Networking
Ruby Systems Programming
Summarized using AI
Ruby Systems Programming
by Andy DelcambreIn the video "Ruby Systems Programming," presented by Andy Delcambre at the Ruby on Ales conference in 2013, the speaker delves into the fundamentals of systems programming, particularly as it pertains to Ruby development. The discussion emphasizes the importance of understanding low-level system components to appreciate how high-level programming works.
Key points covered in the presentation include:
- Introduction to Systems Programming: Clarifying what systems programming entails, which includes writing software that interacts with hardware and provides a platform for application software.
- User Mode vs Kernel Mode: Explaining the two execution modes on the CPU with a focus on user mode where applications run and kernel mode where direct hardware communication occurs.
- System Calls: Discussing the function of system calls as a means for user-mode programs to request services from the kernel, illustrated with examples on common operations and the number of system calls made during a web server request.
- Writing a Web Server in Ruby: Delcambre progresses to demonstrate how a basic web server can be constructed in Ruby, using socket programming to handle incoming connections and serve HTTP responses.
- TCP/IP Fundamentals: He explains the TCP connection process, including the three-way handshake and the structure of HTTP requests and responses.
- Applicability of Concepts: The significance of these concepts is presented as foundational for higher-level frameworks, with references to established Ruby frameworks like Unicorn that still use underlying socket APIs.
In conclusion, Delcambre asserts that understanding the basic principles of systems programming is valuable for any developer, as it deepens comprehension of the infrastructure that supports modern applications. This grasp of systems programming not only enhances programming skills but also fosters appreciation for the workings behind the software we use daily.
00:00:20.400
All right, so I'm going to talk about systems programming. My name is Andy Delcambre, but I go by a different handle on the internet.
00:00:26.960
My last name is not phonetic.
00:00:36.719
I’ve been working on various Ruby projects since I started programming and I've been having a blast with it. We just relaunched a project right after I started.
00:00:42.960
It's been a lot of fun. Similar to Jessica before me, I have a background in computer science.
00:00:48.399
I came to this point in an interesting way. I was actually a computer science professor at a university.
00:00:53.600
I swore up and down until I was a senior in high school that I would never do what my parents did. I planned to rebel and pursue civil engineering.
00:01:04.479
But then I took a class in civil engineering, and I really liked it.
00:01:10.840
I ended up getting a design degree. I can't even find my degree; it’s somewhere in my apartment. No one's ever asked me for it.
00:01:16.560
I don't believe it has helped me much in terms of job opportunities. So, I don’t think having a degree is essential, although I'm glad I have some foundational knowledge.
00:01:22.240
Now, to provide some background on my history: if you search for "Velcro Software" on the internet, you won’t find me or my mom.
00:01:28.880
Instead, you'll find the company that my father and grandfather started together back in the 70s called Open Software.
00:01:34.560
My grandfather started taking night classes in the late 60s to learn how to automate accounting software, making software for small local governments in Louisiana.
00:01:40.400
They did this for about 20 years until the early 90s. My grandfather also did not have a computer science degree.
00:01:45.840
I again do not believe that a computer science degree is required for success in computing.
00:01:52.320
Now, I’ll get into what I will cover today.
00:01:58.000
These are the two classes I took at my university; I didn't take all of them, but I learned bits from both.
00:02:03.600
This is intended to provide a background about all the underlying code that powers the work we do every day, though this is not the stuff we code directly.
00:02:10.640
I find it really interesting, and I am satisfied by my curiosity to understand how these pieces work.
00:02:16.560
Most of this code runs on virtually any UNIX operating system, although the examples I will present are more specifically using Linux.
00:02:23.200
So, the title is "Ruby Systems Programming." What do I mean by systems programming?
00:02:28.720
It essentially refers to writing system software that operates on an operating system.
00:02:34.319
According to Wikipedia, this software is meant to operate and control computer hardware and provide a platform for application software.
00:02:40.080
There are two components: one involves interacting with hardware such as networking, disks, and displays.
00:02:45.519
The second is the platform component, which underlies everything else. It’s not an end in itself.
00:02:51.760
I’m going to start low, discussing how code executes on the computer and then work my way up the stack.
00:02:58.239
At the end, we'll talk about how an actual web server might be written in Ruby using the most basic primitives.
00:03:04.959
First, we’ll discuss how code is executed on a computer.
00:03:10.000
Code can be executed in two modes on the CPU: user mode and kernel mode.
00:03:15.040
Basically, all the code we write runs in user mode. Unless you are hacking on the kernel, you are not running any code in kernel mode.
00:03:21.280
These modes are implemented in the CPU and have different permissions allowing different actions.
00:03:26.800
In user mode, you can generally do two kinds of operations without calling into the kernel.
00:03:33.599
You can perform mathematical operations and you can access memory, but only the memory you have been granted access to.
00:03:40.239
You may have been given access to a stack, and you can read or write that, but you cannot perform I/O operations like networking or disk access.
00:03:45.440
When in kernel mode, the situation is quite the opposite. Here, you can perform almost any action.
00:03:51.760
The kernel can read or write to any memory in the system and can execute any instruction at any time.
00:03:58.239
It communicates with hardware, manages file systems, and interacts with display drivers. In kernel mode, you can do pretty much anything.
00:04:05.360
Every bit of code you write primarily runs in user mode.
00:04:12.560
If, for example, you are logging information and need to write to disk, how do you achieve that?
00:04:17.680
You might think that you write code, switch modes to kernel mode, perform the write, and then switch back to user mode.
00:04:24.720
However, this is not how it works. All of your code runs in user mode.
00:04:29.919
In practice, you utilize system calls, which are API calls to the kernel.
00:04:36.000
Going back to our logging example, you would make a system call to log your file.
00:04:41.600
Your code effectively hands off execution to the kernel.
00:04:46.880
The kernel handles the file operations, returning a pointer to your code after completion.
00:04:52.320
Then your code can continue and call other system functions as necessary.
00:04:58.880
I was curious about how many system calls we make daily.
00:05:03.919
To find out, I used a tool called strace on Linux, which traces system calls made by a specific program.
00:05:10.400
I booted up a web server locally and recorded all system calls that occurred on a request.
00:05:16.880
The output was quite extensive, reflecting how many operations were taking place.
00:05:22.240
You’ll see calls like closing the file and accepting incoming connections.
00:05:27.840
This process executes significantly faster than the video frame rate.
00:05:34.560
Across the entire request, there were 120 system calls made.
00:05:40.880
Some might argue that this shows Ruby is inefficient with system calls.
00:05:46.880
While this may be true, it's also important to understand the multitude of system calls being made.
00:05:52.560
As you're connecting to databases, interacting with caches, and reading files, countless calls are being processed.
00:05:59.520
The sheer volume of activity necessitates these numerous system calls.
00:06:05.920
Given how fundamental system calls are, one might expect the API to be enormous.
00:06:11.680
Interestingly, there are a total of 326 system calls available.
00:06:17.680
However, not all are operational; many are historical or deprecated.
00:06:23.280
In fact, about 65 of these system calls are not implemented, leaving around 260 functional ones.
00:06:29.440
These calls provide a surprisingly small yet powerful API.
00:06:35.120
Now, switching gears, let's focus on web programming and how to write a web server.
00:06:41.680
This section will not cover the entire scope but will focus on receiving connections.
00:06:47.799
A bit of history: back in the 1960s, an operating system called MULTICS was developed at MIT.
00:06:52.480
Ken Thompson and Dennis Ritchie worked on MULTICS at Bell Labs.
00:06:58.720
Although it was a research project that introduced new concepts, it faced numerous issues.
00:07:05.040
Due to its ambitious goals, it wasn't practical for real-world use.
00:07:10.320
Some people from that team at Bell Labs then developed UNIX as a simpler alternative.
00:07:16.960
Originally, UNIX was designed for single-user systems, which is reflected in its name.
00:07:23.360
By the 1970s, UNIX had evolved to support multi-user functionality.
00:07:29.760
During this time, AT&T faced restrictions that limited its ability to sell the operating system.
00:07:35.520
Universities, including UC Berkeley, obtained licenses for the operating system's source code.
00:07:42.400
In 1978, the first BSD version was released, forming the basis for further UNIX development.
00:07:49.280
Bill Joy and his team added programs like CShell and Vi during this period.
00:07:56.160
By 1983, BSD introduced a TCP/IP stack that gained wide adoption, laying the groundwork for networking.
00:08:02.720
Interestingly, the API developed back then is still in use today. BSD sockets remain a standard across operating systems.
00:08:09.480
The API is remarkably simple and persists decades later, showcasing the stability of foundational technologies.
00:08:16.000
Now, let’s review the core components of the BSD socket API.
00:08:23.200
The socket method provides a socket for interaction, while the bind method binds the socket to a specific port.
00:08:29.600
The listen method prepares the socket to accept incoming connections.
00:08:36.080
Each incoming connection generates a new socket for handling communication.
00:08:43.440
Once communication is done, we need to close the socket properly.
00:08:49.360
This process primarily relates to TCP sockets rather than UDP.
00:08:56.560
Now, let’s discuss how TCP works.
00:09:03.600
The basic connection process includes a three-way handshake.
00:09:09.200
The client sends a packet to request and synchronize a connection.
00:09:15.040
The server acknowledges the request and also sends a synchronization packet back.
00:09:20.560
Finally, the client acknowledges back to complete the handshake.
00:09:27.280
Once established, data can flow freely in both directions, handled transparently by the TCP protocol.
00:09:34.080
As requests are sent, they are packaged as data packets.
00:09:41.040
Each packet must be acknowledged to ensure it was received.
00:09:46.640
If any packet is lost, the protocol triggers retransmission.
00:09:54.080
Finally, when communication is done, a four-way handshake is used to close the connection.
00:10:01.680
This involves each side acknowledging the termination, allowing them to shut down in turn.
00:10:07.680
Now, let’s look at the command line in UNIX systems to list open file descriptors.
00:10:13.440
You will see open file descriptors and their states.
00:10:20.560
For example, a program may be listening on port 80 and viewing any connected clients.
00:10:26.720
Now that we've reviewed TCP, let’s get into HTTP, which should feel more familiar.
00:10:32.559
The HTTP request sent across the network consists of several components.
00:10:39.200
The first line contains the method (like GET or POST), the requested path, and the version of HTTP.
00:10:46.080
After this line follow various headers indicating request details.
00:10:53.920
A sample header could include the user agent, host, and accepted content types.
00:11:00.320
On the response side, the server sends back similar lines.
00:11:06.160
The first line contains the HTTP version followed by a status code and its description.
00:11:12.800
As an example, a successful response might return '200 OK'.
00:11:19.760
This is followed by additional headers detailing the response information.
00:11:26.160
Lastly, the response contains the body, such as HTML content.
00:11:32.640
Now, let’s take a look at a simple example of an HTTP server written in Ruby.
00:11:38.880
I will share some code that illustrates the fundamental components of a web server.
00:11:45.760
Don’t try to read everything on the slide. I’ll explain it line by line.
00:11:52.880
Even though this isn't production-ready code, it still showcases how to run an HTTP server.
00:11:58.960
First, we require the socket library from Ruby's standard library for networking.
00:12:06.080
Next, we define some constants to streamline our code.
00:12:13.040
In the main program, we create a new socket using the socket API.
00:12:19.760
The parameters specify the type of socket—IPv4 and TCP in this case.
00:12:26.560
Then we set up our server to listen to connections on a specific address and port.
00:12:33.280
After binding the socket, we call the listen method, allowing it to receive incoming client requests.
00:12:40.080
When the server is ready, it can accept client connections; the first connection will be queued.
00:12:47.680
As connections are accepted, a new client socket is created for communication.
00:12:56.080
Next, we need to parse the incoming request to determine how to respond.
00:13:02.960
We read the first kilobyte of data from the socket and split it to extract the HTTP components.
00:13:10.960
Once we obtain the requested path, we check if the requested file exists.
00:13:18.720
If the file exists, we respond with a 200 OK status and send the file content.
00:13:25.440
We also send appropriate headers, including the content length.
00:13:32.560
If the file does not exist, we return a 404 Not Found response.
00:13:40.080
Finally, we close the connection to signal to the client that no more data will be sent.
00:13:46.720
This process is a complete web server written in only a few lines of Ruby code.
00:13:53.440
Seeing it run demonstrates the simplicity and power of building applications from the ground up.
00:14:00.080
This is a functional web server capable of dynamically serving requests.
00:14:07.040
So despite the fun of building our own servers, one might wonder why it's important.
00:14:15.360
I believe understanding the fundamentals gives us insights into higher-level frameworks.
00:14:23.440
I found similar code patterns within a well-known Ruby server framework, Unicorn.
00:14:31.200
You’ll see similar ideas implemented using the socket APIs.
00:14:39.040
They still utilize raw socket APIs for their networking operations.
00:14:47.360
This shows that regardless of the layers of abstraction, the underlying principles remain vital.
00:14:55.760
Understanding these concepts can enhance your programming skills and deepen your comprehension.
00:15:03.200
In conclusion, I hope you find this information illuminating.
00:15:09.440
It's beneficial to explore the internal workings of systems programming.
00:15:15.760
It helps us appreciate the infrastructure behind our applications.
00:15:22.560
Thank you all for your attention!
Explore all talks recorded at Ruby on Ales 2013
+12