Hi Jiri,
well this is maybe the least important problem that libhttp has. Why don't
you just fix libhttp so that each of its functions either returns errno_t or
an http_error_t that is completely separate type from errno_t?
Regards,
Jiri
---------- Původní e-mail ----------
Od: Jiří Zárevúcky <zarevucky.j...@gmail.com>
Komu: HelenOS development mailing list <helenos-devel@lists.modry.cz>
Datum: 6. 12. 2017 16:19:24
Předmět: [HelenOS-devel] [RFC] Locally extensible error returns
"Hello,
For context: I've been working on fixing our errno.h use for the past
two days. It's going very well, I'll probably be done by tomorrow, and
I'll write a blog post about the entire process after I'm finished.
The issue I'm facing now is simple: libhttp uses errno.h error codes,
but also defines its own bunch of error conditions, mixing them with
returns from libc functions. Obviously, this is not ideal. Such errors
can start conflicting with others on a later date, without any
indication that something is wrong, and it's not possible to just use
strerror() on such a return value, or return it from an interface that
expects libc error codes (for example, imagine a HTTP data transport
abstracted as a pipe -- such code would need to translate
HTTP-specific error codes, but there is no indication on type level
that that's necessary).
That much for context. I thought about possible solutions, and this is
the best I came up so far. Instead of explaining in words, simplified
example of code:
----
// libc header
typedef struct {
const char *name;
const char *description;
} error_t;
extern const error_t *E_NOMEM;
extern const error_t *E_IO;
----
// libhttp header
extern const error_t *HTTP_E_HEADERS;
----
// libc object file
static error_t _NOMEM = { "E_NOMEM", "Out of memory" };
const error_t *E_NOMEM = &_NOMEM;
static error_t _IO = { "E_IO", "IO failed" };
const error_t *E_IO = &_IO;
----
// libhttp object file
static error_t _HEADERS = {"HTTP_E_HEADERS", "HTTP: Failed processing
headers" };
const error_t *HTTP_E_HEADERS = &_HEADERS;
----
// user
const error_t *err = http_func_1(...);
if (err == HTTP_E_HEADERS) {
// process error
} else if (err == E_IO) {
// process other error
} else {
// process all other errors
fprintf(stderr, "Failed http operation: [%s] %s\n", err->name,
err->description);
exit(1);
}
What do you think?
-- jzr
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