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Diffstat (limited to 'internal/media/png-stripper.go')
| -rw-r--r-- | internal/media/png-stripper.go | 211 |
1 files changed, 0 insertions, 211 deletions
diff --git a/internal/media/png-stripper.go b/internal/media/png-stripper.go deleted file mode 100644 index 09126f6a5..000000000 --- a/internal/media/png-stripper.go +++ /dev/null @@ -1,211 +0,0 @@ -// GoToSocial -// Copyright (C) GoToSocial Authors admin@gotosocial.org -// SPDX-License-Identifier: AGPL-3.0-or-later -// -// 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 <http://www.gnu.org/licenses/>. - -package media - -/* - The code in this file is taken from the following source: - https://github.com/google/wuffs/blob/414a011491ff513b86d8694c5d71800f3cb5a715/script/strip-png-ancillary-chunks.go - - It presents a workaround for this issue: https://github.com/golang/go/issues/43382 - - The license for the copied code is reproduced below: - - Copyright 2021 The Wuffs Authors. - - 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 - - https://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. -*/ - -// strip-png-ancillary-chunks.go copies PNG data from stdin to stdout, removing -// any ancillary chunks. -// -// Specification-compliant PNG decoders are required to honor critical chunks -// but may ignore ancillary (non-critical) chunks. Stripping out ancillary -// chunks before decoding should mean that different PNG decoders will agree on -// the decoded output regardless of which ancillary chunk types they choose to -// honor. Specifically, some PNG decoders may implement color and gamma -// correction but not all do. -// -// This program will strip out all ancillary chunks, but it should be -// straightforward to copy-paste-and-modify it to strip out only certain chunk -// types (e.g. only "tRNS" transparency chunks). -// -// -------- -// -// A PNG file consists of an 8-byte magic identifier and then a series of -// chunks. Each chunk is: -// -// - a 4-byte uint32 payload length N. -// - a 4-byte chunk type (e.g. "gAMA" for gamma correction metadata). -// - an N-byte payload. -// - a 4-byte CRC-32 checksum of the previous (N + 4) bytes, including the -// chunk type but excluding the payload length. -// -// Chunk types consist of 4 ASCII letters. The upper-case / lower-case bit of -// the first letter denote critical or ancillary chunks: "IDAT" and "PLTE" are -// critical, "gAMA" and "tEXt" are ancillary. See -// https://www.w3.org/TR/2003/REC-PNG-20031110/#5Chunk-naming-conventions -// -// -------- - -import ( - "encoding/binary" - "io" -) - -const ( - chunkTypeIHDR = 0x49484452 - chunkTypePLTE = 0x504C5445 - chunkTypeIDAT = 0x49444154 - chunkTypeIEND = 0x49454E44 - chunkTypeTRNS = 0x74524e53 -) - -func isNecessaryChunkType(chunkType uint32) bool { - switch chunkType { - case chunkTypeIHDR: - return true - case chunkTypePLTE: - return true - case chunkTypeIDAT: - return true - case chunkTypeIEND: - return true - case chunkTypeTRNS: - return true - } - return false -} - -// pngAncillaryChunkStripper wraps another io.Reader to strip ancillary chunks, -// if the data is in the PNG file format. If the data isn't PNG, it is passed -// through unmodified. -type pngAncillaryChunkStripper struct { - // Reader is the wrapped io.Reader. - Reader io.Reader - - // stickyErr is the first error returned from the wrapped io.Reader. - stickyErr error - - // buffer[rIndex:wIndex] holds data read from the wrapped io.Reader that - // wasn't passed through yet. - buffer [8]byte - rIndex int - wIndex int - - // pending and discard is the number of remaining bytes for (and whether to - // discard or pass through) the current chunk-in-progress. - pending int64 - discard bool - - // notPNG is set true if the data stream doesn't start with the 8-byte PNG - // magic identifier. If true, the wrapped io.Reader's data (including the - // first up-to-8 bytes) is passed through without modification. - notPNG bool - - // seenMagic is whether we've seen the 8-byte PNG magic identifier. - seenMagic bool -} - -// Read implements io.Reader. -func (r *pngAncillaryChunkStripper) Read(p []byte) (int, error) { - for { - // If the wrapped io.Reader returned a non-nil error, drain r.buffer - // (what data we have) and return that error (if fully drained). - if r.stickyErr != nil { - n := copy(p, r.buffer[r.rIndex:r.wIndex]) - r.rIndex += n - if r.rIndex < r.wIndex { - return n, nil - } - return n, r.stickyErr - } - - // Handle trivial requests, including draining our buffer. - if len(p) == 0 { - return 0, nil - } else if r.rIndex < r.wIndex { - n := copy(p, r.buffer[r.rIndex:r.wIndex]) - r.rIndex += n - return n, nil - } - - // From here onwards, our buffer is drained: r.rIndex == r.wIndex. - - // Handle non-PNG input. - if r.notPNG { - return r.Reader.Read(p) - } - - // Continue processing any PNG chunk that's in progress, whether - // discarding it or passing it through. - for r.pending > 0 { - if int64(len(p)) > r.pending { - p = p[:r.pending] - } - n, err := r.Reader.Read(p) - r.pending -= int64(n) - r.stickyErr = err - if r.discard { - continue - } - return n, err - } - - // We're either expecting the 8-byte PNG magic identifier or the 4-byte - // PNG chunk length + 4-byte PNG chunk type. Either way, read 8 bytes. - r.rIndex = 0 - r.wIndex, r.stickyErr = io.ReadFull(r.Reader, r.buffer[:8]) - if r.stickyErr != nil { - // Undo io.ReadFull converting io.EOF to io.ErrUnexpectedEOF. - if r.stickyErr == io.ErrUnexpectedEOF { - r.stickyErr = io.EOF - } - continue - } - - // Process those 8 bytes, either: - // - a PNG chunk (if we've already seen the PNG magic identifier), - // - the PNG magic identifier itself (if the input is a PNG) or - // - something else (if it's not a PNG). - //nolint:gocritic - if r.seenMagic { - // The number of pending bytes is equal to (N + 4) because of the 4 - // byte trailer, a checksum. - r.pending = int64(binary.BigEndian.Uint32(r.buffer[:4])) + 4 - chunkType := binary.BigEndian.Uint32(r.buffer[4:]) - r.discard = !isNecessaryChunkType(chunkType) - if r.discard { - r.rIndex = r.wIndex - } - } else if string(r.buffer[:8]) == "\x89PNG\x0D\x0A\x1A\x0A" { - r.seenMagic = true - } else { - r.notPNG = true - } - } -} |