err(3)

NAME
err - error codes

LIBRARY
libcrypto, -lcrypto

SYNOPSIS
 #include <openssl/err.h>

 unsigned long ERR_get_error(void);
 unsigned long ERR_peek_error(void);
 unsigned long ERR_get_error_line(const char **file, int *line);
 unsigned long ERR_peek_error_line(const char **file, int *line);
 unsigned long ERR_get_error_line_data(const char **file, int *line,
         const char **data, int *flags);
 unsigned long ERR_peek_error_line_data(const char **file, int *line,
         const char **data, int *flags);

 int ERR_GET_LIB(unsigned long e);
 int ERR_GET_FUNC(unsigned long e);
 int ERR_GET_REASON(unsigned long e);

 void ERR_clear_error(void);

 char *ERR_error_string(unsigned long e, char *buf);
 const char *ERR_lib_error_string(unsigned long e);
 const char *ERR_func_error_string(unsigned long e);
 const char *ERR_reason_error_string(unsigned long e);

 void ERR_print_errors(BIO *bp);
 void ERR_print_errors_fp(FILE *fp);

 void ERR_load_crypto_strings(void);
 void ERR_free_strings(void);

 void ERR_remove_state(unsigned long pid);

 void ERR_put_error(int lib, int func, int reason, const char *file,
         int line);
 void ERR_add_error_data(int num, ...);

 void ERR_load_strings(int lib,ERR_STRING_DATA str[]);
 unsigned long ERR_PACK(int lib, int func, int reason);
 int ERR_get_next_error_library(void);

DESCRIPTION
When a call to the OpenSSL library fails, this is usually signalled by the return value, and an error code is stored in an error queue associated with the current thread. The err library provides functions to obtain these error codes and textual error messages.

The ERR_get_error(3) manpage describes how to access error codes.

Error codes contain information about where the error occurred, and what went wrong. ERR_GET_LIB(3) describes how to extract this information. A method to obtain human-readable error messages is described in ERR_error_string(3).

ERR_clear_error(3) can be used to clear the error queue.

Note that ERR_remove_state(3) should be used to avoid memory leaks when threads are terminated.

ADDING NEW ERROR CODES TO OPENSSL
See ERR_put_error(3) if you want to record error codes in the OpenSSL error system from within your application.

The remainder of this section is of interest only if you want to add new error codes to OpenSSL or add error codes from external libraries.

  Reporting errors
Each sub-library has a specific macro XXXerr() that is used to report errors. Its first argument is a function code XXX_F_..., the second argument is a reason code XXX_R_.... Function codes are derived from the function names; reason codes consist of textual error descriptions. For example, the function ssl23_read() reports a "handshake failure" as follows:

 SSLerr(SSL_F_SSL23_READ, SSL_R_SSL_HANDSHAKE_FAILURE);

Function and reason codes should consist of upper case characters, numbers and underscores only. The error file generation script translates function codes into function names by looking in the header files for an appropriate function name, if none is found it just uses the capitalized form such as "SSL23_READ" in the above example.

The trailing section of a reason code (after the "_R_") is translated into lower case and underscores changed to spaces.

When you are using new function or reason codes, run make errors. The necessary #defines will then automatically be added to the sub-library's header file.

Although a library will normally report errors using its own specific XXXerr macro, another library's macro can be used. This is normally only done when a library wants to include ASN1 code which must use the ASN1err() macro.

  Adding new libraries
When adding a new sub-library to OpenSSL, assign it a library number ERR_LIB_XXX, define a macro XXXerr() (both in err.h), add its name to ERR_str_libraries[] (in crypto/err/err.c), and add "ERR_load_XXX_strings()" to the ERR_load_crypto_strings() function (in crypto/err/err_all.c). Finally, add an entry

 L      XXX     xxx.h   xxx_err.c

to crypto/err/openssl.ec, and add xxx_err.c to the Makefile. Running make errors will then generate a file xxx_err.c, and add all error codes used in the library to xxx.h.

Additionally the library include file must have a certain form. Typically it will initially look like this:

 #ifndef HEADER_XXX_H
 #define HEADER_XXX_H

 #ifdef __cplusplus
 extern "C" {
 #endif

 /* Include files */

 #include <openssl/bio.h>
 #include <openssl/x509.h>

 /* Macros, structures and function prototypes */

 /* BEGIN ERROR CODES */

The BEGIN ERROR CODES sequence is used by the error code generation script as the point to place new error codes, any text after this point will be overwritten when make errors is run. The closing #endif etc will be automatically added by the script.

The generated C error code file xxx_err.c will load the header files stdio.h, openssl/err.h and openssl/xxx.h so the header file must load any additional header files containing any definitions it uses.

USING ERROR CODES IN EXTERNAL LIBRARIES
It is also possible to use OpenSSL's error code scheme in external libraries. The library needs to load its own codes and call the OpenSSL error code insertion script mkerr.pl explicitly to add codes to the header file and generate the C error code file. This will normally be done if the external library needs to generate new ASN1 structures but it can also be used to add more general purpose error code handling.

TBA more details

INTERNALS
The error queues are stored in a hash table with one ERR_STATE entry for each pid. ERR_get_state() returns the current thread's ERR_STATE. An ERR_STATE can hold up to ERR_NUM_ERRORS error codes. When more error codes are added, the old ones are overwritten, on the assumption that the most recent errors are most important.

Error strings are also stored in hash table. The hash tables can be obtained by calling ERR_get_err_state_table(void) and ERR_get_string_table(void) respectively.

SEE ALSO
CRYPTO_set_locking_callback(3), ERR_get_error(3), ERR_GET_LIB(3), ERR_clear_error(3), ERR_error_string(3), ERR_print_errors(3), ERR_load_crypto_strings(3), ERR_remove_state(3), ERR_put_error(3), ERR_load_strings(3), SSL_get_error(3)