[addrman] Introduce CAddrMan::Impl to encapsulate addrman implementation.

Introduce the pimpl pattern for CAddrMan to separate the implementation details
from the externally used object representation. This reduces compile-time
dependencies and conceptually clarifies AddrMan's interface from the
implementation specifics.

Since the unit & fuzz tests currently rely on accessing CAddrMan internals, this
commit introduces addrman_impl.h, which is exclusively imported by addrman.cpp
and test files.

Review hint: git diff --color-moved=dimmed-zebra
--color-moved-ws=ignore-all-space

1 files changed, 206 insertions, 0 deletions

diff --git a/src/addrman_impl.h b/src/addrman_impl.h
new file mode 100644
index 0000000000..ee4b55e5c4
--- /dev/null
+++ b/src/addrman_impl.h
@@ -0,0 +1,206 @@
+// Copyright (c) 2021 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_ADDRMAN_IMPL_H
+#define BITCOIN_ADDRMAN_IMPL_H
+
+class AddrManImpl
+{
+public:
+    AddrManImpl(std::vector<bool>&& asmap, bool deterministic, int32_t consistency_check_ratio);
+
+    ~AddrManImpl();
+
+    template <typename Stream>
+    void Serialize(Stream& s_) const EXCLUSIVE_LOCKS_REQUIRED(!cs);
+
+    template <typename Stream>
+    void Unserialize(Stream& s_) EXCLUSIVE_LOCKS_REQUIRED(!cs);
+
+    size_t size() const EXCLUSIVE_LOCKS_REQUIRED(!cs);
+
+    bool Add(const std::vector<CAddress> &vAddr, const CNetAddr& source, int64_t nTimePenalty)
+        EXCLUSIVE_LOCKS_REQUIRED(!cs);
+
+    void Good(const CService &addr, int64_t nTime)
+        EXCLUSIVE_LOCKS_REQUIRED(!cs);
+
+    void Attempt(const CService &addr, bool fCountFailure, int64_t nTime)
+        EXCLUSIVE_LOCKS_REQUIRED(!cs);
+
+    void ResolveCollisions() EXCLUSIVE_LOCKS_REQUIRED(!cs);
+
+    CAddrInfo SelectTriedCollision() EXCLUSIVE_LOCKS_REQUIRED(!cs);
+
+    CAddrInfo Select(bool newOnly) const
+        EXCLUSIVE_LOCKS_REQUIRED(!cs);
+
+    std::vector<CAddress> GetAddr(size_t max_addresses, size_t max_pct, std::optional<Network> network) const
+        EXCLUSIVE_LOCKS_REQUIRED(!cs);
+
+    void Connected(const CService &addr, int64_t nTime)
+        EXCLUSIVE_LOCKS_REQUIRED(!cs);
+
+    void SetServices(const CService &addr, ServiceFlags nServices)
+        EXCLUSIVE_LOCKS_REQUIRED(!cs);
+
+    const std::vector<bool>& GetAsmap() const;
+
+    friend class CAddrManTest;
+    friend class CAddrManDeterministic;
+
+private:
+    //! A mutex to protect the inner data structures.
+    mutable Mutex cs;
+
+    //! Source of random numbers for randomization in inner loops
+    mutable FastRandomContext insecure_rand GUARDED_BY(cs);
+
+    //! secret key to randomize bucket select with
+    uint256 nKey;
+
+    //! Serialization versions.
+    enum Format : uint8_t {
+        V0_HISTORICAL = 0,    //!< historic format, before commit e6b343d88
+        V1_DETERMINISTIC = 1, //!< for pre-asmap files
+        V2_ASMAP = 2,         //!< for files including asmap version
+        V3_BIP155 = 3,        //!< same as V2_ASMAP plus addresses are in BIP155 format
+    };
+
+    //! The maximum format this software knows it can unserialize. Also, we always serialize
+    //! in this format.
+    //! The format (first byte in the serialized stream) can be higher than this and
+    //! still this software may be able to unserialize the file - if the second byte
+    //! (see `lowest_compatible` in `Unserialize()`) is less or equal to this.
+    static constexpr Format FILE_FORMAT = Format::V3_BIP155;
+
+    //! The initial value of a field that is incremented every time an incompatible format
+    //! change is made (such that old software versions would not be able to parse and
+    //! understand the new file format). This is 32 because we overtook the "key size"
+    //! field which was 32 historically.
+    //! @note Don't increment this. Increment `lowest_compatible` in `Serialize()` instead.
+    static constexpr uint8_t INCOMPATIBILITY_BASE = 32;
+
+    //! last used nId
+    int nIdCount GUARDED_BY(cs){0};
+
+    //! table with information about all nIds
+    std::unordered_map<int, CAddrInfo> mapInfo GUARDED_BY(cs);
+
+    //! find an nId based on its network address
+    std::unordered_map<CNetAddr, int, CNetAddrHash> mapAddr GUARDED_BY(cs);
+
+    //! randomly-ordered vector of all nIds
+    //! This is mutable because it is unobservable outside the class, so any
+    //! changes to it (even in const methods) are also unobservable.
+    mutable std::vector<int> vRandom GUARDED_BY(cs);
+
+    // number of "tried" entries
+    int nTried GUARDED_BY(cs){0};
+
+    //! list of "tried" buckets
+    int vvTried[ADDRMAN_TRIED_BUCKET_COUNT][ADDRMAN_BUCKET_SIZE] GUARDED_BY(cs);
+
+    //! number of (unique) "new" entries
+    int nNew GUARDED_BY(cs){0};
+
+    //! list of "new" buckets
+    int vvNew[ADDRMAN_NEW_BUCKET_COUNT][ADDRMAN_BUCKET_SIZE] GUARDED_BY(cs);
+
+    //! last time Good was called (memory only). Initially set to 1 so that "never" is strictly worse.
+    int64_t nLastGood GUARDED_BY(cs){1};
+
+    //! Holds addrs inserted into tried table that collide with existing entries. Test-before-evict discipline used to resolve these collisions.
+    std::set<int> m_tried_collisions;
+
+    /** Perform consistency checks every m_consistency_check_ratio operations (if non-zero). */
+    const int32_t m_consistency_check_ratio;
+
+    // Compressed IP->ASN mapping, loaded from a file when a node starts.
+    // Should be always empty if no file was provided.
+    // This mapping is then used for bucketing nodes in Addrman.
+    //
+    // If asmap is provided, nodes will be bucketed by
+    // AS they belong to, in order to make impossible for a node
+    // to connect to several nodes hosted in a single AS.
+    // This is done in response to Erebus attack, but also to generally
+    // diversify the connections every node creates,
+    // especially useful when a large fraction of nodes
+    // operate under a couple of cloud providers.
+    //
+    // If a new asmap was provided, the existing records
+    // would be re-bucketed accordingly.
+    const std::vector<bool> m_asmap;
+
+    //! Find an entry.
+    CAddrInfo* Find(const CNetAddr& addr, int *pnId = nullptr) EXCLUSIVE_LOCKS_REQUIRED(cs);
+
+    //! Create a new entry and add it to the internal data structures mapInfo, mapAddr and vRandom.
+    CAddrInfo* Create(const CAddress &addr, const CNetAddr &addrSource, int *pnId = nullptr) EXCLUSIVE_LOCKS_REQUIRED(cs);
+
+    //! Swap two elements in vRandom.
+    void SwapRandom(unsigned int nRandomPos1, unsigned int nRandomPos2) const EXCLUSIVE_LOCKS_REQUIRED(cs);
+
+    //! Delete an entry. It must not be in tried, and have refcount 0.
+    void Delete(int nId) EXCLUSIVE_LOCKS_REQUIRED(cs);
+
+    //! Clear a position in a "new" table. This is the only place where entries are actually deleted.
+    void ClearNew(int nUBucket, int nUBucketPos) EXCLUSIVE_LOCKS_REQUIRED(cs);
+
+    //! Move an entry from the "new" table(s) to the "tried" table
+    void MakeTried(CAddrInfo& info, int nId) EXCLUSIVE_LOCKS_REQUIRED(cs);
+
+    //! Mark an entry "good", possibly moving it from "new" to "tried".
+    void Good_(const CService &addr, bool test_before_evict, int64_t time) EXCLUSIVE_LOCKS_REQUIRED(cs);
+
+    //! Add an entry to the "new" table.
+    bool Add_(const CAddress &addr, const CNetAddr& source, int64_t nTimePenalty) EXCLUSIVE_LOCKS_REQUIRED(cs);
+
+    //! Mark an entry as attempted to connect.
+    void Attempt_(const CService &addr, bool fCountFailure, int64_t nTime) EXCLUSIVE_LOCKS_REQUIRED(cs);
+
+    //! Select an address to connect to, if newOnly is set to true, only the new table is selected from.
+    CAddrInfo Select_(bool newOnly) const EXCLUSIVE_LOCKS_REQUIRED(cs);
+
+    /**
+     * Return all or many randomly selected addresses, optionally by network.
+     *
+     * @param[out] vAddr         Vector of randomly selected addresses from vRandom.
+     * @param[in] max_addresses  Maximum number of addresses to return (0 = all).
+     * @param[in] max_pct        Maximum percentage of addresses to return (0 = all).
+     * @param[in] network        Select only addresses of this network (nullopt = all).
+     */
+    void GetAddr_(std::vector<CAddress>& vAddr, size_t max_addresses, size_t max_pct, std::optional<Network> network) const EXCLUSIVE_LOCKS_REQUIRED(cs);
+
+    /** We have successfully connected to this peer. Calling this function
+     *  updates the CAddress's nTime, which is used in our IsTerrible()
+     *  decisions and gossiped to peers. Callers should be careful that updating
+     *  this information doesn't leak topology information to network spies.
+     *
+     *  net_processing calls this function when it *disconnects* from a peer to
+     *  not leak information about currently connected peers.
+     *
+     * @param[in]   addr     The address of the peer we were connected to
+     * @param[in]   nTime    The time that we were last connected to this peer
+     */
+    void Connected_(const CService& addr, int64_t nTime) EXCLUSIVE_LOCKS_REQUIRED(cs);
+
+    //! Update an entry's service bits.
+    void SetServices_(const CService &addr, ServiceFlags nServices) EXCLUSIVE_LOCKS_REQUIRED(cs);
+
+    //! See if any to-be-evicted tried table entries have been tested and if so resolve the collisions.
+    void ResolveCollisions_() EXCLUSIVE_LOCKS_REQUIRED(cs);
+
+    //! Return a random to-be-evicted tried table address.
+    CAddrInfo SelectTriedCollision_() EXCLUSIVE_LOCKS_REQUIRED(cs);
+
+    //! Consistency check, taking into account m_consistency_check_ratio. Will std::abort if an inconsistency is detected.
+    void Check() const EXCLUSIVE_LOCKS_REQUIRED(cs);
+
+    //! Perform consistency check, regardless of m_consistency_check_ratio.
+    //! @returns an error code or zero.
+    int ForceCheckAddrman() const EXCLUSIVE_LOCKS_REQUIRED(cs);
+};
+
+#endif // BITCOIN_ADDRMAN_IMPL_H