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+.idea/
+.code/
+.vscode/
diff --git a/LICENSE b/LICENSE
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--- /dev/null
+++ b/LICENSE
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+                    GNU GENERAL PUBLIC LICENSE
+                       Version 3, 29 June 2007
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+THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+PURPOSE.  THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM
+IS WITH YOU.  SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF
+ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
+
+  16. Limitation of Liability.
+
+  IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
+THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
+GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
+USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
+DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGES.
+
+  17. Interpretation of Sections 15 and 16.
+
+  If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+                     END OF TERMS AND CONDITIONS
+
+            How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+  If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+
+    <program>  Copyright (C) <year>  <name of author>
+    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+<https://www.gnu.org/licenses/>.
+
+  The GNU General Public License does not permit incorporating your program
+into proprietary programs.  If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.  But first, please read
+<https://www.gnu.org/licenses/why-not-lgpl.html>.
diff --git a/config/config.go b/config/config.go
new file mode 100644
index 0000000..599f12c
--- /dev/null
+++ b/config/config.go
@@ -0,0 +1,52 @@
+package config
+
+import (
+	"errors"
+	"fmt"
+	"github.com/BurntSushi/toml"
+	"net/url"
+	"os"
+)
+
+type Config struct {
+	Servers []struct {
+		Name   string `toml:"name"`
+		Prefix string `toml:"prefix"`
+		Proxy  string `toml:"proxy"`
+	} `toml:"servers"`
+	Debug  bool   `toml:"debug"`
+	Listen string `toml:"listen"`
+}
+
+func (c Config) Validate() error {
+	if len(c.Servers) == 0 {
+		return errors.New("no yggdrasil server specified")
+	}
+	for _, s := range c.Servers {
+		if s.Prefix == "" {
+			return fmt.Errorf("missing prefix for yggdrasil server `%v`", s.Name)
+		}
+		_, err := url.Parse(s.Prefix)
+		if err != nil {
+			return fmt.Errorf("invalid prefix for yggdrasil server `%v`: %w", s.Name, err)
+		}
+	}
+	return nil
+}
+
+func Read(path string) (*Config, error) {
+	f, err := os.Open(path)
+	if err != nil {
+		return nil, fmt.Errorf("open: %w", err)
+	}
+	defer func() {
+		_ = f.Close()
+	}()
+	dec := toml.NewDecoder(f)
+	var c Config
+	_, err = dec.Decode(&c)
+	if err != nil {
+		return nil, fmt.Errorf("decode: %w", err)
+	}
+	return &c, nil
+}
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..f39a409
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,45 @@
+module github.com/keuin/ymux-go
+
+go 1.20
+
+require (
+	github.com/BurntSushi/toml v1.3.2
+	github.com/akamensky/argparse v1.4.0
+	github.com/avast/retry-go v3.0.0+incompatible
+	github.com/gin-gonic/gin v1.9.1
+	github.com/imroc/req v0.3.2
+	github.com/rs/zerolog v1.32.0
+	github.com/samber/lo v1.39.0
+	github.com/samber/mo v1.11.0
+	github.com/sourcegraph/conc v0.3.0
+)
+
+require (
+	github.com/bytedance/sonic v1.9.1 // indirect
+	github.com/chenzhuoyu/base64x v0.0.0-20221115062448-fe3a3abad311 // indirect
+	github.com/gabriel-vasile/mimetype v1.4.2 // indirect
+	github.com/gin-contrib/sse v0.1.0 // indirect
+	github.com/go-playground/locales v0.14.1 // indirect
+	github.com/go-playground/universal-translator v0.18.1 // indirect
+	github.com/go-playground/validator/v10 v10.14.0 // indirect
+	github.com/goccy/go-json v0.10.2 // indirect
+	github.com/json-iterator/go v1.1.12 // indirect
+	github.com/klauspost/cpuid/v2 v2.2.4 // indirect
+	github.com/kr/text v0.2.0 // indirect
+	github.com/leodido/go-urn v1.2.4 // indirect
+	github.com/mattn/go-colorable v0.1.13 // indirect
+	github.com/mattn/go-isatty v0.0.19 // indirect
+	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
+	github.com/modern-go/reflect2 v1.0.2 // indirect
+	github.com/pelletier/go-toml/v2 v2.0.8 // indirect
+	github.com/twitchyliquid64/golang-asm v0.15.1 // indirect
+	github.com/ugorji/go/codec v1.2.11 // indirect
+	golang.org/x/arch v0.3.0 // indirect
+	golang.org/x/crypto v0.9.0 // indirect
+	golang.org/x/exp v0.0.0-20220303212507-bbda1eaf7a17 // indirect
+	golang.org/x/net v0.10.0 // indirect
+	golang.org/x/sys v0.12.0 // indirect
+	golang.org/x/text v0.9.0 // indirect
+	google.golang.org/protobuf v1.30.0 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+)
diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..3a30aca
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,116 @@
+github.com/BurntSushi/toml v1.3.2 h1:o7IhLm0Msx3BaB+n3Ag7L8EVlByGnpq14C4YWiu/gL8=
+github.com/BurntSushi/toml v1.3.2/go.mod h1:CxXYINrC8qIiEnFrOxCa7Jy5BFHlXnUU2pbicEuybxQ=
+github.com/akamensky/argparse v1.4.0 h1:YGzvsTqCvbEZhL8zZu2AiA5nq805NZh75JNj4ajn1xc=
+github.com/akamensky/argparse v1.4.0/go.mod h1:S5kwC7IuDcEr5VeXtGPRVZ5o/FdhcMlQz4IZQuw64xA=
+github.com/avast/retry-go v3.0.0+incompatible h1:4SOWQ7Qs+oroOTQOYnAHqelpCO0biHSxpiH9JdtuBj0=
+github.com/avast/retry-go v3.0.0+incompatible/go.mod h1:XtSnn+n/sHqQIpZ10K1qAevBhOOCWBLXXy3hyiqqBrY=
+github.com/bytedance/sonic v1.5.0/go.mod h1:ED5hyg4y6t3/9Ku1R6dU/4KyJ48DZ4jPhfY1O2AihPM=
+github.com/bytedance/sonic v1.9.1 h1:6iJ6NqdoxCDr6mbY8h18oSO+cShGSMRGCEo7F2h0x8s=
+github.com/bytedance/sonic v1.9.1/go.mod h1:i736AoUSYt75HyZLoJW9ERYxcy6eaN6h4BZXU064P/U=
+github.com/chenzhuoyu/base64x v0.0.0-20211019084208-fb5309c8db06/go.mod h1:DH46F32mSOjUmXrMHnKwZdA8wcEefY7UVqBKYGjpdQY=
+github.com/chenzhuoyu/base64x v0.0.0-20221115062448-fe3a3abad311 h1:qSGYFH7+jGhDF8vLC+iwCD4WpbV1EBDSzWkJODFLams=
+github.com/chenzhuoyu/base64x v0.0.0-20221115062448-fe3a3abad311/go.mod h1:b583jCggY9gE99b6G5LEC39OIiVsWj+R97kbl5odCEk=
+github.com/coreos/go-systemd/v22 v22.5.0/go.mod h1:Y58oyj3AT4RCenI/lSvhwexgC+NSVTIJ3seZv2GcEnc=
+github.com/creack/pty v1.1.9/go.mod h1:oKZEueFk5CKHvIhNR5MUki03XCEU+Q6VDXinZuGJ33E=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/gabriel-vasile/mimetype v1.4.2 h1:w5qFW6JKBz9Y393Y4q372O9A7cUSequkh1Q7OhCmWKU=
+github.com/gabriel-vasile/mimetype v1.4.2/go.mod h1:zApsH/mKG4w07erKIaJPFiX0Tsq9BFQgN3qGY5GnNgA=
+github.com/gin-contrib/sse v0.1.0 h1:Y/yl/+YNO8GZSjAhjMsSuLt29uWRFHdHYUb5lYOV9qE=
+github.com/gin-contrib/sse v0.1.0/go.mod h1:RHrZQHXnP2xjPF+u1gW/2HnVO7nvIa9PG3Gm+fLHvGI=
+github.com/gin-gonic/gin v1.9.1 h1:4idEAncQnU5cB7BeOkPtxjfCSye0AAm1R0RVIqJ+Jmg=
+github.com/gin-gonic/gin v1.9.1/go.mod h1:hPrL7YrpYKXt5YId3A/Tnip5kqbEAP+KLuI3SUcPTeU=
+github.com/go-playground/assert/v2 v2.2.0 h1:JvknZsQTYeFEAhQwI4qEt9cyV5ONwRHC+lYKSsYSR8s=
+github.com/go-playground/locales v0.14.1 h1:EWaQ/wswjilfKLTECiXz7Rh+3BjFhfDFKv/oXslEjJA=
+github.com/go-playground/locales v0.14.1/go.mod h1:hxrqLVvrK65+Rwrd5Fc6F2O76J/NuW9t0sjnWqG1slY=
+github.com/go-playground/universal-translator v0.18.1 h1:Bcnm0ZwsGyWbCzImXv+pAJnYK9S473LQFuzCbDbfSFY=
+github.com/go-playground/universal-translator v0.18.1/go.mod h1:xekY+UJKNuX9WP91TpwSH2VMlDf28Uj24BCp08ZFTUY=
+github.com/go-playground/validator/v10 v10.14.0 h1:vgvQWe3XCz3gIeFDm/HnTIbj6UGmg/+t63MyGU2n5js=
+github.com/go-playground/validator/v10 v10.14.0/go.mod h1:9iXMNT7sEkjXb0I+enO7QXmzG6QCsPWY4zveKFVRSyU=
+github.com/goccy/go-json v0.10.2 h1:CrxCmQqYDkv1z7lO7Wbh2HN93uovUHgrECaO5ZrCXAU=
+github.com/goccy/go-json v0.10.2/go.mod h1:6MelG93GURQebXPDq3khkgXZkazVtN9CRI+MGFi0w8I=
+github.com/godbus/dbus/v5 v5.0.4/go.mod h1:xhWf0FNVPg57R7Z0UbKHbJfkEywrmjJnf7w5xrFpKfA=
+github.com/golang/protobuf v1.5.0/go.mod h1:FsONVRAS9T7sI+LIUmWTfcYkHO4aIWwzhcaSAoJOfIk=
+github.com/google/go-cmp v0.5.5 h1:Khx7svrCpmxxtHBq5j2mp/xVjsi8hQMfNLvJFAlrGgU=
+github.com/google/go-cmp v0.5.5/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
+github.com/google/gofuzz v1.0.0/go.mod h1:dBl0BpW6vV/+mYPU4Po3pmUjxk6FQPldtuIdl/M65Eg=
+github.com/imroc/req v0.3.2 h1:M/JkeU6RPmX+WYvT2vaaOL0K+q8ufL5LxwvJc4xeB4o=
+github.com/imroc/req v0.3.2/go.mod h1:F+NZ+2EFSo6EFXdeIbpfE9hcC233id70kf0byW97Caw=
+github.com/json-iterator/go v1.1.12 h1:PV8peI4a0ysnczrg+LtxykD8LfKY9ML6u2jnxaEnrnM=
+github.com/json-iterator/go v1.1.12/go.mod h1:e30LSqwooZae/UwlEbR2852Gd8hjQvJoHmT4TnhNGBo=
+github.com/klauspost/cpuid/v2 v2.0.9/go.mod h1:FInQzS24/EEf25PyTYn52gqo7WaD8xa0213Md/qVLRg=
+github.com/klauspost/cpuid/v2 v2.2.4 h1:acbojRNwl3o09bUq+yDCtZFc1aiwaAAxtcn8YkZXnvk=
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+github.com/kr/pretty v0.3.0 h1:WgNl7dwNpEZ6jJ9k1snq4pZsg7DOEN8hP9Xw0Tsjwk0=
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+github.com/mattn/go-colorable v0.1.13 h1:fFA4WZxdEF4tXPZVKMLwD8oUnCTTo08duU7wxecdEvA=
+github.com/mattn/go-colorable v0.1.13/go.mod h1:7S9/ev0klgBDR4GtXTXX8a3vIGJpMovkB8vQcUbaXHg=
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+github.com/twitchyliquid64/golang-asm v0.15.1/go.mod h1:a1lVb/DtPvCB8fslRZhAngC2+aY1QWCk3Cedj/Gdt08=
+github.com/ugorji/go/codec v1.2.11 h1:BMaWp1Bb6fHwEtbplGBGJ498wD+LKlNSl25MjdZY4dU=
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diff --git a/yggdrasil/muxserver.go b/yggdrasil/muxserver.go
new file mode 100644
index 0000000..7db4021
--- /dev/null
+++ b/yggdrasil/muxserver.go
@@ -0,0 +1,94 @@
+package yggdrasil
+
+import (
+	"fmt"
+	"github.com/avast/retry-go"
+	"github.com/rs/zerolog/log"
+	"github.com/samber/lo"
+	"github.com/samber/mo"
+	"github.com/sourcegraph/conc"
+	"strings"
+	"time"
+)
+
+const (
+	retryInterval = 100 * time.Millisecond
+	maxRetryTimes = 3
+)
+
+type muxServer struct {
+	subServers []Server
+}
+
+func (m muxServer) Name() string {
+	return "muxServer[" + strings.Join(lo.Map(m.subServers, func(item Server, _ int) string {
+		return item.Name()
+	}), ", ") + "]"
+}
+
+func (m muxServer) HasJoined(username string, serverID string) (*HasJoinedResponse, error) {
+	var wg conc.WaitGroup
+	type Ret = *HasJoinedResponse
+	results := make(chan mo.Result[Ret], len(m.subServers))
+	for _, s := range m.subServers {
+		s := s
+		wg.Go(func() {
+			var resp *HasJoinedResponse
+			err := retry.Do(
+				func() error {
+					var err error
+					resp, err = s.HasJoined(username, serverID)
+					return err
+				},
+				retry.Delay(retryInterval),
+				retry.Attempts(maxRetryTimes),
+			)
+			if err != nil {
+				results <- mo.Err[Ret](fmt.Errorf("call hasJoined on server `%v` failed: %w",
+					s.Name(), err))
+			} else {
+				results <- mo.Ok[Ret](resp)
+			}
+		})
+	}
+
+	chPanic := make(chan error, 1)
+	go func() {
+		// wait for all async tasks to finish in another async goroutine
+		// to allow the main request return as early as possible
+		r := wg.WaitAndRecover()
+		close(results)
+		if r != nil {
+			chPanic <- r.AsError()
+		}
+		close(chPanic)
+	}()
+
+	var last *Ret
+	for r := range results {
+		r, err := r.Get()
+		if err != nil {
+			log.Error().Err(err).Msg("hasJoined failed")
+			continue
+		}
+		last = &r
+		// return the first positive result
+		if r.HasJoined() {
+			return r, nil
+		}
+	}
+	if last == nil {
+		// no data generated, all async tasks panicked
+		err := <-chPanic
+		log.Error().Err(err).Msg("all hasJoined async query panicked")
+		return nil, err
+	} else {
+		return *last, nil
+	}
+}
+
+func NewMuxServer(servers ...Server) Server {
+	return muxServer{
+		subServers: servers,
+	}
+}
diff --git a/yggdrasil/realserver.go b/yggdrasil/realserver.go
new file mode 100644
index 0000000..86f4887
--- /dev/null
+++ b/yggdrasil/realserver.go
@@ -0,0 +1,88 @@
+package yggdrasil
+
+import (
+	"encoding/json"
+	"fmt"
+	"github.com/imroc/req"
+	"github.com/rs/zerolog/log"
+	"net/url"
+	"time"
+)
+
+type realServer struct {
+	req       *req.Req
+	apiPrefix string
+	name      string
+}
+
+func (r realServer) Name() string {
+	return r.name
+}
+
+func (r realServer) HasJoined(username string, serverID string) (*HasJoinedResponse, error) {
+	u, err := url.Parse(r.apiPrefix + "/session/minecraft/hasJoined")
+	if err != nil {
+		return nil, fmt.Errorf("url parse: %w", err)
+	}
+	q := u.Query()
+	q.Set("username", username)
+	q.Set("serverId", serverID)
+	u.RawQuery = q.Encode()
+	url2 := u.String()
+	log.Debug().Str("url", url2).Msg("hasJoined request")
+	resp, err := r.req.Get(url2)
+	if err != nil {
+		return nil, fmt.Errorf("http request: %w", err)
+	}
+	respBytes := resp.Bytes()
+	var resp2 HasJoinedResponse
+	// decode JSON only if HTTP status code is OK
+	if resp.Response().StatusCode == 200 {
+		err := json.Unmarshal(respBytes, &resp2)
+		if err != nil {
+			log.Error().
+				Str("body", string(respBytes)).
+				Err(err).
+				Msg("unmarshal response body JSON failed")
+		}
+	}
+	resp2.StatusCode = resp.Response().StatusCode
+	resp2.RawBody = respBytes
+	resp2.ServerName = r.name
+	log.Debug().
+		Int("statusCode", resp2.StatusCode).
+		Str("rawBody", string(respBytes)).
+		Msg("hasJoined response")
+	return &resp2, nil
+}
+
+func NewServer(apiPrefix string, opt ...NewServerOptions) (Server, error) {
+	name := "<unnamed server>"
+	r := req.New()
+	if len(opt) > 0 {
+		if p := opt[0].Proxy; p != "" {
+			err := r.SetProxyUrl(p)
+			if err != nil {
+				return nil, fmt.Errorf("set proxy url: %w", err)
+			}
+		}
+		if t := opt[0].Timeout; t > 0 {
+			r.SetTimeout(t)
+		}
+		if n := opt[0].Name; n != "" {
+			name = n
+		}
+	}
+	return realServer{
+		req:       r,
+		apiPrefix: apiPrefix,
+		name:      name,
+	}, nil
+}
+
+type NewServerOptions struct {
+	Name  string
+	Proxy string
+	// Timeout is HTTP API request timeout
+	Timeout time.Duration
+}
diff --git a/yggdrasil/server.go b/yggdrasil/server.go
new file mode 100644
index 0000000..818f3ed
--- /dev/null
+++ b/yggdrasil/server.go
@@ -0,0 +1,26 @@
+package yggdrasil
+
+type Server interface {
+	// HasJoined returns nil if and only if err != nil
+	HasJoined(username string, serverID string) (*HasJoinedResponse, error)
+	// Name returns a human-readable, unique name of this server
+	Name() string
+}
+
+type HasJoinedResponse struct {
+	StatusCode int    `json:"-"`
+	RawBody    []byte `json:"-"`
+	ServerName string `json:"-"`
+
+	ID         string `json:"id"`
+	Name       string `json:"name"`
+	Properties []struct {
+		Name      string `json:"name"`
+		Value     string `json:"value"`
+		Signature string `json:"signature,omitempty"`
+	} `json:"properties"`
+}
+
+func (r HasJoinedResponse) HasJoined() bool {
+	return r.StatusCode == 200 && r.ID != "" && r.Name != ""
+}
diff --git a/ymux.go b/ymux.go
new file mode 100644
index 0000000..8b09fc8
--- /dev/null
+++ b/ymux.go
@@ -0,0 +1,104 @@
+package main
+
+import (
+	"fmt"
+	"github.com/akamensky/argparse"
+	"github.com/gin-gonic/gin"
+	"github.com/keuin/ymux-go/config"
+	"github.com/keuin/ymux-go/yggdrasil"
+	"github.com/rs/zerolog"
+	"github.com/rs/zerolog/log"
+	"os"
+	"strings"
+)
+
+const applicationJson = "application/json"
+
+func main() {
+	p := argparse.NewParser("ymux-go", "Minecraft Yggdrasil server mux")
+	configFile := p.String("c", "config", &argparse.Options{
+		Required: true,
+		Help:     "path to the config file",
+	})
+	err := p.Parse(os.Args)
+	if err != nil {
+		fmt.Print(p.Usage(err))
+		return
+	}
+
+	cfg, err := config.Read(*configFile)
+	if err != nil {
+		panic(fmt.Errorf("error reading config file: %w", err))
+	}
+	err = cfg.Validate()
+	if err != nil {
+		panic(fmt.Errorf("config validation failed: %w", err))
+	}
+	ss, err := createServers(cfg)
+	if err != nil {
+		panic(err)
+	}
+	s := yggdrasil.NewMuxServer(ss...)
+
+	if cfg.Debug {
+		log.Logger = log.Logger.Level(zerolog.DebugLevel)
+	} else {
+		log.Logger = log.Logger.Level(zerolog.InfoLevel)
+		gin.SetMode(gin.ReleaseMode)
+	}
+	log.Debug().Msg("debug mode is enabled")
+	r := gin.Default()
+	r.GET("/", func(c *gin.Context) {
+		// servers with authlib-injector will call this API on boot
+		// we need this to make them happy
+		c.Data(200, applicationJson, []byte(`{}`))
+	})
+	r.GET("/sessionserver/session/minecraft/hasJoined", func(c *gin.Context) {
+		var args struct {
+			Username string `form:"username"`
+			ServerID string `form:"serverId"`
+		}
+		err := c.ShouldBindQuery(&args)
+		if err != nil {
+			_ = c.AbortWithError(400, err)
+			return
+		}
+		r, err := s.HasJoined(args.Username, args.ServerID)
+		if err != nil {
+			log.Error().Err(err).Msg("ymux hasJoined API failed")
+			_ = c.AbortWithError(500, err)
+			return
+		}
+		log.Info().
+			Str("username", args.Username).
+			Str("serverId", args.ServerID).
+			Str("yggdrasilServer", r.ServerName).
+			Bool("hasJoined", r.HasJoined()).
+			Msg("ymux hasJoined API OK")
+		if r.HasJoined() {
+			c.Data(200, applicationJson, r.RawBody)
+			return
+		}
+		c.Status(204)
+	})
+	err = r.Run(cfg.Listen)
+	if err != nil {
+		panic(fmt.Errorf("error running http server: %w", err))
+	}
+}
+
+func createServers(cfg *config.Config) ([]yggdrasil.Server, error) {
+	var servers []yggdrasil.Server
+	for _, s := range cfg.Servers {
+		s.Prefix = strings.TrimRight(s.Prefix, "/")
+		ys, err := yggdrasil.NewServer(s.Prefix, yggdrasil.NewServerOptions{
+			Name:  s.Name,
+			Proxy: s.Proxy,
+		})
+		if err != nil {
+			return nil, fmt.Errorf("parse server `%v`: %w", s.Name, err)
+		}
+		servers = append(servers, ys)
+	}
+	return servers, nil
+}
diff --git a/ymux.toml b/ymux.toml
new file mode 100644
index 0000000..d18bcfe
--- /dev/null
+++ b/ymux.toml
@@ -0,0 +1,12 @@
+debug = false
+listen = "127.0.0.1:32217"
+
+[[servers]]
+name = "official"
+prefix = "https://sessionserver.mojang.com"
+proxy = ""
+
+[[servers]]
+name = "littleskin"
+prefix = "https://littleskin.cn/api/yggdrasil/sessionserver"
+proxy = ""