text: // Copyright (c) 2012 The Chromium Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file.
  
  #ifndef NET_BASE_UPLOAD_ELEMENT_READER_H_
  #define NET_BASE_UPLOAD_ELEMENT_READER_H_
  
  #include <stdint.h>
  
  #include "net/base/completion_once_callback.h"
  #include "net/base/net_export.h"
  
  namespace net {
  
  class IOBuffer;
  class UploadBytesElementReader;
  class UploadFileElementReader;
  
  // An interface to read an upload data element.
  class NET_EXPORT UploadElementReader {
   public:
    UploadElementReader() = default;
    UploadElementReader(const UploadElementReader&) = delete;
    UploadElementReader& operator=(const UploadElementReader&) = delete;
    virtual ~UploadElementReader() = default;
  
    // Returns this instance's pointer as UploadBytesElementReader when possible,
    // otherwise returns NULL.
    virtual const UploadBytesElementReader* AsBytesReader() const;
  
    // Returns this instance's pointer as UploadFileElementReader when possible,
    // otherwise returns NULL.
    virtual const UploadFileElementReader* AsFileReader() const;
  
    // This function must be called before calling any other method. It is not
    // valid to call any method (other than the destructor) if Init() fails.
    // This method can be called multiple times. Calling this results in resetting
    // the state (i.e. the stream is rewound), and any previously pending Init()
    // or Read() calls are aborted.
    //
    // Initializes the instance synchronously when possible, otherwise does
    // initialization aynschronously, returns ERR_IO_PENDING and runs callback.
    // Calling this method again after a Init() success results in resetting the
    // state.
    virtual int Init(CompletionOnceCallback callback) = 0;
  
    // Returns the byte-length of the element. For files that do not exist, 0
    // is returned. This is done for consistency with Mozilla.
    virtual uint64_t GetContentLength() const = 0;
  
    // Returns the number of bytes remaining to read.
    virtual uint64_t BytesRemaining() const = 0;
  
    // Returns true if the upload element is entirely in memory.
    // The default implementation returns false.
    virtual bool IsInMemory() const;
  
    // Reads up to |buf_length| bytes synchronously and returns the number of
    // bytes read or error code when possible, otherwise, returns ERR_IO_PENDING
    // and runs |callback| with the result. |buf_length| must be greater than 0.
    virtual int Read(IOBuffer* buf,
                     int buf_length,
                     CompletionOnceCallback callback) = 0;
  };
  
  }  // namespace net
  
  #endif  // NET_BASE_UPLOAD_ELEMENT_READER_H_
  