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ReadJpeg: Don't read past the end of the image. (#119)

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This was causing HTTP cameras that didn't send content-length to skip
frames.
This commit is contained in:
Peter Johnson
2018-02-08 20:16:30 -08:00
committed by GitHub
parent 1077ef9fb7
commit c69b8f00d0
1 changed files with 39 additions and 34 deletions
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73
src/main/native/cpp/JpegUtil.cpp
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@@ -133,43 +133,31 @@ bool ReadJpeg(wpi::raw_istream& is, std::string& buf, int* width, int* height) {
*width = 0;
*height = 0;
// read the header
buf.resize(4 + 7);
is.read(&(*buf.begin()), 4 + 7);
// read SOI and first marker
buf.resize(4);
is.read(&(*buf.begin()), 4);
if (is.has_error()) return false;
if (!IsJpeg(buf)) return false;
// Check for valid SOI
auto bytes = reinterpret_cast<const unsigned char*>(buf.data());
size_t pos = 4;
size_t blockLength = bytes[4] * 256 + bytes[5];
bool sofBlock = false;
if (bytes[0] != 0xff || bytes[1] != 0xd8) return false;
size_t pos = 2; // point to first marker
for (;;) {
// Read to the next block + marker
ReadInto(is, buf, blockLength + 2);
if (is.has_error()) return false;
// Process any blocks we just read
if (sofBlock) {
// SOF contains the file size; make sure we actually read enough bytes
if (blockLength >= 7) {
*height = bytes[5] * 256 + bytes[6];
*width = bytes[7] * 256 + bytes[8];
}
sofBlock = false;
}
pos += blockLength;
bytes = reinterpret_cast<const unsigned char*>(buf.data() + pos);
if (bytes[0] != 0xff) return false; // not a tag
if (bytes[1] == 0xda) {
if (bytes[0] != 0xff) return false; // not a marker
unsigned char marker = bytes[1];
if (marker == 0xd9) return true; // EOI, we're done
if (marker == 0xda) {
// SOS: need to keep reading until we reach a normal marker.
// Byte stuffing ensures we don't get false markers.
// Have to read a byte at a time as we don't want to overread.
pos += 2; // point after SOS marker
bool maybeMarker = false;
for (;;) {
ReadInto(is, buf, 1);
if (is.has_error()) return false;
++pos;
bytes = reinterpret_cast<const unsigned char*>(buf.data() + pos);
if (maybeMarker) {
if (bytes[0] != 0x00 && bytes[0] != 0xff &&
@@ -179,20 +167,37 @@ bool ReadJpeg(wpi::raw_istream& is, std::string& buf, int* width, int* height) {
} else if (bytes[0] == 0xff) {
maybeMarker = true;
}
++pos; // point after byte we finished reading
}
// Point back to the start of the block
--pos;
bytes = reinterpret_cast<const unsigned char*>(buf.data() + pos);
--pos; // point back to start of marker
continue;
}
if (bytes[0] != 0xff) return false; // not a tag
if (bytes[1] == 0xd9) return true; // EOI, we're done
if (bytes[1] == 0xc0) sofBlock = true; // SOF
// Go to the next block
// A normal block. Read the length
ReadInto(is, buf, 2); // read length
if (is.has_error()) return false;
// Point to length
pos += 2;
blockLength = bytes[2] * 256 + bytes[3];
bytes = reinterpret_cast<const unsigned char*>(buf.data() + pos);
// Read the block and the next marker
size_t blockLength = bytes[0] * 256 + bytes[1];
ReadInto(is, buf, blockLength);
if (is.has_error()) return false;
bytes = reinterpret_cast<const unsigned char*>(buf.data() + pos);
// Special block processing
if (marker == 0xc0) {
// SOF: contains the file size; make sure we actually read enough bytes
if (blockLength >= 7) {
*height = bytes[3] * 256 + bytes[4];
*width = bytes[5] * 256 + bytes[6];
}
}
// Point to next marker
pos += blockLength;
}
}