Allow searching images by IQDB hash.

Allow clients to pass a `hash` param to search by IQDB hash. This way
clients can search for hashes they've generated themselves, instead of
having to send full images to IQDB.

include/iqdb/haar_signature.h

@@ -15,6 +15,7 @@ struct HaarSignature {
 
   HaarSignature() {};
   explicit HaarSignature(lumin_t avglf, signature_t sig);
+  static HaarSignature from_hash(const std::string hash);
   static HaarSignature from_file_content(const std::string blob);
 
   std::string to_string() const;

src/haar_signature.cpp

@@ -18,6 +18,29 @@ HaarSignature::HaarSignature(lumin_t avglf_, signature_t sig_) {
   std::sort(&sig[2][0], &sig[2][NUM_COEFS]);
 }
 
+HaarSignature HaarSignature::from_hash(const std::string hash) {
+  if (hash.size() != 5 + 2*sizeof(HaarSignature)) {
+    throw param_error("Invalid hash (hash=" + hash + ")");
+  }
+
+  HaarSignature haar;
+  const char* p = hash.c_str() + 5; // skip "iqdb_" prefix
+
+  for (double& avglf : haar.avglf) {
+    sscanf(p, "%16lx", reinterpret_cast<uint64_t*>(&avglf));
+    p += 2 * sizeof(uint64_t);
+  }
+
+  for (int c = 0; c < 3; c++) {
+    for (int16_t& coef : haar.sig[c]) {
+      sscanf(p, "%4hx", &coef);
+      p += 2 * sizeof(int16_t);
+    }
+  }
+
+  return haar;
+}
+
 HaarSignature HaarSignature::from_file_content(const std::string blob) {
   HaarSignature signature;
   std::vector<unsigned char> rchan(NUM_PIXELS * NUM_PIXELS);

src/server.cpp

@@ -104,16 +104,22 @@ void http_server(const std::string host, const int port, const std::string datab
     std::shared_lock lock(mutex_);
 
     int limit = 10;
+    sim_vector matches;
     json data;
 
-    if (!request.has_file("file"))
-      throw imgdb::param_error("`POST /query` requires a `file` param");
-
     if (request.has_param("limit"))
       limit = stoi(request.get_param_value("limit"));
 
-    const auto &file = request.get_file_value("file");
-    const auto matches = memory_db->queryFromBlob(file.content, limit);
+    if (request.has_param("hash")) {
+      const auto hash = request.get_param_value("hash");
+      HaarSignature haar = HaarSignature::from_hash(hash);
+      matches = memory_db->queryFromSignature(haar, limit);
+    } else if (request.has_file("file")) {
+      const auto &file = request.get_file_value("file");
+      matches = memory_db->queryFromBlob(file.content, limit);
+    } else {
+      throw param_error("`POST /query` requires a `file` or `hash` param");
+    }
 
     for (const auto &match : matches) {
       auto image = memory_db->getImage(match.id);