CODEWITHSUNDEEP
pythonaws-api-gatewayaws-lambda
Menglong Li
Menglong Li

Reputation: 2255

AWS API Gateway's querystring is not json format

In aws api gateway, I wanna pass the entire query string into the kinesis through api gateway,

#set($querystring = $input.params().querystring)
"Data": "$util.base64Encode($querystring)"

but the data fetching from kinesis record looks like '{tracker_name=xxxx, tracker=yyyy}', which is not json string format, So I need to take special care of this weird string to make it to json string in aws lambda (Python engine). Any good idea?

Upvotes: 0

Views: 270

Answers (1)

Yuankun
Yuankun

Reputation: 7803

I'm not familiar with the AWS API Gateway, but focusing on the string formatting issue, it is not that hard to write a simple parser to convert it to any other format you want.

As for your description, I write a simple Python parser, hope it can give you some ideas.

class MyParser:

def __init__(self, source):
    # the source string
    self.source = source
    # current position
    self.at = 0
    # current character
    self.ch = source[0] if len(source) > 0 else ''

def error(self, msg):
    '''Print an error message and raise an exception'''

    print '-- Parser abort due to a fatal error: \n-- %s' % msg
    raise ValueError()

def check_char(self, expected):
    '''
    Check if current character is same as the given character.
    If not, raise an exception.
    '''

    if self.at >= len(self.source):
        self.error('At position %d: %c expected, but reached string end' % (self.at, expected))
    elif self.ch != expected:
        self.error('At position %d: %c expected, but %c given' % (self.at, expected, self.ch))

def next_char(self):
    '''Move on to next character in source string.'''

    self.at += 1
    self.ch = self.source[self.at] if len(self.source) > self.at else ''
    return self.ch

def eat_spaces(self):
    '''Eat up white spaces.'''

    while self.ch == ' ':
        self.next_char()

def parse_string(self):
    '''Parse a string value.'''

    s = ''
    while self.ch != '=' and self.ch != ',' and self.ch != '}' and self.at < len(self.source):
        s += self.ch
        self.next_char()
    return s.strip()

def parse_object(self):
    '''Parse an object value.'''

    obj = {}

    # eat '{'
    self.next_char()
    self.eat_spaces()

    while self.ch != '}':
        if self.at >= len(self.source):
            self.error('Malformed source string')

        key = self.parse_string()
        # eat '='
        self.check_char('=')
        self.next_char()
        val = self.parse_value()
        obj[key] = val
        # eat ','
        if self.ch == ',':
            self.next_char()
        self.eat_spaces()

    # eat '}'
    self.next_char()

    return obj

def parse_value(self):
    '''Parse a value.'''

    self.eat_spaces()
    if self.ch == '{':
        return self.parse_object()
    else:
        return self.parse_string()

def parse(self):
    '''Let the game begin.'''

    self.eat_spaces()
    if self.ch != '{':
        self.error('Source string must begin with \'{\'')
    else:
        return self.parse_value()

To use it:

MyParser('{tracker_name=xxxx, tracker=yyyy}').parse()

Upvotes: 1

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