utf8: add function to detect prohibited UTF-16/32 BOM

diff --git a/utf8.c b/utf8.c
index 40f4b142d6983cb134992ffffa07413b75a6cece..83af3a9f6b7b0ea81992154018b0e2083a00685f 100644 (file)
--- a/utf8.c
+++ b/utf8.c
@@ -560,6 +560,32 @@ char *reencode_string_len(const char *in, int insz,
 }
 #endif
 
+static int has_bom_prefix(const char *data, size_t len,
+                         const char *bom, size_t bom_len)
+{
+       return data && bom && (len >= bom_len) && !memcmp(data, bom, bom_len);
+}
+
+static const char utf16_be_bom[] = {0xFE, 0xFF};
+static const char utf16_le_bom[] = {0xFF, 0xFE};
+static const char utf32_be_bom[] = {0x00, 0x00, 0xFE, 0xFF};
+static const char utf32_le_bom[] = {0xFF, 0xFE, 0x00, 0x00};
+
+int has_prohibited_utf_bom(const char *enc, const char *data, size_t len)
+{
+       return (
+         (same_utf_encoding("UTF-16BE", enc) ||
+          same_utf_encoding("UTF-16LE", enc)) &&
+         (has_bom_prefix(data, len, utf16_be_bom, sizeof(utf16_be_bom)) ||
+          has_bom_prefix(data, len, utf16_le_bom, sizeof(utf16_le_bom)))
+       ) || (
+         (same_utf_encoding("UTF-32BE",  enc) ||
+          same_utf_encoding("UTF-32LE", enc)) &&
+         (has_bom_prefix(data, len, utf32_be_bom, sizeof(utf32_be_bom)) ||
+          has_bom_prefix(data, len, utf32_le_bom, sizeof(utf32_le_bom)))
+       );
+}
+
 /*
  * Returns first character length in bytes for multi-byte `text` according to
  * `encoding`.