private bool is_valid_chunk_order()
{
bool IDAT_reached = false;
if (!PNG_Chunks[0].chunk_name.Equals("IHDR"))
{
return(false);
}
for (int i = 1; i < PNG_Chunks.Length; i++)
{
PNG_Chunk chunk = PNG_Chunks[i];
if (chunk.chunk_name.Equals("IDAT"))
{
IDAT_reached = true;
}
else if (chunk.chunk_name.Equals("IEND") &&
!IDAT_reached)
{
return(false);
}
else if (IDAT_reached)
{
return(false);
}
}
return(true);
}
private bool is_valid_chunk_count()
{
string[] chunk_names = { "IHDR",
"tIME",
"pHYs",
"iCCP",
"sRGB",
"sBIT",
"gAMA",
"cHRM",
"PLTE",
"tRNS",
"hIST",
"bKGD",
"IDAT",
"IEND" };
int[] chunk_counts = new int[chunk_names.Length];
// gather the counts
for (int i = 0; i < PNG_Chunks.Length; i++)
{
PNG_Chunk chunk = PNG_Chunks[i];
for (int j = 0; j < chunk_names.Length; j++)
{
if (chunk.chunk_name.Equals(chunk_names[j]))
{
chunk_counts[j]++;
break;
}
}
}
for (int i = 0; i < chunk_counts.Length; i++)
{
if (chunk_names[i].Equals("IHDR") ||
chunk_names[i].Equals("IEND"))
{
if (chunk_counts[i] != 1)
{
return(false);
}
}
else if (chunk_names[i].Equals("IDAT"))
{
if (chunk_counts[i] < 1)
{
return(false);
}
}
else
{
if (chunk_counts[i] > 1)
{
return(false);
}
}
}
return(true);
}
private PNG_Chunk[] parse_chunk_string(string chunk_string)
{
// the layout of each chunk is supposed to be
List <PNG_Chunk> chunk_list = new List <PNG_Chunk>();
while (chunk_string.Length >= 12)
{
// interpret the chunks
chunk_list.Add(new PNG_Chunk(ref chunk_string));
}
// turn the list into an array
PNG_Chunk[] chunk_arr = new PNG_Chunk[chunk_list.Count];
int index = 0;
foreach (PNG_Chunk chunk in chunk_list)
{
chunk_arr[index++] = chunk;
}
return(chunk_arr);
}
private void set_chunk_info()
{
PNG_Chunks = get_png_chunks();
IDHR_p = null;
PLTE_p = null;
List <PNG_Chunk> IDAT_chunk_list = new List <PNG_Chunk>();
IDAT_chunks_p = null;
CRCs_p = new byte[PNG_Chunks.Length][];
PNG_Chunks = get_png_chunks();
for (int i = 0; i < PNG_Chunks.Length; i++)
{
PNG_Chunk chunk = PNG_Chunks[i];
if (chunk.chunk_name.Equals("IHDR"))
{
if (IDHR_p != null)
{
throw new Exception("PNGFileReader: Multiple IDHR chunks detected.");
}
else
{
if (chunk.chunk_length != 13)
{
throw new Exception("PNGFileReader: Invalid IDHR chunk length detected.");
}
IDHR_p = chunk;
}
}
else if (chunk.chunk_name.Equals("PLTE_p"))
{
if (PLTE_p != null)
{
throw new Exception("PNGFileReader: Multiple PLTE chunks detected.");
}
else
{
PLTE_p = chunk;
}
}
else if (chunk.chunk_name.Equals("IDAT"))
{
IDAT_chunk_list.Add(chunk);
}
else if (chunk.is_IEND())
{
// convert IDAT chunk list to chunk array
IDAT_chunks_p = new PNG_Chunk[IDAT_chunk_list.Count];
int index = 0;
foreach (PNG_Chunk IDAT_chunk in IDAT_chunk_list)
{
IDAT_chunks_p[index++] = IDAT_chunk;
}
if (i != PNG_Chunks.Length - 1)
{
throw new Exception("PNGFileReader: Extra chunks after the IEND chunk.");
}
break;
}
// add the CRC to the CRC array
CRCs_p[i] = chunk.chunk_CRC;
}
set_IDHR_info();
set_PLTE_info();
set_IDAT_info();
}
private void set_chunk_info()
{
PNG_Chunks = get_png_chunks();
IDHR_p = null;
PLTE_p = null;
List<PNG_Chunk> IDAT_chunk_list = new List<PNG_Chunk>();
IDAT_chunks_p = null;
CRCs_p = new byte[PNG_Chunks.Length][];
PNG_Chunks = get_png_chunks();
for (int i = 0; i < PNG_Chunks.Length; i++)
{
PNG_Chunk chunk = PNG_Chunks[i];
if (chunk.chunk_name.Equals("IHDR"))
{
if(IDHR_p != null){
throw new Exception("PNGFileReader: Multiple IDHR chunks detected.");
}
else{
if (chunk.chunk_length != 13)
{
throw new Exception("PNGFileReader: Invalid IDHR chunk length detected.");
}
IDHR_p = chunk;
}
}
else if (chunk.chunk_name.Equals("PLTE_p"))
{
if (PLTE_p != null)
{
throw new Exception("PNGFileReader: Multiple PLTE chunks detected.");
}
else
{
PLTE_p = chunk;
}
}
else if (chunk.chunk_name.Equals("IDAT"))
{
IDAT_chunk_list.Add(chunk);
}
else if (chunk.is_IEND())
{
// convert IDAT chunk list to chunk array
IDAT_chunks_p = new PNG_Chunk[IDAT_chunk_list.Count];
int index = 0;
foreach (PNG_Chunk IDAT_chunk in IDAT_chunk_list)
{
IDAT_chunks_p[index++] = IDAT_chunk;
}
if (i != PNG_Chunks.Length - 1)
{
throw new Exception("PNGFileReader: Extra chunks after the IEND chunk.");
}
break;
}
// add the CRC to the CRC array
CRCs_p[i] = chunk.chunk_CRC;
}
set_IDHR_info();
set_PLTE_info();
set_IDAT_info();
}
private PNG_Chunk[] parse_chunk_string(string chunk_string)
{
// the layout of each chunk is supposed to be
List<PNG_Chunk> chunk_list = new List<PNG_Chunk>();
while (chunk_string.Length >= 12)
{
// interpret the chunks
chunk_list.Add(new PNG_Chunk(ref chunk_string));
}
// turn the list into an array
PNG_Chunk[] chunk_arr = new PNG_Chunk[chunk_list.Count];
int index = 0;
foreach (PNG_Chunk chunk in chunk_list)
{
chunk_arr[index++] = chunk;
}
return chunk_arr;
}
// Methods
/// <summary>
/// Returns an array of PNG_Chunk objects that each store information
/// related to that conceptual chunk. The chunks are constructed based
/// off of the PNG specification and the raw PNG file data is passed in
/// for parsing.
///
/// AREAS OF IMPROVEMENT: The checking that the passed in data aligns with
/// the specifications of a PNG file are rather light. If completely invalid
/// data were to be passed in, the method would continue checking regardless
/// of the many potential opportunities to discover the file is invalid and
/// impossible to parse.
/// </summary>
/// <param name="file_data">The raw file data from the PNG format file.</param>
/// <param name="is_valid_png_file">An uninitialized boolean that will determine
/// whether the passed in data represents a valid PNG file.</param>
/// <returns></returns>
private PNG_Chunk[] get_png_chunks(byte[] file_data, out bool is_valid_png_file)
{
if (data_p == null)
{
is_valid_png_file = false;
return(null);
}
Dictionary <string, int> chunk_map = new Dictionary <string, int>();
System.Collections.Generic.List <PNG_Chunk> chunk_list =
new System.Collections.Generic.List <PNG_Chunk>();
string[] expected_headers = { "IHDR", "PLTE", "IDAT", "IEND" };
int expected_header_index = 0;
is_valid_png_file = true;
bool palette_present = false;
// move index past the file header (8 bytes)
int byte_index = 8;
while (byte_index < file_data.Length)
{
PNG_Chunk chunk = new PNG_Chunk(file_data, ref byte_index);
if (chunk_map.ContainsKey(chunk.chunk_name))
{
chunk_map[chunk.chunk_name] += 1;
}
else
{
chunk_map.Add(chunk.chunk_name, 1);
}
if (chunk.chunk_name.Equals("PLTE"))
{
palette_present = true;
if (chunk_map.ContainsKey("bKGD") ||
chunk_map.ContainsKey("hIST") ||
chunk_map.ContainsKey("tRNS"))
{
is_valid_png_file = false;
}
PLTE_p = chunk;
}
// handle flagging the cases where the png file
// has an invalid ordering of the chunks
if (expected_headers[expected_header_index].Equals("IHDR"))
{
if (!chunk.chunk_name.Equals("IHDR"))
{
is_valid_png_file = false;
}
else
{
++expected_header_index;
IHDR_p = chunk;
}
}
else if (expected_headers[expected_header_index].Equals("IDAT"))
{
if (chunk.chunk_name.Equals("IEND"))
{
++expected_header_index;
break;
}
string[] invalid_chunk_names = { "pHYs", "sPLT" };
for (int i = 0; i < invalid_chunk_names.Length; i++)
{
if (chunk.chunk_name.Equals(invalid_chunk_names[i]))
{
is_valid_png_file = false;
}
if (!is_valid_png_file)
{
break;
}
}
}
// handle PLTE sections
else if (!expected_headers[expected_header_index].Equals("PLTE"))
{
if (chunk.chunk_name.Equals("IDAT"))
{
++expected_header_index;
}
// before the palette chunk is found...
else if (!palette_present)
{
string[] invalid_chunk_names = { "bKGD", "hIST", "tRNS" };
for (int i = 0; i < invalid_chunk_names.Length; i++)
{
if (chunk.chunk_name.Equals(invalid_chunk_names[i]))
{
is_valid_png_file = false;
}
if (!is_valid_png_file)
{
break;
}
}
if (chunk.chunk_name.Equals("iCCP") &&
chunk_map.ContainsKey("sBIT"))
{
is_valid_png_file = false;
}
else if (chunk.chunk_name.Equals("sBIT") &&
chunk_map.ContainsKey("iCCP"))
{
is_valid_png_file = false;
}
}
// after the palette chunk is found
else
{
string[] invalid_chunk_names = { "cHRM", "gAMA", "iCCP", "sBIT", "sRGB" };
for (int i = 0; i < invalid_chunk_names.Length; i++)
{
if (chunk.chunk_name.Equals(invalid_chunk_names[i]))
{
is_valid_png_file = false;
}
if (!is_valid_png_file)
{
break;
}
}
}
// add the ancillary chunks coming before PLTE if they exist
if (chunk.chunk_name.Equals("cHRM"))
{
cHRM_p = chunk;
}
else if (chunk.chunk_name.Equals("gAMA"))
{
gAMA_p = chunk;
}
else if (chunk.chunk_name.Equals("iCCP"))
{
iCCP_p = chunk;
}
else if (chunk.chunk_name.Equals("sBIT"))
{
sBIT_p = chunk;
}
else if (chunk.chunk_name.Equals("sRGB"))
{
sRGB_p = chunk;
}
else if (chunk.chunk_name.Equals("bKGD"))
{
bKGD_p = chunk;
if (colour_type == Colour_Types.GREYSCALE ||
colour_type == Colour_Types.GREYSCALE_WITH_ALPHA)
{
bg_greyscale_p = chunk.chunk_data[1];
}
else if (colour_type == Colour_Types.TRUECOLOR ||
colour_type == Colour_Types.TRUECOLOUR_WITH_ALPHA)
{
bg_R_p = chunk.chunk_data[1];
bg_G_p = chunk.chunk_data[3];
bg_B_p = chunk.chunk_data[5];
}
else
{
bg_palette_index_p = chunk.chunk_data[0];
}
}
else if (chunk.chunk_name.Equals("hIST"))
{
hIST_p = chunk;
}
else if (chunk.chunk_name.Equals("tRNS"))
{
tRNS_p = chunk;
if (colour_type == Colour_Types.GREYSCALE)
{
trns_grey_p = chunk.chunk_data[1];
}
else if (colour_type == Colour_Types.TRUECOLOR)
{
trns_R_p = chunk.chunk_data[1];
trns_G_p = chunk.chunk_data[3];
trns_B_p = chunk.chunk_data[5];
}
}
else if (chunk.chunk_name.Equals("pHYs"))
{
pHYs_p = chunk;
}
else if (chunk.chunk_name.Equals("sPLT"))
{
if (sPLT_p == null)
{
sPLT_p = new List <PNG_Chunk>();
}
sPLT_p.Add(chunk);
}
}
else
{
// should have reached end of file already, there is extra
// junk at the end of the file
}
// check the CRC
if (!is_correct_CRC(chunk.chunk_data, chunk.chunk_CRC))
{
is_valid_png_file = false;
// break out of the loop...?
}
// add the chunk to the list
chunk_list.Add(chunk);
// if it's an ancillary chunk where order doesn't matter...record it
if (chunk.chunk_name.Equals("tIME"))
{
tIME_p = chunk;
}
else if (chunk.chunk_name.Equals("iTXt"))
{
if (iTXt_p == null)
{
iTXt_p = new List <PNG_Chunk>();
}
iTXt_p.Add(chunk);
}
else if (chunk.chunk_name.Equals("tEXt"))
{
if (tEXt_p == null)
{
tEXt_p = new List <PNG_Chunk>();
}
tEXt_p.Add(chunk);
}
else if (chunk.chunk_name.Equals("zTXt"))
{
if (zTXt_p == null)
{
zTXt_p = new List <PNG_Chunk>();
}
zTXt_p.Add(chunk);
}
}
// verify the # of each type of chunk
// check the necessary ones first
if (!chunk_map.ContainsKey("IHDR") ||
chunk_map["IHDR"] != 1)
{
is_valid_png_file = false;
}
else if (!chunk_map.ContainsKey("IDAT") ||
chunk_map["IDAT"] < 1)
{
is_valid_png_file = false;
}
else if (!chunk_map.ContainsKey("IEND") ||
chunk_map["IEND"] != 1)
{
is_valid_png_file = false;
}
// check the ancillary chunks now that have 0 or 1 present
string[] ancillary_names = { "tIME", "pHYs", "sBIT", "gAMA", "cHRM", "tRNS", "hIST", "bKGD",
"PLTE" };
foreach (string name in ancillary_names)
{
if (chunk_map.ContainsKey(name) &&
chunk_map[name] != 1)
{
is_valid_png_file = false;
break;
}
}
return(chunk_list.ToArray());
}
