client/Response: add constant MAX_BINARY_SIZE

Use the same chunk size for all binary commands.

src/client/Response.cxx

@@ -59,6 +59,8 @@ Response::Format(const char *fmt, ...) noexcept
 bool
 Response::WriteBinary(ConstBuffer<void> payload) noexcept
 {
+	assert(payload.size <= MAX_BINARY_SIZE);
+
 	return Format("binary: %zu\n", payload.size) &&
 		Write(payload.data, payload.size) &&
 		Write("\n");

src/client/Response.hxx

@@ -77,6 +77,8 @@ public:
 	bool FormatV(const char *fmt, va_list args) noexcept;
 	bool Format(const char *fmt, ...) noexcept;
 
+	static constexpr size_t MAX_BINARY_SIZE = 8192;
+
 	/**
 	 * Write a binary chunk; this writes the "binary" line, the
 	 * given chunk and the trailing newline.