http2: additiona cleanups, fixes and docs

* Follow the model of the existing http code and pass the headers
  in to js as an array. Building the array on the native side then
  converting it to an object on the js side is generally faster than
  building the object on the native side. This also allows us to
  eliminate some duplicated checks.

* Fill in additional doc details

* Work on timeouts

Author: jasnell

doc/api/http2.md

@@ -130,9 +130,9 @@ session.on('stream', (stream, headers, flags) => {
 });
 ```
 
-*Note*: User code will typically not listen for this event directly, and would
-instead register a handler for the `'stream'` event emitted by the `net.Server`
-or `tls.Server` instances returned by `http2.createServer()` and
+On the server side, user code will typically not listen for this event directly,
+and would instead register a handler for the `'stream'` event emitted by the
+`net.Server` or `tls.Server` instances returned by `http2.createServer()` and
 `http2.createSecureServer()`, respectively, as in the example below:
 
 ```js
@@ -164,7 +164,16 @@ not handled, the `'error'` event will be re-emitted on the `Http2Session`.
 
 #### Event: 'timeout'
 
-(TODO: fill in detail)
+After the `http2session.setTimeout()` method is used to set the timeout period
+for this `Http2Session`, the `'timeout'` event is emitted if there is no
+activity on the `Http2Session` after the configured number of milliseconds.
+
+```js
+const session = /** get session somehow **/;
+
+session.setTimeout(2000);
+session.on('timeout', () => { /** .. **/ });
+```
 
 #### http2session.destroy()
 
@@ -182,15 +191,15 @@ longer be used, otherwise `false`.
 
 * Value: {[Settings Object][]}
 
-An object describing the current local settings of this `Http2Session`. The
-local settings are local to *this* `Http2Session` instance.
+A prototype-less object describing the current local settings of this
+`Http2Session`. The local settings are local to *this* `Http2Session` instance.
 
 #### http2session.remoteSettings
 
 * Value: {[Settings Object][]}
 
-An object describing the current remote settings of this `Http2Session`. The
-remote settings are set by the *connected* HTTP/2 peer.
+A prototype-less object describing the current remote settings of this
+`Http2Session`. The remote settings are set by the *connected* HTTP/2 peer.
 
 #### http2session.request(headers[, options])
 
@@ -216,41 +225,79 @@ HTTP/2 request to the connected server.
 This method is only available if `http2session.type` is equal to
 `http2.constants.NGHTTP2_SESSION_CLIENT`.
 
-(TODO: fill in detail)
+```js
+const http2 = require('http2');
+const clientSession = http2.connect('https://localhost:1234');
+const {
+  HTTP2_HEADER_PATH,
+  HTTP2_HEADER_STATUS
+} = http2.constants;
+
+const req = clientSession.request({ [HTTP2_HEADER_PATH]: '/' });
+req.on('response', (headers) => {
+  console.log(HTTP2_HEADER_STATUS);
+  req.on('data', (chunk) => { /** .. **/ });
+  req.on('end', () => { /** .. **/ });
+});
+```
 
 #### http2session.rstStream(stream, code)
 
 * stream {Http2Stream}
-* code {number}
+* code {number} Unsigned 32-bit integer identifying the error code. Defaults to
+  `http2.constant.NGHTTP2_NO_ERROR` (`0x00`)
 
 Sends an `RST_STREAM` frame to the connected HTTP/2 peer, causing the given
-`Http2Stream` to be closed on both sides using error code `code`.
+`Http2Stream` to be closed on both sides using [error code][] `code`.
 
 #### http2session.setTimeout(msecs, callback)
 
 * `msecs` {number}
 * `callback` {Function}
 
-(TODO: fill in detail)
+Used to set a callback function that is called when there is no activity on
+the `Http2Session` after `msecs` milliseconds. The given `callback` is
+registered as a listener on the `'timeout'` event.
 
 #### http2session.shutdown(options[, callback])
 
 * `options` {Object}
   * `graceful` {boolean} `true` to attempt a polite shutdown of the
     `Http2Session`.
-  * `errorCode` {number} The HTTP/2 Error Code to return. Note that this is
-    *not* the same thing as an HTTP Response Status Code.
+  * `errorCode` {number} The HTTP/2 [error code][] to return. Note that this is
+    *not* the same thing as an HTTP Response Status Code. Defaults to `0x00`
+    (No Error).
   * `lastStreamID` {number} The Stream ID of the last successfully processed
     `Http2Stream` on this `Http2Session`.
   * `opaqueData` {Buffer} A `Buffer` instance containing arbitrary additional
     data to send to the peer upon disconnection. This is used, typically, to
     provide additional data for debugging failures, if necessary.
-* `callback` {Function}
+* `callback` {Function} A callback that is invoked after the session shutdown
+  has been completed.
 
 Attempts to shutdown this `Http2Session` using HTTP/2 defined procedures.
 If specified, the given `callback` function will be invoked once the shutdown
 process has completed.
 
+Note that calling `http2session.shutdown()` does *not* destroy the session or
+tear down the `Socket` connection. It merely prompts both sessions to begin
+preparing to cease activity.
+
+During a "graceful" shutdown, the session will first send a `GOAWAY` frame to
+the connected peer identifying the last processed stream as 2<sup>32</sup>-1.
+Then, on the next tick of the event loop, a second `GOAWAY` frame identifying
+the most recently processed stream identifier is sent. This process allows the
+remote peer to begin preparing for the connection to be terminated.
+
+```js
+const session = /** get session somehow **/
+
+session.shutdown({
+  graceful: true,
+  opaqueData: Buffer.from('add some debugging data here')
+}, () => session.destroy());
+```
+
 #### http2session.socket
 
 * Value: {net.Socket|tls.TLSSocket}
@@ -417,7 +464,9 @@ this event is emitted, the `Http2Stream` instance is no longer usable.
 
 #### Event: 'timeout'
 
-(TODO: fill in detail)
+The `'timeout'` event is emitted after no activity is received for this
+`'Http2Stream'` within the number of millseconds set using
+`http2stream.setTimeout()`.
 
 #### Event: 'trailers'
 
@@ -427,7 +476,7 @@ trailing header fields is received. The listener callback is passed the
 
 ```js
 stream.on('trailers', (headers, flags) => {
-  // TODO(jasnell): Fill in example
+  console.log(headers);
 });
 ```
 
@@ -459,36 +508,38 @@ peer.
 
 * Value: {number}
 
-Set to the `RST_STREAM` error code when the `Http2Stream` is destroyed after
-either receiving an `RST_STREAM` frame from the connected peer, calling
-`http2stream.rstStream()`, or `http2stream.destroy()`.
+Set to the `RST_STREAM` [error code][] reported when the `Http2Stream` is
+destroyed after either receiving an `RST_STREAM` frame from the connected peer,
+calling `http2stream.rstStream()`, or `http2stream.destroy()`. Will be
+`undefined` if the `Http2Stream` has not been closed.
 
 #### http2stream.rstStream(code)
 
-* `code` {number}
+* code {number} Unsigned 32-bit integer identifying the error code. Defaults to
+  `http2.constant.NGHTTP2_NO_ERROR` (`0x00`)
 
 Sends an `RST_STREAM` frame to the connected HTTP/2 peer, causing this
-`Http2Stream` to be closed on both sides using error code `code`.
+`Http2Stream` to be closed on both sides using [error code][] `code`.
 
 #### http2stream.rstWithNoError()
 
-Shortcut for `http2stream.rstStream()` using error code `NO_ERROR`.
+Shortcut for `http2stream.rstStream()` using error code `0x00` (No Error).
 
 #### http2stream.rstWithProtocolError() {
 
-Shortcut for `http2stream.rstStream()` using error code `PROTOCOL_ERROR`.
+Shortcut for `http2stream.rstStream()` using error code `0x01` (Protocol Error).
 
 #### http2stream.rstWithCancel() {
 
-Shortcut for `http2stream.rstStream()` using error code `CANCEL`.
+Shortcut for `http2stream.rstStream()` using error code `0x08` (Cancel).
 
 #### http2stream.rstWithRefuse() {
 
-Shortcut for `http2stream.rstStream()` using error code `REFUSED_STREAM`.
+Shortcut for `http2stream.rstStream()` using error code `0x07` (Refused Stream).
 
 #### http2stream.rstWithInternalError() {
 
-Shortcut for `http2stream.rstStream()` using error code `INTERNAL_ERROR`.
+Shortcut for `http2stream.rstStream()` using error code `0x02` (Internal Error).
 
 #### http2stream.session
 
@@ -502,7 +553,15 @@ value will be `undefined` after the `Http2Stream` instance is destroyed.
 * `msecs` {number}
 * `callback` {Function}
 
-(TODO: fill in detail)
+```js
+const http2 = require('http2');
+const client = http2.connect('http://example.org:8000');
+
+const req = client.request({':path': '/'});
+
+// Cancel the stream if there's no activity after 5 seconds
+req.setTimeout(5000, () => req.rstStreamWithCancel());
+```
 
 #### http2stream.state
 
@@ -534,7 +593,7 @@ the headers.
 
 ```js
 stream.on('headers', (headers, flags) => {
-  // TODO(jasnell): Fill in example
+  console.log(headers);
 });
 ```
 
@@ -546,7 +605,7 @@ associated with the headers.
 
 ```js
 stream.on('push', (headers, flags) => {
-  // TODO(jasnell): Fill in example
+  console.log(headers);
 });
 ```
 
@@ -577,18 +636,6 @@ used exclusively on HTTP/2 Servers. `Http2Stream` instances on the server
 provide additional methods such as `http2stream.pushStream()` and
 `http2stream.respond()` that are only relevant on the server.
 
-#### Event: 'request'
-
-The `'request'` event is emitted when a block of headers associated with an
-HTTP request is received. The listener callback is passed the [Headers Object][]
-and flags associated with the headers.
-
-```js
-stream.on('request', (headers, flags) => {
-  // TODO(jasnell): Fill in example
-});
-```
-
 #### http2stream.additionalHeaders(headers)
 
 * `headers` {[Headers Object][]}
@@ -608,18 +655,38 @@ Sends an additional informational `HEADERS` frame to the connected HTTP/2 peer.
   * `weight` {number} Specifies the relative dependency of a stream in relation
     to other streams with the same `parent`. The value is a number between `1`
     and `256` (inclusive).
-* `callback` {Function}
+* `callback` {Function} Callback that is called once the push stream has been
+  initiated.
 
-Initiates a push stream.
-(TODO: fill in detail)
+Initiates a push stream. The callback is invoked with the new `Htt2Stream`
+instance created for the push stream.
+
+```js
+const http2 = require('http2');
+const server = http2.createServer();
+server.on('stream', (stream) => {
+  stream.respond({':status': 200});
+  stream.pushStream({':path': '/'}, (pushStream) => {
+    pushStream.respond({':status': 200});
+    pushStream.end('some pushed data');
+  });
+  stream.end('some data');
+});
+```
 
 #### http2stream.respond([headers[, options]])
 
 * `headers` {[Headers Object][]}
 * `options` {Object}
 
-Initiates a response.
-(TODO: fill in detail)
+```js
+const http2 = require('http2');
+const server = http2.createServer();
+server.on('stream', (stream) => {
+  stream.respond({':status': 200});
+  stream.end('some data');
+});
+```
 
 ### Class: Http2Server
 
@@ -667,7 +734,8 @@ server.on('stream', (stream, headers, flags) => {
 
 #### Event: 'timeout'
 
-(TODO: fill in detail)
+The `'timeout'` event is emitted when there is no activity on the Server for
+a given number of milliseconds set using `http2server.setTimeout()`.
 
 ### Class: Http2SecureServer
 
@@ -717,7 +785,8 @@ server.on('stream', (stream, headers, flags) => {
 
 #### Event: 'timeout'
 
-(TODO: fill in detail)
+The `'timeout'` event is emitted when there is no activity on the Server for
+a given number of milliseconds set using `http2server.setTimeout()`.
 
 ### http2.getDefaultSettings()
 
@@ -882,11 +951,37 @@ server.listen(80);
 * Returns `Http2Session`
 
 Returns a HTTP/2 client `Http2Session` instance.
-(TODO: fill in detail)
+
+```js
+const http2 = require('http2');
+const client = http2.connect('https://localhost:1234');
+
+/** use the client **/
+
+client.destroy();
+```
 
 ### http2.constants
 
-(TODO: Fill in details)
+#### Error Codes for RST_STREAM and GOAWAY
+<a id="error_codes"></a>
+
+| Value | Name                | Constant                                      |
+|-------|---------------------|-----------------------------------------------|
+| 0x00  | No Error            | `http2.constants.NGHTTP2_NO_ERROR`            |
+| 0x01  | Protocol Error      | `http2.constants.NGHTTP2_PROTOCOL_ERROR`      |
+| 0x02  | Internal Error      | `http2.constants.NGHTTP2_INTERNAL_ERROR`      |
+| 0x03  | Flow Control Error  | `http2.constants.NGHTTP2_FLOW_CONTROL_ERROR`  |
+| 0x04  | Settings Timeout    | `http2.constants.NGHTTP2_SETTINGS_TIMEOUT`    |
+| 0x05  | Stream Closed       | `http2.constants.NGHTTP2_STREAM_CLOSED`       |
+| 0x06  | Frame Size Error    | `http2.constants.NGHTTP2_FRAME_SIZE_ERROR`    |
+| 0x07  | Refused Stream      | `http2.constants.NGHTTP2_REFUSED_STREAM`      |
+| 0x08  | Cancel              | `http2.constants.NGHTTP2_CANCEL`              |
+| 0x09  | Compression Error   | `http2.constants.NGHTTP2_COMPRESSION_ERROR`   |
+| 0x0a  | Connect Error       | `http2.constants.NGHTTP2_CONNECT_ERROR`       |
+| 0x0b  | Enhance Your Calm   | `http2.constants.NGHTTP2_ENHANCE_YOUR_CALM`   |
+| 0x0c  | Inadequate Security | `http2.constants.NGHTTP2_INADEQUATE_SECURITY` |
+| 0x0d  | HTTP/1.1 Required   | `http2.constants.NGHTTP2_HTTP_1_1_REQUIRED`   |
 
 ### Headers Object
 
@@ -912,7 +1007,14 @@ prototype. This means that normal JavaScript object methods such as
 `Object.prototype.toString()` and `Object.prototype.hasOwnProperty()` will
 not work.
 
-(TODO: Fill in more detail)
+```js
+const http2 = require('http2');
+const server = http2.createServer();
+server.on('stream', (stream, headers) => {
+  console.log(headers[':path']);
+  console.log(headers.ABC);
+});
+```
 
 ### Settings Object
 
@@ -1012,3 +1114,4 @@ TBD
 [ServerHttp2Stream]: #http2_class_serverhttp2stream
 [Settings Object]: #http2_settings_object
 [Using options.selectPadding]: #http2_using_options_selectpadding
+[error code]: #error_codes