Fix read of number followed by EOF can break subsequent read from seeing EOF

Author: puredanger

README.md

@@ -151,7 +151,8 @@ Change Log
 ----------------------------------------
 
 * next
-  * In `read`, update docstring to specify minimum buffer size if PushbackReader supplied
+  * Fix: `read` of number followed by EOF can break subsequent read from seeing EOF
+  * In `read`, update docstring to specify minimum buffer size when PushbackReader supplied
 * Release [2.5.0] on 2023-Dec-21
   * Fix [DJSON-50]: `read` can take a PushbackReader for repeated read use case
   * Fix `write` docstring to add `:indent` option added in [DJSON-18]

src/main/clojure/clojure/data/json.clj

@@ -33,6 +33,7 @@
   (readChars [_  buffer start bufflen]
     (.read rdr ^chars buffer start bufflen))
   (unreadChar [_ c]
+    ;; ASSERT: c should never be -1 (EOF)
     (.unread rdr c))
   (unreadChars [_ buffer start bufflen]
     (.unread rdr buffer start bufflen))
@@ -63,6 +64,7 @@
           (.getChars ^String s p end ^chars buffer start)))
       (if (pos? n) n -1)))
   (unreadChar [_ _c]
+    ;; ASSERT: c should never be -1 (EOF)
     (set! pos (unchecked-dec pos))
     nil)
   (unreadChars [_ _buffer _start bufflen]
@@ -234,9 +236,11 @@
                          :whitespace
                          (do (.unreadChar stream c)
                              false)
-                         (\, \] \} -1)
+                         (\, \] \})
                          (do (.unreadChar stream c)
                              false)
+                         -1
+                         false
                          (throw (Exception. "JSON error (invalid number literal)")))
                        ;; previous character is a "0"
                        :frac-point
@@ -251,9 +255,11 @@
                          :whitespace
                          (do (.unreadChar stream c)
                              false)
-                         (\, \] \} -1)
+                         (\, \] \})
                          (do (.unreadChar stream c)
                              false)
+                         -1
+                         false
                          ;; Disallow zero-padded numbers or invalid characters
                          (throw (Exception. "JSON error (invalid number literal)")))
                        ;; previous character is a "."
@@ -276,9 +282,11 @@
                          :whitespace
                          (do (.unreadChar stream c)
                              true)
-                         (\, \] \} -1)
+                         (\, \] \})
                          (do (.unreadChar stream c)
                              true)
+                         -1
+                         true
                          (throw (Exception. "JSON error (invalid number literal)")))
                        ;; previous character is a "e" or "E"
                        :exp-symbol
@@ -306,9 +314,11 @@
                          :whitespace
                          (do (.unreadChar stream c)
                              true)
-                         (\, \] \} -1)
+                         (\, \] \})
                          (do (.unreadChar stream c)
                              true)
+                         -1
+                         true
                          (throw (Exception. "JSON error (invalid number literal)"))))))]
     (if decimal?
       (read-decimal (str buffer) bigdec?)

src/test/clojure/clojure/data/json_test.clj

@@ -27,6 +27,24 @@
     (is (= {"foo" "some string"} (json/read pbr)))
     (is (= {"foo" "another long ......................................................... string"} (json/read pbr)))))
 
+(defn read-then-eof [s]
+  (let [r (pbr s)
+        val (json/read r :eof-error? false :eof-value :EOF)]
+    (is (= :EOF (json/read r :eof-error? false :eof-value :EOF)))
+    val))
+
+(deftest read-multiple-eof
+  (are [expected s] (= expected (read-then-eof s))
+    1.2 "1.2"
+    0 "0"
+    1 "1"
+    1.0 "1.0"
+    "abc" "\"abc\""
+    "\u2202" "\"\u2202\""
+    [] "[]"
+    [1 2] "[1, 2]")
+  )
+
 (deftest read-from-reader
   (let [s (java.io.StringReader. "42")]
     (is (= 42 (json/read s)))))