(fn [byte-array])->compressor used by `(freeze <x> {:compressor :auto}),
nil => default

{<hash-or-byte-id> (fn [data-input])->read}

DEPRECATED: prefer `*freeze-fallback`.

(fn [data-output x])->freeze, nil => default

Used when attempting to <freeze/thaw> an object that:
  - Does NOT implement Nippy's Freezable    protocol.
  - DOES     implement Java's  Serializable interface.

In this case, the allowlist will be checked to see if Java's
Serializable interface may be used.

This is a security measure to prevent possible Remote Code Execution
(RCE) when thawing malicious payloads. See [1] for details.

If `freeze` encounters a disallowed Serialized class, it will throw.
If `thaw`   encounters a disallowed Serialized class, it will:

  - Throw if it's not possible to safely quarantine the object
    (object was frozen with Nippy < v2.15.0-final).

  - Otherwise it will return a safely quarantined object of form
    `{:nippy/unthawable {:class-name <> :content <quarantined-ba>}}`.
    - Quarantined objects may be manually unquarantined with
      `read-quarantined-serializable-object-unsafe!`.

There are 2x allowlists:
  - `*freeze-serializable-allowlist*` ; Checked when freezing
  -   `*thaw-serializable-allowlist*` ; Checked when thawing

Example allowlist values:
  - `(fn allow-class? [class-name] true)`            ; Arbitrary predicate fn
  - `#{"java.lang.Throwable", "clojure.lang.*"}` ; Set of class-names
  - `"allow-and-record"`                           ; Special value, see [2]

  Note that class-names in sets may contain "*" wildcards.

Default allowlist values are:
  - default-freeze-serializable-allowlist ; `{"*"}` => allow any class
  -   default-thaw-serializable-allowlist ; A set of common safe classes

Allowlist values may be overridden with `binding`, `alter-var-root`, or:

  - `taoensso.nippy.<freeze/thaw>-serializable-allowlist-base` JVM property
  - `taoensso.nippy.<freeze/thaw>-serializable-allowlist-add`  JVM property

  - `TAOENSSO_NIPPY_<FREEZE/THAW>_SERIALIZABLE_ALLOWLIST_BASE` env var
  - `TAOENSSO_NIPPY_<FREEZE/THAW>_SERIALIZABLE_ALLOWLIST_ADD`  env var

If present, these will be read as comma-separated lists of class names
and formed into sets. Each initial allowlist value will then be:
(into (or <?base> <default>) <?additions>).

  I.e. you can use:
    - The "base" property/var to replace Nippy's default allowlists.
    - The "add"  property/var to add to  Nippy's default allowlists.

The special `"allow-and-record"` value is also possible, see [2].

Upgrading from an older version of Nippy and unsure whether you've been
using Nippy's Serializable support, or which classes to allow? See [2].

See also `taoensso.encore/compile-str-filter` for a util to help easily
build more advanced predicate functions.

Thanks to Timo Mihaljov (@solita-timo-mihaljov) for an excellent report
identifying this vulnerability.

[1] https://github.com/ptaoussanis/nippy/issues/130
[2] See `allow-and-record-any-serializable-class-unsafe`.

Include metadata when freezing/thawing?

DEPRECATED, now called `*thaw-serializable-allowlist*`

Used when attempting to <freeze/thaw> an object that:
  - Does NOT implement Nippy's Freezable    protocol.
  - DOES     implement Java's  Serializable interface.

In this case, the allowlist will be checked to see if Java's
Serializable interface may be used.

This is a security measure to prevent possible Remote Code Execution
(RCE) when thawing malicious payloads. See [1] for details.

If `freeze` encounters a disallowed Serialized class, it will throw.
If `thaw`   encounters a disallowed Serialized class, it will:

  - Throw if it's not possible to safely quarantine the object
    (object was frozen with Nippy < v2.15.0-final).

  - Otherwise it will return a safely quarantined object of form
    `{:nippy/unthawable {:class-name <> :content <quarantined-ba>}}`.
    - Quarantined objects may be manually unquarantined with
      `read-quarantined-serializable-object-unsafe!`.

There are 2x allowlists:
  - `*freeze-serializable-allowlist*` ; Checked when freezing
  -   `*thaw-serializable-allowlist*` ; Checked when thawing

Example allowlist values:
  - `(fn allow-class? [class-name] true)`            ; Arbitrary predicate fn
  - `#{"java.lang.Throwable", "clojure.lang.*"}` ; Set of class-names
  - `"allow-and-record"`                           ; Special value, see [2]

  Note that class-names in sets may contain "*" wildcards.

Default allowlist values are:
  - default-freeze-serializable-allowlist ; `{"*"}` => allow any class
  -   default-thaw-serializable-allowlist ; A set of common safe classes

Allowlist values may be overridden with `binding`, `alter-var-root`, or:

  - `taoensso.nippy.<freeze/thaw>-serializable-allowlist-base` JVM property
  - `taoensso.nippy.<freeze/thaw>-serializable-allowlist-add`  JVM property

  - `TAOENSSO_NIPPY_<FREEZE/THAW>_SERIALIZABLE_ALLOWLIST_BASE` env var
  - `TAOENSSO_NIPPY_<FREEZE/THAW>_SERIALIZABLE_ALLOWLIST_ADD`  env var

If present, these will be read as comma-separated lists of class names
and formed into sets. Each initial allowlist value will then be:
(into (or <?base> <default>) <?additions>).

  I.e. you can use:
    - The "base" property/var to replace Nippy's default allowlists.
    - The "add"  property/var to add to  Nippy's default allowlists.

The special `"allow-and-record"` value is also possible, see [2].

Upgrading from an older version of Nippy and unsure whether you've been
using Nippy's Serializable support, or which classes to allow? See [2].

See also `taoensso.encore/compile-str-filter` for a util to help easily
build more advanced predicate functions.

Thanks to Timo Mihaljov (@solita-timo-mihaljov) for an excellent report
identifying this vulnerability.

[1] https://github.com/ptaoussanis/nippy/issues/130
[2] See `allow-and-record-any-serializable-class-unsafe`.

Experimental, subject to change. Feedback welcome.

Transducer to use when thawing standard Clojure collection types
(vectors, maps, sets, lists, etc.).

Allows fast+flexible inspection and manipulation of data being thawed.

Key-val style data structures like maps will provide `MapEntry` args
to reducing function. Use `map-entry?`, `key`, `val` utils for these.

Example transducers:

  (map (fn [x] (println x) x)) ; Print each coll item thawed

  (comp
    (map    (fn [x] (if (= x :secret) :redacted x))) ; Replace secrets
    (remove (fn [x] ; Remove maps with a truthy :remove?
              (or
                (and (map?       x) (:remove? x))
                (and (map-entry? x) (= (key x) :remove?) (val y)))))))

Note that while this is a very powerful feature, correctly writing
and debugging transducers and reducing fns can be tricky.

To help, if Nippy encounters an errors while applying your xform, it
will throw a detailed `ExceptionInfo` with message
"Error thrown via `*thaw-xform*`" to help you debug.

{[<x> <meta>] <idx>} for freezing, {<idx> <x-with-meta>} for thawing.

Default 128bit AES-CBC encryptor with many-round SHA-512 key-gen.
See also `aes-128-cbc-encryptor`.

Default 128bit AES-GCM encryptor with many-round SHA-512 key-gen.

Password form [:salted "my-password"]
---------------------------------------
USE CASE: You want more than a small, finite number of passwords (e.g. each
          item encrypted will use a unique user-provided password).

IMPLEMENTATION: Uses a relatively cheap key hash, but automatically salts
                every key.

PROS: Each key is independent so would need to be attacked independently.
CONS: Key caching impossible, so there's an inherent trade-off between
      encryption/decryption speed and the difficulty of attacking any
      particular key.

Slower than `aes128-cached`, and easier to attack any particular key - but
keys are independent.

Password form [:cached "my-password"]
---------------------------------------
USE CASE: You want only a small, finite number of passwords (e.g. a limited
          number of staff/admins, or you'll be using a single password to
          encrypt many items).

IMPLEMENTATION: Uses a _very_ expensive (but cached) key hash, and no salt.

PROS: Great amortized encryption/decryption speed. Expensive key hash makes
      attacking any particular key very difficult.
CONS: Using a small number of keys for many encrypted items means that if any
      key _is_ somehow compromised, _all_ items encrypted with that key are
      compromised.

Faster than `aes128-salted`, and harder to attack any particular key - but
increased danger if a key is somehow compromised.

Default 128bit AES-GCM encryptor with many-round SHA-512 key-gen.

Password form [:salted "my-password"]
---------------------------------------
USE CASE: You want more than a small, finite number of passwords (e.g. each
          item encrypted will use a unique user-provided password).

IMPLEMENTATION: Uses a relatively cheap key hash, but automatically salts
                every key.

PROS: Each key is independent so would need to be attacked independently.
CONS: Key caching impossible, so there's an inherent trade-off between
      encryption/decryption speed and the difficulty of attacking any
      particular key.

Slower than `aes128-cached`, and easier to attack any particular key - but
keys are independent.

Password form [:cached "my-password"]
---------------------------------------
USE CASE: You want only a small, finite number of passwords (e.g. a limited
          number of staff/admins, or you'll be using a single password to
          encrypt many items).

IMPLEMENTATION: Uses a _very_ expensive (but cached) key hash, and no salt.

PROS: Great amortized encryption/decryption speed. Expensive key hash makes
      attacking any particular key very difficult.
CONS: Using a small number of keys for many encrypted items means that if any
      key _is_ somehow compromised, _all_ items encrypted with that key are
      compromised.

Faster than `aes128-salted`, and harder to attack any particular key - but
increased danger if a key is somehow compromised.

A predicate (fn allow-class? [class-name]) fn that can be assigned
to `*freeze-serializable-allowlist*` and/or
     `*thaw-serializable-allowlist*` that:

  - Will allow ANY class to use Nippy's Serializable support (unsafe).
  - And will record {<class-name> <frequency-allowed>} for the <=1000
    classes that ~most frequently made use of this support.

`get-recorded-serializable-classes` returns the recorded state.

This predicate is provided as a convenience for users upgrading from
previous versions of Nippy that allowed the use of Serializable for all
classes by default.

While transitioning from an unsafe->safe configuration, you can use
this predicate (unsafe) to record information about which classes have
been using Nippy's Serializable support in your environment.

Once some time has passed, you can check the recorded state. If you're
satisfied that all recorded classes are safely Serializable, you can
then merge the recorded classes into Nippy's default allowlist/s, e.g.:

(alter-var-root #'thaw-serializable-allowlist*
  (fn [_] (into default-thaw-serializable-allowlist
            (keys (get-recorded-serializable-classes)))))

Experimental, subject to change. Feedback welcome.

Wraps value so that future writes of the same wrapped value with same
metadata will be efficiently encoded as references to this one.

(freeze [(cache "foo") (cache "foo") (cache "foo")])
  will incl. a single "foo", plus 2x single-byte references to "foo".

Allows *any* class-name to be frozen using Java's Serializable interface.
This is generally safe since RCE risk is present only when thawing.
See also `*freeze-serializable-allowlist*`.

A set of common safe class-names to allow to be frozen using Java's
Serializable interface. PRs welcome for additions.
See also `*thaw-serializable-allowlist*`.

Extends Nippy to support freezing of a custom type (ideally concrete) with
given id of form:

  * Keyword    - 2 byte overhead, keywords hashed to 16 bit id
  * ℕ∈[1, 128] - 0 byte overhead

NB: be careful about extending to interfaces, Ref. http://goo.gl/6gGRlU.

(defrecord MyRec [data])
(extend-freeze MyRec :foo/my-type [x data-output] ; Keyword id
  (.writeUTF [data-output] (:data x)))
;; or
(extend-freeze MyRec 1 [x data-output] ; Byte id
  (.writeUTF [data-output] (:data x)))

Extends Nippy to support thawing of a custom type with given id:
(extend-thaw :foo/my-type [data-input] ; Keyword id
  (MyRec. (.readUTF data-input)))
;; or
(extend-thaw 1 [data-input] ; Byte id
  (MyRec. (.readUTF data-input)))

Like `freeze` but:
  - Writes data without a Nippy header
  - Drops all support for compression and encryption
  - Must be thawed with `fast-thaw`

Equivalent to (but a little faster than) `freeze` with opts:
  - :compressor nil
  - :encryptor  nil
  - :no-header? true

Like `thaw` but:
  - Drops all support for compression and encryption
  - Supports only data frozen with `fast-freeze`

Equivalent to (but a little faster than) `thaw` with opts:
  - :compressor nil
  - :encryptor  nil
  - :no-header? true

Alpha - subject to change.
Returns truthy iff Nippy *appears* to support freezing the given argument.

`:allow-clojure-reader?` and `:allow-java-serializable?` options may be
used to enable the relevant roundtrip fallback test(s). These tests are
only **moderately reliable** since they're cached by arg type and don't
test for pre/post serialization value equality (there's no good general
way of doing so).

Serializes arg (any Clojure data type) to a byte array.
To freeze custom types, extend the Clojure reader or see `extend-freeze`.

Convenience util: like `freeze`, but writes to `(clojure.java.io/file <file>)`.

Serializes arg (any Clojure data type) to a DataOutput.
This is a low-level util: in most cases you'll want `freeze` instead.

Convenience util: like `freeze`, but returns a Base64-encoded string.
See also `thaw-from-string`.

Returns {<class-name> <frequency>} of the <=1000 classes that ~most
frequently made use of Nippy's Serializable support via
`allow-and-record-any-serializable-class-unsafe`.

See that function's docstring for more info.

Experimental, subject to change. Feedback welcome.

Default net.jpountz.lz4 compressor:
      Ratio: low.
Write speed: very high.
 Read speed: very high.

A good general-purpose compressor, competitive with Snappy.

Thanks to Max Penet (@mpenet) for our first implementation,
Ref. https://github.com/mpenet/nippy-lz4

Like `lz4-compressor` but trades some write speed for ratio.

Default org.tukaani.xz.LZMA2 compressor:
      Ratio: high.
Write speed: _very_ slow (also currently single-threaded).
 Read speed: slow.

A specialized compressor for large, low-write data in space-sensitive
environments.

Public representation of Nippy's internal type schema.
For use by tooling and advanced users.

**HIGHLY EXPERIMENTAL!**
Subject to breaking change without notice.
Currently completely untested, may contain bugs.
Intended for use only by early adopters to give design feedback.

Format:
  {<type-id> {:keys [type-id type-kw payload-spec deprecated?]}},

  - `type-id`: A +ive single-byte identifier like `110`.
               -ive type ids are reserved for custom user-defined types.

  - `type-kw`: A keyword like `:kw-sm`,
    suffixes used to differentiate subtypes of different sizes:
      -0  ; Empty       => 0 byte         payload / element-count
      -sm ; Small       => 1 byte (byte)  payload / element-count
      -md ; Medium      => 2 byte (short) payload / element-count
      -lg ; Large       => 4 byte (int)   payload / element-count
      -xl ; Extra large => 8 byte (long)  payload / element-count

  - `payload-spec` examples:
    - nil                        ; No spec available (e.g. unpredictable payload)
    - []                         ; Type has no payload
    - [[:bytes 4]]               ; Type has a payload of exactly 4 bytes
    - [[:bytes 2] [:elements 2]] ; Type has a payload of exactly 2 bytes, then
                                 ; 2 elements

    - [[:bytes    {:read 2}]
       [:elements {:read 4 :multiplier 2 :unsigned? true}]]

      ; Type has payload of <short-count> bytes, then
      ; <unsigned-int-count>*2 (multiplier) elements

    Note that `payload-spec` can be handy for skipping over items in
    data stream without fully reading every item.

Given a quarantined Serializable object like
{:nippy/unthawable {:class-name <> :content <quarantined-ba>}}, reads and
returns the object WITHOUT regard for `*thaw-serializable-allowlist*`.

**MAY BE UNSAFE!** Don't call this unless you absolutely trust the payload
to not contain any malicious code.

See `*thaw-serializable-allowlist*` for more info.

Default org.iq80.snappy.Snappy compressor:
      Ratio: low.
Write speed: very high.
 Read speed: very high.

A good general-purpose compressor.

Reference data used for tests & benchmarks

Reference data with stuff removed that breaks reader or other utils we'll
be benching with.

Reference data with stuff removed that breaks roundtrip equality.

Deserializes a frozen Nippy byte array to its original Clojure data type.
To thaw custom types, extend the Clojure reader or see `extend-thaw`.

** By default, supports data frozen with Nippy v2+ ONLY **
Add `{:v1-compatibility? true}` option to support thawing of data frozen with
legacy versions of Nippy.

Options include:
  :v1-compatibility? - support data frozen by legacy versions of Nippy?
  :compressor - :auto (checks header, default)  an ICompressor, or nil
  :encryptor  - :auto (checks header, default), an IEncryptor,  or nil

Convenience util: like `thaw`, but reads from `(clojure.java.io/file <file>)`.

Deserializes a frozen object from given DataInput to its original Clojure
data type.

This is a low-level util: in most cases you'll want `thaw` instead.

Convenience util: like `thaw`, but reads from `(clojure.java.io/resource <res>)`.

Convenience util: like `thaw`, but takes a Base64-encoded string.
See also `freeze-to-string`.