diff --git a/tests/test_ext_utils.nim b/tests/test_ext_utils.nim
new file mode 100644
index 0000000000..5335109b71
--- /dev/null
+++ b/tests/test_ext_utils.nim
@@ -0,0 +1,269 @@
+## nim-ws
+## Copyright (c) 2021 Status Research & Development GmbH
+## Licensed under either of
+##  * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE))
+##  * MIT license ([LICENSE-MIT](LICENSE-MIT))
+## at your option.
+## This file may not be copied, modified, or distributed except according to
+## those terms.
+
+import
+  pkg/[asynctest, chronos],
+  ../ws/ext_utils
+
+suite "extension parser":
+  test "single extension":
+    var app: seq[AppExt]
+    let res = parseExt("permessage-deflate", app)
+    check res == true
+    check app.len == 1
+    if app.len == 1:
+      check app[0].name == "permessage-deflate"
+
+  test "single extension quoted bad syntax":
+    var app: seq[AppExt]
+    let res = parseExt("\"zip\"", app)
+    check res == false
+
+  test "basic extensions no param":
+    var app: seq[AppExt]
+    let res = parseExt("permessage-deflate, snappy, bzip", app)
+    check res == true
+    check app.len == 3
+    if app.len == 3:
+      check app[0].name == "permessage-deflate"
+      check app[1].name == "snappy"
+      check app[2].name == "bzip"
+
+  test "basic extensions no param bad syntax":
+    var app: seq[AppExt]
+    let res = parseExt("permessage-deflate, ", app)
+    check res == false
+
+  test "basic extensions no param with trailing leading whitespaces":
+    var app: seq[AppExt]
+    let res = parseExt(" permessage-deflate, snappy, bzip ", app)
+    check res == true
+    check app.len == 3
+    if app.len == 3:
+      check app[0].name == "permessage-deflate"
+      check app[1].name == "snappy"
+      check app[2].name == "bzip"
+
+  test "basic extension with params":
+    var app: seq[AppExt]
+    let res = parseExt("snappy; arg1noval; arg2 = 123; arg3 = \"hello\"", app)
+    check res == true
+    check app.len == 1
+    if app.len == 1:
+      check app[0].name == "snappy"
+      check app[0].params[0].name == "arg1noval"
+      check app[0].params[0].value == ""
+
+      check app[0].params[1].name == "arg2"
+      check app[0].params[1].value == "123"
+
+      check app[0].params[2].name == "arg3"
+      check app[0].params[2].value == "hello"
+
+  test "basic extension with param + fallback":
+    var app: seq[AppExt]
+    let res = parseExt("snappy; arg = 123, snappy", app)
+    check res == true
+    check app.len == 2
+    if app.len == 2:
+      check app[0].name == "snappy"
+      check app[1].name == "snappy"
+
+      check app[0].params[0].name == "arg"
+      check app[0].params[0].value == "123"
+
+  test "extension param no value + fallback":
+    var app: seq[AppExt]
+    let res = parseExt("snappy; arg, snappy", app)
+    check res == true
+    check app.len == 2
+    if app.len == 2:
+      check app[0].name == "snappy"
+      check app[1].name == "snappy"
+
+      check app[0].params[0].name == "arg"
+      check app[0].params[0].value == ""
+
+  test "extension param no value + fallback bad syntax":
+    var app: seq[AppExt]
+    let res = parseExt("snappy; arg = , snappy", app)
+    check res == false
+
+  test "extension param no value + fallback bad syntax":
+    var app: seq[AppExt]
+    let res = parseExt("snappy; arg = , snappy", app)
+    check res == false
+
+  test "extensions bad syntax":
+    var app: seq[AppExt]
+    let res = parseExt("snappy; snappy; ", app)
+    check res == false
+
+  test "extension bad syntax":
+    var app: seq[AppExt]
+    let res = parseExt("snappy; ", app)
+    check res == false
+
+  test "extension param no value bad syntax":
+    var app: seq[AppExt]
+    let res = parseExt("snappy; arg = ", app)
+    check res == false
+
+  test "extension param no value":
+    var app: seq[AppExt]
+    let res = parseExt("snappy; arg", app)
+    check res == true
+    check app.len == 1
+    if app.len == 1:
+      check app[0].name == "snappy"
+      check app[0].params[0].name == "arg"
+      check app[0].params[0].value == ""
+
+  test "extension param not closed quoted value":
+    var app: seq[AppExt]
+    let res = parseExt("snappy; arg = \"wwww", app)
+    check res == false
+
+  test "inlwithasciifilename":
+    var app: seq[AppExt]
+    let res = parseExt("inline; filename=\"foo.html\"", app)
+    check res == true
+    check app[0].params[0].value == "foo.html"
+
+  test "inlwithfnattach":
+    var app: seq[AppExt]
+    let res = parseExt("inline; filename=\"Not an attachment!\"", app)
+    check res == true
+    check app[0].params[0].value == "Not an attachment!"
+
+  test "attwithasciifnescapedchar":
+    var app: seq[AppExt]
+    let res = parseExt("attachment; filename=\"f\\oo.html\"", app)
+    check res == true
+    check app[0].params[0].value == "foo.html"
+
+  test "attwithasciifnescapedquote":
+    var app: seq[AppExt]
+    let res = parseExt("attachment; filename=\"\\\"quoting\\\" tested.html\"", app)
+    check res == true
+    check app[0].params[0].value == "\"quoting\" tested.html"
+
+  test "attwithquotedsemicolon":
+    var app: seq[AppExt]
+    let res = parseExt("attachment; filename=\"Here's a semicolon;.html\"", app)
+    check res == true
+    check app[0].params[0].value == "Here's a semicolon;.html"
+
+  test "attwithfilenameandextparamescaped":
+    var app: seq[AppExt]
+    let res = parseExt("attachment; foo=\"\\\"\\\\\"", app)
+    check res == true
+    check app[0].params[0].value == "\"\\"
+
+  test "attwithasciifilenamenq":
+    var app: seq[AppExt]
+    let res = parseExt("attachment; filename=foo.html", app)
+    check res == true
+    check app[0].params[0].value == "foo.html"
+
+  test "attemptyparam":
+    var app: seq[AppExt]
+    let res = parseExt("attachment; ;filename=foo", app)
+    check res == false
+
+  test "attwithasciifilenamenqws":
+    var app: seq[AppExt]
+    let res = parseExt("attachment; filename=foo bar.html", app)
+    check res == false
+
+  test "attwithfntokensq":
+    var app: seq[AppExt]
+    let res = parseExt("attachment; filename='foo.bar'", app)
+    check res == true
+    check app[0].params[0].value == "'foo.bar'"
+
+  test "attfnbrokentoken":
+    var app: seq[AppExt]
+    let res = parseExt("attachment; filename=foo[1](2).html", app)
+    check res == false
+
+  test "attfnbrokentokeniso":
+    var app: seq[AppExt]
+    let res = parseExt("attachment; filename=foo-ä.html", app)
+    check res == false
+
+  test "attfnbrokentokenutf":
+    var app: seq[AppExt]
+    let res = parseExt("attachment; filename=foo-ä.html", app)
+    check res == false
+
+  test "attmissingdisposition":
+    var app: seq[AppExt]
+    let res = parseExt("filename=foo.html", app)
+    check res == false
+
+  test "attmissingdisposition2":
+    var app: seq[AppExt]
+    let res = parseExt("x=y; filename=foo.html", app)
+    check res == false
+
+  test "attmissingdisposition3":
+    var app: seq[AppExt]
+    let res = parseExt("\"foo; filename=bar;baz\"; filename=qux", app)
+    check res == false
+
+  test "attmissingdisposition4":
+    var app: seq[AppExt]
+    let res = parseExt("filename=foo.html, filename=bar.html", app)
+    check res == false
+  
+  test "emptydisposition":
+    var app: seq[AppExt]
+    let res = parseExt(" ; filename=foo.html", app)
+    check res == false
+    
+  test "doublecolon":
+    var app: seq[AppExt]
+    let res = parseExt(": inline; attachment; filename=foo.html", app)
+    check res == false
+    
+  test "attbrokenquotedfn":
+    var app: seq[AppExt]
+    let res = parseExt(" attachment; filename=\"foo.html\".txt", app)
+    check res == false
+    
+  test "attbrokenquotedfn2":
+    var app: seq[AppExt]
+    let res = parseExt("attachment; filename=\"bar", app)
+    check res == false
+    
+  test "attbrokenquotedfn3":
+    var app: seq[AppExt]
+    let res = parseExt("attachment; filename=foo\"bar;baz\"qux", app)
+    check res == false
+    
+  test "attmissingdelim":
+    var app: seq[AppExt]
+    let res = parseExt("attachment; foo=foo filename=bar", app)
+    check res == false
+    
+  test "attmissingdelim2":
+    var app: seq[AppExt]
+    let res = parseExt("attachment; filename=bar foo=foo", app)
+    check res == false
+    
+  test "attmissingdelim3":
+    var app: seq[AppExt]
+    let res = parseExt("attachment filename=bar", app)
+    check res == false
+    
+  test "attreversed":
+    var app: seq[AppExt]
+    let res = parseExt("filename=foo.html; attachment", app)
+    check res == false
\ No newline at end of file
diff --git a/tests/testcommon.nim b/tests/testcommon.nim
index cf71dbce4d..f4e34de740 100644
--- a/tests/testcommon.nim
+++ b/tests/testcommon.nim
@@ -2,3 +2,4 @@
 
 import ./testframes
 import ./testutf8
+import ./test_ext_utils
diff --git a/ws/ext_utils.nim b/ws/ext_utils.nim
new file mode 100644
index 0000000000..3c334ec3da
--- /dev/null
+++ b/ws/ext_utils.nim
@@ -0,0 +1,159 @@
+## nim-ws
+## Copyright (c) 2021 Status Research & Development GmbH
+## Licensed under either of
+##  * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE))
+##  * MIT license ([LICENSE-MIT](LICENSE-MIT))
+## at your option.
+## This file may not be copied, modified, or distributed except according to
+## those terms.
+
+import
+  std/strutils,
+  pkg/httputils
+
+type
+  ExtParam* = object
+    name* : string
+    value*: string
+
+  AppExt* = object
+    name*  : string
+    params*: seq[ExtParam]
+
+  TokenKind = enum
+    tkError
+    tkSemcol
+    tkComma
+    tkEqual
+    tkName
+    tkQuoted
+    tkEof
+
+  Lexer = object
+    pos: int
+    token: string
+    tok: TokenKind
+
+const
+  WHITES = {' ', '\t'}
+  LCHAR  = {'a'..'z', 'A'..'Z', '-', '_', '0'..'9','.','\''}
+  SEPARATORS = {'`','~','!','@','#','$','%','^','&','*','(',')','+','=',
+                '[','{',']','}', ';',':','\'',',','<','.','>','/','?','|'}
+  QCHAR = WHITES + LCHAR + SEPARATORS
+
+proc parseName[T: BChar](lex: var Lexer, data: openarray[T]) =
+  while lex.pos < data.len:
+    let cc = data[lex.pos]
+    if cc notin LCHAR:
+      break
+    lex.token.add cc
+    inc lex.pos
+
+proc parseQuoted[T: BChar](lex: var Lexer, data: openarray[T]) =
+  while lex.pos < data.len:
+    let cc = data[lex.pos]
+    case cc:
+    of QCHAR:
+      lex.token.add cc
+      inc lex.pos
+    of '\\':
+      inc lex.pos
+      if lex.pos >= data.len:
+        lex.tok = tkError
+        return
+      lex.token.add data[lex.pos]
+      inc lex.pos
+    of '\"':
+      inc lex.pos
+      lex.tok = tkQuoted
+      return
+    else:
+      lex.tok = tkError
+      return
+
+  lex.tok = tkError
+
+proc next[T: BChar](lex: var Lexer, data: openarray[T]) =
+  while lex.pos < data.len:
+    if data[lex.pos] notin WHITES:
+      break
+    inc lex.pos
+  lex.token.setLen(0)
+
+  if lex.pos >= data.len:
+    lex.tok = tkEof
+    return
+
+  let c = data[lex.pos]
+  case c
+  of ';':
+    inc lex.pos
+    lex.tok = tkSemcol
+    return
+  of ',':
+    inc lex.pos
+    lex.tok = tkComma
+    return
+  of '=':
+    inc lex.pos
+    lex.tok = tkEqual
+    return
+  of LCHAR:
+    lex.parseName(data)
+    lex.tok = tkName
+    return
+  of '\"':
+    inc lex.pos
+    lex.parseQuoted(data)
+    return
+  else:
+    lex.tok = tkError
+    return
+
+proc parseExt*[T: BChar](data: openarray[T], output: var seq[AppExt]): bool =
+  var lex: Lexer
+  var ext: AppExt
+  lex.next(data)
+
+  while lex.tok notin {tkEof, tkError}:
+    if lex.tok != tkName:
+      return false
+    ext.name = system.move(lex.token)
+
+    lex.next(data)
+    var param: ExtParam
+    while lex.tok == tkSemCol:
+      lex.next(data)
+      if lex.tok in {tkEof, tkError}:
+        return false
+      if lex.tok != tkName:
+        return false
+      param.name = system.move(lex.token)
+      lex.next(data)
+      if lex.tok == tkEqual:
+        lex.next(data)
+        if lex.tok notin {tkName, tkQuoted}:
+          return false
+        param.value = system.move(lex.token)
+        lex.next(data)
+      ext.params.setLen(ext.params.len + 1)
+      ext.params[^1].name  = system.move(param.name)
+      ext.params[^1].value = system.move(param.value)
+
+      if lex.tok notin {tkSemCol, tkComma, tkEof}:        
+        return false
+      
+    output.setLen(output.len + 1)
+    output[^1].name   = system.move(ext.name)
+    output[^1].params = system.move(ext.params)
+
+    if lex.tok == tkEof:
+      return true
+
+    if lex.tok == tkComma:
+      lex.next(data)
+      if lex.tok != tkName:
+        return false
+      continue
+
+  lex.tok != tkError