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+<a id="pt-spec.txt-3"></a>
+
+# Specification
+
+Pluggable Transport proxies follow the following workflow
+throughout their lifespan.
+
+```text
+     1) Parent process sets the required environment values (3.2)
+        and launches the PT proxy as a sub-process (fork()/exec()).
+
+     2) The PT Proxy determines the versions of the PT specification
+        supported by the parent"TOR_PT_MANAGED_TRANSPORT_VER" (3.2.1)
+
+        2.1) If there are no compatible versions, the PT proxy
+             writes a "VERSION-ERROR" message (3.3.1) to stdout and
+             terminates.
+
+        2.2) If there is a compatible version, the PT proxy writes
+             a "VERSION" message (3.3.1) to stdout.
+
+     3) The PT Proxy parses the rest of the environment values.
+
+        3.1) If the environment values are malformed, or otherwise
+             invalid, the PT proxy writes a "ENV-ERROR" message
+             (3.3.1) to stdout and terminates.
+
+        3.2) Determining if it is a client side forward proxy or
+             a server side reverse proxy can be done via examining
+             the "TOR_PT_CLIENT_TRANSPORTS" and "TOR_PT_SERVER_TRANSPORTS"
+             environment variables.
+
+     4) (Client only) If there is an upstream proxy specified via
+        "TOR_PT_PROXY" (3.2.2), the PT proxy validates the URI
+        provided.
+
+        4.1) If the upstream proxy is unusable, the PT proxy writes
+             a "PROXY-ERROR" message (3.3.2) to stdout and
+             terminates.
+
+        4.2) If there is a supported and well-formed upstream proxy
+             the PT proxy writes a "PROXY DONE" message (3.3.2) to
+             stdout.
+
+     5) The PT Proxy initializes the transports and reports the
+        status via stdout (3.3.2, 3.3.3)
+
+     6) The PT Proxy forwards and transforms traffic as appropriate.
+
+     7) Upon being signaled to terminate by the parent process (3.4),
+        the PT Proxy gracefully shuts down.
+```