(This is a crosspost of a tutorial originally published on my personal blog)

Among other interesting features, Rust has a powerful macro system. Unfortunately, even after reading The Book and various tutorials, when it came to trying to implement a macro which involved processing complex lists of different elements, I still struggled to understand how it should be done, and it took some time till I got to that "ding" moment and started misusing macros for everything :) (ok, not everything as in the i-am-using-macros-because-i-dont-want-to-use-functions-and-specify-types-and-lifetimes everything like I've seen some people do, but anywhere it's actually useful)

CC BY 2.0 image by Conor Lawless

So, here is my take on describing the principles behind writing such macros. It assumes you have read the Macros section from The Book and are familiar with basic macros definitions and token types.

I'll take a Reverse Polish Notation as an example for this tutorial. It's interesting because it's simple enough, you might be already familiar with it from school, and yet to implement it statically at compile time, you already need to use a recursive macros approach.

Reverse Polish Notation (also called postfix notation) uses a stack for all its operations, Continue reading

For some businesses SEO is a bad word, and for good reason. Google and other search engines keep their algorithms a well-guarded secret making SEO implementation not unlike playing a game where the referee won’t tell you all the rules. While SEO experts exist, the ambiguity around search creates an opening for grandiose claims and misinformation by unscrupulous profiteers claiming expertise.

If you’ve done SEO research, you may have come across an admixture of legitimate SEO practices, outdated optimizations, and misguided advice. You might have read that using the keyword meta tag in your HTML will help your SEO (it won’t), that there’s a specific number of instances a keyword should occur on a webpage (there isn’t), or that buying links will improve your rankings (it likely won’t and will get the site penalized). Let’s sift through the noise and highlight some dos and don’ts for performance-based SEO in 2018.

SEO is dead, long live SEO!

Nearly every year since its inception, SEO is declared dead. It is true that the scope of best practices for search engines has narrowed over the years as search engines have become smarter, and much of the benefit Continue reading

This is a guest post by David Urbansky, CEO and Co-Founder of SEMKNOX and Site Search 360. David is a search enthusiast having built natural language search experiences for e-commerce sites and recipe search engines.

As a startup founder, there are always key product decisions to be made when Site Search 360, our key product, is embedded in one context versus another. I’d like to share some experiences, choices, and challenges in our process packaging Site Search 360 for Cloudflare Apps.

What is Site Search 360?

Site Search 360 is a search solution for websites. Offering a search bar on a website improves user experience tremendously if the site has more than just a handful of pages. According to a eConsultancy study, up to 30% of web visitors use the search feature on e-commerce sites and searchers sometimes make up 40% of the revenue. Additionally, Nielsen Group found that 51% of people who did not find what they were looking for with the first query, gave up without refining the search - the search had better work very well then.

Why use the Cloudflare App?

Considering these facts, almost every website should have a search feature. However, implementing Continue reading

It is not uncommon for countries around the world to interrupt Internet access for political reasons or because of social unrest. We've seen this many times in the past (e.g. Gabon, Syria, Togo).

Today, it appears that Internet access in the Democratic Republic of Congo has been greatly curtailed. The BBC reports that Internet access in the capital, Kinshasa was cut on Saturday and iAfrikan reports that the cut is because of anti-Kabila protests.

Our monitoring of traffic from the Democratic Republic of Congo shows a distinct drop off starting around midnight UTC on January 21, 2018. Traffic is down to about 1/3 of its usual level.

We'll update this blog once we have more information about traffic levels.

In April, we wrote about Web Cache Deception attacks, and how our customers can avoid them using origin configuration.

Read that blog post to learn about how to configure your website, and for those who are not able to do that, how to disable caching for certain URIs to prevent this type of attacks. Since our previous blog post, we have looked for but have not seen any large scale attacks like this in the wild.

Today, we have released a tool to help our customers make sure only assets that should be cached are being cached.

A brief re-introduction to Web Cache Deception attack

Recall that the Web Cache Deception attack happens when an attacker tricks a user into clicking a link in the format of http://www.example.com/newsfeed/foo.jpg, when http://www.example.com/newsfeed is the location of a dynamic script that returns different content for different users. For some website configurations (default in Apache but not in nginx), this would invoke /newsfeed with PATH_INFO set to /foo.jpg. If http://www.example.com/newsfeed/foo.jpg does not return the proper Cache-Control headers to tell a web cache not to cache the content, web caches may decide to cache Continue reading

역자주: 이 글은 Marek Majkowski의 https://blog.cloudflare.com/syn-packet-handling-in-the-wild/ 를 번역한 것입니다.

우리 Cloudflare 에서는 실제 인터넷상의 서버 운영 경험이 많습니다. 하지만 이런 흑마술 마스터하기를 게을리하지도 않습니다. 이 블로그에서는 인터넷 프로토콜의 여러 어두운 부분을 다룬 적이 있습니다: understanding FIN-WAIT-2 나 receive buffer tuning과 같은 것들입니다.

CC BY 2.0 image by Isaí Moreno

사람들이 충분히 신경쓰지 않는 주제가 하나 있는데, 바로 SYN 홍수(SYN floods) 입니다. 우리는 리눅스를 사용하고 있는데 리눅스에서 SYN 패킷 처리는 매우 복잡하다는 것을 알게 되었습니다. 이 글에서는 이에 대해 좀 더 알아 보도록 하겠습니다.

두개의 큐의 이야기

일단 만들어진 소켓에 대해 "LISTENING" TCP 상태에는 두개의 분리된 큐가 존재 합니다:

• SYN 큐
• Accept 큐

일반적으로 이 큐에는 여러가지 다른 이름이 붙어 있는데, "reqsk_queue", "ACK backlog", "listen backlog", "TCP backlog" 등이 있습니다만 혼란을 피하기 위해 위의 이름을 사용하도록 하겠습니다.

SYN 큐

SYN 큐는 수신 SYN 패킷^[1] (구체적으로는 struct inet_request_sock)을 저장합니다. 이는 SYN+ACK 패킷을 보내고 타임아웃시에 재시도하는 역할을 합니다. 리눅스에서 재시도 값은 다음과 같이 설정됩니다:

$ sysctl net.ipv4.tcp_synack_retries
net.ipv4.tcp_synack_retries = 5

문서를 보면 다음과 같습니다:

tcp_synack_retries - 정수

    수동 TCP 연결 시도에 대해서 SYNACK를 몇번 다시 보낼지를 지정한다.
    이 값은 255 이하이어야 한다. 기본값은 5이며, 1초의 초기 RTO값을 감안하면
    마지막 재전송은 31초  Continue reading

Democratizing the Internet and making new features available to all Cloudflare customers is a core part of what we do. We're proud to be early adopters and have a long record of adopting new standards early, such as HTTP/2, as well as features that are experimental or not yet final, like TLS 1.3 and SPDY.

Participating in the Internet democracy occasionally means that ideas and technologies that were once popular or ubiquitous on the net lose their utility as newer technologies emerge. SPDY is one such technology. Several years ago, Google drafted a proprietary and experimental new protocol called SPDY. SPDY offered many performance improvements over the aging HTTP/1.1 standard and these improvements resulted in significantly faster page load times for real-world websites. Stemming from its success, SPDY became the starting point for HTTP/2 and, when the new HTTP standard was finalized, the SPDY experiment came to an end where it gradually fell into disuse.

As a result, we're announcing our intention to deprecate the use of SPDY for connections made to Cloudflare's edge by February 21st, 2018.

Remembering 2012

Five and a half years ago, when the majority of the web was unencrypted and web developers Continue reading

Processor problems have been in the news lately, due to the Meltdown and Spectre vulnerabilities. But generally, engineers writing software assume that computer hardware operates in a reliable, well-understood fashion, and that any problems lie on the software side of the software-hardware divide. Modern processor chips routinely execute many billions of instructions in a second, so any erratic behaviour must be very hard to trigger, or it would quickly become obvious.

But sometimes that assumption of reliable processor hardware doesn’t hold. Last year at Cloudflare, we were affected by a bug in one of Intel’s processor models. Here’s the story of how we found we had a mysterious problem, and how we tracked down the cause.

CC-BY-SA-3.0 image by Alterego

Prologue

Back in February 2017, Cloudflare disclosed a security problem which became known as Cloudbleed. The bug behind that incident lay in some code that ran on our servers to parse HTML. In certain cases involving invalid HTML, the parser would read data from a region of memory beyond the end of the buffer being parsed. The adjacent memory might contain other customers’ data, which would then be returned in the HTTP response, and the result was Cloudbleed.

But Continue reading

Tell me if this sounds familiar: any connection from inside the corporate network is trusted and any connection from the outside is not. This is the security strategy used by most enterprises today. The problem is that once the firewall, or gateway, or VPN server creating this perimeter is breached, the attacker gets immediate, easy and trusted access to everything.

CC BY-SA 2.0 image by William Warby

There’s a second problem with the traditional security perimeter model. It either requires employees to be on the corporate network (i.e. physically in the office) or using a VPN, which slows down work because every page load makes extra round trips to the VPN server. After all this hassle, users on the VPN are still highly susceptible to phishing, man-in-the-middle and SQL injection attacks.

A few years ago, Google pioneered a solution for their own employees called BeyondCorp. Instead of keeping their internal applications on the intranet, they made them accessible on the internet. There became no concept of in or outside the network. The network wasn’t some fortified citadel, everything was on the internet, and no connections were trusted. Everyone had to prove they are who they say they are.

Continue reading

Here at Cloudflare, we have a lot of experience of operating servers on the wild Internet. But we are always improving our mastery of this black art. On this very blog we have touched on multiple dark corners of the Internet protocols: like understanding FIN-WAIT-2 or receive buffer tuning.

CC BY 2.0 image by Isaí Moreno

One subject hasn't had enough attention though - SYN floods. We use Linux and it turns out that SYN packet handling in Linux is truly complex. In this post we'll shine some light on this subject.

The tale of two queues

First we must understand that each bound socket, in the "LISTENING" TCP state has two separate queues:

• The SYN Queue
• The Accept Queue

In the literature these queues are often given other names such as "reqsk_queue", "ACK backlog", "listen backlog" or even "TCP backlog", but I'll stick to the names above to avoid confusion.

SYN Queue

The SYN Queue stores inbound SYN packets^[1] (specifically: struct inet_request_sock). It's responsible for sending out SYN+ACK packets and retrying them on timeout. On Linux the number of retries is configured with:

$ sysctl net.ipv4.tcp_synack_retries
net.ipv4.tcp_synack_retries = 5

The docs describe Continue reading

We just turned up Salt Lake City, Utah — Cloudflare's 120th data center. Salt Lake holds a special place in Cloudflare's history. I grew up in the region and still have family there. Back in 2004, Lee Holloway and I lived just up into the mountains in Park City when we built Project Honey Pot, the open source project that inspired the original idea for Cloudflare.

Salt Lake also holds a special place in the history of the Internet. The University of Utah, based there, was one of the original four Arpanet locations (along with UCLA, UC Santa Barbara, and the Stanford Research Institute). The school also educated the founders of great technology companies like Silicon Graphics, Adobe, Atari, Netscape, and Pixar. Many were graduates of the computer graphics department lead by Professors Ivan Sutherland and David Evans.

In 1980, when I was seven years old, my grandmother, who lived a few blocks from the University, gave me an Apple II+ for Christmas. I took to it like a duck to water. My mom enrolled in a continuing education computer course at the University of Utah teaching BASIC programming. I went with her to the classes. Unbeknownst to the Continue reading

Last week the news of two significant computer bugs was announced. They've been dubbed Meltdown and Spectre. These bugs take advantage of very technical systems that modern CPUs have implemented to make computers extremely fast. Even highly technical people can find it difficult to wrap their heads around how these bugs work. But, using some analogies, it's possible to understand exactly what's going on with these bugs. If you've found yourself puzzled by exactly what's going on with these bugs, read on — this blog is for you.

“When you come to a fork in the road, take it.” — Yogi Berra

Late one afternoon walking through a forest near your home and navigating with the GPS you come to a fork in the path which you’ve taken many times before. Unfortunately, for some mysterious reason your GPS is not working and being a methodical person you like to follow it very carefully.

Cooling your heels waiting for GPS to start working again is annoying because you are losing time when you could be getting home. Instead of waiting, you decide to make an intelligent guess about which path is most likely based on past experience and set Continue reading

For many of us, a New Year brings a renewed commitment to eat better, exercise regularly, and read more (especially the Cloudflare blog). But as we enter 2018, there is a unique and significant new commitment approaching -- protecting personal data and complying with the European Union’s (EU) General Data Protection Regulation (GDPR).

As many of you know by now, the GDPR is a sweeping new EU law that comes into effect on May 25, 2018. The GDPR harmonizes data privacy laws across the EU and mandates how companies collect, store, delete, modify and otherwise process personal data of EU citizens.

Since our founding, Cloudflare has believed that the protection of our customers’ and their end users’ data is essential to our mission to help build a better internet.

Image by GregMontani via Wikimedia Commons

Need a Data Processing Agreement?

As we explained in a previous blog post last August, Cloudflare has been working hard to achieve GDPR compliance in advance of the effective date, and is committed to help our customers and their partners prepare for GDPR compliance on their side. We understand that compliance with a new set of privacy laws can be challenging, and we are here Continue reading

I wouldn’t be surprised if the title of this post attracts some Bitcoin aficionados, but if you are such, I want to disappoint you. For me crypto means cryptography, not cybermoney, and the price we pay for it is measured in CPU cycles, not USD.

If you got to this second paragraph you probably heard that TLS today is very cheap to deploy. Considerable effort was put to optimize the cryptography stacks of OpenSSL and BoringSSL, as well as the hardware that runs them. However, aside for the occasional benchmark, that can tell us how many GB/s a given algorithm can encrypt, or how many signatures a certain elliptic curve can generate, I did not find much information about the cost of crypto in real world TLS deployments.

CC BY-SA 2.0 image by Michele M. F.

As Cloudflare is the largest provider of TLS on the planet, one would think we perform a lot of cryptography related tasks, and one would be absolutely correct. More than half of our external traffic is now TLS, as well as all of our internal traffic. Being in that position means that crypto performance is critical to our success, and as it Continue reading

Upgrading a security protocol in an ecosystem as complex as the Internet is difficult. You need to update clients and servers and make sure everything in between continues to work correctly. The Internet is in the middle of such an upgrade right now. Transport Layer Security (TLS), the protocol that keeps web browsing confidential (and many people persist in calling SSL), is getting its first major overhaul with the introduction of TLS 1.3. Last year, Cloudflare was the first major provider to support TLS 1.3 by default on the server side. We expected the client side would follow suit and be enabled in all major browsers soon thereafter. It has been over a year since Cloudflare’s TLS 1.3 launch and still, none of the major browsers have enabled TLS 1.3 by default.

The reductive answer to why TLS 1.3 hasn’t been deployed yet is middleboxes: network appliances designed to monitor and sometimes intercept HTTPS traffic inside corporate environments and mobile networks. Some of these middleboxes implemented TLS 1.2 incorrectly and now that’s blocking browsers from releasing TLS 1.3. However, simply blaming network appliance vendors would be disingenuous. The deeper truth of the Continue reading