Searching for all Occurance of Byte Strings in Binary File

Question

I'm writing a python script to search for several different byte strings within a large binary file and so far it works well but, I have hit a bit of an anomoly. Here is what I have done so far:

for i in range(0, fileSizeBytes):
        data.seek(readOffsetIndex, 0)                                   # Change the file index to last search. 
        print('Starting Read at DEC: %s' % str(readOffsetIndex))
        print('Starting Read at HEX: %s' % str(hex(readOffsetIndex)))
        byte = data.read()                                              # Read the file starting at the new index
        search = byte.find(b'\x00\x00\x00\xbb')                       # Search for this string of bytes

        if search:
            byteOffset = (byteOffset + (busWidth+4))
            startOffset = str(hex(byteOffset-4))
            readOffsetIndex = byteOffset
            print('String Found Starting at: ' + startOffset)
            print('READ SET TO: %s' % str(readOffsetIndex))
            print('READ SET TO: %s' % str(hex(readOffsetIndex)))
            print('---------------------------------------------------')
            csvWriter.writerow(['Bus Width', str(startOffset), str(hex(readOffsetIndex)), grabData(byteOffset-4)])

        if (readOffsetIndex >= fileSizeBytes):                          # Check bounds of file size to kill loop
            csvFile.close()
            break

The only query it is attempying to find is: search = byte.find(b'\x00\x00\x00\xbb'). When I analyze the data, the few records are perfect but when I hit search location 0x189da6b, it goes crazy on me. See the image below for the data output:

It's like is just stops looking for the specific string and starts doing its own thing... Any ideas as to why this is happening? The CSV has a total of 88,900 rows of which, about 90 are valid search strings and the rest are the jibbereist you see in the data.

---

UPDATE #1:

I have found a better way to interate through a Binary file and locate all occurances of a byte string along with the offset of said byte string. Below is a method that does just that:

from bitstring import ConstBitStream

def parse(register_name,byte_data):
    fileSizeBytes = os.path.getsize(bin_file)
    fileSizeMegaBytes = GetFileSize(os.path.getsize(bin_file))
    data = open(bin_file, 'rb')

    s = ConstBitStream(filename=bin_file)
    occurances = s.findall(byte_data, bytealigned=True)
    occurances = list(occurances)
    totalOccurances = len(occurances)
    byteOffset = 0                                                      # True start of Byte string 

    for i in range(0, len(occurances)):
        occuranceOffset = (hex(int(occurances[i]/8)))
        s0f0, length, bitdepth, height, width = s.readlist('hex:16, uint:16, uint:8, 2*uint:16')  
        s.bitpos = occurances[i]
        data = s.read('hex:32')      
        print('Address: ' + str(occuranceOffset) + ' Data: ' + str(data))
        csvWriter.writerow([register_name, str(occuranceOffset), str(data)])

Answer 1

From the documentation

bytes.find(sub[, start[, end]])

Return the lowest index in the data where the subsequence sub is found... Return -1 if sub is not found.

When the find can't locate the substring it will return -1 but in the if statement the -1 is converted into true and your code is executed. Rewrite the condition to the if search != -1: and it should start working.