Jonathan Nieder <[email protected]> writes:
> Signed-off-by: Jonathan Nieder <[email protected]>
> ---
> Junio C Hamano wrote:
>> Jonathan Nieder <[email protected]> writes:
>
>>> -extern int copy_fd(int ifd, int ofd);
>>> +extern int copy_fd(int ifd, int ofd, struct strbuf *err);
>>
>> It is not limited to this single function, but what contract do we
>> envision this "error messages are given back to the caller via
>> strbuf" convention should give between the callers and the callee?
>
> Here's a draft for documentation on that.
Thanks; looks reasonable; even if the discussion between you and
Peff took us to a slightly different direction than what you
described here, the earlier description of long established practice
is a welcome addition.
> Documentation/technical/api-error-handling.txt | 75
> ++++++++++++++++++++++++++
> 1 file changed, 75 insertions(+)
> create mode 100644 Documentation/technical/api-error-handling.txt
>
> diff --git a/Documentation/technical/api-error-handling.txt
> b/Documentation/technical/api-error-handling.txt
> new file mode 100644
> index 0000000..fc68db1
> --- /dev/null
> +++ b/Documentation/technical/api-error-handling.txt
> @@ -0,0 +1,75 @@
> +Error reporting in git
> +======================
> +
> +`die`, `usage`, `error`, and `warning` report errors of various
> +kinds.
> +
> +- `die` is for fatal application errors. It prints a message to
> + the user and exits with status 128.
> +
> +- `usage` is for errors in command line usage. After printing its
> + message, it exits with status 129. (See also `usage_with_options`
> + in the link:api-parse-options.html[parse-options API].)
> +
> +- `error` is for non-fatal library errors. It prints a message
> + to the user and returns -1 for convenience in signaling the error
> + to the caller.
> +
> +- `warning` is for reporting situations that probably should not
> + occur but which the user (and Git) can continue to work around
> + without running into too many problems. Like `error`, it
> + returns -1 after reporting the situation to the caller.
> +
> +Customizable error handlers
> +---------------------------
> +
> +The default behavior of `die` and `error` is to write a message to
> +stderr and then exit or return as appropriate. This behavior can be
> +overridden using `set_die_routine` and `set_error_routine`. For
> +example, "git daemon" uses set_die_routine to write the reason `die`
> +was called to syslog before exiting.
> +
> +Library errors
> +--------------
> +
> +Functions return a negative integer on error. Details beyond that
> +vary from function to function:
> +
> +- Some functions return -1 for all errors. Others return a more
> + specific value depending on how the caller might want to react
> + to the error.
> +
> +- Some functions report the error to stderr with `error`,
> + while others leave that for the caller to do.
> +
> +- errno is not meaningful on return from most functions (except
> + for thin wrappers for system calls).
> +
> +Check the function's API documentation to be sure.
> +
> +Caller-handled errors
> +---------------------
> +
> +An increasing number of functions take a parameter 'struct strbuf *err'.
> +On error, such functions append a message about what went wrong to the
> +'err' strbuf. The message is meant to be complete enough to be passed
> +to `die` or `error` as-is. For example:
> +
> + if (ref_transaction_commit(transaction, &err))
> + die("%s", err.buf);
> +
> +The 'err' parameter will be untouched if no error occured, so multiple
> +function calls can be chained:
> +
> + t = ref_transaction_begin(&err);
> + if (!t ||
> + ref_transaction_update(t, "HEAD", ..., &err) ||
> + ret_transaction_commit(t, &err))
> + die("%s", err.buf);
> +
> +The 'err' parameter must be a pointer to a valid strbuf. To silence
> +a message, pass a strbuf that is explicitly ignored:
> +
> + if (thing_that_can_fail_in_an_ignorable_way(..., &err))
> + /* This failure is okay. */
> + strbuf_reset(&err);
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