How to fix the "Invalid JSON payload received. Unknown name" error - google-app-engine

Question

I try to get a proper response from the Google Safe Browsing API v4. Although I get the error "Invalid JSON payload received. Unknown name".
I have used a payload based on the payload example mentioned at https://developers.google.com/safe-browsing/v4/lookup-api
I have problems with the payload. I think it should be a string, not a real dict. When I use a dict I get the error: TypeError: has type , but expected one of: str, unicode
The code I used is:
result = urlfetch.fetch(url, method=urlfetch.POST, payload=payload)
The url is (with [api-key] is of course my api-key):
https://safebrowsing.googleapis.com/v4/threatMatches:find?key=[api-key]
The payload is the following string (not a python dict):
{
"client": {
"clientId": "myproject",
"clientVersion": "42" },
"threatInfo": {
"threatTypes": ["MALWARE", "SOCIAL_ENGINEERING"],
"platformTypes": ["WINDOWS"],
"threatEntryTypes": ["URL"],
"threatEntries": [ {"url":"http://www.example.com/"} ] }
}
As output I expected some JSON which indicates that this url is safe. However I get the following result:
{
"error": {
"code": 400,
"message": "Invalid JSON payload received. Unknown name \"{\n \"client\": {\n \"clientId\": \"myproject\",\n \"clientVersion\": \"42\"\n },\n \"threatInfo\": {\n \"threatTypes\": [\"MALWARE\", \"SOCIAL_ENGINEERING\"],\n \"platformTypes\": [\"WINDOWS\"],\n \"threatEntryTypes\": [\"URL\"],\n \"threatEntries\": [\n {\"url\":\"http://www.example.com/\"}\n ]\n }\n }\": Cannot bind query parameter. Field '{\n \"client\": {\n \"clientId\": \"myproject\",\n \"clientVersion\": \"42\"\n },\n \"threatInfo\": {\n \"threatTypes\": [\"MALWARE\", \"SOCIAL_ENGINEERING\"],\n \"platformTypes\": [\"WINDOWS\"],\n \"threatEntryTypes\": [\"URL\"],\n \"threatEntries\": [\n {\"url\":\"http://www' could not be found in request message.",
"status": "INVALID_ARGUMENT",
"details": [
{
"#type": "type.googleapis.com/google.rpc.BadRequest",
"fieldViolations": [
{
"description": [similar as the message above]
}
]
}
]
}
}
Any ideas, what is wrong?
Thanks

Answer 1

The urlfetch should contain the HEADER Content-Type: application/json
result = urlfetch.fetch(url, method=urlfetch.POST, payload=payload, headers={'Content-Type': 'application/json'})