[GENERAL] bytea and character encoding when inserting escaped literals

2008-05-05 Thread Lee Feigenbaum 

Hi,

I've searched the archives a fair amount on this topic, but have not 
found quite the answer / explanation I'm looking for. I attribute this 
to my eternal confusion over character encoding issues in all 
environments, so I apologize in advance for what might be a stupid 
question. :)


I'mm running Postgresql 8.3.1 on WinXP. I have a UTF8 database into 
which I'm trying to execute a series of INSERT INTO DDL statements. One 
of the columns in the table I'm inserting into is a BYTEA column, 
intended to hold the bytes that are the representation of a (small) 
image.[1]


I had thought -- apparently erroneously -- that because this is not a 
text based column, that I could send any string of bytes (octets) via my 
INSERT statement to populate values in this column. I'm using escaped 
string literals with hexadecimal representation so my INSERTs look 
something like:


INSERT INTO myTable VALUES (..., E'\x15\x1C\x2F\x00\x02...', ...) ;

As you might be able to guess, I'm getting the error:

  ERROR: Invalid byte sequence for encoding "UTF8": 0x00

(I get the error whether I attempt this via JDBC or via the command-line 
client with client encoding set to UTF8 or WIN1252.)


Again, I was surprised by this error since I thought from the 
documentation at [2] that the server would only expect to be dealing in 
a sequence of octets here, without any character-encoding constraints 
implied by the DB's encoding.


What is the actual cause of this error, and how do I workaround it? Do I 
need to pretend that my data is Unicode character data and specify the 
UTF8 octets for that character data in my E'...' literal?


thanks in advance for any help!

Lee

PS [3]

[1] Actually, this DDL has been converted from that for a different DB 
that uses LONGVARBINARY for this. BYTEA was my best guess for the 
Postgresql equivalent.


[2] http://www.postgresql.org/docs/8.3/interactive/datatype-binary.html

[3] I also was confused as to why 0x00 would be an invalid UTF8 byte 
sequence. On its own, as I understand it, 0x00 is a fine UTF8 byte 
sequence (representing Unicode codepoint 0). And when I (from the 
command line) try to insert other invalid UTF8 sequences -- such as 
INSERT INTO foo VALUES (E'\xC0\x80') I get an error that mentions the 
full byte sequence as invalid: "invalid byte sequence for encoding 
"UTF8": 0xc080". So this further confuses me. :-)


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Re: [GENERAL] bytea and character encoding when inserting escaped literals

2008-05-05 Thread Lee Feigenbaum 

Asche wrote:

Hi Lee,

On 05.05.2008, at 17:07, Lee Feigenbaum wrote:

INSERT INTO myTable VALUES (..., E'\x15\x1C\x2F\x00\x02...', ...) ;


try escaping the backslashes:

INSERT INTO myTable VALUES (..., E'\\x15\\x1C\\x2F\\x00\\x02...', ...) ;


Hi Jan,

Thanks for the suggestion. I should have mentioned in my original 
message that as per your suggestion and the suggestion in the 
documentation, I have tried escaping the backslashes. When I do this, I 
get the error:


  ERROR: invalid input syntax for type bytea

I tried also doing

  INSERT INTO myTable VALUES (..., 
E'\\x15\\x1C\\x2F\\x00\\x02...'::bytea, ...) ;



but get the same errors.

Lee

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Re: [GENERAL] bytea and character encoding when inserting escaped literals

2008-05-05 Thread Lee Feigenbaum 

Asche wrote:

Hi Lee,

Thanks for the suggestion. I should have mentioned in my original 
message that as per your suggestion and the suggestion in the 
documentation, I have tried escaping the backslashes. When I do this, 
I get the error:


 ERROR: invalid input syntax for type bytea

I tried also doing

 INSERT INTO myTable VALUES (..., 
E'\\x15\\x1C\\x2F\\x00\\x02...'::bytea, ...) ;


but get the same errors.


I think i see another problem with your query. You should convert to 
three-digit octal (something like \\001\\002...) not \\x01 (hex?).


Hi Jan,

Thanks, I think I finally see what's happening here (and understand the 
docs) - the bytea type has its own string-serialization (escape format) 
_separate_ from postgresql's normal string literal escaping. So while 
E'\xC0' is postgresql serialization of a string containing whatever 
character maps from 0xC0 in the current encoding, that byte cannot 
directly go into a bytea. Instead, I need to have a doubly-escaped octal 
(specifically) string so that the first escape generates a string like 
\000\001\002 which the bytea processor (somewhere) then re-parses as a 
sequence of bytes.


Would be nice if the bytea parser understood hex representation too, but 
beggars can't be choosers :)


thanks for the help,
Lee



Jan




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