![]() ![]() Rest apis built on http/1.1 will continue to work transparently as before, with no changes to be made to applications "i want to put resource /foo on host ") is transported over the wire. What has changed in http/2 with respect to http/1.1 is the way the http semantic (e.g. this means that it still has http methods such as The main semantic of http has been retained in http/2. How does this affect the existing rest apis built on http/1.1? for now, many are still will continue to work with However, pushing responses is not "magical" - if used incorrectly, it can harm performance. Server push potentially allows the server to avoid this round trip of delay by "pushing" the responses it thinks the client will need into its cache. When a browser requests a page, the server sends the html in the response and then needs to wait for the browser to parse the html and issue requests for all of the embedded assets before it can start sending the javascript, images, and css. Http/2 allows servers to "push" responses proactively into client caches This overhead is considerable, especially when you consider the impact upon mobile clients, which typically see round-trip latency of several hundred milliseconds, even under good conditions. In comparison, even a mild compression on headers allows those requests to get onto the wire within one roundtrip - perhaps even one packet. , which paces packets out on new connections based on how many packets have been acknowledged - effectively limiting the number of packets that can be sent for the first few round trips. ![]() If you assume that a page has about 80 assets (which is conservative in today's web), and each request has 1400 bytes of headers (again, not uncommon, thanks to cookies, referer, etc.), it takes at least 7-8 round trips to get the headers out "on the wire." that's not counting response time - that's just to get them out of the client. Http/2 uses header compression to reduce overhead You can see a demo of how http/2 is working here:Īdditionally, using so many connections unfairly monopolizes network resources, "stealing" them from other, better-behaved applications (e.g., voip). One application opening so many connections simultaneously breaks a lot of the assumptions that tcp was built upon since each connection will start a flood of data in the response, there's a real risk that buffers in the intervening network will overflow, causing a congestion event and retransmits. since many sites use multiple origins, this could mean that a single page load opens more than thirty connections. ![]() With http/1, browsers open between four and eight connections per origin. Http/2 can use one connection for parallelism This, in turn, allows a client to use just one connection per origin to load a page. This forces clients to use a number of heuristics (often guessing) to determine what requests to put on which connection to the origin and when since it's common for a page to load 10 times (or more) the number of available connections, this can severely impact performance, often resulting in a "waterfall" of blocked requests.Īddresses these problems by allowing multiple request and response messages to be in flight at the same time it's even possible to intermingle parts of one message with another on the wire. additionally, pipelining has been found very difficult to deploy, because many intermediaries and servers don't process it correctly. Http/1.1 tried to fix this with pipelining, but it didn't completely address the problem (a large or slow response can still block others behind it). Http/1.x has a problem called "head-of-line blocking," where effectively only one request can be outstanding on a connection at a time. Http/2 is fully multiplexed, instead of ordered and blocking First, let's look at some of the high-level differences:īinary protocols are more efficient to parse, more compact "on the wire," and, most importantly, they are much less error-prone compared to textual protocols like http/1.x, because they often have a number of affordances to "help" with things like whitespace handling, capitalization, line endings, blank lines, and so on.ĭefines four different ways to parse a message in ![]()
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