Problem with My Base64 Encoding CLOB Routine.

Question

I have written a program which reads an xml file into the database
and makes it Base64encoded.
This needs to work on 10g and above
If the read length specified in the code below is greater than the length of the xml_file, then I get the expected result(output).
However if the read length is less than the length of the file, then I get a lot of '==' in the file and as a result, incorrect encoding which means that the file will not be readable through the application.
I'm pretty sure I'm reading the blob lengths correctly, and the problem is somehow related to the base64 encoding.Any help appreciated
[create or replace profile_dir as &profile_dir;
create global temporary table load_xml
(profile_text clob)
on commit delete rows;
create or replace
procedure encode_xml_clobs(p_file_in  in varchar2,
                             p_clob_out out nocopy clob )
as
pragma autonomous_transaction;
    dest_clob   CLOB;
    src_clob    BFILE  := BFILENAME('PROFILE_DIR', p_file_in);
    dst_offset  number := 1 ;
    src_offset  number := 1 ;
    lang_ctx    number := DBMS_LOB.DEFAULT_LANG_CTX;
    warning     number;
-- processing declarations for encoding base64 --
v_xml_string varchar2(32767);
v_string varchar2(32767);
v_start_pos number := 0;
v_read_length number := 1000;
v_final_start_pos number;
v_clob_length number;
type clob_array_type is table of clob index by binary_integer;
clob_array clob_array_type;
v_index number :=0;
-- Declarations for converting base64encoded string to a clob
v_encoded_length number;
v_temp_clob clob;
BEGIN
    -- THE FOLLOWING BLOCK OF CODE WILL ATTEMPT TO INSERT / WRITE THE CONTENTS
    -- OF AN XML FILE TO A CLOB COLUMN. IN THIS CASE, WE WILL USE THE NEW
    -- DBMS_LOB.LoadCLOBFromFile() API WHICH *DOES* SUPPORT MULTI-BYTE
    -- CHARACTER SET DATA.
-- load_xml should be a  Global temporary table with on commit delete rows
    INSERT INTO load_xml(profile_text)
        VALUES( empty_clob())
        RETURNING profile_text INTO dest_clob;
    -- OPENING THE SOURCE BFILE IS MANDATORY
    DBMS_LOB.OPEN(src_clob, DBMS_LOB.LOB_READONLY);
    DBMS_LOB.LoadCLOBFromFile(
          DEST_LOB     => dest_clob
        , SRC_BFILE    => src_clob
        , AMOUNT       => DBMS_LOB.GETLENGTH(src_clob)
        , DEST_OFFSET  => dst_offset
        , SRC_OFFSET   => src_offset
        , BFILE_CSID   => DBMS_LOB.DEFAULT_CSID
        , LANG_CONTEXT => lang_ctx
        , WARNING      => warning
    DBMS_LOB.CLOSE(src_clob);
--    DBMS_OUTPUT.PUT_LINE('Loaded XML File using DBMS_LOB.LoadCLOBFromFile: (ID=1');
-- file now successfully loaded
select dbms_lob.GETLENGTH(profile_text)
into v_clob_length
from load_xml;
-- File now loaded in temporary table
-- we now need to take the clob , convert it to varchar2
v_read_length :=64;
v_xml_string := '';
while v_start_pos <=  v_clob_length
loop
v_index := v_index + 1;
v_string := '';
--dbms_output.put_line('Start_pos=>'||(v_start_pos+1)||' Read Length=>'||v_read_length);
--encode base64
select utl_raw.cast_to_varchar2(
utl_encode.base64_encode(
utl_raw.cast_to_raw(dbms_lob.substr(profile_text,least(v_read_length,v_clob_length-v_start_pos),v_start_pos+1))
  into v_string
  from load_xml;
--dbms_output.put_line(v_string);
v_start_pos  := v_start_pos+v_read_length;
clob_array(v_index) := v_string;
end loop;
p_clob_out := clob_array(1);
for i in 2 .. v_index
loop
dbms_lob.append(p_clob_out,clob_array(i));
end loop;
commit;
END;

Answer 1

Base64 encoding encodes every 3 bytes of input data into 4 bytes of output data. It uses equal signs to indicate nodata and only at the end of the encoded sequence. Try chaning your v_read_length parameter to a multiple of 3 e.g. 960 or 1008 instead of the current 1000. I'm using multiples of 48 because the utl_encode.base64_encode function adds a linebreak for every 48 bytes of input data (64 bytes of output). If you use a value that's not divisible by 48 you will still get a legitimate encoding as long as it's divisible by 3, but you will get some lines longer than others when you append them together.