diff --git a/README.markdown b/README.markdown
index 35ea004..04ce418 100644
--- a/README.markdown
+++ b/README.markdown
@@ -172,6 +172,8 @@ To load this module, just do this
 
 Performs the websocket handshake process on the server side and returns a WebSocket server object.
 
+When the client offers subprotocols, the first one it lists is selected and returned in the `Sec-WebSocket-Protocol` response header. RFC 6455 section 4.2.2 allows exactly one, so the offered list is never echoed back whole.
+
 In case of error, it returns `nil` and a string describing the error.
 
 An optional options table can be specified. The following options are as follows:
@@ -389,13 +391,15 @@ Connects to the remote WebSocket service port and performs the websocket handsha
 
 Before actually resolving the host name and connecting to the remote backend, this method will always look up the connection pool for matched idle connections created by previous calls of this method.
 
+The handshake response is validated per RFC 6455 section 4.1: the status must be `101`, `Upgrade` must be `websocket`, `Connection` must carry the `upgrade` token, `Sec-WebSocket-Accept` must match the key that was sent, any `Sec-WebSocket-Protocol` must be one of the offered subprotocols, and `Sec-WebSocket-Extensions` must be absent since no extension is ever offered. When validation fails the method returns `nil` plus an error message, the underlying socket is closed, and the object is marked fatal.
+
 The third return value of this method contains the raw, plain-text response (status line and headers) to the handshake request. This allows the caller to perform additional validation and/or extract the response headers. When the connection is reused and no handshake request is sent, the string `"connection reused"` is returned in lieu of the response.
 
 An optional Lua table can be specified as the last argument to this method to specify various connect options:
 
 * `protocols`
 
-    Specifies all the subprotocols used for the current WebSocket session. It could be a Lua table holding all the subprotocol names or just a single Lua string.
+    Specifies all the subprotocols used for the current WebSocket session. It could be a Lua table holding all the subprotocol names or just a single Lua string, which may itself be a comma-separated list. The subprotocol the server selects must be one of these, compared verbatim.
 * `origin`
 
     Specifies the value of the `Origin` request header.
diff --git a/lib/resty/websocket/client.lua b/lib/resty/websocket/client.lua
index ce7823d..58700d8 100644
--- a/lib/resty/websocket/client.lua
+++ b/lib/resty/websocket/client.lua
@@ -17,15 +17,18 @@ local re_match = ngx.re.match
 local re_find  = ngx.re.find
 local re_gmatch = ngx.re.gmatch
 local encode_base64 = ngx.encode_base64
+local sha1_bin = ngx.sha1_bin
 local concat = table.concat
 local insert = table.insert
 local char = string.char
 local str_find = string.find
+local str_lower = string.lower
 local str_sub = string.sub
 local rand = math.random
 local rshift = bit.rshift
 local band = bit.band
 local setmetatable = setmetatable
+local ipairs = ipairs
 local type = type
 local debug = ngx.config.debug
 local ngx_log = ngx.log
@@ -79,6 +82,92 @@ local function recv_header(sock, max_header_len)
 end
 
 
+local WS_GUID = "258EAFA5-E914-47DA-95CA-C5AB0DC85B11"
+
+
+-- true if a comma-separated header value carries the given token
+local function has_token(value, token)
+    local iter, err = re_gmatch(value, [[[^,\s]+]], "jo")
+    if not iter then
+        ngx_log(ngx_DEBUG, "failed to parse header value: ", err)
+        return false
+    end
+
+    while true do
+        local m = iter()
+        if not m then
+            return false
+        end
+
+        if str_lower(m[0]) == token then
+            return true
+        end
+    end
+end
+
+
+-- adds every comma-separated token of value to set
+local function add_tokens(set, value)
+    local iter, err = re_gmatch(value, [[[^,\s]+]], "jo")
+    if not iter then
+        ngx_log(ngx_DEBUG, "failed to parse header value: ", err)
+        return
+    end
+
+    while true do
+        local m = iter()
+        if not m then
+            return
+        end
+
+        set[m[0]] = true
+    end
+end
+
+
+-- RFC 6455 section 4.1: the client must fail the connection unless the server
+-- proves it understood the handshake. Without these checks anything that
+-- answers 101 passes for a websocket server, and a duplicated header (parsed
+-- into a table) is a protocol error in its own right.
+local function verify_handshake(resp_headers, key, protocols)
+    local upgrade = resp_headers.upgrade
+    if type(upgrade) ~= "string" or str_lower(upgrade) ~= "websocket" then
+        return nil, "invalid \"Upgrade\" response header"
+    end
+
+    local connection = resp_headers.connection
+    if type(connection) ~= "string" or not has_token(connection, "upgrade") then
+        return nil, "invalid \"Connection\" response header"
+    end
+
+    local accept = resp_headers.sec_websocket_accept
+    if type(accept) ~= "string" then
+        return nil, "missing \"Sec-WebSocket-Accept\" response header"
+    end
+
+    if accept ~= encode_base64(sha1_bin(key .. WS_GUID)) then
+        return nil, "invalid \"Sec-WebSocket-Accept\" response header"
+    end
+
+    -- the server may decline the subprotocol, but it may not invent one.
+    -- RFC 6455 places no case folding on subprotocol names, so they are
+    -- compared verbatim
+    local proto = resp_headers.sec_websocket_protocol
+    if proto ~= nil
+       and (type(proto) ~= "string" or not protocols[proto])
+    then
+        return nil, "invalid \"Sec-WebSocket-Protocol\" response header"
+    end
+
+    -- no extension is ever offered, so none may be accepted
+    if resp_headers.sec_websocket_extensions ~= nil then
+        return nil, "unexpected \"Sec-WebSocket-Extensions\" response header"
+    end
+
+    return true
+end
+
+
 function _M.new(self, opts)
     local sock, err = tcp()
     if not sock then
@@ -175,6 +264,7 @@ function _M.connect(self, uri, opts)
     end
 
     local ssl_verify, server_name, headers, proto_header, origin_header
+    local offered_protocols = {}
     local sock_opts = {}
     local client_cert, client_priv_key
     local header_host
@@ -187,8 +277,14 @@ function _M.connect(self, uri, opts)
                 proto_header = "\r\nSec-WebSocket-Protocol: "
                                .. concat(protos, ",")
 
+                for _, proto in ipairs(protos) do
+                    add_tokens(offered_protocols, proto)
+                end
+
             else
                 proto_header = "\r\nSec-WebSocket-Protocol: " .. protos
+                -- a scalar may still carry a comma-separated list
+                add_tokens(offered_protocols, protos)
             end
         end
 
@@ -406,8 +502,6 @@ function _M.connect(self, uri, opts)
 
     -- error("header: " .. header)
 
-    -- FIXME: verify the response headers
-
     m, err = re_match(header, [[^\s*HTTP/1\.1\s+(\d+)]], "jo")
     if not m then
         return nil, "bad HTTP response status line: " .. header
@@ -432,6 +526,26 @@ function _M.connect(self, uri, opts)
         return nil, "unexpected HTTP response code: " .. m[1], header
     end
 
+    local resp_headers
+    resp_headers, err = self:get_resp_headers()
+    if not resp_headers then
+        err = "failed to parse response headers: " .. err
+
+    else
+        ok, err = verify_handshake(resp_headers, key, offered_protocols)
+    end
+
+    if err then
+        local closing_ok, closing_err = sock:close()
+        if not closing_ok then
+            ngx_log(ngx_DEBUG, "failed to close the underlying socket: ",
+                closing_err, " when handling a failed handshake")
+        end
+
+        self.fatal = true
+        return nil, "failed websocket handshake: " .. err, header
+    end
+
     return 1, nil, header
 end
 
@@ -576,7 +690,9 @@ function _M.get_resp_headers(self)
         return nil, "response header not available"
     end
 
-    local iter, err = re_gmatch(self.resp_header .. "\r\n", "([^:\\s]+):\\s*(.*?)\r\n", "jo")
+    -- RFC 7230 section 3.2.4: leading and trailing OWS is not part of the
+    -- field value, so strip it instead of handing it to the caller
+    local iter, err = re_gmatch(self.resp_header .. "\r\n", "([^:\\s]+):[ \\t]*(.*?)[ \\t]*\r\n", "jo")
     if err then
         return nil, "failed to parse response header: " .. err
     end
diff --git a/lib/resty/websocket/server.lua b/lib/resty/websocket/server.lua
index 64e06ab..6db7723 100644
--- a/lib/resty/websocket/server.lua
+++ b/lib/resty/websocket/server.lua
@@ -13,6 +13,7 @@ local req_sock = ngx.req.socket
 local ngx_header = ngx.header
 local req_headers = ngx.req.get_headers
 local str_lower = string.lower
+local str_match = string.match
 local char = string.char
 local str_find = string.find
 local sha1_bin = ngx.sha1_bin
@@ -85,7 +86,13 @@ function _M.new(self, opts)
     end
 
     if protocols then
-        ngx_header["Sec-WebSocket-Protocol"] = protocols
+        -- RFC 6455 section 4.2.2: the server selects exactly one subprotocol
+        -- from the client's list, so answer with the first one offered
+        -- instead of echoing the whole list back
+        local selected = str_match(protocols, "[^,%s]+")
+        if selected then
+            ngx_header["Sec-WebSocket-Protocol"] = selected
+        end
     end
     ngx_header["Upgrade"] = "websocket"
 
diff --git a/t/handshake_verify.t b/t/handshake_verify.t
new file mode 100644
index 0000000..ac46367
--- /dev/null
+++ b/t/handshake_verify.t
@@ -0,0 +1,541 @@
+# vim:set ft= ts=4 sw=4 et:
+
+use Test::Nginx::Socket::Lua;
+use Cwd qw(cwd);
+
+repeat_each(2);
+
+plan tests => repeat_each() * (3 * blocks());
+
+my $pwd = cwd();
+
+our $HttpConfig = qq{
+    lua_package_path "$pwd/lib/?.lua;;";
+    lua_package_cpath "/usr/local/openresty-debug/lualib/?.so;/usr/local/openresty/lualib/?.so;;";
+};
+
+# all the mock replies below answer the fixed key "dGhlIHNhbXBsZSBub25jZQ=="
+# whose accept value is "s3pPLMBiTxaQ9kYGzzhZRbK+xOo=" (RFC 6455 section 1.3)
+
+no_long_string();
+
+run_tests();
+
+__DATA__
+
+=== TEST 1: a well formed handshake response is accepted
+--- http_config eval: $::HttpConfig
+--- config
+    location = /t {
+        content_by_lua_block {
+            local client = require "resty.websocket.client"
+            local wb = client:new()
+
+            local ok, err = wb:connect("ws://127.0.0.1:7986/",
+                                       { key = "dGhlIHNhbXBsZSBub25jZQ==" })
+            if not ok then
+                ngx.say("failed to connect: ", err)
+                return
+            end
+
+            ngx.say("connected")
+        }
+    }
+--- request
+GET /t
+--- tcp_listen: 7986
+--- tcp_reply eval
+"HTTP/1.1 101 Switching Protocols\r
+Upgrade: websocket\r
+Connection: Upgrade\r
+Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=\r
+\r
+"
+--- response_body
+connected
+--- no_error_log
+[error]
+
+
+
+=== TEST 2: a wrong Sec-WebSocket-Accept is rejected
+--- http_config eval: $::HttpConfig
+--- config
+    location = /t {
+        content_by_lua_block {
+            local client = require "resty.websocket.client"
+            local wb = client:new()
+
+            local ok, err = wb:connect("ws://127.0.0.1:7986/",
+                                       { key = "dGhlIHNhbXBsZSBub25jZQ==" })
+            if not ok then
+                ngx.say("failed to connect: ", err)
+                ngx.say("fatal: ", wb.fatal)
+                return
+            end
+
+            ngx.say("connected")
+        }
+    }
+--- request
+GET /t
+--- tcp_listen: 7986
+--- tcp_reply eval
+"HTTP/1.1 101 Switching Protocols\r
+Upgrade: websocket\r
+Connection: Upgrade\r
+Sec-WebSocket-Accept: 0000000000000000000000000000=\r
+\r
+"
+--- response_body
+failed to connect: failed websocket handshake: invalid "Sec-WebSocket-Accept" response header
+fatal: true
+--- no_error_log
+[error]
+
+
+
+=== TEST 3: a missing Sec-WebSocket-Accept is rejected
+--- http_config eval: $::HttpConfig
+--- config
+    location = /t {
+        content_by_lua_block {
+            local client = require "resty.websocket.client"
+            local wb = client:new()
+
+            local ok, err = wb:connect("ws://127.0.0.1:7986/",
+                                       { key = "dGhlIHNhbXBsZSBub25jZQ==" })
+            if not ok then
+                ngx.say("failed to connect: ", err)
+                return
+            end
+
+            ngx.say("connected")
+        }
+    }
+--- request
+GET /t
+--- tcp_listen: 7986
+--- tcp_reply eval
+"HTTP/1.1 101 Switching Protocols\r
+Upgrade: websocket\r
+Connection: Upgrade\r
+\r
+"
+--- response_body
+failed to connect: failed websocket handshake: missing "Sec-WebSocket-Accept" response header
+--- no_error_log
+[error]
+
+
+
+=== TEST 4: a non-websocket Upgrade is rejected
+--- http_config eval: $::HttpConfig
+--- config
+    location = /t {
+        content_by_lua_block {
+            local client = require "resty.websocket.client"
+            local wb = client:new()
+
+            local ok, err = wb:connect("ws://127.0.0.1:7986/",
+                                       { key = "dGhlIHNhbXBsZSBub25jZQ==" })
+            if not ok then
+                ngx.say("failed to connect: ", err)
+                return
+            end
+
+            ngx.say("connected")
+        }
+    }
+--- request
+GET /t
+--- tcp_listen: 7986
+--- tcp_reply eval
+"HTTP/1.1 101 Switching Protocols\r
+Upgrade: h2c\r
+Connection: Upgrade\r
+Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=\r
+\r
+"
+--- response_body
+failed to connect: failed websocket handshake: invalid "Upgrade" response header
+--- no_error_log
+[error]
+
+
+
+=== TEST 5: a Connection header without the upgrade token is rejected
+--- http_config eval: $::HttpConfig
+--- config
+    location = /t {
+        content_by_lua_block {
+            local client = require "resty.websocket.client"
+            local wb = client:new()
+
+            local ok, err = wb:connect("ws://127.0.0.1:7986/",
+                                       { key = "dGhlIHNhbXBsZSBub25jZQ==" })
+            if not ok then
+                ngx.say("failed to connect: ", err)
+                return
+            end
+
+            ngx.say("connected")
+        }
+    }
+--- request
+GET /t
+--- tcp_listen: 7986
+--- tcp_reply eval
+"HTTP/1.1 101 Switching Protocols\r
+Upgrade: websocket\r
+Connection: close\r
+Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=\r
+\r
+"
+--- response_body
+failed to connect: failed websocket handshake: invalid "Connection" response header
+--- no_error_log
+[error]
+
+
+
+=== TEST 6: the upgrade token is found in a Connection token list
+--- http_config eval: $::HttpConfig
+--- config
+    location = /t {
+        content_by_lua_block {
+            local client = require "resty.websocket.client"
+            local wb = client:new()
+
+            local ok, err = wb:connect("ws://127.0.0.1:7986/",
+                                       { key = "dGhlIHNhbXBsZSBub25jZQ==" })
+            if not ok then
+                ngx.say("failed to connect: ", err)
+                return
+            end
+
+            ngx.say("connected")
+        }
+    }
+--- request
+GET /t
+--- tcp_listen: 7986
+--- tcp_reply eval
+"HTTP/1.1 101 Switching Protocols\r
+Upgrade: WebSocket\r
+Connection: keep-alive, Upgrade\r
+Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=\r
+\r
+"
+--- response_body
+connected
+--- no_error_log
+[error]
+
+
+
+=== TEST 7: a subprotocol that was never offered is rejected
+--- http_config eval: $::HttpConfig
+--- config
+    location = /t {
+        content_by_lua_block {
+            local client = require "resty.websocket.client"
+            local wb = client:new()
+
+            local ok, err = wb:connect("ws://127.0.0.1:7986/",
+                                       { key = "dGhlIHNhbXBsZSBub25jZQ==" })
+            if not ok then
+                ngx.say("failed to connect: ", err)
+                return
+            end
+
+            ngx.say("connected")
+        }
+    }
+--- request
+GET /t
+--- tcp_listen: 7986
+--- tcp_reply eval
+"HTTP/1.1 101 Switching Protocols\r
+Upgrade: websocket\r
+Connection: Upgrade\r
+Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=\r
+Sec-WebSocket-Protocol: json\r
+\r
+"
+--- response_body
+failed to connect: failed websocket handshake: invalid "Sec-WebSocket-Protocol" response header
+--- no_error_log
+[error]
+
+
+
+=== TEST 8: an offered subprotocol is accepted
+--- http_config eval: $::HttpConfig
+--- config
+    location = /t {
+        content_by_lua_block {
+            local client = require "resty.websocket.client"
+            local wb = client:new()
+
+            local ok, err = wb:connect("ws://127.0.0.1:7986/",
+                                       { key = "dGhlIHNhbXBsZSBub25jZQ==",
+                                         protocols = { "xml", "json" } })
+            if not ok then
+                ngx.say("failed to connect: ", err)
+                return
+            end
+
+            ngx.say("connected")
+        }
+    }
+--- request
+GET /t
+--- tcp_listen: 7986
+--- tcp_reply eval
+"HTTP/1.1 101 Switching Protocols\r
+Upgrade: websocket\r
+Connection: Upgrade\r
+Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=\r
+Sec-WebSocket-Protocol: json\r
+\r
+"
+--- response_body
+connected
+--- no_error_log
+[error]
+
+
+
+=== TEST 9: an extension that was never offered is rejected
+--- http_config eval: $::HttpConfig
+--- config
+    location = /t {
+        content_by_lua_block {
+            local client = require "resty.websocket.client"
+            local wb = client:new()
+
+            local ok, err = wb:connect("ws://127.0.0.1:7986/",
+                                       { key = "dGhlIHNhbXBsZSBub25jZQ==" })
+            if not ok then
+                ngx.say("failed to connect: ", err)
+                return
+            end
+
+            ngx.say("connected")
+        }
+    }
+--- request
+GET /t
+--- tcp_listen: 7986
+--- tcp_reply eval
+"HTTP/1.1 101 Switching Protocols\r
+Upgrade: websocket\r
+Connection: Upgrade\r
+Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=\r
+Sec-WebSocket-Extensions: permessage-deflate\r
+\r
+"
+--- response_body
+failed to connect: failed websocket handshake: unexpected "Sec-WebSocket-Extensions" response header
+--- no_error_log
+[error]
+
+
+
+=== TEST 10: a real handshake still succeeds
+--- http_config eval: $::HttpConfig
+--- config
+    location = /ws {
+        content_by_lua_block {
+            local server = require "resty.websocket.server"
+            local wb, err = server:new()
+            if not wb then
+                ngx.log(ngx.ERR, "failed to new websocket: ", err)
+                return ngx.exit(444)
+            end
+
+            local data, typ = wb:recv_frame()
+            wb:send_text(data .. " [" .. typ .. "]")
+        }
+    }
+
+    location = /t {
+        content_by_lua_block {
+            local client = require "resty.websocket.client"
+            local wb = client:new()
+
+            local uri = "ws://127.0.0.1:" .. ngx.var.server_port .. "/ws"
+            local ok, err = wb:connect(uri)
+            if not ok then
+                ngx.say("failed to connect: ", err)
+                return
+            end
+
+            wb:send_text("hello")
+
+            local data, typ, err = wb:recv_frame()
+            if not data then
+                ngx.say("failed to receive frame: ", err)
+                return
+            end
+
+            ngx.say("received: ", data, " (", typ, ")")
+            wb:close()
+        }
+    }
+--- request
+GET /t
+--- response_body
+received: hello [text] (text)
+--- no_error_log
+[error]
+
+
+
+=== TEST 11: trailing whitespace in the response headers is tolerated
+--- http_config eval: $::HttpConfig
+--- config
+    location = /t {
+        content_by_lua_block {
+            local client = require "resty.websocket.client"
+            local wb = client:new()
+
+            local ok, err = wb:connect("ws://127.0.0.1:7986/",
+                                       { key = "dGhlIHNhbXBsZSBub25jZQ==" })
+            if not ok then
+                ngx.say("failed to connect: ", err)
+                return
+            end
+
+            ngx.say("connected")
+        }
+    }
+--- request
+GET /t
+--- tcp_listen: 7986
+--- tcp_reply eval
+"HTTP/1.1 101 Switching Protocols\r
+Upgrade: websocket \r
+Connection: Upgrade\r
+Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=  \r
+\r
+"
+--- response_body
+connected
+--- no_error_log
+[error]
+
+
+
+=== TEST 12: a subprotocol differing only in case is rejected
+--- http_config eval: $::HttpConfig
+--- config
+    location = /t {
+        content_by_lua_block {
+            local client = require "resty.websocket.client"
+            local wb = client:new()
+
+            local ok, err = wb:connect("ws://127.0.0.1:7986/",
+                                       { key = "dGhlIHNhbXBsZSBub25jZQ==",
+                                         protocols = { "json" } })
+            if not ok then
+                ngx.say("failed to connect: ", err)
+                return
+            end
+
+            ngx.say("connected")
+        }
+    }
+--- request
+GET /t
+--- tcp_listen: 7986
+--- tcp_reply eval
+"HTTP/1.1 101 Switching Protocols\r
+Upgrade: websocket\r
+Connection: Upgrade\r
+Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=\r
+Sec-WebSocket-Protocol: JSON\r
+\r
+"
+--- response_body
+failed to connect: failed websocket handshake: invalid "Sec-WebSocket-Protocol" response header
+--- no_error_log
+[error]
+
+
+
+=== TEST 13: a subprotocol list passed as a single string is honoured
+--- http_config eval: $::HttpConfig
+--- config
+    location = /t {
+        content_by_lua_block {
+            local client = require "resty.websocket.client"
+            local wb = client:new()
+
+            local ok, err = wb:connect("ws://127.0.0.1:7986/",
+                                       { key = "dGhlIHNhbXBsZSBub25jZQ==",
+                                         protocols = "xml, json" })
+            if not ok then
+                ngx.say("failed to connect: ", err)
+                return
+            end
+
+            ngx.say("connected")
+        }
+    }
+--- request
+GET /t
+--- tcp_listen: 7986
+--- tcp_reply eval
+"HTTP/1.1 101 Switching Protocols\r
+Upgrade: websocket\r
+Connection: Upgrade\r
+Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=\r
+Sec-WebSocket-Protocol: json\r
+\r
+"
+--- response_body
+connected
+--- no_error_log
+[error]
+
+
+
+=== TEST 14: the server selects one of several offered subprotocols
+--- http_config eval: $::HttpConfig
+--- config
+    location = /ws {
+        content_by_lua_block {
+            local server = require "resty.websocket.server"
+            local wb, err = server:new()
+            if not wb then
+                ngx.log(ngx.ERR, "failed to new websocket: ", err)
+                return ngx.exit(444)
+            end
+            wb:recv_frame()
+        }
+    }
+
+    location = /t {
+        content_by_lua_block {
+            local client = require "resty.websocket.client"
+            local wb = client:new()
+
+            local uri = "ws://127.0.0.1:" .. ngx.var.server_port .. "/ws"
+            local ok, err = wb:connect(uri, { protocols = { "xml", "json" } })
+            if not ok then
+                ngx.say("failed to connect: ", err)
+                return
+            end
+
+            ngx.say("selected: ", wb:get_resp_headers().sec_websocket_protocol)
+            wb:close()
+        }
+    }
+--- request
+GET /t
+--- response_body
+selected: xml
+--- no_error_log
+[error]