mirror of
https://github.com/superseriousbusiness/gotosocial.git
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213 lines
6.6 KiB
Go
213 lines
6.6 KiB
Go
/*
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GoToSocial
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Copyright (C) 2021-2023 GoToSocial Authors admin@gotosocial.org
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU Affero General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU Affero General Public License for more details.
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You should have received a copy of the GNU Affero General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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package media
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/*
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The code in this file is taken from the following source:
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https://github.com/google/wuffs/blob/414a011491ff513b86d8694c5d71800f3cb5a715/script/strip-png-ancillary-chunks.go
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It presents a workaround for this issue: https://github.com/golang/go/issues/43382
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The license for the copied code is reproduced below:
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Copyright 2021 The Wuffs Authors.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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https://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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// strip-png-ancillary-chunks.go copies PNG data from stdin to stdout, removing
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// any ancillary chunks.
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//
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// Specification-compliant PNG decoders are required to honor critical chunks
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// but may ignore ancillary (non-critical) chunks. Stripping out ancillary
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// chunks before decoding should mean that different PNG decoders will agree on
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// the decoded output regardless of which ancillary chunk types they choose to
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// honor. Specifically, some PNG decoders may implement color and gamma
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// correction but not all do.
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//
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// This program will strip out all ancillary chunks, but it should be
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// straightforward to copy-paste-and-modify it to strip out only certain chunk
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// types (e.g. only "tRNS" transparency chunks).
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//
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// --------
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//
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// A PNG file consists of an 8-byte magic identifier and then a series of
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// chunks. Each chunk is:
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//
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// - a 4-byte uint32 payload length N.
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// - a 4-byte chunk type (e.g. "gAMA" for gamma correction metadata).
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// - an N-byte payload.
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// - a 4-byte CRC-32 checksum of the previous (N + 4) bytes, including the
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// chunk type but excluding the payload length.
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//
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// Chunk types consist of 4 ASCII letters. The upper-case / lower-case bit of
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// the first letter denote critical or ancillary chunks: "IDAT" and "PLTE" are
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// critical, "gAMA" and "tEXt" are ancillary. See
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// https://www.w3.org/TR/2003/REC-PNG-20031110/#5Chunk-naming-conventions
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//
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// --------
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import (
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"encoding/binary"
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"io"
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)
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const (
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chunkTypeIHDR = 0x49484452
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chunkTypePLTE = 0x504C5445
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chunkTypeIDAT = 0x49444154
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chunkTypeIEND = 0x49454E44
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chunkTypeTRNS = 0x74524e53
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)
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func isNecessaryChunkType(chunkType uint32) bool {
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switch chunkType {
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case chunkTypeIHDR:
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return true
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case chunkTypePLTE:
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return true
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case chunkTypeIDAT:
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return true
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case chunkTypeIEND:
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return true
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case chunkTypeTRNS:
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return true
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}
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return false
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}
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// pngAncillaryChunkStripper wraps another io.Reader to strip ancillary chunks,
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// if the data is in the PNG file format. If the data isn't PNG, it is passed
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// through unmodified.
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type pngAncillaryChunkStripper struct {
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// Reader is the wrapped io.Reader.
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Reader io.Reader
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// stickyErr is the first error returned from the wrapped io.Reader.
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stickyErr error
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// buffer[rIndex:wIndex] holds data read from the wrapped io.Reader that
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// wasn't passed through yet.
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buffer [8]byte
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rIndex int
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wIndex int
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// pending and discard is the number of remaining bytes for (and whether to
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// discard or pass through) the current chunk-in-progress.
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pending int64
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discard bool
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// notPNG is set true if the data stream doesn't start with the 8-byte PNG
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// magic identifier. If true, the wrapped io.Reader's data (including the
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// first up-to-8 bytes) is passed through without modification.
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notPNG bool
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// seenMagic is whether we've seen the 8-byte PNG magic identifier.
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seenMagic bool
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}
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// Read implements io.Reader.
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func (r *pngAncillaryChunkStripper) Read(p []byte) (int, error) {
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for {
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// If the wrapped io.Reader returned a non-nil error, drain r.buffer
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// (what data we have) and return that error (if fully drained).
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if r.stickyErr != nil {
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n := copy(p, r.buffer[r.rIndex:r.wIndex])
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r.rIndex += n
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if r.rIndex < r.wIndex {
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return n, nil
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}
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return n, r.stickyErr
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}
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// Handle trivial requests, including draining our buffer.
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if len(p) == 0 {
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return 0, nil
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} else if r.rIndex < r.wIndex {
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n := copy(p, r.buffer[r.rIndex:r.wIndex])
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r.rIndex += n
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return n, nil
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}
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// From here onwards, our buffer is drained: r.rIndex == r.wIndex.
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// Handle non-PNG input.
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if r.notPNG {
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return r.Reader.Read(p)
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}
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// Continue processing any PNG chunk that's in progress, whether
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// discarding it or passing it through.
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for r.pending > 0 {
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if int64(len(p)) > r.pending {
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p = p[:r.pending]
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}
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n, err := r.Reader.Read(p)
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r.pending -= int64(n)
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r.stickyErr = err
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if r.discard {
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continue
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}
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return n, err
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}
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// We're either expecting the 8-byte PNG magic identifier or the 4-byte
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// PNG chunk length + 4-byte PNG chunk type. Either way, read 8 bytes.
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r.rIndex = 0
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r.wIndex, r.stickyErr = io.ReadFull(r.Reader, r.buffer[:8])
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if r.stickyErr != nil {
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// Undo io.ReadFull converting io.EOF to io.ErrUnexpectedEOF.
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if r.stickyErr == io.ErrUnexpectedEOF {
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r.stickyErr = io.EOF
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}
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continue
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}
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// Process those 8 bytes, either:
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// - a PNG chunk (if we've already seen the PNG magic identifier),
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// - the PNG magic identifier itself (if the input is a PNG) or
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// - something else (if it's not a PNG).
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//nolint:gocritic
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if r.seenMagic {
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// The number of pending bytes is equal to (N + 4) because of the 4
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// byte trailer, a checksum.
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r.pending = int64(binary.BigEndian.Uint32(r.buffer[:4])) + 4
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chunkType := binary.BigEndian.Uint32(r.buffer[4:])
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r.discard = !isNecessaryChunkType(chunkType)
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if r.discard {
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r.rIndex = r.wIndex
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}
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} else if string(r.buffer[:8]) == "\x89PNG\x0D\x0A\x1A\x0A" {
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r.seenMagic = true
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} else {
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r.notPNG = true
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}
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}
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}
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