From 52da1564e630ce766e33458123996470e8806c3c Mon Sep 17 00:00:00 2001
From: Vincent Lee <vincent@vincent-lee.net>
Date: Wed, 14 Apr 2021 20:22:15 -0500
Subject: [PATCH] Explicitly throw on early EOF in decoder

---
 decode.rkt | 46 ++++++++++++++++++++++++++--------------------
 1 file changed, 26 insertions(+), 20 deletions(-)

diff --git a/decode.rkt b/decode.rkt
index 9300a0b..1d89bc4 100644
--- a/decode.rkt
+++ b/decode.rkt
@@ -5,6 +5,12 @@
 
 (provide cbor-read)
 
+(define (expect-byte port)
+  (define res (read-byte port))
+  (if (byte? res)
+      res
+      (error "Unexpected EOF")))
+
 ; read n bytes from port into buf. n is inferred from the length of buf
 (define (read-n-bytes buf port)
   (define n (bytes-length buf))
@@ -12,34 +18,34 @@
     (if (= cur n)
         buf
         (begin
-          (bytes-set! buf cur (read-byte port))
+          (bytes-set! buf cur (expect-byte port))
           (loop (add1 cur))))))
 
 (define (read-argument port major additional)
   (if (< additional 24)
       additional
       (case additional
-        [(24) (read-byte port)]
+        [(24) (expect-byte port)]
         [(25)
          (bitwise-ior
-          (arithmetic-shift (read-byte port) 8)
-          (read-byte port))]
+          (arithmetic-shift (expect-byte port) 8)
+          (expect-byte port))]
         [(26)
          (bitwise-ior
-          (arithmetic-shift (read-byte port) 24)
-          (arithmetic-shift (read-byte port) 16)
-          (arithmetic-shift (read-byte port) 8)
-          (read-byte port))]
+          (arithmetic-shift (expect-byte port) 24)
+          (arithmetic-shift (expect-byte port) 16)
+          (arithmetic-shift (expect-byte port) 8)
+          (expect-byte port))]
         [(27)
          (bitwise-ior
-          (arithmetic-shift (read-byte port) 56)
-          (arithmetic-shift (read-byte port) 48)
-          (arithmetic-shift (read-byte port) 40)
-          (arithmetic-shift (read-byte port) 32)
-          (arithmetic-shift (read-byte port) 24)
-          (arithmetic-shift (read-byte port) 16)
-          (arithmetic-shift (read-byte port) 8)
-          (read-byte port))]
+          (arithmetic-shift (expect-byte port) 56)
+          (arithmetic-shift (expect-byte port) 48)
+          (arithmetic-shift (expect-byte port) 40)
+          (arithmetic-shift (expect-byte port) 32)
+          (arithmetic-shift (expect-byte port) 24)
+          (arithmetic-shift (expect-byte port) 16)
+          (arithmetic-shift (expect-byte port) 8)
+          (expect-byte port))]
         [(28 29 30) (error "Argument with additional ~a is reserved" additional)]
         [(31) (case major
                 [(0 1 6) (error "Major ~a with additional ~a is malformed" major additional)]
@@ -158,14 +164,14 @@
       (parse-simple-value config additional)
       (case additional
         [(24)
-         (let ([extra (read-byte port)])
+         (let ([extra (expect-byte port)])
            (if (< extra 32)
                (error "Simple value used extra byte to encode ~a when it should have been in the initial byte" extra)
                (parse-simple-value config extra)))]
         [(25)
          (decode-half (bitwise-ior
-                       (arithmetic-shift (read-byte port) 8)
-                       (read-byte port)))]
+                       (arithmetic-shift (expect-byte port) 8)
+                       (expect-byte port)))]
         [(26)
          (define buf (bytes 0 0 0 0))
          (read-n-bytes buf port)
@@ -216,7 +222,7 @@
 
 ; Deserialize one cbor value from the given input port. Can and will be called reentrantly.
 (define (cbor-read config in)
-  (define header (read-byte in))
+  (define header (expect-byte in))
   (let ([major (bitwise-bit-field header 5 8)]
         [additional (bitwise-and header #b11111)])
     ((vector-ref major-dispatch-table major) config in additional)))
-- 
2.45.2