Add support for Readable#discard_until. (#7)

Author: ioquatix

lib/io/stream/readable.rb

@@ -116,17 +116,28 @@ def readpartial(size = nil)
 		# @parameter offset [Integer] The offset to start searching from.
 		# @parameter limit [Integer | Nil] The maximum number of bytes to read while searching.
 		# @returns [Integer | Nil] The index of the pattern, or nil if not found.
-		private def index_of(pattern, offset, limit)
+		private def index_of(pattern, offset, limit, discard = false)
 			# We don't want to split on the pattern, so we subtract the size of the pattern.
 			split_offset = pattern.bytesize - 1
-
+			
 			until index = @read_buffer.index(pattern, offset)
 				offset = @read_buffer.bytesize - split_offset
 
 				offset = 0 if offset < 0
 
-				return nil if limit and offset >= limit
-				return nil unless fill_read_buffer
+				if limit and offset >= limit
+					return nil
+				end
+				
+				unless fill_read_buffer
+					return nil
+				end
+				
+				if discard
+					# If we are discarding, we should consume the read buffer up to the offset:
+					consume_read_buffer(offset)
+					offset = 0
+				end
 			end
 
 			return index
@@ -136,7 +147,8 @@ def readpartial(size = nil)
 		# @parameter pattern [String] The pattern to match.
 		# @parameter offset [Integer] The offset to start searching from.
 		# @parameter limit [Integer] The maximum number of bytes to read, including the pattern (even if chomped).
-		# @returns [String | Nil] The contents of the stream up until the pattern, which is consumed but not returned.
+		# @parameter chomp [Boolean] Whether to remove the pattern from the returned data.
+		# @returns [String | Nil] The contents of the stream up until the pattern, or nil if the pattern was not found. 
 		def read_until(pattern, offset = 0, limit: nil, chomp: true)
 			if index = index_of(pattern, offset, limit)
 				return nil if limit and index >= limit
@@ -149,6 +161,28 @@ def read_until(pattern, offset = 0, limit: nil, chomp: true)
 			end
 		end
 
+		# Efficiently discard data from the stream until encountering pattern.
+		# @parameter pattern [String] The pattern to match.
+		# @parameter offset [Integer] The offset to start searching from.
+		# @parameter limit [Integer] The maximum number of bytes to read, including the pattern.
+		# @returns [String | Nil] The contents of the stream up until the pattern, or nil if the pattern was not found.
+		def discard_until(pattern, offset = 0, limit: nil)
+			if index = index_of(pattern, offset, limit, true)
+				@read_buffer.freeze
+				
+				if limit and index >= limit
+					@read_buffer = @read_buffer.byteslice(limit, @read_buffer.bytesize)
+					
+					return nil
+				end
+				
+				matched = @read_buffer.byteslice(0, index+pattern.bytesize)
+				@read_buffer = @read_buffer.byteslice(index+pattern.bytesize, @read_buffer.bytesize)
+				
+				return matched
+			end
+		end
+		
 		# Peek at data in the buffer without consuming it.
 		# @parameter size [Integer | Nil] The number of bytes to peek at. If nil, peek at all available data.
 		# @returns [String] The data in the buffer without consuming it.

test/io/stream/buffered.rb

@@ -438,6 +438,107 @@ def before
 			expect(write_buffer).to be(:empty?)
 		end
 	end
+	
+	with "#discard_until" do
+		it "can discard data until pattern" do
+			server.write("hello\nworld\ntest")
+			server.close
+			
+			# Discard until "\n" - should return chunk ending with the pattern
+			chunk = client.discard_until("\n")
+			expect(chunk).not.to be_nil
+			expect(chunk).to be(:end_with?, "\n")
+			# Read the remaining data to verify it starts with "world"
+			expect(client.read(5)).to be == "world"
+			
+			# Discard until "t" - should return chunk ending with the pattern  
+			chunk = client.discard_until("t")
+			expect(chunk).not.to be_nil
+			expect(chunk).to be(:end_with?, "t")
+			# Read remaining data
+			expect(client.read).to be == "est"
+		end
+		
+		it "returns nil when pattern not found and discards all data" do
+			server.write("hello world")
+			server.close
+			
+			expect(client.discard_until("\n")).to be_nil
+			# Data should still be available since pattern was not found
+			expect(client.read).to be == "hello world"
+		end
+		
+		it "can discard with a limit" do
+			server.write("hello\nworld\n")
+			server.close
+			
+			# Use peek to verify initial buffer state
+			expect(client.peek).to be == "hello\nworld\n"
+			
+			# Limit too small to find pattern - discards up to limit
+			expect(client.discard_until("\n", limit: 4)).to be_nil
+			
+			# Use peek to verify that 4 bytes were discarded
+			expect(client.peek).to be == "o\nworld\n"
+			
+			# After discarding 4 bytes, should find pattern in remaining data
+			chunk = client.discard_until("\n", limit: 5)
+			expect(chunk).not.to be_nil
+			expect(chunk).to be(:end_with?, "\n")
+			
+			# Use peek to verify final buffer state
+			expect(client.peek).to be == "world\n"
+			expect(client.read).to be == "world\n"
+		end
+		
+		it "handles patterns spanning buffer boundaries" do
+			# Use a small block size to force the pattern to span boundaries
+			client.block_size = 3
+			
+			server.write("ab")
+			server.flush
+			server.write("cdef")
+			server.close
+			
+			# Pattern "cd" spans the boundary between "ab" and "cdef"
+			chunk = client.discard_until("cd")
+			expect(chunk).not.to be_nil
+			expect(chunk).to be(:end_with?, "cd")
+			expect(client.read).to be == "ef"
+		end
+		
+		it "handles large patterns efficiently" do
+			large_pattern = "X" * 20  # Trigger sliding window logic
+			server.write("some data before")
+			server.write(large_pattern)
+			server.write("some data after")
+			server.close
+			
+			chunk = client.discard_until(large_pattern)
+			expect(chunk).not.to be_nil
+			expect(chunk).to be(:end_with?, large_pattern)
+			expect(client.read).to be == "some data after"
+		end
+		
+		with "with 1-byte block size" do
+			it "can discard data with a multi-byte pattern" do
+				server.write("hello\nworld\n")
+				server.close
+				
+				client.block_size = 1
+				
+				chunk1 = client.discard_until("\n")
+				expect(chunk1).not.to be_nil
+				expect(chunk1).to be(:end_with?, "\n")
+				
+				chunk2 = client.discard_until("\n")
+				expect(chunk2).not.to be_nil
+				expect(chunk2).to be(:end_with?, "\n")
+				
+				expect(client.discard_until("\n")).to be_nil
+			end
+		end
+	end
 end
 
 ABidirectionalStream = Sus::Shared("a bidirectional stream") do