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// Copyright 2018 The Hugo Authors. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package transform
import (
"bytes"
"io"
"io/ioutil"
bp "github.com/gohugoio/hugo/bufferpool"
"github.com/gohugoio/hugo/common/herrors"
"github.com/gohugoio/hugo/hugofs"
)
// Transformer is the func that needs to be implemented by a transformation step.
type Transformer func(ft FromTo) error
// BytesReader wraps the Bytes method, usually implemented by bytes.Buffer, and an
// io.Reader.
type BytesReader interface {
// The slice given by Bytes is valid for use only until the next buffer modification.
// That is, if you want to use this value outside of the current transformer step,
// you need to take a copy.
Bytes() []byte
io.Reader
}
// FromTo is sent to each transformation step in the chain.
type FromTo interface {
From() BytesReader
To() io.Writer
}
// Chain is an ordered processing chain. The next transform operation will
// receive the output from the previous.
type Chain []Transformer
// New creates a content transformer chain given the provided transform funcs.
func New(trs ...Transformer) Chain {
return trs
}
// NewEmpty creates a new slice of transformers with a capacity of 20.
func NewEmpty() Chain {
return make(Chain, 0, 20)
}
// Implements contentTransformer
// Content is read from the from-buffer and rewritten to to the to-buffer.
type fromToBuffer struct {
from *bytes.Buffer
to *bytes.Buffer
}
func (ft fromToBuffer) From() BytesReader {
return ft.from
}
func (ft fromToBuffer) To() io.Writer {
return ft.to
}
// Apply passes the given from io.Reader through the transformation chain.
// The result is written to to.
func (c *Chain) Apply(to io.Writer, from io.Reader) error {
if len(*c) == 0 {
_, err := io.Copy(to, from)
return err
}
b1 := bp.GetBuffer()
defer bp.PutBuffer(b1)
if _, err := b1.ReadFrom(from); err != nil {
return err
}
b2 := bp.GetBuffer()
defer bp.PutBuffer(b2)
fb := &fromToBuffer{from: b1, to: b2}
for i, tr := range *c {
if i > 0 {
if fb.from == b1 {
fb.from = b2
fb.to = b1
fb.to.Reset()
} else {
fb.from = b1
fb.to = b2
fb.to.Reset()
}
}
if err := tr(fb); err != nil {
// Write output to a temp file so it can be read by the user for trouble shooting.
filename := "output.html"
tempfile, ferr := ioutil.TempFile("", "hugo-transform-error")
if ferr == nil {
filename = tempfile.Name()
defer tempfile.Close()
_, _ = io.Copy(tempfile, fb.from)
return herrors.NewFileErrorFromFile(err, filename, hugofs.Os, nil)
}
return herrors.NewFileErrorFromName(err, filename).UpdateContent(fb.from, nil)
}
}
_, err := fb.to.WriteTo(to)
return err
}
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