| // | |
| // Copyright 2021 Google LLC | |
| // | |
| // 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. | |
| // The GZipHeader class allows you to parse a gzip header, such as you | |
| // might find at the beginning of a file compressed by gzip (ie, a .gz | |
| // file), or at the beginning of an HTTP response that uses a gzip | |
| // Content-Encoding. See RFC 1952 for the specification for the gzip | |
| // header. | |
| // | |
| // The model is that you call ReadMore() for each chunk of bytes | |
| // you've read from a file or socket. | |
| // | |
| namespace csrblocksparse { | |
| class GZipHeader { | |
| public: | |
| GZipHeader() { Reset(); } | |
| ~GZipHeader() {} | |
| // Wipe the slate clean and start from scratch. | |
| void Reset() { | |
| state_ = IN_HEADER_ID1; | |
| flags_ = 0; | |
| extra_length_ = 0; | |
| } | |
| enum Status { | |
| INCOMPLETE_HEADER, // don't have all the bits yet... | |
| COMPLETE_HEADER, // complete, valid header | |
| INVALID_HEADER, // found something invalid in the header | |
| }; | |
| // Attempt to parse the given buffer as the next installment of | |
| // bytes from a gzip header. If the bytes we've seen so far do not | |
| // yet constitute a complete gzip header, return | |
| // INCOMPLETE_HEADER. If these bytes do not constitute a *valid* | |
| // gzip header, return INVALID_HEADER. When we've seen a complete | |
| // gzip header, return COMPLETE_HEADER and set the pointer pointed | |
| // to by header_end to the first byte beyond the gzip header. | |
| Status ReadMore(const char* inbuf, int inbuf_len, const char** header_end); | |
| private: | |
| // NOLINTNEXTLINE | |
| static const uint8_t magic[]; // gzip magic header | |
| enum { // flags (see RFC) | |
| FLAG_FTEXT = 0x01, // bit 0 set: file probably ascii text | |
| FLAG_FHCRC = 0x02, // bit 1 set: header CRC present | |
| FLAG_FEXTRA = 0x04, // bit 2 set: extra field present | |
| FLAG_FNAME = 0x08, // bit 3 set: original file name present | |
| FLAG_FCOMMENT = 0x10, // bit 4 set: file comment present | |
| FLAG_RESERVED = 0xE0, // bits 5..7: reserved | |
| }; | |
| enum State { | |
| // The first 10 bytes are the fixed-size header: | |
| IN_HEADER_ID1, | |
| IN_HEADER_ID2, | |
| IN_HEADER_CM, | |
| IN_HEADER_FLG, | |
| IN_HEADER_MTIME_BYTE_0, | |
| IN_HEADER_MTIME_BYTE_1, | |
| IN_HEADER_MTIME_BYTE_2, | |
| IN_HEADER_MTIME_BYTE_3, | |
| IN_HEADER_XFL, | |
| IN_HEADER_OS, | |
| IN_XLEN_BYTE_0, | |
| IN_XLEN_BYTE_1, | |
| IN_FEXTRA, | |
| IN_FNAME, | |
| IN_FCOMMENT, | |
| IN_FHCRC_BYTE_0, | |
| IN_FHCRC_BYTE_1, | |
| IN_DONE, | |
| }; | |
| int state_; // our current State in the parsing FSM: an int so we can ++ | |
| uint8_t flags_; // the flags byte of the header ("FLG" in the RFC) | |
| uint16_t extra_length_; // how much of the "extra field" we have yet to read | |
| }; | |
| } // namespace csrblocksparse | |