/// <summary>
/// Find the next JPEG marker, save it in cinfo.unread_marker.
/// Returns false if had to suspend before reaching a marker;
/// in that case cinfo.unread_marker is unchanged.
///
/// Note that the result might not be a valid marker code,
/// but it will never be 0 or FF.
/// </summary>
public bool next_marker()
{
int c;
for ( ; ;)
{
if (!m_cinfo.m_src.GetByte(out c))
{
return(false);
}
/* Skip any non-FF bytes.
* This may look a bit inefficient, but it will not occur in a valid file.
* We sync after each discarded byte so that a suspending data source
* can discard the byte from its buffer.
*/
while (c != 0xFF)
{
m_cinfo.m_marker.m_discarded_bytes++;
if (!m_cinfo.m_src.GetByte(out c))
{
return(false);
}
}
/* This loop swallows any duplicate FF bytes. Extra FFs are legal as
* pad bytes, so don't count them in discarded_bytes. We assume there
* will not be so many consecutive FF bytes as to overflow a suspending
* data source's input buffer.
*/
do
{
if (!m_cinfo.m_src.GetByte(out c))
{
return(false);
}
}while (c == 0xFF);
if (c != 0)
{
/* found a valid marker, exit loop */
break;
}
/* Reach here if we found a stuffed-zero data sequence (FF/00).
* Discard it and loop back to try again.
*/
m_cinfo.m_marker.m_discarded_bytes += 2;
}
if (m_cinfo.m_marker.m_discarded_bytes != 0)
{
m_cinfo.WARNMS(J_MESSAGE_CODE.JWRN_EXTRANEOUS_DATA, m_cinfo.m_marker.m_discarded_bytes, c);
m_cinfo.m_marker.m_discarded_bytes = 0;
}
m_cinfo.m_unread_marker = c;
return(true);
}
/// <summary>
/// Fill the input buffer - called whenever buffer is emptied.
///
/// In typical applications, this should read fresh data into the buffer
/// (ignoring the current state of next_input_byte and bytes_in_buffer),
/// reset the pointer and count to the start of the buffer, and return true
/// indicating that the buffer has been reloaded. It is not necessary to
/// fill the buffer entirely, only to obtain at least one more byte.
///
/// There is no such thing as an EOF return. If the end of the file has been
/// reached, the routine has a choice of ERREXIT() or inserting fake data into
/// the buffer. In most cases, generating a warning message and inserting a
/// fake EOI marker is the best course of action --- this will allow the
/// decompressor to output however much of the image is there. However,
/// the resulting error message is misleading if the real problem is an empty
/// input file, so we handle that case specially.
///
/// In applications that need to be able to suspend compression due to input
/// not being available yet, a false return indicates that no more data can be
/// obtained right now, but more may be forthcoming later. In this situation,
/// the decompressor will return to its caller (with an indication of the
/// number of scan lines it has read, if any). The application should resume
/// decompression after it has loaded more data into the input buffer. Note
/// that there are substantial restrictions on the use of suspension --- see
/// the documentation.
///
/// When suspending, the decompressor will back up to a convenient restart point
/// (typically the start of the current MCU). next_input_byte and bytes_in_buffer
/// indicate where the restart point will be if the current call returns false.
/// Data beyond this point must be rescanned after resumption, so move it to
/// the front of the buffer rather than discarding it.
/// </summary>
public override bool fill_input_buffer()
{
int nbytes = m_infile.Read(m_buffer, 0, InputBufferSize);
if (nbytes <= 0)
{
if (m_start_of_file) /* Treat empty input file as fatal error */
{
m_cinfo.ERREXIT(J_MESSAGE_CODE.JERR_INPUT_EMPTY);
}
m_cinfo.WARNMS(J_MESSAGE_CODE.JWRN_JPEG_EOF);
/* Insert a fake EOI marker */
m_buffer[0] = 0xFF;
m_buffer[1] = (byte)JPEG_MARKER.EOI;
nbytes = 2;
}
initInternalBuffer(m_buffer, nbytes);
m_start_of_file = false;
return(true);
}
/// <summary>
/// This is the default resync_to_restart method for data source
/// managers to use if they don't have any better approach.
/// </summary>
/// <param name="cinfo">An instance of <see cref="jpeg_decompress_struct"/></param>
/// <param name="desired">The desired</param>
/// <returns><c>false</c> if suspension is required.</returns>
/// <remarks>That method assumes that no backtracking is possible.
/// Some data source managers may be able to back up, or may have
/// additional knowledge about the data which permits a more
/// intelligent recovery strategy; such managers would
/// presumably supply their own resync method.<br/><br/>
///
/// read_restart_marker calls resync_to_restart if it finds a marker other than
/// the restart marker it was expecting. (This code is *not* used unless
/// a nonzero restart interval has been declared.) cinfo.unread_marker is
/// the marker code actually found (might be anything, except 0 or FF).
/// The desired restart marker number (0..7) is passed as a parameter.<br/><br/>
///
/// This routine is supposed to apply whatever error recovery strategy seems
/// appropriate in order to position the input stream to the next data segment.
/// Note that cinfo.unread_marker is treated as a marker appearing before
/// the current data-source input point; usually it should be reset to zero
/// before returning.<br/><br/>
///
/// This implementation is substantially constrained by wanting to treat the
/// input as a data stream; this means we can't back up. Therefore, we have
/// only the following actions to work with:<br/>
/// 1. Simply discard the marker and let the entropy decoder resume at next
/// byte of file.<br/>
/// 2. Read forward until we find another marker, discarding intervening
/// data. (In theory we could look ahead within the current bufferload,
/// without having to discard data if we don't find the desired marker.
/// This idea is not implemented here, in part because it makes behavior
/// dependent on buffer size and chance buffer-boundary positions.)<br/>
/// 3. Leave the marker unread (by failing to zero cinfo.unread_marker).
/// This will cause the entropy decoder to process an empty data segment,
/// inserting dummy zeroes, and then we will reprocess the marker.<br/>
///
/// #2 is appropriate if we think the desired marker lies ahead, while #3 is
/// appropriate if the found marker is a future restart marker (indicating
/// that we have missed the desired restart marker, probably because it got
/// corrupted).<br/>
/// We apply #2 or #3 if the found marker is a restart marker no more than
/// two counts behind or ahead of the expected one. We also apply #2 if the
/// found marker is not a legal JPEG marker code (it's certainly bogus data).
/// If the found marker is a restart marker more than 2 counts away, we do #1
/// (too much risk that the marker is erroneous; with luck we will be able to
/// resync at some future point).<br/>
/// For any valid non-restart JPEG marker, we apply #3. This keeps us from
/// overrunning the end of a scan. An implementation limited to single-scan
/// files might find it better to apply #2 for markers other than EOI, since
/// any other marker would have to be bogus data in that case.</remarks>
public virtual bool resync_to_restart(jpeg_decompress_struct cinfo, int desired)
{
/* Always put up a warning. */
cinfo.WARNMS(J_MESSAGE_CODE.JWRN_MUST_RESYNC, cinfo.m_unread_marker, desired);
/* Outer loop handles repeated decision after scanning forward. */
int action = 1;
for ( ; ; )
{
if (cinfo.m_unread_marker < (int)JPEG_MARKER.SOF0)
{
/* invalid marker */
action = 2;
}
else if (cinfo.m_unread_marker < (int)JPEG_MARKER.RST0 ||
cinfo.m_unread_marker > (int)JPEG_MARKER.RST7)
{
/* valid non-restart marker */
action = 3;
}
else
{
if (cinfo.m_unread_marker == ((int)JPEG_MARKER.RST0 + ((desired + 1) & 7))
|| cinfo.m_unread_marker == ((int)JPEG_MARKER.RST0 + ((desired + 2) & 7)))
{
/* one of the next two expected restarts */
action = 3;
}
else if (cinfo.m_unread_marker == ((int)JPEG_MARKER.RST0 + ((desired - 1) & 7)) ||
cinfo.m_unread_marker == ((int)JPEG_MARKER.RST0 + ((desired - 2) & 7)))
{
/* a prior restart, so advance */
action = 2;
}
else
{
/* desired restart or too far away */
action = 1;
}
}
cinfo.TRACEMS(4, J_MESSAGE_CODE.JTRC_RECOVERY_ACTION, cinfo.m_unread_marker, action);
switch (action)
{
case 1:
/* Discard marker and let entropy decoder resume processing. */
cinfo.m_unread_marker = 0;
return true;
case 2:
/* Scan to the next marker, and repeat the decision loop. */
if (!cinfo.m_marker.next_marker())
return false;
break;
case 3:
/* Return without advancing past this marker. */
/* Entropy decoder will be forced to process an empty segment. */
return true;
}
}
}
/*
* Routines for processing APPn and COM markers.
* These are either saved in memory or discarded, per application request.
* APP0 and APP14 are specially checked to see if they are
* JFIF and Adobe markers, respectively.
*/
/// <summary>
/// Examine first few bytes from an APP0.
/// Take appropriate action if it is a JFIF marker.
/// datalen is # of bytes at data[], remaining is length of rest of marker data.
/// </summary>
private static void examine_app0(jpeg_decompress_struct cinfo, byte[] data, int datalen, int remaining)
{
int totallen = datalen + remaining;
if (datalen >= APP0_DATA_LEN &&
data[0] == 0x4A &&
data[1] == 0x46 &&
data[2] == 0x49 &&
data[3] == 0x46 &&
data[4] == 0)
{
/* Found JFIF APP0 marker: save info */
cinfo.m_saw_JFIF_marker = true;
cinfo.m_JFIF_major_version = data[5];
cinfo.m_JFIF_minor_version = data[6];
cinfo.m_density_unit = (DensityUnit)data[7];
cinfo.m_X_density = (short)((data[8] << 8) + data[9]);
cinfo.m_Y_density = (short)((data[10] << 8) + data[11]);
/* Check version.
* Major version must be 1, anything else signals an incompatible change.
* (We used to treat this as an error, but now it's a nonfatal warning,
* because some bozo at Hijaak couldn't read the spec.)
* Minor version should be 0..2, but process anyway if newer.
*/
if (cinfo.m_JFIF_major_version != 1)
cinfo.WARNMS(J_MESSAGE_CODE.JWRN_JFIF_MAJOR, cinfo.m_JFIF_major_version, cinfo.m_JFIF_minor_version);
/* Generate trace messages */
cinfo.TRACEMS(1, J_MESSAGE_CODE.JTRC_JFIF, cinfo.m_JFIF_major_version, cinfo.m_JFIF_minor_version, cinfo.m_X_density,
cinfo.m_Y_density, cinfo.m_density_unit);
/* Validate thumbnail dimensions and issue appropriate messages */
if ((data[12] | data[13]) != 0)
cinfo.TRACEMS(1, J_MESSAGE_CODE.JTRC_JFIF_THUMBNAIL, data[12], data[13]);
totallen -= APP0_DATA_LEN;
if (totallen != ((int)data[12] * (int)data[13] * 3))
cinfo.TRACEMS(1, J_MESSAGE_CODE.JTRC_JFIF_BADTHUMBNAILSIZE, totallen);
}
else if (datalen >= 6 && data[0] == 0x4A && data[1] == 0x46 && data[2] == 0x58 && data[3] == 0x58 && data[4] == 0)
{
/* Found JFIF "JFXX" extension APP0 marker */
/* The library doesn't actually do anything with these,
* but we try to produce a helpful trace message.
*/
switch (data[5])
{
case 0x10:
cinfo.TRACEMS(1, J_MESSAGE_CODE.JTRC_THUMB_JPEG, totallen);
break;
case 0x11:
cinfo.TRACEMS(1, J_MESSAGE_CODE.JTRC_THUMB_PALETTE, totallen);
break;
case 0x13:
cinfo.TRACEMS(1, J_MESSAGE_CODE.JTRC_THUMB_RGB, totallen);
break;
default:
cinfo.TRACEMS(1, J_MESSAGE_CODE.JTRC_JFIF_EXTENSION, data[5], totallen);
break;
}
}
else
{
/* Start of APP0 does not match "JFIF" or "JFXX", or too short */
cinfo.TRACEMS(1, J_MESSAGE_CODE.JTRC_APP0, totallen);
}
}
/// <summary>
/// This is the default resync_to_restart method for data source
/// managers to use if they don't have any better approach.
/// </summary>
/// <param name="cinfo">An instance of <see cref="jpeg_decompress_struct"/></param>
/// <param name="desired">The desired</param>
/// <returns><c>false</c> if suspension is required.</returns>
/// <remarks>That method assumes that no backtracking is possible.
/// Some data source managers may be able to back up, or may have
/// additional knowledge about the data which permits a more
/// intelligent recovery strategy; such managers would
/// presumably supply their own resync method.<br/><br/>
///
/// read_restart_marker calls resync_to_restart if it finds a marker other than
/// the restart marker it was expecting. (This code is *not* used unless
/// a nonzero restart interval has been declared.) cinfo.unread_marker is
/// the marker code actually found (might be anything, except 0 or FF).
/// The desired restart marker number (0..7) is passed as a parameter.<br/><br/>
///
/// This routine is supposed to apply whatever error recovery strategy seems
/// appropriate in order to position the input stream to the next data segment.
/// Note that cinfo.unread_marker is treated as a marker appearing before
/// the current data-source input point; usually it should be reset to zero
/// before returning.<br/><br/>
///
/// This implementation is substantially constrained by wanting to treat the
/// input as a data stream; this means we can't back up. Therefore, we have
/// only the following actions to work with:<br/>
/// 1. Simply discard the marker and let the entropy decoder resume at next
/// byte of file.<br/>
/// 2. Read forward until we find another marker, discarding intervening
/// data. (In theory we could look ahead within the current bufferload,
/// without having to discard data if we don't find the desired marker.
/// This idea is not implemented here, in part because it makes behavior
/// dependent on buffer size and chance buffer-boundary positions.)<br/>
/// 3. Leave the marker unread (by failing to zero cinfo.unread_marker).
/// This will cause the entropy decoder to process an empty data segment,
/// inserting dummy zeroes, and then we will reprocess the marker.<br/>
///
/// #2 is appropriate if we think the desired marker lies ahead, while #3 is
/// appropriate if the found marker is a future restart marker (indicating
/// that we have missed the desired restart marker, probably because it got
/// corrupted).<br/>
/// We apply #2 or #3 if the found marker is a restart marker no more than
/// two counts behind or ahead of the expected one. We also apply #2 if the
/// found marker is not a legal JPEG marker code (it's certainly bogus data).
/// If the found marker is a restart marker more than 2 counts away, we do #1
/// (too much risk that the marker is erroneous; with luck we will be able to
/// resync at some future point).<br/>
/// For any valid non-restart JPEG marker, we apply #3. This keeps us from
/// overrunning the end of a scan. An implementation limited to single-scan
/// files might find it better to apply #2 for markers other than EOI, since
/// any other marker would have to be bogus data in that case.</remarks>
public virtual bool resync_to_restart(jpeg_decompress_struct cinfo, int desired)
{
/* Always put up a warning. */
cinfo.WARNMS(J_MESSAGE_CODE.JWRN_MUST_RESYNC, cinfo.m_unread_marker, desired);
/* Outer loop handles repeated decision after scanning forward. */
int action = 1;
for ( ; ;)
{
if (cinfo.m_unread_marker < (int)JPEG_MARKER.SOF0)
{
/* invalid marker */
action = 2;
}
else if (cinfo.m_unread_marker < (int)JPEG_MARKER.RST0 ||
cinfo.m_unread_marker > (int)JPEG_MARKER.RST7)
{
/* valid non-restart marker */
action = 3;
}
else
{
if (cinfo.m_unread_marker == ((int)JPEG_MARKER.RST0 + ((desired + 1) & 7)) ||
cinfo.m_unread_marker == ((int)JPEG_MARKER.RST0 + ((desired + 2) & 7)))
{
/* one of the next two expected restarts */
action = 3;
}
else if (cinfo.m_unread_marker == ((int)JPEG_MARKER.RST0 + ((desired - 1) & 7)) ||
cinfo.m_unread_marker == ((int)JPEG_MARKER.RST0 + ((desired - 2) & 7)))
{
/* a prior restart, so advance */
action = 2;
}
else
{
/* desired restart or too far away */
action = 1;
}
}
cinfo.TRACEMS(4, J_MESSAGE_CODE.JTRC_RECOVERY_ACTION, cinfo.m_unread_marker, action);
switch (action)
{
case 1:
/* Discard marker and let entropy decoder resume processing. */
cinfo.m_unread_marker = 0;
return(true);
case 2:
/* Scan to the next marker, and repeat the decision loop. */
if (!cinfo.m_marker.next_marker())
{
return(false);
}
break;
case 3:
/* Return without advancing past this marker. */
/* Entropy decoder will be forced to process an empty segment. */
return(true);
}
}
}
/*
* Routines for processing APPn and COM markers.
* These are either saved in memory or discarded, per application request.
* APP0 and APP14 are specially checked to see if they are
* JFIF and Adobe markers, respectively.
*/
/// <summary>
/// Examine first few bytes from an APP0.
/// Take appropriate action if it is a JFIF marker.
/// datalen is # of bytes at data[], remaining is length of rest of marker data.
/// </summary>
private static void examine_app0(jpeg_decompress_struct cinfo, byte[] data, int datalen, int remaining)
{
int totallen = datalen + remaining;
if (datalen >= APP0_DATA_LEN &&
data[0] == 0x4A &&
data[1] == 0x46 &&
data[2] == 0x49 &&
data[3] == 0x46 &&
data[4] == 0)
{
/* Found JFIF APP0 marker: save info */
cinfo.m_saw_JFIF_marker = true;
cinfo.m_JFIF_major_version = data[5];
cinfo.m_JFIF_minor_version = data[6];
cinfo.m_density_unit = (DensityUnit)data[7];
cinfo.m_X_density = (short)((data[8] << 8) + data[9]);
cinfo.m_Y_density = (short)((data[10] << 8) + data[11]);
/* Check version.
* Major version must be 1, anything else signals an incompatible change.
* (We used to treat this as an error, but now it's a nonfatal warning,
* because some bozo at Hijaak couldn't read the spec.)
* Minor version should be 0..2, but process anyway if newer.
*/
if (cinfo.m_JFIF_major_version != 1)
{
cinfo.WARNMS(J_MESSAGE_CODE.JWRN_JFIF_MAJOR, cinfo.m_JFIF_major_version, cinfo.m_JFIF_minor_version);
}
/* Generate trace messages */
cinfo.TRACEMS(1, J_MESSAGE_CODE.JTRC_JFIF, cinfo.m_JFIF_major_version, cinfo.m_JFIF_minor_version, cinfo.m_X_density,
cinfo.m_Y_density, cinfo.m_density_unit);
/* Validate thumbnail dimensions and issue appropriate messages */
if ((data[12] | data[13]) != 0)
{
cinfo.TRACEMS(1, J_MESSAGE_CODE.JTRC_JFIF_THUMBNAIL, data[12], data[13]);
}
totallen -= APP0_DATA_LEN;
if (totallen != ((int)data[12] * (int)data[13] * 3))
{
cinfo.TRACEMS(1, J_MESSAGE_CODE.JTRC_JFIF_BADTHUMBNAILSIZE, totallen);
}
}
else if (datalen >= 6 && data[0] == 0x4A && data[1] == 0x46 && data[2] == 0x58 && data[3] == 0x58 && data[4] == 0)
{
/* Found JFIF "JFXX" extension APP0 marker */
/* The library doesn't actually do anything with these,
* but we try to produce a helpful trace message.
*/
switch (data[5])
{
case 0x10:
cinfo.TRACEMS(1, J_MESSAGE_CODE.JTRC_THUMB_JPEG, totallen);
break;
case 0x11:
cinfo.TRACEMS(1, J_MESSAGE_CODE.JTRC_THUMB_PALETTE, totallen);
break;
case 0x13:
cinfo.TRACEMS(1, J_MESSAGE_CODE.JTRC_THUMB_RGB, totallen);
break;
default:
cinfo.TRACEMS(1, J_MESSAGE_CODE.JTRC_JFIF_EXTENSION, data[5], totallen);
break;
}
}
else
{
/* Start of APP0 does not match "JFIF" or "JFXX", or too short */
cinfo.TRACEMS(1, J_MESSAGE_CODE.JTRC_APP0, totallen);
}
}