ESP8266 Community Forum

The recently added file.read() function has a bug which prevents it from reading binary data which contains a 0xFF byte.

The problem seems to be caused by some EOF checking using an int value of -1 in combination with (signed char) casting of the read character: If the read byte is 255 and then casted to (signed char) this equals to -1 and the function wrongly assumes EOF is reached.

The following test program

gives this output:

Markus Gritsch wrote:The recently added file.read() function has a bug which prevents it from reading binary data which contains a 0xFF byte.

The problem seems to be caused by some EOF checking using an int value of -1 in combination with (signed char) casting of the read character: If the read byte is 255 and then casted to (signed char) this equals to -1 and the function wrongly assumes EOF is reached.

The following test program

Code: Select allfname = 'test.txt'

file.remove(fname)
file.open(fname, 'w')
file.write(string.char(65, 66, 67, 255, 68, 69, 70))
file.close()

print(file.list()[fname] .. ' bytes written')

file.open(fname, 'r')
cont = file.read()
file.close()
print(#cont .. ' bytes read with file.read()')
print(string.byte(cont,1,-1))


gives this output:

Code: Select all7 bytes written
3 bytes read with file.read()
65  66  67


build 20150108.

Thanks zeroday, you are the best! It works perfectly now, and for the first time my webserver can now deliver small images! Nice.

Markus Gritsch wrote:Thanks zeroday, you are the best! It works perfectly now, and for the first time my webserver can now deliver small images! Nice.

can you share example? i am so excited