Drogon – C++14/17-based rapid HTTP and web application framework | Hacker News Reader

Drogon – C++14/17-based rapid HTTP and web application framework

github.com

84 pointsdragonsh52 comments

Always glad to see another contender!

The documentation is very thorough and gives a good overview. Every library should be like this.

That being said, I have written a lot of HTTP servers and clients in C++ so I have some opinions on the design of this library.

Modern C++ really tries to avoid preprocessor macros for the reason that it's really hard to know what is going on. Macros can do anything. So I would suggest you get rid of the code generation including dragon_ctl. Write a library that doesn't need code generation. C++17 has all the tools needed to do this.

Some more contenders: https://github.com/guteksan/REST-CPP-benchmark

Personally, I use cpp-httplib to set up a web service for some old but highly relevant Fortran libraries. I am quite happy with this framework but it is always good to get to know other players in this league.

I have a question. I have also implemented my C++ web framework. I found it is difficult to conform to http spec. There doesn't seem to be a Conformance test?

How do people do it?

If you're writing one for general consumption, I wish you luck.

Developing a trust accounting application for law firms in Drogon. It's an excellent framework written in Modern C++. Very easy to work with. Check out the Source code on git, it is beautifully written. If you are proficient in Modern C++, then this is the framework to use for speedy development. Just as an aside, I migrated the project from Go to C++.

> I migrated the project from Go to C++

Any particular reasons why?

Since you are shooting for modern C++, why not use Botan rather than OpenSSL?

https://botan.randombit.net/

What is the use case for a C++ web framework? Would higher level languages/frameworks make use of this to do some of the heavy lifting? Would a company migrate to something like this once at scale? Or, are there just some people/companies who prefer to use C++?

I currently have an architecture where I have a whole bunch of C++ code doing computational stuff. Later (years after writing the core computational library in C++) I was asked to expose the library via a REST API. At the time I was pretty young (didn't and still don't have the necessary experience to write a web framework myself) and none of the existing C++ web frameworks seemed to work very well. So, I now have a complex architecture with a Java Spring front end that communicates to a C++ backend. Would have been a whole lot simpler all around if I could have easily used C++ for the whole thing.

Writing wrappers to interface c++ libraries with most common scripting languages is (usually) pretty easy. Probably much more so than trying to roll an entire HTTP server in C++.

If you have to roll your own, of course it is, hence why I didn't try... but if there was a mature, easy to integrate HTTP server library I would prefer to keep everything in C++ (or better yet rewrite it all in Rust, but that's a whole other can of worms).

At a previous company most of the business is run on C++ applications that expose web APIs (SOAP/REST), is that web enough for you?

C++ is used because there's a lot of heavy lifting in message handling, transformation, and latency has a big impact on business. Any "glue" layer between a computing backend and a presentation backend adds expensive milliseconds to provide a response. If you just want to handle concurrency without care for much else, your usual dynamically typed language will do, and you solve your problems scaling horizontally.

But latency is something that can't be solved scaling horizontally.

Java or Python are used for less critical stuff (admin/management panels and such), but anything transactional is 99% of the time C++.

That said, the framework had terrible interfaces and it implied linking to a multi-GiB .so library, but in the end relatively few servers could handle 50k (relatively complex) tps with less than 20ms latency. I can barely get 20ms with a hello world django app on my laptop.

> Java or Python are used for less critical stuff (admin/management panels and such), but anything transactional is 99% of the time C++

No.

I take it you are familiar in detail with how Uberphallus' previous employer operates and can give us the correct details instead?

I took it as a general statement, not just about his employer. Maybe I misread.

This is going to become more and more common for media intensive applications.

https://vo.codes uses a Rust HTTP web framework. It's not C++, but it's the exact same use case. High performance compute.

It's not unheard of for ordinary CRUD websites, either. IIRC, the first version of OkCupid was written in C++.

How much more performant is C++ or Rust?

Didn’t Instagram manage to scale Python?

For small teams, wouldn’t the performance of Rust be offset by the productivity lost by not using Python, for example?

Assuming expert programmers in each language.

A lot of Python is coordinating other libraries written in native code, so that part is probably about the same. However, take parsing JSON, which is often used for web RPC, Python is orders of magnitude slower in many cases. In one benchmark, parsing a 100MB array classes with floats, the time within the program after loading the string took around 12s for Python and 0.9s in C++. That is probably extreme, but it negated startup/warmup time and most aspects other than parsing/reifying the data.

But then when you look at memory overhead and scale out, the number of servers/instances needed is both more and for a longer time. This has a cost.

The difference is, getting developers proficient in Python is much easier, and if you cannot get people to make your things, it's kind of a problem. If the majority of the program is inside the library, the performance difference starts to go away in many cases.

I mainly develop serves in C++ but I've used Python. It is my private opinion but when we are talking reasonable size project I do not feel I am loosing any productivity by using C++. Rather the other way around.

I work in a domain where we do tons of computational work in C++. With everyhting being webified now, a C++ backend for a web app would actually be exactly what I need to expose data via rest for a modern frontend.

If you're writing a C++ application, it can be quite useful. I've shared this before:

I worked at a company once that had a really decent HTTP server library... That they put in every program.

You'd launch an app, and to debug it, you'd access http://localhost:9001. From there, you could go to URLs for different libraries in the app. Like, if you had a compression library, you could go http://localhost:9001/compression. It would show stats about the recent work it had done, how long it took, how much CPU, RAM, disk it used. The state of variables now, etc. You could click a button to get it to dump its cache, etc.

If you were running a service on a remote machine, accessing it over HTTP to control it was just awesome. http://r2d2:9001/restart. http://r2d2:9001/quit. http://r2d2:9001/logfile.

Oh, and the services running on that remote machine would register with a system-level monitor. So, if you went to http://r2d2/services, you could see a list of links to connect to all of the running services.

...and every service registered with a global monitor for that service. So, if you knew a Potato process was running somewhere, but you weren't sure which machine it was on, you could find it by going to http://globalmonitor/Potato, and you'd see a list of machines it was running on.

Just all kinds of awesomeness were possible. Can not recommend enough.

And, I mean like, programs with a GUI. Like, picture a game. Except on my second monitor, I had Chrome open, talking to the game's engine. I could use things like WebSockets to stream data to the browser. Like, every time the game engine rendered a shot, I could update it (VNC-style) in the browser window. Except annotated with stats, etc. It was just the most useful way to organize different debug information.

And what was great was that writing a library, and wanting to output information, you wouldn't write it to std out... You'd make HTML content, and write to it. Want to update it? Clear the buffer and write to it again. As a user, if you ever want to read the buffer, you just browse it. Want to update it? Refresh the window. Or better yet, stream it over a websocket. Like Std Out on steroids. If you need to combine the output from a few libraries in a new window, you just write a bit more HTML in your code, and you're doin' it.

It's just another example, in my mind, of the power of libraries. We all get used to thinking of frameworks (IIS, Apache) as the only way to solve a problem, that we forget to even think about putting things together in new and unexpected ways. HTTP as a library - HELL YES.

Using HTML to debug programs, live, is highly under-utilized.

I would say that debugging a program live is highly underrated. There is no inherent reason why building a webserver into everything and using html for visualization is the best way to go. Shared memory can be used and be 100-1000 times faster, which can make a huge difference if you want to visualize large amounts of data like point clouds, pixels, etc. as they change.

In your scenario it sounds like an easy way to make a big step forward, though I don't think that takes it far enough.

Well, for one thing, you're presuming the person who wants to inspect something a) has a debugger, b) knows how to use it, c) that the machine running the application allows access through those ports.

I didn't presume any of those things and I'm not sure where any of those ideas come from. A program can write to shared memory that is read by a separate program. That doesn't take a debugger and it doesn't take 'ports'. I'm actually not sure what you mean by ports.

Sorry, I feel like we're really mis-communicating.

I proposed an idea, and you proceeded to tell me "There is no inherent reason why [my idea] is the best way to go." I think that's a pretty rough way to respond to someone suggesting an idea that might be useful under some circumstances. It's a possibly new tool in your tool-belt. I didn't mean to suggest that a hammer "is the best way to go" for any job. But sometimes the problem is a nail, and a hammer is the best tool.

You highlighted the value of "debugging a program live," which is true, but I thought you meant using a sophisticated debugger (gdb / Visual Studio, etc). For instance, Microsoft Visual Studio has (or used to have) the ability to have plug-ins to help you visualize complex structures in memory of the running process, for instance showing a Bitmap as an actual image on your screen. I thought that's what you meant, or just using gdb or some other sophisticated debugger. But yes, that was my misunderstanding.

Shared memory is nice, and I've used it before, but it required me to store all of my interesting objects in shared memory structures. Which meant changing how my application was written. Yes, sometimes I could see that being amazing. Or I suppose you make a large copy of them.

I've also done the trick where, if I hit a URL on my app, then it took the point clouds, pixels, etc, and provided a rendered PNG image of them. But it could do it without requiring me to restructure my program's memory layout (other than a few multi-threading locks, when needed.) And I've done that over WebSockets, with interactive rendering rates, basically like a VNC. And what was nice about that, again, was that I could run a process on one machine, and debug it (through HTML) from another. And grant that ability to other users, without having to tell them how to install a debugger app, and giving that app access to connect over the network, and etc.

The ports thing was in reference to the ability of Microsoft Visual Studio (and presumably other debuggers) to do remote debugging, attaching themselves to a process running on another computer. So, you have to be able to connect to that process. Whereas my proposal could work on normal HTTP / HTTPS ports, and with authentication, could enable a user to access debug views.

Anyway, yes, I very much agree with you that debugging a program live is highly underrated, and I think it's good if people share different ways to do that.

Very neat! So every "public" API had a corresponding URL which could be publicly accessed over HTTP ?. Sounds like a HTTP-based overlay network within the domain of your application(s).

I use C++ to write business servers that along with managing data do some heavy calculations and reporting. I see no problems at all using C++ (in combination with some libraries) for this purpose. They're blindingly fast and memory efficient. Using modern C++ they're not any more difficult to develop then using "traditional" means.

Pretty much the same as every other language - if you're working in X, and you have a team of X developers, you'll want to use a framework that's also in X so that your toolset doesn't spiral out of control.

In C++ you could link-in a golang webserver, with cgo, or use Spring/Vertx using JNI, but you probably won't.

provide a web api for existing C++ applications and libraries

I'm not sure there is much of a use-case. Most enterprises want to focus on developer productivity. Most modern web frameworks are more than fast enough, whether you use Spring, Kestrel, or ASP.net, it doesn't really matter anymore, even Flask is more than good enough for 99% of use-cases.

Given how capable even cheap cloud hardware is now, optimizing for developer productivity is better than choosing the "very fast" C or Rust framework which no one understands how to program for. Also, C/Rust etc, being harder languages to learn and lower level, tend to be both harder to hire for and also end up with more bugs than the higher level languages.

> Most enterprises want to focus on developer productivity

And that is something that I generally am OK with, to a point. If your application isn’t performance sensitive, have at ‘er and use whatever you feel is going to be the most productive, even if it potentially has higher opex.

Bugs is an interesting thing. There’s two flavours of bugs, basically: requirement errors and implementation errors. High vs low level languages don’t do much to alleviate the first category of bugs at all (e.g. not thinking through how “random shuffle” should work in a music player). High level languages can help reduce the number of coding errors compared too lower level languages, but they do have their own quirks (eg using an empty list as a default argument in Python)

Ultimately, though, it’s all about working within the constraints you’re given, whether time-to-market, development costs, opex costs, system performance, etc. I’m intrigued by this framework because I have a high performance image processing system written in C++17 and there’s been some discussion recently about an HTTP API for it. Why is it in C++ to begin with? It’s on a somewhat resource constrained board (Jetson Nano) and has to run at at least 70fps for what it’s doing. 14 milliseconds to grab the image from the camera, run it through TensorRT, and do something useful with the output. I would have considered Rust as well, but a good chunk of this is leveraging existing C++ libraries (OpenCV, FLIR Spinnaker, TensorRT, etc) and fighting with wrappers and weird impedance mismatches is not my idea of a good time.

>Most enterprises want to focus on developer productivity

While I absolutely agree, it all depends on a scale. If you're using for example 10 cloud instances, x2 performance improvement will not justify extra person-months spent on developing more performant solution. On the other hand if you run 1000000 servers even 1% performance boost might be worth that effort.

There's a additional point: on 4 cloud instances, a x5 performance improvement means you have only one machine to manage instead of several, and then your ops costs are way smaller.

There's a big number of companies who have between 4 and 20 machines for serving Python, Node or PHP apps and spend a lot of efforts managing them with overkill solutions like kubernetes or whatever when it could be a single machine or two using more frugal languages.

Drogon is similar to "drogón" in Spanish, which means "junkie" or someone who takes a lot of drugs.

I guess if we're doing random tidbits.

And "junkie" is a very harmful term to use and implies a moral failing of the drug user.

I knew that name was familiar. Drogon scores nicely in Techempower's benchmarks:

https://www.techempower.com/benchmarks/#section=data-r19&hw=...

Yes indeed it is one of the top performers. But I feel need more real-life examples of companies and systems using it.

Hope it generates some interest among programming community to also look at modern C++ as viable web development platform.

The problem isn't performance, the problem is developer productivity. C++ isn't known for building things quickly. Why would anyone use this over DotNet Core, which is also highly performance but significantly easier to understand. Also building anything in a complex language like C++ means more bugs and errors.

I don't find this to be true at all with modern C++. Doing the same things ends being more straightforward in my experience. Setting up compilation is often more painful and sooner or later I run into some snags with const and map iteration, though those don't end up being long term time sinks.

Doesn’t make any sense at all to go with dot net if the rest of your app is in C++ and something easy like this exists.

> C++ isn't known for building things quickly.

What language is?

If only sticking to deadlines was as easy as changing your programming language!

Alas.

Up to number one in composite score from number nine in the previous round.

Does anybody know why it does so well on the multiple updates test?

Take a look at features on the page:

   1. Support non-blocking I/O based asynchronously reading and writing database (PostgreSQL and MySQL(MariaDB) database);

   2. Support asynchronously reading and writing sqlite3 database based on thread pool;

Sure but actix does the same via tokio-Postgres and is beaten by almost 2x.

Not sure of the exact reason may be because it is directly using the postgresql C client library. Check the implementation of DB client:

https://github.com/an-tao/drogon/blob/master/orm_lib/src/DbC...

I was looking for a C++ HTTP framework a couple of months ago for a hobby project of mine. However, the whole debacle with WinGet and AppGet really left a very horrible taste in my mouth, that I did not want anything to do with a framework built by Microsoft. So I opted for Boost::Beast

edit: I am wrong, see comment below.

Since this project was submitted by project creator, it deserves "Show HN" status (https://news.ycombinator.com/showhn.html).

I am not the creator, just stumbled on it looking for examples in modern C++, was especially looking for C++ 20. Found it interesting and try to share on HN.

I'm not sure if this is interesting to anyone. But, I wanted something a bit more lightweight, so, I'm writing my own kinda/sorta Drogon thing. It's using git and cmake to (hopefully) serve as a better library management system. Here's the 'app' I'm devoloping: https://github.com/brighton36/vuecrudd and here's the project itself: https://github.com/brighton36/prails

Unless I missed something, it says it can auto generate code, but I don't see anything regarding Swagger/OpenAPI

I think it means code generation using drogon_ctl.

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