iqdb: allow searching images by iqdb hash.

Example:

    https://danbooru.donmai.us/iqdb_queries?search[hash]=iqdb_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

The hash may be obtained from a regular IQDB search, or by calculating
it yourself (an exercise for the reader).

app/controllers/iqdb_queries_controller.rb

@@ -3,7 +3,7 @@ class IqdbQueriesController < ApplicationController
 
   def show
     # XXX allow bare search params for backwards compatibility.
-    search_params.merge!(params.slice(:url, :image_url, :file_url, :post_id, :limit, :similarity, :high_similarity).permit!)
+    search_params.merge!(params.slice(:url, :hash, :image_url, :file_url, :post_id, :limit, :similarity, :high_similarity).permit!)
 
     iqdb_params = search_params.to_h.symbolize_keys
     @high_similarity_matches, @low_similarity_matches, @matches = IqdbClient.new.search(**iqdb_params)

app/logical/iqdb_client.rb

@@ -15,8 +15,8 @@ class IqdbClient
   end
 
   concerning :QueryMethods do
-    # Search for an image by file, URL, or post ID.
-    def search(post_id: nil, file: nil, url: nil, image_url: nil, file_url: nil, similarity: 0.0, high_similarity: 65.0, limit: 20)
+    # Search for an image by file, URL, hash, or post ID.
+    def search(post_id: nil, file: nil, hash: nil, url: nil, image_url: nil, file_url: nil, similarity: 0.0, high_similarity: 65.0, limit: 20)
       limit = limit.to_i.clamp(1, 1000)
       similarity = similarity.to_f.clamp(0.0, 100.0)
       high_similarity = high_similarity.to_f.clamp(0.0, 100.0)
@@ -31,16 +31,17 @@ class IqdbClient
         file = download(file_url, :image_url)
       elsif post_id.present?
         file = Post.find(post_id).file(:preview)
-      else
-        return [[], [], []]
       end
 
-      results = query(file, limit: limit)
-      results = results.select { |result| result["score"] >= similarity }.take(limit)
-      matches = decorate_posts(results)
-      high_similarity_matches, low_similarity_matches = matches.partition { |match| match["score"] >= high_similarity }
+      if hash.present?
+        results = query_hash(hash, limit: limit)
+      elsif file.present?
+        results = query_file(file, limit: limit)
+      else
+        results = []
+      end
 
-      [high_similarity_matches, low_similarity_matches, matches]
+      process_results(results, similarity, high_similarity)
     ensure
       file.try(:close)
     end
@@ -59,15 +60,21 @@ class IqdbClient
     # Transform the JSON returned by IQDB to add the full post data for each
     # match.
     # @param matches [Array<Hash>] the array of IQDB matches
-    # @return [Array<Hash>] the array of IQDB matches, with post data
-    def decorate_posts(matches)
+    # @param low_similarity [Float] the threshold for a result to be considered low similarity
+    # @param high_similarity [Float] the threshold for a result to be considered high similarity
+    # @return [(Array, Array, Array)] the set of high similarity, low similarity, and all matches
+    def process_results(matches, low_similarity, high_similarity)
+      matches = matches.select { |result| result["score"] >= low_similarity }
       post_ids = matches.map { |match| match["post_id"] }
       posts = Post.where(id: post_ids).group_by(&:id).transform_values(&:first)
 
-      matches.map do |match|
+      matches = matches.map do |match|
         post = posts.fetch(match["post_id"], nil)
         match.with_indifferent_access.merge(post: post) if post
       end.compact
+
+      high_similarity_matches, low_similarity_matches = matches.partition { |match| match["score"] >= high_similarity }
+      [high_similarity_matches, low_similarity_matches, matches]
     end
   end
 
@@ -80,9 +87,15 @@ class IqdbClient
   end
 
   concerning :HttpMethods do
-    # Search for an image in IQDB.
+    # Search for an image in IQDB by hash.
+    # @param hash [String] the IQDB hash to search
+    def query_hash(hash, limit: 20)
+      request(:post, "query", params: { hash: hash, limit: limit })
+    end
+
+    # Search for an image file in IQDB.
     # @param file [File] the image to search
-    def query(file, limit: 20)
+    def query_file(file, limit: 20)
       media_file = MediaFile.open(file)
       preview = media_file.preview(Danbooru.config.small_image_width, Danbooru.config.small_image_width)
       file = HTTP::FormData::File.new(preview)

app/views/iqdb_queries/show.html.erb

@@ -10,6 +10,7 @@
       <%= search_form_for(iqdb_queries_path, method: :post) do |f| %>
         <%= f.input :post_id, label: "Post ID", input_html: { value: params[:search][:post_id] } %>
         <%= f.input :url, input_html: { value: params[:search][:url] } %>
+        <%= f.input :hash, input_html: { value: params[:search][:hash] } %>
         <%= f.input :file, as: :file %>
         <%= f.submit "Search" %>
       <% end %>