From a14b3740a45931f27a04b4947b5db6972981e72c Mon Sep 17 00:00:00 2001
From: Arun Isaac
Date: Sun, 12 Apr 2026 04:02:47 +0100
Subject: Error out when reading binary files.

---
 kaakaa/tools/base.scm | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/kaakaa/tools/base.scm b/kaakaa/tools/base.scm
index e726c14..a8d7b00 100644
--- a/kaakaa/tools/base.scm
+++ b/kaakaa/tools/base.scm
@@ -17,6 +17,7 @@
 ;;; along with kaakaa.  If not, see <https://www.gnu.org/licenses/>.
 
 (define-module (kaakaa tools base)
+  #:use-module (rnrs exceptions)
   #:use-module (rnrs io ports)
   #:use-module (guix build utils)
   #:use-module (srfi srfi-171)
@@ -24,6 +25,20 @@
   #:export (%list-files
             %base-tools))
 
+(define (binary-file? file)
+  "Return @code{#t} if @var{file} is a binary file. Else, return @code{#f}."
+  ;; We use the following heuristic: If there are character decoding errors in
+  ;; the first 10K characters, we assume that this is a binary file.
+  (guard (c ((or (i/o-decoding-error? c)
+                 (eq? (exception-kind c)
+                      'decoding-error))
+             #t))
+    (call-with-input-file file
+      (lambda (port)
+        (set-port-conversion-strategy! port 'error)
+        (get-string-n port (* 10 1024))))
+    #f))
+
 (define %read
   (tool #:description "Read whole text file, or optionally a subset of its lines.
 
@@ -45,6 +60,11 @@ Line numbers start from 1. Output is the raw file contents without line numbers.
                            "Error: File ~a does not exist~%"
                            path)
                    (exit #f))
+                  ((binary-file? path)
+                   (format (current-output-port)
+                           "Error: File ~a is binary, not text~%"
+                           path)
+                   (exit #f))
                   (else
                    (call-with-input-file path
                      (cut port-transduce
-- 
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