http: add separateHeadersValues option to request and createServer

doc/api/http.md

@@ -179,6 +179,14 @@ changes:
     **Default:** `'lifo'`.
   * `timeout` {number} Socket timeout in milliseconds.
     This will set the timeout when the socket is created.
+  * `separateHeadersValues` {boolean} If set to `true`, the request and the
+    response headers will never be squashed.
+    All request headers will be sent multiple times if the header
+    value was set to an array or set multiple times.
+    All response headers will always be returned as a string if the
+    header has been received once or as an array of strings if the header has
+    been received multiple times.
+    In both cases headers matching is case insensitive.
 
 `options` in [`socket.connect()`][] are also supported.
 
@@ -983,6 +991,10 @@ or
 request.setHeader('Cookie', ['type=ninja', 'language=javascript']);
 ```
 
+If `separateHeadersValues` was set to `true` when the request was created, then
+using this method will always append a new value to the list of values for this
+header.
+
 ### `request.setNoDelay([noDelay])`
 
 <!-- YAML
@@ -1629,6 +1641,10 @@ Reads out a header that's already been queued but not sent to the client.
 The name is case-insensitive. The type of the return value depends
 on the arguments provided to [`response.setHeader()`][].
 
+If `separateHeadersValues` was set to `true` when the server was created, then
+the return value is always a string if the header has been set once or
+an array of strings if the header has been set multiple times.
+
 ```js
 response.setHeader('Content-Type', 'text/html');
 response.setHeader('Content-Length', Buffer.byteLength(body));
@@ -1652,6 +1668,9 @@ added: v7.7.0
 Returns an array containing the unique names of the current outgoing headers.
 All header names are lowercase.
 
+If `separateHeadersValues` was set to `true` when the server was created, an
+header might be present in the list more than once.
+
 ```js
 response.setHeader('Foo', 'bar');
 response.setHeader('Set-Cookie', ['foo=bar', 'bar=baz']);
@@ -1679,6 +1698,10 @@ prototypically inherit from the JavaScript `Object`. This means that typical
 `Object` methods such as `obj.toString()`, `obj.hasOwnProperty()`, and others
 are not defined and _will not work_.
 
+If `separateHeadersValues` was set to `true` when the server was created, then
+the values are always a string if the header will be sent once or
+an array of strings if the header will be sent multiple times.
+
 ```js
 response.setHeader('Foo', 'bar');
 response.setHeader('Set-Cookie', ['foo=bar', 'bar=baz']);
@@ -1788,6 +1811,10 @@ When headers have been set with [`response.setHeader()`][], they will be merged
 with any headers passed to [`response.writeHead()`][], with the headers passed
 to [`response.writeHead()`][] given precedence.
 
+If `separateHeadersValues` was set to `true` when the request was created, then
+using this method will always append a new value to the list of values for this
+header.
+
 ```js
 // Returns content-type = text/plain
 const server = http.createServer((req, res) => {
@@ -2551,11 +2578,15 @@ added: v0.4.0
 -->
 
 * `name` {string} Name of header
-* Returns {string | undefined}
+* Returns {string | string\[] | undefined}
 
 Gets the value of HTTP header with the given name. If such a name doesn't
 exist in message, it will be `undefined`.
 
+If `separateHeadersValues` was set to `true` when the request or the server
+were created, then the return value is always a string if the header has been
+set once or an array of strings if the header has been set multiple times.
+
 ### `outgoingMessage.getHeaderNames()`
 
 <!-- YAML
@@ -2567,6 +2598,9 @@ added: v8.0.0
 Returns an array of names of headers of the outgoing outgoingMessage. All
 names are lowercase.
 
+If `separateHeadersValues` was set to `true` when the request or the server
+were created, an header might be present in the list more than once.
+
 ### `outgoingMessage.getHeaders()`
 
 <!-- YAML
@@ -2594,6 +2628,10 @@ const headers = outgoingMessage.getHeaders();
 // headers === { foo: 'bar', 'set-cookie': ['foo=bar', 'bar=baz'] }
 ```
 
+If `separateHeadersValues` was set to `true` when the request or the server
+were created, then the values are always a string if the header will be sent
+once or an array of strings if the header will be sent multiple times.
+
 ### `outgoingMessage.hasHeader(name)`
 
 <!-- YAML
@@ -2659,6 +2697,10 @@ added: v0.4.0
 
 Sets a single header value for the header object.
 
+If `separateHeadersValues` was set to `true` when the request or the server
+were created, then using this method will always append a new value to the list
+of values for this header.
+
 ### `outgoingMessage.setTimeout(msesc[, callback])`
 
 <!-- YAML
@@ -2865,6 +2907,14 @@ changes:
     [`--max-http-header-size`][] for requests received by this server, i.e.
     the maximum length of request headers in bytes.
     **Default:** 16384 (16 KB).
+  * `separateHeadersValues` {boolean} If set to `true`, incoming requests and
+    server responses headers will never be squashed.
+    All incoming requests headers will always be returned as a string if the
+    header has been received once or as an array of strings if the header has
+    been received multiple times.
+    All server responses headers will be sent multiple times if the header
+    value was set to an array or set multiple times.
+    In both cases headers matching is case insensitive.
 
 * `requestListener` {Function}
 
@@ -3072,6 +3122,14 @@ changes:
     `hostname`. Valid values are `4` or `6`. When unspecified, both IP v4 and
     v6 will be used.
   * `headers` {Object} An object containing request headers.
+  * `separateHeadersValues` {boolean} If set to `true`, the request and the
+    response headers will never be squashed.
+    All request headers will be sent multiple times if the header
+    value was set to an array or set multiple times.
+    All response headers will always be returned as a string if the
+    header has been received once or as an array of strings if the header has
+    been received multiple times.
+    In both cases headers matching is case insensitive.
   * `hints` {number} Optional [`dns.lookup()` hints][].
   * `host` {string} A domain name or IP address of the server to issue the
     request to. **Default:** `'localhost'`.

lib/_http_agent.js

@@ -24,6 +24,7 @@
 const {
   ArrayPrototypeIncludes,
   ArrayPrototypeIndexOf,
+  ArrayIsArray,
   ArrayPrototypePop,
   ArrayPrototypePush,
   ArrayPrototypeShift,
@@ -60,6 +61,7 @@ const {
   validateOneOf,
   validateString,
 } = require('internal/validators');
+const { kSeparateHeadersValues } = require('_http_incoming');
 
 const kOnKeylog = Symbol('onkeylog');
 const kRequestOptions = Symbol('requestOptions');
@@ -344,7 +346,14 @@ Agent.prototype.createSocket = function createSocket(req, options, cb) {
 
 function calculateServerName(options, req) {
   let servername = options.host;
-  const hostHeader = req.getHeader('host');
+  let hostHeader = req.getHeader('host');
+
+  // If the separateHeadersValues is active, the header might be specified
+  // multiple times. In that case we choose the last value.
+  if (req[kSeparateHeadersValues] && ArrayIsArray(hostHeader)) {
+    hostHeader = hostHeader[hostHeader.length - 1];
+  }
+
   if (hostHeader) {
     validateString(hostHeader, 'options.headers.host');
 

lib/_http_client.js

@@ -46,6 +46,7 @@ const assert = require('internal/assert');
 const { once } = require('internal/util');
 const {
   _checkIsHttpToken: checkIsHttpToken,
+  kSeparateHeadersValues,
   freeParser,
   parsers,
   HTTPParser,
@@ -195,6 +196,7 @@ function ClientRequest(input, options, cb) {
   if (maxHeaderSize !== undefined)
     validateInteger(maxHeaderSize, 'maxHeaderSize', 0);
   this.maxHeaderSize = maxHeaderSize;
+  this[kSeparateHeadersValues] = Boolean(options.separateHeadersValues);
 
   const insecureHTTPParser = options.insecureHTTPParser;
   if (insecureHTTPParser !== undefined &&
@@ -726,6 +728,8 @@ function tickOnSocket(req, socket) {
                     0);
   parser.socket = socket;
   parser.outgoing = req;
+  parser[kSeparateHeadersValues] = req[kSeparateHeadersValues];
+
   req.parser = parser;
 
   socket.parser = parser;

lib/_http_common.js

@@ -33,12 +33,12 @@ const { getOptionValue } = require('internal/options');
 const insecureHTTPParser = getOptionValue('--insecure-http-parser');
 
 const FreeList = require('internal/freelist');
-const incoming = require('_http_incoming');
 const {
+  kSeparateHeadersValues,
   IncomingMessage,
   readStart,
   readStop
-} = incoming;
+} = require('_http_incoming');
 
 let debug = require('internal/util/debuglog').debuglog('http', (fn) => {
   debug = fn;
@@ -101,6 +101,7 @@ function parserOnHeadersComplete(versionMajor, versionMinor, headers, method,
   incoming.httpVersion = `${versionMajor}.${versionMinor}`;
   incoming.url = url;
   incoming.upgrade = upgrade;
+  incoming[kSeparateHeadersValues] = parser[kSeparateHeadersValues];
 
   if (socket) {
     debug('requestTimeout timer moved to req');
@@ -272,6 +273,7 @@ module.exports = {
   freeParser,
   methods,
   parsers,
+  kSeparateHeadersValues,
   kIncomingMessage,
   kRequestTimeout,
   HTTPParser,

lib/_http_incoming.js

@@ -22,6 +22,7 @@
 'use strict';
 
 const {
+  ArrayIsArray,
   ObjectDefineProperty,
   ObjectSetPrototypeOf,
   StringPrototypeCharCodeAt,
@@ -34,6 +35,7 @@ const { Readable, finished } = require('stream');
 
 const kHeaders = Symbol('kHeaders');
 const kHeadersCount = Symbol('kHeadersCount');
+const kSeparateHeadersValues = Symbol('kSeparateHeadersValues');
 const kTrailers = Symbol('kTrailers');
 const kTrailersCount = Symbol('kTrailersCount');
 
@@ -112,8 +114,14 @@ ObjectDefineProperty(IncomingMessage.prototype, 'headers', {
       const src = this.rawHeaders;
       const dst = this[kHeaders];
 
-      for (let n = 0; n < this[kHeadersCount]; n += 2) {
-        this._addHeaderLine(src[n + 0], src[n + 1], dst);
+      if (this[kSeparateHeadersValues]) {
+        for (let n = 0; n < this[kHeadersCount]; n += 2) {
+          this._addHeaderLineSeparate(src[n + 0], src[n + 1], dst);
+        }
+      } else {
+        for (let n = 0; n < this[kHeadersCount]; n += 2) {
+          this._addHeaderLine(src[n + 0], src[n + 1], dst);
+        }
       }
     }
     return this[kHeaders];
@@ -131,8 +139,14 @@ ObjectDefineProperty(IncomingMessage.prototype, 'trailers', {
       const src = this.rawTrailers;
       const dst = this[kTrailers];
 
-      for (let n = 0; n < this[kTrailersCount]; n += 2) {
-        this._addHeaderLine(src[n + 0], src[n + 1], dst);
+      if (this[kSeparateHeadersValues]) {
+        for (let n = 0; n < this[kTrailersCount]; n += 2) {
+          this._addHeaderLineSeparate(src[n + 0], src[n + 1], dst);
+        }
+      } else {
+        for (let n = 0; n < this[kTrailersCount]; n += 2) {
+          this._addHeaderLine(src[n + 0], src[n + 1], dst);
+        }
       }
     }
     return this[kTrailers];
@@ -213,8 +227,14 @@ function _addHeaderLines(headers, n) {
     }
 
     if (dest) {
-      for (let i = 0; i < n; i += 2) {
-        this._addHeaderLine(headers[i], headers[i + 1], dest);
+      if (this[kSeparateHeadersValues]) {
+        for (let i = 0; i < n; i += 2) {
+          this._addHeaderLineSeparate(headers[i], headers[i + 1], dest);
+        }
+      } else {
+        for (let i = 0; i < n; i += 2) {
+          this._addHeaderLine(headers[i], headers[i + 1], dest);
+        }
       }
     }
   }
@@ -361,6 +381,20 @@ function _addHeaderLine(field, value, dest) {
   }
 }
 
+// Add the given (field, value) pair to the message, without joining values as
+// in _addHeaderLine. The headers values are always arrays.
+IncomingMessage.prototype._addHeaderLineSeparate = _addHeaderLineSeparate;
+function _addHeaderLineSeparate(field, value, dest) {
+  field = StringPrototypeToLowerCase(field);
+
+  if (ArrayIsArray(dest[field])) {
+    dest[field].push(value);
+  } else if (dest[field] !== undefined) {
+    dest[field] = [dest[field], value];
+  } else {
+    dest[field] = value;
+  }
+}
 
 // Call this instead of resume() if we want to just
 // dump all the data to /dev/null
@@ -385,6 +419,7 @@ function onError(self, error, cb) {
 }
 
 module.exports = {
+  kSeparateHeadersValues,
   IncomingMessage,
   readStart,
   readStop