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;;; json/read.clj: JavaScript Object Notation (JSON) parser
;; by Stuart Sierra, http://stuartsierra.com/
;; January 26, 2009
;; Copyright (c) Stuart Sierra, 2009. All rights reserved. The use
;; and distribution terms for this software are covered by the Eclipse
;; Public License 1.0 (http://opensource.org/licenses/eclipse-1.0.php)
;; which can be found in the file epl-v10.html at the root of this
;; distribution. By using this software in any fashion, you are
;; agreeing to be bound by the terms of this license. You must not
;; remove this notice, or any other, from this software.
;; For more information on JSON, see http://www.json.org/
(ns clojure.contrib.json.read
(:import (java.io PushbackReader StringReader EOFException))
(:use [clojure.contrib.test-is :only (deftest is)]))
(declare read-json)
(defn- read-json-array [#^PushbackReader stream]
;; Expects to be called with the head of the stream AFTER the
;; opening bracket.
(loop [i (.read stream), result []]
(let [c (char i)]
(cond
(= i -1) (throw (EOFException. "JSON error (end-of-file inside array)"))
(Character/isWhitespace c) (recur (.read stream) result)
(= c \,) (recur (.read stream) result)
(= c \]) result
:else (do (.unread stream (int c))
(let [element (read-json stream)]
(recur (.read stream) (conj result element))))))))
(defn- read-json-object [#^PushbackReader stream]
;; Expects to be called with the head of the stream AFTER the
;; opening bracket.
(loop [i (.read stream), key nil, result {}]
(let [c (char i)]
(cond
(= i -1) (throw (EOFException. "JSON error (end-of-file inside object)"))
(Character/isWhitespace c) (recur (.read stream) key result)
(= c \,) (recur (.read stream) nil result)
(= c \:) (recur (.read stream) key result)
(= c \}) (if (nil? key)
result
(throw (Exception. "JSON error (key missing value in object)")))
:else (do (.unread stream i)
(let [element (read-json stream)]
(if (nil? key)
(if (string? element)
(recur (.read stream) element result)
(throw (Exception. "JSON error (non-string key in object)")))
(recur (.read stream) nil (assoc result key element)))))))))
(defn read-json
"Read the next JSON record from stream, which must be an instance of
java.io.PushbackReader."
([] (read-json *in* true nil))
([stream] (read-json stream true nil))
([#^PushbackReader stream eof-error? eof-value]
(loop [i (.read stream)]
(let [c (char i)]
(cond
;; Handle end-of-stream
(= i -1) (if eof-error?
(throw (EOFException. "JSON error (end-of-file)"))
eof-value)
;; Ignore whitespace
(Character/isWhitespace c) (recur (.read stream))
;; Read strings, numbers, true, and false with Clojure reader
(#{\" \- \0 \1 \2 \3 \4 \5 \6 \7 \8 \9} c)
(do (.unread stream i)
(read stream true nil))
;; Read null as nil
(= c \n) (let [ull [(char (.read stream))
(char (.read stream))
(char (.read stream))]]
(if (= ull [\u \l \l])
nil
(throw (Exception. (str "JSON error (expected null): " c ull)))))
;; Read true
(= c \t) (let [rue [(char (.read stream))
(char (.read stream))
(char (.read stream))]]
(if (= rue [\r \u \e])
true
(throw (Exception. (str "JSON error (expected true): " c rue)))))
;; Read false
(= c \f) (let [alse [(char (.read stream))
(char (.read stream))
(char (.read stream))
(char (.read stream))]]
(if (= alse [\a \l \s \e])
false
(throw (Exception. (str "JSON error (expected false): " c alse)))))
;; Read JSON objects
(= c \{) (read-json-object stream)
;; Read JSON arrays
(= c \[) (read-json-array stream)
:else (throw (Exception. (str "JSON error (unexpected character): " c))))))))
(defn read-json-string [string]
(read-json (PushbackReader. (StringReader. string))))
;;; TESTS
(deftest can-read-numbers
(is (= 42 (read-json-string "42")))
(is (= -3 (read-json-string "-3")))
(is (= 3.14159 (read-json-string "3.14159")))
(is (= 6.022e23 (read-json-string "6.022e23"))))
(deftest can-read-null
(is (= nil (read-json-string "null"))))
(deftest can-read-strings
(is (= "Hello, World!" (read-json-string "\"Hello, World!\""))))
(deftest can-read-booleans
(is (= true (read-json-string "true")))
(is (= false (read-json-string "false"))))
(deftest can-ignore-whitespace
(is (= nil (read-json-string "\r\n null"))))
(deftest can-read-arrays
(is (= [1 2 3] (read-json-string "[1,2,3]")))
(is (= ["Ole" "Lena"] (read-json-string "[\"Ole\", \r\n \"Lena\"]"))))
(deftest can-read-objects
(is (= {"a" 1, "b" 2} (read-json-string "{\"a\": 1, \"b\": 2}"))))
(deftest can-read-nested-structures
(is (= {"a" [1 2 {"b" [3 "four"]} 5.5]}
(read-json-string "{\"a\":[1,2,{\"b\":[3,\"four\"]},5.5]}"))))
(deftest disallows-non-string-keys
(is (thrown? Exception (read-json-string "{26:\"z\""))))
(deftest disallows-barewords
(is (thrown? Exception (read-json-string " foo "))))
(deftest disallows-unclosed-arrays
(is (thrown? Exception (read-json-string "[1, 2, "))))
(deftest disallows-unclosed-objects
(is (thrown? Exception (read-json-string "{\"a\":1, "))))
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