Tag Archives: video

mastering libcurl

November 1, 2023 Daniel Stenberg

On November 16 2023, I will do a multi-hour tutorial video on how to use libcurl. How to master it. As a follow-up to my previous video class called mastering the curl command line (at 13,000+ views right now).

This event will run as a live-stream webinar combination. You can opt to join via zoom or twitch. Zoom users can ask questions using voice, twitch viewers can do the same using the chat. For attending via Zoom you need to register, for twitch you can just show up.

It starts at 18:00 CET (09:00 PST, 17:00 UTC)

This session is part one of the planned two-part series. The amount of content is simply too much for me to deliver in a single sitting with intact quality. The second part will happen the following Monday, on November 20. Same time.

Both sessions will be recorded and will be made available for browsing after the fact.

At the time of me putting this blog post up the presentation and therefore agenda is not complete. I have also not yet figured out exactly how to do the split between the two episodes. Below you will find the planned topics that will be covered over the two episodes. Details will of course change in the final presentation.

The idea is that very little about developing with libcurl should be left out. This is the most thorough, most advanced, most in-depth libcurl video you ever saw. And it will be shock-full with source code examples. All examples that are shown in the video, are also provided stand-alone for easy browsing, copy and paste and later reading in a dedicated mastering libcurl GitHub repository.

Part one

The slides for part one.

Part two

The slides for part two.

Mastering libcurl

The project

Reminders about the curl project

getting it

installing
building
debugging
free support
paid support

API and ABI

compatibility
versions
the API is for C
header files
compiling libcurl programs
documentation

Architecture

C89
backends
everything is non-blocking

API fundamentals

content ignorant / URLs / callbacks
basic by default
global init
easy handles
easy options
curl_easy_setopt
curl_easy_perform
curl_easy_cleanup
write callback
multi handle
multi perform
curl_multi_info_read
curl_multi_cleanup
a multi example
caches
curl_multi_socket_action
curl_easy_getinfo

Puppeteering

verbose
debug function
tracing
curl_version / curl_version_info
persistent connections
multiplexing
Downloads
Storing downloads
Compression
Multiple downloads
Maximum file size
Resuming and ranges
Uploads
Multiple uploads
Transfer controls
Stop slow transfers
Rate limiting
Connections
Name resolve tricks
Connection timeout
Network interface
Local port number
Keep alive
Timeouts
Authentication
.netrc
return codes
–libcurl
post transfer meta-data
caches
some words on threads
error handling with libcurl

Share API

sharing data between easy handles

TLS

enable TLS
ciphers
verifying server certificates
custom checks
client certificates
on TLS backends
SSLKEYLOGFILE

Proxies

Proxy type
HTTP proxy
SOCKS proxy (tor)
Authentication
HTTPS proxy
Proxy environment variables
Proxy headers

HTTP

Ranges
HTTP versions
Conditionals
HTTP POST
data with callback
Multipart formpost
Redirects
Modify the HTTP request
HTTP PUT
Cookies
Alternative Services
HSTS
HTTP/2
HTTP/3

HTTP header API

get specific header field after transfer
iterate over many headers

URL API

Parse a URL
extract components
update components
URL encoding/decoding
IDN encoding/decoding
redirects

WebSocket

just a quickie, I did a separate websocket video recently
https://youtu.be/NLIhd0wYO24

Video: Landing code in curl

August 13, 2020 Daniel Stenberg

A few hours ago I ended my webinar on how to get your code contribution merged into curl. Here’s the video of it:

Here are the slides.

cURL and libcurl

Video: testing curl for security

July 2, 2020 Daniel Stenberg

The webinar from June 30, now on video. The slides are here.

cURL and libcurl

video: common mistakes when using libcurl

May 8, 2020 Daniel Stenberg

As I posted previously, I did a webinar and here’s the recording and the slides I used for it.

The slides.

cURL and libcurl

libcurl video tutorial

December 3, 2019 Daniel Stenberg

I’ve watched how my thirteen year old son goes about to acquire information about things online. I am astonished how he time and time again deliberately chooses to get it from a video on YouTube rather than trying to find the best written documentation for whatever he’s looking for. I just have to accept that some people, even some descendants in my own family tree, prefer video as a source of information. And I realize he’s not alone.

So therefore, I bring you, the…

libcurl video tutorial

My intent is to record a series of short and fairly independent episodes, each detailing a specific libcurl area. A particular “thing”, feature, option or area of the APIs. Each episode is also thoroughly documented and all the source code seen on the video is available on the site so that viewers can either follow along while viewing, or go back to the code afterward as a reference. Or both!

I’ve done the four first episodes so far, and they range from five minutes to nineteen minutes a piece. I expect that it might take me a while to just complete the list of episodes I could come up with myself. I also hope and expect that readers and viewers will think of other areas that I could cover so the list of video episodes could easily expand over time.

Feedback

If you have comments on the episodes. If you have suggestion of what to improve or subjects to cover, head over to the libcurl-video-tutorials github page and file an issue or two!

Video setup

I use a Debian Linux installation to develop on. I figure it should be similar enough to many other systems.

Video wise, in each episode I show you my text editor for code, a terminal window for building the code, running what we build in the episode and also for looking up man page information etc. And a small image of myself. Behind those three squares, there’s a photo of a forest (taken by me).

I plan to make each episode use the same basic visuals.

In the initial “setup” episode I create a generic Makefile, which we can reuse in several (all?) other episodes to build the example code easily and swiftly. I’ve previously learned that people consider Makefiles difficult, or sometimes even magic, to work with so I wanted to get that out of the way from the start and then focus more directly on actual C code that uses libcurl.

Receive data episode

Here’s the “receive data” episode as an example of how this can look.

The link: https://bagder.github.io/libcurl-video-tutorials/

Firefox, Network, Technology

Talk: web transport, today and tomorrow

April 13, 2017 Daniel Stenberg

At the Netnod spring meeting 2017 in Stockholm on the 5th of April I did a talk with the title of this post.

Why was HTTP/2 introduced, how well has HTTP/2 been deployed and used, did it deliver on its promises, where doesn’t HTTP/2 perform as well. Then a quick (haha) overview on what QUIC is and how it intends to fix some of the shortcomings of HTTP/2 and TCP. In 28 minutes.

Mozilla, Network, Technology, Web

HTTP/2 in April 2016

April 14, 2016 Daniel Stenberg

On April 12 I had the pleasure of doing another talk in the Google Tech Talk series arranged in the Google Stockholm offices. I had given it the title “HTTP/2 is upon us, and here’s what you need to know about it.” in the invitation.

The room seated 70 persons but we had the amazing amount of over 300 people in the waiting line who unfortunately didn’t manage to get a seat. To those, and to anyone else who cares, here’s the video recording of the event.

If you’ve seen me talk about HTTP/2 before, you might notice that I’ve refreshed the material somewhat since before.

Open Source

Turn many pictures into a movie

March 11, 2016 Daniel Stenberg 1 Comment

Challenge: you have 90 pictures of various sizes, taken in different formats and shapes. Using all sorts strange file names. Make a movie out of all of them, with the images using the correct aspect ratio. And add music. Use only command line tools on Linux.

Solution: this is a solution, you can most likely solve this in 22 other ways as well. And by posting it here, I can find it myself if I ever want to do the same stunt again…

#!/bin/sh

j=0
# convert options
pic="-resize 1920x1080 -background black -gravity center -extent 1920x1080"

# loop over the images
for i in `ls *jpg | sort -R`; do
 echo "Convert $i"
 convert $pic $i "pic-$j.jpg"
 j=`expr $j + 1`
done

# now generate the movie
mp3="file.mp3"
echo "make movie"
ffmpeg -framerate 3 -i pic-%d.jpg -i $mp3 -acodec copy -c:v libx264 -r 30 -pix_fmt yuv420p -s 1920x1080 -shortest out.mp4

Explained

This is a shell script.

The ‘pic’ variable holds command line options for the ImageMagick ‘convert‘ tool. It resizes each picture to 1920×1080 while maintaining aspect ratio and if the pic gets smaller, it is centered and gets a black border.

The loop goes through all files matching *,jpg, randomizes the order with ‘sort’ and then runs ‘convert’ on them one by one and calls the output files pic-[number].jpg where number is increased by one for each image.

Once all images have the correct and same size, ‘ffmpeg‘ is invoked. It is told to produce a movie with 3 photos per second, how to find all the images, to include an mp3 file into the output and to stop encoding when one of the streams ends – this assumes the playing time of the mp3 file is longer than the total time the images are shown so the movie stops when we run out of images to show.