13 files changed, 26 insertions, 15 deletions
diff --git a/doc/src/guide/introduction.asciidoc b/doc/src/guide/introduction.asciidoc
index 374f1f3..fa0e6c6 100644
--- a/doc/src/guide/introduction.asciidoc
+++ b/doc/src/guide/introduction.asciidoc
@@ -46,7 +46,4 @@ In the HTTP protocol, the method name is case sensitive. All standard
 method names are uppercase.
 
 Header names are case insensitive. Gun converts all the header names
-to lowercase, and expects your application to provide lowercase header
-names.
-
-The same applies to any other case insensitive value.
+to lowercase, including request headers provided by your application.
diff --git a/doc/src/manual/gun.asciidoc b/doc/src/manual/gun.asciidoc
index dff927c..2726564 100644
--- a/doc/src/manual/gun.asciidoc
+++ b/doc/src/manual/gun.asciidoc
@@ -267,6 +267,16 @@ ws_opts (#{})::
 
 Options specific to the Websocket protocol.
 
+=== req_headers()
+
+[source,erlang]
+----
+req_headers() :: [{binary() | string() | atom(),   iodata()}]
+               | #{binary() | string() | atom() => iodata()}
+----
+
+Request headers.
+
 === req_opts()
 
 [source,erlang]
@@ -315,6 +325,10 @@ undocumented and must be set to `gun_ws_h`.
 
 == Changelog
 
+* *2.0*: Introduce the type `req_headers()` and extend the
+         types accepted for header names for greater
+         interoperability. Header names are automatically
+         lowercased as well.
 * *2.0*: Function `gun:headers/4,5` introduced.
 * *2.0*: The `keepalive` option is now set to `infinity` by
          default for the HTTP/1.1 protocol, disabling it.
diff --git a/doc/src/manual/gun.connect.asciidoc b/doc/src/manual/gun.connect.asciidoc
index 483b24d..de40e34 100644
--- a/doc/src/manual/gun.connect.asciidoc
+++ b/doc/src/manual/gun.connect.asciidoc
@@ -19,7 +19,7 @@ connect(ConnPid, Destination, Headers, ReqOpts)
 
 ConnPid     :: pid()
 Destination :: gun:connect_destination()
-Headers     :: [{binary(), iodata()}]
+Headers     :: gun:req_headers()
 ReqOpts     :: gun:req_opts()
 StreamRef   :: reference()
 ----
diff --git a/doc/src/manual/gun.delete.asciidoc b/doc/src/manual/gun.delete.asciidoc
index feb64ff..7367adb 100644
--- a/doc/src/manual/gun.delete.asciidoc
+++ b/doc/src/manual/gun.delete.asciidoc
@@ -19,7 +19,7 @@ delete(ConnPid, Path, Headers, ReqOpts)
 
 ConnPid   :: pid()
 Path      :: iodata()
-Headers   :: [{binary(), iodata()}]
+Headers   :: gun:req_headers()
 ReqOpts   :: gun:req_opts()
 StreamRef :: reference()
 ----
diff --git a/doc/src/manual/gun.get.asciidoc b/doc/src/manual/gun.get.asciidoc
index 623c038..64feeab 100644
--- a/doc/src/manual/gun.get.asciidoc
+++ b/doc/src/manual/gun.get.asciidoc
@@ -19,7 +19,7 @@ get(ConnPid, Path, Headers, ReqOpts)
 
 ConnPid   :: pid()
 Path      :: iodata()
-Headers   :: [{binary(), iodata()}]
+Headers   :: gun:req_headers()
 ReqOpts   :: gun:req_opts()
 StreamRef :: reference()
 ----
diff --git a/doc/src/manual/gun.head.asciidoc b/doc/src/manual/gun.head.asciidoc
index 3d92e38..08ce86b 100644
--- a/doc/src/manual/gun.head.asciidoc
+++ b/doc/src/manual/gun.head.asciidoc
@@ -19,7 +19,7 @@ head(ConnPid, Path, Headers, ReqOpts)
 
 ConnPid   :: pid()
 Path      :: iodata()
-Headers   :: [{binary(), iodata()}]
+Headers   :: gun:req_headers()
 ReqOpts   :: gun:req_opts()
 StreamRef :: reference()
 ----
diff --git a/doc/src/manual/gun.headers.asciidoc b/doc/src/manual/gun.headers.asciidoc
index bab1b82..4abcb39 100644
--- a/doc/src/manual/gun.headers.asciidoc
+++ b/doc/src/manual/gun.headers.asciidoc
@@ -17,7 +17,7 @@ headers(ConnPid, Method, Path, Headers, ReqOpts)
 ConnPid   :: pid()
 Method    :: binary()
 Path      :: iodata()
-Headers   :: [{binary(), iodata()}]
+Headers   :: gun:req_headers()
 ReqOpts   :: gun:req_opts()
 StreamRef :: reference()
 ----
diff --git a/doc/src/manual/gun.options.asciidoc b/doc/src/manual/gun.options.asciidoc
index 5b36f22..dfbba7b 100644
--- a/doc/src/manual/gun.options.asciidoc
+++ b/doc/src/manual/gun.options.asciidoc
@@ -19,7 +19,7 @@ options(ConnPid, Path, Headers, ReqOpts)
 
 ConnPid   :: pid()
 Path      :: iodata()
-Headers   :: [{binary(), iodata()}]
+Headers   :: gun:req_headers()
 ReqOpts   :: gun:req_opts()
 StreamRef :: reference()
 ----
diff --git a/doc/src/manual/gun.patch.asciidoc b/doc/src/manual/gun.patch.asciidoc
index c240a4d..cdc8f97 100644
--- a/doc/src/manual/gun.patch.asciidoc
+++ b/doc/src/manual/gun.patch.asciidoc
@@ -22,7 +22,7 @@ patch(ConnPid, Path, Headers, Body, ReqOpts)
 
 ConnPid   :: pid()
 Path      :: iodata()
-Headers   :: [{binary(), iodata()}]
+Headers   :: gun:req_headers()
 Body      :: iodata()
 ReqOpts   :: gun:req_opts()
 StreamRef :: reference()
diff --git a/doc/src/manual/gun.post.asciidoc b/doc/src/manual/gun.post.asciidoc
index aed8b3f..a545a32 100644
--- a/doc/src/manual/gun.post.asciidoc
+++ b/doc/src/manual/gun.post.asciidoc
@@ -22,7 +22,7 @@ post(ConnPid, Path, Headers, Body, ReqOpts)
 
 ConnPid   :: pid()
 Path      :: iodata()
-Headers   :: [{binary(), iodata()}]
+Headers   :: gun:req_headers()
 Body      :: iodata()
 ReqOpts   :: gun:req_opts()
 StreamRef :: reference()
diff --git a/doc/src/manual/gun.put.asciidoc b/doc/src/manual/gun.put.asciidoc
index a60849b..7807d68 100644
--- a/doc/src/manual/gun.put.asciidoc
+++ b/doc/src/manual/gun.put.asciidoc
@@ -22,7 +22,7 @@ put(ConnPid, Path, Headers, Body, ReqOpts)
 
 ConnPid   :: pid()
 Path      :: iodata()
-Headers   :: [{binary(), iodata()}]
+Headers   :: gun:req_headers()
 Body      :: iodata()
 ReqOpts   :: gun:req_opts()
 StreamRef :: reference()
diff --git a/doc/src/manual/gun.request.asciidoc b/doc/src/manual/gun.request.asciidoc
index f5c1cd8..0a50499 100644
--- a/doc/src/manual/gun.request.asciidoc
+++ b/doc/src/manual/gun.request.asciidoc
@@ -17,7 +17,7 @@ request(ConnPid, Method, Path, Headers, Body, ReqOpts)
 ConnPid   :: pid()
 Method    :: binary()
 Path      :: iodata()
-Headers   :: [{binary(), iodata()}]
+Headers   :: gun:req_headers()
 Body      :: iodata()
 ReqOpts   :: gun:req_opts()
 StreamRef :: reference()
diff --git a/doc/src/manual/gun.ws_upgrade.asciidoc b/doc/src/manual/gun.ws_upgrade.asciidoc
index cb9da06..241d916 100644
--- a/doc/src/manual/gun.ws_upgrade.asciidoc
+++ b/doc/src/manual/gun.ws_upgrade.asciidoc
@@ -19,7 +19,7 @@ ws_upgrade(ConnPid, Path, Headers, WsOpts)
 
 ConnPid   :: pid()
 Path      :: iodata()
-Headers   :: [{binary(), iodata()}]
+Headers   :: gun:req_headers()
 WsOpts    :: gun:ws_opts
 StreamRef :: reference()
 ----