Fix input locale detection on Windows

Author: tsjensen

src/boxes.c

@@ -498,7 +498,7 @@ static void activateSystemEncoding()
         if (locale == NULL || setlocale(LC_ALL, locale) == NULL) {
             setlocale(LC_ALL, "");
         }
-        UINT codepage = get_console_codepage(locale_charset());
+        UINT codepage = get_console_codepage(get_default_encoding());
         SetConsoleOutputCP(codepage);
         SetConsoleCP(codepage);
     #else
@@ -547,12 +547,13 @@ int main(int argc, char *argv[])
 
     /* Temporarily set the system encoding, for proper output of --help text etc. */
     activateSystemEncoding();
-    encoding = locale_charset();
+    const char *system_encoding = get_default_encoding();
+    encoding = system_encoding;
 
     handle_command_line(argc, argv);
 
     /* Store system character encoding */
-    encoding = check_encoding(opt.encoding, locale_charset());
+    encoding = check_encoding(opt.encoding, system_encoding);
     log_debug(__FILE__, MAIN, "Character Encoding = %s\n", encoding);
 
     color_output_enabled = check_color_support(opt.color);

src/cmdline.c

@@ -38,6 +38,7 @@
 #include "logging.h"
 #include "query.h"
 #include "tools.h"
+#include "unicode.h"
 #include "cmdline.h"
 
 
@@ -104,7 +105,7 @@ void usage_long(FILE *st)
     fprintf(st, "      --no-kill-blank   Retain leading/trailing blank lines on removal (like -k false)\n");
     fprintf(st, "  -l, --list            List available box designs w/ samples\n");
     fprintf(st, "  -m, --mend            Mend (repair) box\n");
-    fprintf(st, "  -n, --encoding <enc>  Character encoding of input and output [default: %s]\n", locale_charset());
+    fprintf(st, "  -n, --encoding <enc>  Character encoding of input and output [default: %s]\n", get_default_encoding());
     fprintf(st, "  -p, --padding <fmt>   Padding [default: none]\n");
     fprintf(st, "  -q, --tag-query <qry> Query the list of designs by tag\n");
     fprintf(st, "  -r, --remove          Remove box\n");

src/unicode.c

@@ -23,6 +23,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <strings.h>
 
 #include <uniconv.h>
 #include <unictype.h>
@@ -57,6 +58,81 @@ const ucs4_t char_nul = 0x00000000;
 
 
 
+#ifdef _WIN32
+static const char *get_locale_from_environment()
+{
+    const char *locale = getenv("LC_ALL");
+    if (locale == NULL || locale[0] == '\0') {
+        locale = getenv("LC_CTYPE");
+    }
+    if (locale == NULL || locale[0] == '\0') {
+        locale = getenv("LANG");
+    }
+    return locale != NULL && locale[0] != '\0' ? locale : NULL;
+}
+
+
+static int is_all_digits(const char *s)
+{
+    if (s == NULL || s[0] == '\0') {
+        return 0;
+    }
+    for (const char *p = s; *p != '\0'; p++) {
+        if (*p < '0' || *p > '9') {
+            return 0;
+        }
+    }
+    return 1;
+}
+
+
+static const char *extract_locale_encoding(const char *locale)
+{
+    static char encoding_buffer[32];
+    if (locale == NULL) {
+        return NULL;
+    }
+
+    const char *dot = strrchr(locale, '.');
+    if (dot == NULL || dot[1] == '\0') {
+        return NULL;
+    }
+
+    const char *start = dot + 1;
+    const char *end = strchr(start, '@');
+    size_t len = end == NULL ? strlen(start) : (size_t) (end - start);
+    if (len == 0 || len >= sizeof(encoding_buffer)) {
+        return NULL;
+    }
+
+    memcpy(encoding_buffer, start, len);
+    encoding_buffer[len] = '\0';
+    if (strcasecmp(encoding_buffer, "UTF8") == 0
+            || strcasecmp(encoding_buffer, "UTF-8") == 0
+            || strcasecmp(encoding_buffer, "CP65001") == 0
+            || strcmp(encoding_buffer, "65001") == 0)
+    {
+        return "UTF-8";
+    }
+    if ((encoding_buffer[0] == 'C' || encoding_buffer[0] == 'c')
+            && (encoding_buffer[1] == 'P' || encoding_buffer[1] == 'p')
+            && is_all_digits(encoding_buffer + 2))
+    {
+        encoding_buffer[0] = 'C';
+        encoding_buffer[1] = 'P';
+        return encoding_buffer;
+    }
+    if (is_all_digits(encoding_buffer)) {
+        static char codepage_buffer[32];
+        snprintf(codepage_buffer, sizeof(codepage_buffer), "CP%s", encoding_buffer);
+        return codepage_buffer;
+    }
+    return encoding_buffer;
+}
+#endif
+
+
+
 int is_char_at(const uint32_t *text, const size_t idx, const ucs4_t expected_char)
 {
     return text != NULL && u32_cmp(text + idx, &expected_char, 1) == 0;
@@ -265,6 +341,22 @@ char *u32_strconv_to_arg(const uint32_t *src, const char *targetEncoding)
 
 
 
+const char *get_default_encoding()
+{
+    const char *system_encoding = locale_charset();
+
+    #ifdef _WIN32
+        const char *env_encoding = extract_locale_encoding(get_locale_from_environment());
+        if (env_encoding != NULL) {
+            return check_encoding(env_encoding, system_encoding);
+        }
+    #endif
+
+    return system_encoding;
+}
+
+
+
 const char *check_encoding(const char *manual_encoding, const char *system_encoding)
 {
     if (manual_encoding != NULL) {

src/unicode.h

@@ -195,6 +195,15 @@ char *u32_strconv_to_output(const uint32_t *src);
 char *u32_strconv_to_arg(const uint32_t *src, const char *targetEncoding);
 
 
+/**
+ * Determine the default character encoding for input and output text.
+ * On Windows, this prefers an explicit encoding suffix from `LC_ALL`, `LC_CTYPE`,
+ * or `LANG` when present; otherwise it falls back to the CRT locale.
+ * @return the default encoding name
+ */
+const char *get_default_encoding();
+
+
 /**
  * Check if the given `manual_encoding` can be used to covert anything. This should reveal invalid encoding names that
  * have been specified on the command line. If no `manual_encoding` was specified, or if an invalid encoding is