Merge dashpay#6035: backport: merge bitcoin#22648, bitcoin#22497, bitcoin#25355, bitcoin#26065, bitcoin#26837, bitcoin#25993, bitcoin#26838, bitcoin#27937, partial bitcoin#22589, bitcoin#22229 (i2p support: part 2)

0a23820 merge bitcoin#27937: i2p documentation updates (Kittywhiskers Van Gogh)
1dc50d0 merge bitcoin#26838: I2P documentation updates (Kittywhiskers Van Gogh)
5058519 merge bitcoin#25993: Add I2P guidance related to bandwidth and i2pd software version (Kittywhiskers Van Gogh)
859f59b merge bitcoin#26837: I2P network optimizations (Kittywhiskers Van Gogh)
9f80734 merge bitcoin#26065: use the same destination type for transient and persistent addresses (Kittywhiskers Van Gogh)
9bf3829 merge bitcoin#25355: add support for transient addresses for outbound connections (Kittywhiskers Van Gogh)
4977073 merge bitcoin#22497: remove ResetI2PPorts() (Kittywhiskers Van Gogh)
63d5853 merge bitcoin#22648: improve i2p/tor docs and i2p reachable unit tests (Kittywhiskers Van Gogh)
f04ce8b partial bitcoin#22229: consolidate to f-strings (part 1) (Kittywhiskers Van Gogh)
68ea6cc merge bitcoin#22589: update I2P hardcoded seeds and docs for 22.0 (Kittywhiskers Van Gogh)

Pull request description:

  ## Additional Information

  * Dependent on dashpay#6034

  ## Breaking Changes

  * With I2P connections, a new, transient address is used for each outbound connection if `-i2pacceptincoming=0`.

  ## Checklist:

  - [x] I have performed a self-review of my own code
  - [x] I have commented my code, particularly in hard-to-understand areas **(note: N/A)**
  - [x] I have added or updated relevant unit/integration/functional/e2e tests
  - [x] I have made corresponding changes to the documentation
  - [x] I have assigned this pull request to a milestone _(for repository code-owners and collaborators only)_

ACKs for top commit:
  PastaPastaPasta:
    re-utACK [0a23820](dashpay@0a23820); only changed commit title / text

Tree-SHA512: ef426263d7e81a5eec8555db21dcd24f5dbb65f5faa7013c7e0601a4c60ae675813aadf68ebc19936aa15bdbd8f6db88b4bd55dfaf4ac412abbda86fb1ac9c83

Author: PastaPastaPasta

doc/i2p.md

@@ -9,25 +9,33 @@ started with I2P terminology.
 
 ## Run Dash Core with an I2P router (proxy)
 
-A running I2P router (proxy) with [SAM](https://geti2p.net/en/docs/api/samv3)
-enabled is required (there is an [official one](https://geti2p.net) and
-[a few alternatives](https://en.wikipedia.org/wiki/I2P#Routers)). Notice the IP
-address and port the SAM proxy is listening to; usually, it is
-`127.0.0.1:7656`. Once it is up and running with SAM enabled, use the following
-Dash Core options:
+A running I2P router (proxy) is required with the [SAM](https://geti2p.net/en/docs/api/samv3)
+application bridge enabled. The following routers are recommended for use with Dash Core:
+
+- [i2prouter (I2P Router)](https://geti2p.net), the official implementation in
+  Java. The SAM bridge is not enabled by default; it must be started manually,
+  or configured to start automatically, in the Clients page in the
+  router console (`http://127.0.0.1:7657/configclients`) or in the `clients.config` file.
+- [i2pd (I2P Daemon)](https://github.com/PurpleI2P/i2pd)
+  ([documentation](https://i2pd.readthedocs.io/en/latest)), a lighter
+  alternative in C++. It enables the SAM bridge by default.
+
+Note the IP address and port the SAM proxy is listening to; usually, it is
+`127.0.0.1:7656`.
+
+Once an I2P router with SAM enabled is up and running, use the following Dash
+Core configuration options:
 
 ```
 -i2psam=<ip:port>
      I2P SAM proxy to reach I2P peers and accept I2P connections (default:
      none)
 
 -i2pacceptincoming
-     If set and -i2psam is also set then incoming I2P connections are
-     accepted via the SAM proxy. If this is not set but -i2psam is set
-     then only outgoing connections will be made to the I2P network.
-     Ignored if -i2psam is not set. Listening for incoming I2P
-     connections is done through the SAM proxy, not by binding to a
-     local address and port (default: 1)
+     Whether to accept inbound I2P connections (default: 1). Ignored if
+     -i2psam is not set. Listening for inbound I2P connections is
+     done through the SAM proxy, not by binding to a local address and
+     port.
 ```
 
 In a typical situation, this suffices:
@@ -36,26 +44,68 @@ In a typical situation, this suffices:
 dashd -i2psam=127.0.0.1:7656
 ```
 
-The first time Dash Core connects to the I2P router, its I2P address (and
-corresponding private key) will be automatically generated and saved in a file
-named `i2p_private_key` in the Dash Core data directory.
-
 ## Additional configuration options related to I2P
 
-You may set the `debug=i2p` config logging option to have additional
-information in the debug log about your I2P configuration and connections. Run
-`dash-cli help logging` for more information.
+```
+-debug=i2p
+```
+
+Set the `debug=i2p` config logging option to see additional information in the
+debug log about your I2P configuration and connections. Run `dash-cli help
+logging` for more information.
+
+```
+-onlynet=i2p
+```
+
+Make outgoing connections only to I2P addresses. Incoming connections are not
+affected by this option. It can be specified multiple times to allow multiple
+network types, e.g. onlynet=ipv4, onlynet=ipv6, onlynet=onion, onlynet=i2p.
+
+Warning: if you use -onlynet with values other than onion, and the -onion or
+-proxy option is set, then outgoing onion connections will still be made; use
+-noonion or -onion=0 to disable outbound onion connections in this case.
 
-It is possible to restrict outgoing connections in the usual way with
-`onlynet=i2p`. I2P support was added to Dash Core in version 20.0 (fall 2023)
-and there may be fewer I2P peers than Tor or IP ones. Therefore, using
-`onlynet=i2p` alone (without other `onlynet=`) may make a node more susceptible
-to [Sybil attacks](https://en.dash.it/wiki/Weaknesses#Sybil_attack). Use
+I2P support was added to Dash Core in version 20.0 and there may be fewer I2P
+peers than Tor or IP ones. Therefore, using I2P alone without other networks may
+make a node more susceptible to [Sybil
+attacks](https://en.bitcoin.it/wiki/Weaknesses#Sybil_attack). You can use
 `dash-cli -addrinfo` to see the number of I2P addresses known to your node.
 
-## I2P related information in Dash Core
+Another consideration with `onlynet=i2p` is that the initial blocks download
+phase when syncing up a new node can be very slow. This phase can be sped up by
+using other networks, for instance `onlynet=onion`, at the same time.
+
+In general, a node can be run with both onion and I2P hidden services (or
+any/all of IPv4/IPv6/onion/I2P), which can provide a potential fallback if one
+of the networks has issues.
+
+## Persistent vs transient I2P addresses
+
+The first time Dash Core connects to the I2P router, it automatically
+generates a persistent I2P address and its corresponding private key by default
+or if `-i2pacceptincoming=1` is set.  The private key is saved in a file named
+`i2p_private_key` in the Dash Core data directory.  The persistent I2P
+address is used for making outbound connections and accepting inbound
+connections.
+
+In the I2P network, the receiver of an inbound connection sees the address of
+the initiator.  This is unlike the Tor network, where the recipient does not
+know who is connecting to it.
 
-There are several ways to see your I2P address in Dash Core:
+If your node is configured by setting `-i2pacceptincoming=0` to not accept
+inbound I2P connections, then it will use a random transient I2P address for
+itself on each outbound connection to make it harder to discriminate,
+fingerprint or analyze it based on its I2P address.
+
+I2P addresses are designed to be long-lived.  Waiting for tunnels to be built
+for every peer connection adds delay to connection setup time.  Therefore, I2P
+listening should only be turned off if really needed.
+
+## Fetching I2P-related information from Dash Core
+
+There are several ways to see your I2P address in Dash Core if accepting
+incoming I2P connections (`-i2pacceptincoming`):
 - in the debug log (grep for `AddLocal`, the I2P address ends in `.b32.i2p`)
 - in the output of the `getnetworkinfo` RPC in the "localaddresses" section
 - in the output of `dash-cli -netinfo` peer connections dashboard
@@ -73,8 +123,7 @@ to connect to the I2P network. Any I2P router that supports it can be used.
 
 ## Ports in I2P and Dash Core
 
-Dash Core uses the [SAM v3.1](https://geti2p.net/en/docs/api/samv3)
-protocol. One particularity of SAM v3.1 is that it does not support ports,
+One particularity of SAM v3.1 is that it does not support ports,
 unlike newer versions of SAM (v3.2 and up) that do support them and default the
 port numbers to 0. From the point of view of peers that use newer versions of
 SAM or other protocols that support ports, a SAM v3.1 peer is connecting to them
@@ -85,3 +134,40 @@ listening port to 0 when listening for incoming I2P connections and advertises
 its own I2P address with port 0. Furthermore, it will not attempt to connect to
 I2P addresses with a non-zero port number because with SAM v3.1 the destination
 port (`TO_PORT`) is always set to 0 and is not in the control of Dash Core.
+
+## Bandwidth
+
+By default, your node shares bandwidth and transit tunnels with the I2P network
+in order to increase your anonymity with cover traffic, help the I2P router used
+by your node integrate optimally with the network, and give back to the network.
+It's important that the nodes of a popular application like Dash contribute
+as much to the I2P network as they consume.
+
+It is possible, though strongly discouraged, to change your I2P router
+configuration to limit the amount of I2P traffic relayed by your node.
+
+With `i2pd`, this can be done by adjusting the `bandwidth`, `share` and
+`transittunnels` options in your `i2pd.conf` file. For example, to limit total
+I2P traffic to 256KB/s and share 50% of this limit for a maximum of 20 transit
+tunnels:
+
+```
+bandwidth = 256
+share = 50
+
+[limits]
+transittunnels = 20
+```
+
+Similar bandwidth configuration options for the Java I2P router can be found in
+`http://127.0.0.1:7657/config` under the "Bandwidth" tab.
+
+Before doing this, please see the "Participating Traffic Considerations" section
+in [Embedding I2P in your Application](https://geti2p.net/en/docs/applications/embedding).
+
+In most cases, the default router settings should work fine.
+
+## Bundling I2P in a Dash application
+
+Please see the "General Guidance for Developers" section in https://geti2p.net/en/docs/api/samv3
+if you are developing a downstream application that may be bundling I2P with Dash.

doc/release-notes-25355.md

@@ -0,0 +1,5 @@
+P2P and network changes
+-----------------------
+
+- With I2P connections, a new, transient address is used for each outbound
+  connection if `-i2pacceptincoming=0`.

doc/tor.md

@@ -51,11 +51,11 @@ outgoing connections, but more is possible.
     -onlynet=onion  Make outgoing connections only to .onion addresses. Incoming
                     connections are not affected by this option. This option can be
                     specified multiple times to allow multiple network types, e.g.
-                    ipv4, ipv6 or onion. If you use this option with values other
-                    than onion you *cannot* disable onion connections; outgoing onion
-                    connections will be enabled when you use -proxy or -onion. Use
-                    -noonion or -onion=0 if you want to be sure there are no outbound
-                    onion connections over the default proxy or your defined -proxy.
+                    onlynet=ipv4, onlynet=ipv6, onlynet=onion, onlynet=i2p.
+                    Warning: if you use -onlynet with values other than onion, and
+                    the -onion or -proxy option is set, then outgoing onion
+                    connections will still be made; use -noonion or -onion=0 to
+                    disable outbound onion connections in this case.
 
 An example how to start the client if the Tor proxy is running on local host on
 port 9050 and only allows .onion nodes to connect:

src/addrman.cpp

@@ -6,7 +6,6 @@
 #include <addrman.h>
 
 #include <hash.h>
-#include <i2p.h>
 #include <logging.h>
 #include <netaddress.h>
 #include <serialize.h>
@@ -778,100 +777,3 @@ std::vector<bool> CAddrMan::DecodeAsmap(fs::path path)
     }
     return bits;
 }
-
-void CAddrMan::ResetI2PPorts()
-{
-    for (int bucket = 0; bucket < ADDRMAN_NEW_BUCKET_COUNT; ++bucket) {
-        for (int i = 0; i < ADDRMAN_BUCKET_SIZE; ++i) {
-            const auto id = vvNew[bucket][i];
-            if (id == -1) {
-                continue;
-            }
-            auto it = mapInfo.find(id);
-            if (it == mapInfo.end()) {
-                return;
-            }
-            auto& addr_info = it->second;
-            if (!addr_info.IsI2P() || addr_info.GetPort() == I2P_SAM31_PORT) {
-                continue;
-            }
-
-            auto addr_info_newport = addr_info;
-            // The below changes addr_info_newport.GetKey(), which is used in finding a
-            // bucket and a position within that bucket. So a re-bucketing may be necessary.
-            addr_info_newport.port = I2P_SAM31_PORT;
-
-            // Reposition entries of vvNew within the same bucket because we don't know the source
-            // address which led to the decision to store the entry in vvNew[bucket] so we can't
-            // re-evaluate that decision, but even if we could, CAddrInfo::GetNewBucket() does not
-            // use CAddrInfo::GetKey() so it would end up in the same bucket as before the port
-            // change.
-            const auto i_target = addr_info_newport.GetBucketPosition(nKey, true, bucket);
-
-            if (i_target == i) { // No need to re-position.
-                addr_info = addr_info_newport;
-                continue;
-            }
-
-            // Reposition from i to i_target, removing the entry from i_target (if any).
-            ClearNew(bucket, i_target);
-            vvNew[bucket][i_target] = id;
-            vvNew[bucket][i] = -1;
-            addr_info = addr_info_newport;
-        }
-    }
-
-    for (int bucket = 0; bucket < ADDRMAN_TRIED_BUCKET_COUNT; ++bucket) {
-        for (int i = 0; i < ADDRMAN_BUCKET_SIZE; ++i) {
-            const auto id = vvTried[bucket][i];
-            if (id == -1) {
-                continue;
-            }
-            auto it = mapInfo.find(id);
-            if (it == mapInfo.end()) {
-                return;
-            }
-            auto& addr_info = it->second;
-            if (!addr_info.IsI2P() || addr_info.GetPort() == I2P_SAM31_PORT) {
-                continue;
-            }
-
-            auto addr_info_newport = addr_info;
-            // The below changes addr_info_newport.GetKey(), which is used in finding a
-            // bucket and a position within that bucket. So a re-bucketing may be necessary.
-            addr_info_newport.port = I2P_SAM31_PORT;
-
-            const auto bucket_target = addr_info_newport.GetTriedBucket(nKey, m_asmap);
-            const auto i_target = addr_info_newport.GetBucketPosition(nKey, false, bucket_target);
-
-            if (bucket_target == bucket && i_target == i) { // No need to re-position.
-                addr_info = addr_info_newport;
-                continue;
-            }
-
-            // Reposition from (bucket, i) to (bucket_target, i_target). If the latter is
-            // occupied, then move the entry from there to vvNew.
-
-            const auto old_target_id = vvTried[bucket_target][i_target];
-            if (old_target_id != -1) {
-                CAddrInfo& old_target_info = mapInfo[old_target_id];
-
-                old_target_info.fInTried = false;
-                vvTried[bucket_target][i_target] = -1;
-                --nTried;
-
-                const auto new_bucket = old_target_info.GetNewBucket(nKey, m_asmap);
-                const auto new_bucket_i = old_target_info.GetBucketPosition(nKey, true, new_bucket);
-                ClearNew(new_bucket, new_bucket_i);
-
-                old_target_info.nRefCount = 1;
-                vvNew[new_bucket][new_bucket_i] = old_target_id;
-                ++nNew;
-            }
-
-            vvTried[bucket_target][i_target] = id;
-            vvTried[bucket][i] = -1;
-            addr_info = addr_info_newport;
-        }
-    }
-}

src/addrman.h

@@ -464,8 +464,6 @@ class CAddrMan
 
         RemoveInvalid();
 
-        ResetI2PPorts();
-
         Check();
     }
 
@@ -800,14 +798,6 @@ class CAddrMan
     //! Remove invalid addresses.
     void RemoveInvalid() EXCLUSIVE_LOCKS_REQUIRED(cs);
 
-    /**
-     * Reset the ports of I2P peers to 0.
-     * This is needed as a temporary measure because now we enforce port 0 and
-     * only connect to I2P hosts if the port is 0, but in the early days some
-     * I2P addresses with port 8333 were rumoured and persisted into addrmans.
-     */
-    void ResetI2PPorts() EXCLUSIVE_LOCKS_REQUIRED(cs);
-
     friend class CAddrManTest;
     friend class CAddrManDeterministic;
 };