doc: add initial dialer readme

Author: jacobheun

doc/DIALER.md

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+# js-libp2p Dialer
+
+**Synopsis**
+* All Dial Requests in js-libp2p must request a token(s) from the Dialer.
+  * The number of tokens requested should be between 1 and the PER_PEER_LIMIT max set in the Dialer.
+  * If the number of available tokens is less than requested, the Dialer may return less than requested.
+* The number of tokens a DialRequest obtains reflects the maximum number of parallel Multiaddr Dials it can make.
+* If no tokens are available a DialRequest should immediately end and throw. This deviates from the existing queue system to avoid queue congestion and provide more visibility to users.
+* As tokens are limited, DialRequests should be given a prioritized list of Multiaddrs to minimize the potential request time.
+* Once a single Multiaddr Dial has succeeded, all pending dials in that Dial Request should be aborted. All tokens should be immediately released to the Dialer.
+* If all Multiaddr Dials fail, or the DIAL_TIMEOUT max is reached for the entire DialRequest, all in progress dials for that DialRequest should be aborted. All tokens should immediately be released to the Dialer.
+
+## Multiaddr Confidence
+
+**Not Yet Implemented**
+
+An effective dialing system should involve the inclusion of a Confidence system for Multiaddrs. This enables ranking of Multiaddrs so that a prioritized list can be passed to DialRequests to maximize usage of Dialer Tokens.
+
+* All Multiaddrs SHOULD start with a confidence of 1 (give it some trust by default)
+* A failed dial SHOULD lower the confidence by 1, to a min of 0.
+* A successful dial SHOULD increase the confidence of a multiaddr by 1, to a max of 10.
+* Multiaddrs of confidence 0 MAY be pruned if higher confidence addresses exist. If this is done, it should be done an an actual failure. Aborted dials SHOULD NOT be considered failures, but timeouts SHOULD.
+
+## Notes
+
+* A DialRequest gets a set of tokens from the Dialer, up to the PER_PEER_LIMIT max.
+* A DialRequest SHOULD release its tokens after the DIAL_TIMEOUT has expired. This ensures that a peer with a large set of hanging addresses, does not block future dials.
+* Upon releasing the tokens, the Dialer may allocate them to another DialRequest.
+* A DialRequest SHOULD fail if no dial tokens are available. The DialRequest MAY proceed without tokens, but this should be reserved for High Priority actions and should be rare.
+* A DialRequest MUST NOT request more tokens than it has addresses to dial. Example: If the PER_PEER_LIMIT max is 4 and a DialRequest has 1 address, it should only request 1 token.
+* A DialRequest MUST execute parallel dials for each of its addresses up the total number of tokens it has.
+* On a successful dial, the DialRequest MUST abort any other in progress dials, return the successful connection and release all tokens.
+* A new DialRequest SHOULD be given a descending list of prioritized Multiaddrs, based on their confidence. Having higher confidence Multiaddrs first can help minimize the time a DialRequest is active.
+* A failed dial to a Multiaddr SHOULD add that Multiaddr to a temporary denyList.
+* A failed dial to a Multiaddr SHOULD lower the confidence of that Multiaddr.
+* A successful dial to a Multiaddr SHOULD increase the confidence of that Multiaddr.