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122 lines
3.3 KiB
122 lines
3.3 KiB
package pgx
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import (
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"context"
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"errors"
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"io"
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)
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// LargeObjects is a structure used to access the large objects API. It is only valid within the transaction where it
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// was created.
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//
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// For more details see: http://www.postgresql.org/docs/current/static/largeobjects.html
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type LargeObjects struct {
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tx Tx
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}
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type LargeObjectMode int32
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const (
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LargeObjectModeWrite LargeObjectMode = 0x20000
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LargeObjectModeRead LargeObjectMode = 0x40000
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)
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// Create creates a new large object. If oid is zero, the server assigns an unused OID.
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func (o *LargeObjects) Create(ctx context.Context, oid uint32) (uint32, error) {
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err := o.tx.QueryRow(ctx, "select lo_create($1)", oid).Scan(&oid)
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return oid, err
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}
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// Open opens an existing large object with the given mode. ctx will also be used for all operations on the opened large
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// object.
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func (o *LargeObjects) Open(ctx context.Context, oid uint32, mode LargeObjectMode) (*LargeObject, error) {
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var fd int32
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err := o.tx.QueryRow(ctx, "select lo_open($1, $2)", oid, mode).Scan(&fd)
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if err != nil {
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return nil, err
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}
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return &LargeObject{fd: fd, tx: o.tx, ctx: ctx}, nil
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}
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// Unlink removes a large object from the database.
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func (o *LargeObjects) Unlink(ctx context.Context, oid uint32) error {
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var result int32
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err := o.tx.QueryRow(ctx, "select lo_unlink($1)", oid).Scan(&result)
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if err != nil {
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return err
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}
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if result != 1 {
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return errors.New("failed to remove large object")
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}
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return nil
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}
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// A LargeObject is a large object stored on the server. It is only valid within the transaction that it was initialized
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// in. It uses the context it was initialized with for all operations. It implements these interfaces:
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//
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// io.Writer
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// io.Reader
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// io.Seeker
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// io.Closer
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type LargeObject struct {
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ctx context.Context
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tx Tx
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fd int32
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}
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// Write writes p to the large object and returns the number of bytes written and an error if not all of p was written.
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func (o *LargeObject) Write(p []byte) (int, error) {
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var n int
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err := o.tx.QueryRow(o.ctx, "select lowrite($1, $2)", o.fd, p).Scan(&n)
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if err != nil {
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return n, err
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}
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if n < 0 {
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return 0, errors.New("failed to write to large object")
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}
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return n, nil
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}
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// Read reads up to len(p) bytes into p returning the number of bytes read.
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func (o *LargeObject) Read(p []byte) (int, error) {
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var res []byte
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err := o.tx.QueryRow(o.ctx, "select loread($1, $2)", o.fd, len(p)).Scan(&res)
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copy(p, res)
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if err != nil {
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return len(res), err
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}
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if len(res) < len(p) {
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err = io.EOF
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}
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return len(res), err
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}
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// Seek moves the current location pointer to the new location specified by offset.
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func (o *LargeObject) Seek(offset int64, whence int) (n int64, err error) {
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err = o.tx.QueryRow(o.ctx, "select lo_lseek64($1, $2, $3)", o.fd, offset, whence).Scan(&n)
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return n, err
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}
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// Tell returns the current read or write location of the large object descriptor.
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func (o *LargeObject) Tell() (n int64, err error) {
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err = o.tx.QueryRow(o.ctx, "select lo_tell64($1)", o.fd).Scan(&n)
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return n, err
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}
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// Truncate the large object to size.
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func (o *LargeObject) Truncate(size int64) (err error) {
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_, err = o.tx.Exec(o.ctx, "select lo_truncate64($1, $2)", o.fd, size)
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return err
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}
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// Close the large object descriptor.
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func (o *LargeObject) Close() error {
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_, err := o.tx.Exec(o.ctx, "select lo_close($1)", o.fd)
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return err
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}
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