Re: C Extension woes
Re: C Extension woes
От:
Tom Lane <tgl@sss.pgh.pa.us>
Дата:
Andrew Chernow writes:
> Tim Hawes wrote:
>> char *e_var = getenv("PGMASTERKEY");
>> size_t length = VARSIZE(e_var) - VARHDRSZ;
> The VARSIZE macro is for variable length structures, like a text or
> bytea which contains a length and data member. You are using this macro
> on a regular C string "e_var".
The code on the output side is wrong too: if the useful data length is
"length", then the palloc has to ask for length + VARHDRSZ, and that's
also what's got to be put into the length word.
regards, tom lane
C Extension woes
От:
Tim Hawes <thawes@novadine.com>
Дата:
Hello all,
I am trying to write an extension in C that returns a simple environment
variable. The code compiles without any complaint or warning, and it
loads fine into the database, however, when I run the function, I get
disconnected from the server.
Here is my C code:
#include
#include
PG_MODULE_MAGIC;
#include
#include
PG_FUNCTION_INFO_V1(pl_masterkey);
text * pl_masterkey(PG_FUNCTION_ARGS)
{ char *e_var = getenv("PGMASTERKEY"); size_t length = VARSIZE(e_var) - VARHDRSZ;
text * mkey = (text *) palloc(length); VARATT_SIZEP(mkey) = length; memcpy(VARDATA(mkey), e_var, length);
return mkey;
}
And here is the SQL I use to create the function in PostgreSQL:
CREATE FUNCTION pl_masterkey() RETURNS text AS 'pl_masterkey', 'pl_masterkey' LANGUAGE C STRICT;
And the results:
select pl_masterkey();
server closed the connection unexpectedly This probably means the server terminated abnormally before or while processing the request.
The connection to the server was lost. Attempting reset: Failed.
!>
Thanks ahead of time for any and all help.
Re: C Extension woes
От:
Jan Urbański <j.urbanski@students.mimuw.edu.pl>
Дата:
Tim Hawes wrote:
> Hello all,
>
> I am trying to write an extension in C that returns a simple environment
> variable. The code compiles without any complaint or warning, and it
> loads fine into the database, however, when I run the function, I get
> disconnected from the server.
>
> Here is my C code:
>
> #include
> #include
> PG_MODULE_MAGIC;
>
> #include
> #include
>
> PG_FUNCTION_INFO_V1(pl_masterkey);
>
> text * pl_masterkey(PG_FUNCTION_ARGS)
> {
> char *e_var = getenv("PGMASTERKEY");
> size_t length = VARSIZE(e_var) - VARHDRSZ;
>
> text * mkey = (text *) palloc(length);
> VARATT_SIZEP(mkey) = length;
> memcpy(VARDATA(mkey), e_var, length);
>
> return mkey;
> }
Oh, you confused a lot of things.
You need something like
Datum pl_masterkey(PG_FUNCTION_ARGS) { char *e_var = getenv("PGMASTERKEY"); PG_RETURN_TEXT_P(cstring_to_text(e_var));
}
You don't need to mess with anything varlena-related (liek VARSIZE),
it's all handled for you.
Also, read up on how to declare user-defined C functions in Postgres
(they always need to return Datum).
Cheers,
Jan
--
Jan Urbanski
GPG key ID: E583D7D2
ouden estin
Re: C Extension woes
От:
Andrew Chernow <ac@esilo.com>
Дата:
Tim Hawes wrote:
>
> text * pl_masterkey(PG_FUNCTION_ARGS)
> {
> char *e_var = getenv("PGMASTERKEY");
> size_t length = VARSIZE(e_var) - VARHDRSZ;
>
>
The VARSIZE macro is for variable length structures, like a text or
bytea which contains a length and data member. You are using this macro
on a regular C string "e_var". Try this instead:
size_t length = e_var != NULL ? strlen(e_var) : 0;
--
Andrew Chernow
eSilo, LLC
every bit counts
http://www.esilo.com/
Re: C Extension woes
От:
Tim Hawes <thawes@novadine.com>
Дата:
Thank you for your replies, however, it still is not working, see below...
Andrew Chernow wrote:
> Tim Hawes wrote:
>>
>> text * pl_masterkey(PG_FUNCTION_ARGS)
>> {
>> char *e_var = getenv("PGMASTERKEY");
>> size_t length = VARSIZE(e_var) - VARHDRSZ;
>>
>>
>
> The VARSIZE macro is for variable length structures, like a text or
> bytea which contains a length and data member. You are using this
> macro on a regular C string "e_var". Try this instead:
>
> size_t length = e_var != NULL ? strlen(e_var) : 0;
>
@Jan: It appears the cstring_to_text function is unique to the latest
PostgreSQL code. I do not have a def for that for PostgreSQL 8.2, and
currently I am stuck working with that version. I changed the return
value to Datum, and I had previously only copied from the examples at:
http://www.postgresql.org/docs/8.2/interactive/xfunc-c.html
@Andrew: here is my new code:Datum pl_masterkey(PG_FUNCTION_ARGS)
{ char *e_var = getenv("PGMASTERKEY"); size_t length = e_var != NULL ? strlen(e_var) : 0;
text * mkey = (text *) palloc(length); VARATT_SIZEP(mkey) = length; memcpy(VARDATA(mkey), e_var, length);
PG_RETURN_TEXT_P(mkey);
}
now gets:
select pl_masterkey();
ERROR: invalid memory alloc request size 4294967293
Re: C Extension woes
От:
Jan Urbański <j.urbanski@students.mimuw.edu.pl>
Дата:
Tim Hawes wrote:
> @Jan:
> It appears the cstring_to_text function is unique to the latest
> PostgreSQL code. I do not have a def for that for PostgreSQL 8.2, and
Oh, I'm sorry, I forgot about that. cstring_to_text has been added only
recently (it's not even it 8.3, silly me).
> Datum pl_masterkey(PG_FUNCTION_ARGS)
> {
> char *e_var = getenv("PGMASTERKEY");
> size_t length = e_var != NULL ? strlen(e_var) : 0;
>
> text * mkey = (text *) palloc(length);
> VARATT_SIZEP(mkey) = length;
> memcpy(VARDATA(mkey), e_var, length);
>
> PG_RETURN_TEXT_P(mkey);
> }
You forgot to palloc space for the varlena header. You need an extra
VARHDRSZ bytes for the header, in addition to what is needed for your data.
Try something like this:
Datum
pl_masterkey(PG_FUNCTION_ARGS)
{ char *e_var; size_t length; text *mkey;
e_var = getenv("PGMASTERKEY"); length = e_var ? strlen(e_var) : 0; mkey = (text *) palloc(VARHDRSZ + length);
VARATT_SIZEP(mkey) = VARHDRSZ + length; memcpy(VARDATA(mkey), e_var, length);
PG_RETURN_TEXT_P(mkey);
}
--
Jan Urbanski
GPG key ID: E583D7D2
ouden estin
Re: C Extension woes
От:
Tim Hawes <thawes@novadine.com>
Дата:
Ok, that worked!
Thank you very much, Jan and others who gave their input.
I did see Tom's input for the VARHDRSZ and tried that, but forgot to add
that again
when I called VARATT_SIZEP
Jan Urbański wrote:
> Tim Hawes wrote:
>
>> @Jan:
>> It appears the cstring_to_text function is unique to the latest
>> PostgreSQL code. I do not have a def for that for PostgreSQL 8.2, and
>
> Oh, I'm sorry, I forgot about that. cstring_to_text has been added
> only recently (it's not even it 8.3, silly me).
>
>> Datum pl_masterkey(PG_FUNCTION_ARGS)
>> {
>> char *e_var = getenv("PGMASTERKEY");
>> size_t length = e_var != NULL ? strlen(e_var) : 0;
>>
>> text * mkey = (text *) palloc(length);
>> VARATT_SIZEP(mkey) = length;
>> memcpy(VARDATA(mkey), e_var, length);
>>
>> PG_RETURN_TEXT_P(mkey);
>> }
>
> You forgot to palloc space for the varlena header. You need an extra
> VARHDRSZ bytes for the header, in addition to what is needed for your
> data.
> Try something like this:
>
> Datum
> pl_masterkey(PG_FUNCTION_ARGS)
> {
> char *e_var;
> size_t length;
> text *mkey;
>
> e_var = getenv("PGMASTERKEY");
> length = e_var ? strlen(e_var) : 0;
> mkey = (text *) palloc(VARHDRSZ + length);
>
> VARATT_SIZEP(mkey) = VARHDRSZ + length;
> memcpy(VARDATA(mkey), e_var, length);
>
> PG_RETURN_TEXT_P(mkey);
> }
>
