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| author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-05-04 12:19:15 +0000 |
|---|---|---|
| committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-05-04 12:19:15 +0000 |
| commit | 6eb9c5a5657d1fe77b55cc261450f3538d35a94d (patch) | |
| tree | 657d8194422a5daccecfd42d654b8a245ef7b4c8 /doc/src/sgml/html/lo-examplesect.html | |
| parent | Initial commit. (diff) | |
| download | postgresql-13-upstream.tar.xz postgresql-13-upstream.zip | |
Adding upstream version 13.4.upstream/13.4upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'doc/src/sgml/html/lo-examplesect.html')
| -rw-r--r-- | doc/src/sgml/html/lo-examplesect.html | 284 |
1 files changed, 284 insertions, 0 deletions
diff --git a/doc/src/sgml/html/lo-examplesect.html b/doc/src/sgml/html/lo-examplesect.html new file mode 100644 index 0000000..80c29c1 --- /dev/null +++ b/doc/src/sgml/html/lo-examplesect.html @@ -0,0 +1,284 @@ +<?xml version="1.0" encoding="UTF-8" standalone="no"?> +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>34.5. Example Program</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets V1.79.1" /><link rel="prev" href="lo-funcs.html" title="34.4. Server-Side Functions" /><link rel="next" href="ecpg.html" title="Chapter 35. ECPG — Embedded SQL in C" /></head><body id="docContent" class="container-fluid col-10"><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">34.5. Example Program</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="lo-funcs.html" title="34.4. Server-Side Functions">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="largeobjects.html" title="Chapter 34. Large Objects">Up</a></td><th width="60%" align="center">Chapter 34. Large Objects</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 13.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="ecpg.html" title="Chapter 35. ECPG — Embedded SQL in C">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="LO-EXAMPLESECT"><div class="titlepage"><div><div><h2 class="title" style="clear: both">34.5. Example Program</h2></div></div></div><p> + <a class="xref" href="lo-examplesect.html#LO-EXAMPLE" title="Example 34.1. Large Objects with libpq Example Program">Example 34.1</a> is a sample program which shows how the large object + interface + in <span class="application">libpq</span> can be used. Parts of the program are + commented out but are left in the source for the reader's + benefit. This program can also be found in + <code class="filename">src/test/examples/testlo.c</code> in the source distribution. +</p><div class="example" id="LO-EXAMPLE"><p class="title"><strong>Example 34.1. Large Objects with <span class="application">libpq</span> Example Program</strong></p><div class="example-contents"><pre class="programlisting"> +/*----------------------------------------------------------------- + * + * testlo.c + * test using large objects with libpq + * + * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group + * Portions Copyright (c) 1994, Regents of the University of California + * + * + * IDENTIFICATION + * src/test/examples/testlo.c + * + *----------------------------------------------------------------- + */ +#include <stdio.h> +#include <stdlib.h> + +#include <sys/types.h> +#include <sys/stat.h> +#include <fcntl.h> +#include <unistd.h> + +#include "libpq-fe.h" +#include "libpq/libpq-fs.h" + +#define BUFSIZE 1024 + +/* + * importFile - + * import file "in_filename" into database as large object "lobjOid" + * + */ +static Oid +importFile(PGconn *conn, char *filename) +{ + Oid lobjId; + int lobj_fd; + char buf[BUFSIZE]; + int nbytes, + tmp; + int fd; + + /* + * open the file to be read in + */ + fd = open(filename, O_RDONLY, 0666); + if (fd < 0) + { /* error */ + fprintf(stderr, "cannot open unix file\"%s\"\n", filename); + } + + /* + * create the large object + */ + lobjId = lo_creat(conn, INV_READ | INV_WRITE); + if (lobjId == 0) + fprintf(stderr, "cannot create large object"); + + lobj_fd = lo_open(conn, lobjId, INV_WRITE); + + /* + * read in from the Unix file and write to the inversion file + */ + while ((nbytes = read(fd, buf, BUFSIZE)) > 0) + { + tmp = lo_write(conn, lobj_fd, buf, nbytes); + if (tmp < nbytes) + fprintf(stderr, "error while reading \"%s\"", filename); + } + + close(fd); + lo_close(conn, lobj_fd); + + return lobjId; +} + +static void +pickout(PGconn *conn, Oid lobjId, int start, int len) +{ + int lobj_fd; + char *buf; + int nbytes; + int nread; + + lobj_fd = lo_open(conn, lobjId, INV_READ); + if (lobj_fd < 0) + fprintf(stderr, "cannot open large object %u", lobjId); + + lo_lseek(conn, lobj_fd, start, SEEK_SET); + buf = malloc(len + 1); + + nread = 0; + while (len - nread > 0) + { + nbytes = lo_read(conn, lobj_fd, buf, len - nread); + buf[nbytes] = '\0'; + fprintf(stderr, ">>> %s", buf); + nread += nbytes; + if (nbytes <= 0) + break; /* no more data? */ + } + free(buf); + fprintf(stderr, "\n"); + lo_close(conn, lobj_fd); +} + +static void +overwrite(PGconn *conn, Oid lobjId, int start, int len) +{ + int lobj_fd; + char *buf; + int nbytes; + int nwritten; + int i; + + lobj_fd = lo_open(conn, lobjId, INV_WRITE); + if (lobj_fd < 0) + fprintf(stderr, "cannot open large object %u", lobjId); + + lo_lseek(conn, lobj_fd, start, SEEK_SET); + buf = malloc(len + 1); + + for (i = 0; i < len; i++) + buf[i] = 'X'; + buf[i] = '\0'; + + nwritten = 0; + while (len - nwritten > 0) + { + nbytes = lo_write(conn, lobj_fd, buf + nwritten, len - nwritten); + nwritten += nbytes; + if (nbytes <= 0) + { + fprintf(stderr, "\nWRITE FAILED!\n"); + break; + } + } + free(buf); + fprintf(stderr, "\n"); + lo_close(conn, lobj_fd); +} + + +/* + * exportFile - + * export large object "lobjOid" to file "out_filename" + * + */ +static void +exportFile(PGconn *conn, Oid lobjId, char *filename) +{ + int lobj_fd; + char buf[BUFSIZE]; + int nbytes, + tmp; + int fd; + + /* + * open the large object + */ + lobj_fd = lo_open(conn, lobjId, INV_READ); + if (lobj_fd < 0) + fprintf(stderr, "cannot open large object %u", lobjId); + + /* + * open the file to be written to + */ + fd = open(filename, O_CREAT | O_WRONLY | O_TRUNC, 0666); + if (fd < 0) + { /* error */ + fprintf(stderr, "cannot open unix file\"%s\"", + filename); + } + + /* + * read in from the inversion file and write to the Unix file + */ + while ((nbytes = lo_read(conn, lobj_fd, buf, BUFSIZE)) > 0) + { + tmp = write(fd, buf, nbytes); + if (tmp < nbytes) + { + fprintf(stderr, "error while writing \"%s\"", + filename); + } + } + + lo_close(conn, lobj_fd); + close(fd); + + return; +} + +static void +exit_nicely(PGconn *conn) +{ + PQfinish(conn); + exit(1); +} + +int +main(int argc, char **argv) +{ + char *in_filename, + *out_filename; + char *database; + Oid lobjOid; + PGconn *conn; + PGresult *res; + + if (argc != 4) + { + fprintf(stderr, "Usage: %s database_name in_filename out_filename\n", + argv[0]); + exit(1); + } + + database = argv[1]; + in_filename = argv[2]; + out_filename = argv[3]; + + /* + * set up the connection + */ + conn = PQsetdb(NULL, NULL, NULL, NULL, database); + + /* check to see that the backend connection was successfully made */ + if (PQstatus(conn) != CONNECTION_OK) + { + fprintf(stderr, "Connection to database failed: %s", + PQerrorMessage(conn)); + exit_nicely(conn); + } + + /* Set always-secure search path, so malicious users can't take control. */ + res = PQexec(conn, + "SELECT pg_catalog.set_config('search_path', '', false)"); + if (PQresultStatus(res) != PGRES_TUPLES_OK) + { + fprintf(stderr, "SET failed: %s", PQerrorMessage(conn)); + PQclear(res); + exit_nicely(conn); + } + PQclear(res); + + res = PQexec(conn, "begin"); + PQclear(res); + printf("importing file \"%s\" ...\n", in_filename); +/* lobjOid = importFile(conn, in_filename); */ + lobjOid = lo_import(conn, in_filename); + if (lobjOid == 0) + fprintf(stderr, "%s\n", PQerrorMessage(conn)); + else + { + printf("\tas large object %u.\n", lobjOid); + + printf("picking out bytes 1000-2000 of the large object\n"); + pickout(conn, lobjOid, 1000, 1000); + + printf("overwriting bytes 1000-2000 of the large object with X's\n"); + overwrite(conn, lobjOid, 1000, 1000); + + printf("exporting large object to file \"%s\" ...\n", out_filename); +/* exportFile(conn, lobjOid, out_filename); */ + if (lo_export(conn, lobjOid, out_filename) < 0) + fprintf(stderr, "%s\n", PQerrorMessage(conn)); + } + + res = PQexec(conn, "end"); + PQclear(res); + PQfinish(conn); + return 0; +} + +</pre></div></div><br class="example-break" /></div><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navfooter"><hr></hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="lo-funcs.html" title="34.4. Server-Side Functions">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="largeobjects.html" title="Chapter 34. Large Objects">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ecpg.html" title="Chapter 35. ECPG — Embedded SQL in C">Next</a></td></tr><tr><td width="40%" align="left" valign="top">34.4. Server-Side Functions </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 13.4 Documentation">Home</a></td><td width="40%" align="right" valign="top"> Chapter 35. <span xmlns="http://www.w3.org/1999/xhtml" class="application">ECPG</span> — Embedded <acronym xmlns="http://www.w3.org/1999/xhtml" class="acronym">SQL</acronym> in C</td></tr></table></div></body></html>
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