error "Non-hex digit used for Unicode escape"

*Backtrace*

Debugger entered--Lisp error: (error "Non-hex digit used for Unicode escape")
  byte-code("\301\300\"\210\300\302\"\207" [error debug "net-read error: %S"] 3)
  epc:net-read-or-lose(#<process epc con 3>)
  epc:process-available-input([cl-struct-epc:connection "epc con 3" #<process epc con 3> #<buffer *epc con 3*> ("epc con 3" nil (methods . [cl-struct-deferred (lambda (args) (epc:log "SIG METHODS: %S" args) (epc:handler-methods [cl-struct-epc:manager "bundle exec ruby unicode.rb" #<process epc:server:2> ("bundle" "exec" "ruby" "unicode.rb") 51500 #0 nil (...) nil] (caadr args))) deferred:default-errorback deferred:default-cancel nil nil nil]) (epc-error . [cl-struct-deferred (lambda (args) (epc:log "SIG EPC-ERROR: %S" args) (apply (quote epc:handler-epc-error) [cl-struct-epc:manager "bundle exec ruby unicode.rb" #<process epc:server:2> ("bundle" "exec" "ruby" "unicode.rb") 51500 #0 nil (...) nil] (epc:args args))) deferred:default-errorback deferred:default-cancel nil nil nil]) (return-error . [cl-struct-deferred (lambda (args) (epc:log "SIG RET-ERROR: %S" args) (apply (quote epc:handler-return-error) [cl-struct-epc:manager "bundle exec ruby unicode.rb" #<process epc:server:2> ("bundle" "exec" "ruby" "unicode.rb") 51500 #0 nil (...) nil] (epc:args args))) deferred:default-errorback deferred:default-cancel nil nil nil]) (return . [cl-struct-deferred (lambda (args) (epc:log "SIG RET: %S" args) (apply (quote epc:handler-return) [cl-struct-epc:manager "bundle exec ruby unicode.rb" #<process epc:server:2> ("bundle" "exec" "ruby" "unicode.rb") 51500 #0 nil (...) nil] (epc:args args))) deferred:default-errorback deferred:default-cancel nil nil nil]) (call . [cl-struct-deferred (lambda (args) (epc:log "SIG CALL: %S" args) (apply (quote epc:handler-called-method) [cl-struct-epc:manager "bundle exec ruby unicode.rb" #<process epc:server:2> ("bundle" "exec" "ruby" "unicode.rb") 51500 #0 nil (...) nil] (epc:args args))) deferred:default-errorback deferred:default-cancel nil nil nil]))] #<process epc con 3>)
  epc:process-filter([cl-struct-epc:connection "epc con 3" #<process epc con 3> #<buffer *epc con 3*> ("epc con 3" nil (methods . [cl-struct-deferred (lambda (args) (epc:log "SIG METHODS: %S" args) (epc:handler-methods [cl-struct-epc:manager "bundle exec ruby unicode.rb" #<process epc:server:2> ("bundle" "exec" "ruby" "unicode.rb") 51500 #0 nil (...) nil] (caadr args))) deferred:default-errorback deferred:default-cancel nil nil nil]) (epc-error . [cl-struct-deferred (lambda (args) (epc:log "SIG EPC-ERROR: %S" args) (apply (quote epc:handler-epc-error) [cl-struct-epc:manager "bundle exec ruby unicode.rb" #<process epc:server:2> ("bundle" "exec" "ruby" "unicode.rb") 51500 #0 nil (...) nil] (epc:args args))) deferred:default-errorback deferred:default-cancel nil nil nil]) (return-error . [cl-struct-deferred (lambda (args) (epc:log "SIG RET-ERROR: %S" args) (apply (quote epc:handler-return-error) [cl-struct-epc:manager "bundle exec ruby unicode.rb" #<process epc:server:2> ("bundle" "exec" "ruby" "unicode.rb") 51500 #0 nil (...) nil] (epc:args args))) deferred:default-errorback deferred:default-cancel nil nil nil]) (return . [cl-struct-deferred (lambda (args) (epc:log "SIG RET: %S" args) (apply (quote epc:handler-return) [cl-struct-epc:manager "bundle exec ruby unicode.rb" #<process epc:server:2> ("bundle" "exec" "ruby" "unicode.rb") 51500 #0 nil (...) nil] (epc:args args))) deferred:default-errorback deferred:default-cancel nil nil nil]) (call . [cl-struct-deferred (lambda (args) (epc:log "SIG CALL: %S" args) (apply (quote epc:handler-called-method) [cl-struct-epc:manager "bundle exec ruby unicode.rb" #<process epc:server:2> ("bundle" "exec" "ruby" "unicode.rb") 51500 #0 nil (...) nil] (epc:args args))) deferred:default-errorback deferred:default-cancel nil nil nil]))] #<process epc con 3> "000016(return 4 \"\\u{2026}\")\n")
  #[(G100400 G100401 G100402 G100403 G100404 G100405 p m) "\303J	\n#\207" [G100400 p m epc:process-filter] 4](--connection-- --channel-- --connection-process-- --connection-buf-- --connection-name-- --connection-id-- #<process epc con 3> "000016(return 4 \"\\u{2026}\")\n")
  apply(#[(G100400 G100401 G100402 G100403 G100404 G100405 p m) "\303J	\n#\207" [G100400 p m epc:process-filter] 4] --connection-- --channel-- --connection-process-- --connection-buf-- --connection-name-- --connection-id-- (#<process epc con 3> "000016(return 4 \"\\u{2026}\")\n"))
  (lambda (&rest --cl-rest--) (apply (quote #[(G100400 G100401 G100402 G100403 G100404 G100405 p m) "\303J	\n#\207" [G100400 p m epc:process-filter] 4]) (quote --connection--) (quote --channel--) (quote --connection-process--) (quote --connection-buf--) (quote --connection-name--) (quote --connection-id--) --cl-rest--))(#<process epc con 3> "000016(return 4 \"\\u{2026}\")\n")
  accept-process-output(#<process epc con 3> 0 150 t)
  epc:sync([cl-struct-epc:manager "bundle exec ruby unicode.rb" #<process epc:server:2> ("bundle" "exec" "ruby" "unicode.rb") 51500 [cl-struct-epc:connection "epc con 3" #<process epc con 3> #<buffer *epc con 3*> ("epc con 3" nil (methods . [cl-struct-deferred (lambda (args) (epc:log "SIG METHODS: %S" args) (epc:handler-methods #0 (caadr args))) deferred:default-errorback deferred:default-cancel nil nil nil]) (epc-error . [cl-struct-deferred (lambda (args) (epc:log "SIG EPC-ERROR: %S" args) (apply (quote epc:handler-epc-error) #0 (epc:args args))) deferred:default-errorback deferred:default-cancel nil nil nil]) (return-error . [cl-struct-deferred (lambda (args) (epc:log "SIG RET-ERROR: %S" args) (apply (quote epc:handler-return-error) #0 (epc:args args))) deferred:default-errorback deferred:default-cancel nil nil nil]) (return . [cl-struct-deferred (lambda (args) (epc:log "SIG RET: %S" args) (apply (quote epc:handler-return) #0 (epc:args args))) deferred:default-errorback deferred:default-cancel nil nil nil]) (call . [cl-struct-deferred (lambda (args) (epc:log "SIG CALL: %S" args) (apply (quote epc:handler-called-method) #0 (epc:args args))) deferred:default-errorback deferred:default-cancel nil nil nil]))] nil ((4 . [cl-struct-deferred deferred:default-callback deferred:default-errorback deferred:default-cancel [cl-struct-deferred (lambda (&rest --cl-rest--) (apply (quote #[... "\211\nL)\207" [G100437 v x] 3]) (quote --result--) --cl-rest--)) deferred:default-errorback deferred:default-cancel [cl-struct-deferred deferred:default-callback (lambda (&rest --cl-rest--) (apply ... ... --cl-rest--)) deferred:default-cancel nil nil nil] nil nil] nil nil])) nil] [cl-struct-deferred deferred:default-callback deferred:default-errorback deferred:default-cancel [cl-struct-deferred (lambda (&rest --cl-rest--) (apply (quote #[(G100437 x) "\211\nL)\207" [G100437 v x] 3]) (quote --result--) --cl-rest--)) deferred:default-errorback deferred:default-cancel [cl-struct-deferred deferred:default-callback (lambda (&rest --cl-rest--) (apply (quote #[(G100438 er) "\211\303\nBL)\207" [G100438 v er error] 4]) (quote --result--) --cl-rest--)) deferred:default-cancel nil nil nil] nil nil] nil nil])
  epc:call-sync([cl-struct-epc:manager "bundle exec ruby unicode.rb" #<process epc:server:2> ("bundle" "exec" "ruby" "unicode.rb") 51500 [cl-struct-epc:connection "epc con 3" #<process epc con 3> #<buffer *epc con 3*> ("epc con 3" nil (methods . [cl-struct-deferred (lambda (args) (epc:log "SIG METHODS: %S" args) (epc:handler-methods #0 (caadr args))) deferred:default-errorback deferred:default-cancel nil nil nil]) (epc-error . [cl-struct-deferred (lambda (args) (epc:log "SIG EPC-ERROR: %S" args) (apply (quote epc:handler-epc-error) #0 (epc:args args))) deferred:default-errorback deferred:default-cancel nil nil nil]) (return-error . [cl-struct-deferred (lambda (args) (epc:log "SIG RET-ERROR: %S" args) (apply (quote epc:handler-return-error) #0 (epc:args args))) deferred:default-errorback deferred:default-cancel nil nil nil]) (return . [cl-struct-deferred (lambda (args) (epc:log "SIG RET: %S" args) (apply (quote epc:handler-return) #0 (epc:args args))) deferred:default-errorback deferred:default-cancel nil nil nil]) (call . [cl-struct-deferred (lambda (args) (epc:log "SIG CALL: %S" args) (apply (quote epc:handler-called-method) #0 (epc:args args))) deferred:default-errorback deferred:default-cancel nil nil nil]))] nil ((4 . [cl-struct-deferred deferred:default-callback deferred:default-errorback deferred:default-cancel [cl-struct-deferred (lambda (&rest --cl-rest--) (apply (quote #[... "\211\nL)\207" [G100437 v x] 3]) (quote --result--) --cl-rest--)) deferred:default-errorback deferred:default-cancel [cl-struct-deferred deferred:default-callback (lambda (&rest --cl-rest--) (apply ... ... --cl-rest--)) deferred:default-cancel nil nil nil] nil nil] nil nil])) nil] get-unicode nil)
  (message "%S" (epc:call-sync epc (quote get-unicode) (quote nil)))
  (let (epc) (setq epc (epc:start-epc "bundle" (quote ("exec" "ruby" "unicode.rb")))) (message "%S" (epc:call-sync epc (quote get-unicode) (quote nil))) (epc:stop-epc epc))
  eval((let (epc) (setq epc (epc:start-epc "bundle" (quote ("exec" "ruby" "unicode.rb")))) (message "%S" (epc:call-sync epc (quote get-unicode) (quote nil))) (epc:stop-epc epc)) nil)
  eval-last-sexp-1(nil)
  eval-last-sexp(nil)
  call-interactively(eval-last-sexp nil nil)
  command-execute(eval-last-sexp)

client.el

(require 'epc)

(let (epc)
  (setq epc (epc:start-epc "bundle" '("exec" "ruby" "unicode.rb")))
  ;; (message "%S" (epc:call-sync epc 'get-ok '())) ; => "ok"
  (message "%S" (epc:call-sync epc 'get-unicode '())) ; => "…"
  ;; (message "%S" (epc:call-sync epc 'get-escaped-unicode '())) ; => "\\u2026"
  ;; (message "%S" (epc:call-sync epc 'get-stripped-unicode '())) ; => "…"
  (epc:stop-epc epc))

Gemfile

source 'https://rubygems.org'

gem "twitter"
gem "elrpc"

Gemfile.lock

GEM
  remote: https://rubygems.org/
  specs:
    addressable (2.4.0)
    buftok (0.2.0)
    domain_name (0.5.20160216)
      unf (>= 0.0.5, < 1.0.0)
    elparser (0.0.7)
      racc (~> 1)
    elrpc (0.0.6)
      elparser (~> 0.0)
    equalizer (0.0.10)
    faraday (0.9.2)
      multipart-post (>= 1.2, < 3)
    http (1.0.2)
      addressable (~> 2.3)
      http-cookie (~> 1.0)
      http-form_data (~> 1.0.1)
      http_parser.rb (~> 0.6.0)
    http-cookie (1.0.2)
      domain_name (~> 0.5)
    http-form_data (1.0.1)
    http_parser.rb (0.6.0)
    json (1.8.3)
    memoizable (0.4.2)
      thread_safe (~> 0.3, >= 0.3.1)
    multipart-post (2.0.0)
    naught (1.1.0)
    racc (1.4.14)
    simple_oauth (0.3.1)
    thread_safe (0.3.5)
    twitter (5.16.0)
      addressable (~> 2.3)
      buftok (~> 0.2.0)
      equalizer (= 0.0.10)
      faraday (~> 0.9.0)
      http (~> 1.0)
      http_parser.rb (~> 0.6.0)
      json (~> 1.8)
      memoizable (~> 0.4.0)
      naught (~> 1.0)
      simple_oauth (~> 0.3.0)
    unf (0.1.4)
      unf_ext
    unf_ext (0.0.7.2)

PLATFORMS
  ruby

DEPENDENCIES
  elrpc
  twitter

BUNDLED WITH
   1.11.2

unicode.rb

#!/usr/bin/env ruby

require "elrpc"

server = Elrpc.start_server

server.def_method "get-ok" do |arg|
  "ok"
end

server.def_method "get-unicode" do |arg|
  "\u{2026}"
end

server.def_method "get-escaped-unicode" do |arg|
  "\\u{2026}"
end

server.def_method "get-stripped-unicode" do |arg|
  "\u2026"
end

server.wait