Deed

A fast, zero-deps binary encoding and decoding library for Clojure.

Table of Contents

• About
• Motivation
• Installation & Requirements
• Quick Demo
• API
  • Simple Encode and Decode
  • Encoding to Memory
  • Sequential Encoding and Decoding
  • Low-Level API
  • API Options
• GZipped Streams
• Versioning and Backward Compatibility
• Appending to a File
• Handle Unsupported Types
• Supported Types
• Extending Custom Types
  • Encode
  • Decode
  • Macros
  • Grouping Fields
• Handling Defrecords
• Contrib
  • Base64
  • VectorZ
• Binary Format
• Benchmarks

About

Deed is a library to dump any value into a byte array and read it back. It supports plenty of types out from the box: Java primitives, most of the Clojure types, Java collections, date and time, and so on. It supports even such tricky types as atoms, refs, and input streams. The full list of supported types is shown in the "Supported Types" section below.

Deed can be extended with custom types with ease. There is a contrib package that extends encoding and decoding logic for vectors from the the well-known mikera/vectorz library.

Deed is written in pure Java and thus is pretty fast (see the "Benchmarks" section). It's about 30-50% faster than Nippy.

It doesn't rely on the built-in Java Serializable interface for security reasons. Every type is processed manually.

Deed provides convenient API for reading the frozen data lazily one by one.

Motivation

Obviously you would ask why doing this if we already have Nippy? This is what I had in mind while working on Deed:

1. The library must be absolutely free from dependencies. This is true for the deed-core package: it's written in pure Java with no dependencies at all. By adding it into a project, you won't blow up you uberjar, nor you will have troubles with building a native image with GraalVM.

2. Any part of Deed that requires 3rd-party stuff must be a sub-library. So you have precise control of what you use and what you don't

3. Unlike Nippy, Deed never falls back to native Java serialization. There is no such an option. Thus, your application cannot be attacked by someone who has forged a binary dump.

4. Deed is simple: it blindly works with input- and output byte streams having no idea what's behind them. It doesn't take compression nor encryption into account -- yet there are utilities for streams.

5. The library provides API which personally I consider more convenient than Nippy's. Namely, Deed can lazily iterate on a series of encoded data instead of reading the whole dump at once.

6. Finally, why not using popular and cross-platform formats like JSON, Message Pack, or YAML? Well, because of poor types support. JSON has only primitive types and collections, and nothing else. Extending it with custom types is always a pain. At the same time, I want my decoded data be as close to the origin data as possible, say, LocalDateTime be an instance of LocalDateTime but not a string or java.util.Date. Sometimes, preserving metadata is crucial. To handle all of these cases, there now a way other than making your own library.

Installation & Requirements

Deed requires Java version at least 16 to run. Tested with Clojure 1.9.0.

The core module with basic encode and decode capabilities:

;; lein
[com.github.igrishaev/deed-core "0.1.0"]

;; deps
com.github.igrishaev/deed-core {:mvn/version "0.1.0"}

Base64 module do encode and decode from/into base64 on the fly:

;; lein
[com.github.igrishaev/deed-base64 "0.1.0"]

;; deps
com.github.igrishaev/deed-base64 {:mvn/version "0.1.0"}

Vectorz module extends Deed with a number of Vector* classes from the mikera/vectorz library:

;; lein
[com.github.igrishaev/deed-vectorz "0.1.0"]

;; deps
com.github.igrishaev/deed-vectorz {:mvn/version "0.1.0"}

Quick Demo

This is a very brief example of how to dump the data into a file. Prepare the namespace with imports:

(ns demo
  (:require
   [clojure.java.io :as io]
   [deed.core :as deed]))

Declare the file and the data:

(def file
  (io/file "dump.deed"))

(def data
  {:number 1
   :string "hello"
   :bool true
   :nil nil
   :symbol 'hello/test
   :simple-kw :test
   :complex-kw :foo/bar
   :vector [1 2 :test nil 42 "hello"]
   :map {:test {:bar {'dunno {"lol" [:kek]}}}}
   :set #{:a :b :c}
   :atom (atom {:abc 42})})

Pass them into the encode-to function as follows:

(deed/encode-to data file)

And this is it! If you examine the file with any kind of a hex editor, you'll see a binary payload:

xxd /path/to/dump.deed

00000000: 0001 0001 0000 0000 0000 0000 0000 0000  ................
00000010: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000020: 0000 003b 0000 000b 004a 0000 0006 6e75  ...;.....J....nu
00000030: 6d62 6572 000e 004a 0000 0006 7379 6d62  mber...J....symb
00000040: 6f6c 004b 0000 000a 6865 6c6c 6f2f 7465  ol.K....hello/te
00000050: 7374 004a 0000 000a 636f 6d70 6c65 782d  st.J....complex-
00000060: 6b77 004a 0000 0007 666f 6f2f 6261 7200  kw.J....foo/bar.
00000070: 4a00 0000 0673 7472 696e 6700 2b00 0000  J....string.+...
00000080: 0568 656c 6c6f 004a 0000 0006 7665 6374  .hello.J....vect
00000090: 6f72 002e 0000 0006 000e 000c 0000 0000  or..............
000000a0: 0000 0002 004a 0000 0004 7465 7374 0000  .....J....test..
000000b0: 000c 0000 0000 0000 002a 002b 0000 0005  .........*.+....
000000c0: 6865 6c6c 6f00 4a00 0000 036e 696c 0000  hello.J....nil..
000000d0: 004a 0000 0004 626f 6f6c 0029 004a 0000  .J....bool.).J..
000000e0: 0003 7365 7400 3300 0000 0300 4a00 0000  ..set.3.....J...
000000f0: 0163 004a 0000 0001 6200 4a00 0000 0161  .c.J....b.J....a
00000100: 004a 0000 0009 7369 6d70 6c65 2d6b 7700  .J....simple-kw.
00000110: 4a00 0000 0474 6573 7400 4a00 0000 0461  J....test.J....a
00000120: 746f 6d00 3000 3b00 0000 0100 4a00 0000  tom.0.;.....J...
00000130: 0361 6263 000c 0000 0000 0000 002a 004a  .abc.........*.J
00000140: 0000 0003 6d61 7000 3b00 0000 0100 4a00  ....map.;.....J.
00000150: 0000 0474 6573 7400 3b00 0000 0100 4a00  ...test.;.....J.
00000160: 0000 0362 6172 003b 0000 0001 004b 0000  ...bar.;.....K..
00000170: 0005 6475 6e6e 6f00 3b00 0000 0100 2b00  ..dunno.;.....+.
00000180: 0000 036c 6f6c 002e 0000 0001 004a 0000  ...lol.......J..
00000190: 0003 6b65 6b                             ..kek

Now that you have a .deed file, read it back using the decode-from function:

(def data-back
  (deed/decode-from file))

Print the data-back to ensure it keeps the origin types:

{:number 1,
 :symbol hello/test,
 :complex-kw :foo/bar,
 :string "hello",
 :vector [1 2 :test nil 42 "hello"],
 :nil nil,
 :bool true,
 :set #{:c :b :a},
 :simple-kw :test,
 :atom #<Atom@75f6dd87: {:abc 42}>,
 :map {:test {:bar {dunno {"lol" [:kek]}}}}}

Compare them to ensure we didn't loose anything. Since atoms cannot be compared, we dissoc them from both sides:

(= (dissoc data :atom) (dissoc data-back :atom))
;; true

Deed supports plenty of built-in Clojure and Java types. The next section describes which API it provides to manage the data.

API

Simple Encode and Decode

The encode-to function accepts two parameters: a value and an output. The value is an instance of any supported type (a map, a vector, etc).

The output is anything that can be coerced to the output stream using the io/output-stream function. It could be a file, another output stream, a byte array, or similar. If you pass a string, it's treated as a file name which will be created.

Examples:

(deed/encode-to {:foo 123} "test.deed")

(deed/encode-to {:foo 123} (io/file "test2.deed"))

(deed/encode-to {:foo 123} (-> "test3.deed"
                               io/file
                               io/output-stream))

All the three invocations above dump the same map {:foo 123} into different files.

To read the data back, invoke the decode-from function. It accepts anything that can be coerced into an input stream using the io/input-stream function. It might be a file, another stream, a byte array, or a name of a file.

(deed/decode-from "test.deed")
;; {:foo 123}

(deed/decode-from (io/file "test2.deed"))
;; {:foo 123}

(deed/decode-from (-> "test3.deed"
                      io/file
                      io/input-stream))
;; {:foo 123}

Encoding to Memory

The functions below rely on external IO resources. If you want to dump the data into memory, use the encode-to-bytes function. It returns a byte array without any IO interaction:

(def buf
  (deed/encode-to-bytes {:test 123}))

(println (vec buf))

[0 1 0 1 0 0 ... 59 0 0 0 1 0 74 0 0 0 4 116 101 115 116 0 12 0 0 0 0 0 0 0 123]

There is no an opposite decode-from-bytes function because a byte array is already a data source for the decode-from function. Just pass the result into it:

(deed/decode-from buf)
;; {:test 123}

Sequential Encoding and Decoding

We often dump vast collections to explore them afterwards. Say, you're going to write 10M of database rows into a file to find a broken row with a script.

The functions above encode and decode a single value. That's OK for primitive types and maps but not good for vast collections. For example, if you encode a vector of 10M items into a file and read it back, you'll get the same vector of 10M items. That's unlikely you need all of these at once: you'd better to iterate on them one by one.

This is the case that encode-seq-to and decode-seq-from functions cover. The first function accepts a collection of items and writes them sequentially. It's not a vector any longer but a series of items written one after another. The encode-seq-to invocation returns the number of items written:

(deed/encode-seq-to [1 2 3] "test.deed")
;; 3

Instead of a vector, there might be a lazy sequence, or anything that can be iterated.

If you read the dump using decode-from, you'll get the first item only:

(deed/decode-from "test.deed")
1

To read all of them, use decode-seq-from:

(deed/decode-seq-from "test.deed")
[1 2 3]

What is the point to use sequential encoding? Because with a special API, you can read them lazily one by one.

The with-decoder macro takes two parameters: the binding symbol and the input. Internally, it creates a Decoder instance and binds it to the first symbol. The decode-seq function returns a lazy sequence of items from a decoder:

(deed/with-decoder [d "test.deed"]
  (doseq [item (deed/decode-seq d)]
    (println item)))
;; 1
;; 2
;; 3

You must process items before you exit the with-decoder macro.

The form above might be rewritten using the with-open macro. Since the Decoder object implements AutoCloseable interface, it handles the .close method which in turn closes the underlying stream.

(with-open [d (deed/decoder "test.deed")]
  (doseq [item (deed/decode-seq d)]
    (println item)))

In fact, you don't even need to pass the decoder object into decode-seq because it implements the Iterable Java interface. Just iterate the decoder:

(deed/with-decoder [d "test.deed"]
  (mapv inc d))
;; [2 3 3]

(deed/with-decoder [d "test.deed"]
  (doseq [item d]
    (println "item is" item)))
;; item is 1
;; item is 2
;; item is 3

The items are read lazily so you won't saturate memory.

Low-Level API

Deed provides low-level API for conditional or imperative encoding. The encode function writes a value into an instance of the Encoder class. You can use it in a cycle with some condition:

(deed/with-encoder [e "test.deed"]
  (doseq [x (range 1 32)]
    (when (even? x)
      (deed/encode e x))))

The decode function reads an object from the Decoder instance. When the end of the stream is met, you'll get a special EOF object that you can check using the eof? preficate:

(deed/with-decoder [d "test.deed"]
  (loop [i 0]
    (let [item (deed/decode d)]
      (if (deed/eof? item)
        (println "EOF")
        (do
          (println "item" i item)
          (recur (inc i)))))))

;; item 0 2
;; item 1 4
;; item 2 6
;; item 3 8
;; item 4 10
;; item 5 12
;; item 6 14
;; item 7 16
;; item 8 18
;; item 9 20
;; item 10 22
;; item 11 24
;; item 12 26
;; item 13 28
;; item 14 30
;; EOF

The low-level API is useful for precise control on encoding and decoding.

API Options

Most of the functions accept an optional map of parameters. Here is a list of options supported at the moment:

Name	Default	Meaning
:deref-timeout-ms	5000	The number of milliseconds to wait when derefing futures.
:object-chunk-size	0xFF	The number of object chunk when encoding uncountable collections (e.g. lazy seqs).
:byte-chunk-size	0xFFFF	The number of byte chunk when encoding input streams.
:uncountable-max-items	Integer.MAX_VALUE	The max number of items to process when encoding uncountable collections (e.g. lazy seqs).
:encode-unsupported?	true	If true, dump every unsupported object into a string (see below). Otherwise, throw an error.
:io-temp-file?	false	When deciding previously encoded input stream, write its payload into a temp file.
:save-meta?	true	Preserve metadata for objects what have it.
:append?	false	Write at the end of an existing dump (see below).

That's unlikely you'll need to change any of these, yet in rare cases they might help.

GZipped Streams

Deed has a couple of functions that turn any input or output into GZIPInputStream and GZIPOutputStream instances respectfully. It allows to compress the data on the fly. Here is how you compress:

(with-open [out (deed/gzip-output-stream "dump.deed.gz")]
  (deed/encode-to [1 2 3] out))

And decompress:

(with-open [in (deed/gzip-input-stream "dump.deed.gz")]
  (deed/decode-from in))
;; [1 2 3]

Keep in mind that compression saves disk space but consumes CPU usage.

Versioning and Backward Compatibility

Deed has a built-in versioning system. Every time you encode something, the library emits a leading Header object with a version of the protocol. At the moment of writing this, the version is just 1. When decoding, this version number is read from the header before parsing any other objects.

If any breaking changes appear in encode/decode logic, two things will take place in the next release:

• the constant HEADER_VERSION will be bumped from 1 to 2 so any further encoding will have protocol version 2 as well;

• a corresponding encode/decode logic will be wrapped into a switch...case branch depending on the current version of the protocol.

At that very moment, Deed has protocol version 1 with no branching, yet there is a room for extending. Adding new OIDs and types won't change the protocol version.

Appending to a File

In rare cases, you'd like to append data to an existing file. This might be done in two steps. First, you initiate the FileOutputStream object manually and pass the true boolean flag meaning the data is put at the end of a file:

(with-open [out (new FileOutputStream file true)]
  ...)

Second, when encoding the data into such an output, specify the {:append? true} option. In this case, Deed won't emit a leading deed.Header object:

(with-open [out (new FileOutputStream file true)]
  (deed/encode-to {:hello 123} out {:append? true}))

Handle Unsupported Types

By default, when Deed doesn't know how to encode an object, it turns it into a string using the standard .toString method. Than it makes a special Unsupported object that tracks full class name and the text payload. Let's present it with a custom deftype declaration:

(deftype MyType [a b c])

(def mt (new MyType :hello "test" 42))

(deed/encode-to mt "test.deed")

(deed/decode-from "test.deed")
;; #<Unsupported@b918edf: {:content "demo.MyType@4376ae5c", :class "demo.MyType"}>

The Unsupported object can be checked with the unsupported? predicate:

(def mt-back
  (deed/decode-from "test.deed"))

(deed/unsupported? mt-back)
;; true

To coerce it to Clojure, just deref it:

@mt-back
{:content "demo.MyType@4376ae5c", :class "demo.MyType"}

Above, the "demo.MyType@4376ae5c" string doesn't say much. This is because the default .toString implementation of deftype lacks fields. That's why it's always worth overriding the .toString method for custom types:

(deftype MyType [a b c]
  Object
  (toString [_]
    (format "<MyType: %s, %s, %s>" a b c)))

(def mt (new MyType :hello "test" 42))

(deed/encode-to mt "test.deed")

(def mt-back
  (deed/decode-from "test.deed"))

(str mt-back)
;; "Unsupported[className=demo.MyType, content=<MyType: :hello, test, 42>]"

@mt-back
;; {:content "<MyType: :hello, test, 42>", :class "demo.MyType"}

Now the content has fields, so at least you can observe them.

When the :encode-unsupported? boolean option is false, Deed throws an exception by facing an unsupported object:

(deed/encode-to mt "test.deed" {:encode-unsupported? false})

;; Execution error at deed.Err/error (Err.java:14).
;; Cannot encode object, type: demo.MyType, object: <MyType: :hello, test, 42>

Supported Types

The table below renders types supported by Deed out from the box:

OID	TAG	Class	Comment
0x0000	NULL	null (nil)
0x0001	HEADER	deed.Header	A leading object with general info about encoding
0x0002	UNSUPPORTED	deed.Unsupported	A wrapper for unsupported objects
0x0003	META		Specifies an object with metadata
0x0004	INT	int, java.lang.Integer
0x0005	INT_ZERO		A special OID for 0 int
0x0006	INT_ONE		A special OID for 1 int
0x0007	INT_MINUS_ONE		A special OID for -1 int
0x0008	SHORT	short, java.lang.Short
0x0009	SHORT_ZERO		A special OID for 0 short
0x000A	SHORT_ONE		A special OID for 1 short
0x000B	SHORT_MINUS_ONE		A special OID for -1 short
0x000C	LONG	long, java.lang.Long
0x000D	LONG_ZERO
0x000E	LONG_ONE
0x000F	LONG_MINUS_ONE
0x0010	IO_INPUT_STREAM	java.io.InputStream	When decoding, the bytes are put into a ByteArrayInputStream. It's also possible to put them into a temp file and obtain a FileInputStream
0x0011	IO_READER	-	Not implemented
0x0012	IO_FILE	-	Not implemented
0x0013	IO_BYTEBUFFER	java.nio.ByteBuffer
0x0014	ARR_BYTE	byte[]
0x0015	ARR_INT	int[]
0x0016	ARR_SHORT	short[]
0x0017	ARR_BOOL	boolean[]
0x0018	ARR_FLOAT	float[]
0x0019	ARR_DOUBLE	double[]
0x001A	ARR_OBJ	Object[]
0x001B	ARR_LONG	long[]
0x001C	ARR_CHAR	char[]
0x001D	REGEX	java.util.regex.Pattern
0x001E	CLJ_SORTED_SET	clojure.lang.PersistentTreeSet	A sorted set usually created with (sorted-set ...)
0x001F	CLJ_SORTED_SET_EMPTY		A special OID for an empty sorted set
0x0020	CLJ_SORTED_MAP	clojure.lang.PersistentTreeMap	A sorted map usually created with (sorted-map ...)
0x0021	CLJ_SORTED_MAP_EMPTY		An empty sorted map
0x0022	URI	java.net.URI
0x0023	URL	java.net.URL
0x0024	EXCEPTION	java.lang.Exception	Keeps message, class name, stack trace, cause (recursively encoded), and all the suppressed exceptions
0x0025	IO_EXCEPTION
0x0026	THROWABLE
0x0027	EX_INFO
0x0028	EX_NPE
0x0029	BOOL_TRUE	boolean, java.lang.Boolean	True value only
0x002A	BOOL_FALSE	boolean, java.lang.Boolean	False value only
0x002B	STRING	java.lang.String	Stored as a number of bytes + bytes
0x002C	STRING_EMPTY		A special OID indicating an empty string
0x002D	CHAR	char, java.lang.Character
0x002E	CLJ_VEC	clojure.lang.APersistentVector	A standard Clojure vector
0x002F	CLJ_VEC_EMPTY		A special OID indicating an empty vector
0x0030	CLJ_ATOM	clojure.lang.Atom	Gets deref-ed when encoding
0x0031	CLJ_REF	clojure.lang.Ref	Gets deref-ed when encoding
0x0032	FUTURE	java.util.concurrent.Future	Deed .gets the value using timeout from options. When time is up, an exception is throw. When decoded, it's returned as an instance of deed.FutureWrapper: a fake object that mimics a future.
0x0033	CLJ_SET	clojure.lang.APersistentSet	A standard Clojure immutable set
0x0034	CLJ_SET_EMPTY		A special OID indicating an empty set
0x0035	CLJ_LAZY_SEQ	clojure.lang.LazySeq	Encode a lazy sequence produced with map, for, etc. Stored as a collection of chunks like <chunk-len><items...>. When decoding, read until the chunk of zero length is met.
0x0036	CLJ_SEQ	Type depends on the origin collection	Becomes a vector when decoding
0x0037	CLJ_LIST	clojure.lang.PersistentList
0x0038	CLJ_LIST_EMPTY		A special OID indicating an empty list
0x0039	CLJ_QUEUE	clojure.lang.PersistentQueue
0x003A	CLJ_QUEUE_EMPTY		A special OID indicating an empty queue
0x003B	CLJ_MAP	clojure.lang.APersistentMap
0x003C	CLJ_MAP_EMPTY	clojure.lang.APersistentMap	An empty Clojure map
0x003D	CLJ_MAP_ENTRY	clojure.lang.MapEntry	A pair of key and value
0x003E	CLJ_RECORD	clojure.lang.IRecord	An instance of defrecord object. When decoding, becomes an ordinary map. To preserve the origin type, use the handle-record macro (see below).
0x003F	CLJ_TR_VEC	c.l.PersistentVector$TransientVector	A transient Clojure vector.
0x0040	JVM_MAP	java.util.Map	A Java map, usually an instance of HashMap.
0x0041	JVM_MAP_ENTRY	java.util.Map$Entry
0x0042	UUID	java.util.UUID
0x0043	JVM_LIST	java.util.List	When decoding, becomes an instance of ArrayList.
0x0044	JVM_LIST_EMPTY	java.util.List	A stub for an empty list.
0x0045	JVM_VECTOR	java.util.Vector
0x0046	JVM_VECTOR_EMPTY		An empty Java vector.
0x0047	JVM_ITERABLE	java.lang.Iterable	Encoded as uncounted chunked sequence of objects
0x0048	JVM_ITERATOR		When decoding, becomes an instance of ArrayList.
0x0049	JVM_STREAM	java.util.stream.Stream
0x004A	CLJ_KEYWORD	clojure.lang.Keyword
0x004B	CLJ_SYMBOL	clojure.lang.Symbol
0x004C	UTIL_DATE	java.util.Date
0x004D	DT_LOCAL_DATE	java.time.LocalDate
0x004E	DT_LOCAL_TIME	java.time.LocalTime
0x004F	DT_LOCAL_DATETIME	java.time.LocalDateTime
0x0050	DT_OFFSET_DATETIME	java.time.OffsetDateTime
0x0051	DT_OFFSET_TIME	java.time.OffsetTime
0x0052	DT_DURATION	java.time.Duration
0x0053	DT_PERIOD	java.time.Period
0x0054	DT_ZONED_DATETIME	java.time.ZonedDateTime
0x0055	DT_ZONE_ID	java.time.ZoneId
0x0056	DT_INSTANT	java.time.Instant
0x0057	SQL_TIMESTAMP	java.sql.Timestamp
0x0058	SQL_TIME	java.sql.Time
0x0059	SQL_DATE	java.sql.Date
0x005A	BYTE	byte, java.lang.Byte
0x005B	BYTE_ZERO		A stub for byte 0
0x005C	BYTE_ONE		A stub for byte 1
0x005D	BYTE_MINUS_ONE		A stub for byte -1
0x005E	FLOAT	float, java.lang.Float
0x005F	FLOAT_ZERO		A stub for float 0
0x0060	FLOAT_ONE		A stub for float 1
0x0061	FLOAT_MINUS_ONE		A stub for float -1
0x0062	DOUBLE	double, java.lang.Double
0x0063	DOUBLE_ZERO		A stub for double 0
0x0064	DOUBLE_ONE		A stub for double 1
0x0065	DOUBLE_MINUS_ONE		A stub for double -1
0x0066	JVM_BIG_DEC	java.math.BigDecimal
0x0067	JVM_BIG_INT	java.math.BigInteger
0x0068	CLJ_BIG_INT	clojure.lang.BigInt
0x0069	CLJ_RATIO	clojure.lang.Ratio
0x006A	VECTORZ_AVECTOR	mikera.vectorz.AVector	See the deed-vectorz package

Extending Custom Types

Encode

Although Deed handles plenty of types, you can easily have a type that is unknown to it. Handling such a type is a matter of two things: extending both encoding and decoding logic.

Imagine you have a custom deftype with three fields:

(deftype SomeType [x y z]
  ...)

Here is how you extend the encoding logic. First, declare a custom OID number for it. The number must be short (two bytes) meaning the range from -32768 to 32767. When declaring such an OID, please ensure it doens't overlap with pre-existing OIDs.

(def SomeTypeOID 4321)

Then extend the IEncode protocol with that type:

(extend-protocol deed/IEncode
  SomeType
  (-encode [this encoder]
    (deed/writeOID encoder SomeTypeOID) ;; !
    (deed/encode encoder (.-x this))
    (deed/encode encoder (.-y this))
    (deed/encode encoder (.-z this))))

Or vice versa: extend the type with the protocol:

(extend-type SomeType
  deed/IEncode
  (-encode [this encoder]
    (deed/writeOID encoder SomeTypeOID) ;; !
    (deed/encode encoder (.-x this))
    (deed/encode encoder (.-y this))
    (deed/encode encoder (.-z this))))

Pay attention that in both cases the first expression must be the writeOID invocation. The OID is always put first because decoding logic relies on it. Then we encode custom fields x, y, and z.

Encoding might be a bit easier if you extend a type with IEncode when declaring it. In this case, the -encode method has direct access to x, y, and z as they were local variables.

(deftype SomeType [x y z]
  deed/IEncode
  (-encode [this encoder]
    (deed/writeOID encoder SomeTypeOID)
    (deed/encode encoder x)
    (deed/encode encoder y)
    (deed/encode encoder z)))

Since encode is a general function, it handles any types. You don't bother if x is a number, or a string, or a keyword, or a nested SomeType instance.

Decode

Extend the decoding counterpart by adding implementation to the -decode multimethod. The branching value is the OID you declared:

(defmethod deed/-decode SomeTypeOID
  [_ decoder]
  (let [x (deed/decode decoder)
        y (deed/decode decoder)
        z (deed/decode decoder)]
    (new SomeType x y z)))

Here, we retrieve x, y, and z fields back and componse a new instance of SomeType. Let's check it quckly:

(def _buf
  (deed/encode-to-bytes (new SomeType 1 2 3)))

(deed/decode-from _buf)
;; #object[demo.SomeType 0x47e19f78 "demo.SomeType@47e19f78"]

The order of writing and reading fields does matter, of course. If you mix them, you'll get a broken object back.

Macros

There is a couple of macros that extend protocols and multimethods under the hood: expand-encode and expand-decode. The first one accepts an OID, a type (class), and a couple of symbols to bind: the current Encoder instance and the current value you process. Then there is a body that encodes fields:

(deed/expand-encode [MyOID SomeType encoder some-type]
  (deed/encode encoder (.-x some-type))
  (deed/encode encoder (.-y some-type))
  (deed/encode encoder (.-z some-type)))

Pay attention, you don't call writeOID inside the body because it's already a part of the macro.

The expand-decode macro accepts an OID and a symbol bound to the current Decoder instance. Inside, you decode fields and compose an object:

(deed/expand-decode [MyOID decoder]
  (let [x (deed/decode decoder)
        y (deed/decode decoder)
        z (deed/decode decoder)]
    (new AnotherType x y z)))

Grouping Fields

Above, we encoded and decoded fields x, y and z one by one. This is ok for a time being, but what if one day you need to add one more field? If you add it, you cannot read it from a decoder any longer because it will break the pipeline. Here is an example:

;; before
(deftype SomeType [x y z]
  ...)

;; after
(deftype SomeType [x y z a]
  ...)

Now you alter the -decode multimethod so it retrieves the a field as well:

(defmethod deed/-decode SomeTypeOID
  [_ decoder]
  (let [x (deed/decode decoder)
        y (deed/decode decoder)
        z (deed/decode decoder)
        a (deed/decode decoder)]
    (new SomeType x y z a)))

When reading an old dump made before adding a to SomeType, it will lead to a mysterious bug. The a value belongs to another item that has been written after SomeType. It might not even trigger an exception but rather return a weird data.

To solve this, collect fields into a single collection and emit it into the encoder. A map is the best candidate:

(deftype SomeType [x y z]
  deed/IEncode
  (-encode [this encoder]
    (let [fields {:x x :y y :z z}]
      (deed/writeOID encoder SomeTypeOID)
      (deed/encode encoder fields))))

When decoding, split that map on fields:

(defmethod deed/-decode SomeTypeOID
  [_ decoder]
  (let [{:keys [x y z]}
        (deed/decode decoder)]
    (new SomeType x y z)))

Now that you have introduced a new a field into the type, just add it into the :keys vector and pass into the constructor:

(defmethod deed/-decode SomeTypeOID
  [_ decoder]
  (let [{:keys [x y z a]}
        (deed/decode decoder)]
    (new SomeType x y z a)))

The a field, since missing in the origin map, will be nil. You can add any kind of default fallback, for example merge the decoded map with defaults:

(def Defaults
  {:x 1
   :y "this"
   :z true
   :a {:some "map"}})

(defmethod deed/-decode SomeTypeOID
  [_ decoder]
  (let [decoded
        (deed/decode decoder)

        {:keys [x y z a]}
        (merge Defaults decoded)]

    (new SomeType x y z a)))

With this approach, you'll be safe when extending types and reading old dumps.

Handling Defrecords

By default, records defined with the defrecord macro are read as Clojure maps. This is because they're created at runtime and thus are not known to Deed. To preserve the origin type, either you extend a record with the IEncode protocol and extend the -decode multimethod as described above. Another way is to use the handle-record macro that does the same. It accepts just two arguments: a unique OID and the type of a record:

(defrecord Bar [x y])

(deed/handle-record 4321 Bar)

The body of the macro is missing as you don't need to pass anything else. Internally, a record is still encoded as a Clojure map but using the OID you passed. When decoding this map, before it gets returned to the user, it's wrapped into the <YourType>/create invocation which creates a record instance from a map.

Contrib

Deed comes with some minor packages that will make your life a bit easier.

Base64

The package deed-base64 brings functions to encode values into a base64-encoded stream, and read them back. This is useful when passing encoded data throughout a text format, for example JSON. The package relies on Base64OutputStream and Base64InputStream classes from the Apacke Commons Codec library. As it's a third-party dependency, the functionalty is shipped in a sub-package.

A quick example:

(ns deed-base64-demo
  (:require
   [deed.core :as deed]
   [deed.base64 :as b64]))

(with-open [out (-> "dump.deed.b64"
                    (b64/base64-output-stream))]
  (deed/encode-to [1 2 3] out))

The base64-output-stream function wraps any source and makes an instance of Base64OutputStream. As you write to it, the data gets silently base64-encoded:

(slurp "dump.deed.b64")
"AAEAAQAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAuAAAAAwAOAAwAAAAAAAAAAgAMAAAAAAAAAAM="

Read it again by wrapping the file into the base64-input-stream function:

(with-open [in (-> "dump.deed.b64"
                   (io/file)
                   (b64/base64-input-stream))]
  (deed/decode-from in))

;; [1 2 3]

The deed.base64 namespace provides a number of shortcuts, namely:

Function	Comment
encode-to-base64-bytes	Encode a single value into base64 byte array
encode-seq-to-base64-bytes	Encode a sequence of values into a base64 byte array
encode-to-base64-string	Encode a single value into a base64 string
encode-seq-to-base64-string	Encode a sequence of values into a base64 string
decode-from-base64-bytes	Decode a single value from a base64 byte array
decode-from-base64-string	Decode a single value from a base64 string
decode-seq-from-base64-bytes	Decode a sequence of values from base64 byte array
decode-seq-from-base64-string	Decode a sequence of values from base64 string

Their signatures are similar to what we've covered so far.

VectorZ

The deed-vectorz package extends Deed with classes the from the mikera/vectorz library. These vectors are good for fast computations. A brief demo:

(ns demo
  (:require
   [deed.core :as deed]
   [deed.vectorz :as vz])
  (:import
   (mikera.vectorz Vectorz)))

(def vz
  (Vectorz/create (double-array [1.1 2.2 3.3])))

(def dump
  (deed/encode-to-bytes vz))

(deed/decode-from dump)
;; #object[mikera.vectorz.Vector3 0x5ecb1a9a "[1.1,2.2,3.3]"]

The Vectorz class is a general factory for other classes like Vector1, Vector2 and similar. Deed extends the AVector class which is common for all of these.

Binary Format

The binary payload of Deed is quite simple. It consists from the following pattern:

<2-byte-OID><content><2-byte-OID><content>...

At the beginning, there is always a deed.Header object with general information about how encoding was made. At the moment, it only tracks the version of the protocol and nothing else. The header has constant size of 30 bytes where unused bytes are reserved. In there future, there might be more data in the header.

The content depend on the nature of a type. Say, if it's an integer, there are always four bytes. If it's a string, than we have four-byte length of the upcoming byte array, and then the array by itself.

Counted collections are encoded whis way too. First, there is a total length of a collection, and the items encoded one by one. As the items might be of different types, they have their own OIDs:

<2-byte-vector-id><4-byte-vector-length><oid-item-1><payload-item-1><oid-item-2><payload-item-2>

This section, perhaps is not too detailed at the moment, will be extended in the future. For now, check out the source code: see the Encoder.java and Decoder.java files.

Benchmarks

Deed is a bit faster than Nippy as it's written mostly in Java. The time difference depends on the nature of data being processed, but in general Deed is about 1.3-1.5 times faster. Here are encoding metrics made on two various machines using the Criterium library:

Decode measurements made for the same data:

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Ivan Grishaev, 2024