WifiClient::write refactoring (second attempt) (#2177)

* WiFiClient: use DataSource for writes

* ESP8266WebServer: delegate writing to WiFiClient

* ESP8266WebServer: set write timeout before sending content

libraries/ESP8266WiFi/src/include/DataSource.h

@@ -0,0 +1,113 @@
+/* DataSource.h - a read-only object similar to Stream, but with less methods
+ * Copyright (c) 2016 Ivan Grokhotkov. All rights reserved.
+ * This file is distributed under MIT license.
+ */
+#ifndef DATASOURCE_H
+#define DATASOURCE_H
+
+#include <assert.h>
+
+class DataSource {
+public:
+    virtual ~DataSource() {}
+    virtual size_t available() = 0;
+    virtual const uint8_t* get_buffer(size_t size) = 0;
+    virtual void release_buffer(const uint8_t* buffer, size_t size) = 0;
+
+};
+
+class BufferDataSource : public DataSource {
+public:
+    BufferDataSource(const uint8_t* data, size_t size) :
+        _data(data),
+        _size(size)
+    {
+    }
+
+    size_t available() override
+    {
+        return _size - _pos;
+    }
+
+    const uint8_t* get_buffer(size_t size) override
+    {
+        assert(_pos + size <= _size);
+        return _data + _pos;
+    }
+
+    void release_buffer(const uint8_t* buffer, size_t size) override
+    {
+        assert(buffer == _data + _pos);
+        _pos += size;
+    }
+
+protected:
+    const uint8_t* _data;
+    const size_t _size;
+    size_t _pos = 0;
+};
+
+template<typename TStream>
+class BufferedStreamDataSource : public DataSource {
+public:
+    BufferedStreamDataSource(TStream& stream, size_t size) :
+        _stream(stream),
+        _size(size)
+    {
+    }
+
+    size_t available() override
+    {
+        return _size - _pos;
+    }
+
+    const uint8_t* get_buffer(size_t size) override
+    {
+        assert(_pos + size <= _size);
+        if (_bufferSize < size) {
+            _buffer.reset(new uint8_t[size]);
+            _bufferSize = size;
+        }
+        size_t cb = _stream.readBytes(reinterpret_cast<char*>(_buffer.get()), size);
+        assert(cb == size);
+        return _buffer.get();
+    }
+
+    void release_buffer(const uint8_t* buffer, size_t size) override
+    {
+        _pos += size;
+    }
+
+protected:
+    TStream& _stream;
+    std::unique_ptr<uint8_t[]> _buffer;
+    size_t _size;
+    size_t _pos = 0;
+    size_t _bufferSize = 0;
+};
+
+class ProgmemStream
+{
+public:
+    ProgmemStream(PGM_P buf, size_t size) :
+        _buf(buf),
+        _left(size)
+    {
+    }
+
+    size_t readBytes(char* dst, size_t size)
+    {
+        size_t will_read = (_left < size) ? _left : size;
+        memcpy_P((void*)dst, (PGM_VOID_P)_buf, will_read);
+        _left -= will_read;
+        _buf  += will_read;
+        return will_read;
+    }
+
+protected:
+    PGM_P _buf;
+    size_t _left;
+};
+
+
+#endif //DATASOURCE_H