/// <summary>
/// Reads chunks before first IDAT. Position before: after IDHR (crc included)
/// Position after: just after the first IDAT chunk id Returns length of first
/// IDAT chunk , -1 if not found
/// </summary>
void ReadFirstChunks()
{
if (!FirstChunksNotYetRead())
{
return;
}
int clen = 0;
bool found = false;
byte[] chunkid = new byte[4]; // it's important to reallocate in each
this.CurrentChunkGroup = ChunksList.CHUNK_GROUP_1_AFTERIDHR;
while (!found)
{
clen = PngHelperInternal.ReadInt4(inputStream);
offset += 4;
if (clen < 0)
{
break;
}
PngHelperInternal.ReadBytes(inputStream, chunkid, 0, 4);
offset += 4;
if (PngCsUtils.UnSafeEquals(chunkid, Pngcs.Chunks.ChunkHelper.b_IDAT))
{
found = true;
this.CurrentChunkGroup = ChunksList.CHUNK_GROUP_4_IDAT;
// add dummy idat chunk to list
chunksList.AppendReadChunk(new PngChunkIDAT(ImgInfo, clen, offset - 8), CurrentChunkGroup);
break;
}
else if (PngCsUtils.UnSafeEquals(chunkid, Pngcs.Chunks.ChunkHelper.b_IEND))
{
throw new IO.IOException($"END chunk found before image data (IDAT) at offset={offset}");
}
string chunkids = ChunkHelper.ToString(chunkid);
if (chunkids.Equals(ChunkHelper.PLTE))
{
this.CurrentChunkGroup = ChunksList.CHUNK_GROUP_2_PLTE;
}
ReadChunk(chunkid, clen, false);
if (chunkids.Equals(ChunkHelper.PLTE))
{
this.CurrentChunkGroup = ChunksList.CHUNK_GROUP_3_AFTERPLTE;
}
}
int idatLen = found ? clen : -1;
if (idatLen < 0)
{
throw new IO.IOException("first idat chunk not found!");
}
iIdatCstream = new PngIDatChunkInputStream(inputStream, idatLen, offset);
idatIstream = Zlib.ZlibStreamFactory.createZlibInputStream(iIdatCstream, true);
if (!crcEnabled)
{
iIdatCstream.DisableCrcCheck();
}
}
/// <summary>
/// Reads (and processes ... up to a point) chunks after last IDAT.
/// </summary>
void ReadLastChunks()
{
CurrentChunkGroup = ChunksList.CHUNK_GROUP_5_AFTERIDAT;
// PngHelper.logdebug("idat ended? " + iIdatCstream.isEnded());
if (!iIdatCstream.IsEnded())
{
iIdatCstream.ForceChunkEnd();
}
int clen = iIdatCstream.GetLenLastChunk();
byte[] chunkid = iIdatCstream.GetIdLastChunk();
bool endfound = false;
bool first = true;
bool skip = false;
while (!endfound)
{
skip = false;
if (!first)
{
clen = PngHelperInternal.ReadInt4(inputStream);
offset += 4;
if (clen < 0)
{
throw new IO.IOException($"bad len {clen}");
}
PngHelperInternal.ReadBytes(inputStream, chunkid, 0, 4);
offset += 4;
}
first = false;
if (PngCsUtils.UnSafeEquals(chunkid, ChunkHelper.b_IDAT))
{
skip = true; // extra dummy (empty?) idat chunk, it can happen, ignore it
}
else if (PngCsUtils.UnSafeEquals(chunkid, ChunkHelper.b_IEND))
{
CurrentChunkGroup = ChunksList.CHUNK_GROUP_6_END;
endfound = true;
}
ReadChunk(chunkid, clen, skip);
}
if (!endfound)
{
throw new IO.IOException($"end chunk not found - offset={offset}");
}
// PngHelper.logdebug("end chunk found ok offset=" + offset);
}
/// <summary>
/// Constructs a PNGReader objet from a opened Stream
/// </summary>
/// <remarks>The constructor reads the signature and first chunk (IDHR)<seealso cref="FileHelper.CreatePngReader(string)"/>
/// </remarks>
/// <param name="filename">Optional, can be the filename or a description.</param>
public PngReader(IO.Stream inputStream, string filename)
{
this.filename = filename != null ? filename : string.Empty;
this.inputStream = inputStream;
this.chunksList = new ChunksList(null);
this.metadata = new PngMetadata(chunksList);
this.offset = 0;
// set default options
this.CurrentChunkGroup = -1;
this.ShouldCloseStream = true;
this.MaxBytesMetadata = 5 * 1024 * 1024;
this.MaxTotalBytesRead = 200 * 1024 * 1024; // 200MB
this.SkipChunkMaxSize = 2 * 1024 * 1024;
this.SkipChunkIds = new string[] { "fdAT" };
this.ChunkLoadBehaviour = Pngcs.Chunks.ChunkLoadBehaviour.LOAD_CHUNK_ALWAYS;
// starts reading: signature
byte[] pngid = new byte[8];
PngHelperInternal.ReadBytes(inputStream, pngid, 0, pngid.Length);
offset += pngid.Length;
if (!PngCsUtils.UnSafeEquals(pngid, PngHelperInternal.PNG_ID_SIGNATURE))
{
throw new IO.IOException("Bad PNG signature");
}
CurrentChunkGroup = ChunksList.CHUNK_GROUP_0_IDHR;
// reads first chunk IDHR
int clen = PngHelperInternal.ReadInt4(inputStream);
offset += 4;
if (clen != 13)
{
throw new System.Exception($"IDHR chunk len!=13 ?? Is:{clen}");
}
byte[] chunkid = new byte[4];
PngHelperInternal.ReadBytes(inputStream, chunkid, 0, 4);
if (!PngCsUtils.UnSafeEquals(chunkid, ChunkHelper.b_IHDR))
{
throw new IO.IOException($"IHDR not found as first chunk??? [{ChunkHelper.ToString(chunkid)}]");
}
offset += 4;
PngChunkIHDR ihdr = (PngChunkIHDR)ReadChunk(chunkid, clen, false);
bool alpha = (ihdr.Colormodel & 0x04) != 0;
bool palette = (ihdr.Colormodel & 0x01) != 0;
bool grayscale = (ihdr.Colormodel == 0 || ihdr.Colormodel == 4);
// creates ImgInfo and imgLine, and allocates buffers
ImgInfo = new ImageInfo(ihdr.Cols, ihdr.Rows, ihdr.Bitspc, alpha, grayscale, palette);
rowb = new byte[ImgInfo.BytesPerRow + 1];
rowbprev = new byte[rowb.Length];
rowbfilter = new byte[rowb.Length];
interlaced = ihdr.Interlaced == 1;
deinterlacer = interlaced ? new PngDeinterlacer(ImgInfo) : null;
// some checks
if (ihdr.Filmeth != 0 || ihdr.Compmeth != 0 || (ihdr.Interlaced & 0xFFFE) != 0)
{
throw new IO.IOException("compmethod or filtermethod or interlaced unrecognized");
}
if (ihdr.Colormodel < 0 || ihdr.Colormodel > 6 || ihdr.Colormodel == 1 || ihdr.Colormodel == 5)
{
throw new IO.IOException($"Invalid colormodel {ihdr.Colormodel}");
}
if (ihdr.Bitspc != 1 && ihdr.Bitspc != 2 && ihdr.Bitspc != 4 && ihdr.Bitspc != 8 && ihdr.Bitspc != 16)
{
throw new IO.IOException($"Invalid bit depth {ihdr.Bitspc}");
}
}