skia2/include/core/SkData.h

/*
 * Copyright 2011 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#ifndef SkData_DEFINED
#define SkData_DEFINED

#include "SkRefCnt.h"

struct SkFILE;
class SkStream;

/**
 *  SkData holds an immutable data buffer. Not only is the data immutable,
 *  but the actual ptr that is returned (by data() or bytes()) is guaranteed
 *  to always be the same for the life of this instance.
 */
class SK_API SkData : public SkRefCnt {
public:
    SK_DECLARE_INST_COUNT(SkData)

    /**
     *  Returns the number of bytes stored.
     */
    size_t size() const { return fSize; }

    bool isEmpty() const { return 0 == fSize; }

    /**
     *  Returns the ptr to the data.
     */
    const void* data() const { return fPtr; }

    /**
     *  Like data(), returns a read-only ptr into the data, but in this case
     *  it is cast to uint8_t*, to make it easy to add an offset to it.
     */
    const uint8_t* bytes() const {
        return reinterpret_cast<const uint8_t*>(fPtr);
    }

    /**
     *  USE WITH CAUTION.
     *  This call will assert that the refcnt is 1, as a precaution against modifying the
     *  contents when another client/thread has access to the data.
     */
    void* writable_data() {
        if (fSize) {
            // only assert we're unique if we're not empty
            SkASSERT(this->unique());
        }
        return fPtr;
    }

    /**
     *  Helper to copy a range of the data into a caller-provided buffer.
     *  Returns the actual number of bytes copied, after clamping offset and
     *  length to the size of the data. If buffer is NULL, it is ignored, and
     *  only the computed number of bytes is returned.
     */
    size_t copyRange(size_t offset, size_t length, void* buffer) const;

    /**
     *  Returns true if these two objects have the same length and contents,
     *  effectively returning 0 == memcmp(...)
     */
    bool equals(const SkData* other) const;

    /**
     *  Function that, if provided, will be called when the SkData goes out
     *  of scope, allowing for custom allocation/freeing of the data's contents.
     */
    typedef void (*ReleaseProc)(const void* ptr, void* context);

    /**
     *  Create a new dataref by copying the specified data
     */
    static SkData* NewWithCopy(const void* data, size_t length);

    /**
     *  Create a new data with uninitialized contents. The caller should call writable_data()
     *  to write into the buffer, but this must be done before another ref() is made.
     */
    static SkData* NewUninitialized(size_t length);

    /**
     *  Create a new dataref by copying the specified c-string
     *  (a null-terminated array of bytes). The returned SkData will have size()
     *  equal to strlen(cstr) + 1. If cstr is NULL, it will be treated the same
     *  as "".
     */
    static SkData* NewWithCString(const char cstr[]);

    /**
     *  Create a new dataref, taking the ptr as is, and using the
     *  releaseproc to free it. The proc may be NULL.
     */
    static SkData* NewWithProc(const void* ptr, size_t length, ReleaseProc proc, void* context);

    /**
     *  Call this when the data parameter is already const and will outlive the lifetime of the
     *  SkData. Suitable for with const globals.
     */
    static SkData* NewWithoutCopy(const void* data, size_t length) {
        return NewWithProc(data, length, DummyReleaseProc, NULL);
    }

    /**
     *  Create a new dataref from a pointer allocated by malloc. The Data object
     *  takes ownership of that allocation, and will handling calling sk_free.
     */
    static SkData* NewFromMalloc(const void* data, size_t length);

    /**
     *  Create a new dataref the file with the specified path.
     *  If the file cannot be opened, this returns NULL.
     */
    static SkData* NewFromFileName(const char path[]);

    /**
     *  Create a new dataref from a SkFILE.
     *  This does not take ownership of the SkFILE, nor close it.
     *  The caller is free to close the SkFILE at its convenience.
     *  The SkFILE must be open for reading only.
     *  Returns NULL on failure.
     */
    static SkData* NewFromFILE(SkFILE* f);

    /**
     *  Create a new dataref from a file descriptor.
     *  This does not take ownership of the file descriptor, nor close it.
     *  The caller is free to close the file descriptor at its convenience.
     *  The file descriptor must be open for reading only.
     *  Returns NULL on failure.
     */
    static SkData* NewFromFD(int fd);

    /**
     *  Attempt to read size bytes into a SkData. If the read succeeds, return the data,
     *  else return NULL. Either way the stream's cursor may have been changed as a result
     *  of calling read().
     */
    static SkData* NewFromStream(SkStream*, size_t size);

    /**
     *  Create a new dataref using a subset of the data in the specified
     *  src dataref.
     */
    static SkData* NewSubset(const SkData* src, size_t offset, size_t length);

    /**
     *  Returns a new empty dataref (or a reference to a shared empty dataref).
     *  New or shared, the caller must see that unref() is eventually called.
     */
    static SkData* NewEmpty();

private:
    ReleaseProc fReleaseProc;
    void*       fReleaseProcContext;
    void*       fPtr;
    size_t      fSize;

    SkData(const void* ptr, size_t size, ReleaseProc, void* context);
    explicit SkData(size_t size);   // inplace new/delete
    virtual ~SkData();


    // Objects of this type are sometimes created in a custom fashion using sk_malloc_throw and
    // therefore must be sk_freed. We overload new to also call sk_malloc_throw so that memory
    // can be unconditionally released using sk_free in an overloaded delete. Overloading regular
    // new means we must also overload placement new.
    void* operator new(size_t size) { return sk_malloc_throw(size); }
    void* operator new(size_t, void* p) { return p; }
    void operator delete(void* p) { sk_free(p); }

    // Called the first time someone calls NewEmpty to initialize the singleton.
    friend SkData* sk_new_empty_data();

    // shared internal factory
    static SkData* PrivateNewWithCopy(const void* srcOrNull, size_t length);

    static void DummyReleaseProc(const void*, void*) {}

    typedef SkRefCnt INHERITED;
};

/** Typedef of SkAutoTUnref<SkData> for automatically unref-ing a SkData. */
typedef SkAutoTUnref<SkData> SkAutoDataUnref;

#endif