gpextprotocal.c
#include "postgres.h"
#include "fmgr.h"
#include "funcapi.h"
#include "access/extprotocol.h"
#include "catalog/pg_proc.h"
#include "utils/array.h"
#include "utils/builtins.h"
#include "utils/memutils.h"
/* Our chosen URI format. We can change it however needed */
typedef struct DemoUri
{
char *protocol;
char *path;
} DemoUri;
static DemoUri *ParseDemoUri(const char *uri_str);
static void FreeDemoUri(DemoUri* uri);
/* Do the module magic dance */
PG_MODULE_MAGIC;
PG_FUNCTION_INFO_V1(demoprot_export);
PG_FUNCTION_INFO_V1(demoprot_import);
PG_FUNCTION_INFO_V1(demoprot_validate_urls);
Datum demoprot_export(PG_FUNCTION_ARGS);
Datum demoprot_import(PG_FUNCTION_ARGS);
Datum demoprot_validate_urls(PG_FUNCTION_ARGS);
/* A user context that persists across calls. Can be
declared in any other way */
typedef struct {
char *url;
char *filename;
FILE *file;
} extprotocol_t;
/*
* The read function - Import data into GPDB.
*/
Datum
myprot_import(PG_FUNCTION_ARGS)
{
extprotocol_t *myData;
char *data;
int datlen;
size_t nread = 0;
/* Must be called via the external table format manager */
if (!CALLED_AS_EXTPROTOCOL(fcinfo))
elog(ERROR, "myprot_import: not called by external
protocol manager");
/* Get our internal description of the protocol */
myData = (extprotocol_t *) EXTPROTOCOL_GET_USER_CTX(fcinfo);
if(EXTPROTOCOL_IS_LAST_CALL(fcinfo))
{
/* we're done receiving data. close our connection */
if(myData && myData->file)
if(fclose(myData->file))
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not close file \"%s\": %m",
myData->filename)));
PG_RETURN_INT32(0);
}
if (myData == NULL)
{
/* first call. do any desired init */
const char *p_name = "myprot";
DemoUri *parsed_url;
char *url = EXTPROTOCOL_GET_URL(fcinfo);
myData = palloc(sizeof(extprotocol_t));
myData->url = pstrdup(url);
parsed_url = ParseDemoUri(myData->url);
myData->filename = pstrdup(parsed_url->path);
if(strcasecmp(parsed_url->protocol, p_name) != 0)
elog(ERROR, "internal error: myprot called with a
different protocol (%s)",
parsed_url->protocol);
FreeDemoUri(parsed_url);
/* open the destination file (or connect to remote server in
other cases) */
myData->file = fopen(myData->filename, "r");
if (myData->file == NULL)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("myprot_import: could not open file \"%s\"
for reading: %m",
myData->filename),
errOmitLocation(true)));
EXTPROTOCOL_SET_USER_CTX(fcinfo, myData);
}
/* ==========================================
* DO THE IMPORT
* ========================================== */
data = EXTPROTOCOL_GET_DATABUF(fcinfo);
datlen = EXTPROTOCOL_GET_DATALEN(fcinfo);
/* read some bytes (with fread in this example, but normally
in some other method over the network) */
if(datlen > 0)
{
nread = fread(data, 1, datlen, myData->file);
if (ferror(myData->file))
ereport(ERROR,
(errcode_for_file_access(),
errmsg("myprot_import: could not write to file
\"%s\": %m",
myData->filename)));
}
PG_RETURN_INT32((int)nread);
}
/*
* Write function - Export data out of GPDB
*/
Datum
myprot_export(PG_FUNCTION_ARGS)
{
extprotocol_t *myData;
char *data;
int datlen;
size_t wrote = 0;
/* Must be called via the external table format manager */
if (!CALLED_AS_EXTPROTOCOL(fcinfo))
elog(ERROR, "myprot_export: not called by external
protocol manager");
/* Get our internal description of the protocol */
myData = (extprotocol_t *) EXTPROTOCOL_GET_USER_CTX(fcinfo);
if(EXTPROTOCOL_IS_LAST_CALL(fcinfo))
{
/* we're done sending data. close our connection */
if(myData && myData->file)
if(fclose(myData->file))
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not close file \"%s\": %m",
myData->filename)));
PG_RETURN_INT32(0);
}
if (myData == NULL)
{
/* first call. do any desired init */
const char *p_name = "myprot";
DemoUri *parsed_url;
char *url = EXTPROTOCOL_GET_URL(fcinfo);
myData = palloc(sizeof(extprotocol_t));
myData->url = pstrdup(url);
parsed_url = ParseDemoUri(myData->url);
myData->filename = pstrdup(parsed_url->path);
if(strcasecmp(parsed_url->protocol, p_name) != 0)
elog(ERROR, "internal error: myprot called with a
different protocol (%s)",
parsed_url->protocol);
FreeDemoUri(parsed_url);
/* open the destination file (or connect to remote server in
other cases) */
myData->file = fopen(myData->filename, "a");
if (myData->file == NULL)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("myprot_export: could not open file \"%s\"
for writing: %m",
myData->filename),
errOmitLocation(true)));
EXTPROTOCOL_SET_USER_CTX(fcinfo, myData);
}
/* ========================================
* DO THE EXPORT
* ======================================== */
data = EXTPROTOCOL_GET_DATABUF(fcinfo);
datlen = EXTPROTOCOL_GET_DATALEN(fcinfo);
if(datlen > 0)
{
wrote = fwrite(data, 1, datlen, myData->file);
if (ferror(myData->file))
ereport(ERROR,
(errcode_for_file_access(),
errmsg("myprot_import: could not read from file
\"%s\": %m",
myData->filename)));
}
PG_RETURN_INT32((int)wrote);
}
Datum
myprot_validate_urls(PG_FUNCTION_ARGS)
{
List *urls;
int nurls;
int i;
ValidatorDirection direction;
/* Must be called via the external table format manager */
if (!CALLED_AS_EXTPROTOCOL_VALIDATOR(fcinfo))
elog(ERROR, "myprot_validate_urls: not called by external
protocol manager");
nurls = EXTPROTOCOL_VALIDATOR_GET_NUM_URLS(fcinfo);
urls = EXTPROTOCOL_VALIDATOR_GET_URL_LIST(fcinfo);
direction = EXTPROTOCOL_VALIDATOR_GET_DIRECTION(fcinfo);
/*
* Dumb example 1: search each url for a substring
* we don't want to be used in a url. in this example
* it's 'secured_directory'.
*/
for (i = 1 ; i <= nurls ; i++)
{
char *url = EXTPROTOCOL_VALIDATOR_GET_NTH_URL(fcinfo, i);
if (strstr(url, "secured_directory") != 0)
{
ereport(ERROR,
(errcode(ERRCODE_PROTOCOL_VIOLATION),
errmsg("using 'secured_directory' in a url
isn't allowed ")));
}
}
/*
* Dumb example 2: set a limit on the number of urls
* used. In this example we limit readable external
* tables that use our protocol to 2 urls max.
*/
if(direction == EXT_VALIDATE_READ && nurls > 2)
{
ereport(ERROR,
(errcode(ERRCODE_PROTOCOL_VIOLATION),
errmsg("more than 2 urls aren't allowed in this protocol ")));
}
PG_RETURN_VOID();
}
/* --- utility functions --- */
static
DemoUri *ParseDemoUri(const char *uri_str)
{
DemoUri *uri = (DemoUri *) palloc0(sizeof(DemoUri));
int protocol_len;
uri->path = NULL;
uri->protocol = NULL;
/*
* parse protocol
*/
char *post_protocol = strstr(uri_str, "://");
if(!post_protocol)
{
ereport(ERROR,
(errcode(ERRCODE_SYNTAX_ERROR),
errmsg("invalid protocol URI \'%s\'", uri_str),
errOmitLocation(true)));
}
protocol_len = post_protocol - uri_str;
uri->protocol = (char *)palloc0(protocol_len + 1);
strncpy(uri->protocol, uri_str, protocol_len);
/* make sure there is more to the uri string */
if (strlen(uri_str) <= protocol_len)
ereport(ERROR,
(errcode(ERRCODE_SYNTAX_ERROR),
errmsg("invalid myprot URI \'%s\' : missing path",
uri_str),
errOmitLocation(true)));
/* parse path */
uri->path = pstrdup(uri_str + protocol_len + strlen("://"));
return uri;
}
static
void FreeDemoUri(DemoUri *uri)
{
if (uri->path)
pfree(uri->path);
if (uri->protocol)
pfree(uri->protocol);
pfree(uri);
}
Parent topic: Installing the External Table Protocol