add readme for smart dialer JSON config

x/smart/README.md

@@ -0,0 +1,128 @@
+# Smart Dialer
+
+The **Smart Dialer** searches for a strategy that unblocks DNS and TLS for a given list of test domains. It takes a config describing multiple strategies to pick from.
+
+## JSON config for the Smart Dialer
+
+The config that the Smart Dialer takes is in a JSON format. Here is an example:
+
+```json
+{
+  "dns": [
+      {"system": {}},
+      {"https": {"name": "8.8.8.8"}},
+      {"https": {"name": "9.9.9.9"}}
+  ],
+  "tls": [
+      "",
+      "split:2",
+      "tlsfrag:1"
+  ]
+}
+```
+
+### DNS Configuration
+
+*   The `dns` field specifies a list of DNS resolvers to test.
+*   Each DNS resolver can be one of the following types:
+    *   `system`: Use the system resolver. Specify with an empty object.
+    *   `https`: Use an encrypted DNS over HTTPS (DoH) resolver.
+    *   `tls`: Use an encrypted DNS over TLS (DoT) resolver.
+    *   `udp`: Use a UDP resolver.
+    *   `tcp`: Use a TCP resolver.
+
+#### DNS-over-HTTPS Resolver (DoH)
+
+```json
+{
+  "https": {
+    "name": "dns.google",
+    "address": "8.8.8.8"
+  }
+}
+
+```
+
+*   `name`: The domain name of the DoH server.
+*   `address`: The host:port of the DoH server. Defaults to `name`:443.
+
+#### DNS-over-TLS Resolver (DoT)
+
+```json
+{
+  "tls": {
+    "name": "dns.google",
+    "address": "8.8.8.8"
+  }
+}
+```
+
+*   `name`: The domain name of the DoT server.
+*   `address`: The host:port of the DoT server. Defaults to `name`:853.
+
+#### UDP Resolver
+
+```json
+{
+  "udp": {
+    "address": "8.8.8.8"
+  }
+}
+```
+
+*   `address`: The host:port of the UDP resolver.
+
+#### TCP Resolver
+
+```json
+{
+  "tcp": {
+    "address": "8.8.8.8"
+  }
+}
+```
+
+*   `address`: The host:port of the TCP resolver.
+
+### TLS Configuration
+
+*   The `tls` field specifies a list of TLS transports to test.
+*   Each TLS transport is a string that specifies the transport to use.
+*   For example, `override:host=cloudflare.net|tlsfrag:1` specifies a transport that uses domain fronting with Cloudflare and TLS fragmentation. See the [config documentation](https://pkg.go.dev/github.com/Jigsaw-Code/outline-sdk/x/config#hdr-Config_Format) for details.
+
+### Using the Smart Dialer
+
+To use the Smart Dialer, create a `StrategyFinder` object and call the `NewDialer` method, passing in the list of test domains and the JSON config. The `NewDialer` method will return a `transport.StreamDialer` that can be used to create connections using the found strategy. For example:
+
+```go
+finder := &smart.StrategyFinder{
+    TestTimeout:  5 * time.Second,
+    LogWriter:   os.Stdout,
+    StreamDialer: &transport.TCPDialer{},
+    PacketDialer: &transport.UDPDialer{},
+}
+
+configBytes := []byte(`
+{
+  "dns": [
+      {"system": {}},
+      {"https": {"name": "8.8.8.8"}},
+      {"https": {"name": "9.9.9.9"}}
+  ],
+  "tls": [
+      "",
+      "split:2",
+      "tlsfrag:1"
+  ]
+}
+`)
+
+dialer, err := finder.NewDialer(context.Background(), []string{"www.google.com"}, configBytes)
+if err != nil {
+    // Handle error.
+}
+
+// Use dialer to create connections.
+```
+
+Please note that this is a basic example and may need to be adapted for your specific use case.