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// Copyright (C) 2017-2018, 2021 Luke Shumaker <lukeshu@lukeshu.com>
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program. If not, see <https://www.gnu.org/licenses/>.
package libfastimport
import (
"bufio"
"io"
"git.lukeshu.com/go/libfastimport/textproto"
"github.com/pkg/errors"
)
// A Backend is something that consumes a fast-import stream; the
// Backend object provides methods for writing to it. A program that
// reads from a Backend would itself be a frontend.
//
// You may think of a "Backend" object as a "Writer" object, though it was not
// given that name because the GetMark, CatBlob, and Ls methods
// actually provide 2-way communication.
type Backend struct {
fastImportClose io.Closer
fastImportFlush *bufio.Writer
fastImportWrite *textproto.FIWriter
catBlob *textproto.CatBlobReader
inCommit bool
err error
onErr func(error) error
}
// NewBackend creates a new Backend object that writes to the given
// io.WriteCloser.
//
// Optionally, you may also provide an io.Reader that responses to
// "cat-blob", "get-mark", and "ls" commands can be read from.
//
// Optionally, you may also provide an onErr function that can be used
// to handle or transform errors when they are encountered.
func NewBackend(fastImport io.WriteCloser, catBlob io.Reader, onErr func(error) error) *Backend {
ret := &Backend{}
ret.fastImportClose = fastImport
ret.fastImportFlush = bufio.NewWriter(fastImport)
ret.fastImportWrite = textproto.NewFIWriter(ret.fastImportFlush)
if catBlob != nil {
ret.catBlob = textproto.NewCatBlobReader(catBlob)
}
ret.onErr = func(err error) error {
ret.err = err
// Close the underlying writer, but don't let the
// error mask the previous error.
err = ret.fastImportClose.Close()
if ret.err == nil {
ret.err = err
}
if onErr != nil {
ret.err = onErr(ret.err)
}
return ret.err
}
return ret
}
// Do tells the Backend to do the given command.
//
// It is an error (panic) if Cmd is a type that may only be used in a
// commit but we aren't in a commit.
func (b *Backend) Do(cmd Cmd) error {
if b.err != nil {
return b.err
}
switch {
case !cmdIs(cmd, cmdClassInCommit):
_, b.inCommit = cmd.(CmdCommit)
case !b.inCommit && !cmdIs(cmd, cmdClassCommand):
panic(errors.Errorf("Cannot issue commit sub-command outside of a commit: %[1]T(%#[1]v)", cmd))
}
err := cmd.fiCmdWrite(b.fastImportWrite)
if err != nil {
return b.onErr(err)
}
err = b.fastImportFlush.Flush()
if err != nil {
return b.onErr(err)
}
if _, isDone := cmd.(CmdDone); isDone {
return b.onErr(nil)
}
return nil
}
// GetMark gets the SHA-1 referred to by the given mark from the
// Backend.
//
// It is an error (panic) to call GetMark if NewBackend did not have a
// cat-blob reader passed to it.
func (b *Backend) GetMark(cmd CmdGetMark) (sha1 string, err error) {
err = b.Do(cmd)
if err != nil {
return
}
line, err := b.catBlob.ReadLine()
if err != nil {
err = b.onErr(err)
return
}
sha1, err = cbpGetMark(line)
if err != nil {
err = b.onErr(err)
}
return
}
// CatBlob gets the SHA-1 and content of the specified blob from the
// Backend.
//
// It is an error (panic) to call CatBlob if NewBackend did not have a
// cat-blob reader passed to it.
func (b *Backend) CatBlob(cmd CmdCatBlob) (sha1 string, data string, err error) {
err = b.Do(cmd)
if err != nil {
return
}
line, err := b.catBlob.ReadLine()
if err != nil {
err = b.onErr(err)
return
}
sha1, data, err = cbpCatBlob(line)
if err != nil {
err = b.onErr(err)
}
return
}
// Ls gets information about the file at the specified path from the
// Backend.
//
// It is an error (panic) to call Ls if NewBackend did not have a
// cat-blob reader passed to it.
func (b *Backend) Ls(cmd CmdLs) (mode Mode, dataref string, path Path, err error) {
err = b.Do(cmd)
if err != nil {
return
}
line, err := b.catBlob.ReadLine()
if err != nil {
err = b.onErr(err)
return
}
mode, dataref, path, err = cbpLs(line)
if err != nil {
err = b.onErr(err)
}
return
}
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