PowerShell is unable to reliably round-trip JSON by default. How can I ensure that such JSON is correctly round-tripped?
Here is a minimal example of the broken round-trip serialization:
PS> '{"a":[{"b":{}}]}' | ConvertFrom-Json | ConvertTo-Json -Compress
{"a":[{"b":""}]}
The unexpected change from {} to "" results in JSON which is no longer valid.
This is under version 5.1:
PS> $PSVersionTable.PSVersion.ToString()
5.1.15063.674
Similarly, '[{"b":{}]' | ConvertFrom-Json | ConvertTo-Json is also questionable, as discussed in https://windowsserver.uservoice.com/forums/301869-powershell/suggestions/15123162-convertto-json-doesn-t-serialize-simple-objects-pr. However, consider that questionable nature not covered in this question.
A little bit of PEBKAC, a little bit of Why Is That The Behavior?!
It seems to be an issue with -Depth and the pruning logic. Setting a "higher depth" results in round-trip behavior working as expected. Having the truncation end as a string, as opposed to say null, seems unfortunate - although possibly consistent if one finds that "To String" is the correct termination.
Change to "" (unexpected):
PS> '{"a":[{"b":{}}]}' | ConvertFrom-Json | ConvertTo-Json -Compress -Depth 2
'{"a":[{"b":""}]}'
Round-trip (expected):
PS> '{"a":[{"b":{}}]}' | ConvertFrom-Json | ConvertTo-Json -Compress -Depth 3
'{"a":[{"b":{}}]}'