Compression (#147)

* enable header detection in util::decompress and also use it for gziped data

* expose zlib windowBits so mbgl::util::compress can be used for different formats

* also expose windowBits in decompress function for consistency

include/mbgl/util/compression.hpp

@@ -5,8 +5,10 @@
 namespace mbgl {
 namespace util {
 
-std::string compress(const std::string& raw);
-std::string decompress(const std::string& raw);
+enum CompressionFormat { ZLIB = 15, GZIP = 15 + 16, DEFLATE = -15, DETECT = 15 + 32 };
+
+std::string compress(const std::string& raw, int windowBits = CompressionFormat::ZLIB);
+std::string decompress(const std::string& raw, int windowBits = CompressionFormat::DETECT);
 
 } // namespace util
 } // namespace mbgl

platform/default/src/mbgl/storage/mbtiles_file_source.cpp

@@ -13,6 +13,7 @@
 #include <mbgl/util/thread.hpp>
 #include <mbgl/util/url.hpp>
 #include <mbgl/util/chrono.hpp>
+#include <mbgl/util/compression.hpp>
 
 #include <mbgl/storage/sqlite3.hpp>
 
@@ -75,47 +76,6 @@ public:
         return (((uint8_t) v[0]) == 0x1f) && (((uint8_t) v[1]) == 0x8b);
     }
 
-    // Some Mbtiles store GZIP-ed tile data, this function is used for decompression
-    std::string decompress_string(const std::string &data) {
-
-        constexpr uint32_t OUT_SIZE = 8192;
-
-        int ret;
-        char outbuffer[OUT_SIZE];
-        std::string outstring;
-
-        z_stream zs{};
-
-        // Init inflate to gzip mode
-        if (inflateInit2(&zs, (16 + MAX_WBITS)) != Z_OK)
-            return "";
-
-        zs.next_in = (Bytef *) data.data();
-        zs.avail_in = (unsigned int) data.size();
-
-
-        // get the decompressed bytes blockwise using repeated calls to inflate
-        do {
-            zs.next_out = reinterpret_cast<Bytef *>(outbuffer);
-            zs.avail_out = OUT_SIZE;
-
-            ret = inflate(&zs, 0);
-
-            if (outstring.size() < zs.total_out) {
-                outstring.append(outbuffer, zs.total_out - outstring.size());
-            }
-
-        } while (ret == Z_OK);
-
-        inflateEnd(&zs);
-
-        if (ret != Z_STREAM_END) { // an error occurred that was not EOF
-            return "";
-        }
-
-        return outstring;
-    }
-
     // Generate a tilejson resource from .mbtiles file
     void request_tilejson(const Resource &resource, ActorRef<FileSourceRequest> req) {
         auto path = url_to_path(resource.url);
@@ -258,7 +218,7 @@ public:
                 response.error.release();
 
                 if (is_compressed(*response.data)) {
-                    response.data = std::make_shared<std::string>(decompress_string(*response.data));
+                    response.data = std::make_shared<std::string>(util::decompress(*response.data));
                 }
             }
         }

platform/default/src/mbgl/util/compression.cpp

@@ -37,12 +37,12 @@ namespace util {
 // cause a link error.
 #undef compress
 
-std::string compress(const std::string &raw) {
+std::string compress(const std::string &raw, int windowBits) {
     z_stream deflate_stream;
     memset(&deflate_stream, 0, sizeof(deflate_stream));
 
     // TODO: reuse z_streams
-    if (deflateInit(&deflate_stream, Z_DEFAULT_COMPRESSION) != Z_OK) {
+    if (deflateInit2(&deflate_stream, Z_DEFAULT_COMPRESSION, Z_DEFLATED, windowBits, 8, Z_DEFAULT_STRATEGY) != Z_OK) {
         throw std::runtime_error("failed to initialize deflate");
     }
 
@@ -72,12 +72,12 @@ std::string compress(const std::string &raw) {
     return result;
 }
 
-std::string decompress(const std::string &raw) {
+std::string decompress(const std::string &raw, int windowBits) {
     z_stream inflate_stream;
     memset(&inflate_stream, 0, sizeof(inflate_stream));
 
     // TODO: reuse z_streams
-    if (inflateInit(&inflate_stream) != Z_OK) {
+    if (inflateInit2(&inflate_stream, windowBits) != Z_OK) {
         throw std::runtime_error("failed to initialize inflate");
     }