How to create two wired virtual serial ports on Linux?

fvicente — Fri, 19 Feb 2010 18:18:32 +0000

To create two bridged virtual serial ports use the following command:
socat -d -d pty,raw,echo=0 pty,raw,echo=0

The output will show you which are the virtual ports (or pseudo terminals) created, e.g.:
2010/02/19 16:16:33 socat[9662] N PTY is /dev/pts/3 2010/02/19 16:16:33 socat[9662] N PTY is /dev/pts/4 2010/02/19 16:16:33 socat[9662] N starting data transfer loop with FDs [3,3] and [5,5]

Note: if you are using Ubuntu and you do not have this command, try:
sudo apt-get install socat

Image source

How do I compare two binary files on Linux?

fvicente — Fri, 19 Feb 2010 17:51:00 +0000

The easiest way I found is dumping the binaries into text files using hexdump and then comparing them with your favourite program (diff, Meld, etc.). E.g.:
hexdump -C a.bin >a.txt hexdump -C b.bin >b.txt diff a.txt b.txt

Image source

Extracting FLV meta tags with Python

fvicente — Sat, 06 Feb 2010 00:07:36 +0000

I’ve stolen this code from http://code.activestate.com/recipes/457406/ which in turn was stolen / ported from http://inlet-media.de/flvtool2 , made some small fixes in bugs related to the date conversion function, object and array unmarshaling, file name hardcoded, etc… If you want to learn more about the FLV format and metatags read Acrobat’s Video File Format Specification Version 10

from struct import unpack
from datetime import datetime

class FLVReader(dict):
    """
    Reads metadata from FLV files
    """

    # Tag types
    AUDIO = 8
    VIDEO = 9
    META = 18
    UNDEFINED = 0

    def __init__(self, filename):
        """
        Pass the filename of an flv file and it will return a dictionary of meta
        data.
        """
        # Lock on to the file
        self.file = open(filename, 'rb')
        self.signature = self.file.read(3)
        assert self.signature == 'FLV', 'Not an flv file'
        self.version = self.readbyte()
        self.typeFlags = self.readbyte()
        self.dataOffset = self.readint()
        extraDataLen = self.dataOffset - self.file.tell()
        self.extraData = self.file.read(extraDataLen)
        self.readtag()

    def readtag(self):
        unknown = self.readint()
        tagType = self.readbyte()
        dataSize = self.read24bit()
        timeStamp = self.read24bit()
        unknown = self.readint()
        if tagType == self.AUDIO:
            print "Can't handle audio tags yet"
        elif tagType == self.VIDEO:
            print "Can't handle video tags yet"
        elif tagType == self.META:
            endpos = self.file.tell() + dataSize
            self.event = self.readAMFData()
            metaData = self.readAMFData()
            # We got the meta data.
            # Our job is done.
            # We are complete
            self.update(metaData)
        elif tagType == self.UNDEFINED:
            print "Can't handle undefined tags yet"

    def readint(self):
      data = self.file.read(4)
      return unpack('>I', data)[0]

    def readshort(self):
      data = self.file.read(2)
      return unpack('>H', data)[0]

    def readbyte(self):
      data = self.file.read(1)
      return unpack('B', data)[0]

    def read24bit(self):
      b1, b2, b3 = unpack('3B', self.file.read(3))
      return (b1 << 16) + (b2 << 8 ) + b3

    def readAMFData(self, dataType=None):
        if dataType is None:
            dataType = self.readbyte()
        funcs = {
            0: self.readAMFDouble,
            1: self.readAMFBoolean,
            2: self.readAMFString,
            3: self.readAMFObject,
            8: self.readAMFMixedArray,
           10: self.readAMFArray,
           11: self.readAMFDate
        }
        func = funcs[dataType]
        if callable(func):
            return func()

    def readAMFDouble(self):
        return unpack('>d', self.file.read(8))[0]

    def readAMFBoolean(self):
        return self.readbyte() == 1

    def readAMFString(self):
        size = self.readshort()
        return self.file.read(size)

    def readAMFObject(self):
        result = {}
        data = True
        while data:
            size = self.readshort()
            key = self.file.read(size)
            dataType = self.readbyte()
            if not key and dataType == 9:
                break
            data = self.readAMFData(dataType)
            result[key] = data
        return result

    def readAMFMixedArray(self):
        size = self.readint()
        result = {}
        i = 0
        while i < size:
            key = self.readAMFString()
            dataType = self.readbyte()
            if not key and dataType == 9:
                break
            result[key] = self.readAMFData(dataType)
            i += 1
        return result

    def readAMFArray(self):
        size = self.readint()
        result = []
        i = 0
        while i < size:
            result.append(self.readAMFData())
            i += 1
        return result

    def readAMFDate(self):
        date = self.readAMFDouble()/1000
        localoffset = self.readshort()
        return datetime.fromtimestamp(date)

if __name__ == '__main__':
    import sys
    from pprint import pprint
    if len(sys.argv) == 1:
        print 'Usage: %s filename [filename]...' % sys.argv[0]
        print 'Where filename is a .flv file'
        print 'eg. %s myfile.flv' % sys.argv[0]
    for fn in sys.argv[1:]:
        x = FLVReader(fn)
        pprint(x)

Download this code snippet from here

from struct import unpack
from datetime import datetime

class FLVReader(dict):
    ”"”
    Reads metadata from FLV files
    ”"”

    # Tag types
    AUDIO = 8
    VIDEO = 9
    META = 18
    UNDEFINED = 0

    def __init__(self, filename):
        ”"”
        Pass the filename of an flv file and it will return a dictionary of meta
        data.
        ”"”
        # Lock on to the file
        self.file = open(filename, ’rb’)
        self.signature = self.file.read(3)
        assert self.signature == ’FLV’, ’Not an flv file’
        self.version = self.readbyte()
        self.typeFlags = self.readbyte()
        self.dataOffset = self.readint()
        extraDataLen = self.dataOffset - self.file.tell()
        self.extraData = self.file.read(extraDataLen)
        self.readtag()

    def readtag(self):
        unknown = self.readint()
        tagType = self.readbyte()
        dataSize = self.read24bit()
        timeStamp = self.read24bit()
        unknown = self.readint()
        if tagType == self.AUDIO:
            print ”Can’t handle audio tags yet”
        elif tagType == self.VIDEO:
            print ”Can’t handle video tags yet”
        elif tagType == self.META:
            endpos = self.file.tell() + dataSize
            self.event = self.readAMFData()
            metaData = self.readAMFData()
            # We got the meta data.
            # Our job is done.
            # We are complete
            self.update(metaData)
        elif tagType == self.UNDEFINED:
            print ”Can’t handle undefined tags yet”

    def readint(self):
      data = self.file.read(4)
      return unpack(‘>I’, data)[0]

    def readshort(self):
      data = self.file.read(2)
      return unpack(‘>H’, data)[0]

    def readbyte(self):
      data = self.file.read(1)
      return unpack(‘B’, data)[0]

    def read24bit(self):
      b1, b2, b3 = unpack(’3B’, self.file.read(3))
      return (b1 << 16) + (b2 << 8) + b3

    def readAMFData(self, dataType=None):
        if dataType is None:
            dataType = self.readbyte()
        funcs = {
            0: self.readAMFDouble,
            1: self.readAMFBoolean,
            2: self.readAMFString,
            3: self.readAMFObject,
            8: self.readAMFMixedArray,
           10: self.readAMFArray,
           11: self.readAMFDate
        }
        func = funcs[dataType]
        if callable(func):
            return func()

def readAMFDouble(self):
return unpack(‘>d’, self.file.read(8))[0]

def readAMFBoolean(self):
return self.readbyte() == 1

    def readAMFString(self):
        size = self.readshort()
        return self.file.read(size)

    def readAMFObject(self):
        result = {}
        data = True
        while data:
            size = self.readshort()
            key = self.file.read(size)
            dataType = self.readbyte()
            if not key and dataType == 9:
                break
            data = self.readAMFData(dataType)
            result[key] = data
        return result

    def readAMFMixedArray(self):
        size = self.readint()
        result = {}
        i = 0
        while i < size:
            key = self.readAMFString()
            dataType = self.readbyte()
            if not key and dataType == 9:
                break
            result[key] = self.readAMFData(dataType)
            i += 1
        return result

    def readAMFArray(self):
        size = self.readint()
        result = []
        i = 0
        while i < size:
            result.append(self.readAMFData())
            i += 1
        return result

    def readAMFDate(self):
        date = self.readAMFDouble()/1000
        localoffset = self.readshort()
        return datetime.fromtimestamp(date)

if __name__ == ’__main__’:
    import sys
    from pprint import pprint
    if len(sys.argv) == 1:
        print ’Usage: %s filename [filename]…’ % sys.argv[0]
        print ’Where filename is a .flv file’
        print ’eg. %s myfile.flv’ % sys.argv[0]
    for fn in sys.argv[1:]:
        x = FLVReader(fn)
        pprint(x)

(HTML) Table cell not inheriting style

fvicente — Fri, 05 Jun 2009 00:24:27 +0000

The goal of this new blog category called “Programming FAQ” is to publish short posts with day to day programming problems and their solutions, or at least provide a tip to find the proper solution to your problem. And today we start with this simple and stupid problem that can happen to anyone with poor HTML experience like me. “My HTML table does not seems to inherit the style from a parent element”, here is the example:




	
	
		
			BLUE TEXT

In the below example I would expect to see the “BLUE TEXT” in blue, but is not (at least in FireFox). So what the hell is wrong with my code? probably many things but because I’m not interested in following/reading the W3C recommendations for my uncle’s home page, here is one possible solution: Add the transitional DOCTYPE to your document, or the DOCTYPE that adequate better to your page (read more here). E.g.:

So, now you know. Never forget the DOCTYPE it is very important… Why? read this… It has to do with poor standards, browsers and all that crap.

AlferSoft Blog » Programming FAQ

How to create two wired virtual serial ports on Linux?

Image source

How do I compare two binary files on Linux?

Image source

Extracting FLV meta tags with Python

(HTML) Table cell not inheriting style