~/ on the Range

What do download accelerators, streaming video, and the HTML 5 `` element have in common? They all rely on range requests to transmit data efficiently. Range requests are HTTP's brilliantly simple answer to the question, "How do I download just a portion of a given file?" Although they're supported by most web frameworks, Node doesn't handle range requests out of the box. To that end, we'll be going down to the bare metal as we examine the relevant portions of the HTTP/1.1 spec, learn how to handle such requests correctly, and discuss why they're so useful.

Transcript

1. ~/ on the Range
2. HTTP/1.1 “Physics for Physics Majors”
3. Client Server Proxy Gateway Tunnel Request Response
4. // HTTP server. var http = require("http") http.Server(function (request, response) { response.writeHead(200, { "Content-Type": "text/plain", "Content-Length": 13 }) response.end("Hello, world.") }).listen(1900)
5. // TCP client (`telnet`). var net = require("net") net.connect(1900, function () { this.write("GET / HTTP/1.1\r\n") this.end("\r\n") }).pipe(process.stdout)
6. HTTP/1.1 200 OK Content-Type: text/plain Content-Length: 13 Date: Tue, 16 Oct 2012 00:20:00 GMT Connection: keep-alive Hello, world. Status Line Headers Body
7. 100 200 300 400 500 Information Request acknowledged Success Received, understood, and accepted Redirection Client intervention Client Error Bad request Server Error Unfulfillable request
8. General Request Response Entity Cache-Control, Connection, Date, Pragma, Trailer, Transfer-Encoding, Upgrade, Via, Warning Accept, Accept-Charset, Accept-Encoding, Accept-Language, Authorization, Expect, From, Host, If-Match, If-Modified- Since, If-None-Match, If-Range, If-Unmodified-Since, Max- Forwards, Proxy-Authorization, Range, Referer, TE, User-Agent Accept-Ranges, Age, ETag, Location, Proxy- Authenticate, Retry-After, Server, Vary, WWW- Authenticate Allow, Content-Encoding, Content-Language, Content- Length, Content-Location, Content-MD5, Content-Range, Content-Type, Expires, Last-Modified
9. Encoding
10. HTTP/1.1 200 OK Content-Type: text/plain Date: Tue, 16 Oct 2012 00:20:00 GMT Connection: keep-alive Transfer-Encoding: chunked d Hello, world. 0 Hex Size Indicators parseInt("d", 16) == 13
11. Content-Type Content-Encoding The media type of the entity gzip compression; requires decoding
12. Methods
13. GET HEAD POST PUT DELETE OPTIONS TRACE CONNECT
14. Ranges
15. Request Response Range, If-Range Accept-Ranges: bytes Range, If-Range Content-Range Range, If-Range Content-Length Content-Range Content-Length Content-Range Date Content-Range ETag, Content-Location, Expires, Cache-Control, Vary
16. First 500 bytes Next 500 bytes Last 500 bytes Last 500 bytes First and last bytes only bytes=0-499 bytes=500-999 bytes=-500 bytes=9500- bytes=0-0,-1 npm install range-parser
17. First 500 bytes Next 500 bytes All except for first 500 bytes Last 500 bytes Requested range not satisfiable bytes 0-499/1234 bytes 500-999/1234 bytes 500-1233/1234 bytes 734-1233/1234 *
18. Non-Contiguous Ranges
19. HTTP/1.1 206 Partial Content Date: Tue, 16 Oct 2012 00:20:00 GMT Accept-Ranges: bytes Content-Type: multipart/byteranges; boundary=BOUNDARY --BOUNDARY ... --BOUNDARY ... --BOUNDARY--
20. Content-Type: text/plain Content-Range: bytes 1602-1745/422279 The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information systems. Content-Type: text/plain Content-Range: bytes 193409-193586/422279 be displayed when this actually happens. The indication need not be a dialog box; it could be an icon (for example, a picture of a rotting fish) or some other indicator.
21. Partial PUT Requests
22. var contentRange, pattern, match if (request.method == "PUT") { contentRange = request.headers["content-range"] pattern = /^bytes ((?:\d+-\d+)|\*)\/(\d+|\*)$/ if ((match = pattern.exec(contentRange))) { request.pipe(fs.createWriteStream("target", { "start": +match[1].split("-")[0] || 0, "flags": "r+" })) } }
23. Use Cases
24. Resuming interrupted downloads Efficiently retrieving large media files Download accelerators Granular caching
25. Thank you! @kitcambridge git.io/kit