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Short Intro

Simple File Transfer is a socket programming exercise written in C language. You can submit a pull request after completing the task. Your pull request will be reviewed by me (@ammarfaizi2), and then you will get suggestion, feedback and maybe a request to change something before your PR be merged to the master branch.

Note: Target platform is only Linux.

Pull request is welcomed through GitHub repository (https://github.com/TeaInside/simple_file_transfer).

Task

You have to write TCP client and server. The goal is simply to transfer a file from client to server.

Getting started

Requirements

  • Git
  • GNU Make
  • C compiler (gcc or clang)
  • Linux environment

Installation for Ubuntu

sudo apt-get install gcc make git -y;

Do the exercise

  • Fork the GitHub repository.
  • Clone your fork repository.
  • Create your directory by copying the template to users/<your_username>. For example:
cp -rf template users/myusername;
cd users/myusername;
  • Write your code in your own directory.
  • To compile the code, simply you can just use make command.
make;
  • Test your program, make sure it works perfectly.
  • Submit a pull request on GitHub repository (merge to the master branch).

Technical Explanation

Protocol

In this exercise, we have our own protocol. The data structure in this protocol is represented by this packed struct:

typedef struct __attribute__((packed)) packet_t {
	uint64_t	file_size;
	uint8_t		file_name_len;
	char		file_name[0xffu];
} packet_t;

This struct is sent by the client to server. The file content should be placed after the struct. To make a better abstraction, you can use the following union:

union uni_pkt {
	packet_t	packet;
	char		raw_buf[N]; // Feel free to control the N size as your buffer size
};

File content should be placed at offset raw_buf[sizeof(packet_t)] at the beginning of buffer. In the next cycle of receiving file content, you may overwrite it from &raw_buf[0] with file content.

Communication Direction

  • The server only recv(), it doesn't need to call send().
  • The client only send(), it doesn't need to call recv().

Keep it simple as this is a simple file transfer.

Where to save the file?

Save the file to a relative directory named uploaded_files (it is provided in the template).

Security

Simply make sure the server doesn't accept a file name that contains .. (double dots). If the client sends a file name that contains this pattern, just close it, don't write anything to the disk.

Notes

  • If the file name sent by the client is the same with existing file, just overwrite the existing file with it.
  • If the client closes the connection before it finished to transfer all content. Write any partial bytes the server has received.
  • Make sure you have no memory leak. Use valgrind as memcheck should be helpful.
  • Make sure you sync anything to the disk before the program exits.
  • Make sure you close all socket file descriptors before the program exits.
  • You need an interrupt handler to make sure resources are synced and closed properly. Catch SIGINT, SIGTERM and SIGHUP in your interrupt handler, and then sync and close your resources before exit.
  • Ignore SIGPIPE.

Minimal Working Example

You can see the minimal working example in users/ammarfaizi2. Or simply visit:

https://github.com/TeaInside/simple_file_transfer/tree/master/users/ammarfaizi2

Question and Help

Feel free to ask a question via GitHub repository issue. I will reach you when I get the time.

License

This project is licensed under the GNU GPL v2 license. However, there are some exceptions. This project was licensed under the MIT license, and people were contributing their code under the MIT license.

So some user's directories are still licensed under the MIT license. I can't change the license without their permission.

Files that are licensed under the MIT license

  • Any file in directory users/aviezab
  • Any file in directory users/rLapz