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pull_parser.cr
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pull_parser.cr
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# This class allows you to consume JSON on demand, token by token.
class JSON::PullParser
getter kind : Symbol
getter bool_value : Bool
getter int_value : Int64
getter float_value : Float64
getter string_value : String
getter raw_value : String
property max_nesting = 512
def initialize(input)
@lexer = Lexer.new input
@kind = :EOF
@bool_value = false
@int_value = 0_i64
@float_value = 0.0
@string_value = ""
@raw_value = ""
@object_stack = [] of Symbol
@skip_count = 0
@location = {0, 0}
next_token
case token.type
when :null
@kind = :null
when :false
@kind = :bool
@bool_value = false
when :true
@kind = :bool
@bool_value = true
when :INT
@kind = :int
@int_value = token.int_value
@raw_value = token.raw_value
when :FLOAT
@kind = :float
@float_value = token.float_value
@raw_value = token.raw_value
when :STRING
@kind = :string
@string_value = token.string_value
when :"["
begin_array
when :"{"
begin_object
else
unexpected_token
end
end
def read_begin_array
expect_kind :begin_array
read_next
end
def read_end_array
expect_kind :end_array
read_next
end
def read_array
read_begin_array
while kind != :end_array
yield
end
read_end_array
end
def read_begin_object
expect_kind :begin_object
read_next
end
def read_end_object
expect_kind :end_object
read_next
end
def read_object_key
read_string
end
def read_object
read_begin_object
while kind != :end_object
key = read_object_key
yield key
end
read_end_object
end
def read_null
expect_kind :null
read_next
nil
end
def read_bool
expect_kind :bool
@bool_value.tap { read_next }
end
def read_int
expect_kind :int
@int_value.tap { read_next }
end
def read_float
case @kind
when :int
@int_value.to_f.tap { read_next }
when :float
@float_value.tap { read_next }
else
parse_exception "expecting int or float but was #{@kind}"
end
end
def read_raw
case @kind
when :null
read_next
"null"
when :bool
@bool_value.to_s.tap { read_next }
when :int, :float
@raw_value.tap { read_next }
when :string
@string_value.to_json.tap { read_next }
when :begin_array
JSON.build { |json| read_raw(json) }
when :begin_object
JSON.build { |json| read_raw(json) }
else
unexpected_token
end
end
def read_raw(json)
case @kind
when :null
read_next
json.null
when :bool
json.bool(@bool_value)
read_next
when :int, :float
json.raw(@raw_value)
read_next
when :string
json.string(@string_value)
read_next
when :begin_array
json.array do
read_begin_array
while kind != :end_array
read_raw(json)
end
read_end_array
end
when :begin_object
json.object do
read_begin_object
while kind != :end_object
json.string(@string_value)
read_object_key
read_raw(json)
end
read_end_object
end
else
unexpected_token
end
end
def read_string
expect_kind :string
@string_value.tap { read_next }
end
def read_bool_or_null
read_null_or { read_bool }
end
def read_int_or_null
read_null_or { read_int }
end
def read_float_or_null
read_null_or { read_float }
end
def read_string_or_null
read_null_or { read_string }
end
def read_array_or_null
read_null_or { read_array { yield } }
end
def read_object_or_null
read_null_or { read_object { |key| yield key } }
end
def read_null_or
if @kind == :null
read_next
nil
else
yield
end
end
def on_key(key)
read_object do |some_key|
some_key == key ? yield : skip
end
end
def on_key!(key)
found = false
value = uninitialized typeof(yield)
read_object do |some_key|
if some_key == key
found = true
value = yield
else
skip
end
end
unless found
raise "JSON key not found: #{key}"
end
value
end
def read_next
read_next_internal
@kind
end
def read?(klass : Bool.class)
read_bool if kind == :bool
end
def read?(klass : Int8.class)
read_int.to_i8 if kind == :int
end
def read?(klass : Int16.class)
read_int.to_i16 if kind == :int
end
def read?(klass : Int32.class)
read_int.to_i32 if kind == :int
end
def read?(klass : Int64.class)
read_int.to_i64 if kind == :int
end
def read?(klass : UInt8.class)
read_int.to_u8 if kind == :int
end
def read?(klass : UInt16.class)
read_int.to_u16 if kind == :int
end
def read?(klass : UInt32.class)
read_int.to_u32 if kind == :int
end
def read?(klass : UInt64.class)
read_int.to_u64 if kind == :int
end
def read?(klass : Float32.class)
return read_int.to_f32 if kind == :int
return read_float.to_f32 if kind == :float
end
def read?(klass : Float64.class)
return read_int.to_f64 if kind == :int
return read_float.to_f64 if kind == :float
end
def read?(klass : String.class)
read_string if kind == :string
end
private def read_next_internal
current_kind = @kind
while true
case token.type
when :null
@kind = :null
next_token_after_value
return
when :true
@kind = :bool
@bool_value = true
next_token_after_value
return
when :false
@kind = :bool
@bool_value = false
next_token_after_value
return
when :INT
@kind = :int
@int_value = token.int_value
@raw_value = token.raw_value
next_token_after_value
return
when :FLOAT
@kind = :float
@float_value = token.float_value
@raw_value = token.raw_value
next_token_after_value
return
when :STRING
@kind = :string
@string_value = token.string_value
if current_kind == :begin_object
if next_token.type != :":"
unexpected_token
end
else
next_token_after_value
end
return
when :"["
begin_array
return
when :"]"
@kind = :end_array
next_token_after_array_or_object
return
when :"{"
begin_object
return
when :"}"
@kind = :end_object
next_token_after_array_or_object
return
when :","
obj = current_object()
@lexer.skip = false if @skip_count == 1
if obj == :object
next_token_expect_object_key
else
next_token
end
@lexer.skip = true if @skip_count == 1
case token.type
when :",", :"]", :"}", :EOF
unexpected_token
end
if obj == :object && token.type == :STRING
@kind = :string
@string_value = token.string_value
if next_token.type != :":"
unexpected_token
end
return
end
when :":"
case next_token.type
when :",", :":", :"]", :"}", :EOF
unexpected_token
end
when :EOF
@kind = :EOF
return
else
unexpected_token
end
end
end
def skip
@lexer.skip = true
skip_internal
@lexer.skip = false
end
def line_number
@location[0]
end
def column_number
@location[1]
end
def location
@location
end
private def skip_internal
@skip_count += 1
case @kind
when :null, :bool, :int, :float, :string
read_next
when :begin_array
@skip_count += 1
read_begin_array
while kind != :end_array
skip_internal
end
@skip_count -= 1
read_end_array
when :begin_object
@skip_count += 1
read_begin_object
while kind != :end_object
read_object_key
skip_internal
end
@skip_count -= 1
read_end_object
else
unexpected_token
end
@skip_count -= 1
end
private def begin_array
@kind = :begin_array
push_in_object_stack :array
case next_token.type
when :",", :"}", :":", :EOF
unexpected_token
end
end
private def begin_object
@kind = :begin_object
push_in_object_stack :object
case next_token_expect_object_key.type
when :STRING, :"}"
# OK
else
unexpected_token
end
end
private def current_object
@object_stack.last?
end
private def token
@lexer.token
end
private def next_token
@location = {@lexer.token.line_number, @lexer.token.column_number}
@lexer.next_token
end
private def next_token_expect_object_key
@location = {@lexer.token.line_number, @lexer.token.column_number}
@lexer.next_token_expect_object_key
end
private def next_token_after_value
case next_token.type
when :",", :"]", :"}"
# Ok
else
if @object_stack.empty?
@kind = :EOF
else
unexpected_token
end
end
end
private def next_token_after_array_or_object
unless @object_stack.pop?
unexpected_token
end
case next_token.type
when :",", :"]", :"}"
# OK
when :EOF
unless @object_stack.empty?
unexpected_token
end
else
unexpected_token
end
end
private def expect_kind(kind)
parse_exception "Expected #{kind} but was #{@kind}" unless @kind == kind
end
private def unexpected_token
parse_exception "Unexpected token: #{token}"
end
private def parse_exception(msg)
raise ParseException.new(msg, token.line_number, token.column_number)
end
private def push_in_object_stack(symbol)
if @object_stack.size >= @max_nesting
parse_exception "Nesting of #{@object_stack.size + 1} is too deep"
end
@object_stack.push(symbol)
end
end