NAME

       sd_bus_error, SD_BUS_ERROR_MAKE_CONST, SD_BUS_ERROR_NULL, sd_bus_error_free,
       sd_bus_error_set, sd_bus_error_setf, sd_bus_error_set_const, sd_bus_error_set_errno,
       sd_bus_error_set_errnof, sd_bus_error_set_errnofv, sd_bus_error_get_errno,
       sd_bus_error_copy, sd_bus_error_move, sd_bus_error_is_set, sd_bus_error_has_name,
       sd_bus_error_has_names_sentinel, sd_bus_error_has_names - sd-bus error handling

SYNOPSIS

       #include <systemd/sd-bus.h>

       typedef struct {
               const char *name;
               const char *message;
               ...
       } sd_bus_error;

       SD_BUS_ERROR_MAKE_CONST(name, message)

       SD_BUS_ERROR_NULL

       void sd_bus_error_free(sd_bus_error *e);

       int sd_bus_error_set(sd_bus_error *e, const char *name, const char *message);

       int sd_bus_error_setf(sd_bus_error *e, const char *name, const char *format, ...);

       int sd_bus_error_set_const(sd_bus_error *e, const char *name, const char *message);

       int sd_bus_error_set_errno(sd_bus_error *e, int error);

       int sd_bus_error_set_errnof(sd_bus_error *e, int error, const char *format, ...);

       int sd_bus_error_set_errnofv(sd_bus_error *e, int error, const char *format, va_list ap);

       int sd_bus_error_get_errno(const sd_bus_error *e);

       int sd_bus_error_copy(sd_bus_error *dst, const sd_bus_error *e);

       int sd_bus_error_move(sd_bus_error *dst, sd_bus_error *e);

       int sd_bus_error_is_set(const sd_bus_error *e);

       int sd_bus_error_has_name(const sd_bus_error *e, const char *name);

       int sd_bus_error_has_names_sentinel(const sd_bus_error *e, ...);

       #define sd_bus_error_has_names(e, ...) sd_bus_error_has_names_sentinel(e, ..., NULL)

DESCRIPTION

       The sd_bus_error structure carries information about a D-Bus error condition, or lack
       thereof. The functions described below may be used to set and query fields in this
       structure.

       •   The name field contains a short identifier of an error. It should follow the rules for
           error names described in the D-Bus specification, subsection Valid Names[1]. A number
           of common, standardized error names are described in sd-bus-errors(3), but additional
           domain-specific errors may be defined by applications.

       •   The message field usually contains a human-readable string describing the details, but
           might be NULL.

       An unset sd_bus_error structure should have both fields initialized to NULL, and signifies
       lack of an error, i.e. success. Assign SD_BUS_ERROR_NULL to the structure in order to
       initialize both fields to NULL. When no longer necessary, resources held by the
       sd_bus_error structure should be destroyed with sd_bus_error_free().

       sd_bus_error_set() sets an error structure to the specified name and message strings. The
       strings will be copied into internal, newly allocated memory. It is essential to free the
       contents again when they are not required anymore (see above). Do not use this call on
       error structures that have already been set. If you intend to reuse an error structure,
       free the old data stored in it with sd_bus_error_free() first.

       sd_bus_error_set() will return an errno-like value (see errno(3)) determined from the
       specified error name name. If name is NULL, it is assumed that no error occurred, and 0 is
       returned. If name is nonnull, a negative value is always returned. If e is NULL, no error
       structure is initialized, but name is still converted into an errno-style value.

       Various well-known D-Bus errors are converted to well-known errno counterparts, and the
       other ones to -EIO. See sd-bus-errors(3) for a list of well-known error names. Additional
       error mappings may be defined with sd_bus_error_add_map(3).

       sd_bus_error_set() is designed to be conveniently used in a return statement. If message
       is NULL, no message is set. This call can fail if no memory may be allocated for the name
       and message strings, in which case an SD_BUS_ERROR_NO_MEMORY error will be set instead and
       -ENOMEM returned.

       sd_bus_error_setf() is similar to sd_bus_error_set(), but takes a printf(3) format string
       and corresponding arguments to generate the message field.

       sd_bus_error_set_const() is similar to sd_bus_error_set(), but the string parameters are
       not copied internally, and must hence remain constant and valid for the lifetime of e. Use
       this call to avoid memory allocations when setting error structures. Since this call does
       not allocate memory, it will not fail with an out-of-memory condition as
       sd_bus_error_set() may, as described above. Alternatively, the SD_BUS_ERROR_MAKE_CONST()
       macro may be used to generate a literal, constant bus error structure on-the-fly.

       sd_bus_error_set_errno() will immediately return 0 if the specified error parameter error
       is 0. Otherwise, it will set name from an errno-like value that is converted to a D-Bus
       error.  strerror_r(3) will be used to set message. Well-known D-Bus error names will be
       used for name if applicable, otherwise a name in the "System.Error."  namespace will be
       generated. The sign of the specified error number is ignored and the absolute value is
       used implicitly. If the specified error error is non-zero, the call always returns a
       negative value, for convenient usage in return statements. This call might fail due to
       lack of memory, in which case an SD_BUS_ERROR_NO_MEMORY error is set instead, and -ENOMEM
       is returned.

       sd_bus_error_set_errnof() is similar to sd_bus_error_set_errno(), but in addition to
       error, takes a printf(3) format string and corresponding arguments. The message field will
       be generated from format and the arguments.

       sd_bus_error_set_errnofv() is similar to sd_bus_error_set_errnof(), but takes the format
       string parameters as va_arg(3) parameter list.

       sd_bus_error_get_errno() converts the name field of an error structure to an errno-like
       (positive) value using the same rules as sd_bus_error_set(). If e is NULL, 0 will be
       returned.

       sd_bus_error_copy() will initialize dst using the values in e, if e has been set with an
       error value before. Otherwise, it will return immediately. If the strings in e were set
       using sd_bus_error_set_const(), they will be shared. Otherwise, they will be copied.
       Before this call, dst must be unset, i.e. either freshly initialized with NULL or reset
       using sd_bus_error_free().

       sd_bus_error_copy() generally returns 0 or a negative errno-like value based on the input
       parameter e: 0 if it was unset and a negative integer if it was set to some error,
       similarly to sd_bus_error_set(). It may however also return an error generated internally,
       for example -ENOMEM if a memory allocation fails.

       sd_bus_error_move() is similar to sd_bus_error_copy(), but will move any error information
       from e into dst, resetting the former. This function cannot fail, as no new memory is
       allocated. Note that if e is not set, dst is initialized to SD_BUS_ERROR_NULL. Moreover,
       if dst is NULL no operation is executed on it and resources held by e are freed and reset.
       Returns a converted errno-like, non-positive error value.

       sd_bus_error_is_set() will return a non-zero value if e is non-NULL and an error has been
       set, false otherwise.

       sd_bus_error_has_name() will return a non-zero value if e is non-NULL and an error with
       the same name has been set, false otherwise.

       sd_bus_error_has_names_sentinel() is similar to sd_bus_error_has_name(), but takes
       multiple names to check against. The list must be terminated with NULL.
       sd_bus_error_has_names() is a macro wrapper around sd_bus_error_has_names_sentinel() that
       adds the NULL sentinel automatically.

       sd_bus_error_free() will destroy resources held by e. The parameter itself will not be
       deallocated, and must be free(3)d by the caller if necessary. The function may also be
       called safely on unset errors (error structures with both fields set to NULL), in which
       case it performs no operation. This call will reset the error structure after freeing the
       data, so that all fields are set to NULL. The structure may be reused afterwards.

REFERENCE OWNERSHIP

       sd_bus_error is not reference-counted. Users should destroy resources held by it by
       calling sd_bus_error_free(). Usually, error structures are allocated on the stack or
       passed in as function parameters, but they may also be allocated dynamically, in which
       case it is the duty of the caller to free(3) the memory held by the structure itself after
       freeing its contents with sd_bus_error_free().

RETURN VALUE

       The functions sd_bus_error_set(), sd_bus_error_setf(), and sd_bus_error_set_const() always
       return 0 when the specified error value is NULL, and a negative errno-like value
       corresponding to the name parameter otherwise. The functions sd_bus_error_set_errno(),
       sd_bus_error_set_errnof() and sd_bus_error_set_errnofv(), return 0 when the specified
       error value is 0, and a negative errno-like value corresponding to the error parameter
       otherwise. If an error occurs internally, one of the negative error values listed below
       will be returned. This allows those functions to be conveniently used in a return
       statement, see the example below.

       sd_bus_error_get_errno() returns false when e is NULL, and a positive errno value mapped
       from e->name otherwise.

       sd_bus_error_copy() and sd_bus_error_move() return a negative error value converted from
       the source error, and zero if the error has not been set. This allows those functions to
       be conveniently used in a return statement, see the example below.

       sd_bus_error_is_set() returns a non-zero value when e and the name field are non-NULL,
       zero otherwise.

       sd_bus_error_has_name(), sd_bus_error_has_names(), and sd_bus_error_has_names_sentinel()
       return a non-zero value when e is non-NULL and the name field is equal to one of the given
       names, zero otherwise.

   Errors
       Return value may indicate the following problems in the invocation of the function itself:

       -EINVAL
           Error was already set in the sd_bus_error structure when one the error-setting
           functions was called.

       -ENOMEM
           Memory allocation failed.

       On success, sd_bus_error_set(), sd_bus_error_setf(), sd_bus_error_set_const(),
       sd_bus_error_set_errno(), sd_bus_error_set_errnof(), sd_bus_error_set_errnofv(),
       sd_bus_error_copy(), and sd_bus_error_move() will return a negative converted errno-style
       value, or 0 if the error parameter is NULL or unset. D-Bus errors are converted to the
       integral errno-style value, and the mapping mechanism is extensible, see the discussion
       above. This effectively means that almost any negative errno-style value can be returned.

EXAMPLES

       Example 1. Using the negative return value to propagate an error

           /* SPDX-License-Identifier: CC0-1.0 */

           #include <errno.h>
           #include <string.h>
           #include <unistd.h>
           #include <sd-bus.h>

           int writer_with_negative_errno_return(int fd, sd_bus_error *error) {
             const char *message = "Hello, World!\n";

             ssize_t n = write(fd, message, strlen(message));
             if (n >= 0)
               return n; /* On success, return the number of bytes written, possibly 0. */

             /* On error, initialize the error structure, and also propagate the errno
              * value that write(2) set for us. */
             return sd_bus_error_set_errnof(error, errno, "Failed to write to fd %i: %m", fd);
           }

NOTES

       These APIs are implemented as a shared library, which can be compiled and linked to with
       the libsystemd pkg-config(1) file.

SEE ALSO

       systemd(1), sd-bus(3), sd-bus-errors(3), sd_bus_error_add_map(3), errno(3), strerror_r(3)

NOTES

        1. Valid Names
           http://dbus.freedesktop.org/doc/dbus-specification.html#message-protocol-names