utils: Do not return eof if matched at beginning.

* email/utils.scm (read-while, read-bytes-till): Do not return eof if
matched at beginning. Return empty string or bytevector respectively.
* tests/utils.scm ("read-bytes-till returns empty bytevector on match
at beginning", "read-while returns empty string on match at
beginning"): New tests.

2 files changed, 30 insertions, 8 deletions

diff --git a/email/utils.scm b/email/utils.scm
index 70153be..984f07e 100644
--- a/email/utils.scm
+++ b/email/utils.scm
@@ -1,5 +1,5 @@
 ;;; guile-email --- Guile email parser
-;;; Copyright © 2018, 2019 Arun Isaac <arunisaac@systemreboot.net>
+;;; Copyright © 2018, 2019, 2020 Arun Isaac <arunisaac@systemreboot.net>
 ;;;
 ;;; This file is part of guile-email.
 ;;;
@@ -24,7 +24,7 @@
   #:use-module (ice-9 textual-ports)
   #:use-module (rnrs bytevectors)
   #:use-module ((rnrs io ports)
-                #:select (call-with-bytevector-output-port))
+                #:select (call-with-port))
   #:use-module (rnrs io simple)
   #:use-module (srfi srfi-1)
   #:use-module (srfi srfi-26)
@@ -58,8 +58,14 @@ back into PORT."
         (read-while-loop output))
        (else (unget-string port x)))))
 
-  (let ((str (call-with-output-string read-while-loop)))
-    (if (string-null? str) (eof-object) str)))
+  (call-with-port (open-output-string)
+    (lambda (out)
+      (let ((read-result (read-while-loop out))
+            (str (get-output-string out)))
+        (if (and (eof-object? read-result)
+                 (string-null? str))
+            read-result
+            str)))))
 
 (define (read-bytes-till port sequence)
   "Read bytes from PORT until byte SEQUENCE is seen or end-of-file is
@@ -82,9 +88,14 @@ reached. If SEQUENCE is seen, unget it to PORT and return."
        (else (put-u8 out octet)
              (read-bytes-and-write-till in out sequence)))))
 
-  (let ((bv (call-with-bytevector-output-port
-             (cut read-bytes-and-write-till port <> sequence))))
-    (if (bytevector=? bv (make-bytevector 0)) (eof-object) bv)))
+  (call-with-values open-bytevector-output-port
+    (lambda (out get-bytevector)
+      (let ((read-result (read-bytes-and-write-till port out sequence))
+            (bv (get-bytevector)))
+        (if (and (eof-object? read-result)
+                 (bytevector=? bv #vu8()))
+            read-result
+            bv)))))
 
 (define (get-line-with-delimiter port)
   "Read a line from PORT and return it as a string including the
diff --git a/tests/utils.scm b/tests/utils.scm
index 7681c72..ce8fdb2 100644
--- a/tests/utils.scm
+++ b/tests/utils.scm
@@ -1,5 +1,5 @@
 ;;; guile-email --- Guile email parser
-;;; Copyright © 2019 Arun Isaac <arunisaac@systemreboot.net>
+;;; Copyright © 2019, 2020 Arun Isaac <arunisaac@systemreboot.net>
 ;;;
 ;;; This file is part of guile-email.
 ;;;
@@ -35,4 +35,15 @@
    (call-with-input-string ""
      (cut read-while <> read identity))))
 
+(test-equal "read-bytes-till returns empty bytevector on match at beginning"
+  (call-with-port (open-bytevector-input-port #vu8(1 2 3))
+    (cut read-bytes-till <> #vu8(1 2)))
+  #vu8())
+
+(test-equal "read-while returns empty string on match at beginning"
+  (call-with-input-string "foo\nbar"
+    (lambda (port)
+      (read-while port get-line (negate (cut string-prefix? "foo" <>)))))
+  "")
+
 (test-end "utils")