snappy/snappy-sinksource.h

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#ifndef THIRD_PARTY_SNAPPY_SNAPPY_SINKSOURCE_H_
#define THIRD_PARTY_SNAPPY_SNAPPY_SINKSOURCE_H_

#include <stddef.h>

namespace snappy {

// A Sink is an interface that consumes a sequence of bytes.
class Sink {
 public:
  Sink() { }
  virtual ~Sink();

  // Append "bytes[0,n-1]" to this.
  virtual void Append(const char* bytes, size_t n) = 0;

  // Returns a writable buffer of the specified length for appending.
  // May return a pointer to the caller-owned scratch buffer which
  // must have at least the indicated length.  The returned buffer is
  // only valid until the next operation on this Sink.
  //
  // After writing at most "length" bytes, call Append() with the
  // pointer returned from this function and the number of bytes
  // written.  Many Append() implementations will avoid copying
  // bytes if this function returned an internal buffer.
  //
  // If a non-scratch buffer is returned, the caller may only pass a
  // prefix of it to Append().  That is, it is not correct to pass an
  // interior pointer of the returned array to Append().
  //
  // The default implementation always returns the scratch buffer.
  virtual char* GetAppendBuffer(size_t length, char* scratch);

  // For higher performance, Sink implementations can provide custom
  // AppendAndTakeOwnership() and GetAppendBufferVariable() methods.
  // These methods can reduce the number of copies done during
  // compression/decompression.

  // Append "bytes[0,n-1] to the sink. Takes ownership of "bytes"
  // and calls the deleter function as (*deleter)(deleter_arg, bytes, n)
  // to free the buffer. deleter function must be non NULL.
  //
  // The default implementation just calls Append and frees "bytes".
  // Other implementations may avoid a copy while appending the buffer.
  virtual void AppendAndTakeOwnership(
      char* bytes, size_t n, void (*deleter)(void*, const char*, size_t),
      void *deleter_arg);

  // Returns a writable buffer for appending and writes the buffer's capacity to
  // *allocated_size. Guarantees *allocated_size >= min_size.
  // May return a pointer to the caller-owned scratch buffer which must have
  // scratch_size >= min_size.
  //
  // The returned buffer is only valid until the next operation
  // on this ByteSink.
  //
  // After writing at most *allocated_size bytes, call Append() with the
  // pointer returned from this function and the number of bytes written.
  // Many Append() implementations will avoid copying bytes if this function
  // returned an internal buffer.
  //
  // If the sink implementation allocates or reallocates an internal buffer,
  // it should use the desired_size_hint if appropriate. If a caller cannot
  // provide a reasonable guess at the desired capacity, it should set
  // desired_size_hint = 0.
  //
  // If a non-scratch buffer is returned, the caller may only pass
  // a prefix to it to Append(). That is, it is not correct to pass an
  // interior pointer to Append().
  //
  // The default implementation always returns the scratch buffer.
  virtual char* GetAppendBufferVariable(
      size_t min_size, size_t desired_size_hint, char* scratch,
      size_t scratch_size, size_t* allocated_size);

 private:
  // No copying
  Sink(const Sink&);
  void operator=(const Sink&);
};

// A Source is an interface that yields a sequence of bytes
class Source {
 public:
  Source() { }
  virtual ~Source();

  // Return the number of bytes left to read from the source
  virtual size_t Available() const = 0;

  // Peek at the next flat region of the source.  Does not reposition
  // the source.  The returned region is empty iff Available()==0.
  //
  // Returns a pointer to the beginning of the region and store its
  // length in *len.
  //
  // The returned region is valid until the next call to Skip() or
  // until this object is destroyed, whichever occurs first.
  //
  // The returned region may be larger than Available() (for example
  // if this ByteSource is a view on a substring of a larger source).
  // The caller is responsible for ensuring that it only reads the
  // Available() bytes.
  virtual const char* Peek(size_t* len) = 0;

  // Skip the next n bytes.  Invalidates any buffer returned by
  // a previous call to Peek().
  // REQUIRES: Available() >= n
  virtual void Skip(size_t n) = 0;

 private:
  // No copying
  Source(const Source&);
  void operator=(const Source&);
};

// A Source implementation that yields the contents of a flat array
class ByteArraySource : public Source {
 public:
  ByteArraySource(const char* p, size_t n) : ptr_(p), left_(n) { }
  ~ByteArraySource() override;
  size_t Available() const override;
  const char* Peek(size_t* len) override;
  void Skip(size_t n) override;
 private:
  const char* ptr_;
  size_t left_;
};

// A Sink implementation that writes to a flat array without any bound checks.
class UncheckedByteArraySink : public Sink {
 public:
  explicit UncheckedByteArraySink(char* dest) : dest_(dest) { }
  ~UncheckedByteArraySink() override;
  void Append(const char* data, size_t n) override;
  char* GetAppendBuffer(size_t len, char* scratch) override;
  char* GetAppendBufferVariable(
      size_t min_size, size_t desired_size_hint, char* scratch,
      size_t scratch_size, size_t* allocated_size) override;
  void AppendAndTakeOwnership(
      char* bytes, size_t n, void (*deleter)(void*, const char*, size_t),
      void *deleter_arg) override;

  // Return the current output pointer so that a caller can see how
  // many bytes were produced.
  // Note: this is not a Sink method.
  char* CurrentDestination() const { return dest_; }
 private:
  char* dest_;
};

}  // namespace snappy

#endif  // THIRD_PARTY_SNAPPY_SNAPPY_SINKSOURCE_H_