A variant of the PostgreSQL convert_from() function that avoids the 'invalid byte sequence for encoding' error by emitting hex escapes for any bytes that don't encode

convert_from_or_escape.sql

-- A variant of the built-in 'convert_from' function that doesn't give up when it encounters invalid characters, but rather replaces them with 0x hex equivalents.
-- The last 'locator' arg lets you specify which record you're processing.
--
-- Sample use:
-- jira=# select convert_from_or_escape('Invalid chars: \344\274\232\345\223\241\350\252?\350\250\274\343\203\207\343\203\242\343\203\232\343\203\274\343\202\270\343?\270\343\202\210\343?\206\343?\223\343??\357\274?</h3>'::bytea, 'utf-8', 'At table foo line 123');
-- NOTICE:  At table foo line 123: Replacing bad chars '0xe8 0xaa 0x3f' with '0xe8aa3f'
-- NOTICE:  At table foo line 123: Replacing bad chars '0xe3 0x3f 0xb8' with '0xe33fb8'
-- NOTICE:  At table foo line 123: Replacing bad chars '0xe3 0x3f 0x86' with '0xe33f86'
-- NOTICE:  At table foo line 123: Replacing bad chars '0xe3 0x3f 0x93' with '0xe33f93'
-- NOTICE:  At table foo line 123: Replacing bad chars '0xe3 0x3f 0x3f' with '0xe33f3f'
-- NOTICE:  At table foo line 123: Replacing bad chars '0xef 0xbc 0x3f' with '0xefbc3f'
-- ┌────────────────────────────────────────────────────────────────────────────────────────┐
-- │                                 convert_from_or_escape                                 │
-- ├────────────────────────────────────────────────────────────────────────────────────────┤
-- │ Invalid chars: 会員0xe8aa3f証デモページ0xe33fb8よ0xe33f860xe33f930xe33f3f0xefbc3f</h3> │
-- └────────────────────────────────────────────────────────────────────────────────────────┘
-- (1 row)
-- jeff@redradishtech.com, 23/May/17
CREATE OR REPLACE FUNCTION convert_from_or_escape(input bytea, encoding varchar, locator varchar DEFAULT null) RETURNS text AS
$$
DECLARE
        temp bytea := null;             -- Working copy of our input
        oldtemp bytea := null;   
        errormessage text;
        errstate text;
        invalidchars bytea;
        invalidchars_str varchar;
        invalidchars_str_trimmed varchar;
BEGIN
        temp = input;
        -- Repeatedly attempt to convert_from() the string held in temp. Each time it fails, replace the chars that caused the failure and try again.
        LOOP
                BEGIN
                        RETURN convert_from(temp, encoding);
                EXCEPTION WHEN OTHERS THEN
                        GET STACKED DIAGNOSTICS errormessage = MESSAGE_TEXT, errstate = RETURNED_SQLSTATE;
                        IF errstate = '22021' THEN      -- This is the 'Invalid byte sequence for encoding' error
                                -- Here, errormessage is something like: invalid byte sequence for encoding "UTF8": 0xc3 0x3f
                                invalidchars_str = regexp_replace(errormessage, '^.*: ', '');           -- Strip the 'invalid byte sequence for encoding "UTF8": ' part of the error message, leaving just the invalid chars, e.g. '0xc3 0x3f'         
                                invalidchars_str_trimmed = regexp_replace(invalidchars_str, '(^| )0x', '', 'g');        -- Strip '0x' and whitespace to leave just the hex digits
                                invalidchars = decode(invalidchars_str_trimmed, 'hex'); -- Decode hex with decode(..., 'hex'), giving us a bytea result
                                RAISE NOTICE '%Replacing bad chars ''%'' with ''0x%''', coalesce(locator || ': ', ''), invalidchars_str, invalidchars_str_trimmed;
                                oldtemp = temp;
                                temp = replace_binary(temp, invalidchars, '0x' || invalidchars_str_trimmed::bytea);
                                IF oldtemp = temp THEN
                                        RAISE EXCEPTION 'We were unable to fix bad characters by applying regex % to %', invalidchars, encode(oldtemp, 'escape');
                                END IF;
                        ELSE
                                RAISE EXCEPTION 'Unhandled error: %', errormessage;
                        END IF;
                END;
        END LOOP;
END;
$$
LANGUAGE plpgsql;

Thanks!!