Add read-values and write-values

read-values dispatches to the ReadValues protocol. It returns an
iterator via an ObjectReader derived from the supplied mapper.
The returned iterator is reified in a manner similar to Eduction to
support reduction and sequence construction over it.

write-values relies on two protocols - WriteValues for the output
destination, similarly to WriteValue, and WriteAll for the type being
written, which can be an array or an Iterable.
It writes an array or iterable to destination via a SequenceWriter.
Importantly, write-values distables automatic flushing on serialization
to get good performance.

src/clj/jsonista/core.clj

@@ -60,13 +60,13 @@
       RatioSerializer FunctionalKeywordSerializer)
     (com.fasterxml.jackson.core JsonGenerator$Feature JsonFactory)
     (com.fasterxml.jackson.databind
-      JsonSerializer ObjectMapper module.SimpleModule
+      JsonSerializer ObjectMapper SequenceWriter
       SerializationFeature DeserializationFeature Module)
     (com.fasterxml.jackson.databind.module SimpleModule)
     (java.io InputStream Writer File OutputStream DataOutput Reader)
     (java.net URL)
     (com.fasterxml.jackson.datatype.jsr310 JavaTimeModule)
-    (java.util List Map Date)
+    (java.util List Map Date Iterator)
     (clojure.lang Keyword Ratio Symbol)))
 
 (defn- ^Module clojure-module
@@ -194,6 +194,38 @@
   (-read-value [this ^ObjectMapper mapper]
     (.readValue mapper this ^Class Object)))
 
+(defprotocol ReadValues
+  (-read-values [this mapper]))
+
+(extend-protocol ReadValues
+
+  (Class/forName "[B")
+  (-read-values [this ^ObjectMapper mapper]
+    (.readValues (.readerFor mapper ^Class Object) ^bytes this))
+
+  nil
+  (-read-values [_ _])
+
+  File
+  (-read-values [this ^ObjectMapper mapper]
+    (.readValues (.readerFor mapper ^Class Object) this))
+
+  URL
+  (-read-values [this ^ObjectMapper mapper]
+    (.readValues (.readerFor mapper ^Class Object) this))
+
+  String
+  (-read-values [this ^ObjectMapper mapper]
+    (.readValues (.readerFor mapper ^Class Object) this))
+
+  Reader
+  (-read-values [this ^ObjectMapper mapper]
+    (.readValues (.readerFor mapper ^Class Object) this))
+
+  InputStream
+  (-read-values [this ^ObjectMapper mapper]
+    (.readValues (.readerFor mapper ^Class Object) this)))
+
 (defprotocol WriteValue
   (-write-value [this value mapper]))
 
@@ -214,6 +246,50 @@
   (-write-value [this value ^ObjectMapper mapper]
     (.writeValue mapper this value)))
 
+(defprotocol WriteAll
+  (-write-all [this ^SequenceWriter writer]))
+
+(extend-protocol WriteAll
+
+  (Class/forName "[Ljava.lang.Object;")
+  (-write-all [this ^SequenceWriter w]
+    (.writeAll w ^"[Ljava.lang.Object;" this))
+
+  Iterable
+  (-write-all [this ^SequenceWriter w]
+    (.writeAll w this)))
+
+(defprotocol WriteValues
+  (-write-values [this values mapper]))
+
+(defmacro ^:private -write-values*
+  [this value mapper]
+  `(doto ^SequenceWriter
+       (-write-all
+        ~value
+        (-> ~mapper
+            (.writerFor Object)
+            (.without SerializationFeature/FLUSH_AFTER_WRITE_VALUE)
+            (.writeValuesAsArray ~this)))
+     (.close)))
+
+(extend-protocol WriteValues
+  File
+  (-write-values [this value ^ObjectMapper mapper]
+    (-write-values* this value mapper))
+
+  OutputStream
+  (-write-values [this value ^ObjectMapper mapper]
+    (-write-values* this value mapper))
+
+  DataOutput
+  (-write-values [this value ^ObjectMapper mapper]
+    (-write-values* this value mapper))
+
+  Writer
+  (-write-values [this value ^ObjectMapper mapper]
+    (-write-values* this value mapper)))
+
 ;;
 ;; public api
 ;;
@@ -259,3 +335,54 @@
    (-write-value to object default-object-mapper))
   ([to object ^ObjectMapper mapper]
    (-write-value to object mapper)))
+
+(defn- wrap-values
+  [^Iterator iterator]
+  (reify
+    Iterable
+    (iterator [this] iterator)
+    Iterator
+    (hasNext [this] (.hasNext iterator))
+    (next [this] (.next iterator))
+    (remove [this] (.remove iterator))
+    clojure.lang.IReduceInit
+    (reduce [_ f val]
+      (loop [ret val]
+        (if (.hasNext iterator)
+          (let [ret (f ret (.next iterator))]
+            (if (reduced? ret)
+              @ret
+              (recur ret)))
+          ret)))
+    clojure.lang.Sequential))
+
+(defn read-values
+  "Decodes a sequence of values from a JSON as an iterator
+  from anything that satisfies [[ReadValue]] protocol.
+  By default, File, URL, String, Reader and InputStream are supported.
+
+  The returned object is an Iterable, Iterator and IReduceInit.
+  It can be reduced on via [[reduce]] and turned into a lazy sequence
+  via [[iterator-seq]].
+
+  To configure, pass in an ObjectMapper created with [[object-mapper]],
+  see [[object-mapper]] docstring for the available options."
+  "Read a stream of values via an iterator.
+  Returned object is an Iterable, Iterator and reducible, similar to Eduction."
+  ([object]
+   (wrap-values (-read-values object default-object-mapper)))
+  ([object ^ObjectMapper mapper]
+   (wrap-values (-read-values object mapper))))
+
+(defn write-values
+  "Encode values as JSON and write using the provided [[WriteValue]] instance.
+  By default, File, OutputStream, DataOutput and Writer are supported.
+
+  By default, values can be an array or an Iterable.
+
+  To configure, pass in an ObjectMapper created with [[object-mapper]],
+  see [[object-mapper]] docstring for the available options."
+  ([to object]
+   (-write-values to object default-object-mapper))
+  ([to object ^ObjectMapper mapper]
+   (-write-values to object mapper)))