http: runtime deprecate legacy HTTP parser

The legacy HTTP parser, used by default in versions of Node.js prior to
12.0.0, is deprecated. The legacy HTTP parser cannot be guaranteed to be
supported after April 2021. This commit introduces a deprecation warning
for the legacy HTTP parser.

PR-URL: #37603
Refs: #31441
Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>

doc/api/cli.md

@@ -383,6 +383,10 @@ Specify the file name of the heap profile generated by `--heap-prof`.
 ### `--http-parser=library`
 <!-- YAML
 added: v11.4.0
+changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/37603
+    description: The legacy HTTP parser will emit a deprecation warning.
 -->
 
 Chooses an HTTP parser library. Available values are:
@@ -392,6 +396,8 @@ Chooses an HTTP parser library. Available values are:
 
 The default is `llhttp`, unless otherwise specified when building Node.js.
 
+The `legacy` HTTP parser is deprecated and will emit a deprecation warning.
+
 This flag exists to aid in experimentation with the internal implementation of
 the Node.js http parser.
 This flag is likely to become a no-op and removed at some point in the future.

doc/api/deprecations.md

@@ -2469,12 +2469,15 @@ Module.createRequireFromPath() is deprecated. Please use [`module.createRequire(
 ### DEP0131: Legacy HTTP parser
 <!-- YAML
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/37603
+    description: Runtime deprecation.
   - version: v12.3.0
     pr-url: https://github.com/nodejs/node/pull/27498
     description: Documentation-only.
 -->
 
-Type: Documentation-only
+Type: Runtime
 
 The legacy HTTP parser, used by default in versions of Node.js prior to 12.0.0,
 is deprecated. This deprecation applies to users of the

src/node_http_parser_impl.h

@@ -26,6 +26,9 @@
 
 #include "node.h"
 #include "node_buffer.h"
+#ifndef NODE_EXPERIMENTAL_HTTP
+#include "node_process.h"
+#endif  /* NODE_EXPERIMENTAL_HTTP */
 #include "util.h"
 
 #include "async_wrap-inl.h"
@@ -1021,6 +1024,10 @@ void InitializeHttpParser(Local<Object> target,
 #ifndef NODE_EXPERIMENTAL_HTTP
   static uv_once_t init_once = UV_ONCE_INIT;
   uv_once(&init_once, InitMaxHttpHeaderSizeOnce);
+  ProcessEmitDeprecationWarning(
+    env,
+    "The legacy HTTP parser is deprecated.",
+    "DEP0131").IsNothing();
 #endif  /* NODE_EXPERIMENTAL_HTTP */
 }
 

test/parallel/test-http-parser-legacy-deprecation.js

@@ -0,0 +1,11 @@
+'use strict';
+const common = require('../common');
+
+// Flags: --http-parser=legacy
+require('http');
+
+common.expectWarning({
+  DeprecationWarning:
+    ['The legacy HTTP parser is deprecated.',
+     'DEP0131']
+});