Here is a test program that defines a Guile extension to convert invalid UTF-8 bytes to a string using each of the failed conversion handlers described at
https://www.gnu.org/software/guile/manual/html_node/Conversion-to_002ffrom-C.html#index-scm_005ft_005fstring_005ffailed_005fconversion_005fhandler ``` #include <libguile.h> static char str[] = { 208, 151, 208, 178, 208, 184, 209, 135, 208, 176, 208, 185, 208, 189, 208, 184, 208, 102, 97, 109, 105, 108, 121 }; SCM error_test (void) { return scm_from_stringn (str, sizeof(str), "UTF-8", SCM_FAILED_CONVERSION_ERROR); } SCM question_mark_test (void) { return scm_from_stringn (str, sizeof(str), "UTF-8", SCM_FAILED_CONVERSION_QUESTION_MARK); } SCM escape_test (void) { return scm_from_stringn (str, sizeof(str), "UTF-8", SCM_FAILED_CONVERSION_ESCAPE_SEQUENCE); } void init_test () { scm_c_define_gsubr ("conversion-error-test", 0, 0, 0, error_test); scm_c_define_gsubr ("conversion-question-mark-test", 0, 0, 0, question_mark_test); scm_c_define_gsubr ("conversion-escape-test", 0, 0, 0, escape_test); } ``` If I compile this program using ``` gcc $(pkg-config --cflags --libs guile-3.0) -shared -o libguile-conversion-test.so -fPIC test.c ``` load the resulting extension into Guile, and run the functions, all of them throw errors. I would expect SCM_FAILED_CONVERSION_ERROR to throw an error, of course, and SCM_FAILED_CONVERSION_ESCAPE_SEQUENCE is documented as being irrelevant to converting C strings to Scheme. However, I would not expect using SCM_FAILED_CONVERSION_QUESTION_MARK to throw a conversion error. Here is the output I get from Guile: ``` GNU Guile 3.0.9 Copyright (C) 1995-2023 Free Software Foundation, Inc. Guile comes with ABSOLUTELY NO WARRANTY; for details type `,show w'. This program is free software, and you are welcome to redistribute it under certain conditions; type `,show c' for details. Enter `,help' for help. scheme@(guile-user)> (load-extension "./libguile-conversion-test.so" "init_test") scheme@(guile-user)> (conversion-error-test) ice-9/boot-9.scm:1685:16: In procedure raise-exception: Throw to key `decoding-error' with args `("scm_from_utf8_stringn" "input locale conversion error" 0 #vu8(208 151 208 178 208 184 209 135 208 176 208 185 208 189 208 184 208 102 97 109 105 108 121))'. Entering a new prompt. Type `,bt' for a backtrace or `,q' to continue. scheme@(guile-user) [1]> ,q scheme@(guile-user)> (conversion-question-mark-test) ice-9/boot-9.scm:1685:16: In procedure raise-exception: Throw to key `decoding-error' with args `("scm_from_stringn" "input locale conversion error" 92 #vu8(208 151 208 178 208 184 209 135 208 176 208 185 208 189 208 184 208 102 97 109 105 108 121))'. Entering a new prompt. Type `,bt' for a backtrace or `,q' to continue. scheme@(guile-user) [1]> ,q scheme@(guile-user)> (conversion-escape-test) ice-9/boot-9.scm:1685:16: In procedure raise-exception: Throw to key `decoding-error' with args `("scm_from_stringn" "input locale conversion error" 92 #vu8(208 151 208 178 208 184 209 135 208 176 208 185 208 189 208 184 208 102 97 109 105 108 121))'. Entering a new prompt. Type `,bt' for a backtrace or `,q' to continue. ``` Note that it is possible to convert those bytes to a string without an error using bytevector->string, which is documented as the Scheme interface to scm_from_stringn: https://www.gnu.org/software/guile/manual/html_node/Conversion-to_002ffrom-C.html#index-scm_005ffrom_005fstringn ``` scheme@(guile-user)> (use-modules (ice-9 iconv)) scheme@(guile-user)> (bytevector->string #vu8(208 151 208 178 208 184 209 135 208 176 208 185 208 189 208 184 208 102 97 109 105 108 121) "UTF-8" 'substitute) $1 = "Звичайни�family" ```
