Class: Dalli::Protocol::Meta::ResponseProcessor

Inherits:
Object
  • Object
show all
Defined in:
lib/dalli/protocol/response_processor.rb

Overview

Class that encapsulates logic for processing meta protocol responses from memcached. Includes logic for pulling data from an IO source and parsing into local values. Handles errors on unexpected values.

Constant Summary collapse

EN = 
'EN'
END_TOKEN = 
'END'
EX = 
'EX'
HD = 
'HD'
MN = 
'MN'
NF = 
'NF'
NS = 
'NS'
OK = 
'OK'
RESET = 
'RESET'
STAT = 
'STAT'
VA = 
'VA'
VERSION = 
'VERSION'
SERVER_ERROR = 
'SERVER_ERROR'
T_OK = 
[OK].freeze
T_RESET = 
[RESET].freeze
T_EN_HD = 
[EN, HD].freeze
T_VERSION = 
[VERSION].freeze
T_VA_EN_HD = 
[VA, EN, HD].freeze
T_HD_NF_EX = 
[HD, NF, EX].freeze
T_HD_NS_NF_EX = 
[HD, NS, NF, EX].freeze
T_VA_NF_NS_EX = 
[VA, NF, NS, EX].freeze
T_END_TOKEN_STAT = 
[END_TOKEN, STAT].freeze

Instance Method Summary collapse

Constructor Details

#initialize(io_source, value_marshaller) ⇒ ResponseProcessor

Returns a new instance of ResponseProcessor.



36
37
38
39
 
# File 'lib/dalli/protocol/response_processor.rb', line 36

def initialize(io_source, value_marshaller)
  @io_source = io_source
  @value_marshaller = value_marshaller
end

Instance Method Details

#bitflags_from_tokens(tokens) ⇒ Object 



238
239
240
 
# File 'lib/dalli/protocol/response_processor.rb', line 238

def bitflags_from_tokens(tokens)
  value_from_tokens(tokens, 'f').to_i
end

#body_len_from_tokens(tokens) ⇒ Object 



284
285
286
 
# File 'lib/dalli/protocol/response_processor.rb', line 284

def body_len_from_tokens(tokens)
  value_from_tokens(tokens, 's').to_i
end

#build_metadata_result(tokens) ⇒ Object 



86
87
88
89
90
91
92
93
94
95
96
97
 
# File 'lib/dalli/protocol/response_processor.rb', line 86

def build_metadata_result(tokens)
  {
    value: nil, cas: cas_from_tokens(tokens),
    won_recache: tokens.include?('W'), stale: tokens.include?('X'),
    lost_recache: tokens.include?('Z'),
    # Explicit miss marker: EN means the key does not exist.  A tombstoned
    # item is NOT a miss -- it answers VA/HD with the X flag set -- and a
    # stored nil under cache_nils is not one either, so neither can be
    # inferred from value or cas alone.
    miss: tokens.first == EN
  }
end

#cas_from_tokens(tokens) ⇒ Object 



242
243
244
 
# File 'lib/dalli/protocol/response_processor.rb', line 242

def cas_from_tokens(tokens)
  value_from_tokens(tokens, 'c').to_i
end

#consume_all_responses_until_mn ⇒ Object 



160
161
162
163
164
165
 
# File 'lib/dalli/protocol/response_processor.rb', line 160

def consume_all_responses_until_mn
  tokens = next_line_to_tokens

  tokens = next_line_to_tokens while tokens.first != MN
  true
end

#decr_incr ⇒ Object 



125
126
127
128
129
130
131
 
# File 'lib/dalli/protocol/response_processor.rb', line 125

def decr_incr
  tokens = error_on_unexpected!(T_VA_NF_NS_EX)
  return false if [NS, EX].include?(tokens.first)
  return nil if tokens.first == NF

  read_line.to_i
end

#error_on_unexpected!(expected_codes) ⇒ Object

Raises:



228
229
230
231
232
233
234
235
236
 
# File 'lib/dalli/protocol/response_processor.rb', line 228

def error_on_unexpected!(expected_codes)
  tokens = next_line_to_tokens

  return tokens if expected_codes.include?(tokens.first)

  raise Dalli::ServerError, tokens.join(' ').to_s if tokens.first == SERVER_ERROR

  raise Dalli::DalliError, "Response error: #{tokens.first}"
end

#flush ⇒ Object 



143
144
145
146
147
 
# File 'lib/dalli/protocol/response_processor.rb', line 143

def flush
  error_on_unexpected!(T_OK)

  true
end

#full_response_from_buffer(tokens, body, resp_size) ⇒ Object 



184
185
186
187
 
# File 'lib/dalli/protocol/response_processor.rb', line 184

def full_response_from_buffer(tokens, body, resp_size)
  value = @value_marshaller.retrieve(body, bitflags_from_tokens(tokens))
  [tokens.first == VA, cas_from_tokens(tokens), key_from_tokens(tokens), value, resp_size]
end

#getk_response_from_buffer(buf, offset = 0) ⇒ Object

This method returns an array of values used in a pipelined getk process. The first value is the number of bytes by which to advance the pointer in the buffer. If the complete response is found in the buffer, this will be the response size. Otherwise it is zero.

The remaining three values in the array are the ResponseHeader, key, and value.



199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
 
# File 'lib/dalli/protocol/response_processor.rb', line 199

def getk_response_from_buffer(buf, offset = 0)
  # Find the header terminator starting from offset
  term_idx = buf.byteindex(TERMINATOR, offset)
  return [0] unless term_idx

  header = buf.byteslice(offset, term_idx - offset)
  tokens = header.split
  header_len = header.bytesize + TERMINATOR.length

  # The body len is removed from the tokens array
  body_len = body_len_from_tokens(tokens)

  # We have a complete response that has no body.
  # This is either the response to the terminating
  # noop or, if the status is not MN, an intermediate
  # error response that needs to be discarded.
  return [true, header_len] if body_len.zero?

  resp_size = header_len + body_len + TERMINATOR.length
  # The header is in the buffer, but the body is not.  As we don't have
  # a complete response, don't advance the buffer
  return [0] unless buf.bytesize >= offset + resp_size

  # The full response is in our buffer, so parse it and return
  # the values
  body = buf.byteslice(offset + header_len, body_len)
  full_response_from_buffer(tokens, body, resp_size)
end

#hit_status_from_tokens(tokens) ⇒ Object

Returns true if item was previously hit, false if first access, nil if not requested The h flag returns h0 (first access) or h1 (previously accessed)



265
266
267
268
269
270
 
# File 'lib/dalli/protocol/response_processor.rb', line 265

def hit_status_from_tokens(tokens)
  hit_token = tokens.find { |t| t.start_with?('h') && t.length == 2 }
  return nil unless hit_token

  hit_token[1] == '1'
end

#key_from_tokens(tokens) ⇒ Object 



254
255
256
257
258
259
260
261
 
# File 'lib/dalli/protocol/response_processor.rb', line 254

def key_from_tokens(tokens)
  encoded_key = value_from_tokens(tokens, 'k')
  if tokens.delete('b')
    KeyRegularizer.decode(encoded_key)
  else
    encoded_key
  end
end

#last_access_from_tokens(tokens) ⇒ Object

Returns seconds since last access, or nil if not requested The l flag returns l



274
275
276
 
# File 'lib/dalli/protocol/response_processor.rb', line 274

def last_access_from_tokens(tokens)
  value_from_tokens(tokens, 'l').to_i
end

#meta_delete ⇒ Object 



120
121
122
123
 
# File 'lib/dalli/protocol/response_processor.rb', line 120

def meta_delete
  tokens = error_on_unexpected!(T_HD_NF_EX)
  tokens.first == HD
end

#meta_get_with_metadata(cache_nils: false, return_hit_status: false, return_last_access: false, return_ttl_remaining: false) ⇒ Object

Returns a hash with all requested metadata:

  • :value - the cached value (or nil if miss)
  • :cas - the CAS value (if return_cas was requested)
  • :won_recache - true if client won the right to recache (W flag)
  • :stale - true if the item is stale (X flag)
  • :lost_recache - true if another client is already recaching (Z flag)
  • :hit_before - true/false if item was previously accessed (h flag, if requested)
  • :last_access - seconds since last access (l flag, if requested)

Used by meta_get for comprehensive metadata retrieval. Supports thundering herd protection (N/R flags) and metadata flags (h/l/u).



75
76
77
78
79
80
81
82
83
84
 
# File 'lib/dalli/protocol/response_processor.rb', line 75

def meta_get_with_metadata(cache_nils: false, return_hit_status: false, return_last_access: false,
                           return_ttl_remaining: false)
  tokens = error_on_unexpected!(T_VA_EN_HD)
  result = build_metadata_result(tokens)
  result[:hit_before] = hit_status_from_tokens(tokens) if return_hit_status
  result[:last_access] = last_access_from_tokens(tokens) if return_last_access
  result[:ttl_remaining] = ttl_remaining_from_tokens(tokens) if return_ttl_remaining
  result[:value] = parse_value_from_tokens(tokens, cache_nils)
  result
end

#meta_get_with_value(cache_nils: false) ⇒ Object 



41
42
43
44
45
46
47
 
# File 'lib/dalli/protocol/response_processor.rb', line 41

def meta_get_with_value(cache_nils: false)
  tokens = error_on_unexpected!(T_VA_EN_HD)
  return cache_nils ? ::Dalli::NOT_FOUND : nil if tokens.first == EN
  return true unless tokens.first == VA

  @value_marshaller.retrieve(read_data(tokens[1].to_i), bitflags_from_tokens(tokens))
end

#meta_get_with_value_and_cas ⇒ Object 



49
50
51
52
53
54
55
56
57
 
# File 'lib/dalli/protocol/response_processor.rb', line 49

def meta_get_with_value_and_cas
  tokens = error_on_unexpected!(T_VA_EN_HD)
  return [nil, 0] if tokens.first == EN

  cas = cas_from_tokens(tokens)
  return [nil, cas] unless tokens.first == VA

  [@value_marshaller.retrieve(read_data(tokens[1].to_i), bitflags_from_tokens(tokens)), cas]
end

#meta_get_without_value ⇒ Object 



59
60
61
62
 
# File 'lib/dalli/protocol/response_processor.rb', line 59

def meta_get_without_value
  tokens = error_on_unexpected!(T_EN_HD)
  tokens.first == EN ? nil : true
end

#meta_set_append_prepend ⇒ Object 



113
114
115
116
117
118
 
# File 'lib/dalli/protocol/response_processor.rb', line 113

def meta_set_append_prepend
  tokens = error_on_unexpected!(T_HD_NS_NF_EX)
  return false unless tokens.first == HD

  true
end

#meta_set_with_cas ⇒ Object 



106
107
108
109
110
111
 
# File 'lib/dalli/protocol/response_processor.rb', line 106

def meta_set_with_cas
  tokens = error_on_unexpected!(T_HD_NS_NF_EX)
  return false unless tokens.first == HD

  cas_from_tokens(tokens)
end

#next_line_to_tokens ⇒ Object 



303
304
305
306
 
# File 'lib/dalli/protocol/response_processor.rb', line 303

def next_line_to_tokens
  line = read_line
  line&.split || []
end

#parse_value_from_tokens(tokens, cache_nils) ⇒ Object 



99
100
101
102
103
104
 
# File 'lib/dalli/protocol/response_processor.rb', line 99

def parse_value_from_tokens(tokens, cache_nils)
  return cache_nils ? ::Dalli::NOT_FOUND : nil if tokens.first == EN
  return unless tokens.first == VA

  @value_marshaller.retrieve(read_data(tokens[1].to_i), bitflags_from_tokens(tokens))
end

#pipelined_delete_non_deletions ⇒ Object

Consumes the responses to a batch of quiet (pipelined) delete requests, which are terminated by a noop (MN). In quiet mode memcached suppresses the success response for each deleted key, so every line received before the terminator corresponds to a key that was NOT deleted -- a miss (NF) or an error. Returns that count so callers can derive the number of successful deletes as (keys_sent - non_deletions).



174
175
176
177
178
179
180
181
182
 
# File 'lib/dalli/protocol/response_processor.rb', line 174

def pipelined_delete_non_deletions
  non_deletions = 0
  tokens = next_line_to_tokens
  until tokens.first == MN
    non_deletions += 1
    tokens = next_line_to_tokens
  end
  non_deletions
end

#read_data(data_size) ⇒ Object 



308
309
310
 
# File 'lib/dalli/protocol/response_processor.rb', line 308

def read_data(data_size)
  @io_source.read(data_size + TERMINATOR.bytesize)&.chomp!(TERMINATOR)
end

#read_line ⇒ Object 



299
300
301
 
# File 'lib/dalli/protocol/response_processor.rb', line 299

def read_line
  @io_source.read_line&.chomp!(TERMINATOR)
end

#reset ⇒ Object 



149
150
151
152
153
 
# File 'lib/dalli/protocol/response_processor.rb', line 149

def reset
  error_on_unexpected!(T_RESET)

  true
end

#stale_from_tokens(tokens) ⇒ Object

Detects the X presence flag, set when an item has been marked stale by a prior md key I. Uses strict equality (Array#any? with a String pattern compares with ==) so a future value-bearing flag beginning with X cannot be mistaken for it.



250
251
252
 
# File 'lib/dalli/protocol/response_processor.rb', line 250

def stale_from_tokens(tokens)
  tokens.any?('X')
end

#stats ⇒ Object 



133
134
135
136
137
138
139
140
141
 
# File 'lib/dalli/protocol/response_processor.rb', line 133

def stats
  tokens = error_on_unexpected!(T_END_TOKEN_STAT)
  values = {}
  while tokens.first != END_TOKEN
    values[tokens[1]] = tokens[2]
    tokens = next_line_to_tokens
  end
  values
end

#ttl_remaining_from_tokens(tokens) ⇒ Object

Returns seconds of TTL remaining; -1 when the item has no expiry. The t flag returns t.



280
281
282
 
# File 'lib/dalli/protocol/response_processor.rb', line 280

def ttl_remaining_from_tokens(tokens)
  value_from_tokens(tokens, 't').to_i
end

#value_from_tokens(tokens, flag) ⇒ Object 



288
289
290
291
292
293
294
295
296
297
 
# File 'lib/dalli/protocol/response_processor.rb', line 288

def value_from_tokens(tokens, flag)
  # NB: as an optimization, we're mutating the matching token in place
  # so there is a baked assumption that we're only accessing each token at most once.
  index = tokens.find_index { |t| t.start_with?(flag) }
  if index
    tokens.delete_at(index).delete_prefix!(flag)
  else
    0
  end
end

#version ⇒ Object 



155
156
157
158
 
# File 'lib/dalli/protocol/response_processor.rb', line 155

def version
  tokens = error_on_unexpected!(T_VERSION)
  tokens.last
end