cpl_vsil_subfile.cpp

/******************************************************************************
 *
 * Project:  VSI Virtual File System
 * Purpose:  Implementation of subfile virtual IO functions.
 * Author:   Frank Warmerdam, warmerdam@pobox.com
 *
 ******************************************************************************
 * Copyright (c) 2005, Frank Warmerdam <warmerdam@pobox.com>
 * Copyright (c) 2009-2014, Even Rouault <even dot rouault at spatialys.com>
 *
 * SPDX-License-Identifier: MIT
 ****************************************************************************/

#include "cpl_port.h"
#include "cpl_vsi.h"

#include <cerrno>
#include <cstddef>
#include <cstring>
#if HAVE_FCNTL_H
#include <fcntl.h>
#endif
#include <limits>

#include "cpl_conv.h"
#include "cpl_multiproc.h"
#include "cpl_string.h"
#include "cpl_vsi_virtual.h"

/************************************************************************/
/* ==================================================================== */
/*                           VSISubFileHandle                           */
/* ==================================================================== */
/************************************************************************/

class VSISubFileHandle final : public VSIVirtualHandle
{
    CPL_DISALLOW_COPY_ASSIGN(VSISubFileHandle)

  public:
    VSILFILE *fp = nullptr;
    vsi_l_offset nSubregionOffset = 0;
    vsi_l_offset nSubregionSize = 0;
    bool bAtEOF = false;
    bool bError = false;

    VSISubFileHandle() = default;
    ~VSISubFileHandle() override;

    int Seek(vsi_l_offset nOffset, int nWhence) override;
    vsi_l_offset Tell() override;
    size_t Read(void *pBuffer, size_t nSize, size_t nMemb) override;
    size_t Write(const void *pBuffer, size_t nSize, size_t nMemb) override;
    void ClearErr() override;
    int Eof() override;
    int Error() override;
    int Close() override;
};

/************************************************************************/
/* ==================================================================== */
/*                   VSISubFileFilesystemHandler                        */
/* ==================================================================== */
/************************************************************************/

class VSISubFileFilesystemHandler final : public VSIFilesystemHandler
{
    CPL_DISALLOW_COPY_ASSIGN(VSISubFileFilesystemHandler)

  public:
    VSISubFileFilesystemHandler() = default;
    ~VSISubFileFilesystemHandler() override = default;

    static int DecomposePath(const char *pszPath, CPLString &osFilename,
                             vsi_l_offset &nSubFileOffset,
                             vsi_l_offset &nSubFileSize);

    VSIVirtualHandle *Open(const char *pszFilename, const char *pszAccess,
                           bool bSetError,
                           CSLConstList /* papszOptions */) override;
    int Stat(const char *pszFilename, VSIStatBufL *pStatBuf,
             int nFlags) override;
    int Unlink(const char *pszFilename) override;
    int Mkdir(const char *pszDirname, long nMode) override;
    int Rmdir(const char *pszDirname) override;
    char **ReadDirEx(const char *pszDirname, int nMaxFiles) override;
};

/************************************************************************/
/* ==================================================================== */
/*                             VSISubFileHandle                         */
/* ==================================================================== */
/************************************************************************/

VSISubFileHandle::~VSISubFileHandle()
{
    VSISubFileHandle::Close();
}

/************************************************************************/
/*                               Close()                                */
/************************************************************************/

int VSISubFileHandle::Close()

{
    if (fp == nullptr)
        return -1;
    int nRet = VSIFCloseL(fp);
    fp = nullptr;

    return nRet;
}

/************************************************************************/
/*                                Seek()                                */
/************************************************************************/

int VSISubFileHandle::Seek(vsi_l_offset nOffset, int nWhence)

{
    bAtEOF = false;

    if (nWhence == SEEK_SET)
    {
        if (nOffset >
            std::numeric_limits<vsi_l_offset>::max() - nSubregionOffset)
            return -1;
        nOffset += nSubregionOffset;
    }
    else if (nWhence == SEEK_CUR)
    {
        // handle normally.
    }
    else if (nWhence == SEEK_END)
    {
        if (nSubregionSize != 0)
        {
            nOffset = nSubregionOffset + nSubregionSize;
            nWhence = SEEK_SET;
        }
    }
    else
    {
        errno = EINVAL;
        return -1;
    }

    return VSIFSeekL(fp, nOffset, nWhence);
}

/************************************************************************/
/*                                Tell()                                */
/************************************************************************/

vsi_l_offset VSISubFileHandle::Tell()

{
    vsi_l_offset nBasePos = VSIFTellL(fp);
    if (nBasePos >= nSubregionOffset)
        return nBasePos - nSubregionOffset;
    return 0;
}

/************************************************************************/
/*                                Read()                                */
/************************************************************************/

size_t VSISubFileHandle::Read(void *pBuffer, size_t nSize, size_t nCount)

{
    size_t nRet = 0;
    if (nSubregionSize == 0)
    {
        nRet = VSIFReadL(pBuffer, nSize, nCount, fp);
    }
    else
    {
        if (nSize == 0)
            return 0;

        const vsi_l_offset nCurOffset = VSIFTellL(fp);
        if (nCurOffset >= nSubregionOffset + nSubregionSize)
        {
            bAtEOF = true;
            return 0;
        }

        const size_t nByteToRead = nSize * nCount;
        if (nCurOffset + nByteToRead > nSubregionOffset + nSubregionSize)
        {
            const int nRead = static_cast<int>(
                VSIFReadL(pBuffer, 1,
                          static_cast<size_t>(nSubregionOffset +
                                              nSubregionSize - nCurOffset),
                          fp));
            nRet = nRead / nSize;
        }
        else
        {
            nRet = VSIFReadL(pBuffer, nSize, nCount, fp);
        }
    }

    if (nRet < nCount)
    {
        if (fp->Eof())
            bAtEOF = true;
        else /* if (fp->Error()) */
            bError = true;
    }

    return nRet;
}

/************************************************************************/
/*                               Write()                                */
/************************************************************************/

size_t VSISubFileHandle::Write(const void *pBuffer, size_t nSize, size_t nCount)

{
    bAtEOF = false;

    if (nSubregionSize == 0)
        return VSIFWriteL(pBuffer, nSize, nCount, fp);

    if (nSize == 0)
        return 0;

    const vsi_l_offset nCurOffset = VSIFTellL(fp);
    if (nCurOffset >= nSubregionOffset + nSubregionSize)
        return 0;

    const size_t nByteToWrite = nSize * nCount;
    if (nCurOffset + nByteToWrite > nSubregionOffset + nSubregionSize)
    {
        const int nWritten = static_cast<int>(VSIFWriteL(
            pBuffer, 1,
            static_cast<size_t>(nSubregionOffset + nSubregionSize - nCurOffset),
            fp));
        return nWritten / nSize;
    }

    return VSIFWriteL(pBuffer, nSize, nCount, fp);
}

/************************************************************************/
/*                             ClearErr()                               */
/************************************************************************/

void VSISubFileHandle::ClearErr()

{
    fp->ClearErr();
    bAtEOF = false;
    bError = false;
}

/************************************************************************/
/*                              Error()                                 */
/************************************************************************/

int VSISubFileHandle::Error()

{
    return bError;
}

/************************************************************************/
/*                                Eof()                                 */
/************************************************************************/

int VSISubFileHandle::Eof()

{
    return bAtEOF;
}

/************************************************************************/
/* ==================================================================== */
/*                       VSISubFileFilesystemHandler                    */
/* ==================================================================== */
/************************************************************************/

/************************************************************************/
/*                           DecomposePath()                            */
/*                                                                      */
/*      Parse a path like /vsisubfile/1000_2000,data/abc.tif into an    */
/*      offset (1000), a size (2000) and a path (data/abc.tif).         */
/************************************************************************/

int VSISubFileFilesystemHandler::DecomposePath(const char *pszPath,
                                               CPLString &osFilename,
                                               vsi_l_offset &nSubFileOffset,
                                               vsi_l_offset &nSubFileSize)

{
    if (!STARTS_WITH(pszPath, "/vsisubfile/"))
        return FALSE;

    osFilename = "";
    nSubFileOffset = 0;
    nSubFileSize = 0;

    nSubFileOffset =
        CPLScanUIntBig(pszPath + 12, static_cast<int>(strlen(pszPath + 12)));
    for (int i = 12; pszPath[i] != '\0'; i++)
    {
        if (pszPath[i] == '_' && nSubFileSize == 0)
        {
            // -1 is sometimes passed to mean that we don't know the file size
            // for example when creating a JPEG2000 datastream in a NITF file
            // Transform it into 0 for correct behavior of Read(), Write() and
            // Eof().
            if (pszPath[i + 1] == '-')
                nSubFileSize = 0;
            else
                nSubFileSize = CPLScanUIntBig(
                    pszPath + i + 1, static_cast<int>(strlen(pszPath + i + 1)));
        }
        else if (pszPath[i] == ',')
        {
            osFilename = pszPath + i + 1;
            return TRUE;
        }
        else if (pszPath[i] == '/')
        {
            // Missing comma!
            return FALSE;
        }
    }

    return FALSE;
}

/************************************************************************/
/*                                Open()                                */
/************************************************************************/

VSIVirtualHandle *
VSISubFileFilesystemHandler::Open(const char *pszFilename,
                                  const char *pszAccess, bool /* bSetError */,
                                  CSLConstList /* papszOptions */)

{
    if (!STARTS_WITH_CI(pszFilename, "/vsisubfile/"))
        return nullptr;

    CPLString osSubFilePath;
    vsi_l_offset nOff = 0;
    vsi_l_offset nSize = 0;

    if (!DecomposePath(pszFilename, osSubFilePath, nOff, nSize))
    {
        errno = ENOENT;
        return nullptr;
    }
    if (nOff > std::numeric_limits<vsi_l_offset>::max() - nSize)
    {
        return nullptr;
    }

    /* -------------------------------------------------------------------- */
    /*      We can't open the containing file with "w" access, so if        */
    /*      that is requested use "r+" instead to update in place.          */
    /* -------------------------------------------------------------------- */
    if (pszAccess[0] == 'w')
        pszAccess = "r+";

    /* -------------------------------------------------------------------- */
    /*      Open the underlying file.                                       */
    /* -------------------------------------------------------------------- */
    VSILFILE *fp = VSIFOpenL(osSubFilePath, pszAccess);

    if (fp == nullptr)
        return nullptr;

    /* -------------------------------------------------------------------- */
    /*      Setup the file handle on this file.                             */
    /* -------------------------------------------------------------------- */
    VSISubFileHandle *poHandle = new VSISubFileHandle;

    poHandle->fp = fp;
    poHandle->nSubregionOffset = nOff;
    poHandle->nSubregionSize = nSize;

    // In read-only mode validate (offset, size) against underlying file size
    if (strchr(pszAccess, 'r') != nullptr && strchr(pszAccess, '+') == nullptr)
    {
        if (VSIFSeekL(fp, 0, SEEK_END) != 0)
        {
            poHandle->Close();
            delete poHandle;
            return nullptr;
        }
        vsi_l_offset nFpSize = VSIFTellL(fp);
        // For a directory, the size will be max(vsi_l_offset) / 2
        if (nFpSize == ~(static_cast<vsi_l_offset>(0)) / 2 || nOff > nFpSize)
        {
            poHandle->Close();
            delete poHandle;
            return nullptr;
        }
        if (nOff + nSize > nFpSize)
        {
            nSize = nFpSize - nOff;
            poHandle->nSubregionSize = nSize;
        }
    }

    if (VSIFSeekL(fp, nOff, SEEK_SET) != 0)
    {
        poHandle->Close();
        delete poHandle;
        poHandle = nullptr;
    }

    return poHandle;
}

/************************************************************************/
/*                                Stat()                                */
/************************************************************************/

int VSISubFileFilesystemHandler::Stat(const char *pszFilename,
                                      VSIStatBufL *psStatBuf, int nFlags)

{
    if (!STARTS_WITH_CI(pszFilename, "/vsisubfile/"))
        return -1;

    CPLString osSubFilePath;
    vsi_l_offset nOff = 0;
    vsi_l_offset nSize = 0;

    memset(psStatBuf, 0, sizeof(VSIStatBufL));

    if (!DecomposePath(pszFilename, osSubFilePath, nOff, nSize))
    {
        errno = ENOENT;
        return -1;
    }

    const int nResult = VSIStatExL(osSubFilePath, psStatBuf, nFlags);

    if (nResult == 0)
    {
        if (nSize != 0)
            psStatBuf->st_size = nSize;
        else if (static_cast<vsi_l_offset>(psStatBuf->st_size) >= nOff)
            psStatBuf->st_size -= nOff;
        else
            psStatBuf->st_size = 0;
    }

    return nResult;
}

/************************************************************************/
/*                               Unlink()                               */
/************************************************************************/

int VSISubFileFilesystemHandler::Unlink(const char * /* pszFilename */)
{
    errno = EACCES;
    return -1;
}

/************************************************************************/
/*                               Mkdir()                                */
/************************************************************************/

int VSISubFileFilesystemHandler::Mkdir(const char * /* pszPathname */,
                                       long /* nMode */)
{
    errno = EACCES;
    return -1;
}

/************************************************************************/
/*                               Rmdir()                                */
/************************************************************************/

int VSISubFileFilesystemHandler::Rmdir(const char * /* pszPathname */)

{
    errno = EACCES;
    return -1;
}

/************************************************************************/
/*                             ReadDirEx()                              */
/************************************************************************/

char **VSISubFileFilesystemHandler::ReadDirEx(const char * /* pszPath */,
                                              int /* nMaxFiles */)
{
    errno = EACCES;
    return nullptr;
}

/************************************************************************/
/*                 VSIInstallSubFileFilesystemHandler()                 */
/************************************************************************/

/*!
 \brief Install /vsisubfile/ virtual file handler.

 \verbatim embed:rst
 See :ref:`/vsisubfile/ documentation <vsisubfile>`
 \endverbatim
 */

void VSIInstallSubFileHandler()
{
    VSIFileManager::InstallHandler("/vsisubfile/",
                                   new VSISubFileFilesystemHandler);
}