Prior behavior for HttpClient was to parse the body as JSON when
responseType was set to 'json', even if the response was
unsuccessful. This changed due to a recent bugfix, and
unsuccessful responses had their bodies treated as strings.
There is no guarantee that if a service returns JSON in the
successful case that it will do so for errors. However, users
indicate that most APIs in the wild do work this way. Therefore,
this commit changes the error case behavior to attempt a JSON
parsing of the response body, and falls back on returning it as
a string if that fails.
PR Close#19773
Currently HttpClient sends requests for JSON data with the
XMLHttpRequest.responseType set to 'json'. With this flag, the browser
will attempt to parse the response as JSON, but will return 'null' on
any errors. If the JSON response contains an XSSI-prevention prefix,
this will cause the browser's parsing to fail, which is unrecoverable.
The only compelling reason to use the responseType 'json' is for
performance (especially if the browser offloads JSON parsing to a
separate thread). I'm not aware of any browser which does this currently,
nor of any plans to do so. JSON.parse and responseType 'json' both
end up using the same V8 code path in Chrome to implement the parse.
Thus, this change switches all JSON parsing in HttpClient to use
JSON.parse directly.
Fixes#18396, #18453.
PR Close#18466
HttpClient is an evolution of the existing Angular HTTP API, which exists
alongside of it in a separate package, @angular/common/http. This structure
ensures that existing codebases can slowly migrate to the new API.
The new API improves significantly on the ergonomics and features of the legacy
API. A partial list of new features includes:
* Typed, synchronous response body access, including support for JSON body types
* JSON is an assumed default and no longer needs to be explicitly parsed
* Interceptors allow middleware logic to be inserted into the pipeline
* Immutable request/response objects
* Progress events for both request upload and response download
* Post-request verification & flush based testing framework
