
+}
+
+fn usz! TestReader.read(TestReader *r, char[] bytes)
+{
+    usz left = r.bytes.len - r.index;
+    if (left == 0) return 0;
+    usz n = min(left, bytes.len);
+    mem::copy(bytes.ptr, &r.bytes[r.index], n);
+    r.index += n;
+    return n;
+}
+
+StreamInterface testReader_interface = {
+    .read_fn = fn(s, char[] bytes) => ((TestReader*)s.data).read(bytes),
+};