Lab 3: ImageDB with Bloom Filter




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Lab 3: ImageDB with Bloom Filter

WARNING: Please note the change in SHA1 submission instructions.
In terms of number of lines you need to write to complete this lab, it is very short. You only need to write
about 9 lines of code. One line for Task 1, 8 lines for Task 2. The amount of time needed depends on
how comfortable you are with modular arithmetic and bitwise operations.
We assume a client­server setup in this lab. The server (imgdb) will eventually be our distributed hash
table (DHT) node, but in this lab, we assume there is only one such node.
% imgdb [ ‐b <beginID ‐e <endID ]
Upon start up, the server loads up its database with images from an “images” folder under the current
working directory (where you run the server from). For each image, the server computes a SHA1 value
from which an ID is derived. Only those images whose IDs fall within the range of the server’s IDs will
be loaded onto its database. When an image is loaded onto a database, it is also entered into a Bloom
filter by computing three indices from the above SHA1 value. The function to load the database and
populate the Bloom filter is provided to you in the support code under function imgdb::loaddb(). You
should study this function carefully to see how to generate a SHA1 value from an image name and also
how to generate an ID and populate the Bloom filter from the SHA1 value. By default, the range of the
server is (0, 0], i.e., the full identifier ring. You can use the ‐b and ‐e command line options to set the
begin and end values of the server’s ID range.
The client (netimg) works similarly to the client in Lab1. It simply connects to the server specified with
the ‐s command line option, and sends a query for an image, specified with the ‐q command line option.
If the server has the image, it returns it to the client. Otherwise, it returns an imsg_t packet with the
im_found set to NETIMG_NFOUND and the client simply prints out an appropriate error message. The full
client code is provided as part of the support code. You don’t have to write any client code.
Task 1
Your first task is the write the function ID_inrange(ID, begin, end) in hash.cpp. Given an ID, return
true (1) if ID is between begin and end modulo HASH_IDMAX+1, defined in hash.h. For example, 147 is
between (138, 150] but not between (150, 200], whereas 210 is between (200, 10]. This function is used
by imgdb::loaddb(), so you can observe its working by modifying the server’s ID range (using ‐b and ‐e
command line options) and watching which images in the database are loaded. This task takes all but one
line of code.
Task 2
Your second task is to complete the imgdb::searchdb(imgname) function in imgdb.cpp. You’re asked to
compute the SHA1 value of the given imgname. From the computed SHA1 value, you’re asked to compute
the object ID and to determine if the image name is present in the bloom filter. You want to throughly
understand how imgdb::loaddb() works before attempting this function. This task takes about 8 lines of
We make some assumptions for this and subsequent labs and for programming assignment 2.
We assume an object ID size of 8 bits. To compute an object ID, we “fold up” a 160­bit SHA1
value into 8 bits. So the probability of IDs colliding become much higher. For the images, once we
have a hit on the Bloom filter, we simply do a linear search of the database. A match requires
matching both the image’s ID and name, which also resolves any hashing collision (false positive)
for us.
We assume a fixed maximum size of the image database, IMGDB_MAXDBSIZE. Once this capacity is
reached, we simply print out a message to inform the user that we’re not adding more images, but
the server continues to run otherwise.
We assume that once loaded, images are never removed. So we don’t have to worry about holes in
the database or resetting the Bloom filter.
We assume that only one image is read into memory at any one time. Each time there is a search
hit, the image will be read from file. Please be sure to use the ltga.cpp provided with this support
code and not the one from earlier labs as this one does memory management to allow for reuse of
the LTGA object.
Support Code
Since Lab3 support code contains solution to parts of PA1, it will be made available only to those who
have turned in PA1. To those who have turned in PA1, the support code will be available as lab3.tgz in
the Course Folder by the end of day Friday, 1/30, after PA1’s due date. At that time, if your pa1 folder is
not empty, we will assume that you have turned in your PA1, your write permission to the folder will be
revoked, and you will be given read permission to the Lab3 support code. If you want to use some late
days on your PA1, please leave your pa1 folder empty. You will not have access to the Lab3 support code
until you have turned in your PA1. If you’ve decided not to turn in PA1, please email sugih and you will
be given access.
You can also find refimgdb (the one from Lab1 has been renamed refimgdb‐lab1), refnetimg, and an
images folder in the usual course FILES folder. If you’d like to download the images to your own
computer, you can grab images.tgz (22.5 MB). As usual both refnetimg and refimgdb were compiled on
CAEN’s GNU/Linux, so don’t try to run them on Debian, Ubuntu, Mac OS X, or Windows machines.
Recall that the complete source code for netimg in included in the support code, so you should be able to
build the client on your local platform. The support code has been built and tested on Linux, Mac OS X,
and Windows. If you’re not using the provided Makefile, note that imgdb.cpp must be compiled with the
compiler option ‐DLAB3 for the main() function to be included.
Windows specific note:
On Windows, you’d need to install the OpenSSL library to build imgdb. I’ve updated the Windows
section of the Building Socket Program course note with links and instructions to install and use
the OpenSSL library.
Since we’re reading both from files and from sockets, we can no longer simply redefine close() to
closesocket(). Instead, you’d have to use each one specifically, or you can use the provided
Testing Your Code
Run imgdb without any command line option. Run netimg to connect to the running imgdb and request for
ShipatSea.tga. The image should be served and displayed. Now run:
% imgdb ‐b 220 ‐e 20
You should see “*in range*” printed next to the name of each image whose ID is within your imgdb’s ID
Next run netimg to connect to the running imgdb and request for ShipatSeat.tga. Assuming the ID you
compute for ShipatSea.tga is outside the (220, 20] range, you should get an
imgdb: ShipatSea.tga: Bloom filter miss.
message on server side and
netimg: ShipatSea.tga image not found.
on the client side. Test for other boundary conditions.
Submission Instructions
Test your compilation! Your submission must compile without errors.
Your “Lab3 files” comprises your hash.cpp and imgdb.cpp files.
To turn in your Lab3:
1. Submit the SHA1’s of your Lab3 files on the CTools Assignments page. (If the URL doesn’t work
for you, just click the “Assignments” item on the left menu of the CTools page for EECS 489.)
Once you’ve submitted your SHA1’s, don’t make any more changes to the files, or your SHA1’s
will become invalid.
2. Upload your Lab3 files by pointing your web browser to Course folder and navigate to your lab3
folder under your uniqname. Or you can scp the files to your lab3 folder on IFS:
This path is accessible from any machine you’ve logged into using your ITCS (
password. Please report any problems to ITCS.
3. Keep your own backup copy! Don’t make any more changes to the files once you’ve submitted
your final SHA1’s.
The timestamp of your SHA1 submission on CTools’ Assignments page will be your time of submission.
If this is past the deadline, your submission will be considered late. You are allowed multiple
“submissions” without late­policy implications as long as you respect the deadline. CTools keeps only
your last submission.
Do NOT turn in an archival (.zip or .tgz) file, instead please turn in your solution files individually.
Turn in ONLY the files you have modified. Do not turn in support code we provided that you haven’t
modified. Do not turn in any binary files (object files, executables, or images) with your assignment.
Do remove all printf()’s or cout’s and cerr’s and any other logging statements you’ve added for
debugging purposes. You should debug using a debugger, not with printf()’s. If we can’t understand the
output of your code, you will get zero point.