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February 4, 2019 19:19
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Progressive Enrichment Demo Notes
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| Notes on server-side of https://fonts.gstatic.com/experimental/incxfer_demo | |
| - it's currently tied to Google internal serving so just open sourcing code isn't helpful | |
| /experimental/incxfer, args: | |
| - font - string identifying font, e.g. Lobster:400 | |
| - cp_current - csv of codepoints UA has | |
| - cp_needed - csv of codepoints UA would like to have | |
| - retain_gids - whether gids should be stable | |
| - diff_type - lets demo support different diff algorithms | |
| NOTE: csv of codepoints clearly isn't want we want long-term; I was in a hurry :) | |
| Server logic is, roughly: | |
| subset_before = subset(font).to_codepoints(cp_current) | |
| subset_after = subset(font).to_codepoints(cp_needed + cp_current) | |
| delta = delta(diff_type).from(subset_before).to(subset_after).build() | |
| Subset is done by calling hb_subset. | |
| The most interesting delta is done doing Brotli Shared Dictionary, | |
| using the subset_before (which the client already has) as the dictionary. | |
| Code to compute this is shown in brdelta.cc. | |
| We also compute some additional information that is only needed to display comparisons in the UI. |
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| // WARNING: experimental demo quality code | |
| // Only functions of potential interest are shown | |
| #include "third_party/absl/strings/bytestream.h" | |
| #include "third_party/brotli/dec/decode.h" | |
| #include "third_party/brotli/enc/encode.h" | |
| bool CompressStreamWithDictionary(uint32_t quality, strings::ByteSource* source, | |
| strings::ByteSink* sink, | |
| BrotliEncoderPreparedDictionary* dictionary) { | |
| BrotliEncoderState* state = | |
| BrotliEncoderCreateInstance(nullptr, nullptr, nullptr); | |
| if (state == nullptr) { | |
| return false; | |
| } | |
| if (!BrotliEncoderSetParameter(state, BROTLI_PARAM_QUALITY, quality)) { | |
| return false; | |
| } | |
| if (!BrotliEncoderSetParameter(state, BROTLI_PARAM_SIZE_HINT, | |
| source->Available())) { | |
| return false; | |
| } | |
| if (!BrotliEncoderAttachPreparedDictionary(state, dictionary)) { | |
| return false; | |
| } | |
| size_t available_in, available_out = 0, bytes_written = 0; | |
| BROTLI_BOOL result = BROTLI_TRUE; | |
| while (source->Available() > 0 && result) { | |
| absl::string_view sp = source->Peek(); | |
| available_in = sp.size(); | |
| const uint8_t* next_in = reinterpret_cast<const uint8_t*>(sp.data()); | |
| result = BrotliEncoderCompressStream(state, BROTLI_OPERATION_PROCESS, | |
| &available_in, &next_in, | |
| &available_out, nullptr, nullptr); | |
| size_t buffer_size = 0; | |
| const uint8_t* buffer = BrotliEncoderTakeOutput(state, &buffer_size); | |
| if (buffer_size > 0) { | |
| sink->Append(reinterpret_cast<const char*>(buffer), buffer_size); | |
| bytes_written += buffer_size; | |
| } | |
| source->Skip(sp.size() - available_in); | |
| } | |
| while (result && !BrotliEncoderIsFinished(state)) { | |
| available_in = 0; | |
| const uint8_t* next_in = nullptr; | |
| result = BrotliEncoderCompressStream(state, BROTLI_OPERATION_FINISH, | |
| &available_in, &next_in, | |
| &available_out, nullptr, nullptr); | |
| size_t buffer_size = 0; | |
| const uint8_t* buffer = BrotliEncoderTakeOutput(state, &buffer_size); | |
| if (buffer_size > 0) { | |
| sink->Append(reinterpret_cast<const char*>(buffer), buffer_size); | |
| bytes_written += buffer_size; | |
| } | |
| } | |
| BrotliEncoderDestroyInstance(state); | |
| return result; | |
| } | |
| bool UncompressStreamWithDictionary(strings::ByteSource* source, | |
| strings::ByteSink* sink, size_t dict_size, | |
| const uint8_t* dict) { | |
| BrotliDecoderState* state = | |
| BrotliDecoderCreateInstance(nullptr, nullptr, nullptr); | |
| if (state == nullptr) { | |
| return false; | |
| } | |
| if (!BrotliDecoderAttachDictionary(state, BROTLI_SHARED_DICTIONARY_RAW, | |
| dict_size, dict)) { | |
| BrotliDecoderDestroyInstance(state); | |
| return false; | |
| } | |
| size_t available_in, available_out = 0; | |
| BrotliDecoderResult result = BROTLI_DECODER_RESULT_SUCCESS; | |
| while (source->Available() > 0 && result != BROTLI_DECODER_RESULT_ERROR) { | |
| absl::string_view sp = source->Peek(); | |
| available_in = sp.size(); | |
| const uint8_t* next_in = reinterpret_cast<const uint8_t*>(sp.data()); | |
| result = BrotliDecoderDecompressStream(state, &available_in, &next_in, | |
| &available_out, nullptr, nullptr); | |
| source->Skip(sp.size() - available_in); | |
| size_t buffer_size = 0; | |
| const uint8_t* buffer = BrotliDecoderTakeOutput(state, &buffer_size); | |
| if (buffer_size > 0) { | |
| sink->Append(reinterpret_cast<const char*>(buffer), buffer_size); | |
| } else if (result == BROTLI_DECODER_RESULT_SUCCESS) { | |
| // Decoding is finished and all output is pushed. | |
| break; | |
| } | |
| } | |
| while (result == BROTLI_DECODER_RESULT_NEEDS_MORE_OUTPUT) { | |
| available_in = 0; | |
| const uint8_t* next_in = nullptr; | |
| result = BrotliDecoderDecompressStream(state, &available_in, &next_in, | |
| &available_out, nullptr, nullptr); | |
| size_t buffer_size = 0; | |
| const uint8_t* buffer = BrotliDecoderTakeOutput(state, &buffer_size); | |
| if (buffer_size > 0) { | |
| sink->Append(reinterpret_cast<const char*>(buffer), buffer_size); | |
| } | |
| } | |
| BrotliDecoderDestroyInstance(state); | |
| return result == BROTLI_DECODER_RESULT_SUCCESS && source->Available() == 0; | |
| } |
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