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f0efa5aec1
There were various places in our codebase which conjured up a StringInfo by manually assigning the StringInfo fields and setting the data field to point to some existing buffer. There wasn't much consistency here as to what fields like maxlen got set to and in one location we didn't correctly ensure that the buffer was correctly NUL terminated at len bytes, as per what was documented as required in stringinfo.h Here we introduce 2 new functions to initialize StringInfos. One allows callers to initialize a StringInfo passing along a buffer that is already allocated by palloc. Here the StringInfo code uses this buffer directly rather than doing any memcpying into a new allocation. Having this as a function allows us to verify the buffer is correctly NUL terminated. StringInfos initialized this way can be appended to and reset just like any other normal StringInfo. The other new initialization function also accepts an existing buffer, but the given buffer does not need to be a pointer to a palloc'd chunk. This buffer could be a pointer pointing partway into some palloc'd chunk or may not even be palloc'd at all. StringInfos initialized this way are deemed as "read-only". This means that it's not possible to append to them or reset them. For the latter of the two new initialization functions mentioned above, we relax the requirement that the data buffer must be NUL terminated. Relaxing this requirement is convenient in a few places as it can save us from having to allocate an entire new buffer just to add the NUL terminator or save us from having to temporarily add a NUL only to have to put the original char back again later. Incompatibility note: Here we also forego adding the NUL in a few places where it does not seem to be required. These locations are passing the given StringInfo into a type's receive function. It does not seem like any of our built-in receive functions require this, but perhaps there's some UDT out there in the wild which does require this. It is likely worthy of a mention in the release notes that a UDT's receive function mustn't rely on the input StringInfo being NUL terminated. Author: David Rowley Reviewed-by: Tom Lane Discussion: https://postgr.es/m/CAApHDvorfO3iBZ%3DxpiZvp3uHtJVLyFaPBSvcAhAq2HPLnaNSwQ%40mail.gmail.com |
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